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close this bookFAO manual on the submission and evaluation of pesticide residues data for the estimation of maximum residue levels in food and feed (1997)
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View the document6.1 Guidelines for predicting dietary intake
View the document6.2 Estimation of supervised trial median values

6.1 Guidelines for predicting dietary intake

The JMPR has, from the beginning, tried to arrive at predictions about the intake of pesticide residues on the basis of available data. In taking the MRL as the residue level and using the dietary patterns for the quantity of food consumed, the JMPR arrived at the Theoretical Maximum Daily Intake or TMDI. The JMPR was well aware of the fact that TMDI calculations result in a gross overestimation of the intake. On the other hand, existing uses of the pesticide not brought to the attention of the JMPR could result in a minor underestimation of the residue intake.

Until recently the dietary intake calculations have been carried out according to the Guidelines for predicting dietary intake of pesticide residues published by WHO in 1989. The dietary intake of any particular pesticide residue is obtained by multiplying the residue level in the food by the amount of commodity intakes from a "global" and five "cultural" diets, also called "regional" diets. Total intake of the pesticide residue in each of the diet groups is then obtained by summing the intakes from all commodities containing the residue concerned. The correction factors include the residue level in the edible portion of the commodity, the reduction or increase of the residues on commercial processing such as canning and milling, and the reduction or increase in the level of residue on preparation or cooking of the food. This leads to the Estimated Maximum Daily Intake or EMDI. According to the Guidelines, EMDI calculations should only be carried out when the TMDI exceeds the ADI for a pesticide. However, the EMDI is still based on the assumption that all crops have been treated with the pesticide in question and with residues in the raw commodity at a level corresponding to the MRL, and this will also give rise to an overestimate of the intake.

The guidelines also described a more realistic intake calculation, the so-called Estimated Daily Intake or EDI. In this calculation, several reduction factors are taken into account which are only available at national levels. EDI calculations were therefore only to be carried out at a national level by those with adequate information on food consumption, the use of a given pesticide locally, and the nature and the amount of imported food.

Based on the request of the CCPR a Joint FAO/WHO Consultation on Guidelines for predicting the Dietary Intake of Pesticide Residues was held in York, United Kingdom, 2-6 May 1995. Its main objectives were to review the existing guidelines and to recommend feasible approaches for improving the reliability and accuracy of methods for predicting the dietary intake of pesticide residues to promote a greater acceptance of Codex MRLs by governments and, most importantly, by consumers. The report of the consultation (WHO/FNU/FOS/95.11) contained recommendations for improving estimates of dietary intake, most notably the use of supervised trials median residue (STMR) levels in lieu of MRLs in the calculation of International Estimated Daily Intakes (IEDIs) and National Estimated Daily Intakes (NEDIs).

The IEDI incorporates those factors which can be applied at international level and which comprise a subset of the factors that might be considered at national level. The factors to be considered for IEDI calculations are:

· Median residue data from supervised trials (not on MRLs);

· Residue definitions, which include all metabolites and degradation products of toxicological concern;

· For residues at or below the limit of determination (indicated with *), the median residue should be estimated to be the LOD except when evidence from trials and supporting studies suggests that that residues are essentially zero;

· The edible portion;

· Effects on residue levels due to storage, processing or cooking practices;

· Other known uses of the pesticide.

The National Estimated Daily Intake (NEDI) should be based on the same factors as for the IEDI, but the following additional factors based on national use pattern of the pesticides and food consumption data should also be taken in consideration, which would result in a refinement of NEDI:

· Proportion of crop or food commodity treated;

· Proportion of crop domestically produced and imported;

· Compliance monitoring and surveillance data;

· Total diet (market basket) studies;

· Food consumption data, including that of subgroups of the population.

The revised guidelines for intake calculations are under preparation by the WHO Secretariat.

According to those recommendations where TMDI calculations are carried out by the JMPR, they should be based on "cultural" diets rather than the "global" diet, and some changes were proposed in the calculation system. However, the Consultation emphasised that the best use should be made of all available data and recommended that calculations of EMDIs should be discontinued to promote calculations of International Estimated Daily Intake (IEDI) and National Estimated Daily Intake (NEDI). The recommended procedure is illustrated in Figure 6.1.

A further Joint FAO/WHO Consultation on Food Consumption and Exposure Assessment of Chemicals will be held in 1997 at WHO Headquarters in Geneva. The Consultation will follow up certain recommendations of the York Consultation, particularly in the development of regional diets and in addressing issues related to implementation of the recommendation on intake assessment for acute hazards.

Figure 6.1. Scheme for assessment of dietary intake of pesticide residues for chronic hazards

The JMPR will continue the estimation of TMDIs for (old) pesticides where data are not available for estimating IEDIs, but emphasised that when information was available a better estimate of intake should be derived from the IEDI method.