Search

BACKGROUND: Variations in soil properties with depth influence retention and degradation of pesticides. Understanding how soil properties within a profile affect pesticide retention and degradation will result in more accurate prediction by simulation models of pesticide fate and potential groundwater contamination. Metolachlor is more persistent than other acetanilide herbicides in the soil environment and has the potential to leach into groundwater. Reasonably, information is needed about the dissipation and eventual fate of metolachlor in subsoils. The objectives were to evaluate the adsorption and desorption characteristics and to determine the dissipation rates of metolachlor in both surface and subsurface soil samples. RESULTS: Adsorption of metolachlor was greater in the high-organic-matter surface soil than in subsoils. Lower adsorption distribution coefficient (Kads) values with increasing depth indicated less adsorption at lower depths and greater leaching potential of metolachlor after passage through the surface horizon. Desorption of metolachlor showed hysteresis, indicated by the higher adsorption slope (1/nads) compared with the desorption slope (1/ndes). Soils that adsorbed more metolachlor also desorbed less metolachlor. Metolachlor dissipation rates generally decreased with increasing soil depth. The first-order dissipation rate was highest at the 0–50 cm depth (0.140 week−1) and lowest at the 350–425 cm depth (0.005 week−1). Degradation of the herbicide was significantly correlated with microbial activity in soils. CONCLUSION: Metolachlor that has escaped degradation or binding to organic matter at the soil surface might leach into the subsurface soil where it will dissipate slowly and be subject to transport to groundwater. Copyright © 2009 Society of Chemical Industry

A novel bacterial strain FJ1117YT was isolated from an enrichment culture with the herbicide simetryn. The isolate was capable of degrading the herbicide supplied as the sole sulfur source in an aquatic batch culture. The strain FJ1117YT was identified as that belonging to Rhodococcus sp. on the basis of comparative morphology, physiological characteristics and comparison of the 16S rRNA gene sequence. The biodegradation pathway of simetryn was established by isolating the methylsulfinyl analogue as the first metabolite and by identification of the methylsulfonyl intermediate and the hydroxy analogue by liquid chromatography–mass spectrometry (LC-MS) and/or nuclear magnetic resonance (NMR) analysis. The results indicate that the methylthio group was progressively oxidised and hydrolysed by the strain FJ1117YT. The same strain is also able to metabolise other methylthio-s-triazines such as ametryn, desmetryn, dimethametryn and prometryn through similar pathways. Copyright © 2007 Society of Chemical Industry

Variations in soil properties with depth influence retention and degradation of pesticides. Understanding how soil properties within a profile affect pesticide retention and degradation will result in more accurate prediction by simulation models of pesticide fate and potential groundwater contamination. Metolachlor is more persistent than other acetanilide herbicides in the soil environment and has the potential to leach into groundwater. Reasonably, information is needed about the dissipation and eventual fate of metolachlor in subsoils. The objectives were to evaluate the adsorption and desorption characteristics and to determine the dissipation rates of metolachlor in both surface and subsurface soil samples.Adsorption of metolachlor was greater in the high-organic-matter surface soil than in subsoils. Lower adsorption distribution coefficient (K(ads)) values with increasing depth indicated less adsorption at lower depths and greater leaching potential of metolachlor after passage through the surface horizon. Desorption of metolachlor showed hysteresis, indicated by the higher adsorption slope (1/n(ads)) compared with the desorption slope (1/n(des)). Soils that adsorbed more metolachlor also desorbed less metolachlor. Metolachlor dissipation rates generally decreased with increasing soil depth. The first-order dissipation rate was highest at the 0-50 cm depth (0.140 week(-1)) and lowest at the 350-425 cm depth (0.005 week(-1)). Degradation of the herbicide was significantly correlated with microbial activity in soils.Metolachlor that has escaped degradation or binding to organic matter at the soil surface might leach into the subsurface soil where it will dissipate slowly and be subject to transport to groundwater.

A moderately persistent herbicide, simazine, has been used globally and detected as a contaminant in soil and water. The authors have isolated a simazine-degrading bacterium from a simazine-degrading bacterial consortium that was enriched using charcoal as a microhabitat. The isolate, strain CDB21, was gram-negative, rod-shaped (0.5-0.6 microm x 1.0-1.2 microm) and motile by means of a single polar flagellum. Based on 16S rRNA sequence analysis, strain CDB21 was identified as a novel beta-proteobacterium exhibiting 100% sequence identity with the uncultured bacterium HOClCi25 (GenBank accession number AY328574). PCR using primers that were specific for the genes of the atrazine-degrading enzymes (atzABCDEF) of Pseudomonas sp. strain ADP showed that strain CDB21 also possessed the entire set of genes of these enzymes. Nucleotide sequences of the atzCDEF genes of strain CDB21 were 100% identical to those of Pseudomonas sp. strain ADP. Sequence identity of the atzA genes between these bacteria was 99.7%. The 398-nucleotide upstream fragment of the atzB gene of strain CDB21 was 100% identical to ORF30 of Pseudomonas sp. strain ADP, and the 1526-nucleotide downstream fragment showed 99.8% sequence similarity to the atzB gene of the pseudomonad.