Degradation and adsorption of 14C-mecoprop (MCPP) in surface soils and in subsoil. Influence of temperature, moisture content, sterilization and concentration on degradation

Abstract

Degradation and adsorption of 14C-ringlabelled mecoprop was determined in three different soil types under different environmental conditions. Degradation was also determined in subsurface soil. The adsorption of MCPP was low with Kd-values of 0.1–0.2 and Koc-values of 8, 13 and 5, respectively in the three soil types. The correlation between mecoprop disappearance at 2 mg kg−1 and 14CO2-evolution showed that when 12% 14C was evolved as 14CO2, half of the mecocrop was decomposed. Estimated half-life times in the three surface soils were 3, 3 and 4 days, respectively at 20°C. When the degradation was determined at 20, 10 and 5°C the estimated half-life was 3, 12 and 20 days, respectively. The degradation rate of mecoprop increased initially with a doubling time of 1.4, 4.9 and 6.9 days, respectively at 20, 10 and 5°C but with a 14-day lag-phase at 5°C. In dry and in flooded soil (25 and 200% of total water holding capacity) estimated half lives were 10 and 15 days, respectively. At 0.2 mg kg−1 the half-life was 1.3 days compared to the 3 days at 2 mg kg−1. In sterile soil no degradation was observed. In soil sampled at 0–33, 33–66 and 66–99 cm depth the estimated half-life time of mecoprop (0.05 mg kg−1) was 7, 70 and 34 days, respectively at 10°C.