DSpace at VNU: Contamination by persistent organic pollutants in dumping sites of Asian developing countries: Implication of emerging pollution sources

Arch Environ Contam Toxicol 50, 474–481 (2006) DOI: 10.1007/s00244-005-1087-3 Contamination by Persistent Organic Pollutants in Dumping Sites of Asian Developing Countries: Implication of Emerging Pollution Sources N H Minh,1 T B Minh,1 N Kajiwara,1 T Kunisue,1 A Subramanian,1 H Iwata,1 T S Tana,2 R Baburajendran,3 S Karuppiah,3 P H Viet,4 B C Tuyen,5 S Tanabe1 Center for Marine Environmental Studies, Ehime University (CMES), Bunkyo-cho 2-5, Matsuyama 790-8577, Japan Social and Cultural Observation Unit, Cabinet of the Council of Minister, Phnom Penh, Cambodia Centre of Advanced Study in Marine Biology, Annamalai University, Annamalai Nagar, 608 002, India Centre for Environmental Technology and Sustainable Development, Hanoi National University, Hanoi, Vietnam Nong Lam University, Hochiminh, Vietnam Received: April 2005 /Accepted: 15 August 2005 Abstract In Asian developing countries, large amounts of municipal wastes are dumped daily in open dumping sites without proper management This practice may cause several adverse environmental consequences and increased health risk to local communities To elucidate contamination by persistent organic pollutants (POPs)—including dichloro-diphenyl-trichloroethane and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), chlordanes, hexachlorobenzene (HCB), and polychlorinated biphenyls (PCBs)—in such dumping sites, soil samples were collected from open dumping sites and respective control sites in Cambodia, India, and Vietnam from 1999 through 2001 Our results demonstrated that DDTs, PCBs, and HCHs were dominant contaminants in the dumping sites However, the contamination pattern was not consistent, showing higher HCHs in India than in Cambodia and Vietnam Interestingly, in all of the countries, extremely higher levels of POPs were observed in the dumping sites compared with those in the respective control sites, suggesting significant amplification of POP contamination in the dumping sites of Asian developing countries Mean concentrations of DDTs and PCBs were 350 and 140 ng/g dry weight, respectively, in the dumping sites of Cambodia and 26 and 210 ng/g, respectively, in India These residue levels were hundreds to thousands times higher than those in general soils, implying possible risk to human health of the local communities, especially to the rag pickers, including children who work in these sites to collect recyclable materials Composition of DDT compounds suggested their recent use in populated areas, which in turn might have caused increased levels of DDTs in the open dumping sites In addition, composition of HCH isomers revealed their different use pattern in different countries During the past few decades, several persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) and Correspondence to: S Tanabe; email: shinsuke@agr.ehime-u.ac.jp organochlorine pesticides (OCPs), were used extensively in Asian developing countries for industry, agriculture, and vector control Available data demonstrated approximately 4.9 million tons of hexachlorocyclohexanes (HCHs) and 400 thousand tons of dichloro-diphenyl-trichloroethane and its metabolites (DDTs) were produced in China between the 1950s and 1980s, accounting for 33% and 20% of world production, respectively (Zhang et al 2002) In India, annual consumption of pesticides is approximately 85,000 metric tons, of which DDTs, HCHs, and malathion accounted for 70% (Gupta 2004) In other countries such as Vietnam, use of OCPs—including DDTs, HCHs, etc., continued until 1995 (Sinh et al 1999) Persistence of such chemicals in soils, air, and water, together with natural processes such as evaporation to the atmosphere and washout by rain and flood, give rise to their ubiquitous distribution in the environment and eventual penetration into food chains and bioaccumulate in humans Public concern about contamination by POPs increased recently because several of these compounds are identified as hormone disrupters, which can alter normal function of endocrine and reproductive systems in humans and wildlife (Cheek et al 1999; Colborn et al 1993; Kelce 1995; Vos et al 2000) Recognition of these consequences has led to the international restriction and ban on 12 POPs, including dioxins, PCBs, and several OCPs, to limit their harmful impacts on global environment and human health (Anonymous 2001) Although prohibitions on uses of POPs have been implemented in developed nations, a number of them are still in use in Asian developing countries For instance, recent input of DDTs to environment has been recorded constantly in China, India, and Vietnam (Minh et al 2002; Monirith et al 2003; Nakata et al 2004) Because of the ability of POPs to undergo long-range transport, their continuous use in Asian developing countries may cause contamination in other parts of the globe as well, even in pristine areas such as the Arctic and Antarctic In addition, recycling of POPs from contaminated soils into the atmosphere is another pollution source to the global environment (Harner et al 2001) All of these facts may further 475 Dumping Sites of Asian Developing Countries support the previous assumption that contamination by POPs still remains a critical environmental issue in Asian developing countries (Tanabe 2002) In Asian developing countries, because of the lack of advanced facilities, large amounts of municipal wastes from populated areas are directly dumped into open dumping sites with very poor management This practice raises public concern over potential harmful effects to local communities and the environment These concerns probably become more pragmatic when recent intensive studies demonstrated increased human health risk caused by exposure to toxic chemicals, such as dioxins and related compounds, and heavy metals in these dumping sites (Minh et al 2003; Agusa et al 2003) Given that several POPs have been used extensively for various purposes in Asian developing countries, their increased contamination in these open dumping sites is likely However, no comprehensive study so far has examined potential sources of POPs pollution as well as their effects to the environment and human health In this study, we report, for the first time, increased contamination by several POPs, such as PCBs, DDTs, HCHs, HCB, and CHLs (chlordane-related compounds), in dumping sites from Asian developing countries, suggesting open dumping sites as significant pollution sources of POPs in the region was transferred to a multilayer column packed with silica gel, H2SO4-absorbed silica gel, and AgNO3-absorbed silica gel Three layers in the column was packed in the following order: 0.5 g silica gel, g H2SO4-absorbed silica gel, 0.5 g silica gel, g AgNO3absorbed silica gel and, finally, 0.5 g Na2SO4 After transferring the samples into the multilayer column, the elution was made by passing 250 ml 5% dichloromethane in hexane through the column The collected mixture was concentrated by KD and blown down by nitrogen to exactly ml Hexane-washed water was added to wash this ml solution three time Four ml of this solution was collected by pipette for further cleanup by gel-permeation chromatography and separated by Florisil (Wako Chemicals USA) chromatography column to obtain PCB and OCP fractions as previously described (Minh et al 2003) The final solution was further concentrated, if necessary, before instrumental analysis PCBs, DDTs, HCHs, CHLs, and HCB were quantified by gas chromatography (GC)–electroncapture detection (ECD) (Agilent 6890N) using DB-1 fused silica capillary column (30 m · 0.25 mm i.d · 0.25-lm film thickness) The column oven temperature was programmed from 60°C (1 minute) to 160°C at a rate of 20°C/min, held for 10 minutes, then increased to 260°C at a rate of 2°C/min, and held for 20 minutes The PCB standard used for quantification was a mixture of 62 PCB congeners (Wellington, Ontario, Canada) Concentrations of individually resolved peaks of PCB isomers and congeners were summed to obtain total PCB concentrations Recovery rates obtained by this procedure were as follows: HCHs 85% to 91%; HCB 91%; PCBs 108%; CHLs 87% to 98%, and DDTs 82% to 103% A procedural blank was run for every batch of five samples for crossverification Materials and Methods Sample Collection Soil samples were collected from some municipal dumping sites in Hanoi and Hochiminh (Vietnam), Chennai (India), and Phnom Penh (Cambodia) from 1999 through 2001 Urban or agricultural soils were also collected in appropriate sites that were at least approximately 30 km far away from any dumping site and hereafter referred as control samples relative to the dumping soil samples Locations and major characteristics of dumping and control sites are shown in Figure In general, the open dumping sites were located close to human habitats, and many people work in the dumping sites of Cambodia and India to collect reusable materials Soil samples were collected at depths from to 10 cm at five points with an area of approximately 25 m2, combined together, and considered as a representative sample Soils were kept in clean plastic bags, maintained at 4°C, transported to our laboratory in Japan, and stored at –20°C until chemical analysis Analytic Method POPs in soil samples were analyzed according to the method described by Iwata et al (1994) with some modifications Briefly, 15 ml hexane-washed water followed by 100 ml acetone was added to a conical flask containing 15 g air-dried soil The flask was shaken vigorously for 60 minutes in an electric shaker, and soil solution was filtered into a separating funnel containing 600 ml hexanewashed water and 100 ml hexane The funnel was shaken for 15 minutes and kept in a stand for at least hours to entirely separate the aqueous from the hexane layers The aqueous layer was discharged, and the hexane layer was washed three times with 100 ml water times Hexane volume in the final solution was measured for calculating recovery from the initial 100 ml and then concentrated by Kuderna-Danish (KD) apparatus to approximately 10 ml and further blown down by nitrogen stream to ml This 5-ml solution Statistical Analysis The statistical analysis was performed with StatView Version software (SAS, Cary, NC) SpearmanÕs rank correlation test was used to examine significance of correlation between residue levels of the contaminants Results and Discussion Residue Levels and Contamination Pattern of POPs in the Dumping Sites In general, DDTs and PCBs were found in high levels in dumping sites of Vietnam, India, and Cambodia (Table 1) Contamination pattern of POPs in Cambodia and Vietnam followed the order of DDTs > PCBs > HCHs > CHLs > HCB In contrast, the pattern in India revealed higher levels of HCHs than DDTs (PCBs > HCHs > DDTs > CHLs > HCB) The difference in such patterns indicates more extensive use of HCHs in India compared with Cambodia and Vietnam The residue patterns in our study highlighted contamination by DDTs, PCBs, and HCHs in Asian developing countries Concentrations of PCBs and DDTs in dumping site soils varied largely with their highest concentrations found in Chennai and Phnom Penh, respectively (Table 1) Interestingly, levels of PCBs and DDTs in all the dumping sites were higher than those in the respective control sites, implying their increased contamination in such dumping sites However, the extent of difference between residue levels in the dumping site soils and the control soils also varied in different countries Although in India and Cambodia, PCBs and DDTs concentrations in the dumping site soils were hundreds to thousands of times higher than their control soils, in Vietnam this difference was not very high, suggesting larger amplification of the contamination in the dumping sites of India and Cambodia compared with Vietnam 476 N H Minh et al Fig Sampling locations in Vietnam, Cambodia, and India Particularly, DDTs levels in Cambodian dumping sites were >15 times higher than the other dumping sites and 300 times higher compared with the respective control sites Heavy dumping in the relatively small area of dumping sites in Cambodia (Minh et al 2003) might have led to the higher concentrations of DDTs in this area It is noteworthy that Monirith et al (2003) reported low levels of DDTs in mussels collected from coastal areas of Cambodia In this context, such highly contaminated dumping sites in Cambodia would be of particular concern as they become pollution sources of DDTs to the environment and biota During the sampling surveys, we observed a large number of local people working in such dumping sites to collect reusable waste Therefore, the increased contamination by POPs such as PCBs and DDTs in Indian and Cambodian dumping site soils may increase toxic exposure and cause health risks to the local communities, especially rag pickers In contrast to the ranking of PCBs and DDTs in the dumping site soils, residue levels in the control soils of such countries followed the opposite pattern, showing the highest concentration in Vietnam followed by Cambodia and India (Table 1) In fact, higher concentrations of PCBs and DDTs in mussels, birds, and human breast milk collected from Vietnam compared with other Asian developing countries were also reported in previous studies (Monirith et al 2003; Minh et al 2002; Minh et al 2004) In Vietnam, likely source of PCBs could be releases from old electric capacitors and transformers, which were imported into Vietnam until the mid-1980s (Sinh et al 1999) In addition, additional sources of PCBs might relate to different kinds of military heavy weapons used extensively during the Vietnam War as suggested earlier (Thao et al 1993) Similarly, more intensive use of DDT in past decades in Vietnam probably caused higher background levels in the environment as well as food chains In Asian developing countries, DDT has been used extensively for both agriculture and vector control during the last few decades (Tanabe et al 1994) Although its application in agriculture is now officially prohibited in most of the countries, the use for vector control is allowed to continue in some countries such as India, China, Thailand, Myanmar, etc (Anonymous 2001) This could be a plausible reason for relatively higher DDTs levels in urban compared with rural areas (Minh et al 2001; Nhan et al 2001; Phuong et al 1998) Continuous application of DDT in highly populated areas for vector control and other hygienic purposes might have led to the presence of DDTs in municipal waste Accumulating such garbage in small areas such as open dumping sites in turn might have amplified the levels of DDTs in soil In global comparison, PCBs levels in dumping site soils were compared with those in general soils worldwide, including industrial countries, which are known to have higher background levels of PCBs (Breivik et al 2002; Meijer et al 2003) In general, PCB levels in the global background soils were considerably lower than those in the dumping site soils of India and Cambodia and slightly lower than those of Vietnam (Table 2) This fact again highlighted the importance of open dumping sites as pollution sources of PCBs in Asian developing countries Moreover, increased concentrations of PCBs in our sampling sites under tropical conditions may enhance their recycling from soil to atmosphere and undergoing long-range atmospheric transport to reach regions at higher latitudes (Wania and Mackay 1996) In this context, large number of open dumping sites in Asian developing countries may be important sources of such chemicals to the global environment As a consequence of insufficient management in the open dumping sites, PCBs may again escape from these sites to contaminate the local environment and pose health risks to local communities DDT concentrations in dumping sites of Asian developing countries were higher than urban soils from many locations over the world (Table 2) DDT levels in dumping sites were probably higher or comparable with those in agricultural soils collected in the early 1990s from areas with intensive application of DDT such as the United States, Argentina, and Russia It should be emphasized that although DDTs are no longer used in some regions such as North America and Europe, their re-emission from DDT-contaminated soils still remains as an important source of DDTs to the atmosphere, making them available for longrange transport to remote areas such as the Arctic region (Harner et al 2001) In this aspect, emerging pollution sources of DDTs in Asian developing countries may not be only an environmental issue for the region but also a concern for the global environment Mean concentrations of HCHs, CHLs, and HCB were rather low compared with DDTs and PCBs, except in India However, their levels in dumping-site soils were also higher compared with those in control soils Particularly, HCH levels in the Indian dumping-site soils were much higher than those in control soils (Table 1) as well as other 477 Dumping Sites of Asian Developing Countries Table Concentration (ng/g dry weight) of POPsa in dumping-site and control-site soils from Asian developing countries Sample Vietnam, Hanoi (DS) DP-04 DP-05 DP-07 DP-09 DP-10 DP-11 DP-12 Mean Vietnam, Hanoi (CS) Pso-1 Pso-2 Pso-3 Mean Vietnam, Hochiminh (DS) VSDS-04 VSDS-05 VSDS-07 VSDS-08 VSDS-09 VSDS-10 Mean Vietnam, Hochiminh (CS) VSDO-02 VSDO-03 VSDO-04 Mean India, Chennai (DS) IDS-2 IDS-7 IDS-10 IDS-4 IDS-9 IDS-13 Mean India, Chennai (CS) ICS-16 ICS-20 Mean Cambodia, Phnom Pen (DS) DSS-6 DSS-8 DSS-11 DSS-12 DSS-13 DSS-14 DSS-15 DSS-16 Mean Cambodia, Phnom Penh (CS) DPS-1 DPS-6 Mean PCBs DDTs 20 11 2.2 19 19 3.1 6.9 12 11 10 1.9 48 52 3.9 6.0 19 0.080 0.18 0.18 1.3 1.4