Seasonal Disappearance and Volatilization of Toxaphene and DDT from a Cotton Field

Abstract

AbstractVolatilization and subsequent aerial transport is thought to be a major pathway of pesticide disappearance from application sites. Corroborative evidence obtained for agricultural pesticides under field conditions is scarce. The contribution of volatilization to the overall disappearance of toxaphene (chlorinated camphene) and DDT [1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl)ethane] from cotton (Gossypium hirsutum L.) was studied under field conditions in the “Delta” section of Mississippi. Drought conditions prevailed throughout most of the study. Measurements were made during two periods: (i) a 10.7‐d period after toxaphene was applied by ground equipment to 50‐cm‐tall cotton plants, and (ii) a 32.7‐d period after a similar application of a mixture of toxaphene and DDT to the same plants. Variable amounts of pesticide were unaccounted for (toxaphene, 17% first application, 54% second application; DDT, 72%) and were apparently lost during application and the following 3‐h period before sampling of air, soil, and plants was begun. The calculated 50% disappearance times of toxaphene (4.7 d, first application; and 10.8 d second application) and DDT (10.3 d) on plants agreed reasonably well with previously reported values. Pesticide disappearance rates were linear functions of the pesticide loads on the plants. The volatile loss of toxaphene (as quantified by the last four chromatographic peaks) during the 10.7‐d test period after the first application was 17% of the amount intercepted by the plants. The comparable volatile loss during the first 10.7 d after the second application (32.7‐d test period) was 33% of the amount on the plants. Total toxaphene and DDT volatile losses during the complete 32.7‐d test period were 53 and 58% of the amounts on the plants, respectively. Because of dry weather, no measurable pesticide volatilization occurred from soil. Disappearance rate changes, as well as volatilization rate changes, for toxaphene and DDT applied at the same time were approximately equal. The study provides additional evidence that post‐application volatilization from plants is a major pathway of pesticide transport.