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ARS Home » Research » Publications at this Location » Publication #84848
Title: CHLORPYRIFOS DEGRADATION IN TURKISH SOIL

Author
item YUCEL, ULKU - TURKISH ATOM. ENERGY AUTH
item YLIM, MURAT - TURKISH ATOM. ENERGY AUTH
item GOZEK, KIYMET - TURKISH ATOM. ENERGY AUTH
item Helling, Charles
item SARYKAYA, YUKSEL - ANKARA UNIV, TURKEY

Submitted to: Pesticide Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Chlorpyrifos is a major, broad-spectrum insecticide used world-wide. Although its use is increasing significantly in Turkey, no published information about its environmental fate in Turkish soil was discovered. To determine such information about chlorpyrifos' persistence and metabolism, radiolabeled chlorpyrifos was incubated aerobically in biologically active soils from surface and subsurface zones. During 3 months, evolved radioactive carbon dioxide was measured as indicative of total mineralization of the original insecticide; analyzed as well were chlorpyrifos itself, its metabolite 3,5,6-trichloropyridinol (TCP), and soil-bound residues. This research demonstrated, for the first time, that chlorpyrifos dissipates rapidly (50% loss in 18-20 days) in a typical Turkish agricultural soil, a process probably accelerated by soil alkalinity (pH 8). Once formed, TCP is quickly metabolized by soil microorganisms or, in part, immobilized as soil bound residue; in this research, the relatively new technique of supercritical fluid extraction was found to be capable of removing such bound TCP, thereby providing a more accurate assessment of environmental residues and dissipation of chlorpyrifos. The research results will be useful in risk assessments associated with the use of chlorpyrifos in Turkey and elsewhere. 

Technical Abstract: Degradation of chlorpyrifos, an insecticide used widely in Turkey and elsewhere, was evaluated in laboratory studies. Surface (0-15 cm) and subsurface (40-60 cm) silty clay loam soils from a pesticide-untreated field were incubated aerobically in biometer flasks for 97 days at 25øC. The treatment was 2 ug/g [2,6-pyridinyl-14C]chlorpyrifos, with 74 kBq radioactivity per 100-g soil flask. Evolved 14CO2 was monitored in KOH traps throughout the experiment. Periodically, soil subsamples were also methanol-extracted [ambient shaking, then supercritical fluid extraction (SFE)], then analyzed by thin-layer chromatography. Total 14C and unextractable soil-bound 14C residues were determined by combustion. From the surface and subsurface soils, 41 and 43% of the applied radiocarbon was evolved as 14CO2 during 3 months incubation. Chlorpyrifos dissipation half-times, based on 50% loss of the parent insecticide in surface and subsurface soils, were 20 and 18 days, respectively, during the first 4 weeks, with very rapid loss during the first week. By 97 days, chlorpyrifos residues and their relative concentration (in surface/subsurface) as % of applied 14C were: 14CO2 (40.6/42/6), chlorpyrifos (13.1/12.4), soil-bound residues (11.7/11.4), and 3,5,6-trichloropyridinol (TCP) (3.8/4.8). Chlorpyridinol was largely extracted by simple shaking with methanol, whereas TCP was mainly removed only by SFE. The short persistence of chlorpyrifos probably relates to the high soil pH (7.9-8.1).