Toxic threat: To gauge the impact of harmful chemicals on humans and wildlife, researchers are focusing on fetal damage caused by exposure to contaminants

Just as Love Canal brought the threat of cancer and chemicals into people's backyards during the 1970s, many observers say a growing scientific hypothesis will dramatically alter the perception of chemicals as environmental health threats in the next century. New research is focusing on endocrine disruption - damage to the fetus caused by exposure to harmful chemicals. The endocrine system is a sensitive system of glands and hormones responsible for proper development of the brain and reproductive organs, as well as other bodily functions. Some researchers hypothesize that extremely small doses of toxic compounds such as PCBs might disrupt the hormonal balance of the developing fetus, resulting in permanent neurological, reproductive and immune system changes. As a result, endocrine disruption - along with cancer - will become a yardstick by which contaminants are evaluated.

While there is scientific uncertainty about the endocrine disruption process in humans, some experts warn this new research might have profound health implications, particularly for children. The Agency for Toxic Substances and Disease Registry (ATSDR), a federal research agency affiliated with the Department of Health and Human Services, reported this year that "many environmentally persistent compounds have the potential to disrupt the normal functions of the endocrine system," which "may have a serious impact on reproductive and developmental parameters in wildlife and human populations." Research is focusing on the subtle effects of chemical exposure (such as diminished intelligence) on the developing young and the embryo, and shifting away from the traditional emphasis on cancer. Some of the most compelling data comes from studies of children born to mothers who consumed PCB-contaminated fish from the Great Lakes.

ATSDR points out that children who were exposed in the womb to higher levels of PCBs from their mothers' consumption of Great Lakes fish are three times more likely to have lower than average IQ scores and twice as likely to be two grade levels behind their peers in reading comprehension. They have poorer short-term and long-term memory and difficulty paying attention. These effects occur at PCB levels only slightly above those found in the general population. Other studies of exposed infants have shown lower birth weights, reduced motor reflexes, poorer neuromuscular function, weakened immune systems, susceptibility to infections and reduced attentiveness, among other problems.