Average residue Ievels of DDT + TDE in flue-cured tobacco decreased from 6.1 ppm in 1970 to 0.85 ppm in 1972. DDT + TDE residues in Burley also dropped sharply from previous levels. In 1972 one sample from Kentucky contained 8.17 ppm; all other Burley samples were less than 0.25 ppm. DDT + TDE residues also declined in fire-cured and air-cured types; of these samples Tennessee dark air-cured tobacco contained the highest average residue (3.5 ppm of DDT + TDE). In 1972 over 90 % of the flue-cured samples were positive for toxaphene. Since each of our samples was a composite of tobacco from 10 farmers, we cannot conclude from this result that 90 % of the individual piles contained toxaphene. Significant amounts of toxaphene were found in other types also; for example, 50 % of the 1972 Burley samples had toxaphene concentrations greater than 0.5 ppm. Average endosulfan levels decreased between 1970 and 1972 in flue-cured and Burley tobaccos. However, in all of the dark air and dark fire-cured samples from Tennessee endosulfan residues exceeded 5 ppm. Average endrin residues were at or near the low detection limit in alI samples except fire-cured and dark air-cured tobacco from Tennessee; these averaged 0.26 and 0.17 ppm, respectively.
High-performance liquid chromatography (HPLC) with C18 reverse-phase columns was used to determine residues of fluvalinate and permethrin applied in the field to flue-cured tobacco in 1980 and 1981. Methods were developed to determine residue levels in both green and cured samples. In 1980 field tests, residues of fluvalinate applied at rates of 0.1 and 0.2 kg/ha averaged 3.3 and 7.2 ppm, respectively, on green tobacco harvested immediately after application, and declined to 0.3 and 2.7 ppm by 12 days after application. In 1981, with the same application rates, residues averaged 1.7 and 3.0 ppm (0 time) and declined to 0.4 and 0.5 ppm after 16 days, respectively. A new formulation of fluvalinate, applied at 0.06 and 0.01 kg/ha, averaged 0.9 and 1.3 ppm on day 0 and declined to 0.3 and 0.6 ppm after 16 days, respectively. Flue curing reduced fluvalinate residues approximately by 61 % both years. Immediately after application, residues of permethrin, applied at 0.2 kg/ha, averaged 9.6 ppm in 1980 and at application rates of 0.1 and 0.2 kg/ha averaged 3.5 and 3.8 ppm, respectively, in 1981. Residues declined to 7.0 ppm after 12 days in 1980 and to 3.2 and 3.5 ppm after 16 days in 1981. Losses of permethrin due to curing averaged 67 %.
Indirect contamination of tobacco by DDT, TDE, endrin, dieldrin, and toxaphene was investigated under field conditions. Levels of DDT + TDE in soil ranged from << 0.01 to 0.18 ppm, and those in cured leaves ranged from 0.11 to 1.69 ppm. The lower stalk position at the major test location generally had greater concentrations of DDT + TDE than the middle and upper positions, but distribution of these insecticides among leaf positions was variable for other locations. Residues of DDT in the bottom stalk position were positively correlated with those in the soil. Plant-bed soils did not appear to be a major source of DDT + TDE residues in cured tobacco. Residues of endrin and dieldrin were near or below the limit of detection (0.01 ppm) in soil and cured leaf. Residues of toxaphene ranged from << 0.1 to 4.7 ppm in soil and << 0.3 to 7.7 ppm on tobacco. Toxaphene residues in the bottom and top stalk positions were positively correlated with residues in soil. Contamination by toxaphene appeared to be attributable to uptake from soil and to movement of the insecticide as drift or vapour through the air.
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