November/December 1998
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November/December 1998 |
by Michael Gilbertson
One role of the IJC is to review water quality objectives and make appropriate recommendations to the two governments. The Great Lakes Science Advisory Board held a workshop in March 1998 to discuss the adequacy of existing water quality objectives for protection of organisms, including humans, living in the Great Lakes basin and exposed to persistent toxic substances from Great Lakes food chains.
Background
Research on the reproduction of Great Lakes wildlife in the 1960s and 1970s showed that predator birds and mammals, such as eagles, ospreys, gulls, terns and mink were severely affected by exposures to persistent toxic substances. There was a high incidence of embryo mortality and deformities, indicating that the persistent toxic substances were having embryotoxic and teratogenic effects.
The question at that time was whether there would be similar effects on humans who were eating fish from the Great Lakes.
The first epidemiological study was undertaken in the 1980s in western Michigan and provided evidence of neurological effects on infants resulting from prenatal exposure to persistent toxic substances as a result of maternal consumption, in the 1970s, of Lake Michigan fish prior to pregnancy. Subsequent testing of these children has shown that the children with the highest prenatal exposures have irreversible deficits on their ability to behave and to learn. Similar findings have been reported in a new cohort of infants, started in upper New York state in 1990, who were exposed prenatally to persistent toxic substances from maternal consumption of Lake Ontario fish in the 1980s.
The research on the reproduction of wildlife and on the developmental effects in infants exposed to persistent toxic substances, was important in the formulation of the ideas about endocrine disruptions. The various stages of the normal development of the embryo, fetus and infant are under the control of specific chemical messengers that are programmed to be released from a certain point and accepted at another at a certain concentration and particular time. Many chemicals, including many persistent toxic substances that have been released to the environment, interfere with these chemical messengers and cause irreversible damage to the developing fetus. These effects include changes in the development and function of the reproductive system, deficits in neurological development affecting behavior and learning, and deficits in the development of the immune system.
In this decade, the U.S. and Canadian governments have made significant progress in developing water quality objectives and criteria for persistent toxic substances. For example, the U.S. Environmental Protection Agency (EPA) has developed water quality criteria for persistent toxic substances, under the Great Lakes Initiative, for protection of aquatic life, human health and wildlife.
The Workshop
The first question for the Great Lakes Science Advisory Board during its workshop was whether the water quality criteria developed by U.S. EPA would be sufficiently stringent to protect the fetus from the developmental effects of persistent toxic substances, and particularly from the neurological effects. Monitoring the effects of persistent toxic substances on human health is particularly difficult and, therefore, the second question was whether the restoration of wildlife populations could be used as a surrogate for the achievement of the protection of human health.
Adequacy of Water Quality Criteria
Independent presentations by two senior scientists, Dr. Milton Clark from U.S. EPA and Dr. Deborah Rice from Health Canada, showed remarkable consistency in analyzing the available epidemiological and experimental studies. The two scientists showed that the neurological findings in humans were supported by the results of the studies in monkeys and that the reference doses from these two data sources compared favorably. In addition, the water quality criteria derived from the cancer risk method, calculated as part of the Great Lakes Initiative, do seem to provide sufficient protection from neurobehavioral and reproductive effects of PCBs and dioxins.
The available monitoring data indicate, however, that the present concentrations of these chemicals in water are about a hundred times higher than these criteria and that further remedial action will have to be undertaken to protect people from the increased likelihood of cancer from eating Great Lakes fish and from increasing the probability of neurological effects on infants from maternal consumption of Great Lakes fish prior to pregnancy.
Presentations and discussion at the workshop confirmed that, despite the significant improvements in water quality during the past two decades, there are still persistent toxic substances in fish at concentrations that pose threats to human health and in some cases are associated with actual effects on the more highly exposed human populations.
The Bald Eagle -- A Surrogate for Human Health Protection
The restoration and normal reproduction of a Great Lakes population of bald eagles might be a useful surrogate for the protection of human health, particularly in relation to the effects on neurological development from prenatal exposures to persistent toxic substances. There are, however, differences in the criteria derived from experimental versus empirical evidence. The IJC has advocated the bald eagle as a specific indicator of the virtual elimination of persistent toxic substances from the Great Lakes. There are historic databases of the status and reproductive success of the Great Lakes bald eagle population, and of the long-term monitoring of the concentrations of persistent toxic substances in addled eggs. There is a network of banders who have been collecting this information and samples while banding the young bald eagles in the Great Lakes basin. The development of water quality criteria to restore the Great Lakes populations of bald eagles nesting in habitat along the shorelines has taken two different approaches. The relationship between contaminant concentrations and reproductive success is well documented and there are field measurements of the empirical bioaccumulation factors that show certain persistent toxic substances, such as PCBs, increase in concentration from 25 million to 100 million times between water and bald eagle eggs.
In the development of the water quality criteria for the Great Lakes Initiative, scientists have used data derived from experimental dose-response relationships and bioaccumulation factors. The criteria based on the empirical field data are about ten times more stringent than the levels for protection of humans from the carcinogenic effects, whereas the criteria based on the experimental data are about ten-times less stringent.
Summary
These conclusions point to the continuing need for governments to implement their policy as stated in the Great Lakes Water Quality Agreement that the discharge of any or all persistent toxic substances be virtually eliminated. They also point to the need for the Parties to continue funding for monitoring population status and reproductive success of bald eagles as an indicator, not only of whether the virtual elimination policy of the Agreement is being implemented, but also whether human health is being protected.
Michael Gilbertson is a biologist with the International Joint Commission.