MRLs are estimated for individual pesticides or veterinary drug residues in various food commodities. They are based on good agricultural practice (pesticides) or good practice in the use of veterinary drugs in which the product has been used in an efficacious manner and appropriate withdrawal periods have been followed. They are expressed as either the parent compound or a metabolite that is, or is representative of, the residue of toxicological concern in the food commodity. MRLs are not based upon toxicological data, but crude estimates of their toxicological significance are usually made by comparing the acceptable daily intake (ADI) with a calculation of the total intake of the residue based on the MRLs and food intake data of these commodities for which MRLs have been established.