News reports frequently include stories about toxic chemicals in our food, water, and environment. But what does it mean to label a substance either "toxic" or "nontoxic"?
Toxicity indicates the degree to which a substance is poisonous to biological organisms, including humans. The traditional way to test toxicity is to count how many laboratory organisms die or suffer impaired health when exposed to various concentrations of a substance. However, in recent years this method of estimating the degree of risk posed by chemical contaminants has come under attack. The controversy focuses on how best to determine the toxicity of selected chemicals in order to set limits designed to protect public health. Two opposing points of view on this issue are presented below.