AI HOC QUOC GIA THANH PHO HO CH MINH TRNG AI HOC KHOA HOC XA HOI VA NHAN VAN

___________ L HUY B (Ch bin)

C HC MI TRNG

TP 2

(Phn chuyn )

Cong tac vien:

THAI VAN NAM, NGUYEN NGOC QUYNH, TO VAN TRNG, LU QUOC DUNG, O TH KIM CHI, PHAN TH MY HANH, NGUYEN TH HONG THUY, NGUYEN TH PHNG UYEN, CUNG THE TAI, LE UYEN MINH, PHAM VIET ANH, ANG TH KIM THOA, AO TH TRAM ANH, LE TH AI NNG, NGUYEN HOANG LAN THANH, NGUYEN TRAN THIEN AN, TRAN NGOC LE, NGUYEN NHAT TRNG, LE AO AN XUAN, TRAN TH NGOC OANH.

NHA XUAT BAN AI HOC QUOC GIA

THANH PHO HO CH MINH 2006

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CHNG 0

TONG QUAT VE OC HOC MOI TRNG (Ecotoxicology An overview)

0.1. NH NGHA

Trong quyen "oc hoc moi trng" (NXB HQGTPHCM 2000, tai ban 2002) chung toi a neu mot so nh ngha va khai niem ve oc hoc moi trng. ay chung toi ch xin nhac lai mot vai nguyen ly c ban cho ban oc tien theo doi.

oc hoc moi trng (Environmental Toxicology) (HMT) hay con goi la "oc hoc sinh thai" (Ecotoxicology). HMT la nganh hoc c ban cua moi trng hoc, chuyen nghien cu ve chat va lng cua cac hieu ng xau do cac tac nhan ly hoc, hoa hoc, sinh hoc gay ra cho ca the, quan the hay quan xa sinh vat va he sinh thai.

HMT gom hai phan: 1 khoa hoc ly thuyet c ban ve cac chat oc va 2 khoa hoc ng dung.

0.2. CHAT OC

0.2.1. nh ngha

Chat oc la bat ky chat nao co the gay ra cac hieu ng xau, tham ch gay t vong cho ngi, sinh vat va he sinh thai (HST).

0.2.2. Phan loai

a Phan theo ac tnh sinh hoc: Chat oc co the la oc chat va co the la oc to.

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oc chat (toxicant) e ch vai tro tac nhan hoa hoc gay oc cua no.

oc to (toxin) e ch vai tro va ban chat sinh hoc cua chat oc o

b Phan theo ban chat

oc ban chat (Natural Toxicity): Co nhng chat oc vi mot lieu lng rat nho cung gay oc.

oc lieu lng (Dose Toxicity): Co nhng chat mot lieu lng nho khong gay oc tham ch con la dinh dng. Nhng khi vt qua mot lieu lng nhat nh oi vi mot sinh vat trong mot thi ky nhat nh se gay hieu ng oc.

Suy cho cung, tat cac cac chat eu la nhng chat oc tiem tang.

c Phan loai theo tiem nang hoat tnh

Loai cac tac nhan gay oc tiem tang (Potential Toxicity): gom tac nhan hoa hoc (t nhien, nhan tao, hu c, vo c), tac nhan vat ly (tac nhan ac thu, bc xa, vi song), tac nhan sinh hoc (cac oc to cua nam, vi khuan, thc vat, ong vat) co kha nang gay ngo oc cho sinh vat nhng hien tai cha the hien. No ch bieu hien oc tnh khi co ieu kien moi trng thch hp.

Loai cac tac nhan gay oc hoat tnh (Actual Toxicity): cung gom tat ca nhng tac nhan gay oc nh tren nhng ang dang hoat ong the hien oc tnh, hien tai gay hai sinh vat.

d Phan laai theo dang, the ton tai:

Cac dang the hien cua tac nhan oc co the la khong kh, nc, thc pham, dc pham, my pham va san pham tieu thu, qua tiep xuc da.

e Phan loai theo tnh nang:

Dang cap tnh: Nguy cap, co the gay chet tuc thi, ngan han, thng oi vi lieu cao hoac nong o cao va so t ngi b anh hng nh khi lam o hoa chat, thoat chat thai oc hai ra khong kh.

Dang man tnh: Am ton tai trong c the sinh vat va quan the, dai han, thng oi vi lieu lng va nong o thap, xay ra cho so ngi ong hn, hoac rat lau (thng oi vi lieu lng va nong o rat nho, nhieu ngi mac phai nh trng hp nhiem oc thc pham, o nhiem kim loai nang hoac o nhiem nc).

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Con co the phan theo nhieu cach khac nhau na, tuy theo muc ch nghien cu... S nhiem oc co the xay ra trong nha, ni lam viec hoac bat ky ni nao.

0.3. LIEU LNG OC CHAT, OC TO

La mot n v cua s xuat hien cac tac nhan hoa hoc, ly hoc hay sinh hoc. Lieu lng co the bieu th qua n v khoi lng hoac the tch tren n v trong lng c the (mg, g, ml/ kg trong lng c the) hoac theo n v khoi lng hay the tch tren n v be mat c the (mg, g, mg/ m2 dien tch be mat c the).

0.4. NONG O OC CHAT, OC TO

La bieu hien ty le lng oc chat oc to trong moi trng b nhiem oc, co n v trong lng tren mot n v dung tch. V du, vi nong o khong kh b nhiem oc co the c the hien qua n v khoi lng hay the tch tren phan trieu the tch khong kh (ppm) hay mg, g/ m3 khong kh. Nong o trong nc co the dien ta qua n v khoi lng/ lt nc (mg/l hay ppm, g/l, hay 1 phan ty ppb).

0.5 QUA TRNH VAN CHUYEN CUA OC CHAT, OC TO

ng i cua oc chat xay ra ben ngoai va ben trong c the. Chuyen ong ben ngoai c the lien quan en cac yeu to moi trng, nh ieu kien kh hau, ac tnh hoa ly cua hoa chat, tnh tan neu hoa chat c phat hien trong nc. Khuyech ai sinh hoc co the xay ra. ng xam nhap cua hoa chat oi vi ong vat va con ngi gom da day, ruot (do an uong), ng ho hap (do ht th), ng da (do tiep xuc).

S dch chuyen cua oc chat ben trong c the phu thuoc cac yeu to anh hng cau truc sinh hoc cua hoa chat trong c the. No bao gom nhng thuoc tnh ve hoa hoc va vat ly nh kch c phan t, ieu kien nhiem oc, trang thai sc khoe cua sinh vat.

oc chat phai di chuyen t iem tiep xuc vi c the, iem b nhiem, vao ng mau theo tuan hoan mau. Trong mau, oc chat co the thoat ra thanh dang t do, khong lien ket, hoac no lien ket protein (thng oi vi albumin). Hoa chat co the thoat khoi ng mau va xam nhap vao cac mo khac nhau ni o no co the c

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chuyen hoa sinh hoc (v du, gan); lu gi (mo m), ao thai (than) hoac tao ra mot phan ng (trong nao bo). Viec keo dai phan ng phu thuoc vao nong o cua hoa chat iem tren bo phan tiep nhan, ai lc cua no va hoat tnh rieng. Hoa chat phai xuyen qua mang te bao, la phospho lipid hai lp, bang qua trnh tieu ton nang lng, nh qua trnh van chuyen tch cc hoac qua trnh khong tieu ton nang lng nh qua trnh van chuyen thu ong. Chuyen ong xuyen qua mang te bao co the lien quan en phng tien ac biet. Co nhng qua trnh ac biet ma hoa chat co the xam nhap te bao. Mot trong nhng qua trnh o la nhap noi bao.

Cau truc sinh hoc cua hoa chat trong c the c xem xet theo hnh thai cua no trong c the gom co: hap thu, phan phoi, chuyen hoa sinh hoc, ao thai va s van ong cua cac qua trnh nay. Cac qua trnh nay xac nh gia tr cua hoa chat san sang tng tac vi bo phan tiep nhan. Gia tr nay cua hoa chat c goi la "kha nang tiep nhan sinh hoc".

Nhng yeu to anh hng ngng ti han gom lieu lng va cau truc hoa hoc, tnh nhay cam va tnh trang sc khoe cua sinh vat ap ng, ban chat cua cac phan ng nhan biet. Tnh nhay cam cua cac phng phap dung trong o ac phan ng se anh hng en ngng phat hien.

Cac quan he lieu phan ng cho thay s lien he gia lieu lng va phan ng nhan thay mot quan the. Chung thng c bieu dien bang mot ng cong vi tung o la mc o phan ng, lieu lng c bieu dien theo so hoc hoac logarit. Co mot so kieu ng bieu dien lieu ap ng, ng bieu dien lieu ap ng cai tien va lieu ap ng so lng.

gian o lieu ap ng cai tien, cac anh hng c xac nh trong mot c quan rieng biet va nong o c cai tien nh mot lieu lng hoa chat. Nhng ca the trong mot quan the co the co ng bieu dien lieu ap ng cai tien khac nhau v s a dang sinh hoc. ng bieu dien lieu ap ng nh lng hoac ng bieu dien tat ca hoac khong lien he vi lieu lng hoa chat oi vi tan so ap ng cua quan the. Phan ng thng la mot hien tng tat ca hoac khong hoac co the la mot ch dau trc ve mot hieu ng tai hai. gian o lieu

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ap ng nh lng, tan so thay the cho o ln cua khoang lieu ap ng cai tien.

ap ng lai cua sinh vat oi vi mot tac nhan gay oc co the c dung e nhan biet hien tng nhiem oc. Khi xay ra ieu nay, phan ng c goi la ch th sinh hoc cua b nhiem oc. Ch th sinh hoc can ac hieu oi vi tac nhan, xay ra ong vat va con ngi va can co o tin cay nhat nh. Hnh 0.1 la gian o tng quan gia lieu lng oc chat va kha nang ap ng ien hnh

Hnh 0.1: ng cong ap ng lieu lng ien hnh (Nguon: Borzelleca, medical college of virginia, richmond,virginia, USA, 1997)

Hnh 0.2. Gian o lieu lng Phan hoi cai tien (Nguon: Borzelleca, medical college of virginia, richmond,virginia, USA, 1997)

Cc ai

Lieu lng

Ngng ti han

ap ng cc ai

Ngng gii han

Khong ap ng

Phan

hoi

ie

n h

nh

100%

Log lieu lng (mg/kg)

Hoat tnh ben trong

50%

ED50Pha

n ho

i

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Co mot so phng phap dung gian o lieu lng ap ng e so sanh o oc cua cac oc chat. Neu phan ng c xac nh theo gian o lieu lng log: o doc ln hn, oc chat manh hn. Ngha la khi lieu lng tang t se dan en s thay oi phan ng ln. S dung log lieu lng, anh hng cua LD50 hoac ED50 co the c xac nh. ay la lieu gay ra 50% phan ng cc ai cho mot ca the (gian o lieu lng ap ng cai tien) hoac la lieu gay ra phan ng cua 50% ca the trong quan the (gian o lieu lng ap ng nh lng). Mot v du cua ED50 la LD50 hoac lieu gay chet trung bnh cua mot hoa chat mot lieu n. LD50 la lieu gay chet 50% quan the sinh vat trong nhng ieu kien th nghiem xac nh ro rang. LD50 co the c dung lam c s phan loai tnh oc. V du, Ottoboni (1991) e ngh mot bang sau: Lieu gay chet qua ng mieng: botulinum toxin, 0,0001mtg/kg trong lng c the; nicotine 0,5mg/kg trong lng c the, DDT 100mg/kg trong lng c the, aspirin 1500mg/kg trong lng c the; muoi 3000mg/kg trong lng c the, ethyl alcohol 10.000mg/kg trong lng c the, ng 30.000mg/kg trong lng c the (gia tr gan ung). So sanh ED50 khong mang y ngha ay u nh khi so sanh o doc v ED50 ch la mot iem tren ng bieu dien va no khong cung cap thong tin ve quan he that s gia lieu lng va phan ng cung nh khong xac nh c ngng gii han. Nong o hoa chat iem tiep nhan tuy thuoc vao mc o trong mau. Nong o trong mau phu thuoc vao lieu lng cua hoa chat ma sinh vat b nhiem va cac ieu kien b nhiem. S hp ly cac mc lieu lng la can thiet khi so sanh phan ng oi vi cung mot hoa chat, cung mot lieu lng c dung khi co s khac nhau ve sinh vat nhiem oc, ve n v o lng. V du: 200g chuot nhan lieu lng 100mg/kg trong lng c the, hoa chat se nhan tng ng 0,061mg/cm2 dien tch be mat c the; 70kg ngi nhan cung loai hoa chat cung lieu lng la 100mg/kg trong lng c the se nhan tng ng la 0,388mg/cm2 dien tch be mat c the. Khong co so lieu thuyet phuc ve cac phng phap khac u viet hn. Thong thng, lieu lng c bieu dien qua mg/kg trong lng c the.

0.6. HAP THU, NHIEM OC, PHAN PHOI VA AO THAI OC CHAT CUA SINH VAT 0.6.1. Hap thu, nhiem oc Phan tren ta a e cap ve lieu lng, nong o, va noi ky ve

phan ng sinh hoc oi vi mot chat oc trc tiep tuy thuoc vao ban

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chat, lieu lng cua hoa chat tac dung len c quan tiep nhan. Co s khac nhau quan trong gia nhiem oc va lieu lng. S nhiem oc la s hien dien cua chat la xam nhap vao c the cua cac ca the. n v cua nhiem oc hoa chat la thng dung la ppm hoac n v khoi lng/ m3 khong kh, lt nc, kg thc pham. V du, nhiem oc da thng bieu dien qua nong o cua dung dch tiep xuc vi dien tch be mat.

Khi nhiem oc, trc tien chat oc phai thong qua moi trng i vao c the, di chuyen vao te bao qua be mat tiep xuc cua c the (nh ng da, phoi, da day, ruot) goi la s hap thu, trng hp ac biet hn, s hap thu t moi trng vao mau hoac he bach huyet. T nhng he thong lu hanh nay, oc chat xuyen qua mot vai, mot so hoac tat ca cac mo trong c the, qua trnh nay c goi la s phan phoi. Van chuyen oc chat t he thong lu hanh vao cac mo con c goi la s hap thu, no tng t nh qua trnh van chuyen mot hoa chat t be mat c the vao he thong tuan hoan. V vay, luon phai xem xet ca hai phng dien cua s hap thu chat oc:

S di chuyen t be mat c the vao trong mau (hoac lympho). S di chuyen t mau vao trong cac mo. e hieu qua trnh hap thu cac chat hoa hoc t be mat c the

vao mau va t mau vao cac mo, can khao sat cau truc va ban chat hoa hoc cua mang te bao. V trong hau het trng hp, chat oc qua mang te bao nay phai xuyen qua va at en iem ch e tao phan ng sinh hoc. Hnh 0.3 gii thieu mot te bao ong vat co vu tieu bieu cho thay mot t trong so nhieu cau truc di te bao; mot phan nho cua mang te bao trong hnh 0.4 cho thay hnh anh cua cac phospholipid va cac protein tao nen mang te bao.

Hnh 0.3. S o minh hoa mot te bao ong vat co vu

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Hnh 0.4. S o minh hoa cua mot phan te bao ong vat co vu

(Nguon: R.C.Shank, University Of California, Irvine, USA, 1997)

Trong hnh 0.4, phan t phospholipid cho thay dang oval vi hai uoi va mang protein co dang xoan mang cc dng va am.

Hnh 0.5 the hien mot phan t phospholipid la phan cau tao chnh cua mang te bao. Trong hnh nay, phosphatidylcholine c dung nh mot th du (co mot so phan t dang tng t khac trong mang te bao), loai co cc nh au phan t nc hoa tan va khong cc nh dang uoi lipid hoa tan cua phan t c the hien.

Hnh 0.5. Mot phan t phospholipid

(Nguon: R. C. Shank, University of California, irvine, USA, 1997)

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Co mot so iem ac biet e hieu ro hn qua trnh hap thu va ao thai. Mang te bao giong nh mot mang dau (dch dau) trong moi trng nc. Cac protein dang cau trong dch kham cua mang te bao dang t do di chuyen doc theo mat phang cua mang (hnh 0.6). Mot so protein nay hoan tat viec i xuyen qua mang te bao tao mot kenh di chuyen dang nc bang qua mang lipid nho nhng phan t hoa tan trong nc va cac ion co the khuyech tan thong qua nhng kenh nay, trong khi nhng phan t hoa tan trong lipid khuech tan t do thong qua thanh phan phospholipid cua mang te bao. So ln phan t hoa tan trong nc khong the bang qua mang te bao ngoai tr c cau van chuyen ac biet cac protein co the xuyen qua trong ca hai trng hp hap thu va ao thai bi mot qua trnh ac biet goi la s tham bao. C cau van chuyen ac biet ve hap thu khong c thao luan trong giao trnh nay.

V phan ln dien tch be mat cua mang te bao la phospholipid, cac hp chat hoa tan trong lipid xuyen qua mang te bao se nhanh hn so vi cac hp chat hoa tan trong nc rat kho vt qua mang te bao ngoai tr qua cac kenh protein. V vay, tren c s cau truc cua mang te bao, s hap thu co the mang mot ac tnh tong quat la:

Cac hp chat hoa tan trong lipid c hoa tan t cac be mat c the dien ra nhanh hn (thng la nhanh hn nhieu) cac hp chat hoa tan trong nc, ngoai tr cac hp chat hoa tan trong nc xuyen qua mang te bao bi mot c cau van chuyen ac biet.

Con ng chnh ma cac chat oc hai t moi trng xam nhap vao c the la thong qua da, phoi, ng da day, ruot.

Vai hoa chat ngoai lai co the tac ong trc tiep len mat ngoai cua mang nhay te bao, ket hp vi mot protein ac biet (bo phan tiep nhan) trong mang. Phan ng vi protein ac biet tren mang nay co the tao nen hp chat noi sinh e dch chuyen t mang nhay te bao en cac noi bao quan khac trong te bao, nh cac nhan, e tao nen mot phan ng sinh hoc.

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Hau het cac chat oc c hap thu qua cac te bao bieu b, tuyen mo hoi va chan toc, chiem dien tch 1% so vi tong dien tch da, mot t chat oc c hap thu hoan toan cac iem nay. Lp mo sng la lp ngoai cung cua bieu b va c tao thanh t cac te bao khong nhan, c sng hoa, cac te bao chet cha chat sng (mot protein si). Cac te bao lien ket vi nhau e hnh thanh mang te bao linh ong, chat che. Lp sng c phu len mot lp lipid mong. Cac bieu b la mot gii han cho s hap thu. oc chat co cc xuat hien e khuech tan ra be mat ben ngoai cua cac si keratin (sng) cua lp mo

Hnh 0.7. Cau truc te bao cua mot bieu b (Nguon: R.C.Shank, University Of California, Irvine, USA, 1997)

Hnh 0.6. Cau truc mot mang te bao ong vat co vu

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sng hydrate hoa. oc chat a dau (k nc) hoa tan va khuech tan thong qua lipid khong ngam nc gia cac si protein. Mc khuech tan co lien quan en s hoa tan lipid va ty le nghch vi trong lng phan t. e mot oc chat c hap thu qua da vao he tuan hoan no phai xuyen qua mot so lp te bao.

Mc o lam sach cua cac oc chat t bieu b vao he thong tuan hoan phu thuoc vao o day cua da, anh hng cua van chuyen mau, s dch chuyen cua dch ruot, he bach huyet va cac yeu to khac. S hap thu nhanh hn, mat o mau cao hn, s phan phoi ln hn va ap suat khuech tan se lam cho oc chat xam nhap vao cac te bao cua c the. Mc hap thu khac nhau cac khu vc vc khac nhau tren da ngi c ch ra hnh 0.8.

Hnh 0.8. Cac v tr hap thu chat oc tren c the ngi qua da

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0.6.2. S hap thu cua cac chat oc phoi

Phoi ngi co hn 50m2 dien tch be mat phe nang, khoang cach gia bieu mo phe nang va thanh ong mao dan mau xap x 10 microns (hnh 0.9).

Cac kh hoa tan trong nc hoa tan trong mang nhay cua ng th va co the tch tu o, gay ra s nguy hiem cuc bo; cac kh hoa tan trong lipid khuech tan qua mang phe nang mc o phu thuoc vao he so ty le lipid/ nc va lng kh hoa tan trong mau. The kh c hoa tan phu thuoc vao kch thc cac hat va tnh trang kh ong, he so ty le lipid/ nc va mot so yeu to khac.

Cac hat co ng knh ln hn 10 m th thng tac ong en he ho hap tren ac biet la mui va kh quan. Cac hat co ng knh t 15 m tac ong en nhanh cuong phoi, di va ong phe nang. Cac hat co ng knh nho hn 1 m thng tac ong en tui phe nang. Cac hat tren ng ho hap tren cuoi nhanh cuong phoi thng c chuyen dan len nh cac mao bieu b va cuoi cung c khac ra ngoai hoac nuot vao ng tieu hoa. Mc o van chuyen cua cac mao bieu b la kha nhanh, o bang mm/phut hoac cm/phut tuy thuoc vao v tr tren ng ho hap va ban chat cac hat. Thng hn 90% cac hat dnh vao mang nhay co the a ra khoi phoi trong vong 1h. Cac hat tren nhanh cuong phoi di co the c mang en vung co mao bieu b bi cac ai thc bao va dch phe nang; s di chuyen tuy thuoc vao dong bach cau, hoat ong cua ong mao dan, s van ong cua

Hnh 0.9. Mat cat lien he gia thanh phe nang va thanh ong mao dan (Nguon: R. C. Shank, University of California, Irvine, USA, 1997)

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thanh phe nang, ban chat dnh ket cua chat nhay tren ng ho hap va lc ay cua long nhanh cuong phoi. Co khoang 50% tong so vat chat c lam sach trong mot ngay, oc lap vi ban chat cua oc chat; nhng hat con lai se c lam sach trong vai ngay hoac hang nam tuy thuoc vao loai hp chat. Cac hat hoa tan t nhat trong ong nhay th c lam sach cham nhat. Cac hat hoa tan trong phe nang khuech tan trc tiep vao he mach mau phoi; cac hat khong hoa tan co the xam nhap cham vao da day vao mau thong qua he bach huyet.

0.6.3. S hap thu chat oc bang ng da day ruot

S hap thu co the xay ra t mieng en ng ruot. Mot cach tong quat, cac hp chat c hap thu theo ty le cac hp chat thoat ra nong o cao nhat va dang hoa tan trong lipid ln nhat trong ng ruot. Cac chat oc rat giong nhau trong cau truc dinh dng va ien giai co the c van chuyen hoat hoa vao trong mau (V du: 5 fluo racil bi pyrimidine van chuyen; ch bi calcium van chuyen).

Cac hat co ng knh vai tram Angstroms (1 Ao = 108cm = 0,1 nanomet) vao trong bieu mo ruot, c van chuyen qua te bao chat trong cac tui tr, c thai vao nhng ke h cua mang va roi xam nhap vao cac he bach cau cua chat nhay; giong nh s hap thu chat beo (v du, cac hat thuoc nhuom Azo, co ng knh vai tram Ao, cac hat nha mu co ng knh 2.200 Ao, botulinum toxin. Xem hnh 0.10.

(Nguon: R.C.Shank, University of California, Irvine, USA, 1997) Hnh 0.10. S van chuyen cac hat vat chat qua bieu mo ruot

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Cac hnh thc chuyen hoa sinh hoa quan trong xay ra trong ng da day ruot co the thay oi s hap thu hoac thay oi tnh oc. Nhng s chuyen hoa nay xay ra do vi sinh (thc vat) va/ hoac trong cac te bao bieu mo tren ng.

Nhieu chat oc co tnh axt yeu hoac kiem yeu va thoat khoi vao dung dch nh mot chat hon hp cua ion hoa (pronton hoa) va dang lien ket. Nhng trng hp t cc hn dang lien ket th thng c dung cho chat hoa tan trong lipid va la dang se khuech tan nhanh qua mang lipid. Ty le cua mot oc chat thoat khoi lien ket phu thuoc vao s phan ly co nh cua hp chat va ch so pH cua dung dch ma no c hoa tan.

S phan bo va ao thai chat oc tuy thuoc:

1. Cac khoang cha nc

2. Cac khoang cha lipid

3. Lien ket ai phan t

4. Qua ng nhau thai

5. Qua ng nao, dch nao tuy

6. ao thai qua ho hap

7. ao thai qua than

8. ao thai qua mat

9. Qua trao oi chat

10. Qua ng sa, o mo hoi, nc bot, nc mat, bai tiet th cap.

Lien ket protein cua cac chat oc th giong nhau, oi vi lien ket c chat enzym va lien ket dc pham c quan tiep nhan, tr phi c chat khong phan huy hoac khong co bat ky qua trnh phan ng sinh hoc nao. Khong co lien ket cong hoa tr, ch co lien ket ion va v vay qua trnh la thuan nghch (lien ket cong hoa tr thng c xem nh mot chat kiem hoa cua arylation va khong c xem xet ay).

Lien ket xuat hien hai loai protein cua nguyen sinh chat va mo, khong phai tat ca protein lien ket vi mot oc chat eu cung mot pham vi, mc o lien ket phu thuoc vao kieu va so lng v tr lien ket tren protein va ch so pH cua dung dch.

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Albumin rat quan trong (cha 50% dch trng protein), no co xap x 100 cc dng va 100 cc am cac iem lien ket (COO O S NH 3+ = NH2+ NH2+) pH 7,4 tnh am cua albumin hn tnh dng, pH 5 co khoang 500 cho moi phan t. Phan ng sinh hoc do oc chat gay ra phu thuoc vao nong o cac chat oc khong lien ket dang dch tng.

Cac chat oc dang lien ket ben vng vi protein cua mau se tch tu trong c the va co the gay nguy hiem. Cac hp chat lien ket dch tng co the c giai phong, tach ra ot ngot do s xam nhap cua cac hp chat mi co the canh tranh vi chung cung mot thi iem lien ket.

V du: oi vi mot vai tre s sinh, khi gan thieu enzyme glucuronyl transferase, chat co kha nang ket hp vi bilirubin (C32H36N4O6) tao ra san pham hemoglobin thoai hoa th mot lng ln bilirubin c sinh ra tch tu trong dch tng albumin (hyper bilirubinemia). Neu tre em dung sulfonamide hoac vitamin K thay the bilirubin t albumin, bilirubin co the c phong thch va vao nao gay benh Kernicterus (chng benh khi phat trien se pha huy cac te bao than kinh trong nao).

0.6.4. Mc hap thu

Can lu y, y ngha cua hieu ng gay oc la s tap trung cua chat oc iem tac ong au tien.Trong hau het trng hp, s hap thu xuat hien do s khuech tan thu ong, cho nen, mot mc ty le gradient nong o gia iem hap thu va mau, mc hap thu c dien ta bi phng tnh ham mu hoac con goi la phng trnh ong lc th nhat:

Log M = logMo

Trong o:

Mo = Nong o ban au cua hoa chat ngoai lai iem hap thu

M = nong o cua hoa chat ngoai lai thi gian t iem hap thu

ka: hang so toc o hap thu, tng ng vi 0,693/t1/2 t1/2 = ban ky hap thu; la khoang thi gian khi M/ Mo =1/2

kat 2.30

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Th du, nong o cua mot chat oc thc pham trong da day xac nh mc o o chat oc c hap thu t da day vao mau, khi nong o cua oc chat trong da day tang len, nh s hap thu vao mau, mc o oc chat c hap thu cung tang len.

Hau het cac chat oc nong o thap c loai bo khoi c the tuy theo nong o cua chung trong mau va s trao oi chat vi cac hp chat hoa tan trong nc. a so cac chat oc lieu lng cao, s trao oi enzyme co the bao hoa va mc trao oi la hang so, neu chat oc hoa tan trong lipid, s ao thai chung se kho khan va mc o ao thai tr thanh zero order (chuoi zero) (hang so, khong lien he vi nong o mau) en khi nong o chat oc thap hn mc bao hoa.

0.7. PHAN NG LAI OC CHAT CUA SINH VAT VA HIEU NG OC

0.7.1. Nhng khai niem

Phan ng lai cua sinh vat oi vi anh hng cua oc chat la s phan ng cua c the hoac mot bo phan c the (th du nh he c bap) oi vi mot kch thch (Duffus,1974). S kch thch co the co mot so dang va cng o phan ng thng phu thuoc cng o kch thch. Kch thch manh hn tao phan ng manh hn. Khi mot oc chat gay kch thch, s phan ng thng phu thuoc lieu lng chat oc va chu ng cua moi sinh vat. Mot phan ng con la mot hieu ng.

Mot hieu ng xau, thng ton hay ngo oc, la s thay oi co hai hoac la mot phan ng oi vi tac nhan hoa hoc hay vat ly. Duffus nh ngha: Mot hieu ng xau la s thay oi ve hnh thai, ve sinh ly, ve tang trng, phat trien hoac tuoi tho cua mot sinh vat, ket qua la lam giam kha nang chu ng, lam suy yeu kha nang e khang, tang nguy c stress, tang tnh nhay cam oi vi hieu ng nguy hai t tac ong moi trng. Hieu ng xau co the va phai va bien mat sau o hoac nghiem trong hn, oi khi khong the hoi phuc. Th du, d ng ho hap hoac thay oi hoa tnh huyet thanh co the tnh trang nhe va phuc hoi nhng ung th lai la van e nghiem trong, oi khi khong the cu van.

Mot tac nhan hoa hoc hoac vat ly co the gay ra hieu ng xau hoac nguy hai do thay oi tnh nguyen ven, thay oi cau truc hoac/ va thay oi chc nang cua mo te bao. Ngoai ra con gay anh hng en s tang trng, phat trien, lien lac, lu thong, hoi phuc va tuoi tho.

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Cac hieu ng co the ngc lai va ket qua la s phuc hoi hoac khong the phuc hoi dan en t vong.

Nhng hieu ng mem bao gom thay oi thc an cung cap va/ hoac tang trong c the, thay oi hoat tnh enzyme hoac thay oi ln cac mo va c quan. Nhng hieu ng xau nghiem trong bao gom thay oi cau truc va chc nang trong cac mo, bieu hien s suy giam chc nang lam viec bnh thng, khong phuc hoi cau truc t sao chep te bao cua ARN, tham ch t vong. Nhng thay oi co y ngha ve mat thong ke theo cach thong thng khong co ngha la s thay oi sinh hoc ang chu y v y ngha thong ke khong bao ham y ngha sinh hoc.

Nhng phan ng gay ra bi cac tac nhan hoa hoc, vat ly co the la tc th hoac dan dan, em du hoac d doi, co the phuc hoi hay khong phuc hoi, cuc bo hoac he thong, phan ng ac d hoac d ng thong thng, trc tiep hoac gian tiep, co li hoac xau. Phan ng oi vi tac nhan phu thuoc vao cac ieu kien b nhiem bao gom ng xam nhap thi gian mac phai, lieu lng hoac mc o nhiem oc.

Phan ng cuc bo dien ra tai ni hap thu hoac tiep xuc gia c quan va chat kch thch va mot phan ng theo he thong xay ra mot hoac nhieu ni ngoai ni b hap thu oc chat. D ng hoac phan ng ac biet nhay cam la mot phan ng oi khang cua he mien nhiem. Mot phan ng ac d la loai phan ng khong bnh thng, khong theo chu ky, bao gom phan ng cua he mien nhiem hoac co the gay ra bi s khac nhau ve di truyen trong cau truc gen.

Co nhieu loai phan ng xay ra khi co tng tac gia hoa chat va bo phan tiep nhan, gom co thay oi ve hnh the tong quat, thay oi te vi hoac thay oi trong cac chc nang sinh ly, sinh hoa. Cac phan ng co the khong ac hieu nh viem, hoai t hoac ac hieu nh ot biet gien, d tat, ung th. Thay oi co the dien ra lap tc hoac dan dan, co the hoi phuc hoac khong; co tnh cuc bo hoac he thong, co the n gian hoac phc tap, co the co li hoac co hai. Phan ng co the anh hng en tnh ong nhat, chc nang, s tang trng qua trnh hoi phuc, lien lac cua te bao. Nhn chung, phan ng co the lam tang hoac giam chc nang. Tuy nhien, c s t nhien cua te bao th khong the b thay oi do chat hoa hoc, th du te bao c khong the b bien oi thanh te bao bai tiet. C s cua nhng hieu ng xau hoac thng ton mc o te bao la s thay oi noi can bang.

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0.7.2. Cac nhan to anh hng en kha nang phan ng lai

Mot vai yeu to co the anh hng en phan ng cua mot hoa chat gom co: ac tnh ly hoa, o tinh khiet, o ben vng cua hoa chat, ieu kien anh hng (lieu lng bao nhieu?), thi gian (thi iem, tan so, keo dai bao lau?), bang con ng nao (cach thc xam nhap, ac tnh di truyen, loai, giong, gii, tnh, tuoi, trong lng c the, tnh trang sc khoe cua sinh vat thi iem tiep xuc, s co mat cua hoa chat khac (tng tac), ieu kien moi trng (nhiet o, o am, ap suat kh quyen, o sang, ni c tru, tieng on, cac hoa chat trong moi trng, cac yeu to xa hoi), s phu hp hoac sai biet, tnh nhay cam rieng. Phan ng phu thuoc so lng cac bo phan tiep nhan, pham vi lien ket hoa chat bo phan tiep nhan, nong o hoa chat tai iem tiep nhan.

Anh hng cua mot hoa chat len hoat ong cua mot hoa chat khac c goi la s tng tac. Ket qua phan ng co the cong them (1 + 1 = 2); khong cong them (1 + 1 = 1 hoac 0), hoac cong nhan len (1 + 1 = 5); thong thng kho oan biet.

Phan ng oi vi mot tac nhan hoa hoc, vat ly phu thuoc vao lieu lng va so lng cua bo phan tiep nhan ang hien dien va hoat tnh cua no. lieu lng thap, phan ng co the khong c nhan biet. Khi tang lieu lng va so lng cua quan he chat c quan tiep nhan, mot phan ng ang chu y se c ghi nhan. Lieu lng thap nhat e nhan ra mot phan ng o c c goi la ngng ti han cua lieu lng. Mot phan ng se khong c nhan biet neu lieu di ngng ti han. Moi sinh vat co mot ngng ti han rieng, xac nh bang thc nghiem. Trong mot chuoi phan ng, co mot ngng ti han cho moi gian oan cua qua trnh. Nhan dien mot ngng co ngha la vi mot nong o chat kch thch hoac tac nhan nao o, chat kch thch hoac tac nhan o se tao ra phan ng. Phan ng nhan thay va cac phng phap nh lng, tnh nhay cam co the anh hng en viec xac nh ngng ti han. Co the ra nhng ngng ti han bang so cho te bao, mo, c quan va c quan nguyen ven khac.

Lieu lng thch hp cua dc pham tac nhan vat ly co the c dung e cha benh, th du s dung bc xa cac yeu to se anh hng en ket qua cua tng tac gia tac nhan hoa hoc hoac vat ly vi mot

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c quan gom co lieu lng, the trang (c a), ac tnh hoa hoc cua tac nhan, thi gian tac dung, tnh trang sc khoe cua he sinh thai hoac sinh vat thi iem b nhiem.

Mot hoa chat hoac tac nhan vat ly thong thng bat au tng tac vi mot mo hay c quan ac biet goi la "mo ch" hay "c quan ch" (c quan tiep nhan tac dung). Mo ch hay mo nhay cam co cha vung nhay cam ac biet hoac cac te bao tiep nhan tac nhan. Mot chat tiep nhan co the xem la bay hoa chat khi mot tac nhan hoa hoc tng tac vi mot chat tiep nhan ac thu e tao ra phan ng no, c goi la chat tiep nhan phan ng trung gian. Khi mot tac nhan hoa hoc tao ra mot phan ng khong tng tac vi chat tiep nhan ac thu, phan ng c goi la mot phan ng khong ac hieu. Bo phan tiep nhan la ni tng tac vi tac nhan hoa hoc, vat ly ben ngoai hoac ben trong te bao ch, la iem nhay cam va ni xay ra phan ng. Tiep nhan co the xay ra ba ni: tren be mat cua te bao, oi khi con goi la kieu I; trong nang te bao c goi la kieu II; trong nhan te bao, c goi la kieu III. Ket qua cua tng tac bo phan tiep nhan hoa hoc la khi au mot day chuyen phan ng sinh hoa tao nen phan ng c nhan dien. Moi tac nhan hoa hoc hoac loai hoa chat co bo phan tiep nhan ac thu, th du, tiep nhan chat giam au. Chung co the khong ac hieu, th du, s pha huy do an mon gay ra bi a xt. Bo phan tiep nhan chat oc co tnh rieng biet, ac thu nh cac ai phan t, thng la cac protein, bao gom protein ieu hoa, enzyme, protein van chuyen, protein cau truc.

Phan ng oi vi mot tng tac hoa hoc bo phan tiep nhan la tao ra so lng cac bo phan tiep nhan trong luc tng tac xay ra hoac cac dang phc hp. So lng cac bo phan tiep nhan tuy thuoc ai lc cua bo phan tiep nhan oi vi hoa chat, nong o hoa chat san sang tng tac vi bo phan tiep nhan, thi gian tac dung va cac yeu to phc tap khac. Cac phc hp hoa hoc bo phan tiep nhan tao nen phan ng. Ai lc la lc hap dan gia mot hoa chat va mot bo phan tiep nhan.

Khi mot hoa chat va mot bo phan tiep nhan tng tac tao nen mot phc hp, bo phan tiep nhan se gia tang hoat tnh. Khi ieu nay xay ra, chat hoa hoc c goi la mot chat kch thch; khi o, chat kch thch bam vao bo phan tiep nhan va hoat hoa chung. Khi mot chat hoa hoc bam vao mot bo phan tiep nhan nhng khong hoat hoa

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no, phan ng khong xay ra, va chat hoa hoc goi la chat oi khang. Khi mot chat hoa hoc bam vao mot bo phan tiep nhan va ch hoat hoa mot phan, phan ng co the xay ra va chat hoa hoc c goi la chat kch thch mot phan. Kha nang cua mot phc hp hoa chat bo phan tiep nhan e tao ra phan ng c goi la hoat tnh rieng hay tnh hieu qua neu hoa chat la mot dc pham. Bo phan tiep nhan phai bam dnh hoa chat, c hoat hoa khi co hoa chat va bat au mot chuoi phan ng lien tiep. Chat kch thch tao ra mot phan ng tng tac c bieu dien di dang ng cong quan he gia lieu lng ap ng. Chat oi khang co the c phan loai thanh hai loai: co tnh canh tranh hoac khong co tnh canh tranh. Chat oi khang canh tranh tng tac cung mot iem cua bo phan tiep nhan, ch co no bam vao bo phan tiep nhan. Chat oi khang khong canh tranh lien ket cong hoa tr vi bo phan tiep nhan va thng xuyen bat hoat no.

Lien ket hoa hoc gia mot oc chat va mot bo phan tiep xuc co the gom cac loai: lien ket cong hoa tr, lien ket ion, lien ket hydro hoac lc Van der Waals lien ket t nhien se anh hng en thi gian tac dung cua phc hp hoa chat bo phan tiep nhan va thi gian cua hieu ng. Lien ket cong hoa tr thng khong ao ngc c, con lien ket ion, lien ket hydro, lien ket Van der Waals th co the ao ngc c.

e bo phan tiep nhan tao nen mot phan ng trc het no phai lien ket vi chat hoa hoc. Thong thng ay khong phai la lien ket cong hoa tr, co the ao chieu va tuan theo luat tac dung khoi lng. Cng o cua tng tac c goi la ai lc, no xac nh o manh, hoat tnh cua hoa chat. Khi lien ket, bo phan tiep nhan phai c hoat hoa, o la qua trnh tn hieu tai nap, mot ch so xac nh hoat tnh rieng. Viec nay c theo sau bi mot chuoi lien tiep cac phan ng tao nen hieu qua cc ai cua phan ng. Tien trnh nay c goi la tiep nhan ap ng ghep oi va c ket hp vi chat truyen tin th cap e khuyech ai tn hieu t bo phan tiep nhan hoat tnh.

0.8. S AO THAI OC CHAT

Viec loai bo chat oc t c the goi la s ao thai oc chat. Qua trnh nay thng at c nh hoat ong ac biet cua than (tao nc tieu), gan (tao mat) va phoi (th ra cac hp chat dang hi) hay qua da

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do phat tan mo hoi. Qua trnh ao thai co c che tng t vi qua trnh hap thu, van chuyen cac hoa chat tham thau qua cac mang sinh hoc theo chenh lech nong o hoa chat (gradient nong o); cac hoa chat di chuyen t cac khoang co nong o cao en cac khoang co nong o thap.

Cac hp chat hoa tan trong nc co the nhanh chong c ao thai bi than thong qua bai tiet nc tieu (thng la cac hp chat co khoi lng phan t di 400) va bi gan thong qua mat (thng la cac hp chat co khoi lng phan t ln hn 300). Qua trnh ao thai co c s tng t vi qua trnh hap thu, van chuyen cac hoa chat tham thau qua cac mang sinh hoc theo chenh lech nong o hoa chat (gradient nong o); cac hoa chat di chuyen t cac khoang co nong o cao en cac khoang co nong o thap.

Tng t trng hp hap thu, co nhng qua trnh ac biet co the tac ong chong lai chenh lech nong o va co the di chuyen cac hp chat hoa tan trong nc nhanh chong xuyen qua cac mang lipid, s tiet mat (mot dang dch) bi gan la mot th du cua mot mo thoat khoi cac te bao hp chat hoa hoc hoa tan c trong nc.

Cac hp chat hoa tan trong lipid co the ao thai mot cach cham chap, va nh vay cuoi cung vao ng bai tiet dch cua c the nh nc tieu, mat. Cho nen, cac hp chat hoa tan trong lipid c gi trong c the thi gian dai hoac en khi chung c trao oi chat vi cac chat dan xuat hoa tan trong nc. Cac hp chat hoa tan trong lipid c loc t mau mot cach nhanh chong nh than c tai hap thu vao than trc khi thai ra khoi c quan bang ng tieu. Than co the loai bo ch cac hp chat hoa tan trong nc va trong cac trng hp ac biet, cac hp chat co tnh chat hoa hoc ac trng dang anion hoac cation co he thong van chuyen hoat ong e di chuyen cac hp chat nay t dch tng vao trong nc tieu.

0.9. GIAI QUYET VAN E O NHIEM THC CHAT LA GIAI QUYET VAN E OC HOC MOI TRNG

0.9.1. Moi quan he gia oc hoc moi trng va o nhiem moi trng

oc hoc moi trng va o nhiem moi trng la hai khai niem co cho khac nhau nhng trong cung mot logic cua khoa hoc moi trng ve

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mat gay hai cho con ngi va he sinh thai. Trc het, t 2 nh ngha chung ta thay co s lien he khang kht va nhan qua gia chung.

oc hoc moi trng la mot nganh khoa hoc chuyen nghien cu nguon goc, hanh vi va cac tac ong gay hai cua oc chat, oc to trong moi trng oi vi cac sinh vat song va he sinh thai.

O nhiem moi trng la hien tng lam thay oi cac thanh phan cua moi trng theo chieu hng xau i vt qua mot gii han nhat nh, gay anh hng len sinh vat va con ngi.

Va bat ky mot chat oc, chat o nhiem nao khi c a vao moi trng th se chu tac ong cua cac yeu to t nhien va khi tiep xuc vi c the sinh vat se gay ra cac tac ong len sinh vat thong qua viec chuyen hoa cac chat va co the gay bien oi ve sinh hoa dan ti gay benh cho c the theo s o sau:

Chuyen hoa

Chat o nhiem>Chat oc >C the, He sinh thai

Tac ong gay oc

Theo nh cac nhan biet tren th bat ky cac hien tng o nhiem moi trng nao cung eu do cac tac nhan gay o nhiem ma cac tac nhan gay o nhiem goi la chat o nhiem va no chnh la cac oc chat moi trng va co the c the hien bang s o sau:

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Cac nguon gay o nhiem

Chat thai

O nhiem moi trng

Chat o nhiem

oc hoc moi trng

oc chat

Sinh vat va he sinh thai

T s o tren ta thay gia oc hoc moi trng va o nhiem moi trng co moi quan he mat thiet vi nhau. Tat ca cac trng hp o nhiem moi trng eu do cac tac nhan gay o nhiem ma cac tac nhan gay o nhiem chnh la cac oc chat cua oc hoc moi trng.

Muc tieu cua oc hoc moi trng la phat hien cac tac chat (hoa hoc, vat ly, sinh hoc) co nguy c gay oc e co the d oan, anh gia cac s co va co bien phap ngan nga nhng tac hai oi vi cac qua trnh t nhien (bao gom ca con ngi) trong he sinh thai. Cac th nghiem vat ly, hoa hoc, sinh hoc a cung lien ket thc hien e d oan cac anh hng xau cua oc chat co the xay ra trong moi trng (Le Huy Ba, 2000).

Trong o oc chat, oc to (toxicant, toxin) c nh ngha la mot vat chat (subtance) co the gay ra nhng anh hng bat li hoac cai chet cho sinh vat song. Vat chat ay co the la tieng on (anh hng vat ly), hoa chat (anh hng hoa hoc), vi khuan (anh hng sinh hoc) Ch co the trong nh ngha nay lam cho khai niem oc to co mot ngoai dien logic rat rong ln. V the co the noi, xung quanh ta moi cai eu oc va khong co cai nao khong oc (All things are poison and none that are not!). ieu quyet nh mot vat chat tr thanh oc to la tuy thuoc vao lieu tac dung (dose), cach thc vat

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chat xam nhap vao c the song va thi gian tiep xuc vi lieu. Qua trnh tiep xuc vi lieu goi la s phi nhiem (exposure). Hay noi cach khac, mot oc to tr nen oc la tuy thuoc vao s phi nhiem.

0.9.2. Giai quyet o nhiem moi trng x ly oc chat, oc to

X ly o nhiem la khai niem bao gom ca viec quan ly, han che o nhiem, e phong o nhiem, khac phuc o nhiem. Trong o, han che va e phong o nhiem la viec lam kho khan nhat va la muc tieu cho moi trng ben vng. Nh vay, khi nghien cu giai quyet van e ve moi trng, chung ta phai tm hieu xem nhng tac nhan, tac chat nao gay ra o nhiem moi trng, t o co giai phap, phng an thch hp. oc hoc moi trng nghien cu nguon goc cac oc chat, oc to, cac phan ng, cac anh hng tac ong cua cac oc chat trong moi trng (at, nc, khong kh) giup hieu ro ban chat cac hien tng o nhiem moi trng xay ra xung quanh va a ra nhng giai phap tch cc nham ngan chan nhng tac ong co hai en moi trng, he sinh thai va quan trong hn la con ngi.

Neu giai quyet van e moi trng ma khong hieu ro ban chat, tc la khong nhan biet c nhng oc chat, oc to nao trong van e o nhiem ay th thc chat chung ta cha hieu ro nguyen nhan gay o nhiem, ma a khong hieu ro, khong tm ra c nguyen nhan th ng mong g giai phap a ra la ung, la phu hp ch ng noi en toi u. Noi mot cach nom na la neu cha nhan dang c oc chat, oc to trong o nhiem th cung giong nh khong chan oan c benh, the th lieu thuoc a ra chac chan la khong tr c benh roi, co khi lai tien mat tat mang.

ieu o cung co ngha rang khi chung ta nhan mat, ch ten c nhng oc chat, oc to nao trong tng loai o nhiem th van e a ra giai phap phong tranh va x ly cung de dang va hieu qua hn. Xin n c mot vai th du trong moi trng khong kh e chng minh nhan nh giai quyet van e moi trng thc chat la giai quyet van e oc hoc moi trng.

Trong o nhiem khong kh, mot thong so c quan tam hang au o la bui. Trong oc hoc moi trng th bui nam trong phan oc hoc moi trng khong kh. Bui la nhng hat nho kch thc t 1

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en vai tram m trong o nguy hiem va gay oc la bui co kch thc t 15 m.

+ O nhiem bui florua c phat sinh giong nh kh florua, anh hng oi vi thc vat, lam chay la, huy hoai te bao bieu b, nhat la te bao mo phan sinh, gay chet cay. Suc vat an phai florua se mau gia hn.

+ O nhiem bui ch: sinh ra t cac hoat ong cua cac phng tien giao thong. Nhng ngi thng xuyen tiep xuc vi giao thong nh lai xe, cong an giao thong, ban xang dau co ham lng ch ln hn nhng ngi khac. Neu ham lng ch len ti 0,8ppm th se phat sinh benh thieu mau, hong cau giam ro ret va gay roi loan oi vi than.

+ O nhiem bui than, bui amiang va bui bao mon gia lop va ng oto (khi oto chay tren ng, ac biet la khi phanh oto, cac banh xe se ma sat vi mat ng lam mon ng va banh xe gay ra bui a, bui cao su va bui amiang). Cac loai bui nay cung vi bui than, bui a eu co anh hng xau en con ngi, ong vat va thc vat. oi vi thc vat no cung gay ra benh chet hoai, lam rung la, lam giam hoa qua va nang suat cay trong, lam be qua va teo hat.

+ O nhiem bui sinh vat: la cac hat bui co mang theo cac vi trung, vi khuan, vi rut. ay la bui gay ra cac benh ho hap.

Vay e x ly cac chat o nhiem trong moi trng chung ta phai xac nh ham lng, kha nang tac ong cua chung oi vi he sinh thai ngha la chung ta i xac nh tnh oc cua cac oc chat co trong moi trng. Hien nay co nhieu phng phap a ra nham giai quyet o nhiem bui nh:

+ Giam lng phat thai cac nguon phat sinh bui

Bien phap cong nghe Thay the nguyen, nhien lieu Thay oi quy trnh cong nghe. Bien phap luat le ong ca nha may lac hau sinh bui nhieu. ong ca tam thi khi co s co.

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Tang cng giam sat s phat thai. + Giam s tac ong cua nguon thai oi vi moi trng.

Nang cao ong khoi. Tap trung cac ong thai gan nhau lai chung mot ong. Gia tang khoang cach t nguon ti nhng vung b tac ong. oi vi bui giao thong co the trong cay xanh ven ng e

hap thu bui.

Chung qui lai, x ly bui la tm cach thu gom lng bui sinh ra tc la lam triet tieu oc chat do bui sinh ra. Bui la mot oc chat moi trng va la tac nhan gay benh chnh cua cac benh bui phoi, gay ra cac benh nh: viem phoi, kh thung phoi, ung th phoi, viem mui d ng, hen phe quan Va giai quyet o nhiem bui la giai quyet cac van e ve oc hoc cua bui va a co cac bien phap giai quyet nh tren. o la cach giai quyet tai nguon cua oc hoc moi trng. Triet tieu o nhiem moi trng tc la giam thieu nhiem oc cho sinh vat va con ngi trong moi trng. Tat nhien, ben canh bien phap nay chung ta con nhieu bien phap na cua oc hoc..

0.9.3. Cac dang o nhiem gay oc moi trng

0.9.3.1. O nhiem va gay oc moi trng nc

+ O nhiem vo c: do cac hoat ong cua cong nghiep, nong nghiep thai ra moi trng cac chat oc hai co nguon goc vo c gay o nhiem moi trng. Tuy theo cac nganh cong nghiep ma se thai ra moi trng cac chat khac nhau, con oi vi nong nghiep o la cac hoa chat bao ve thc vat, phan bon d tha.

Cac chat gay o nhiem: kim loai nang nh Al, Zn, Fe, As, Hg, Cd, Pb; mui; mau

+ O nhiem hu c: Cac nganh cong nghiep ac thu tao ra nh: che bien thc pham, thuoc da, che bien thuy san, Trong nong nghiep dung hoa chat bao ve thc vat co cac nhom chc hu c, cac loai phan bon hu c Nhu cau sinh hoat cua con ngi cung la mot nguon gay o nhiem hu c rat ln.

Cac chat o nhiem: cac hp chat hu c khong ben, cac vi sinh vat gay benh: E.Coli, Coliform, cac vi trung va sieu vi trung song

31

trong nc o nhiem hoac la o nhiem dinh dng: NO3, PO43 Tuy thuoc vao ac iem cac nganh san xuat ma nc thai co thanh phan khac nhau. Ta co the tom tat trong bang sau:

Bang 0.1. Cac chat gay o nhiem ong thi la gay oc cho sinh vat va he sinh thai

Cong nghiep Chat o nhiem chnh Gay oc

Chat o nhiem phu Gay oc

+ Che bien sa

+ Che bien o hop, rau qua ong lanh.

+ Che bien bia, ru

+ Che bien tht

+ Xay bot

+ Luyen thep

+ C kh

+ Thuoc da

+ Xi mang

+ San xuat knh

+ San xuat phan hoa hoc

Phan am

Phan lan

Chat hu c ban phan huy, gay thoi, SS

Chat hu c ban phan huy, gay thoi, SS

Chat hu c ban phan huy, gay thoi, SS, chat ran co the lang, N, P.

Chat hu c ban phan huy, gay thoi, SS, chat ran co the lang, dau m.

Chat hu c ban phan huy, gay thoi, SS, nhiet o

Dau m, pH, NH4+, CN

phenol, SS. Fe, Sn, Cr,Zn,..

Hu c gay thoi, dau m SS,CN, Cr,Zn, Ni, Pb, Cd

Chat hu c ban phan huy, gay thoi, SS, mau, kim loai nang, NH4+, dau m, phenol, sulphua

Bui, SS, amian,

SS

Chat mang mau, tong P, N, TOC,

Chat mang mau, tong P, N, TOC, T0.

TDS, chat mang mau, chat gay o uc, bot noi.

NH4+,TDS,P, chat mang mau

Chat hu c ban phan huy, gay thoi, TOC,TDS

Clo, SO42,...

N, P, TDS, coliform

Cromat, P, Zn, sulphua, TDS

Chat hu c ban phan huy, gay thoi, Cromat, Zn, Cu, Cr, Fe, Sn, TDS

PO43, SO42, hp chat hu c

o uc, clo hu c, P, kim loai nang, phenol,

Chat hu c ban phan huy, gay thoi, phenol, F, silicat, CN, kim loai nang,

Cl, CN, Pb, N, P, TOC, Zn, o

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+ Hoa chat hu c

+ Hoa chat vo c

+ Hoa dau

+ Nhiet ien

NH4+, TDS, NO3, SO42, ure

TSS,TDS,dau noi

axit, kiem, tong chat ran, SS, TDS, Cl, pH

NH4+, Chat hu c ban phan huy, gay thoi, Cr, dau, phenol, SS,TDS, sulphua,

Cl2, dau, SS

uc

Cu, Fe, TDS, Zn.

0.9.3.2. O nhiem va gay oc moi trng khong kh

O nhiem khong kh la hien tng lam cho khong kh sach thay oi thanh phan, tnh chat trc bat ky nguyen nhan nao, vt qua mot gii han cho phep, co nguy c gay oc, tac hai ti thc vat va ong vat, en moi trng xung quanh, en sc khoe con ngi. Qua trnh gay o nhiem roi gay oc khong kh co cac bc sau:

- Nguon gay o nhiem co nguy c khong kiem soat c.

- Qua trnh phat tan, lan truyen trong kh quyen c xem nh la moi trng trung gian.

- Nguon tiep nhan chat o nhiem khong kh la do ong vat, thc vat, con ngi.

Cac nguon va cac chat gay o nhiem roi tien ti gay nhiem oc khong kh (Bang 0.2)

Bang 0.2. Lng o nhiem va gay oc cho khong kh

Trieu tan/nam Nguon CO Bui SOx THC NOx

Giao thong 111.0 0.7 1.0 19.5 11.7

ot cong nghiep 0.8 6.8 26.5 0.6 10.0

Qua trnh CN 11.4 13.1 6.0 5.5 0.2

X ly chat thai ran 7.2 1.4 0.3 2.0 0.9

ot cui go noi chung 16.8 3.4 0.3 7.1 9.4

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Nguon thai ra CO2:

+ Hoat ong trong khu vc nang lng lam gia tang lng kh thai CO2 vao kh quyen chu yeu la do qua trnh ot chay nhien lieu.

+ Nan ot pha rng lam gian oan chu trnh chuyen hoa CO2 thanh O2 trong kh quyen cung ong gop 10 15 % kh CO2 vao kh quyen.

+ Giao thong van tai ong gop lam tang khoang 20% lng CO2 vao kh quyen.

Nguon thai ra CH4:

+ Chu yeu t cac qua trnh sinh hoc nh s phan giai k kh cua at ngap nc va ruong lua, t cac qua trnh bien oi yem kh, t cac khu chan nuoi gia suc, gia cam va t s phan huy cua cac bai rac va chat hu c di at.

+ Thoat ra t qua trnh khai thac, van chuyen va s dung kh ot thien nhien.

Nguon thai ra N2O:

+ Do viec ot chay nhien lieu, chiem 2030% tong lng N2O sinh ra.

+ Sinh ra t qua trnh t nhien va qua trnh nitrat hoa thuy phan.

Nguon thai ra CFC:

+ Cac nganh cong nghiep san xuat may lanh, may ieu hoa nhiet o, cac nha may san xuat xe hi

Nguon thai ra cac chat kh goc lu huynh: SO2, H2S, COS

+ Chu yeu t cac hoat ong nong nghiep, t cac hoat ong vi sinh vat trong t nhien, t s phun trao nui la.

Kh thai cong nghiep oi vi moi loai hnh san xuat cong nghiep co cac kh thai khac

nhau vi nong o, lu lng khong giong nhau.

Nganh cong nghiep luyen kim: Do quy mo nho, cong nghe lac hau nen moi trng khong kh trong nganh nay ang thi ky bao

34

ong. Bui va cac chat oc trong kh thai cua luyen coc, luyen gang, luyen thep va luyen thiec nh CO, CO2, HC, Benzen, SO2, SO3, NH3, AsH3la nguon gay o nhiem ln.

Nganh phan bon hoa hoc: Phan gay o nhiem bao gom: CO, CO2, SO2, NH3, chu yeu khau hoa than.

Nganh cong nghiep vat lieu xay dng: bao gom cong nghiep san xuat ximang, san xuat voi, gach, ngoi, thuy tinh, knh xay dng. oi vi nganh nay, o nhiem khong kh la rat nghiem trong, bao gom: SO2 (24000 tan/nam), CO2 (3,5.106 tan/nam), CO2 (3,5.106 tan/nam), CO (3,87.106 tan/nam), NOx (9026 tan/ nam), bui bay theo khoi (0,125.106 tan/nam). Viec x ly con nhieu kho khan va ton kem.

Nganh giay: H2S, clo, methylmercaptan, dimetylsulit kha oc. Cong nghiep det nhuom: Kh thai t cac khau tay trang: Clo.

Hien mau, in: NO2, hoa chat hu c, acid (CH3COOH, H2SO4).

T lo hi, may phat ien: SO2, NOx, CO, aldehyde, hydrocacbon

Kh thai giao thong van tai Chu yeu gom: Pb, SO2, NOx, CO,VOC, o on, rung

Sau ay xin lay trng hp o nhiem va gay oc cua ch lam v du. Cac ong c chay xang dau la nguon goc sinh ra o nhiem ch trong kh quyen. Ch di dang tetraetyl ch Pb(C2H5)4 c cho vao xang e nang cao ch so octan (mot trong nhng ch tieu chat lng chnh cua xang), chong hien tng no sm. Khi xang c ot chay trong ong c xe, 75% lng ch c thai vao moi trng va lng ch nay chiem 95% tong lng ch trong cac thanh pho ln. Qua trnh ot xang thai ra muoi ch theo phan ng sau:

Pb(C2H5 )4 + O2 +(Br, Cl) PbCl2 +PbBr2 +PbBrCl +CO2 +H2O Trung bnh c mot xe tieu thu 1000 L xang th thai ra moi

trng 0,3 kg Pb. Do o ay la nguon o nhiem ch chnh trong khong kh, chung co the bay i xa gay o nhiem khong kh, at va nc, gay oc sinh vat trong he sinh thai, nguy hiem hn la gay nhieu benh nan y cho con ngi, ac biet la tre em.

35

Theo cac nghien cu cua My, Pb co the xam nhap vao c the qua 3 con ng sau:

ng ho hap: Thong qua phoi va i khap c the.Moi ngay 1 ngi co the hap thu 6 9g ch neu lng ch thai co trong khong kh la 30 g.

Hap thu qua ng tieu hoa: do thc an, thc uong b nhiem ch. Qua mot so luan an tot nghiep tai ai hoc Nong Lam TPHCM cho thay ham lng ch trong cac mau rau muong, bap cai phan tch tai cac huyen ngoai thanh TP Ho Ch Minh la rat cao.

Hap thu qua ng da: qua cho da b tray xc. Cac anh hng cua ch oi vi cac he thong trong c the con

ngi:

He thong tao huyet: anh hng en qua trnh tong hp Hemoglobin, gay thieu hong cau va thieu huyet sac to.

He thong than kinh: Ch anh hng ti ca he thong than kinh trung ng va he thong than kinh ngoai bien. Benh nao do nhiem oc ch hu c thai ra t xang dau rat de gay t vong.

He tim mach: Ch gay co mach ngoai vi, cac mach nho, gay x va ong mach va do o ch gay tang huyet ap, ngoai ra con anh hng ti c tim va ong mach vanh.

He tiet nieu: Than la c quan ao thai ch nhng cung la c quan hap thu ch nhieu nhat, do vay neu s hap thu ch qua nhieu va keo dai th de b suy than.

He tieu hoa: Anh hng ti gan, mat va gay cac cn au bung do ch.

He sinh san: Lam giam kha nang sinh san oi vi phu n va lam anh hng ti qua trnh rung trng.

Anh hng en noi tiet ma chu yeu la cac chc nang cua tuyen giap.

Anh hng en xng khp do ch tch luy trong xng (khoang 95%) va thi gian ban huy la 10.000 ngay, do o nhng ngi b nhiem oc ch thng hay b au khp xng.

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Moi tng quan gia ham lng ch trong khong kh vi ham lng ch trong mau:

Neu ch da vao ho hap trc tiep th so gia ch trong mau va ch trong khong kh vao khoang 1,6 oi vi ngi ln va oi vi tre em. Do vay neu ham lng ch trong khong kh 1 g/m3 th hy vong giam ham lng ch trong mau la 2g/dl oi vi ngi ln va 4 g/dl oi vi tre em. Chu ky ban ra cua ch trong mau khoang 36 ngay nen ham lng ch trong mau co the c coi la ng vi nhng thay oi cua ch t moi trng xung quanh trong 2 thang.

Vi nhng tac ong va neu, ch c xem nh la mot oc chat oi vi c the ngi va gay o nhiem moi trng khong kh. Vay giai quyet van e o nhiem moi trng khong kh nay chnh la giai quyet oc chat ch Pb. Tai Viet Nam a co nhieu hoi thao khoa hoc ban ve van e nay cung nh bien phap e thc hien viec khong s dung xang pha ch.

e chuyen oi sang xang khong pha ch ong thi am bao ch so octan, ngi ta thay ch bang mot hay nhieu phu gia khac nhau, pha them cac cau t co so octan cao hoac thc hien nhng qua trnh nang cao chat lng xang.

T thang 07/2001, Thanh pho Ho Ch Minh a cam s dung xang khong ch va ket qua nong o ch tai cac iem o nam 2002 giam ang ke so vi nhng lan o trc o nam 1996, 1997, 1999 (Bang 0.3)

Bang 0.3. Nong o trung bnh cua ch trong khong kh tai cac iem o qua cac nam

Ch Pb (g/m3 ) Thi

iem o Nga t inh Tien Hoang

ien Bien Phu Nga t

Hang Xanh Phu Lam

Nga t Bay Hien

Nga sau Cong Hoa

09/96 10/96 11/96 12/96 01/97

2.2 3.8 3.1 3.0 3.2

2.5 2.6 2.6 2.6 2.6

1.7 1.6 1.6 1.7 2.0

37

02/97 03/97 04/97 08/99 09/99 10/99

12/06/2002

2.8 3.1 3.1 2.8 3.1 3.4

0.830 (9h 45)

2.1 2.4 2.2 2.2 2.4 2.8

0.920 (8h10)

1.7 1.6 1.7 1.6 1.8 2.1

0.315 (8h 30)

0.158 (9h 40)

(Nguon: S KHCN va S TNMT TP HCM, 2002)

0.9.3.3. O nhiem va gay oc t chat thai ran

La cac chat ran b loai ra trong qua trnh song, sinh hoat, hoat ong san xuat cua con ngi va ong vat. Chat thai ran cua mot qua trnh san xuat nay co the la nguyen lieu cho mot qua trnh san xuat khac. Noi en o nhiem rac thai la noi en o nhiem kh t bai rac va o nhiem nc r ra t bai rac. Bang 0.4 va 0.5 trnh bay thanh phan kh va nc r ra t mot bai rac ien hnh:

Bang 0.4. Thanh phan kh o nhiem t bai rac se gay oc cho sinh vat va he sinh thai theo thi gian chon lap

Thanh phan kh (% the tch) Thi gian (thang) Nit Carbonic Metan

03 5.2 88 5

36 3.8 76 21

612 0.4 65 29

1218 1.1 52 40

1824 0.4 53 47

2430 0.2 52 48

3036 1.3 46 51

3642 0.9 50 47

4248 0.4 51 48

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Theo bang tren ta thay rac sinh ra cac chat kh gom: NH3, CO2, CH4. Ngoai ra con co them CO, H2, H2S, NH2 cung eu la kh oc.

Bang 0.5. Thanh phan cac chat o nhiem, chat oc cua nc r t bai rac

Nong o(mg/l) Thanh phan

Trung bnh

SS 500

N hu c 200

NNH3 200

NNO3 25

Phosphat tong cong 30

PPO4 20

o kiem 3000

o cng (mg CaCO3/l) 3.000

Ca 1.000

Mg 250

K 300

Na 500

Cl 500

SO2 300

Sat tong cong 60

T bang tren chung ta thay nc t bai rac co cac chat hu c ban phan huy gay thoi, gay oc. Ham lng Nhu c, NNH3 cao.

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CHNG 1

OC HOC MOI TRNG DIOXIN (Ecotoxicology of Dioxin)

Ngay nay cung vi s phat trien cua khoa hoc cong nghe xuat hien hang loat van e lien quan khac. Ben canh nhng thanh tu a at c th nhng kho khan ma con ngi gap phai cung khong phai la nho. Cong nghiep giay, cong nghiep hoa chat phat trien, nganh nong nghiep co c nhng vu mua boi thu, con ngi hng ti mot moi trng song trong sach, lanh manh bang cach tien hanh thieu huy rac thai. Va nhieu thanh tu khac trong phat trien cong nghiep. Tat ca nhng thanh tu nay i lien va song song vi no la s phat thai dioxin mot loai chat thai hu c nhan tao ben vng c biet en la mot trong nhng chat oc nhat.

Viet Nam, s d dioxin c quan tam nghien cu nhieu khong phai bi cac nganh tren phat trien qua mc ma chu yeu do s phat huy oc tnh cua dioxin oi vi ngi dan Viet Nam sau cuoc chien tranh Viet Nam My, trong suot may chuc nam qua. Lng dioxin nay do My a s dung trong cuoc chien tranh mien Nam Viet Nam. Trong qua trnh nghien cu, tm hieu nhieu ac tnh cua dioxin c phat hien.

V vay nghien cu oc chat dioxin va nhng anh hng cua no oi vi sinh vat la can thiet va kha thiet thc trong ieu kien cua Viet Nam.

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1.1. TONG QUAN VE DIOXIN

1.1.1 Gii thieu ve dioxin

Dioxin la chat oc nhan tao, cho en nay DDT va dioxin c con ngi biet en la oc nhat. Dioxin co tnh huy diet con ngi va moi trng rat ln. Ve ban chat no la mot loai thuoc diet co, co the lam cay coi rung het la va chet.

Ham lng dioxin co the lam cho chuot chet la 0,0022 mg/kg (LD50, Lethal Dose 50, lieu lng gay chet 50% sinh vat khao sat), ham lng tng ng co the gay t vong cho ngi la 0,1 mg (trong lng khoang 50 kg).

Theo anh gia cua cac nha khoa hoc tham gia Hoi ngh quoc Te ve chat oc da cam/Dioxin to chc tai Ha Noi t ngay 3 en ngay 6 thang 3 nam 2002 th anh hng cua chat oc Da Cam/Dioxin oi vi moi trng va sc khoe con ngi Viet Nam se co kha nang keo dai en nam 2050.

1.1.2. Cau tao, tnh chat, phan loai va oc tnh cua dioxin

Dioxin a clo hoa hay con goi la cac chat CDD, la mot nhom cac hydrocacbon cha clo co cau truc tng t nhau bi hai cau oxy noi hai nguyen t carbon ke nhau thuoc moi vong. Cac hp chat CDD la nhom cua cac hydrocacbon lien ket vi clo, chung giong nhau ve cau truc. Cau truc c ban la phan t dibenzopdioxin (DD) bao gom hai vong benzen c noi vi cac cacbon v tr para bi hai nguyen t oxygen, nhng ay ta chu yeu noi en cac chat thuoc ong phan cua nhom TCDD Tetra chlorinated dioxin ma ien hnh la 2,3,7,8 TCDD (2,3,7,8 Tetrachloro dibenzo p dioxin), mot loai chat oc nhat oi vi ong vat co vu trong nhom CDD.

Thuat ng chat oc mau Da Cam a tng c noi en Viet Nam thc chat la dioxin mot loai chat diet co (chu yeu la 2,3,7,8 TCDD). S d no mang ten goi nay v trong cuoc chien tranh Viet Nam quan oi My a s dung cac thung, c sn cac dai doc mau da cam ben ngoai, co cha chat nay e rai xuong mot so vung mien Nam nham tao ieu kien tieu diet quan oi ta.

41

Cac chat diet co nay eu cha cac hoocmon mo phong cac chat pha huy cay trong va cay rng bang cach pha huy hoac lam roi loan chc nang trao oi chat, gi nc cua cay trong va cay rng nen tham thc vat, mua mang b huy diet rat nhanh sau khi tiep xuc vi chung. Viec xac nh mc o o nhiem va tac hai cua chung oi hoi cac chuyen gia phai am hieu ve lnh vc nay va cac thiet b ky thuat lien quan khac.

Cac nguon phat sinh dioxin la t cong nghe che bien giay s dung cac thuoc tay co clo, cong nghe nha PVC (polyvinylchloride), cong nghe hoa chat va cong nghe san xuat cac thiet b cach ien, chat ban dan Tat ca chung chiem 5% tong lng dioxin phat thai vao moi trng. Con lai 95% o nhiem dioxin la do thieu ot cac phe thai nh dung cu y khoa, o chi tre em bang nha deo cha clo.

a. Cong thc cau tao

O

O

Cl

Cl

O

O

Cl

Cl

b. Tnh chat

Dioxin clo hoa co dang trang thai ran khong mau hoac ket tinh cua trang thai tinh khiet. Dioxin clo hoa co ai lc tao

2,3,7,8 Tetrachlorodibenzo p dioxin, la ong phan thuoc nhom

Tetra chlorinated dioxin

42

thanh cac hat va de dang tach thanh nhng hat trong khong kh, nc va at.

Ban than chung la mot chat de nong chay, nhiet o nong chay la 295oC. Dioxin ben vng trong moi trng va t b phan huy do cac yeu to ben ngoai nh nhiet o, o am, hoa chat Dioxin t tan trong dung moi hu c va khong tan trong nc. Dioxin co the chu c nhiet t 800 1000oC, nhng b pha huy bi tia cc tm hoac anh sang mat tri. Dioxin hoan toan khong b phan huy sinh hoc bi cac vi sinh vat thong thng nen chung ton tai ben vng trong moi trng. Chu ky ban phan huy cua dioxin la t 3 en 12 nam.

c. Phan loai

Cac hp chat trong nhom dioxin bao gom 75 hp chat khac nhau. Ho CDD c chia thanh 8 nhom hoa chat da tren so lng nguyen t clo trong phan t. Nhom co 1 nguyen t clo goi la dioxin n clo hoa (monochlorinated dioxin = MCD). Nhom co 2 en 8 nguyen t clo c goi la dioxin 2 clo (dichlorinated dioxin = DCDD), dioxin 3 clo (trichlorinated dioxin = TrCDD), dioxin 4 clo (tetrachlorinated dioxin =TCDD), dioxin 5 clo (pentachlorinated dioxin = PeCDD), dioxin 6 clo (hexachlorinated dioxin = HxCDD), dioxin 7 clo (heptachlorinated dioxin = HpCDD) va dioxin 8 clo (octachlorinated dioxin = OCDD).

Cac nguyen t clo co the gan vao phan t dioxin bat ky v tr nao trong 8 v tr, ten cua moi CDD cho biet ca so lng va v tr cua cac nguyen t clo. Trong o, TCDD (Tetrachlorinated dioxin), ien hnh la 2,3,7,8 TCDD, mot trong so cac CDD co oc tnh manh nhat va c nghien cu rong rai nhat trong cac ho nha CDD, c coi la nguyen mau ve mat oc tnh cho cac CDD giong dioxin.

Theo nh ngha mi nhat cua EPA Hoa Ky ngay 12/6/2000, ten dioxins dung e ch mot tap hp cua 29 hp chat gay tac ong sinh hoa (biochemical effects) tng t tren ong vat th nghiem.

d. oc tnh

Dioxin la chat oc nhan tao nguy hiem nhat do t tan trong nc, co ai lc cao vi lipid va rat ben vng trong moi trng. oc

43

tnh tuy thuoc vao oi tng tiep nhan nh CDD c tao ra do y muon va ngoai y muon cua con ngi trong qua trnh: san xuat cong nghiep, giao thong van tai, chien tranh, ot nhien lieu

CDD co pham vi phan tan rong va chung ton tai di dang tho hay long. Sau o viec phat thai hay di chuyen CDD co the xay ra, tham ch ca nhng ni no khong c tao ra trong cac qua trnh san xuat a c xem xet.

ioxins la cac phc hp rat ben vng, co ai lc oi vi lipid, kem phan huy sinh hoc va co xu hng tch luy sinh hoc. Mot trong nhng dau hieu cho thay s lay nhiem va tch luy dioxin trong c the la chng ban clo mot can benh ve da. ac biet la 2,3,7,8 TCDD, khi b nhiem chat nay co the gay ung th, ton thng da, gan, tuyen giap, tac dung tren lipid huyet thanh, ai thao ng, cac tac dung len he tim mach, ho hap mien dch, than kinh va sinh san. Chi tiet ve oc tnh cua Dioxins c trnh bay cu the trong cac phan sau (anh hng cua dioxins ti sinh vat).

1.1.3. Cac nguon phat sinh dioxin

Trong tat ca cac thanh phan cua moi trng, ngi ta eu o c nong o cua dioxin: khong kh, nc be mat, nc ngam, at va chat lang can. Trc ay, trong san xuat va s dung cac hp chat clo nh chlorlophenol va thuoc diet co phenolxy clohoa la nguon quan trong thai dioxin vao moi trng, ngay nay cac qua trnh ot chay/thieu huy la c cho nguon quan trong nhat (Zook va Rappe, 1994). Nguon ot chay, thieu huy quan trong bao gom: thieu huy rac thai y te, rac thai ran thanh pho, rac thai oc hai va chat bun thai; cong nghiep than a, dau, ot chay go, luyen kim th cap, lo xi mang, ot nhien lieu diezel va ot dau, go nhng ni c tru (Clemaent va cong s, 1985; Thoma, 1988; Zook va Rappe, 1994).

Phat thai vao khong kh Dioxin c giai phong vao khong kh t nhieu nguon khac

nhau, t qua trnh ot chay, san xuat va s dung hoa chat tap nhiem CDD, chu yeu la cac nguon mang tnh chat on nh. Cac nguon nay hau het lien quan en cac hoat ong cong nghiep nh san xuat, che

44

tac hoac tai cac nguon khuech tan hay phan tan, ma hau het lien quan en viec dung va ng dung cac san pham co cha CDD phat ra hoac la t hai nguon phan loai, sau o chung co the di chuyen tren pham vi rong. Do o co the phat hien dioxin trong khong kh t nhng a iem xa nguon phat thai.

a. T qua trnh ot chay

Cac qua trnh tham gia trong s hnh thanh dioxin bao gom nhieu phan ng hoa hoc xay ra trong khi ot cac hp chat hu c vi s co mat cua clo. Gan ay, EPA a xac nh cac loai nguon chiem phan tram cao nhat trong giai phong 2,3,7,8 TCDD vao kh quyen nh sau: 68% t thieu huy rac thai thanh pho, 12,3 % t thieu huy rac thai y te, 8,9% t san xuat ximang, 4,3 % t cac chat thai nguy hiem cua cac lo nung, 3,5% t s luyen nhom th cap va 3% t s ot chay sinh hoc khac.

Tuy nhien, co mot so t bang chng cho thay, chay rng va s phun trao nui la cung co the hnh thanh dioxin (Crummett, 1982). Tashiro va cong s (1990) a phat hien c nong o cua tong CDD trong khong kh dao ong t 15 400pg/m3. Cac mau a c thu thap t nhng may thu thap co nh 10m tren mat at va t khoi cua may bay khi bay. Cac mau at c thu thap trc khi chay xac nh c la 43ppt OCDD t 1 trong 4 mau kiem tra. Sau khi chay, OCDD xac nh c 3 trong 4 mau at vi nong o 46,1 va 270ppt. Do c mau nho nen a can tr viec phan tch thong ke, khong co ket luan g them c rut ra theo cac tac gia. Tuy nhien khong co thong tin nao ve nguon goc cua 2,3,7,8TCDD (ai dien ien hnh nhat cua ho CDD) ke ca trong t nhien va t nghien cu nhan chung hoc.

b. T qua trnh san xuat va s dung cac hoa chat tap nhiem va mot so thuoc diet co

CDD c biet la vet tap nhiem cua mot so hoa chat hoa hoc cha clo cong nghiep nh chlorophenol (Buser, 1987). CDD co the vo tnh c tao thanh nh la san pham phu trong qua trnh san xuat cua chlorophenol.

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2, 3, 7, 8 TCDD c tao thanh trong qua trnh san xuat 2,4,5 TCP (2,4,5 Trichlorophenol), chung c s dung trong cac thap lam lanh va trong cac qua trnh san xuat giay, bot giay, thuoc da, thuoc sat khuan hexachlorrophene 2, 3, 7, 8 TCDD chu yeu co cac chat lang ong ay (dau thai) con lai sau khi hexachlorophene c tinh che (Freeman va cs. 1986).

S dung thuoc diet co co goc trochlorophenol trong nong nghiep va trong thi chien nh 2,4,5 T (2,4,5 Trichlorophenol acid) va Silvex (mot loai thuoc diet co co quan he gan gui vi 2,4,5 T) cung a lam giai phong dioxin vi nong o thap nhieu nc (EPA, 1987). V du: chat da cam c s dung nh mot chat lam rung la trong chien tranh Viet Nam t nam 1962 en 1970, b tap nhiem vi nong o trung bnh 2ppm cua chat 2,3,7,8 TCDD.

Ben canh o, cac tai nan cong nghiep cung a thai vao khong kh mot lng ln cac chat ho nha CDD. Nam 1976, t nhat 1,3 kg 2,3,7,8 TCDD a c thai vao khong kh (no la ket qua cua s co cong nghiep tai ICMESA nha may hoa hoc gan Seveso, Y). Viec thai nay a lam tap nhiem mot vung dan c khoang 2,8km2 (Mocarelli va cong s. 1991).

Bon ieu kien rieng le hoac noi ket vi nhau, nguyen nhan cua s tai tao ra dioxin va phat thai vao khong kh la:

- Cac qua trnh co nhiet o cao (tren 200C) hoac s ot chay khong hoan toan

- Cacbon hu c

- Clo

- Dioxin cha trong kh thai

c. T cac qua trnh t nhien

Hoa hoc vi lng cua ly thuyet la (Trace Chemistry of Fire Hypothesis) gi y rang CDD cung co the hnh thanh t cac qua trnh ot chay khac nhau bao gom cac nguon t nhien nh chay rng va s phun trao nui la (Crummett 1982). Tuy nhien, con co t bang chng gi y rang cac qua trnh t nhien nh vay co the la nguon th yeu

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cua cac thanh phan nay trong moi trng. Ch co cac d lieu t mot nghien cu a tm ra rang CDD c o trc tiep trong qua trnh thai ra t nhng vu chay rng.

Ngoai ra, nhng con ng phan huy sinh hoc hoan toan cung tao ra dioxin. Nhieu loai nam lam muc go va mot na cac loai nam bac cao s dung hp chat clo hoa va hp chat oxy hoa e phan huy lignin. Nh o, chung co the tiep can vi cellulose, nguon nang lng cua chung. Nhng loai sinh vat nay chuyen hoa clo vo c trong muoi thanh tat ca cac loai chat hu c clo hoa (chu yeu la CH3Cl, nhng cung co phenol clo hoa hay nhng hp chat tng t) rat hu hieu. Phan con lai cua qua trnh phan huy go la axit humic clo hoa va lignin clo hoa trong nc, hp chat mun clo hoa va phenol clo hoa trong at. S chuyen hoa t cac phenol clo hoa thanh dioxin ch qua mot bc nho can en hydroperoxide, do cac vi sinh vat tao ra. Nh vay, ngoai cac iem nong gan nhng lo ot cu va nhng nguon khac, lng dioxin cao nhat la trong rng. Qua trnh phan huy sinh hoc bun ay o th va qua trnh u cac vat lieu hu c t nhien thai ra lng dioxin gap 3 lan lng thai cua lo ot. Co the c che sinh hoc cung tng t nh tren, trong o qua trnh oxy hoa se lam xuat hien chlorophenol t nhien.

Phat thai vao nc Dioxin phat thai vao nc co the xay ra trong qua trnh o nc

thai b o nhiem hoac s dung cac hoa chat co cha dioxin. Chung ngam vao nc qua nhieu c che khac nhau: co the do dong chay ra t cac o th, s lien thong cac cong ranh thoat nc va s thai trc tiep t cac phng tien s dung trong cong nghiep hay do lang ong cua cac hat t cac nguon ot chay, t qua trnh chay va troi dat cua viec s dung truoc tr sau co cha cac thanh phan lien quan tao ra dioxin, hoac qua trnh loc nc t nhng vung chat thai co cha cac thanh phan nay Dioxin co the ton tai trong qua trnh phat thai neu nh trong qua trnh phat thai no c tao thanh hoac tham nhap vao cac qua trnh o. Tom lai, cac qua trnh ien hnh co the tao ra dioxin:

- Phat thai nc phat thai t qua trnh san xuat bot giay va s dung clo.

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- Phat thai nc phat thai t qua trnh san xuat hoa chat lien quan en Clo

- Nc thai t viec s dung thuoc bao ve thc vat co cha dioxin hay thuoc nhuom cac nganh nh: det, da, go

Tieu chuan c s dung e xac nh s phat thai dioxin tiem tang vao nc bao gom:

- Phat thai nc thai lien quan en Clo hoac cac san pham lien quan en CDD, hoac s ot chay, s tro hoa va cac qua trnh nhiet khac

- S dung thuoc tr sau nhiem CDD (ac biet Pentaclophenol 2.4.5T).

- Chat tay ra t cac kho hoac ni o phat thai b nhiem dioxin.

Phat thai vao at Nguon CDD phat thai vao at chu yeu do cac nguyen nhan sau:

s dung trc tiep cac san pham tap nhiem CDD vao at, o thai xuong at nhng bun cong ranh cua nha may giay, phat thai vao at thong qua cac qua trnh moi trng khac nh t khong kh theo hat ma ri xuong at hay t nc ngam vao at. Trong moi trng hp at se giup CDD lang xuong va chung co the lan truyen vao chuoi thc an thong qua s hap thu cua ong thc vat.

Viec san xuat trichlorophenol thng pham, cung nh cac san pham dan xuat khac nh 2,4,5 T va cac chat diet sinh khac, a lam phat sinh mot lng ln cac phe thai cha CDD.

Nh a noi tren ve vu no tai Seveso, Y, qua trnh san xuat 2,4,5 T, do s co, a giai phong mot am may chat oc chu yeu la 2,3,7,8 TCDD (c tnh khoang 1,3kg), nhng manh nho t am may o a bao phu mot vung khoang xap x 700 acres (2,8km2). Sau tai nan cong nghiep nay, cac nha khoa hoc a tien hanh o cac mau at tai ba vung va thu c ket qua nh sau:

- Vung A: vung nhiem nang nhat, nong o TCDD trung bnh la 230 g/m2 (cc ai 5.477g/m2) dan c trong vung a tan c.

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- Vung B: vung b nhiem nhe hn, nong o TCDD trung bnh la 3g/m2 (cc ai 43,9g/m2) dan trong vung a c khuyen cao la khong nen an cac san pham moi trng tai a phng.

- Vung R: la vung b nhiem nhe nhat nhng nong o TCDD trung bnh cung en 0,9g/m2 (cc ai 9,7g/m2).

Phat thai lan trong san pham Nam 1985, Cuc moi trng EPA, My, khi thc hien chng

trnh The National Dioxin Study a a ra phat hien mi la hp chat clo dung e tay trang bot giay a tao thanh dioxin. Do o, cac san pham s dung bao b bang giay Seveso eu b nhiem oc dioxin. Dioxin luon la san pham i kem, chung thng lien ket ben vng vi xenlulo cua giay va t co kha nang tach khoi tam li dung e hap thu. o la ly do khien cac san pham nay la nguon phat sinh dioxin.

Mot so san pham tieu dung co cha dioxin:

Thuoc la va khoi thuoc la: Cac san pham nay chu yeu cha cac ho nha CDD (theo Lofroth va Zebuhr, 1992), tuy nhien HpCDD la chat ong ang phong phu nhat c phat hien, chiem co the ti 90% CDD toan phan.

San pham giay: CDD a hnh thanh trong qua trnh tay trang giay, v vay chung c tm thay trong nhieu loai san pham giay khac nhau. Beck va cs 1988, 1989 a tm thay dioxin trong mau th cua giay loc ca phe, trong o, 2,3,7,8 TCDD chiem nhieu nhat nong o trung bnh 3,85 ppt va ty le loc vao la 25%, ieu nay cho thay ngi uong ca phe loc vi giay loc cha 5ppt 2,3,7,8 TCDD co the hap thu mot lng nho moi ngay.

Cac CDD eu co trong giay in bao, mo mat (my pham) va giay tai sinh nong o t

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Thuoc nhuom va cac chat mau: Mac du dioxin khong c noi en trong nghien cu cac chat sap nen va chat mau nhuom violet 23 chat hnh thanh t clo, nhng ngi ta a tm thay OCDD trong chat mau Blue 106 vi nong o t 18066 en 41953 ng/g (ppt).

San pham vai det: Mot nghien cu gan ay a phat hien ra cac nguon CDD co lan trong hang vai det (Horstmann va Mclachlan, 1994).

Chat ton lu trong dch tay sach kho: Phan tch hoa hoc cac chat ton lu trong dung moi cua qua trnh tay sach kho c trc nam 1993 cho thay nhng chat thai t cac may moc dung perchloroethylene co cha CDD va dioxin c phat hien co trong 21/ 28 mau th (Towara va cong s, 1992).

Kh thai xe co: Dioxin c tm thay trong kh thai cua xe o to t 4 xe cua Thuy ien chay bang xang pha ch vi nong o trung bnh t 0,05 en 0,3ng/ 24,8 km. Tuy nhien, viec phat thai bang con ng nay la khong ang lo ngai v hien nay rat t quoc gia s dung xang pha ch.

Cac nguon chnh cua s o nhiem moi trng lien quan en CDD trc nay la san xuat va s dung cac chat hoa hoc hu c cha clo va s dung clo trong cong nghiep san xuat bot giay va san xuat giay. Trong nhng qua trnh nay cac yeu to thuc ay s tao thanh dioxin la:

- o tang nhiet o.

- Moi trng kiem.

- S xuat hien cua tia cc tm.

- S xuat hien cua tia phong xa, cac phan ng hon hp, qua trnh hoa hoc.

1.2 DIEN THE SINH THAI CUA DIOXIN

Dioxin la chat rat oc, rat ben vng trong cac tat ca cac moi trng. Dioxin sinh ra do ot chay co the di chuyen tren dien rong trong khong kh. Chung tham ch co the b lang ong vao at, nc be mat hoac cay coi di dang kho hoac t. Dioxin lang ong trong at se hap thu manh cac chat hu c. Dioxin khong the ngam vao

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mach nc ngam nhng co the xam nhap vao bau kh quyen tren phan bui at hoac vao nc be mat, sau o i vao nc be mat dong chay. Trong cac moi trng nay, do ac tnh t tan trong nc va a lipid cao nen dioxin de dang b hap thu bi cac thuy sinh vat, mac du ay chung co the lien ket vi cac chat hu c l lng.

Cac qua trnh chuyen dang chiem u the tac dung en so phan cua dioxin trong moi trng la s phan huy do anh sang mat tri tren be mat va s phan tan boc hi trong pha kh.

1.2.1. Dien the cua dioxin trong moi trng khong kh

Cac qua trnh ot chay hnh nh ong gop vao s co mat khap ni cua dioxin trong moi trng. Trong qua trnh phan tan vao kh quyen dioxin c phan cach gia pha hi va pha lien ket. Tuy nhien, do ap suat hi cua dioxin rat thap nen lng dioxin ton tai pha hi t hn lng c hap thu vao cac vat the. Trong moi trng kh quyen dioxin b kiem soat bi hai yeu to moi trng o la ap suat hi va nhiet o kh quyen. Vi ap suat hi dao ong t 7,4.104 en 3,4.105mmHg, hp chat 2,3,7,8 TCDD bien thanh dang trung gian.

CDD ve mat ly hoc c loai ra khoi kh quyen qua s lang ong t (ra sach bi nc ma va sng), phan t lang ong kho (lc trong trng cua cac hat), lang ong kho pha kh (hap thu CDD trong pha hi vao be mat thc vat). nhiet o khoang 280C dioxin co xu hng ton tai trong pha hi con nhiet o lanh hn (16200C) chung lai co khuynh hng gan vao cac hat nhieu hn. Theo Nash va Beall (1980), ch 12% 2,3,7,8 TCDD rai tren lp at co co xanh co kha nang tao thanh chat nhu tng hoa.

Da tren thi gian phan huy do anh sang cua dioxin trong dung dch, ngi ta cho rang cac dioxin pha kh cung b phan huy do anh sang trong khong kh, tuy nhien cac phan ng vi goc hydroxyl se chiem u the. oi vi TCDD thi gian phan huy do anh sang t 1,3 en 7,1 ngay. Dioxin gan vi cac hat c loai tr bang lang ong t hoac kho co thi gian ton tai trong khong kh khoang 10 ngay.

Mo hnh chu chuyen trong moi trng cua CDD can s hieu biet cua nhieu thong so c ban ve vat ly va hoa hoc nh s hoa tan trong

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nc, ap suat hi, nh luat hang so cua Herry, he so rieng phan octanolnc (Kow) va he so rieng phan cacbon hu c (Koc).

1.2.2. Dien bien cua dioxin trong moi trng at

Dioxin xam nhap vao at, ong lai hoac quyen chat vao at, vao bun song thanh nhng o nho. Viec di chuyen dioxin trong at rat kho khan. Khi dioxin xam nhap vao moi trng at gay tac ong trc tiep len moi trng at va ong thi no cung b moi trng at hap thu, phan ng va bien thanh nhng chat t o nhiem hn hoac co li cho moi trng. Nh vay ma nong o dioxin trong at giam dan theo thi gian.

V o hoa tan trong nc va ap lc hi cua chung rat thap, dioxin chu yeu thay lp at di lp be mat vai milimet b hap thu manh va di chuyen theo phng thang ng, ac biet la trong at co ham lng chat cacbon hu c cao (Yanders va cong s, 1989), cu the la 2,3,7,8TCDD se di chuyen nhanh va tang len trong at neu cac dung moi hu c co the hoa tan chung co mat ong thi. Theo Mcpeter va Overcash, 1993, s dung mot hon hp dung moi gom tetradecane va 1butanol cho vao at nhiem TCDD, ket hp vi chieu sang mat tri a lam cho 61 85% TCDD b quang phan sau 60 ngay. ieu nay c giai thch la do dung moi co hieu qua trong viec chuyen chat nay t o sau 60cm len mat at theo con ng boc hi, tren be mat at, s quang phan co the xay ra.

S quang phan cua 2,3,7,8TCDD trong at la cham hn so vi trong moi trng nc, theo Paustenbach va cs. 1992 thi gian ban huy cua chung tren be mat at la t 9 en 15 nam, con at di be mat la t 25 en 100 nam. Ngoai ra, dioxin ton lu trong at con phu thuoc vao lieu lng, cac ieu kien moi trng nh ma, gio, lu lut, xoi mon, vao mc o tiep xuc va s chuyen hoa cac vi sinh vat trong at.

Bang 1.1. Thi gian ban phan giai dioxin

at Thi gian ban phan huy

Tang at 0.1cm

Tang at mat

o sau hn

De b quang phan

915 nam

25100 nam

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Dioxin co mat trong moi trng at gay tac ong ti cac sinh vat co li, thng lam cho chung chet i hoac xuat hien nhng ton hai khac nh ot bien gen d dang ong thi dioxin cung tac ong trc tiep len ong thc vat neu vi nong o u ln.

1.2.3. Dien the cua dioxin trong moi trng nc

Dioxin la chat ran kha ben, t tan trong nc (0,2 x 103mg/l). Dioxin co the di chuyen xa trong nguon nc. Trong moi trng nc, dioxin ton tai di dang ket dnh vi cac chat l lng, tham nhap vao bun ay va tch tu trong c the thuy sinh vat nh co, ca, tom, ngheu Dioxin vao c the ca qua hoat ong suc bun va thc an cua ca. Theo Hallet va Brooksbank, 1986, phan ln dioxin i vao lp nc be mat se ket hp rat chac vi cac hat hu c l lng (cac manh vun, cac chat am t) va cac hat at b xoi mon.

Cac CDD b bien mat khoi nc chu yeu bang con ng quang phan, khi co nhng ieu kien nhat nh (khi b chieu sang bi tia t ngoai va khi co mat cua mot chat cho hydro hu c) chung b quang phan nhanh chong. Thi gian ban huy quang phan oi vi 2,3,7,8 TCDD hoa tan di anh sang mat tri la t 118 gi trong mua ong, 51 gi trong mua thu, xuong 27 gi trong mua xuan va ch con 21 gi trong mua he (Podoll va cong s, 1986). Theo Stehl va cong s, 1973, thi gian ban huy s quang phan oi vi 2,3,7,8 TCDD trong isooctane c anh gia la 40 phut vi mot nguon sang at cach 0,5m va 3 gi oi vi nguon sang at cach 1m. Trong cac hp chat thuoc nhom nay th 2,3,7,8 TCDD co toc o phan huy nhanh nhat.

Ben canh o, dioxin mot phan nho c chuyen khoi nc do bay hi vao kh quyen, gan vao cac hat va can lang, hoac bi s tch luy sinh hoc nh cac he sinh vat thuy sinh. Thi gian ban huy cua s bay hi oi vi 2,3,7,8TCDD c tnh toan oi vi cac ao ho la 32 ngay va oi vi cac con song la 16 ngay (Podoll va cong s, 1986). C che bien mat chu yeu oi vi cac CDD khoi nc la s lang vi 70 80% cac chat CDD gan vao cac hat. Cac CDD gan vao cac hat lang co the c hoa tan tr lai trong nc neu cac chat lang nay b khuay len.

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Khi nghien cu cac loai sinh vat trong nc nhiem dioxin th ngi ta thng chu y nhieu en ca tom, nhat la cac loai song lp sau (ay ao, ho, song ngoi), hoac trong bun, trong ca tre, ln, v ay la nhng loai tch tu dioxin nhieu nhat trong nc.

Theo Maine, nhom tac gia a nghien cu va khao sat s ton d va tch tu sinh hoc trong ca cua song Penoscot River cho thay, ham lng dioxin trong ca va cac loai thuy sinh la ang ke (trong khi o nguon thai chu yeu la do cong nghiep). Nh vay, nc song ho Viet Nam se co nhng ton d rat ln do anh hng cua chat oc hoa hoc ma quan oi My a rai xuong Viet Nam.

Trong cac moi trng khac nhau nong o dioxin cung ton tai khac nhau, nhieu nhat ven bien roi en rng nui va ong bang.

1.2.4. Tac hai cua dioxin oi vi thc vat he sinh thai rng

Dioxin la hoa chat co trong thanh phan chat oc mau da cam, ban chat la mot loai thuoc diet co lam cho cay coi rung het la va chet. Ngoai ra chat oc dioxin con lam anh hng en chat lng dinh dng cua cu, qua, hat. Ham lng cac hp cha chat nit trong hat b giam i rat nhieu. Qua nghien cu, cac nha khoa hoc cho biet nit tong trong hat lua sau 14 ngay b rai thuoc la 0,98%, trong khi o cac hat lua khong b nhiem la 116%. Nit tong trong hat bap sau 3 ngay b rai thuoc la 0,74%, con hat bap bnh thng la 1,14%.

Nhieu loai cay rng phai hng chu mot khoi lng ln chat oc dioxin rat nang ne, ngay sau o trut het tang la, tan rng b pha v, dan dan mot so cay chet kho, mot so cay khac chet tng phan. Ben canh o co mot so cay sau thi gian dai phuc hoi lai nh cu, khong b anh hng ti sinh trng. Hien tng o cho thay anh hng cua chat oc dioxin oi vi tham thc vat phu thuoc vao nhieu yeu to khac nhau, mot trong nhng yeu to o la ban chat cua cay. Tnh man cam cua moi loai la khac nhau oi vi chat oc dioxin. Hau qua au tien la lam thay oi s can bang sinh thai trong rng.

Sau khi rai chat oc hoa hoc, cac quan the rng cung b tac ong manh me, so lng va giong loai b giam hoac co kha nang b tiet chung. Chu s tac ong manh nhat la cac loai chim, thu an co

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ln, keo theo cac thu an tht. Khi cay chet lam cho thu mat nguon thc an, nc uong nen c the thu gay ra nhng bien oi sinh ly va sinh hoc cua chung. Chnh v vay nhieu loai thu a di tan ra ngoai vung b nhiem oc, mot so khac tru lai th khong phat trien.

1.2.5. Tac hai cua dioxin oi vi ong vat, con ngi

a. oi vi ong vat

TCDD la mot trong nhng hoa chat oc hai gay nen nhng hien tng benh ly ac hieu nh sut can, teo tuyen c, c che mien dch, sinh ung th va gay quai thai. oi vi loai gam nham, ngi ta a neu len la viec tiep xuc vi TCDD trong qua trnh hnh thanh he thong mien dch cua ca the gay nen tnh trang c che cac chc nang cua te bao ma ve nhieu phng dien giong nh hien tng cat bo tuyen c trong thi ky s sinh.

Chu ky ban phan huy cua dioxin trong c the chuot khoang 32 ngay. oc tnh dioxin gay ra rat ro ret va khac nhau. Chang han oi vi chuot la 20 45 microgam/kg trong lng c the (qua ng mieng). Trong khi o oi vi tho la 115 microgam/kg, kh la 70, ech la 1000. ac biet la chuot me co cha b nhiem oc dioxin khong chet nhng sinh ra the he chuot co tap tnh khong bnh thng.

Chat oc dioxin co nguy hai en ca, lam huy hoai thc an cua ca nh sinh khoi rong tao giam ang ke, keo theo cac loai cua, tom, cac loai than mem (ngheu, so, oc) cung b anh hng khong kem.

Ben canh o cac loai con trung, ac biet la loai ong mat co vai tro thu phan, rat nhay cam vi dioxin. Bo Rua cung b nhiem oc vi Dioxin trong giai oan au trung. Ngc lai cac quan the Rep lai tang nhanh ve so lng do cac loai con trung an Rep b thiet hai kha nhieu.

b. oi vi con ngi

Dioxin la nguyen nhan gay o nhiem cho ngi lieu lng nhiem oc khoang 0,0003 mg/g so vi trong lng c the, gay kch thch da, chong mat, au au, buon non, co the gay ngo oc cap tnh va ch 1mg se dan en t vong. Ngoai ra, dioxin con gay ngo oc cho phoi thai, d dang va mang tnh duy truyen nong o nhiem oc rat thap.

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Mac du 2,3,7,8dioxin ch chiem t le rat thap trong chat oc da cam (khoang hai phan trieu, tc la trong 1kg chat oc mau da cam co 2mg dioxin). mc o nay th khong gay t vong cho ngi, nhng no tiem tang trong con ngi, en mot ngng nhat nh se sinh ra cac benh sinh ly, anh hng en the he sau nay nh chet phoi thai, h thai, gay d dang, khuyet tat, mot so tre thay b h ham ech, cac c quan cha co u, than kinh kem phat trien

Ngoai ra chung con gay benh tren da: theo Herxheimer (1899), nhng cong nhan san xuat TCDD khi b nhiem th da cua ho b noi mun trng ca, sau o dien bien tang dan, co the b en roi loet. Co the dioxin tan trong m cua chat nhn di da va tac ong chu yeu la clo. Benh nhan co the nang hn, co the b teo gan roi chet. Hoac la oi vi mot so ngi s dung nc thm co chat beo e boi len da, bang chng la bi kch cua phan rom hexaclorophen Morhange gay benh:

Viem mat Ngo oc cap tnh, o, phu ket mac Viem mong mat, giac mac. Sau cap tnh co the th phat suy nhc mat 81,3% nan

nhan Viet Nam (Ton That Tung, 1977 ).

Gay ung th: GS. Ton That Tung va mot so cac nha khoa hoc nc ngoai cho rang dioxin la tac nhan gay benh ung th, nhat la ung th gan. Van e nay c GS. Michael S. Delnison giai thch la do dioxin co ai lc rat manh oi vi protein, chung se hnh thanh lien ket vi cac phan t protein lam thay oi he thong gien trong c the ngi gay anh hng en AND, ong thi cung lam cac gien thay oi theo hng d hnh gay ra nhng khoi u ac tnh lam tien e cho can benh ung th quai ac.

Ngoai ra chung con gay ra hien tng xuat huyet: chay mau ng tieu hoa tren suc vat th nghiem va ca theo doi tren ngi. Ton thng gan: cac dau hieu lam sang va ch tieu men gan a cho cac nha khoa hoc khang nh rang gan la c quan b dioxin gay ton thng trc nhat, tham ch gay t vong. Say thai, quai thai va roi

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loan nhiem sac the: t le say thai va quai thai phu n va gia suc trong vung o nhiem rat cao. Say thai i cung vi roi loan nhiem sac the, gay quai thai, chet bao thai. Cac d tat nay co the xay ra bi ba c che sau:

Th nhat, dioxin van ton tai trong thien nhien, nh vay van con tac ong en phoi thai.

Th hai, dioxin trong thien nhien a mat i nhng van con ton lu trong c the ngi.

Th ba, dioxin co the khong ton tai trong thien nhien va c the ngi nhng ton thng ve cau truc di truyen khi tiep xuc vi dioxin (ve sinh hoc, ve di chng di truyen) ve sau nay dan en s xuat hien cac d tat bam sinh.

Theo nghien cu cua cac chuyen gia th t le tat bam sinh tang cao the he con cua nhng ngi thuoc nhom mau B. Mat o tinh trung giam nhom mau B, t le tinh trung d dang, pH tinh dch tang, nhng yeu to nay khong anh hng en kha nang sinh san cua cac oi tng. Nhng co mot so nghien cu cho rang s mat kha nang thu tinh nam co nhieu nguyen nhan va khong loai tr cac nguyen nhan ke tren.

S nhiem oc trong c the ngi thong qua ba con ng:

Tham thau qua da Ho hap Tieu hoa (do an phai thc pham b nhiem oc). Ngay khi xam nhap vao c the, dioxin theo ng mau en cac

c quan va cac mo nhay cam, chung lam thay oi dien tch te bao va pha huy chc nang te bao o. Di tac ong cua dioxin, cac te bao gia khong chet i va cung khong c thay the bi cac te bao tre. Chung phat trien manh me lam mat chc nang lien ket cac te bao vi nhau tao thanh cac khoi u hay con goi la ung th.

Khi tiep xuc vi 2,3,7,8TCDD cac hp chat cha Clo con ang trong buong t cung hoac sau khi sinh ra a lam anh hng en hoat ong chc nang tinh than tre em a ln va ang phat trien. Cac

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anh hng phat trien gom ca nhc ong va cng ong, cung nh hien tng giam sut tap trung chu y, kha nang nhan thc va phat trien van ong, anh hng ngay trong t cung va ngay khi sinh. Dioxin tan trong sa me, cho nen viec nuoi con bang sa me se anh hng en con cai.

Cac tac nhan trong moi trng tac ong vao vat lieu di truyen mc gen hoac mc o nhien sac the. Sau khi b tac ong trong nhieu trng hp gen co the co kha nang t sa cha e tr lai trang thai bnh thng, mot so ot bien trang thai lan, khong bieu hien ra kieu hnh. V vay ch phat hien mc o te bao, nhat la nhng ngi d hp t (heterozygates).

Dioxin khong co tnh chat gay ot bien nhng can chu y en hoat tnh th phat cua dioxin, bao gom cac qua trnh sinh hoa b bien oi. Trc het la s chuyen hoa cac monooxygenaza, v cac san pham cua cac phan ng tren co the tr thanh cac chat phat ong trong qua trnh sinh trng va ca cac qua trnh di truyen oc hoc trong c the. S suy giam hoat tnh chc nang cua he mien dch tren nen cua cac dao dong chuyen hoa chung, cac roi loan ve thc bao cung vi s tham gia tang san xuat peroxit, cung co the lam pha huy cau truc AND hoac protein, tham gia vao s phuc hoi cac ton thng tren. Khi chuyen dch tng quan cua cac phan ng oxy hoa kh. TCDD co the gay anh hng en s chuyen hoa cac axit nucleic va kha nang cha lanh cac ton thng co the do b cam ng bi cac tac ong noi ngoai sinh, ke ca cac tac ong tien tac nhan ot bien.

cac nc cong nghiep phat trien, do o nhiem moi trng nen trong c the ngi co mot lng dioxin nhat nh, trung bnh lng dioxin trong mo m ngi M, Canada, Nhat la 6 7 ppt. Nh the ham lng dioxin trong mo ngi mien Nam Viet Nam cao hn ngi thuoc nc cong nghiep phat trien t 2 3 lan. Do VN la mot nc ang phat trien, ky nghe cha cao nen ngh rang lng dioxin cao trong c the ngi MNVN la do hau qua lau dai cua chat oc da cam e lai.

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1.2.6. Tac hai cua dioxin sau chien tranh Viet Nam

a. Cac phng tien dung e rai dioxin

May bay C123 bay o cao 50 m phun vao mua kho thang 13 hang nam, moi ngay 2 lan vao luc 7 h30 sang va 4 h chieu, lien tuc tren 10 nam nham muc ch lam chay rng.

May bay UH1B phun chat oc pha hoai cay trong Phun t xe o to, xe boc thep, tau thuy. Theo thong ke th dien tch at b rai chat oc mau da cam

trong chien tranh Viet Nam cho trong bang 1.2 va 1.3.

Bang 1.2. Dien tch at b rai Viet Nam t nam 19621969 (theo tai lieu cua Bo Quoc phong My)

Nam at rng (ha) at canh tac (ha) Tong so (ha)

Tong so 1.824.240 202.000 2.026.240

Bang 1.3. Dan so va dien tch b rai chat oc hoa hoc trong chien tranh Viet Nam

Stt Ten tnh

Tong so dan

So dan trong vung b rai

% Dien tch (km2)

Dien tch b rai (km2)

%

1 TP Ho Ch Minh 3.419.978 72.000 2,1 2.029 530 26

2 Bnh Tr Thien 1.901.713 146.000 7,6 18.340 3.678 20

3 Quang Nam, a Nang 1.529.520 103.000 6,7 11.989 2.639 22

4 Ngha Bnh 2.095.520 179.000 8,5 11.900 2.049 17

5 Gia LaiKon Tum 2.095.354 42.000 6,5 25.536 3.301 12

6 ac Lac 595.906 62.000 12,6 19.800 727 8

7 Phu Khanh 490.198 94.000 7,9 9.804 1.638 16

8 Lam ong 188.637 52.000 13,1 9.933 720 7

9 Thuan Hai 396.637 88.000 9,3 11.374 1.918 16

10 Song Be 659.093 152.000 14,6 9.859 4.217 41

11 Tay Ninh 684.006 97.000 14,1 4.030 1.480 36

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12 ong Nai 1.304.799 300.000 23,0 7.578 3.773 49

13 Long An 957.246 91.000 9,4 4.355 528 13

14 Tien Giang 1.264.498 49.000 3,8 2.377 156 6

15 Ben Tre 1.041.838 189.000 18,1 2.225 444 19

16 ong Thap 1.182.787 25.000 12,1 3.393 100 3

17 An Giang 1.532.262 3.000 0,2 3.492 11 0,3

18 Kien Giang 994.673 35.000 3,5 6.358 298 5

19 Hau Giang 2.232.891 57.000 2,5 6.126 270 4

20 Cu Long 1.540.00 10.000 0,6 3.854 306 8

21 Minh Hai 1.219.595 104.000 8,5 7.697 1.226 16

22 K Vung TauCon ao 91.610 9.000 9,7 249 36 14

Tong cong 26.225.729

1.000.000 7,5 182.299 30.101 16,51

(Bang thong ke cua Le Cao ai va cong tac vien nam 1986)

Ham lng dioxin tac ong manh me en moi trng at vung nay at biet la vung A Li thuoc tnh Tha Thien Hue. Theo ket qua nghien cu cua GS. Le Cao ai va cong s, ta thay