Pesticide residues risk assessment

Improvements in pesticide residue risk assessment practices should improve the scientific basis for managing pesticide residues in foods and the FQPA provides a blueprint for making such improvements. While most of the FQPA provisions are considered in theory to represent improvements in the risk assessment process, the practical adoption of methods to comply with such... 

W.G. Fong, Regulatory aspects pesticide registration, risk assessment and tolerance, residue analysis, and monitoring, in Pesticide Residues in Foods Methods, Techniques, and Regulations, ed. W.G. Fong, H.A. Moye, J.N. Seiber, and J.R Toth, WUey, New York, Chapt. 7 (1999). 

Dr Georg Geisler is a product safety expert and modeller working with RCC Ltd, a Contract Research Organisation based in Basel, Switzerland. In this function, he conducts environmental risk assessments of pesticides, biocides and other chemicals, as well as safety assessments for pesticide residues in the food chain. In 2003, Georg Geisler earned his Ph.D. on environmental life-cycle assessment of pesticides at ETH Zurich. In 1999, he had received a Diploma in environmental chemistry at the Friedrich-Schiller University, Jena, Germany. 

Relationship of pesticide residue analysis, regulation, and risk assessment... 

The activities of enforcement laboratories should not be focused on irrelevant problems. Therefore, a clear definition of the relevant residue is needed. In the crops and food sector, procedures are well established to derive the two residue definitions, one for risk assessment and one for monitoring, from metabolism studies. As far as environmental samples are concerned, there is much potential for improvement. There are no clear criteria as to which metabolites should be included in monitoring and control programs. Additionally, the development of criteria for nonpriority pesticides, e.g., naturally occurring compounds or low-risk products, which can be excluded from monitoring exercises would be helpful for laboratories and evaluators. 

The definitions of method detection and quantification limits should be reliable and applicable to a variety of extraction procedures and analytical methods. The issue is of particular importance to the US Environmental Protection Agency (EPA) and also pesticide regulatory and health agencies around the world in risk assessment. The critical question central to risk assessment is assessing the risk posed to a human being from the consumption of foods treated with pesticides, when the amount of the residue present in the food product is reported nondetect (ND) or no detectable residues . 

Today, when a pesticide with no detectable residues is registered for use, a Tolerance or maximum residue limit (MRL) is established at the lowest concentration level at which the method was validated. However, for risk assessment purposes it would be wrong to use this number in calculating the risk posed to humans by exposure to the pesticide from the consumption of the food product. This would be assuming that the amount of the pesticide present in all food products treated with the pesticide and for which no detectable residues were found is just less than the lowest level of method validation (LLMV). The assumption is wrong, but there is no better way of performing a risk assessment calculation unless the limit of detection (LOD) and limit of quantification (LOQ) of the method were clearly defined in a uniformly acceptable manner. 

One common objective of an LSMBS is to refine the estimates of actual exposure of consumers to ingredients or impurities in one or more products. For example, study results might be intended to determine a realistic human dietary exposure to pesticide residues in fresh fruits and vegetables. The advent of the Food Quality Protection Act of 1996 (FQPA) has produced an enhanced focus on the exposure of children to pesticides. A well-designed and implemented LSMBS would afford the opportunity to delineate better the exposure and risk to children and other population subgroups. The LSMBS would provide consumer-level data at or near the point of consumption, allowing the refined, relevant, and realistic assessments of dietary exposure. 

The need to develop and use chiral chromatographic techniques to resolve racemates in pesticide residues will be driven by new hazard and risk assessments undertaken using data from differential metabolism studies. The molecular structures of many pesticides incorporate chiral centers and, in some cases, the activity differs between enantiomers. Consequently, in recent years manufacturers have introduced resolved enantiomers to provide pesticides of higher activity per unit mass applied. For example, the fungicide metalaxyl is a racemic mix of R- and 5-enantiomers, both having the same mode of action but differing considerably in effectiveness. The -enantiomer is the most effective and is marketed as a separate product metalaxyl-M. In future, it will not be satisfactory to rely on hazard/risk assessments based on data from metabolism studies of racemic mixes. The metabolism studies will need to be undertaken on one, or more, of the resolved enantiomers. 

In the USA, the passage of the Food Quality Protection Act (FQPA) of 1996 has had a significant impact on the determination of residues in drinking water. FQPA requires that all sources of a pesticide be included in its risk assessment, so the potential exposure from drinking water containing a particular pesticide could be a significant... 

When humans contact a chemical residue such as a pesticide on a treated surface, some of the deposit can be dislodged or transferred to skin or clothing. Ultimately, a portion of the amount transferred may be absorbed and constitute the absorbed daily dose (ADD). The ADD provides the most precise estimate of exposure that can be practically obtained for humans and has become the most useful expression of exposure for risk assessment and risk management. 

In considering pesticide residues, it was clearly shown that crops from organic production systems contain no or significantly lower levels of pesticide residues than crops from conventional systems (Baker et al., 2002). However, while some scientists are concerned about the potential health impacts from such residues (Porter et al., 1999 Benbrook, 2002), pesticide legislators maintain that current pesticide risk assessments and pesticide registration procedures are adequate and that residues below the current legal limits can not have a negative health impact in humans (e.g. PSD, 2006). 

EPA released the first case study of cumulative risks from 24 OPs in food for scientific review in mid-2000. Public comments were solicited and several scientific panel (SAP) meetings were held on various aspects of EPA s quantitative methods. In December 2001 a preliminary OP-CRA (cumulative risk assessment) was released, this time encompassing 30 OPs, additional foods, more residue data and all major routes of exposure. Public comments were solicited again and another series of SAP meetings were held. The revised final OP-CRA was issued in June 2002 after more than 20 SAP meetings and four rounds of public comment (US Environmental Protection Agency, 2002). It is the most sophisticated and data-rich pesticide risk assessment ever carried out. 

Carvalho FP, Villeneuve JP, Cattini C, Tolosa I, Montenegro-Guillen S, Lacayo M, Cruz A (2002) Ecological risk assessment of pesticide residues in coastal lagoons of Nicaragua. J Environ Monit 4(5) 778-787... 

The Food Quality Protection Act (FQPA) of 1996 mandated that the US EPA carry out risk assessments that consider the cumulative effects of exposure to pesticides having a common mechanism of toxicity, as well as consider exposure to each pesticide by various routes of exposure (e.g., dermal, dietary, inhalation) and sources (e.g., residues in food and water) in an aggregate manner [19]. To accomplish this, there needs to be sufficient evidence supporting a common adverse effect that is associated with a common mechanism of action in specific target tissues. To date, the required criteria necessary to establish a common mechanism of toxicity with a specific toxic effect for the pyrethroids are not available [1,8,98]. 

Gelardi RC, Mountford MK. 1993. infant formulas evidence of the absence of pesticide residues. Meeting of the American Industrial Health Council on the Domestic Agenda for Risk Assessment, Washington D.C., USA, December 1, 1992. Regul Toxicol Pharmacol 17(2 Part 1) 181-192. 

Contemporary risk assessment practices for pesticides in foods require far more data than simply the residue levels evaluated in government monitoring programs. Exposure to pesticides is determined by multiplying the residue levels on food by the amount of the food item consumed once determined, exposure is compared with standard toxicological criteria derived from animal toxicology studies to determine the acceptability of the exposure. 

The determination of the estimated levels of exposure is obviously a critical component of the risk assessment process. Both pesticide residue levels and food consumption estimates must be considered. Methods for determining exposure are frequently classified as deterministic and probabilistic methods (Winter, 2003). 

Finally, an equally Important component of ground water risk assessment Is toxicity. Only rarely have levels of pesticides In well water been detected which would cause acute toxicity, unless Improper disposal caused the contamination. Rather, as can be seen In Table III, the pesticide levels are usually In the low ppb range. Therefore, our current toxicity concerns are usually for chronic human toxicity or, occasionally, aquatic toxicity. There Is also the possibility of organisms receiving toxic amounts of pesticide residues over time via blomagnlf1catIon. 

The main FAO/WHO expert bodies include the Joint FAO/WHO Expert Committee on Food Additives (JECFA), the Joint FAO/WHO Meetings on Pesticide Residues (JMPR), and the Joint FAO/ WHO Expert Meetings on Microbiological Risk Assessment (JEMRA). Codex Alimentarius provides lists of MRLs for pesticides and veterinary drugs, and maximum levels for food additives. 

An approach that is sometimes helpful, particularly for recent pesticide risk assessments, is to use the parameter values that result in best fit (in the sense of LS), comparing the fitted cdf to the cdf of the empirical distribution. In some cases, such as when fitting a log-normal distribution, formulae from linear regression can be used after transformations are applied to linearize the cdf. In other cases, the residual SS is minimized using numerical optimization, i.e., one uses nonlinear regression. This approach seems reasonable for point estimation. However, the statistical assumptions that would often be invoked to justify LS regression will not be met in this application. Therefore the use of any additional regression results (beyond the point estimates) is questionable. If there is a need to provide standard errors or confidence intervals for the estimates, bootstrap procedures are recommended. 

The many worst-case assumptions built into cancer risk assessments are there because of policy decisions, not because of scientific ones, and they confuse attempts to allocate money effectively for public health. For example, EPA estimates of synthetic pesticide residues in the diet have used the theoretical maximum human residue that is anticipated under the most severe field application conditions, which is often a large overestimate compared to the measured residues in food. Despite the EPA s estimated high risks from exposures to several pesticides, the U.S. Food and Drug Administration detected no residues of those pesticides in the food samples in its Total Diet Study.59... 

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