Spatial variability in the degradation rates of isoproturon and chlorotoluron in a clay soil

Repeated treatment with fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) resulted in enhanced biodegradation of this nematicide in two United Kingdom soils with a high pH (>7.7). In contrast, degradation of fenamiphos was slow in three acidic United Kingdom soils (pH 4.7 to 6.7), and repeated treatments did not result in enhanced biodegradation. Rapid degradation of fenamiphos was observed in two Australian soils (pH 6.7 to 6.8) in which it was no longer biologically active against plant nematodes. Enhanced degrading capability was readily transferred from Australian soil to United Kingdom soils, but only those with a high pH were able to maintain this capability for extended periods of time. This result was confirmed by fingerprinting bacterial communities by 16S rRNA gene profiling of extracted DNA. Only United Kingdom soils with a high pH retained bacterial DNA bands originating from the fenamiphos-degrading Australian soil. A degrading consortium was enriched from the Australian soil that utilized fenamiphos as a sole source of carbon. The 16S rRNA banding pattern (determined by denaturing gradient gel electrophoresis) from the isolated consortium migrated to the same position as the bands from the Australian soil and those from the enhanced United Kingdom soils in which the Australian soil had been added. When the bands from the consortium and the soil were sequenced and compared they showed between 97 and 100% sequence identity, confirming that these groups of bacteria were involved in degrading fenamiphos in the soils. The sequences obtained showed similarity to those from the genera Pseudomonas, Flavobacterium, and Caulobacter. In the Australian soils, two different degradative pathways operated simultaneously: fenamiphos was converted to fenamiphos sulfoxide (FSO), which was hydrolyzed to the corresponding phenol (FSO-OH) or was hydrolyzed directly to fenamiphos phenol. In the United Kingdom soils in which enhanced degradation had been induced, fenamiphos was oxidized to FSO and then hydrolyzed to FSO-OH, but direct conversion to fenamiphos phenol did not occur.Enhanced biodegradation of pesticides after their repeated application to soils has been widely reported (6,26). In some circumstances, enhancement of degradation does not occur, and the specific factors that lead to adaptation of microbial communities in some soils and not in others are not known. Pesticide degradation in soil is influenced by both biotic and abiotic factors, which act in tandem and complement one another in the microenvironment. The role of abiotic factors in development and stability of enhanced degradation has received little attention.Fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) is an organophosphate insecticide-nematicide, which is widely used for the control of ectoparasitic, endoparasitic, and free-living nematodes in horticultural and other field crops (18). The biological efficacy of fenamiphos has been reported to be significantly reduced by enhanced biodegradation (2,15,17,20). It i...

Section: Discussionmentioning

confidence: 99%

Role of Soil pH in the Development of EnhancedBiodegradation ofFenamiphos

Singh

Walker

Morgan

et al. 2003

“…A recent pesticide database (Footprint, 2007; http://www.eu -footprint.org/ppdb.html, accessed April 2010) reports half-life values (days) in soil, derived from laboratory studies at 20°C, of 73.5 for azoxystrobin, 59 for chlorotoluron, and 226 for epoxyconazole. However, a certain variability exists, and in other research half-lives are longer, i.e., more than 2 years (at 10°C) for epoxyconazole (4), 62 to 107 days for azoxystrobin (10), and 30 to 200 days for chlorotoluron (36), showing that significant degradation should be measured on a time scale of months or years (8, 9) according to the results of a recent review on pesticide persistence (3).The use of such persistent pesticides on agricultural fields can have a high impact on the environment through leaching into aquifers and altering the microbial community and processes in the soil. Investigations of structural and functional changes in soil microbial communities have been done using several methods, including the fatty acid profiling method (14,27,29).…”

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confidence: 99%

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confidence: 99%

Effect of Pesticide Inoculation, Duration of Composting, and Degradation Time on the Content of Compost Fatty Acids, Quantified Using Two Methods

Cardinali

Otto

Vischetti

et al. 2010

Compost biobeds can promote biodegradation of pesticides. The microbial community structure changes during the composting process, and simple methods can potentially be used to follow these changes. In this study the microbial identification (MIDI) and ester-linked (EL) procedures were used to determine the composition of fatty acid methyl esters (FAMEs) in composts aged 3 and 12 months, inoculated with 3 recalcitrant pesticides (azoxystrobin, chlorotoluron, and epoxyconazole and a coapplication of all three) after 0, 56, and 125 days of degradation. Pesticide persistence was high, and after 125 days the residue was 22 to 70% of the applied amount depending mostly on the composting age. Seventy-one FAMEs belonging to nine groups were detected. The EL method provided three times as many detections as did the MIDI method and was more sensitive for all FAME groups except alcohol. Thirty-six and five FAMEs were unique to the EL and MIDI methods, respectively. The extraction method was of importance. The EL method provided a higher number of detections for 57 FAMEs, and the MIDI method provided a higher number for 9 FAMEs, while the two methods were equal for 5 FAMEs; thus, the EL method provided a more uniform overall FAME profile. Effects of the other factors were not always clear. Inoculation with pesticide did not influence the FAME profile with the MIDI method, while it influenced cyclopropane and monounsaturated content with the EL method. Composting age and degradation time had an effect on some groups of FAMEs, and this effect was greater with the EL method. The use of some FAMEs as biomarkers to follow microbial community succession was likely influenced by the type of compost and other factors.Plant protection has become a key factor in intensive agriculture, but the widespread use of pesticides can be toxic to nontarget organisms and can lead to ecosystem alterations. Formulated chlorotoluron (a herbicide), azoxystrobin (a fungicide), and epoxyconazole (a fungicide) are commonly used at the postemergence stage mainly for cereals, to control broadleaved weeds and grasses and to control some foliar and soilborne diseases, respectively.Most information on pesticide persistence is derived from registration documents, few studies appear in the scientific literature, and independent research is always suggested. A recent pesticide database (Footprint, 2007; http://www.eu -footprint.org/ppdb.html, accessed April 2010) reports half-life values (days) in soil, derived from laboratory studies at 20°C, of 73.5 for azoxystrobin, 59 for chlorotoluron, and 226 for epoxyconazole. However, a certain variability exists, and in other research half-lives are longer, i.e., more than 2 years (at 10°C) for epoxyconazole (4), 62 to 107 days for azoxystrobin (10), and 30 to 200 days for chlorotoluron (36), showing that significant degradation should be measured on a time scale of months or years (8, 9) according to the results of a recent review on pesticide persistence (3).The use of such persistent pesticides on agricultural fi...

“…The phenyl-urea herbicides are of particular significance in this respect, since several members of the group, including isoproturon (IPU) [3-(4-isopropylphenyl)-1,1-dimethylurea] and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] are degraded slowly in soil and are susceptible to leaching. As a result, IPU and diuron are frequently detected as contaminants of agricultural catchments in Europe (23).Studies of the fate of IPU in agricultural fields on contrasting soil types have revealed considerable spatial variability in degradation rates across fields (2,26,27). At two such sites in the United Kingdom, Deep Slade field in Warwickshire and Brimstone farm in Oxfordshire, IPU half-life in soil was found to vary between 6 and 30 days, with degradation rate linked to soil pH.…”

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confidence: 99%

“…Studies of the fate of IPU in agricultural fields on contrasting soil types have revealed considerable spatial variability in degradation rates across fields (2,26,27). At two such sites in the United Kingdom, Deep Slade field in Warwickshire and Brimstone farm in Oxfordshire, IPU half-life in soil was found to vary between 6 and 30 days, with degradation rate linked to soil pH.…”

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confidence: 99%

In-Field Spatial Variability in the Degradation of the Phenyl-Urea Herbicide Isoproturon Is the Result of Interactions between Degradative Sphingomonas spp. and Soil pH

Bending¹,

Lincoln²,

Sørensen

et al. 2003

147

Substantial spatial variability in the degradation rate of the phenyl-urea herbicide isoproturon (IPU) [3-(4-isopropylphenyl)-1,1-dimethylurea] has been shown to occur within agricultural fields, with implications for the longevity of the compound in the soil, and its movement to ground-and surface water. The microbial mechanisms underlying such spatial variability in degradation rate were investigated at Deep Slade field in Warwickshire, United Kingdom. Most-probable-number analysis showed that rapid degradation of IPU was associated with proliferation of IPU-degrading organisms. Slow degradation of IPU was linked to either a delay in the proliferation of IPU-degrading organisms or apparent cometabolic degradation. Using enrichment techniques, an IPU-degrading bacterial culture (designated strain F35) was isolated from fast-degrading soil, and partial 16S rRNA sequencing placed it within the Sphingomonas group. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified bacterial community 16S rRNA revealed two bands that increased in intensity in soil during growth-linked metabolism of IPU, and sequencing of the excised bands showed high sequence homology to the Sphingomonas group. However, while F35 was not closely related to either DGGE band, one of the DGGE bands showed 100% partial 16S rRNA sequence homology to an IPU-degrading Sphingomonas sp. (strain SRS2) isolated from Deep Slade field in an earlier study. Experiments with strains SRS2 and F35 in soil and liquid culture showed that the isolates had a narrow pH optimum (7 to 7.5) for metabolism of IPU. The pH requirements of IPU-degrading strains of Sphingomonas spp. could largely account for the spatial variation of IPU degradation rates across the field.Concern about the environmental impact of pesticides most frequently arises from their ability to leach from soil and contaminate water resources. The phenyl-urea herbicides are of particular significance in this respect, since several members of the group, including isoproturon (IPU) [3-(4-isopropylphenyl)-1,1-dimethylurea] and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] are degraded slowly in soil and are susceptible to leaching. As a result, IPU and diuron are frequently detected as contaminants of agricultural catchments in Europe (23).Studies of the fate of IPU in agricultural fields on contrasting soil types have revealed considerable spatial variability in degradation rates across fields (2,26,27). At two such sites in the United Kingdom, Deep Slade field in Warwickshire and Brimstone farm in Oxfordshire, IPU half-life in soil was found to vary between 6 and 30 days, with degradation rate linked to soil pH. Further studies by Bending et al. (3) demonstrated that soil pH controlled the ease of induction of growth-linked metabolism, with slow degradation rates at lower soil pH linked to apparent cometabolic degradation of the compound. At the Deep Slade site, various bacteria capable of degrading IPU have been isolated (8,19,21). However, the relative importance of each in the degradation...