Drug and chemical residues in domestic animals.

Given the large number of chemical substances that may find their way into the food supply, a system is needed to monitor their presence. The U. S. Department of Agriculture's Meat and Poultry Inspection Program routinely tests for chemical residues in animals coming to slaughter. Pesticides, heavy metals, growth promotants (hormones and hormonelike agents), and antibiotics are included. Samples are taken statistically so that inferences as to national incidence of residues can be drawn. When a problem is identified, a more selective sampling is designed to help follow up on the initial regulatory action. In testing for pesticides, only DDT and dieldrin are found with any frequency and their levels are decreasing; violative residues of any chlorinated hydrocarbon are generally a result of an industrial accident rather than agricultural usage. Analyses for heavy metals have revealed detectable levels of mercury, lead, and others, but none at levels that are considered a health hazard. Of the hormone or hormonelike substances, only diethylstilbestrol has been a residue problem and its future is uncertain. The most extensive monitoring for veterinary drugs is on the antimicrobials, including sulfonamides, streptomycin, and the tetracycline group of antibiotics that constitute the bulk of the violations; their simultaneous use prophylactically and therapeutically has contributed to the problem in certain cases. A strong, well-designed user education program on proper application of pesticides, chemicals, and veterinary drugs appears to be one method of reducing the incidence of unwanted residues.