Chlorpyrifos degradation in turkish soil

Abstract

Degradation of chlorpyrifos was evaluated in laboratory studies. Surface (0–15 cm) and subsurface (40–60 cm) clay loam soils from a pesticide‐untreated field were incubated in biometer flasks for 97 days at 25°C. The treatment was 2 ug g^‐1 [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. The time required for 50% loss of the parent insecticide in surface and subsurface soils was about 10 days. By 97 days, chlorpyrifos residues and their relative concentration (in surface/subsurface) as % of applied ¹⁴C were: ¹⁴CC>2 (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). Chlorpyrifos 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).

Key words:

• Soil biodegradation
• chlorpyrifos
• trichloropyridinol residues
• supercritical fluid extraction