Evaluation of Residues and Contaminants in Food: Difficulties and Significance

Abstract

It was not the intention of this paper to show the analytical difficulties in residue analysis in food, but to draw the attention to the standard for such procedures, the Maximum Residue Limits (MRLs) for residues and contaminants in food. Only when the substance under question yields a discrete No Observable (Adverse) Effect Level (NO(A)EL) in the assay with sensitive laboratory animals, can the MRL for a specific food be derived with a formal correlation of NOEL, safety factors, body weight and food consumption. The NOEL however, is only discrete for substances with a clear dose-response relationship. For tumor-initiating (and perhaps tumor- promoting) substances this equation is not valid. As some of these substances have an environmental impact on food and a MRL setting is required at all costs to shut down the source and to protect the consumer (the latter intention is carried out first, but would be useless if performed in isolation), the MRL is just a compromise between the analytical possibilities of trace analysis and the mean occurrence in food. Specific problems are involved in the residues of veterinary drugs in food of animal origin, especially antibiotics. It seems obvious, apart from the more pharmacologic- toxicologic difficulties, that the analytical state-of-the-art needs considerable improvement to assure the consumer’s protection by the means of MRLs. The setting of a MRL for polychlorinated dibenzodioxins is difficult due to the discrepancy of the present contamination situation, the desired figure under the premise of precautionary health care and the tolerable daily intake (TDI). In the case of PCBs and aflatoxin M1 in milk, the established MRLs have led to an improvement of the situation for different reasons. The lower of the two MRLs for AFM1 in milk has helped to exert considerable influence on the feedstuff industry to limit the precursor in feed for dairy cattle. In the case of PCBs, herd’s bulk milk was officially designated as an indicator substrate to trace the pollution back to the origin to eliminate the source.