Residue, pesticide definition

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 . 

To demonstrate the validity of an analytical method, data regarding working range/ calibration, recovery, repeatability, specificity and LOQ have to be provided for each relevant sample matrix. Most often these data have to be collected from several studies, e.g., from several validation reports of the developer of the method, the independent laboratory validation or the confirmatory method trials. If the intended use of a pesticide is not restricted to one matrix type and if residues are transferred via feedstuffs to animals and finally to foodstuffs of animal origin, up to 30 sets of the quality parameters described above are necessary for each analyte of the residue definition. Table 2 can be used as a checklist to monitor the completeness of required data. 

In contrast to many other validation protocols, the description of the NMKL validation process starts with the protocol of planned validation. This protocol should include, e.g., the needs of the client, available equipment, the chemical form in which the analyte occurs (i.e., in pesticide analysis the residue definition), matrix types, the availability of reference materials and the working range. Consequently, an extra paragraph is dedicated to the requirements for the documentation of validation results, which refers to the rules in Section 5.4.4 of EN 45001 (amended by ISO 17025). 

Oxime carbamates are generally applied either directly to the tilled soil or sprayed on crops. One of the advantages of oxime carbamates is their short persistence on plants. They are readily degraded into their metabolites shortly after application. However, some of these metabolites have insecticidal properties even more potent than those of the parent compound. For example, the oxidative product of aldicarb is aldicarb sulfoxide, which is observed to be 10-20 times more active as a cholinesterase inhibitor than aldicarb. Other oxime carbamates (e.g., methomyl) have degradates which show no insecticidal activity, have low to negligible ecotoxicity and mammalian toxicity relative to the parent, and are normally nondetectable in crops. Therefore, the residue definition may include the parent oxime carbamate (e.g., methomyl) or parent and metabolites (e.g., aldicarb and its sulfoxide and sulfone metabolites). The tolerance or maximum residue limit (MRL) of pesticides on any food commodity is based on the highest residue concentration detected on mature crops at harvest or the LOQ of the method submitted for enforcement purposes if no detectable residues are found. For example, the tolerances of methomyl in US food commodities range from 0.1 to 6 mg kg for food items and up to 40 mg kg for feed items. ... 

Fuhr F, Ophoff H, Burauel P. Wanner U, Haider K (1998) Modification of definition of bound residues. In Fuhr F, Phoff H (eds) Pesticide bound residues in soils. Wiley-VCH, Weinheim, pp 175-176... 

The only apprehension of prospective industrial radiation processors with the nonmeasurability criterion comes from the analogies with the history of pesticide residues in foods U). Pesticides are cleared on the basis of either zero tolerance or finite tolerance, and use is rated as safe for a zero-tolerance pesticide when the residue on foods cannot be measured. However, improvements in measurement techniques with time have changed the definition of zero tolerance, sometimes abruptly. Radiation processors are apprehensive of similar experiences with radioactivity induced in food. 

The question of pesticide residues and their environmental implications must be considered in the context of the active ingredient and its accompanying trace materials. The lUPAC definition of a pesticide residue is "any substance or mixture of substances in or on any substrate resulting from the use of a pesticide and includes any derivatives, such as degradation and conversion products, metabolites, reaction products and impurities (11). The significance of that residue depends on the toxicological properties of the substance and the degree of exposure. Thus, by definition, materials associated with the pesticide in the formulation must necessarily be considered as "pesticide residues". 

The complex composition of toxaphene also creates nomenclature problems. Initially, toxaphene was the trademark of the product manufactured by the Hercules Inc. However, due to the non-restricted use of the trademark, toxaphene has become a general term for this pesticide. Further frequently applied terms were camphechlor , polychlorinated bornanes , camphenes , and ter-penes , as well as chlorobornanes . The expression toxaphene is not the same as the trademark Toxaphene , since residues in the environment may also originate from other technical products (see Table 2). Toxaphene is the reaction product of the chlorination of technical camphene is a suitable definition of the expression used in the scientific language [27]. Owing to the problems with abbreviations as described below, toxaphene will be used in the following chapters as a synonym for the compounds of technical toxaphene. 

Definitive confirmation of pesticide residues was obtained by comparison of parent and fragment ion intensities and mass numbers of eluted pesticides and reference pesticides. Table I lists the residues encountered and the mass numbers and intensities of the characteristic fragments employed for identification in the adipose tissue sample. The mass spectral fragmentation patterns for all the compounds included in Table I with the exception of -HCH have been adequately discussed by other investigators (7). 

Of all the systems which have been utilized for the analysis of pesticide residues, combined gas chromatography-mass spectrometry afiFords a particularly useful approach because positive identification of the components of a mixture can be made without prior separation at sensitivities compatible with the limited quantities of residues generally available. From the results of recent studies involving the application of this technique, it has been demonstrated that available residue analytical methods provide efficient isolation and adequate cleanup of extracts of human, animal, and environmental media in most cases to permit gas chromatographic-mass spectrometric analyses with maximum confidence. Additionally, it has been shown that this combined technique will conveniently provide definitive and conclusive confirmation of residue identity as well as characterization of residues and their metabolites of unknown structure. 

Once a method is established, precision may be determined by suitable replicated experiments. However it is in inter-laboratory trails that the problems with environmental methods often show up. It is accepted that for trace analysis RSD values of tens of percent are likely. In studies conducted in Western Australia on pesticide residues in bovine fat RSD values for dieldrin were 12% and for dia-zonium were 28%. It is typical to see a quarter of the laboratories in such a trial producing values that could be termed outliers. In the previously mentioned study, 5 laboratories out of 26 had z> 3 for aldrin. In a parallel study RSD values for petroleum in dichloromethane and water were 40% and 25%, respectively. The conclusions of these studies was that there was poor comparability because of the different methods used, that accreditation apparently made no difference to the quality of results, and that a lack of understanding of definitions of the quantities to be analysed (for example gasoline range organics ) caused non-method errors. In relation to methods, this is contrary to the conclusion of van Nevel et al. who asserted that the results of the IMEP round of analyses of trace elements in natural and synthetic waters showed no dependence on method [11]. If properly validated methods do yield comparable results, then one conclusion from the range of studies around the world is that many environmental methods are not validated. It may be that validated methods are indeed used, but not for exactly the systems for which they were validated. 

Organic EARMING A set of agricultural practices in which no artificial fertilisers, hormones, pesticides or herbicides are used. Organic farming is increasingly popular in developed countries as consumers become more concerned over the potential health hazards of chemical residues in food. Boxes 1.1 and 1.2 (pp. 3-5) provide a more detailed definition. 

The conclusion of all of these data is that vegetables and fruits are good for us. The epidemiological data support this contention. This is the same produce that has been sampled by the FDA and found to contain trace residue levels of almost 100 pesticides. The fact that these same vegetables contain trace levels of pesticides indicates that a diet of fruits and vegetables on the whole is extremely beneficial to one s health. The definitive human trials—in fact some 170 of them—to assess the health effects of trace pesticide consumption have been conducted. The results are the same. Fruits and vegetables are good for you. As Mom—who was 88 at the time I wrote this book—has always said ... 

---