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Environmental and Biotic Contamination by Persistent Organic Pollutants (Pops) in the Asia-Pacific Region
Shinsuke Tanabe
Center for Marine Environmental Studies (CMES), Ehime University
Bunkyo-cho 2-5, Matsuyama 790-8577, Japan
E-mail: shinsuke@agr.ehime-u.ac.jp, 2011-07-13

Abstract

This article reviews the results of comprehensive investigations conducted in our laboratory, Center for Marine Environmental Studies (CMES), Ehime University over the past three decades on the distribution, sources, temporal trends and toxic impacts of the bioaccumulative persistent organic pollutants (POPs) in the Asia-Pacific region with a particular emphasis on the developing countries. Prominent contamination was found in the regions where they have been heavily used. The eastern Asian region is probably a potential source of pollution, particularly by the new contaminants such as polybrominated diphenyls ethers (PBDEs). These groups of contaminants, together with polychlorinated biphenyls, exhibited either decreasing or increasing trends depending on the extent of industrialization in the Asian developing region, indicating the necessity for long term monitoring. The open dumping sites for municipal wastes in major cities are significant sources of many toxic chemicals, and these areas are probably one of the challenges for future research due to the possible long term impacts on the environmental quality and human health. The formation of dioxins and related compounds in such dumping sites and their elevated residues found in breast milk of residents living in and around warrant long term impacts of dioxins upon next generations. Comprehensive and long term monitoring programs are still urgently needed with close collaboration and proper capacity building in developing countries in order to mitigate POPs emission and their risk on ecosystems and human health.

Key words: Persistent organic pollutants (POPs), Asia-Pacific region, developing countries, contamination status, temporal trends, human exposure, human health, open dumping site

Introduction

The last decades of the 20th century have witnessed a steady increase in the pace and extent of various environmental problems such as biodiversity loss, changes in water quality, land use and climate change. Among these, the issue of environmental pollution caused by persistent organic pollutants (POPs) has become increasingly important because their usage in large quantities have resulted in many negative impacts including environmental deterioration and health effects on wildlife. In particular, many chemicals are known to pose endocrine disrupting effects, which are probably the cause for various reproductive abnormalities observed in wildlife species (Colborn et al., 1996). Among a variety of endocrine disrupters, chemicals with severe toxicity, high accumulation potential in the body, and persistence in the environment are the most hazardous for wildlife. Organochlorine (OC) compounds, such as dichlorodiphenyl trichloroethane and its metabolites (DDTs), hexachlorocyclo-hexane isomers (HCHs), chlordane related compounds (CHLs) and polychlorinated biphenyls (PCBs) have received considerable attention due to their potential to degrade environmental quality and to pose ecological risk. Mass production and consumption of these OCs started after the Second World War. DDTs, HCHs and CHLs were heavily used as insecticides for agriculture and public health purposes including malaria eradication. PCBs are mainly used for industrial purposes such as dielectric fluids in transformers and capacitors. Although many developed nations prohibited production and usage of certain OCs in the 1970s and 1980s due to a deep concern regarding their toxic impacts on human and wildlife, they are still used in some developing countries.

Dioxins and related compounds (DRCs) including polychlorinated dibenzo-p- dioxins (PCDDs), dibenzofurans (PCDFs) and coplanar PCBs should also be paid particular attention due to their highest toxicity among OCs investigated. They are "unintentionally" generated by incineration and/or byproducts during the manufacturing processes of some other chemicals. According to a national survey by the Japanese Ministry of Environment (1999), elevated contamination of DRCs were widely detected in wildlife in Japan such as fish-eating animals like kites and cetaceans collected throughout Japanese coastal waters. In developed countries, decrease in the residue levels of DRCs in human breast milk have been reported recently due to the implementation of highly efficient incinerators and strict regulations on the production and usage of hazardous chemicals (LaKind et al., 2001). On the other hand, in developing countries, environmental pollution by DRCs may still increase because of poor management on the release of these contaminants. Although it has been suspected that the residents in Asian developing countries have been exposed to relatively high levels of DRCs, very less information is available on human exposure to these contaminants in these countries.

As an additional new contaminant, polybrominated diphenyl ethers (PBDEs), the popular brominated flame retardants, are now a worldwide problem even in remote areas, and Asia-Pacific region is not an exception (Birnbaum and Staskal, 2004; Ikonomou et al., 2002; Ueno et al., 2004). PBDEs are structurally similar to PCBs and DDTs and, therefore, their chemical properties, persistence and distribution in the environment follow similar patterns. Studies on the environmental behavior of PBDEs are chiefly derived from Europe, North America and the Arctic. Despite the usage of vast amounts of these compounds in Asia-Pacific region, there is paucity of data on the prevalence of PBDEs in Asian environment. Urgent investigations are necessary to identify sources of PBDEs in Asia as well as to quantify emissions and document their potential environmental fate in this region.

This article comprehensively reviews outcomes of investigations conducted in our laboratory during the past three decades on distribution, sources and temporal trends of contamination by bioaccumulative and persistent organic contaminants in wildlife and human from various countries in Asia-Pacific region with an emphasis on the extent of knowledge gained from collaborative studies with Asian environmental scientists. Results of multi-media monitoring surveys were compiled to discuss the fate of POPs in the environment and bio-indicative animals including human in regional and global points of view. Results compiled in this review mainly came from studies employing samples archived in the environmental specimen bank (es-BANK) of Ehime University, Japan, which contains about 1,300 biological species and 110,000 samples from many developing and developed countries (Tanabe, 2006).

Overview of Pops Contamination in the Asia-Pacific Region

Contamination Status and Distribution

In addition to the multi-media monitoring of the environmental samples, the use of human and animal tissues as bioindicators has proved to be a very suitable concept to address various important issues of pollution by persistent organic polluants (POPs) (Tanabe and Subramanian, 2006). Since bivalves have been suggested as suitable bioindicators for monitoring trace toxic contaminant levels in coastal waters (Goldberg, 1975), we have been using mussel as a sentinel animal to elucidate the pollution sources in the Asia-Pacific region (Tanabe et al., 2000; Monirith et al., 2003a; Ramu et al., 2007). Our latest survey conducted by Ramu et al. (2007) during 2003 - 2005 revealed that DDTs residue levels were highest in mussel samples from the coastal waters of South China ( Fig. 1(1198)). The higher contribution of p,p'-DDT, the main component in the formulation, in mussels may indicate the presence of current emission sources of DDT in China, despite the official ban on its usage in 1983. On the other hand, PCBs levels in mussels in developed nations including Japan were clearly higher than those in developing countries ( Fig. 1(1198)).

Noteworthily, widespread contamination by PBDEs in the coastal waters of Asia became apparent with the highest concentration in mussel samples from Hong Kong ( Fig. 1(1198)) (Tanabe et al., 2008). Another study focused on cetaceans also showed the highest PBDEs concentrations in samples from Hong Kong, suggesting that developing nations may also have significant pollution sources for PBDEs (Kajiwara et al., 2006). The Pearl River Delta in Hong Kong has a number of electronic and telecommunication industries, as well as a number of private manufacturing operations that have transformed this delta into one of the fastest growing industrial manufacturing areas in the world (Zheng et al., 2004). Estimates suggest that one out of three computers manufactured in the world are assembled in this region (Mai et al., 2005). As PBDEs are commonly incorporated into polymers for use in electronic components, the high levels of PBDEs in wildlife from Hong Kong may be due to the discharge of effluents derived from materials used in the production or the dismantling of electronic equipment, the so-called "e-waste". In addition, our recent survey on more than 20 sites along Korean coastal waters revealed that blue mussels contained very high concentrations of PBDEs (mean: 91 ng g-1; range: 6.6 - 440 ng g-1 lipid wt; Ramu et al., 2007), which is one of the highest levels ever reported for the mussels from Asia-Pacific. Elevated residues of PBDEs in mussels from Korea indicate that this region is a potential source of these new chemicals in eastern Asia.

Temporal Trends of Contamination

In recent years, several of our studies were conducted aiming at assessing the temporal trends of contamination by both classical and new POPs using various bioligical samples as bioindicators. Growth in interest on PBDE flame retardants has been as exponential as their apparent increase in the environment over the past 20 - 25 years in North America (Ikonomou et al., 2002; Norstrom et al., 2002; Rayne et al., 2003) and Europe (Norén and Meironyté, 2000; Thomsen et al., 2002). However, there is still very little information on PBDE contamination and its temporal trend from other regions of the world, including the Asia-Pacific region. Therefore, we have carried out comprehensive investigations to provide an in-depth understanding of the historical trends of contamination by PBDEs since 1972, in the fat tissues of northern fur seals (Callorhinus ursinus) inhabiting and migrating in the North Pacific, in comparison to classical OCs (Tanabe et al., 1994; Kajiwara et al., 2004). The lowest PBDE levels were in the fur seals collected in 1972, with the peak concentration around 1991-1994, and then, decreased to about 50% in 1997-1998 ( Fig. 2(1102)). On the other hand, OCs in northern fur seals showed the highest levels in the 1970s to early 1980s and then decreased. Compositions of higher brominated congeners increased since 1972, while some lower brominated congeners decreased, implying a change in the pattern of use, particularly the increased usage of highly brominated diphenyl ethers during 1972-1998. In the meantime, PCB compositions in fur seals showed no temporal variation, suggesting a continuous input of PCBs intothe marine environment in significant quantities. As peak concentrations of PBDEs occurred later than the OCs, it is essential to follow-up the patterns of PBDEs pollution that may be of great concern in the future.

Furthermore, to examine temporal changes in the past 20 years around Japan and 10 years around China, we analyzed PBDEs and OCs in the blubber of the marine mammals, melon-headed whales (Peponocephala electra) stranded along Japanese coasts in 1982 and 2001 and finless porpoises (Neophocaena phocaenoides) from Chinese waters in 1990/01 and 2000/01, respectively. In whales from Japan, PBDE levels in 2001 were significantly higher than 1982, showing about ten times increase ( Fig. 3(1249)). Similarly, finless porpoises from China showed five times increase during the past 10 years, indicating that PBDEs usage in China also increased drastically in the past decade (Ramu et al., 2006). When we compared PBDE congener patterns, higher contributions of hexa-BDEs were observed in whales collected in 2001 than those in 1982. This is a similar trend found in northern fur seals from the Pacific coast of Japan (Kajiwara et al., 2004), indicating a possible change in the source products.

On the other hand, congener profiles in porpoises from China did not shift to higher BDE congeners, implying a continuous discharge of lower BDE commercial mixtures such as Penta-BDE.

Asian countries consumed about half of the annual worldwide consumption of PBDEs in 2001 (BSEF, 2004; Watanabe and Sakai, 2003). In Asia, the major portion of formulation was estimated to be consumed by countries other than Japan, suggesting that considerable amounts of PBDEs have also been used in some developing countries in Asia, probably in nations with high economic growth rate. The high economic growth rate in China undoubtedly accelerated the industrial and human activities involving the usage of modern chemicals including PBDEs. Higher levels of PBDEs in mussels and small cetaceans from Hong Kong, mussels from Korea (Ramu et al., 2007; Kajiwara et al., 2006) and in fish from the East China Sea (Ueno et al., 2004) as well as the increasing temporal trend of PBDEs levels in wildlife from Chinese coasts may suggest their expanding usage and dumping in China and nearby countries (Ramu et al., 2006). Moreover, the import of waste electronic products like computers, television etc. used in developed nations in Asian developing countries such as China as trash has been reported (Hileman, 2002; Schmidt, 2002). In some cases, the wastes were burnt in open dumping sites, which may pose a concern on the formation of chlorinated and brominated dioxins. A series of our investigations underlines the need for long-term monitoring of PBDEs pollution in Chinese coastal waters as well as other countries in the Asia-Pacific region. It is also imperative to find out the pollution sources of PBDEs in the entire Asian region.

Human Exposure and Human Health Implications

Monitoring the Status of Contamination Using Breast Milk As Bioindicator

The presence of POPs in humans is always viewed with concern because of their potential for various biological effects such as teratogenicity, carcinogenicity, neurotoxicity and immunotoxicity (Nicholson and Landrigan, 1994). In the previous review (Tanabe and Subramanian, 2006), we pointed out that human tissue samples, particularly breast milk, collected in a non-destructive manner, are among the best samples for measuring both spatial and temporal variations of persistent organic pollutants. The advantage of using human tissue samples is that background information such as age, reproduction and possible route of exposure can be accurately obtained from the subjects.

Very recently, we have conducted various studies on the contamination status of PTS comprising PCDDs, PCDFs, PCBs, and OC insecticides such as DDTs, HCHs, chlordane compounds (CHLs), and hexachlorobenzene (HCB) in human breast milk collected from general public and the residents around open dumping sites of municipal wastes in Asian developing countries such as India, Cambodia, Vietnam, Philippines, Malaysia, Indonesia, and China during 1999-2003 (Kunisue et al., 2002, 2004a, b, c; Minh et al., 2004; Sudaryanto et al., 2005a, 2005b, 2006, Subramanian et al., 2007; Devanathan et al., 2009).

Mean lipid-normalized concentrations of POPs and toxic equivalents (TEQs) of DRCs, which were estimated based on human/mammal toxic equivalency factors (TEFs) proposed by WHO (Van den Berg et al., 1998), in human breast milk collected from general public in Asian countries such as India, Cambodia, Vietnam, Philippines, Malaysia, Indonesia, China, and Japan duirng 1999-2003 are illustrated in Fig. 4(1094) (Kunisue et al., 2002, 2004a, b, c, d; Minh et al., 2004; Sudaryanto et al., 2005a, 2005b, 2006). In general, relatively high concentrations of DDTs were detected in human breast milk from Asian developing countries, while elevated residue levels of TEQs of DRCs, PCBs, and CHLs were observed in Japanese breast milk. This trend of pollution was also observed in the Asia-Pacific Mussel Watch Program of POPs, in which mussels were employed as bioindicators (Monirith et al., 2003a). Our recent studies on wildlife have demonstrated that DRCs, PCBs, and CHLs were predominant contaminants in wildlife from Japan (Kunisue et al., 2003, 2006).

Among Asian developing countries, concentrations of DDTs in human breast milk from Vietnam, China, Cambodia, and Malaysia were relatively higher than those from other countries. It has been previously reported that DDTs were predominant in environmental media, biota, and foodstuff from these Asian developing countries. In Vietnam, higher levels of DDTs in sediments from densely populated areas as compared to those from paddy field were reported, indicating recent application of DDTs for public health purposes such as malaria control rather than for agriculture (Nhan et al., 2001). In addition, our previous studies also demonstrated elevated residue levels of DDTs in wild avian species and foodstuff from Vietnam (Kannan et al., 1997; Kunisue et al., 2003; Minh et al., 2002). Although fewer comprehensive investigations on POP pollution in Cambodia are available due to lack of monitoring of such pollutants because of long-term civil war, available studies reported that DDT has been used to control parasites of fish in cage culture (Tana, 1996) and relatively high residue levels of DDTs were observed in fish (Monirith et al., 1999). Higher levels of DDTs were also detected in inland resident avian species (Monirith et al., 2003b). In China, it has been recently reported that not only DDTs but also HCHs were predominant in various environmental samples along the coastal areas and foodstuff (Chen et al., 2002; Nakata et al., 2002; Zhou et al., 2001). The investigation on pollution by DDTs and HCHs in sediment cores indicated recent input of these contaminants into coastal areas from inland (Zhang et al., 2002). In addition, the investigation on pollution by DDTs in fish and mussels collected from aquaculture cages in coastal waters showed high proportions of p,p'-DDT suggesting recent releases of this chemical to the environment (Klumpp et al., 2002). Although the study on POPs pollution in Malaysia is very limited, Zakaria et al. (2003) reported relatively high levels of p,p'-DDT in water and sediments from agricultural areas compared with other POPs. Considering the above observations, it can be suspected that DDT may be in use illegally in some Asian developing countries and the residents are constantly exposed to this contaminant.

In Chinese and Indian human breast milk, notably higher concentrations of HCHs were observed compared with other Asian countries. This reflects a huge amount of usage in the past and possible recent illegal use of technical HCH in these two countries. The total usage of technical HCH was estimated as 4.46 and 1.00 million metric tons in China and India, respectively, which are the largest and second largest quantities in the world (Li et al., 1998). As described earlier, relatively high residue levels of HCHs have been recently reported in Chinese environmental media and foodstuff (Chen et al., 2002; Nakata et al., 2002; Zhou et al., 2001). Our studies revealed elevated residue levels of HCHs in wild avian species and foodstuff from India (Kannan et al., 1997; Kunisue et al., 2003; Tanabe et al., 1998). These results indicate that considerable sources of HCHs are still present in the environment of these countries, and that technical HCH may be in use for public health purposes in these two countries leading to the exposure of residents to HCHs.

Open Dumping Sites for Municipal Wastes - a Significant &Quot;Hot Spot&Quot; of Dioxin Contamination in Asian Developing Countries

In Asian developing countries, the presence of large open dumping sites of municipal wastes in the suburban areas of major cities is the prime source of critical DRCs pollution. In those dumping sites, variety of municipal wastes are burnt under low temperature by spontaneous combustion or intentional incineration, leading to secondary formation of DRCs. We found that the residue levels of DRCs were significantly higher in soils from those dumping sites than the agricultural and urban soils collected far from these areas (reference sites), indicating that the dumping sites are potential sources of DRCs (Minh et al., 2003). To understand the possible toxic impacts of DRCs on human, we attempted to elucidate the contamination status of DRCs in human breast milk collected from the residents around the dumping sites of municipal wastes in India, Cambodia, and Vietnam and compared with those from reference sites (Kunisue et al., 2004b).

As a result, it was found that the concentrations of DRCs in human breast milk from the dumping site in India were significantly higher than those from the reference site and those from Cambodia and Vietnam ( Fig. 5(1245)), indicating that significant pollution sources of DRCs are present in the dumping site of India and the residents around there have been exposed to relatively higher levels of these contaminants than the other two developing countries. To understand the magnitude of contamination in human breast milk from the dumping sites in India, Cambodia, and Vietnam, TEQs levels were compared with the values for human breast milk from general public of other countries since 1990. Because I-TEFs were mainly used to calculate TEQs, the reported data were recalculated by using WHO-TEFs for comparison. The levels of TEQs in human breast milk from India (38 pg TEQs g-1 lipid wt.) were comparable to or higher than those from developed countries (Becher et al., 1995; Dawailly et al., 1992; Fürst et al., 1994; Gonzalez et al., 1996; Kiviranta et al., 1999; Kunisue et al., 2004d; Liem et al., 1995; Schecter et al., 1990; Schuhmacher et al., 1999). This suggests that the residents around the dumping sites of India have been exposed to comparable levels of DRCs in the general public of developed countries. On the other hand, the levels of TEQs in human breast milk from Cambodia (9.2 pg TEQs g-1 lipid wt.) and Vietnam (13 pg TEQs g-1 lipid wt.) were lower than those from developed countries and comparable to those from other developing countries (Kunisue et al., 2004c; Paumgartten et al., 2000; Schecter et al., 1990; Sudaryanto et al., 2005a, 2005b). In developed countries, it is claimed that the residue levels of DRCs in human breast milk decreased recently (LaKind et al., 2001), because of the installation of highly efficient incinerators and strict regulations on the production and usage of various chemicals. On the other hand, it can be anticipated in Asian developing countries that the pollution by DRCs may increase further and hence the residue levels in human breast milk may also increase in future, because the release of these contaminants are not controlled very much even now.

Although residue levels of DRCs in soils collected from the open dumping sites in Asian developing countries were apparently higher, the levels of DRCs in human breast milk from the residents around the dumping sites in Cambodia and Vietnam were not significantly higher than those from reference sites (Minh et al., 2003; Kunisue et al., 2004b). This implies that the residents around the dumping sites in Cambodia and Vietnam have not been greatly exposed to DRCs originating from the dumping sites. However, residue levels of these contaminants in Indian samples around the dumping site were notably higher ( Fig. 5(1245)). In India, buffaloes and cows reared near the waste dumping site mainly feed on dumped leftovers. The residents around the dumping site constantly drink the milk collected from these bovines. On the other hand, in Cambodia and Vietnam, livestock such as buffaloes and cows are not reared around the dumping sites. To elucidate whether bovine milk is a potential source of DRCs for the residents around the dumping site in India, residue levels of these contaminants in the milk of buffaloes and cows collected there were estimated (Kunisue et al., 2004b).

DRCs were detected in elevated levels in the samples from dumping sites in all the bovine milk samples analyzed. This indicates that buffaloes and cows feeding in the dumping site of India consume greater amounts of DRCs through contaminated soils and/or garbage, and that daily intake of these bovine milk by the residents around the dumping site in India is one of the possible reasons why TEQs levels in human breast milk collected from the dumping site were significantly higher than those from the reference site. In India, dietary consumption of dairy products is generally higher than other countries, and average consumption of milk in India by a person per day rose from 135 g in 1980 to 176 g in 1990 (John et al., 2001). The residents around the dumping site in India constantly drink the milk collected from buffaloes and cows reared near those sites. Assuming that an adult weighing 60 kg drink 176g per day of buffalo or cow milk investigated in our study, estimated daily intake of TEQs from bovine milk from the dumping site was from 1 to 4 pg TEQs kg-1 day-1 _ well below the range of TDI proposed by WHO (Van Leeuwen et al., 2000), and only in one buffalo milk sample the value exceeded TDI ( Fig. 6(1153)).

Even though the values are within TDI, the residents around the dumping site in India are exposed to considerably high levels of DRCs and hence may be at greater risk of exposure to these contaminants via bovine milk.

Risk Assessment for Infants

It is realized that the presence of POPs in human breast milk has been of great concern because these lipophilic chemicals are readily transferred to and absorbed by infants. In case of dioxins, it is reported that one- to three-month-old infants absorb above 90% of most dioxin congeners present in their mothers milk (Dahl et al., 1995; McLachlan, 1993; Pluim et al., 1993), hence they may be exposed to relatively high levels of POPs during this period. To understand the magnitude of exposure to POPs by infants, we estimated the daily intake (DI) from the levels of these contaminants in human breast milk observed in Asian countries, based on the assumption that an infant ingests 700 ml milk per day and the weight of an infant is 5 kg (Kunisue et al., 2002, 2004a, b, c, d; Minh et al., 2004; Sudaryanto et al., 2005a, 2005b, 2006) and compared the values with the guideline standards proposed by WHO and Health Canada (Van Leeuwen et al., 2000; Oostdam et al., 1999).

As expected, the relatively higher DIs of TEQs were observed in the infants from Japan and the dumping site in India when compared with those from other countries and DIs in all the cases exceeded 1-4 pg TEQs kg-1 day-1, the tolerable daily intake (TDI) ( Table 1(1080)). In addition, DIs of PCBs, CHLs in Japanese, and DIs of DDTs in Chinese, Vietnamese, Cambodian, Malaysian, and DIs of HCHs in Chinese and Indian, and DIs of HCB in Chinese infants were relatively higher, and the DIs of these contaminants in some individuals exceeded the TDIs ( Table 1(1080)). It is argued that DRCs induce various toxic effects such as cancer in animal bodies (Birnbaum, 1994). Furthermore, p,p'-DDE and ?-HCH, the compounds that are generally abundant in human breast milk, have been reported as an androgen antagonist and environmental estrogen, respectively (Keice et al., 1995; Willett et al., 1998). These observations imply that abundance of POPs in human breast milk may adversely affect development and reproductive systems of Asian children. However, it is difficult to draw any firm conclusion from Table 1(1080) whether adverse effects by POPs have already occurred in Asian infants, because TDIs used here are estimated based on life span exposure. Not only TDIs of life span but also TDIs of POPs estimated from breast-feeding period may also be important (LaKind et al., 2000).

Breast-feeding is essential for the infants, as recommended elsewhere (LaKind et al., 2000; Longnecker and Rogan, 2001). Nevertheless, it is necessary to reduce the levels of organohalogens in human breast milk, especially organochlorine insecticides such as DDTs and HCHs in Asian developing countries and dioxins in Indian dumping site, to save the infants from possible toxic effects. In case of dioxins, it is estimated that 86% of dioxins in human breast milk comes through mobilization from adipose tissue and 14% from dietary sources, and so it may be difficult to reduce dioxin concentrations in human breast milk through short-term dietary control (Koppe, 1995). This means that the females have to lessen their exposure to POPs from dietary source from the earlier days of their life span. It is necessary to elucidate whether recent input and illegal use of organochlorine insecticides are present and to investigate temporal trends of POPs pollution in Asian developing countries to remedy the situation. Furthermore, in the dumping sites of Asian developing countries, especially India, urgent control and regulation of pollution sources of DRCs are required.

Conclusions and Recommendations

Considering these critical issues of POPs pollution, it is clear that continued and constant efforts should be made to deal with the environmental problems caused by these toxic chemicals. Over more than five decades when persistent organic chemicals were first used, despite considerable attempts to reduce their emissions, they continue to pose challenges for mankind and the scientific community is still in the initial steps to mitigate the ill effects of these toxic chemicals on the environmental quality, biodiversity and human health. Comprehensive and long term monitoring programs should be implemented urgently in close collaboration and proper capacity building in the areas where hot spots of pollution are conspicuous. In this regard, well designed monitoring of temporal trends of contamination in developing countries over extended period is crucial for tracing the unrevealed sources and predicting future prospects of their pollution state. In addition, the issues on human exposure of toxic chemicals, particularly among the people currently residing in extremely poor living conditions such as open dumping sites for municipal waste in major urban areas and dumping sites for electronic wastes (e-wastes) in developing countries should be the prime target for future research.

Acknowledgements

The author wishes to thank Dr. A. Subramanian, Ehime University, Japan for critical reading of the manuscript. This study was supported by Grants-in-Aid for Scientific Research (S) (No. 20221003) from Japan Society for the Promotion of Science (JSPS), and the "Global COE Program" from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and JSPS.

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Index of Images

Figure 1 Geographical Distribution of DDTS, PCBS and Pbdes Concentrations in Mussels from Coastal Waters of Some Asian Countries.

Figure 1 Geographical Distribution of DDTS, PCBS and Pbdes Concentrations in Mussels from Coastal Waters of Some Asian Countries.

Figure 2 Temporal Trends in Concentrations of Pbdes and PCBS in Female Northern Fur Seals Collected from 1972 to 1998. Horizontal Bars Indicate Mean Values. Data from Tanabe Et Al. (1994) and Kajiwara Et Al. (2004).

Figure 2 Temporal Trends in Concentrations of Pbdes and PCBS in Female Northern Fur Seals Collected from 1972 to 1998. Horizontal Bars Indicate Mean Values. Data from Tanabe Et Al. (1994) and Kajiwara Et Al. (2004).

Figure 3 Temporal Changes in Pbde Levels in Marine Mammals Found Stranded along the Coasts of China and Japan. Data from Ramu Et Al. (2006)

Figure 3 Temporal Changes in Pbde Levels in Marine Mammals Found Stranded along the Coasts of China and Japan. Data from Ramu Et Al. (2006)

Figure 4 Concentrations of DDTS, HCHS, PCBS, Pbdes and DRCS (Teqs) in Human Breast Milk Collected from General Population in Asian Countries

Figure 4 Concentrations of DDTS, HCHS, PCBS, Pbdes and DRCS (Teqs) in Human Breast Milk Collected from General Population in Asian Countries

Figure 5 Comparison of the Concentrations of Dioxins and Related Compounds in Human Breast Milk from Dumping (D) and Reference (R) Sites in Asian Developing Countries.the Circles and Bars Represent Mean and Range Values, Respectively. * P<0.05, ** P<0.01, Mann -Whitney U Test.

Figure 5 Comparison of the Concentrations of Dioxins and Related Compounds in Human Breast Milk from Dumping (D) and Reference (R) Sites in Asian Developing Countries.the Circles and Bars Represent Mean and Range Values, Respectively. * P<0.05, ** P<0.01, Mann -Whitney U Test.

Figure 6 Estimated Daily Intake of Teqs by Adults through Bovine Milk Collected from the Dumping and Reference Sites in India. DB, Buffalo Milk from the Dumping Site; DC, Cow Milk from the Dumping Site; RB, Buffalo Milk from the Reference Site, and RC, Cow Milk from the Reference Site.

Figure 6 Estimated Daily Intake of Teqs by Adults through Bovine Milk Collected from the Dumping and Reference Sites in India. DB, Buffalo Milk from the Dumping Site; DC, Cow Milk from the Dumping Site; RB, Buffalo Milk from the Reference Site, and RC, Cow Milk from the Reference Site.

Table 1 Estimated Daily Intakes of Persistent Organic Pollutants by Infants in Asian Countries

Table 1 Estimated Daily Intakes of Persistent Organic Pollutants by Infants in Asian Countries

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