CODEX

Following application of a product such as chlorpyrifos for agricultural pest management purposes, trace residues may be present at harvest. This can occur on agricultural commodities such as fruits, vegetables, or cereal grains or in processed commodities such as fruit juices, vegetable oils, and flours. Thus, government regulatory authorities have established maximum residue limits (MRLs) or tolerances as a check on compliance with national good agricultural practice (i.e., the approved product label) and to control international trade. An MRL is defined as the “maximum concentration of a residue that is legally permitted or recognized as acceptable in, or on, a food, agricultural commodity or animal feed as set by Codex or a national regulatory authority” (IUPAC, 1996). In some countries, such as the U.S., MRLs are referred to as “tolerances”, and in general the two terms are synonymous.

MRLs are most typically established based on data from supervised field trials, in which residues at harvest are determined across a set of actual use conditions (e.g., different fields, geographic areas, and/or years) and according to the highest permitted application rate, the maximum number of seasonal applications, and the minimum pre-harvest interval (i.e., time between last application and harvesting). These worst-case residue values are then evaluated and the maximum residue level set near or slightly above the highest residue value observed. Residues present at or below the MRL level are an indication that the product label and good agricultural practice was followed. The potential health implications of such a residue level are generally evaluated prior to MRL establishment through a dietary risk assessment (42KB PDF) process to ensure that potential human exposures will not exceed the acceptable daily intake as determined from toxicology testing.

On the international level, the Codex Alimentarius Commission has sought to establish a globally applicable listing of harmonized MRLs to support international trade. Thus, many countries refer to Codex MRLs when considering regulatory and trade aspects of pesticide residues. In addition, regulatory authorities in a number of individual countries or regional associations may also set national MRLs based on approved uses and/or import MRLs to accommodate international trade considerations. The most widely recognized bodies which establish national MRLs include regulatory authorities in Australia, Canada, the European Union member nations, Japan, New Zealand, and the U.S. Specific listings of existing MRLs for chlorpyrifos and other pesticides may be found at the following links: