Degradation of mecoprop at different concentrations in surface and sub-surface soil

Abstract

Biodegradation of [ring- 14 C] mecoprop (2-(4-chloro-2-methylphenoxy) propionic acid) was determined in surface and sub-surface soil at concentrations of 0.0005, 0.05, 0.5, 5, 50, 500, 5000 and 25 000 mg kg -1 . The kinetics of mineralisation were evaluated from the mineralisation rates as a function of time and by non-linear regression analysis. In the sub-surface soil, degradation was 6-8 times slower than in surface soil, but the shape of the curves was the same in both layers. At concentrations between 0.0005 and 0.5 mg kg -1 , in both surface and sub-surface soil, degradation was initially zero-order followed by first-order kinetics. At 5 to 500 mg kg -1 in surface soil and 5 to 50 mg kg -1 in sub-surface soil the degradation rate was initially either constant or decreasing followed by exponential degradation indicating increasing populations of mecoprop decomposers in the soil. At 5000 and 25 000 mg kg -1 in the surface soil and at 500, 5000 and 25 000 mg kg -1 in the sub-surface soil, the degradation was negligible, as determined by the percentage [ 14 C] carbon dioxide evolved. By non-linear regression, the three-half order model was found to describe the mineralisation.