Estimated maximum residue intake

Methyl parathion is approved only for use on crops. The maximum amount of methyl parathion residue allowed by the Food and Drug Administration (FDA) and EPA on crops used as food is 0.1-1 ppm. The FDA has monitored the food supply for pesticides for a number of years. FDA purchases many kinds of foods through Market Basket Surveys and analyzes them for residue levels of pesticides. These FDA studies allow scientists to estimate the daily intake of pesticides. Generally, the FDA monitoring studies conclude that the U.S. food supply contains only very small amounts of pesticides that are not a concern. However, there have been some reports of the illegal use of methyl parathion inside homes. For more information, see Section 1.7 and Chapter 6. 

S. C. Fitzpatrick, S. D. Brynes, and G. B. Guest, Dietary intake estimates as a menas to the harmonization of maximum residue levels for veterinary drugs, J. Vet. Pharmacol. Ther, 18, 325 (1995). 

When calculating chronic dietary exposure, the deterministic models use point values for both food consumption and residue concentration, thereby yielding a point estimate of dietary exposure. In the US, the initial chronic dietary exposure estimate is the Theoretical Maximum Residue Contribution (TMRC) and is analogous to the Theoretical Maximum Daily Intake (TMDI) used to estimate chronic dietary exposure in the EU. Both the TMRC and the TMDI are relatively conservative estimates of dietary expostire. The TMRC is calculated as the product of the mean consumption value and the US pesticide tolerance [6]. In the EU, the TMDI is calculated as the product of the mean consumption value and the Maximum Residue Limit (MRL) [7]. The objective of both calculations is essentially identical to calculate an estimate of the central tendency of the dietary exposure. Both calculated values use the central tendency dietary exposure estimate as the estimate of chronic (long-term) dietary exposure and calculate it using mean consumption data and the maximum residue permitted on the commodity. 

For all chemicals, carcinogens or not, a final step must be completed after establishing the ADI a value must be assigned for the amount that would be allowed in a particular foodstuff. Consumption estimates for foods or commodities that might contain the chemical are needed along with estimates of total intake from all sources. This calculation is used to establish the maximum residue level (MRL) for any particular commodity. 

To determine the possible exposure level via the food, the "theoretical daily intake" (TDl) was calculated. This figure was derived by utilizing data on the rate of disappearance of the food item in Canada, provided by Statistics Canada, and determining from these data, the consumption of the crop per capita (assuming disappearance rate and consumption to be comparable). It was assumed that the total crop could have residues present at about the level of analytical sensitivity of the method of detection. Thus based on the consumption level and the maximum residue level, an estimate of exposure from each crop can be calculated. The total exposure from all crops is the TDI. 

No allowable daily intake of atrazine in the human diet has been established, although 0.0375 mg/kg BW daily has been proposed -equivalent to 2.25 mg daily for a 60-kg adult, or 1.5 mg/kg diet, based on 1.5 kg food daily. In humans, the theoretical maximum residue contribution (TRMC) - a worst case estimate of dietary exposure - is 0.77 mg daily, assuming 1.5 kg of food eaten daily this is equivalent to 0.51 mg/kg diet, or 0.013 mg/kg BW daily for a 60-kg person. Another TRMC calculation is based on 0.233 mg daily per 1.5 kg diet, equivalent to 0.156 mg/kg diet, or 0.0039 mg/kg... 

There is today a tendency to consider the numerical values of the ADI as an overall maximum safe index for chronic ingestion toxicity. While this attitude might be justified in certain cases (ADIs for pesticide residues and certain individual food additives, or classes of food additives), it should be borne in mind that in most cases the niXmerical values of the ADI are derived from dose-effect curves and not from dose-response curves. In order to circumvent this difficulty the JECFA and JMPR have consistently recommended that the application of an ADI always be accompanied by studies on estimations of potential daily intakes of food additives and pesticide residues in food. 

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