Kinetics of linuron and metribuzin degradation in soil

Abstract

The disappearance of linuron and metribuzin was studied during laboratory incubation of soil samples which had been taken from several depths at three sites, and treated with the pesticides. Temperature and water content of the soils were varied. There was a tendency for the rate of loss to be slower in soil taken from deeper horizons than in surface soil but the differences were not large. In only ten out of forty experiments did the value 1 for the apparent order of reaction fall within 95% confidence limits. In the remaining experiments the apparent reaction order was greater than 1 with eight values higher than 4. For one soil, the reaction order for linuron was markedly lower for incubation at 22°C compared with incubations at 10°C. The results could be explained on the basis that the systems were complex, involving consecutive or competing reactions. An alternative possibility is that the apparent complexities were artifacts brought about by the inherent limitations of the laboratory incubation system.

Elucidating the Key Member of a Linuron-Mineralizing Bacterial Community by PCR and Reverse Transcription-PCR Denaturing Gradient Gel Electrophoresis 16S rRNA Gene Fingerprinting and Cultivation

“…The rates of dissipation in agricultural soils determined by laboratory and field experiments are highly variable, with values ranging from days to several years (2,8,9,11,16,23). Linuron is frequently detected in surface and ground waters near or below areas with intensive use, and in one extreme case, linuron was detected in a drinking-water well in concentrations up to 2,800 g liter Ϫ1 (2).…”

Degradation of Metribuzin in Two Soil Types of Lebanon

“…[5,7,11] However, the existence of an inverse relationship between metribuzin degradation and soil temperature was demonstrated. It was found that at 20 • C decomposition of metribuzin was slower than it was at 10 • C. Chemical decomposition of metribuzin continued in the soils stored at -37 • C. [10] Metribuzin may undergo acid hydrolysis where the thiomethyl group at position 3 is broken to release the diketometribuzin (DK). [12] Other studies showed that even at 52 • C metribuzin in an aqueous medium could convert to DK.…”

“…[5,9] The possibility of consecutive reactions and competitiveness between the loss of the amino group and that of the thiomethyl group was suggested as a possible explanation for these results. [10] Temperature plays an important role in the degradation of metribuzin. A linear relationship between degradation and temperature has been demonstrated.…”

Efficiency of methanol:Water solutions for metribuzin extraction from selected soils

“…In addition, it could cause chemical decomposition or extraction of compounds from soil which may interfere with metribuzin determination. In spite of extensive evaluation of different solvent systems varying in extradant ratios (3,8,9,10,12,19) for extraction efficiencies, the efficiency of methanol as an extractant for some U.S. soils of different chemical and physical properties has not been thoroughly investigated.…”