Wildlife Studies Suggest Chemical Threat to Humans
By Cat Lazaroff
WASHINGTON, DC, August 13, 2002 (ENS) - Exposure to certain endocrine disrupting environmental contaminants is harming wildlife, concludes a new report from the International Program on Chemical Safety. However, the report, which assesses what science already knows about the effects of these compounds, finds scant evidence that endocrine disruptors are harming humans.
"The evidence that human health has been adversely affected" by exposure to endocrine disrupting chemicals is "generally weak," note the authors of the report, "Global Assessment of the State-of-the-Science of Endocrine Disruptors." The study reviewed available literature in an attempt to answer whether chemicals which have the potential to interfere with the normal functioning of the endocrine system are threatening the health of humans, wildlife and the environment.
The report also concludes that there is "sufficient evidence" that exposure to endocrine disruptors has harmed some wildlife species. Because of continuing concerns and scientific uncertainties, studies on the potential effects posed by these chemicals should remain a high global priority requiring coordinated and strengthened international research strategies, the authors state.
"The last two decades have witnessed growing scientific concerns and public debate over the potential adverse effects that may result from exposure to a group of chemicals that have the potential to alter the normal functioning of the endocrine system in wildlife and humans," the report begins.
"These concerns have stimulated many national governments, international organizations, scientific societies, the chemical industry, and public interest groups to establish research programs, organize conferences and workshops, and form expert groups and committees," to study the effects of endocrine disruptors.
The current study attempts to compile the reports produced by these varied sources, and learn whether the body of evidence can prove whether endocrine disruptors are having harmful effects.
A variety of health problems may be linked to exposure to endocrine disruptors, the study notes, including reduced sperm counts, breast cancer and other malfunctions of the endocrine system. The endocrine system includes the glands that regulate body processes through the secretion of hormones.
Other potential problems include altered immune, nervous system and thyroid function, and hormone related cancers.
"The evidence that wildlife have been affected adversely by exposures to [endocrine disruptors] is extensive," the authors wrote.
The harm inflicted upon birds by exposure to the insecticide DDT demonstrates how these chemicals can harm wildlife, the study says. Populations of several birds of prey species in the United States were threatened when DDT exposure produced thinning of egg shells, causing birds to accidentally crush their own eggs.
More recently, a pesticide spill in Lake Apopka, Florida, provided a well publicized example of endocrine disruptive effects in alligators, the report notes. A variety of sexual and developmental abnormalities were observed that have been attributed to high levels of various chemical contaminants.
Other long lasting endocrine disruptors in the environment include polychlorinated biphenyls (PCBs), which now contaminate river bottom mud in many regions. Exposure to PCBs and other related chemicals has been shown to impair the reproductive and immune function of Baltic seals, resulting in marked population declines.
"Studies in wildlife have been proposed as 'sentinels' of human exposure," to endocrine disruptors, the report notes. "However, given the diversity of wildlife, caution must be taken" in extrapolating these results to humans, as research has focused primarily on only a few species of wildlife, the authors said.
"Overall, the current scientific knowledge provides evidence that certain effects observed in wildlife can be attributed to chemicals that function" as endocrine disruptors, they wrote. "However, in most cases, the evidence of a causal link is weak, and most effects have been observed in areas where chemical contamination is high."
Likewise, "analysis of the human data by itself, while generating concerns, has so far failed to provide firm evidence of direct causal associations" between low level exposure to endocrine disuptors and harm to humans. "Despite these difficulties, exposure to [endocrine disruptors] has been suggested to play a role in adverse health outcomes, and concerns remain."
The authors cite reports of a decline since the 1930s in human sperm quality in several countries, and altered sex ratios, with more boy babies being born than girls. Exposure to certain endocrine disruptors may also be associated with endometriosis, an inflammation of the uterus.
Concerns have been raised about the influence of endocrine disruptors on the timing of puberty, but the possible mechanisms of action and role of other factors such as nutrition need to be clarified, the authors wrote.
The report calls for increased research efforts around the globe. "This assessment has clearly demonstrated that further research is necessary to address the uncertainties that remain in this field of study," the report concludes. "Our current understanding of the effects posed by [endocrine disruptors] to wildlife and humans is incomplete."
"We cannot wait decades for precise causal mechanisms to be established," said Gwynne Lyons of the World Wildlife Fund in the United Kingdom. "We owe it to our children and to wildlife to act now to eliminate exposure to man made hormone disrupting chemicals."
The report is the result of a global comprehensive review of the publicly available scientific literature on endocrine disruptors organized by the International Program on Chemical Safety (IPCS). The IPCS is sponsored by the World Health Organization (WHO), the United Nations Environment Program (UNEP) and the International Labor Organization.
The U.S. Environmental Protection Agency (EPA) joined health and environmental agencies from Australia, Canada, Norway, Japan and the European Commission nations in funding the study.
This assessment was requested in 1997 by the Intergovernmental Forum on Chemical Safety, the 1997 Declaration of the Environment Leaders of the Eight on Children's Environmental Health, and endorsed by the 50th World Health Assembly in 1997.
More than 60 international scientific experts contributed to the report either as IPCS Steering Group Members, chapter leaders, authors or reviewers.
The study is available in full at: http://www.who.int/pcs/emerg_site/edc/global_edc_TOC.htm