How strong is the evidence of a link between environmental chemicals and adverse effects on human reproductive health?

Surveys show that the public suspects that synthetic (manmade) chemicals released into the environment, especially pesticides, have adverse effects on human health and cause disease, including cancer. In reality, few scientifically documented examples support this view, especially for effects on the general population. However, the observation that many synthetic chemicals have intrinsic hormonal activity—they are “endocrine disruptors”—has reopened this debate. Pressure groups have called for all synthetic environmental chemicals with the potential to cause harm to be phased out or banned, whereas the chemical industry argues that such action must be based on proof of harm. Vociferous cases have been made on both sides, each lacking definitive data. Yet it is clear that environmental and lifestyle factors are key determinants of human disease—accounting for perhaps 75% of most cancers. New understanding and emerging results are reshaping our thinking, as is the recognition that establishing cause and effect for environmental chemical exposures is a daunting task.