How are MRLs and MLs set?
Most of the MRLs and MLs are set by the Codex Alimentarius Commission and its Members. Proposals are made by the Codex Committees. After approval by the CAC the Committee will develop a draft standard that is to be adopted by the CAC and its Members. The standards are then implemented by the Codex member states in their national food safety systems. The Members are allowed to establish additional national standards as long as these are not in conflict with the Codex standards. The European Union for example has established different standards that are not in the Codex list, such as the MLs for dioxins and PCBs in Regulation 915/2023. This standard does not exist in Codex Stan 193-1995.
Setting MRLs
Residues are chemical substances that are intentionally used by production of foods. A Maximum Residue Level (MRL) is the highest concentration of a residue allowed in or on food or feed when the substance is applied correctly, following its instructions. A MRL is a compliance standard, not a human safety standard, but it is evaluated via risk assessments to ensure that no human health concern would be posed by the residue level allowed by an MRL. The key topics of setting a MRL are thus that the chemical substances are applied correctly, and that they do not pose any health issues for the consumers. Consequently, information is needed on these topics for setting MRLs. Obtaining these data is the responsibility of the producers of the residue. They have to perform field studies or trials. The foods are to be treated with optimal dose levels; optimal means: in relation to its function. E.g. for pesticides the optimal dose level is the dose to be sprayed by farmers that is most effective to fight the intended plague. After harvest the foods are analyzed to determine the remaining concentrations (hence: "residues"). So, the field studies define the residual concentrations after correct use.
The other topic is the evaluation of the residual concentrations in foods. By combining the concentrations of the residue with the consumption quantities of the foods, one can calculate the intake of the residue. That intake is to be compared with the ADI of the substance. Studies to set the ADI are also the responsibility of the producer. When the intake is smaller than the ADI, then the use of the residue is authorized and a MRL can be set. If the residual concentrations from the field studies are not safe for the consumer, then the residue is not authorized and its use is "forbidden". For forbidden residues the MRL is set at the detection limit of the chemical. If the substance is authorized for use, then MRLs will be set for the chemical substance and the foods. A draft MRL is set at the optimal concentration from the field studies, and send to risk managers of the Codex member states (or EU) for discussion, to be updated and approved as the final MRL.
The MRL and the maximal permissible concentration. Ascorbyl stearate (E304) was chosen to investigate whether the MRL is based on functional concentrations or on health risks. It has a MRL of 80 mg per kg of dried fruit. Using data from EFSA's CEFCD it was calculated that the average consumption of dried fruit in Europe is 0.4 gram per kg body weight per day. Fruit with 80 mg (compliant to the MRL) of E304 per kg leads to a daily intake is 32 ug per kg whereas the ADI is 1250 ug per kg (JECFA, 1973). It can be calculated (for example with EAST) that the ADI of E304 is exceeded by consumption of dried fruit with 3125 (1250 ÷ 0.4) mg per kg ascorbyl stearate. So, the MRL of E304 is substantially lower than the health based maximal permissible concentration.
Setting MLs
Maximum Levels (MLs) refer to contaminants and toxins. These chemical substances can be found in food or animal feed as a result of accidental contamination. The sources of the contaminants are very hard to control. Consequently, concentrations of contaminants in foods will vary substantially, depending of the production sites, or storage and transport, or industrial processes. To acquire information about the variation of the concentrations in different regions it is needed to collect foods and feed and to determine the concentrations of contaminants in foods on the market by chemical analysis. The responsibility for these monitoring programs lies with the members (not with the producers).
MLs are set for excluding foods with the highest concentrations from the market. The cut-off point is usually the 95th percentile of the variation. Doing so, a small percentage of the production will be rejected with limited impact on food security. There is no test on the health impact of the cut-off point. It is therefore possible that foods that comply to MLs might contain concentrations that pose health risks. There is also no authorization of use as the contaminants are not used intentionally. The cut-off point becomes the draft ML; the ML is then finally set by the Codex (or EU) Members after discussion about its impact.
An example of an ML with possible health risks is the EU-ML of 1.0 mg per kg for mercury in bonito and tuna.With a concentration of 1.0 mg per kg it just complies to the standard and can therefore be traded. Consumption of these fishes in Spain and Italy is on average about 3 gram per kg body weight per week, leading to an intake of 3 ug per kg body weight per week. The TWI of 1.6 ug per kg body weight per week (EFSA, 2005) is then exceeded. It must thus be clear that the ML is not based on consumer's health, and a HBGV can be exceeded by the consumption of foods that meet the MLs.