Marine Pollution Bulletin 60 (2010) 780–785

Contents lists available at ScienceDirect

Marine Pollution Bulletin

journal homepage: www.elsevier .com/locate /marpolbul

Baseline

Effects of environmental regulations on heavy metal pollution decline in coresediments from Manila Bay

Takahiro Hosono a,*, Chih-Chieh Su b, Fernando Siringan c, Atsuko Amano d, Shin-ichi Onodera e

a Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japanb Institute of Oceanography, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwanc Marine Science Institute, University of the Philippines, Diliman, Quezon City 1101, Philippinesd Institute of Geoscience and Geoinformation, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8561, Japane Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan

a r t i c l e i n f o a b s t r a c t

Keywords:Manila BayCore sedimentsHeavy metal polutionPb isotope ratio

0025-326X/$ - see front matter � 2010 Elsevier Ltd.doi:10.1016/j.marpolbul.2010.03.005

* Corresponding author. Tel./fax: +81 96 342 3935.E-mail address: hosono@kumamoto-u.ac.jp (T. Ho

We investigated the high-resolution heavy metal pollution history of Manila Bay using heavy metal con-centrations and Pb isotope ratios together with 210Pb dating to find out the effects of environmental reg-ulations after the 1990s. Our results suggested that the rate of decline in heavy metal pollution increaseddramatically from the end of the 1990s due to stricter environmental regulations, Administrative Order No.42, being enforced by the Philippines government. The presented data and methodology should form thebasis for future monitoring, leading to pollution control, and to the generation of preventive measures atthe pollution source for the maintenance of environmental quality in the coastal metropolitan city ofManila. Although this is the first report of a reduction in pollution in Asian developing country, our resultssuggest that we can expect to find similar signs of pollution decline in other parts of the world as well.

� 2010 Elsevier Ltd. All rights reserved.

Heavy metal pollution in marine sediments is increasingly rec-ognized in Asian metropolitan cities undergoing economic growth(Jiang et al., 2001). Quantitative studies of marine core sedimentshave shown that heavy metal accumulation is occurring in devel-oping areas of Asian countries, e.g. Manila Bay in the Philippines(Prudente et al., 1994), Jakarta Bay in Indonesia (Williams et al.,2000), the Pearl River Estuary in China (Ip et al., 2004), southwest-ern Taiwan (Hung and Hsu, 2004), and Liaodong Bay in China (Xuet al., 2009). In response to this problem, many Asian countries (i.e.Indonesia, Malaysia, the Philippines, Singapore, Thailand, and Viet-nam) have been accelerating the introduction of stricter environ-mental regulations since the 1990s (Shelton and Kiss, 2005).However, reductions in pollution have not yet been reported ordiscussed. The effects of environmental regulations on sedimentconditions are now of great concern both to the governmentsand to the citizens of these countries.

Manila Bay, a semi-closed marine inlet of the Philippine Sea(Fig. 1), has an area of ca. 1700 km2, an average depth of 17 m,and an estimated volume of 28.9 km3 (Velasquez et al., 2002). Itis an important area for fisheries and aquaculture. The influenceof heavy metal pollution on ecosystems has not been clearly shown(Prudente et al., 1997). However, the bay receives significant dis-charges of domestic and industrial wastes (Chua et al., 1989),

All rights reserved.

sono).

and significant toxic metal accumulations have been reported inbottom sediments (Prudente et al., 1994), and in the water (Velas-quez et al., 2002). In an earlier study of estuary sediments near thePasig River (Fig. 1), the vertical increase in metal concentrations(Pb, Cd, Zn, and Cu) in bulk sediments was recorded (Prudenteet al., 1994). In 1977, the Philippines government established a ba-sic legal framework for environmental protection, the PresidentialDecree PD1151. This was further developed, and in the 1990s anew law governing environmental management, Administrative Or-der No. 42, came into effect (Global Environmental Forum, 1997).However, since the earlier study by Prudente et al. (1994), no fur-ther results have been reported, and the status of metal pollutionand the effects of environmental regulation are not yet clearlyunderstood.

Marine and estuary sediments commonly act as a sink for river-borne metals produced by weathering of watershed rocks, and bydischarge of pollutants such as domestic wastewaters, urban run-off, and industrial and agricultural effluents (Callender, 2005). Hea-vy metals deposited in sediments are not removed by biogenicprocesses. Therefore, concentration data for metals in sedimentcores can be used as ‘‘pollution archives” in combination withradioisotope chronologies such as 210Pb dating (Church et al.,2006; Mil-Homens et al., 2006; Cantwell et al., 2007; Irabienet al., 2008; Krom et al., 2009). Stable Pb isotope ratios(206Pb/207Pb) have been used as tracers for identifying the source(s)of Pb (natural or anthropogenic) in marine and estuary core

MNL3

MNL2

MNL1

14°54’

14°42’

14°30’

14°18’

Corregidor Island

Philippine Sea

Manila Bay

Pampa

nga R

iver

PasigRiver

MetroManila

14°24’

14°36’

14°48’

120°30’ 120°42’ 120°54’120°36’ 120°48’ 120°60’

10 km

200km

Study area

N13º

N17º

N9º

E121º

E125º

Luzon

Mindanao

Palawan

Philippines

Fig. 1. Map showing sampling locations for sediment cores (MNL1, MNL2, and MNL3) in Manila Bay.

T. Hosono et al. / Marine Pollution Bulletin 60 (2010) 780–785 781

sediments (Hirao et al., 1986; Graney et al., 1995; Hung and Hsu,2004; Ip et al., 2004; Lima et al., 2005; Tang et al., 2008; Xuet al., 2009). Pb isotope ratios do not fractionate by physicochem-ical reactions in marine environments (Faure, 1986), so 206Pb/207Pbratios should provide critical information for reconstructing pollu-tion histories, especially in areas where sedimentation processesare complicated. This study aims to investigate the effects of envi-ronmental regulations since the 1990s by reconstructing the high-resolution heavy metal pollution history of Manila Bay using sedi-ment metal concentrations and Pb isotope ratios together with210Pb dating. The results of this study are important for the devel-opment of pollution control strategies for the coastal environmentof Manila metropolitan city, and for other developing areas of theworld.

Three sediment cores (MNL1, MNL2, and MNL3) were collectedon 26 May 2006 from the central to southern side of Manila Bay(Fig. 1) using a gravity core sampler (Kajak–Brinkhurst type gravitycorer). The sample properties are summarized in Table 1. SampleMNL1 was collected at the extension of the Pasig River, where sed-iments are largely transported by river flow. Samples MNL2 andMNL3 were collected from the southern part of Manila Bay. Wesuggest that these cores retain average information on the pollu-tion of a wide area of the bay. An acrylic core sampler, 50 cm inlength and 5 cm in diameter, was used to obtain sediment coresof 22–45 cm at each site (Table 1). The sediment cores were sec-tioned at 1 cm intervals using a thin plastic cutter. The sampleswere immediately stored in plastic bags, frozen, and then trans-ported to the laboratory where they were stored in a freezer at�30 �C. The frozen sediments were freeze-dried and water con-tents were measured. Sediment fragments larger than 1 mm andseashells were carefully removed by hand. Grain sizes were

analyzed using a laser diffraction particle analyzer (LS13 320, Beck-man Coulter). Samples for heavy metal concentration determina-tion and Pb isotope analysis were pulverized in a tungstencarbide vessel using a Herzog HP–MS.

Dilute and leaches are commonly employed to extract metalsfrom sediment matrices. For Manila Bay samples, we followedthe acid leach procedure with 1 M HNO3 + 1.75 M HCl solution de-scribed by Graney et al. (1995). The leached fraction contains hea-vy metals from most of the extractable components in thesediments except for silicate minerals, and has been widely usedin reconstructing metal pollution histories (Graney et al., 1995;Lima et al., 2005). Dried sediment samples (0.3 g) were placed in5 mL polypropylene tubes and acid solution (3 mL) was added.The leachates were separated by centrifugation, transferred intoTeflon� beakers and heated at 100 �C on a hot plate. Dried sampleswere remelted by dropping nitric acid and diluted to 1% high puritynitric acid solutions for chemical analysis. The sediment metal con-centrations were measured by inductively coupled plasma massspectrometry (ICP–MS; ELAN 6100DRCII, Perkin–Elmer) at the Cen-ter for Advanced Marine Core Research, Kochi University, Japanusing indium as the internal standard. Analytical precision forthe instrument was better than 2%, and replicate analysis of oneof the samples (MNL2 depth = 20–21 cm) yield a 5% precision(2r, n = 20). The toxic metals analyzed were Cu, Zn, As, Cd, Hg,and Pb. Data for Cu, Zn, and Pb varied significantly in the core sam-ples, and could therefore be used in the study; the other metalswere present in very low concentrations or did not show any clearconcentration features. Stable Pb isotope ratios (206Pb/207Pb) wereanalyzed using solutions the same as those used for measuringheavy metal concentrations. The ratios of 206Pb/207Pb were deter-mined using ICP–MS (ELAN 6100DRCII, Perkin–Elmer) under the

Table 1Properties of sediment core samples collected from Manila Bay.

Core I.D. Sampling location Sampling sea depth (m) Core length (cm) Water content (%) Grain size

Latitude Longitude Clay (av.) % Silt (av.) % Sand (av.) %

MNL1 N14�3103500 E120�4701900 24 22 65.9–83.7 3.9–45.9(36.2)

18.2–65.6(52.7)

0–77.9(14.7)

MNL2 N14�2900400 E120�4101500 33 40 69.0–86.6 19.2–52.3(41.8)

44.1–70.8(51.0)

1.1–16.2(7.2)

MNL3 N14�2500100 E120�3805800 38 45 60.7–77.3 4.3–28.4(18.0)

35.5–76.3(62.4)

0–60.2(19.6)

782 T. Hosono et al. / Marine Pollution Bulletin 60 (2010) 780–785

analytical conditions described by Gallon et al. (2005). An interna-tional standard reference material (SRM 981 Common Pb IsotopeStandard, National Institute of Standards and Technology) wasmeasured after every three samples for calibration and qualitychecking. Relative standard deviations (SRD) were better than0.5% for 206Pb/207Pb (2r, n = 39). Mean 206Pb/207Pb values werenormalized to standard values of 206Pb/207Pb = 1.0933.

Sedimentation rates and sediment chronologies were estimatedusing 210Pb (half-life: 22.3 yr) dating techniques using an a-spec-trometer at the Institute of Oceanography, National Taiwan Uni-versity, according to well-established methods (Huh and Su,1999). 210Pb radioisotope activities were measured for sectionedsamples of all three cores. Sedimentation rates were calculatedusing an advection–diffusion model, with the assumption that sed-iment fluxes and the associated 210Pb are reasonably constant ondecadal to centennial timescales at a given site (Berger and Heath,1968; Huh and Su, 1999). This method is basically the same as Ap-pleby and Oldfield’s ‘‘simple model CIC” (Appleby and Oldfield,1992). According to the previous study (Sombrito et al., 2004),the 137Cs activity in the sediments is low and cannot be a good timemarker in Manila Bay. Although we do not have the 137Cs data asan independent chronology method for checking the results calcu-lated from excess 210Pb profiles, our results show good agreementwith some previous studies in the Manila Bay (Sombrito et al.,2004; Sta. Maria et al., 2009) and that give us a strong confidenceon our chronology results.

All of the cores had a well-mixed layer with constant 210Pbex

activity at the top, for mixing depths of 6 cm (MNL1), 6 cm(MNL2), and 5 cm (MNL3) (Fig. 2). The best estimates of depositionrates for these cores were 0.077 cm yr�1 from a depth of 6–18 cmfor MNL1, and 0.66 cm yr�1 from a depth of 6–28 cm and0.037 cm yr�1 for a depth of 28–31 cm for MNL2. Sedimentationrates for MNL3 were variable (0.11–1.42 cm yr�1) at depths of 5–44 cm. The increase in sedimentation rates over the last 100 years(Fig. 2) is associated with land-use change in watershed areas afterWorld War II, or with ash deposition from the eruption of the Pina-tubo Volcano on 15 June 1991 (Sombrito et al., 2004; Sta. Mariaet al., 2009). The coarse grain particles observed in MNL3 core sed-iments (Fig. 2 and Table 1) might have been transported by localevents such as flooding or changes in bottom currents. Overall,the estimated range of sedimentation rates in the study area wasquite variable (0.037–1.42 cm yr�1), which corresponds well withpreviously published data (0.2 to ca. 2 cm yr�1; Sombrito et al.,2004; Sta. Maria et al., 2009). Detailed mechanisms for sedimenta-tion rate changes will be discussed in a separate paper.

Vertical profiles of Zn, Cu, and Pb concentrations and206Pb/207Pb ratios for the three cores are shown in Fig. 2. Generally,the sediments exhibit specific vertical variations in Zn, Cu, and Pbconcentrations in each core (Fig. 2 and Table 2). The minimum val-ues, 50–61 ppm (Zn), 23–27 ppm (Cu), and 7–9 ppm (Pb), are typ-ically found at the bottom of the cores and are regarded as baselinevalues. The maximum values, 94–96 ppm (Zn), 37–39 ppm (Cu),and 16–19 ppm (Pb), are observed at the middle to upper partsof the cores. In terms of concentrations, there are no significant dif-

ferences in Zn, Cu, and Pb ranges among the different samplingsites. Similarly, the 206Pb/207Pb ratios in all three cores show com-mon features (Fig. 2 and Table 2): the minimum values (1.120–1.132) are found at the bottom, while the maximum values(1.152–1.166) are typically observed in the upper parts of thecores. Contaminated marine or estuary sediments in Asian coun-tries typically have 206Pb/207Pb ratios of around 1.15–1.19 (TokyoBay, Japan: Hirao et al., 1986; Pearl River Estuary, China: Ip et al.,2004; Victoria Harbour, Hong Kong: Tang et al. 2008; LiaodongBay, China: Xu et al., 2009). The increases in 206Pb/207Pb ratios inthe sediments from 1.120–1.132 to 1.152–1.166 with increasingPb concentrations (7–9 to 16–19 ppm) towards the upper partsof the cores clearly indicate accumulation of anthropogenic Pb inthe bay with time, although the lengths of the collected cores fromthe three sites differ (22–45 cm). This tendency is less obvious forMNL3 (Fig. 2), probably because of the complicated sedimentationprocess mentioned above. We will therefore use MNL1 and MNL2for further discussion of the pollution history.

Since sedimentation rates varied significantly with time as wellas among the sampling sites, ‘‘flux” (concentration times massaccumulation rate) might be a better parameter to assess temporalmetal accumulation changes. However, calculated flux values forcore MNL2, e.g. for Pb, showed unrealistically sudden gap betweenbefore (0.4–0.5 lg cm�2 yr�1) and after the year 1960 (8.1–12.5 lg cm�2 yr�1). Increasing in flux values at MNL2 site mightbe related to increasing amounts of suspended particles via volca-nic ash as well as from the land erosion, which accelerated absorp-tion of metals in marine water to deposit. However, the occurrenceof this phenomenon has not been fully clarified yet and furtherinvestigations are needed to elucidate this problem. Nevertheless,concentration data obtained here are still useful in assessing thetemporal pollution trends for MNL1 and MNL2 cores with constantor simple change in sedimentation rates.

It can be seen from the MNL2 core profile (Fig. 2) that the Zn, Cu,and Pb concentrations, and the 206Pb/207Pb ratios were lowest atthe core bottom (Zn = 50 ppm, Cu = 23 ppm, Pb = 7 ppm;206Pb/207Pb = 1.12) in the period before 1900. These values are re-garded as the baseline values, which were present before theoccurrence of heavy metal pollution. The population of the Manilametropolitan area expanded more than 1600% in the period 1900–1970, when economic growth and industrialization started to in-crease (Fig. 3). Accordingly, despite low fractionation, heavy metalconcentrations increased from 1900 until around 1970 (toZn = 90 ppm, Cu = 38 ppm, and Pb = 14 ppm), with a simultaneousincrease in 206Pb/207Pb ratios (up to 1.154) (Fig. 2). The trends inheavy metal concentrations and isotope ratios of the core samplescollected near the Pasig River estuary (MNL1) correspond well tothe trends shown in MNL2 within the period 1900–1970 (Fig. 2).These results clearly suggest that heavy metal pollution started be-fore 1900 and worsened until at least around 1970. This interpre-tation corresponds well with previous reports (Prudente et al.,1994).

From 1970 to the end of the 1990s, fairly constant patterns of Znand Cu concentrations are observed in MNL2; in contrast, moder-

190019201940196019802000

(Year)

26 28 30 32 34 3650 60 70 80 90 8 10 12 14 16 18 1.12 1.14 1.160

10

20

30

40

1900 2000Year Zn (ppm) Cu (ppm) Pb (ppm) 206Pb/207Pb

MNL1

Dep

th (c

m)

20 40 60 80

40 60 80 100 1.12 1.14 1.1620 25 30 35 6 8 10121416180

10

20

30

40

1900 2000Year Zn (ppm) Cu (ppm) Pb (ppm) 206Pb/207Pb

MNL2

Dep

th (c

m)

20 40 60 80

30 50 70 90 1.12 1.14 1.1615 20 25 30 35 8 10 12 14 160

10

20

30

40

1900 2000Year Zn (ppm) Cu (ppm) Pb (ppm) 206Pb/207Pb

MNL3

Dep

th (c

m)

20 40 60 80

1900192019401960

1980

2000

(Year)

Mixing layer

190019201940

1960

1980

2000

(Year)

Mixing layer

Mixing layer

0 10 20 30

10 30 50 70

04 05

clay size grain (%)

silt size grain (%)

0 10 20 30

10 30 50 70

04 05

clay size grain (%)

silt size grain (%)

0 10 20 30

10 30 50 70

04 05

clay size grain (%)

silt size grain (%)

error

error

error

Fig. 2. Temporal distribution of Zn, Cu, and Pb concentrations, and of 206Pb/207Pb ratios, for three cores (MNL1, MNL2, and MNL3) collected on 26 May 2006. Proportions (%) ofclay and silt size particles and 210Pb dating data are also shown.

T. Hosono et al. / Marine Pollution Bulletin 60 (2010) 780–785 783

ate, but still increasing, Pb concentration patterns and 206Pb/207Pbratios are seen (Fig. 2). Roughly similar patterns are observed for

MNL3 (Fig. 2). There are three possible reasons for the reductionin heavy metal accumulations during this period, in spite of the

Table 2Summary of analytical results for sediment core samples collected from Manila Bay.

Core I.D. Zn (ppm) Cu (ppm) Pb (ppm) 206Pb/207Pb

MNL1 55–95 26.5–36.8 8.9–18.9 1.132–1.160MNL2 50–96 22.9–38.6 7.3–19.0 1.120–1.166MNL3 61–94 23.7–37.2 8.4–15.9 1.129–1.152

784 T. Hosono et al. / Marine Pollution Bulletin 60 (2010) 780–785

population increase (Fig. 3): (1) the effect of the 1977 legal frame-work for environmental protection, Presidential Decree PD1151,(Global Environmental Forum, 1997); (2) decreases in industrialoutput caused by economic crises (Fig. 3) such as the Second OilCrisis in 1979 and the Asian Financial Crisis of 1997, and/or polit-ical problems; and (3) a dilution effect due to increasing sedimen-tation rates. However, the pattern of economic depression isclearly different from that observed for heavy metal concentrationsin the core samples (Fig. 3). Moreover, the observed patterns ofheavy metal concentrations and isotope ratios for MNL2 (Fig. 2)are similar to those for MNL1, where sedimentation rates havebeen constant over the last 100 years, although resolution forMNL1 is not as good as it is for MNL2. These observations stronglysupport the idea that establishment of the Presidential DecreePD1151 was to some extent effective in reducing pollution. More-over, the Presidential Decree PD1151 did not ban the use of leadedgasoline, which is a major source of Pb pollution (Callender,2005). This could be the reason why only Pb pollution continuedto increase over the time. Consequently, it is assumed that a partialdecline in pollution was achieved from the 1970s to the end of the1990s.

Reductions in Zn, Cu, and Pb concentrations can be clearly seenin all three cores from the end of the 1990s to the present time(Fig. 2), despite increases in population and in economic activity(Fig. 3). In the 1990s, with the aim of protecting the natural envi-ronment and the health of its citizens, the Philippines governmentintroduced a new law for environmental management, Administra-tive Order No. 42 (Global Environmental Forum, 1997). This newlaw introduced stricter environmental regulation of water quality,air pollution, and industrial wastes, and provided a more severe

1900 1910 1920 1930 1940 1950 19

12

8

6

4

2

0

Popu

latio

n (m

illion

)

14

16

12

20

Pb (p

pm)

Year

Presidential Decr

10

WWII

GDP per c

18

Cu

Pb

AdAb

Fig. 3. Comparisons of heavy metal pollution trends in Manila Bay with changes in the1997), the population of Manila, and GDP per capita of the Philippines (Maddison, 2009)selected to show the pollution changes taking place in Manila Bay.

punishment of polluters than did the previous version. It also abol-ished the use of leaded gasoline throughout the country. The sharpdeclines in Zn and Cu, as well as Pb, concentrations in the sedimentcores reflect the results of the enforcement of Administrative OrderNo. 42 in the 1990s (Figs. 2 and 3). It can therefore be concludedunequivocally that the rate of decline in heavy metal pollution in-creased dramatically from the end of the 1990s due to stricterenvironmental regulations being enforced by the Philippinesgovernment.

The heavy metal contents at the surface mixing layers are basi-cally lower than those of the sediments at peak pollution periods(Fig. 2). However, these values, especially for Pb, are still higherthan the baseline values. In addition, the 206Pb/207Pb ratios in themixing layers are still at the levels of the highest values (ca.1.15–1.16) (Fig. 2), which are identical to the isotopic ratios at peakpollution times. Therefore, metal contamination is still occurring tosome extent and pollutants are still being stored in the deeperparts of the sediments. Heavy metal pollution of the bottom sedi-ments in Manila Bay is still an important matter of concern, andcontinuous monitoring is needed for better management of coastalenvironments. The presented data and methodology should formthe basis for future monitoring, leading to pollution control, andto the generation of preventive measures at the pollution sourcefor the maintenance of environmental quality in the coastal metro-politan city of Manila. It can be seen from these results that currentlevels of heavy metal pollution in Manila Bay are decreasing as aresult of environmental regulations enforced in the late 1990s.The full compliance with the environmental laws and regulationsis important in stopping heavy metal pollution problems in thisarea. Heavy metal pollution of marine environments in some eco-nomically developed Asian metropolitan cities (Tokyo and Osaka)have already been attenuated since the 1970s (Hirao et al., 1986;Hoshika et al., 1991) by enforcement of environmental policiesand domestic regulations. As mentioned previously, similar envi-ronmental regulations have recently been applied in some devel-oping Asian countries (Shelton and Kiss, 2005), although declinesin heavy metal pollution have not yet been reported, except inManila, as reported in this study. Our results suggest that we can

60 1970 1980 1990 2000 2010

3000

2500

2000

1500

1000

0

GD

P per capita (1990 Int. GK$)

ee PD1151

Population500

Economic crisis

apita

30

35

40

50

45 Cu (ppm

)

ministrative Order No.42olition of the use of leaded gasoline

Philippines government environmental regulations (Global Environmental Forum,as an economic indicator. The Cu and Pb concentrations in sediment core MNL2 are

T. Hosono et al. / Marine Pollution Bulletin 60 (2010) 780–785 785

expect to find similar signs of pollution decline in other Asiancountries as well.

Acknowledgments

We thank Peter Zamora and other staff at the Geological Ocean-ography Laboratory of the Marine Science Institute, University ofthe Philippines for their help with sediment core sampling. We alsothank Dr. Kei Okamura at the Center for Advanced Marine Core Re-search (CMCR), Kochi University, Japan for supporting ICP–MSanalysis. Sociological and economic data were supplied by Dr. To-moyo Toyota and Dr. Shinji Kaneko at the Research Institute forHumanity and Nature (RIHN) and Hiroshima University, Japan,respectively. We are grateful to Dr. Yu Umezawa at Nagasaki Uni-versity, Japan for fruitful discussions. This study was funded by theGrant-in-Aid for Young Scientists (A) (No. 20681003), with addi-tional support from the ‘‘Human Impacts on Urban SubsurfaceEnvironments” Research Project at RIHN, and from the cooperativeresearch program of CMCR, Kochi University (No. 07B015).

References

Appleby, P.G., Oldfield, F., 1992. Application of lead-210 to sedimentation studies.In: Ivanovich, M., Harmon, R.S. (Eds.), Uranium-series Disequilibrium:Applications to Earth, Marine, and Environmental Sciences. Clarendon Press,Oxford, pp. 731–778.

Berger, W.H., Heath, G.R., 1968. Vertical mixing in pelagic sediments. J. Mar. Res. 26,134–143.

Callender, E., 2005. Heavy metals in the environment – historical trends. In: Lokkar,B.S., (Ed.), Environmental Geochemistry. In: Holland, H.D., Turekian, K.K., (Eds.),Treatise on Geochemistry. Elsevier, Pergamon, Oxford. pp. 67–106.

Cantwell, M.G., King, J.W., Burgess, R.M., Appleby, P.G., 2007. Reconstruction ofcontaminant trends in a salt wedge estuary with sediment cores dated using amultiple proxy approach. Mar. Environ. Res. 64, 225–246.

Chua, T.E., Oaw, J.N., Guarin, F.Y., 1989. The environmental impact of aquacultureand the effects of pollution on coastal aquaculture development in SoutheastAsia. Mar. Pollut. Bull. 20, 335–343.

Church, T.M., Sommerfield, K., Velinsky, D.J., Point, D., Benoit, C., Amouroux, D., Plaa,D., Donard, O.F.X., 2006. Marsh sediments as records of sedimentation,eutrophication and metal pollution in the urban Delaware Estuary. Mar.Chem. 102, 72–95.

Faure, G., 1986. Principles of Isotope Geology. John Wiley and Sons, New York.Gallon, C., Tessier, A., Gobeil, C., Beaudin, L., 2005. Sources and chronology of

atmospheric lead deposition to a Canadian Shield lake: Inferences from Pbisotopes and PAH profiles. Geochim. Cosmochim. Acta 69, 3199–3210.

Global Environmental Forum, 1997. Overseas environmental measures of Japanesecompanies (Philippines). Research report on trends in environmentalconsiderations related to overseas activities of Japanese companies 1996.<http://www.env.go.jp/earth/coop/oemjc/>.

Graney, J.R., Halliday, A.N., Keeler, G.J., Nriagu, J.O., Robbins, J.A., Norton, S.A., 1995.Isotopic record of lead pollution in lake sediments from the northeastern UnitedStates. Geochim. Cosmochim. Acta 59, 1715–1728.

Hirao, Y., Mabuchi, H., Fukada, E., Tanaka, H., Imamura, T., Todoroki, H., Kimura, K.,Matsumoto, E., 1986. Lead isotope ratios in Tokyo Bay sediments and theirimplications in the lead consumption of Japanese industries. Geochem. J. 20, 1–15.

Hoshika, A., Shiozawa, T., Kawana, K., Tanimoto, T., 1991. Heavy metal pollution insediment from the Seto Inland Sea. Jpn. Mar. Pollut. Bull. 23, 101–105.

Huh, C.-A., Su, C.-C., 1999. Sedimentation dynamics in the East China Sea elucidatedfrom 210Pb, 137Cs and 239, 240Pu. Mar. Geol. 160, 183–196.

Hung, J.-J., Hsu, C.-L., 2004. Present state and historical changes of trace metalpollution in Kaoping coastal sediments, southwestern Taiwan. Mar. Pollut. Bull.49, 986–998.

Ip, C.C.M., Li, X.D., Zhang, G., Farmer, J.G., Wai, O.W.H., Li, Y.S., 2004. Over onehundred years of trace metal fluxes in the sediments of the Pearl River Estuary,South China. Environ. Pollut. 132, 157–172.

Irabien, M.J., Cearreta, A., Leorri, E., Gómez, J., Viguri, J., 2008. A 130 year record ofpollution in the Suances estuary (southern Bay of Biscay): implications forenvironmental management. Mar. Pollut. Bull. 56, 1719–1727.

Jiang, Y., Kirkman, H., Hua, A., 2001. Megacity development: managing impacts onmarine environments. Ocean Coast. Manage. 44, 293–318.

Krom, M.D., Carbo, P., Clerici, S., Cundy, A.B., Davies, I.M., 2009. Sources and timingof trace metal contamination to sediments in remote sealochs, N.W. Scotland.Estuar. Coast. Shelf Sci. 83, 239–251.

Lima, A.L., Bergquist, B.A., Boyle, E.A., Reuer, M.K., Dudas, F.O., Reddy, C.M., Eglinton,T.I., 2005. High-resolution historical records from Pettaquamscutt River basinsediments: 2. Pb isotopes reveal a potential new stratigraphic marker. Geochim.Cosmochim. Acta 69, 1813–1824.

Maddison, A., 2009. Statistics on world population, GDP and per capita GDP, 1-2006AD. <http://www.ggdc.net/maddison/>.

Mil-Homens, M., Stevens, R.L., Boer, W., Abrantes, F., Cato, I., 2006. Pollution historyof heavy metals on the Portuguese shelf using 210Pb-geochronology. Sci. TotalEnviron. 367, 466–480.

Prudente, M., Ichihashi, H., Tatsukawa, R., 1994. Heavy metal concentrations insediments from Manila Bay, Philippines and inflowing rivers. Environ. Pollut.86, 33–83.

Prudente, M., Kim, E.-Y., Tanabe, S., Tatsukawa, R., 1997. Metal levels in somecommercial fish species from Manila Bay, the Philippines. Mar. Pollut. Bull. 34,671–674.

Shelton, D., Kiss, A., 2005. Judicial Handbook on Environmental Law. United NationsEnvironment Programme.

Sombrito, E.Z., Bulos, A.dM., Sta Maria, E.J., Honrado, M.C.V., Azanza, R.V., Furio, E.F.,2004. Application of 210Pb-drived sedimentation rates and dinoflagellate cystanalyses in understanding Pyrodinium bahamense harmful algal blooms inManila Bay and Malampaya Sound. Philippines J. Environ. Radioactiv. 76, 177–194.

Sta Maria, E.J., Sringan, F.P., Bulos, A.dM., Sombrito, E.Z., 2009. Estimating sedimentaccumulation rates in Manila Bay, a marine pollution hot spot in the Seas of EastAsia. Mar. Pollut. Bull. 59, 164–174.

Tang, C.W., Ip, C.C.M., Zhang, G., Shin, P.K.S., Qian, P.Y., Li, X.D., 2008. The spatial andtemporal distribution of heavy metals in sediments of Victoria Harbour, HongKong. Mar. Pollut. Bull. 57, 816–825.

Velasquez, I.B., Jacinto, G.S., Valera, F.S., 2002. The speciation of dissolved copper,cadmium and zinc in Manila Bay. Philippines Mar. Pollut. Bull. 45, 210–217.

Williams, T.M., Rees, J.G., Setiapermana, D., 2000. Metals and trace organiccompounds in sediments and waters of Jakarta Bay and the Pulau SeribuComplex. Indonesia Mar. Pollut. Bull. 40, 277–285.

Xu, B., Yang, X., Gu, Z., Zhang, Y., Chen, Y., Lv, Y., 2009. The trend and extent of heavymetal accumulation over last one hundred years in the Liaodong Bay, China.Chemosphere 75, 442–446.