Pesticides and pesticide residues

Gas chromatography has been widely used in foods, petroleum products, pesticide and pesticide residues, pharmaceutical products, environmental monitoring, chnical chemistry and a number of other fields. The major advantages of modern GC reside in the high resolution, the speed, the sensitivity, and the precision and the accuracy that characterises it. An overview of each factor is given below. 

Capillary electrophoresis (CE) represents an important tool with several advantages for determining pesticides and pesticide residues in environmental samples due to its intrinsic simplicity and high efficiency. Target analytes should be ionic or easily ionized. Some limitations arise from a lack of selective detectors, although CE-MS interfacing has become more affordable. 

Labeled compounds offer many advantages for food science. The extreme sensitivity of radioactivity measurement enables one to determine and characterize biologically important trace elements and compounds (e.g., pesticides and pesticide residues) in food samples. 

When illegal residues have been found in monitoring studies conducted by the FDA or USD A, the reason has often been that no U.S. tolerance had been requested for that particular pesticide in that specific crop. For example, an imported crop would be deemed to be adulterated and would be seized at the port of entry into the United States if found to contain a pesticide residue in the absence of a tolerance in that crop. This is so even if tolerances have been set for the same pesticide in several crops grown in the United States and the pesticide had been used to control a pest that does not exist in the United States. Furthermore, an international maximum residue level (MRL) might already have been estabUshed for that pesticide—crop combination under the Codex system of standards for food of importance in international trade. The U.S. GAO issued two reports on food safety and pesticides in 1991 (89,90). 

P. A. Cunniff, ed.. Official Methods of Analysis of AO AC International, 16th ed., Vols. I and II, AO AC International, Arlington, Va., 1995. Vol. I includes Pesticide Formulations and Pesticide Residues. Over 2100 coUabotatively tested, approved methods for chemical and microbiological analyses, with 149 new methods, 103 revised/updated methods, methods using anibody-based test kits, enzyme immunoassay, and annual supplements containing new and revised methods chemical and common names of all dmgs and pesticides easy-to-locate references. 

Pesticide Analytical Manual, Food and Dmg Administration, Rockville, Md., Vol. I, 1990, and Vol. II, 1989. Includes multiresidue methods used by U.S. FDA to routinely check foods for pesticide residues, and single residue methods for certain pesticides not detected by any of the multiresidue methods. 

The documented occurrence of pesticides in surface water is indicative that mnoff is an important pathway for transport of pesticide away from the site of appHcation. An estimated 160 t of atra2ine, 71 t of sima2ine, 56 t of metolachlor, and 18 t of alachlor enter the Gulf of Mexico from the Mississippi River annually as the result of mnoff (47). Field appHcation of pesticides inevitably leads to pesticide contamination of surface mnoff water unless mnoff does not occur while pesticide residues remain on the surface of the soil. The amount of pesticides transported in a field in mnoff varies from site to site. It is controUed by the timing of mnoff events, pesticide formulation, physical—chemical properties of the pesticide, and properties of the soil surface (48). Under worst-case conditions, 10% or more of the appHed pesticide can leave the edge of the field where it was appHed. 

W. G. Fong, A. Moye,J. Seiber, andj. Toth, Pesticide Residue Methodology in Foods Methods, Techniques and Regulations, imptogtess. 

The U.S. FDA monitors foods for half of the approximately 300 pesticides having official EPA tolerances as weU as a number of other pesticides that have no official tolerances. Multiresidue methods, most of which are based on chromatography protocols, are employed (7). Not aU pesticides are monitored on aU foods and sampling (qv) is purposely biased to catch possible problems. The overaU iacidence of iUegal pesticide residue is, however, quite smaU 1% for domestic surveiUance samples and 3% for imported foods. The methods employed can usuaUy quantify residues present at 0.01 ppm. Quantitation limits range from 0.005 to 1 ppm. 

UK Ministry of Agriculture Fisheries and Food and Flealth and Safety Executive, Annual Report of the Working Party on Pesticide Residues in Food (1997), MAFF Publications, London, 1997. lARC, Monographs on the Evabiation of the Carcinogenic Risk of Chemicals to Hnmans Volume 56 Some Naturally Occurring Substances Food Items and Constituents, Heterocyclic Aromatic Amines and Mycotoxins, WFIO, Geneva, 1979, p. 397. 

The processing of cotton, from the field to the cloth, releases both inorganic and organic particulate matter to the atmosphere. Also, adhering pesticide residues may be emitted at the cotton gin exhaust. Table 30-19 lists the emission factors for particulate matter from cotton ginning operations. 

Regulation on mles for provisions of Directive 86/362/EEC and Directive 90/642/EEC on the maximum levels of pesticide residues... 

Problems that rank relatively high in duee of the four typos, or at least medium in all four, include criteria air pollutiuits, stratospheric ozone depletion, pesticide residues on food, and other pesticide risks (runoff and air deposition of pesticides)... 

On-line LC-GC has frequently been used as a clean-up technique for the analysis of trace levels of contaminants (pesticides, plasticizers, dyestuffs and toxic organic chemicals) in water and food products. Several different approaches have been proposed for the analysis of contaminants by on-line LC-GC. Since pesticide residues occur at low concentration in water, soil or food, extraction and concentration is needed before GC analysis is carried out. 

In 1994, Nam and King (68) developed a SFE/SFC/GC instrumentation system for the quantitative analysis of organochlorine and organophosphorus pesticide residues in fatty food samples (chicken fat, ground beef and lard). In this way, SFC was used as an on-line clean-up step to remove extracted material. The fraction containing pesticide residues is then diverted and analysed by GC. 

K. Grob and R Kalin, Attempt foi an on-line size exclusion clnomatography method for analyzing pesticide residues in foods , 7. Agric. Food Chem. 39 1950-1953(1991). 

P. Van Zoonen, E. A. Hogendoom, G. R. Van der Hoof and R. A. Baumann, Selectivity and sensitivity in coupled chromatographic techniques as applied in pesticide residue analysis . Trends. Anal. Chem. 11 11-17 (1992). 

E. A. Hogendoorn, C. E. Goewie and P. van Zoonen, Application of HPEC column switching in pesticide residue analysis, Eresenius , ]. Anal. Chem. 339 348-356 (1991). 

---