Problems in the safety evaluation of tissue residues

Toxicologists must contend with many uncertainties in the establishment of safe conditions for use of a particular agent when that level of use is based on the interpretation of toxicologic studies. Some of these traditional difficulties are discussed this paper. The regulatory review scientist who is involved in the determination of the safe level of use of an agent administered to food producing animals is faced with some additional problems. Accurately determining the exposure of the population to a residue in edible tissue is somewhat difficult because of the limited nature of the data available on the national eating pattern. Judgment must be made on the safety of edible tissue after the administration of substances which may be complex mixtures of a known or unknown nature. In situations where known agents are administered the toxicologist must have information regarding te qualitative and quantitative nature of the residue that would be ingested by humans. Additionally, the regulatory toxicologist is faced with making a safety extrapolation from th test animal to humans when the test animal may not have been exposed to the same metabolites present in the edible tissue that may be ingested by humans.