Various processes degrade synthetic chemicals—pesticides, pharmaceuticals, biocides, and industrials—in the environment (1, 2). Consequently, the environment may be exposed to a mixture of the parent compounds and any resulting degradation products (degradates). Recent advances in analytical methodology and greater access to analytical standards have advanced degradates research (3, 4). Specifically, research on pesticides has found degradates in surface water (5–10), groundwater (11–13), precipitation (14–16), air (17, 18), and sediment (19, 20). Pharmaceuticals and detergent degradates also exist in the environment (21–23). Figure 1 shows that degradates were detected as often as or more frequently than the parent compound.

Although some regulatory schemes require information about the impacts of degradates on human and environmental health, that information does not exist for many compounds (25, 26). Pesticides are the exception. In this article, we bring together the available data to address the environmental behavior of degradates and their effects on organisms and discuss how to identify substances of potential concern. In addition, we cite gaps in the current knowledge and make recommendations for future research requirements. While the article focuses on pesticides, we believe these observations can be extended to biologically active compounds and some industrial substances.