pesticides, fungicides, herbicides, agricultural pollution, industrial pollution, pollutant concentration, exposure, pollutant persistence, toxic substances, toxicology, synthetic organic molecules, endocrine disruptors, mutagens, teratogens, carcinogen, persistent organic pollutants (POPs), heavy metals, chlorinated hydrocarbons, dose-response relationship, median lethal dose, phase-outs, PCBs, dieldrin

Most chemical elements and many compounds are absolutely necessary for life. But, at certain concentrations, they become toxic to living organisms. Toxicology attempts to determine safe concentrations, exposures, and risks to health of various chemicals. Discovering when a substance is hazardous can be difficult because toxicologists must extrapolate from animal studies, discover the life stage (particularly fetal, perinatal, or elderly) when a human has a "window" of sensitivity, take into account genetic variability, and determine if the effects are cumulative, take a long time to show, or work synergistically with other chemicals. Important chemical pollutants are endocrine disruptors, mutagens, teratogens (impacting embryos), and carcinogens. Suspect substances of particular concern have been persistent organic pollutants (POPs) such as PCBs and chlorinated hydrocarbons (dieldrin) and heavy metals such as mercury.

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