Contamination and toxic effects of persistent endocrine disrupters in marine mammals and birds
Introduction
Many endocrine disrupters have been found in a range of environmental media and biota, and their toxic impacts to wildlife and humans are of concern (Colborn et al., 1996). Among these endocrine disrupters, the most hazardous for wild animals are those that have severe toxicity, high accumulation potential in the body and persistence in the environment. As representative chemicals having such properties, organochlorine compounds like DDTs, hexachlorocyclohexanes (HCHs), chlordane compounds (CHLs) and polychlorinated biphenyls (PCBs) have attracted great attention due to their potential to degrade environmental quality and to pose ecological risk. The organochlorine insecticides such as DDTs, HCHs and CHLs have been used as insecticides for agriculture and public health purposes including Malaria eradication. PCBs have been mainly used for industrial purposes such as dielectric fluids in transformers and capacitors. Substantial production and usage of these organochlorines started after the Second World War, but due to concerns regarding their toxic impact on humans and wildlife, many developed nations prohibited production and usage during the 1970s and 1980s. However, some developing countries are still using these organochlorines. The compounds are chemically stable and therefore quite persistent in the environment. Additionally, they have a strong bioaccumulative nature, are highly toxic to wildlife and humans, and are known to affect endocrine function.
The present paper provides an overview of contamination and toxic effects of persistent endocrine disrupters in marine wildlife, particularly in higher trophic animals such as marine mammals and birds, with an emphasis on the extent of knowledge gained so far from collaborative studies with Asian environmental scientists.
Section snippets
Global contamination
As a first comprehensive global monitoring survey, we have examined contamination by organochlorine endocrine disrupters. Due to the large production and worldwide use of organochlorines, these chemicals dispersed all over the globe. In this context, we found that the pollution sources of PCBs are located in developed nations, whereas the sources of organochlorine insecticides are present in developing countries. Apart from emission sources, the sink of these pollutants has been found to be
Ubiquitous contamination in the ecosystem
Our another finding was ubiquitous distribution, both spatially and temporally, of organochlorines in marine mammals, and characteristic bioaccumulation due to their specific physiological functions.
When comparing the number of chemicals detected in marine mammals in the 1960s to that in the 1990s, only five organochlorines and mercury were detected in 81 marine mammal in the 1960s. However, in the 1990s, 265 organic pollutants and 50 elements have been detected from more than 5000 marine
Occurrence of toxic effects
In general, the abnormalities suspected to be elicited by exposure to toxic environmental contaminants have been largely found and specifically reported in marine mammals. Additionally, physiological dysfunction by exposure to toxic contaminants has also been suggested in marine mammals based on the examination of some biomarkers such as CYP enzymes and hormones.
Since 1960s, sterility, abortion, stillbirths etc. have been observed in pinnipeds and cetaceans from coastal areas of some developed
Future trends in contamination
It is essential to understand the future trends in contamination in order to evaluate the risks posed by persistent endocrine disrupters. Hence, we have examined the historical trends of organochlorine residue levels in archived fat tissues of mammary glands of northern fur seals collected from northern North Pacific (Tanabe et al., 1994b). PCB and DDT residue levels were found to be maximum in the early 1970s and then decreased. DDT levels declined continuously even in the 1980s and 1990s, and
Contamination by dioxins and related compounds
The dioxins and related compounds such as polychlorinated-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar PCBs are of growing concern due to their toxic effects in marine mammals and birds. According to a comprehensive national survey by the Japanese Ministry of Environment (1999), dioxins and related compounds were widely detected in Japanese wildlife, and fish-eating animals such as kites and cetaceans also contained very high concentrations. Interestingly, terrestrial
Perspective of dioxin pollution
In order to reduce and phase out persistent organic pollutants (POPs), an intergovernmental treaty will be ratified in 2004 (UNEP, 2000). Global pollution by many POPs is expected to decrease in the future. However, the developing countries may continue to be a potential source of certain POPs, particularly dioxins and related compounds.
In the urban regions of developing countries, large scale dumping of municipal wastes is common. A variety of wastes, including plastics, metals, papers, woods
Acknowledgements
The author wishes to thank Dr. K. Kannan, Michigan State University, for critical reading of this manuscript. This study was supported by a Grant-in-Aid for Scientific Research on Priority Areas (A) from the Scientific Research Program of the Japanese Ministry of Education, Science, Sports, Culture and Technology (grant no. 13027101) and for Scientific Research (A) of Japan Society for the Promotion of Science (grant no. 12308030). Financial assistance was also provided by “Formation and
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