Assessment of fat-soluble pesticide residues in animal commodities

Introduction,Pesticide residues in animal commodities may arise from the use of plant protection products onfeedstuffs, from direct application to livestock and/or to animal housings. To understand the residuebehaviour of pesticides in animals and finally to estimate maximum residue levels (MRLs) forproducts of animal origin (PAO), results obtained from livestock metabolism and feeding (or externaltreatment) studies have to be evaluated. General guidance with respect to livestock metabolism andfeeding studies as well as dietary burden calculations on EU level was set out in Annexes II and III ofthe Council Directive 91/414/EEC and was detailed in the guidance documents SANCO 7030/VI/95and SANCO 7031/VI/95. Harmonized guidelines were also developed by OECD ("Livestockmetabolism", "Residues in Livestock"). These documents will be utilized in future assessments.This presentation gives a short overview of the major guidance provided up to now and focuses thenon ongoing developments concerning the estimation of MRLs for animal commodities in the EU.Compounds, which are designated as fat-soluble require specific consideration because the residuesare not uniformly distributed in animal tissues but accumulate in fat, so that the varying fat content ofanimals or derived animal products has a huge effect on pesticide levels in these products. In recentyears the JMPR has been developing principles for regulation of fat-soluble pesticides in meat, fatand milk. The current methods are complex and therefore a comprehensive overview of the basicprinciples and assessment procedures for fat-soluble pesticide residues is provided.Richter A, Michalski B, Banasiak U, Herrmann MMetabolism studies are the first step in the assessment procedure and are conducted to provide adetailed understanding of the distribution, accumulation and nature of the residue in edible tissues,milk and eggs. In general they are carried out on ruminants (cows or goats) and poultry (chickens)with 3-5 days of oral dosing of the substance (parent and/or plant metabolite) which is radiolabelledin a stable position. Additional studies on pigs are necessary where it appears that metabolicpathways in laboratory animals and ruminants differ.Based on the information from metabolism studies, and taking into account analytical andtoxicological aspects, residue definitions for monitoring and risk assessment are proposed.Livestock feeding studies using unlabelled compounds are conducted to determine realistic residuelevels in products of animal origin which will result from repeated daily dosing of farm animals for atleast 28 days (1x dose, 3-5 x dose, 10 x dose). The study period must be long enough to reachplateau levels and to observe the rate of depletion when the dosing ceases. Studies are required forall species that will be exposed significantly through feed (ruminants, poultry, pigs).For estimation of residue levels (HR and STMR values) and MRLs, information obtained fromlivestock feeding studies is combined with that from anticipated dietary burden, which is calculatedfrom residue levels in feed items and standard animal diets.The 2005 Joint Meeting on Pesticide Residues (JMPR) revisited the criteria for determining acompound as fat-soluble. The following aspects were suggested for consideration:The distribution of the residue between muscle and fat tissues as observed in livestock metabolismand feeding studies.The log of the octanol/water partition coefficient (log POW) of individual components of the residuedefinition.It should be noted that only in the absence of other useful information on the partitioning of therelevant residue, the log POW should be used as the prime indicator for fat solubility. Residues with alog POW > 3 are likely to be fat-soluble.Recommendations for milk and milk products1. To express MRLs for milk on whole commodity basis, using 4 % as nominal fat content. Theestablished MRLs should be indicated with the suffix "F".2. To express MRLs for low fat milk products (fat content < 2 %) on whole milk basis.3. To convert MRLs for milk to milk products, the established MRL for milk is multiplied by 25. Theresultant value should be expressed on a fat basis. Some guidance for interpretation of this approach: - MRLs for whole milk: The residue concentration is calculated for the whole product from themeasured concentration in the milk fat, so the MRL would be 1/25th of residue level measured infat.- MRLs for milk products with fat content < 2 %: The applied MRL should be half that specified formilk.- MRLs for milk products with fat content > 2 %: The applied MRL should be 25 times the MRLspecified for milk, expressed on fat basis (the resulting value applies to the fat extracted from themilk product).2004 JMPR decided that two MRLs should be recommended where data permit this: one for wholemilk and one for milk fat. So MRLs for milk products can be calculated from the two values takinginto account the fat content of the respective product.Ongoing developments on EU levelBasic principles for evaluating fat-soluble pesticide residuesDesigning pesticides as fat-solubleEvaluation of fat-solubility by means of examples