Tolerance level refers to the maximum allowable amount of chemical residue, such as a pesticide, legally permitted in food. Tolerance levels are determined by government agencies such as the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA), and are based on the results of testing, primarily animal testing. This testing determines the dosage level at which few or no effects are observed. This dose is then adjusted to a human equivalency dose with a margin of error built in for added safety.

While pesticides play an important role in modern society, and are used for a variety of purposes, not until recent decades was it clear how dangerous and persistent many pesticides are. The EPA monitors only a small fraction of pesticides, and in many cases their probable effects on the environment are unknown. Pesticide tolerance levels are particularly important worldwide, since pesticides...