In the European Union, zero tolerance provisions were established for substances which are not permitted or explicitly prohibited to occur at any concentration level in food or animal feed. The dilemma in dealing with zero tolerances is demonstrated by the example of malachite green and crystal violet, two compounds used as veterinary drugs for the antifungal and antiparasitic treatment of (ornamental) fish. Zero tolerance applies to residues of both compounds in food for human consumption, as both compounds are not registered for use as veterinary drugs with food-producing animals. Legally, zero tolerance also applies if residues in fish are not caused by illegal treatment but by unintentional contamination via municipal sewage effluents. Often, the definition of a non-harmful residue level is difficult or even impossible for substances with zero tolerances. In this case, both compounds and/or their leuco metabolites have been classified as genotoxic and/or carcinogenic. In light of the precautionary principle it appears to be necessary to adhere to the zero tolerance approach for most of the anthropogenic residues and contaminants in food or animal feed.

Zero tolerances are playing an important and often underestimated role in routine analysis of chemical pollutants occurring in food or animal feed. Zero tolerance provisions were established for substances which are not permitted or explicitly prohibited to occur at any concentration level in food or animal feed. In the European Union (EU) zero tolerances were introduced to give human consumers and animals the greatest possible protection from substances with a possible hazard potential within the intendment of the hazard prevention principles and …