Specifications for pesticides

Testing of pesticide products is important because, where products meet their specifications, they can be expected to be effective and to pose no unexpected risks in use. 

Where products do not comply with specifications, they should not be purchased and regulatory authorities should take appropriate action. Where products already held by the end-user fail to meet specifications, decisions on what to do with them can only be made on a case-by-case basis. End-users in this situation should take steps to avoid the problem in future by purchasing products of good quality only improving storage conditions and/or using products within two years or before the expiry date (whichever is the sooner). 

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The WHO Pesticide Evaluation Scheme (WHOPES), set up in 1960, is the only international programme that promotes and coordinates the testing and evaluation of pesticides intended for public health use. The International Code of Conduct on the Distribution and Use of Pesticides (2) constitutes the framework for WHOPES in promoting the safe handling and use, efficacy, cost-effective application and quality control of pesticide products/formulations for public health use. WHOPES develops specifications for pesticides and application equipment for use in international trade and quality control. 

These activities have enabled WHOPES to plan for the expansion of the Scheme to include the testing and evaluation of a greater variety of pesticides. In recent years, WHOPES has also vigorously promoted the use of WHO specifications for public health pesticides in accordance with the International Code of Conduct on Distribution and Use of Pesticides. Examples of such efforts include the development and wide distribution of guidelines for the purchase of pesticides for public health use, provision of access to WHO specifications for pesticides and their test methods on the Internet, and an increase in the number of WHO collaborating centres for quality control of pesticides (currently three). 

The published list of common names and chemical names of pesticides contained in Annex 1 of Specifications for pesticides used in public health insecticides, molluscicides, repellerts, methods 11) should be reformatted to make the presentation clearer. After the common name, the International Organization for Standardization (ISO), International Union of Pure and Applied Chemistry (lUPAC) and Chemical Abstract (CA) names should be printed with the Chemical Abstract Service (CAS) number and the CIPAC number. 

Specifications for pesticides used in public heaith insecticides, moiluscicides, repeiients, methods, 7th ed. Geneva, Worid Health Organization, 1997, Annex 1 (unpublished document WHO/CTD/WHOPES/ 97.1 available on request from Communicable Disease Control, Prevention and Eradication, World Health Organization, 1211 Geneva 27, Switzerland). 

WHO specifications for pesticides intended for dispersion/dilution in water should incorporate a specification for persistent foam, to minimize the potential for heterogeneous distribution of active ingredient and for eontamination of the clothes and the skin of the user. CIPAC method MT 47.2 (5) and the method given in the FAO Manual (4) (maximum 60ml after 1 minute) should be used. 

Following a series of meetings that began in 1965, a manual on the use of FAO specifications for plant protection products was published in 1971 (1). The FAO development of pesticides was on similar lines to those previously established by WHO and published in the handbook "Specifications for Pesticides Used in Public Health" (1967) (2). The preparation of sep-... 

Specifications for Pesticides Used in Public Health", World Health Organization, Geneva, 1967. 

Manual on Development and Use of FAO and WHO Specifications for Pesticides, March 2006 Revision of First Edition (available only on the internet, http //whqlibdoc.who.int/ publications/2006/9251048576 eng update 2006.pdf)... 

Sample preparation for TLC is covered in Chapter 4 of Ref. 1, with an emphasis on biological samples. Preparation of food samples (65), and of various sample types (foods, environmental samples, human and animal samples) specifically for pesticide analysis (66-68) was described for TLC by Sherma, The only complete chapter on sample preparation for TLC was written by Sherma (69). A chapter on sample preparation for chromatographic analysis contains much useful information pertaining to samples for TLC (Chapter 8, Ref. 44), The CRC Handbooks of Chromatography describe sample preparation methods for different classes of compounds. Sections on sample preparation related to specific compound types will be found in most of the applications chapters in Part II of this Handbook. 

Fluorescence gives numerous possibilities in the detection of pesticides. One possibility is the well-known fluorescence quenching, which can be observed on TLC plates impregnated with a fluorescent indicator sensitized for U V 254 and/or 366 nm. A second possibility is much more specific for pesticides. Some compounds exhibit native fluorescence or can be easily transformed into such compounds. For example, carbaryl produces, after alkaline hydrolysis, a-naphtolate anion, which is strongly fluorescent. Its residues can be measured by in situ spectrofluoiimetiy (66). 

Drinking Water Health Advisories for Pesticides, Office of Drinking Water, U.S. Environmental Protection Agency, Lewis Pubhshets, Chelsea, Mich., 1989. Includes data used for evaluating 1-day, 10-day, and longer-term health advisories for 50 pesticides which have a potential for being found in drinking water, with specific references as sources of information. 

An enzymatic assay can also be used for detecting anatoxin-a(s). " This toxin inhibits acetylcholinesterase, which can be measured by a colorimetric reaction, i.e. reaction of the acetyl group, liberated enzymatically from acetylcholine, with dithiobisnitrobenzoic acid. The assay is performed in microtitre plates, and the presence of toxin detected by a reduction in absorbance at 410 nm when read in a plate reader in kinetic mode over a 5 minute period. The assay is not specific for anatoxin-a(s) since it responds to other acetylcholinesterase inhibitors, e.g. organophosphoriis pesticides, and would need to be followed by confirmatory tests for the cyanobacterial toxin. 

The reagent sequence is specific for endosulfan and phosphamidon. Other insecticides, e.g. organochlorine insecticides, such as endrin, aldrin, dieldrin, DDT and BHC, organophosphorus insecticides, such as malathion, parathion, dimethoate, quinalphos, phorate and fenitrothion, or carbamate insecticides, such as baygon, car-baryl and carbofuran do not react. Neither is there interference from amino acids, peptides or proteins which might be extracted from the biological material together with the pesticides. 

A recent method to screen the urine for alkyl phosphates as an indicator of exposure to organophosphate insecticides shows that the method can be used to determine environmental exposure to a specific organophosphate pesticide. The method was found to be sensitive, identifying low levels of exposure to insecticides in the environment by quantitation of urinary phosphates (Davies and Peterson 1997). The test is limited in that it is only useful for assessing recent exposure, due to the short half-life of the organophosphate pesticides. 

Agarwal et al. 1978), the quantification of these specific enzymes may indicate that exposure to endosulfan has occurred. Blood tests, such as decay curves for aminopyrine in plasma, which are semiquantitative indices of liver enzyme induction, have been used successfully in the past to demonstrate enzyme induction in pesticide-exposed workers. Because numerous chemicals found at hazardous waste sites also induce these hepatic enzymes, these measurements are not specific for endosulfan exposure. However, measurements of enzyme activity, together with the detection of the parent compound or its metabolites in tissue or excreta, can be useful indicators of exposure. All of these potential biomarkers require further verification in epidemiological studies. Further studies with focus on the development of methods to separate and measure the estrogenicity of endosulfan in in vitro assays would be valuable since these assays are more sensitive and discriminative than other conventional biomarkers. Preliminary results have been presented by Sonnenschein et al. (1995). 

The presence of Increased eunounts of NDPA in trlfluralin was observed In a matter 6f days In the tin containers stored at ambient temperatures. No corrosion Inhibitors were added to the tin containers. Container manufacturers use a flux In the tinning process, many contain either nitrite or nitrate salts. Thus, the potential for the nltrosatlng agents exists as part of the metallic film In a seemingly clean tin container. In addition. Archer and Wlshnok (1976) demonstrated the formation of nltrosamlnes from constituents of polymeric liners of metal cans. Container specifications are vital for pesticide formulations prone to be nltrosated. 

Owing to the complexity of multi-residue methods for products of animal origin, it is not possible to outline a simple scheme however, readers should refer to methods described in two references for detailed guidance (Analytical Methods for Pesticides in Foodstuffs, Dutch method collection and European Norm EN 1528. ) There is no multi-method specifically designed for body fluids and tissues. The latter matrix can be partly covered by methods for products of animal origin. However, an approach published by Frenzel et al may be helpful (method principle whole blood is hemolyzed and then deproteinized. After extraction of the supernatant, the a.i. is determined by GC/MS. The LOQ is in the range 30-200 ag depending on the a.i.). 

Until 1991, manufacturers seeking authorizations for pesticides had to fulfil country-specific requirements of validation of enforcement methods. The term enforcement method means analytical methods which are developed for post-registration control and monitoring purposes. The harmonization of these requirements was initiated with the European Economic Community (EEC) Council Directive 91/414/EEC and temporarily finalized with the Guidance Document on Residue Analytical Methods SANCO/825/00 rev. 6, dated 20 June 2000 [Santd et Protection des Consommateurs (SANCO)]. The evaluation of validation studies by the competent authority is conducted by comparison of these European Union (EU) requirements with the study results and most often without any practical experience of the method. Some details of this evaluation are discussed below. 

In summary, the procedure of the Nordic Committee describes a comprehensive validation protocol, but it is not specially designed for pesticide residue analysis and has no preferences with regard to single- or inter-laboratory validation. Therefore, if it is applied to pesticide residue methods, some specific validation requirements should be added. The procedure clearly lists all necessary steps of validation and adjusts its recommendations to the degree of previous external validation. 

Specificity is unsurpassed. Traditionally, MS was performed on very large and expensive high-resolution sector instruments operated by experienced specialists. The introduction of low-resolution (1 amu), low-cost, bench-top mass spectrometers in the early 1980s provided analysts with a robust analytical tool with a more universal range of application. Two types of bench-top mass spectrometers have predominated the quadrupole or mass-selective detector (MSD) and the ion-trap detector (ITD). These instruments do not have to be operated by specialists and can be utilized routinely by residue analysts after limited training. The MSD is normally operated in the SIM mode to increase detection sensitivity, whereas the ITD is more suited to operate in the full-scan mode, as little or no increase in sensitivity is gained by using SIM. Both MSDs and ITDs are widely used in many laboratories for pesticide residue analyses, and the preferred choice of instrument can only be made after assessment of the performance for a particular application. 

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