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  • 1

    1

    PHN A: C CHT HC I CNG

    CHNG I

    MT S VN C BN V C CHT HC

    Ni dung chng 1 nhm gii thiu mt s khi nim c bn trong c cht hc nh: c cht hc, cht c, c tnh, c lc, ng c, cc ngun gy c, cch phn loi cht c, phn loi ng c... Cc kin thc v cc qu trnh ng hc, c ch gy ng c v cc yu t nh hng n tc dng ca cht c cng c cp n trong chng ny.

    1. Mt s khI nim

    1.1. c cht hc

    a. nh ngha v i tng ca c cht hc

    c cht hc l mt ngnh khoa hc chuyn nghin cu v cc cht c, bao gm vic pht hin ra cc cht c, c tnh l ho hc ca chng v nhng nh hng sinh hc cng nh bin php x l nhng hu qu do chng gy ra. c cht hc - toxicology c ngun gc t ting Hy Lp: toxikon - cht c, logos - khoa hc.

    T xa xa, i tng ca c cht hc ch l mt s t cht c c s dng u c ngi v sc vt. Ngy nay, c cht hc hin i nghin cu tnh cht l ha ca cc cht c c ngun gc thc vt, khong v tng hp, c ch gy c, mi tng tc gia cht c v c th.

    c cht hc Th y l mn khoa hc nghin cu v cc cht c v tc ng ca chng i vi c th ng vt.

    c cht hc th y l mt phn c bit ca c cht hc, l mn hc thc nghim lm sng. i tng ca mn hc l nghin cu v tnh cht, tc dng, ngha ca cht c, nguyn nhn gy ng c, sinh bnh hc, triu chng, chn on v iu tr ng c.

    b. S lin quan ca c cht hc th y vi cc mn hc khc

    L mn hc thc nghim lm sng, c cht hc th y c lin quan n hng lot cc mn hc:

    - Mn ha hc v dc l hc cung cp nhng hiu bit c bn v tnh cht ha hc, ng hc, c ch tc dng ca cc cht c c ngun gc v c v hu c.

    - Mn thc vt, vi sinh vt v ng vt gip nghin cu cc c t thc vt, ng vt, nm v cn trng.

    c cht hc c bit c quan h gn gi vi cc mn hc:

    - Sinh l bnh: nghin cu v sinh bnh hc, v tin trin ca bnh do ng c.

    - Ho sinh: c th b ng c gy ra nhiu bin i cc ch tiu ha hc, hm lng v cht lng men, hm lng cc hormon gi vai tr quan trng trong trao i cht. Xc nh nhng bin i ny bng cc phng php nghin cu ho sinh l rt cn thit phn tch tin trin ca qu trnh ng c.

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    - Bnh l hc: cung cp phng php m khm v phn tch cc bnh tch i th, vi th gip chn on ng c.

    - Dch t hc: gip phn bit bnh do ng c vi cc bnh truyn nhim, k sinh trng.

    - V sinh th y v thc n gia sc lin quan n phng php phng ng c.

    c. Cc lnh vc nghin cu ca c cht hc

    Cc lnh vc nghin cu ca c cht hc lin quan n nhn y v th y gm:

    - c cht hc m t: nh gi nguy c do phi nhim vi cht c hoc mi trng thng qua cc kt qu thu c t cc xt nghim c tnh.

    - c cht hc c ch: Gii thch c ch gy c, t c th d on nguy c v c s khoa hc iu tr ng c.

    - c cht hc lm sng: Nghin cu cc bnh do ng c, nhim c, cch chn on v iu tr ng c, nhim c.

    - c cht hc phn tch: Nghin cu cc phng php pht hin v th nghim cht c v cc cht chuyn ho ca chng trong vt phm sinh hc v mi trng. y l mt ngnh ca ho phn tch.

    - c cht hc mi trng: Nghin cu s chuyn vn ca cht c v cc cht chuyn ho ca chng trong mi trng, trong chui thc phm v tc dng c ca cc cht ny trn c th v trn qun th.

    - c cht hc cng nghip: Nghin cu v nh hng c hi ca mi trng lao ng cng nghip i vi ngi v sc vt.

    - c cht hc php y: Cc xt nghim c cht v khm lm sng cc trng hp ng c, nhim c mang tnh php l.

    1.2. Cht c

    a. Khi nim cht c

    Cht c (poison) l nhng cht v c hay hu c c ngun gc thin nhin hay do tng hp, khi nhim vo c th v t n nng nht nh c th gy hiu qu dc hi cho c th sng.

    Gary D. Osweiler li a ra nh ngha v cht c nh sau: cht c l nhng cht rn, lng hoc kh, khi nhim vo c th theo ng ung hoc cc ng khc s gy nh hng n cc qu trnh sng ca cc t bo ca cc c quan, t chc. Cc tc ng ny ph thuc vo bn cht v c lc ca cc cht c.

    Khi nim khc ca cht c l c t (toxin) c dng ch cc cht c c sn sinh (c ngun gc) t cc qu trnh sinh hc ca c th v c gi l c t sinh hc (biotoxin).

    Trong qu trnh nghin cu v cht c cn lu mt s im sau:

    - Cht c l mt khi nim mang tnh nh lng. Mi cht u c mt liu no v cng v hi vi liu rt thp. Gii hn gia 2 liu l phm vi cc tc dng sinh hc. Theo Paracelsus (1493 - 1541): tt c mi cht u l cht c, khng c cht no khng phi l cht c. Liu lng thch hp s phn bit c mt cht c v mt thuc. Aspinrin (acid acetyl salicylic) l thuc h st chng vim c dng trong iu tr t nhiu

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    nm nay, nhng c th gy cht ngi vi liu 0,2 - 0,5 g/Kg. St, ng, magne, km l nhng nguyn t vi lng cn thit trong thnh phn thc n chn nui, nhng nu qu liu th c th gy ng c.

    - V mt sinh hc, mt cht c th c vi loi ny nhng li khng c vi loi khc. Carbon tetraclorid gy c mnh cho gan trn nhiu loi, nhng t hi hn i vi g. Mt s loi th c th n l c c dc c cha belladon.

    - Mt cht c th khng c khi dng mt mnh, nhng li rt c khi dng phi hp vi cht khc. Piperonyl butoxid rt t c vi loi c v v cn trng khi dng mt mnh, nhng c th lm tng c tnh rt mnh ca cc cht dng cng do n c tc dng c ch cc enzym chuyn ho cht l (xenobiotic - metabolizing enzymes) ca c th.

    - c tnh ca mt cht c c th thay i khi xm nhp vo c th qua cc ng khc nhau nh: qua ng ung, ng h hp, qua da, qua ng tim...

    b. Khi nim c tnh v c lc

    - Khi nim c tnh: c dng miu t tnh cht gy c ca cht c i vi c th sng.

    - Khi nim c lc: l lng cht c trong nhng iu kin nht nh gy nh hng c hi hoc nhng bin i sinh hc c hi cho c th.

    Khi nghin cu v c lc, cn quan tm n mi quan h gia liu lng cht gy c v p ng ca c th b ng c. Theo quy nh quc t, liu lng ca cht c c tnh bng milligram (mg) cht c/1kg khi lng c th gy nh hng sinh hc nht nh.

    mt s loi ng vt hoang d hoc loi c, c lc c th hin bng nng cc cht c trong thc n ng vt hoc nc. Nng gy t vong (LC - Lethal Concentration) l nng cht c thp nht trong 1 kg thc n chn nui hoc trong 1 lt nc (i vi c) gy cht ng vt. c lc trong ng c cp tnh c tnh theo LC50 - nng gy cht 50% ng vt.

    * Mt s khi nim v liu lng c s dng xc nh c lc ca cht c:

    - ED50 (Effective Dose): liu c tc dng vi 50% ng vt th nghim.

    - Liu ti a khng gy c (HNTP - Highest Nontoxic Dose): l liu lng ln nht ca thuc hoc cht c khng gy nhng bin i bnh l cho c th.

    - Liu thp nht c th gy c (TDL - Toxic Dose Low): Khi cho gp i liu ny s khng gy cht ng vt.

    - Liu gy c (TDH - Toxic Dose High): l liu lng s to ra nhng bin i bnh l. Khi cho gp i liu ny s gy cht ng vt.

    - Liu cht (LD - Lethal Dose): l liu lng thp nht gy cht ng vt. LD c cc t l khc nhau nh: LD1- liu gy cht 1% ng vt; LD50: liu gy cht 50% ng vt; LD100: liu gy cht 100% ng vt.

    * an ton ca thuc: c xc nh da trn cc ch s:

    - Ch s iu tr (TI - Therapeutic Index): l t s gia LD50 v ED50.

    LD50 TI = ED50

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    - Tiu chun an ton (SSM- Standart Safety Margin) l t s gia LD1 v ED99:

    LD1 SSM = ED99

    c. Phn loi cht c

    Cht c c th c phn loi theo nhiu cch: theo ngun gc, bn cht l ho ca cht c, phng php phn tch cht c, c lc, tc ng ca cht c trn cc h c quan ca c th v ngun ly nhim cht c.

    * Phn loi theo ngun gc cht c:

    - Cht c c ngun gc thin nhin: ng vt, thc vt, vi sinh vt.

    - Cht c c ngun gc tng hp, bn tng hp.

    * Phn loi theo bn cht l ho ca cht c:

    - Cc cht c dng kh, lng, cht rn.

    - Cc cht c v c: kim loi, kim, axit, baz.

    - Cc hp cht hu c: cc hp cht cha carbon, cc loi thuc tr su, aldehyd, cc axit hu c, cc ester, cc hp cht cha nit, cc hp cht cha lu hunh, cc alcaloid, glycosid.

    * Phn loi theo phng php phn tch cht c: theo Stas-Otto

    - Cht c ho tan trong nc hay cc dung dch axit, kim.

    - Cht c ho tan trong ether.

    - Cht c c th chit tch c trong cc dung mi hu c.

    * Phn loi cht c theo c lc

    Bng 1.1. Phn loi cht c theo c lc

    Phn loi c lc (LD50)

    Rt c (extremely toxic) < 1mg/kg

    c lc cao (highly toxic) 1 - 50 mg/kg

    c lc trung bnh (moderately toxic) 50-500 mg/kg

    c lc thp (slightly toxic) 0,5 - 5 g/kg

    Khng gy c (practically nontoxic ) 5 - 15g/kg

    Khng c hi (relatively harmless) >15g/kg

    * Phn loi theo tc ng ca cht c trn cc h c quan ca c th:

    - Cc cht c tc ng trn h thn kinh: cafein, strychnin, cyanid, ch, hexachlorophen, thuc tr su clo hu c...

    - Cc cht c tc ng trn h tiu ho: asen, selen, canxi clorua, sulfat ng, mui thy ngn v c...

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    - Cc cht c tc ng trn gan, mt: tetraclorua carbon, phenol, aflatoxin, fumonisin, acetaminophen, toluen, ng...

    - Cc cht c tc ng trn thn: thuc khng sinh nhm aminoglycosid, oxytetracyclin, sulfonamid, kim loi nng, ochratoxin...

    - Cc cht c tc ng trn h h hp: carbon monoxid, kim loi nng, carbon dioxid, formaldehyd, thuc tr su phospho hu c, fumonisin...

    - Cc cht c tc ng trn h tim, mch: digitalis, digitoxin, cafein, cocain, monesin, amphetamin...

    - Cc cht c tc ng trn h mu: aspirin, benzen, chloramphenicol, chlorpromazin, estrogen, phenylbutazol, T2 mycotoxin (y l cc cht gy thiu mu).

    - Cc cht c tc ng trn h sinh sn: testosteron, zearalenon, dicoumarol, corticosteroid, fumonisin, ch, cadmi, selen...

    - Cc cht c tc ng trn da: acid, base, formaldehyd, iodin, mui thy ngn, phenol, cc cht nhy cm quang hc...

    * Phn loi theo tc dng c bit ca cht c:

    - Cht c gy ung th:

    + Cc cht c c ngun gc thin nhin: aflatoxin B1, alcaloid pyrolizidin, aquilid A trong cy dng x, alcanylbenzen trong cy de vng.

    + Hp cht ung th hnh thnh khi ch bin thc phm: nitrosamin, cc cht hydratcarbon a vng thm, cc amin d vng.

    + Mt s thuc th y: diethylstibestrol (DES).

    - Cht c gy t bin: Hu ht cc cht gy ung th u c tc dng gy t bin.

    - Cht c gy qui thai: cc hp cht este phospho hu c, thuc tr su loi carbamat, thuc dit nm cha thy ngn, cloramphenicol.

    * Phn loi theo ngun gy c:

    - Cc cht gy nhim khng kh, nc v thc phm

    - Cc cht ph gia trong thc phm

    - Cc ho cht trong cng nghip v cc dung mi.

    - Thuc bo v thc vt, thuc th y.

    - Cc ngun khc.

    d. Cc ngun cht c

    Con ngi v ng vt c th b ng c bi rt nhiu cht c n t nhiu ngun trong cuc sng.

    * Cc cht gy nhim khng kh, nc v thc phm

    - Bn cht cc cht gy nhim k

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