Removal of DDT and Related Chlorinated Hydrocarbon Residues from Alfalfa Hay T. E. A r c h e r a n d D. G. C r o s b y
Oven heat removed approximately 34% of the residues of DDT and related chlorinated hydrocarbon insecticides from alfalfa feeds containing 16.5 moisture. When the samples were saturated with water, removal increased to 86%, while more than 50% of initial DDT residues on alfalfa green
z
chop were removed by commercial dehydration processes. The same residues were removed almost completely by the vapors of various common solvents (water, 86%; isopropyl alcohol, 93z; benzene, 97%; and pentane, 7 3
z).
any commercial feeds contain residues of D D T and related chlorinated hydrocarbon insecticides (DDT-RCH) in the low parts-per-million range. Pesticides pass rapidly from feeds into milk, eggs, and other animal products and, once established, cannot be eliminated immediately simply by withdrawing the contaminated feed. Various workers have demonstrated the uptake of D D T and other chlorinated hydrocarbon pesticides from feed by dairy animals and the subsequent appearance of the pesticides in the milk fat (Brown et nl., 1966; Crosby et a/., 1967; Laben et a/., 1966 a. b ; Williams et c i / . , 1964). Archer and Crosby (1967) reported the characteristics of the extraction, nature, and location of D D T - R C H residues in alfalfa hay. The effect of dehydration upon residues in alfalfa of aldrin, chlordan, parathion, toxaphene (Stansbury and Dahm, 1951), and malathion (Rai et d., 1957) has been discussed. The purpose of the present work was to find means by which D D T - R C H residues on common alfalfa feeds might intentionally be removed or detoxified. Such methods, where economical, would improve both the value of the feed as a marketable commodity and the potential marketability of animal products containing residues from this source; they would be of particular value in instances of accidental overapplication or drift contamination. The observations that D D T is relatively volatile. especially in the presence of water (Bowman et ( I / . , 1959) and remains near the plant surfaces in alfalfa (Archer and Crosby, 1967). might provide the basis for effective practical removal of its residues.
raphy (GLC) procedures were employed routinely, either separately or in combination. The G L C method of Crosby and Archer (1966) was used, except that a 6-foot X l/s-inch stainless steel column packed with 10% DC200 silicone grease on 100- to 200-mesh G a s Chrom Q was used occasionally instead of the one specified. Samples were analyzed both with and without alkaline dehydrohalogenation, and the results are reported on a dryweight basis. Recovery was essentially quantitative. Thin-layer chromatography was employed for screening and, in combination with GLC, as a n analytical tool. Silica gel H absorbent, pentane solvent, and the silver nitrate-2-phenoxyethanol color test (Mitchell. 1958) were preferred. For quantitative work, chromstogram areas containing the unknowns were extracted from the silica gel with benzene or pentane after comparing R , values (0.41, D D E ; 0.26, D D T ; 0.14, D D D ) with those of parallel standard pesticide tracers, and the extracts were analyzed by G L C . H a y Samples. Hay samples were obtained from fields in Yolo County, Calif. The fields had not received intentional treatment with pesticides during the previous season, so the existing residues represent accidental contamination. Sampling and extraction methods were described by Archer and Crosby (1967). Moisture content was determined a t the time of treatment (immediately after harvest in the case of fresh alfalfa); field-cured hay contained 16.547,, air-dried green-chop 9.57,, commercially dehydrated hay 5 % . and alfalfa pellets 5.8% moisture. Chopped, mixed, composited hay samples were subsampled for use in the various experiments. Vapor Treatments. Vapor treatments of hay were METHODS A S D MATERIALS performed in the apparatus shown in Figure 1. The vapors were generated in the 3-liter boiler and passed Detection and Determination of Pesticides. Thinfrom the spreader through hay packed in the treatment layer chromatography (TLC) and gas-liquid chromatogcolumn, and the condensed vapors were collected in 500-ml. fractions in the cold trap. Subsainples of hay .~~ (100 grams) were washed with vapor from 2 liters of Agricultural Toxicology and Residue Research Laborasolvent, condensation in the lines and treatment column tory, University of California, Davis, Calif. 95616
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VOL. 16, NO. 4, JL'LY-AUG. 1968 623
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Table I.
Sample
-Vapor Generator
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Effect of Oven Heat on DDT-RCH Residues in Alfalfa Hay OvenInitial Heated11 Residue, Residue,
