Recently there has been much controversy concerning the use of DOT as a pesticide. This has resulted in partial or total ban on it in several countries. In this country DOT is being phased out over a period of two years (1.). In 1.968 DOT was removed from recommended compounds for tobacco (3).. lnspite of the removal of DOT as a pesticide for tobacco our studies are important for two reasons: First, tobacco leaf is cured and mellowed before .its use in the manufacture of cigarettes. This usually takes about two or three years and causes the possibility of carryover of DOT on cigarettes for several years. Second, the studies throw light on the mechanisms of the reactions involved in the degradation of pesticides in tobacco smokes. This paper is divided into two sections: Section l. deals with the isolation and identification of the degradation products from the pyrolysis of p,p'-DDT in a nitrogen atmosphere. Section 2 deals with the pyrolytic degradation of p,p'-DDT intimately mixed with tobacco. SJ:CTION 1 Pyrolysis of p,p'•DDT In a Nitrogen Atmosphere Very little work has been reported on the pyrolysis of DOT. Cavenah and ]ohns (7) have studied pyrolysis of DOT, but this was in conjunction with their method of identifying DOT by its "pyrolysis spectra". Recently, Mosier, Guenzi, and Miller (1.5) have proposed a free radical mechanism for photodecomposition of DOT. Some of their mechanisms are similar to those reported herein although reaction conditions were very different. • Presented as two papers entitled: "Isolation and Identification of the Degradation Products from the Pyrolysis of p,p'-DDT •in a Nitrogen .Atmosphere" and "Degradation of p,p'-DDT in Tobacco Smokes" before the 23rd Tobacco Chemists' Research Conference at Philadelphia, October 1969. Detailed description of the methods to be published at a later da.te.

The possibility of using laboratory mice to obtain information relative to establishment of reentry intervals for pesticide-treated fields was investigated. Pre-and postexposure blood cholinesterase levels of mice exposed for 10 hours to insecticidetreated (field applications) tobacco, cotton, or apple leaves were determined at 24 hour intervals. Differences were found between insecticides with respect to both initial inhibition and residuality as well as different types of foliage, rates of application, and formulation.

A procedure is described for estimating total resi-were substituted into the equation, and the caldues of DDT and T D E in tobacco from the anal-

1. Chlorinated hydrocarbon insecticides and other halogenated compounds, probably biphenyls, were found to be associated with human hair at concentrations less than 1 p.p.m. 2. In experiments with rats, chlorinated 14C-hydrocarbon insecticides and polychlorinated biphenyls were excreted in hair in all instances, but excretion was less with the more labile compounds. 3. Excretion via hair may be a significant factor in eliminating chlorinated hydrocarbons which resist metabolism.

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.