The Experts below are selected from a list of 1962 Experts worldwide ranked by ideXlab platform
Dean G Thompson - One of the best experts on this subject based on the ideXlab platform.
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impact of Hexazinone and metsulfuron methyl on the zooplankton community of a boreal forest lake
Environmental Toxicology and Chemistry, 1993Co-Authors: Dean G Thompson, Stephen B Holmes, Kerrie L Wainiokeizer, L Macdonald, Keith R SolomonAbstract:The impact of Hexazinone and metsulfuron methyl herbicides on the zooplankton community of a typical boreal forest lake was investigated using in situ enclosures and a replicated multiple-treatment-level experimental design. Concentration-dependent reductions of zooplankton abundance in response to Hexazinone treatment were readily apparent, whereas metsulfuron methyl generated only marginal effects. Field-based, nonlinear regression estimates of EC50 (<6.0 mg L−1) for Hexazinone-induced reduction of zooplankton abundance suggest that abundance of various zooplankton taxa may be expected following chronic exposure to environmentally realistic concentrations of this herbicide (i.e., approximately 1 mg L−1). Time to recovery was proportional to exposure level, with definite recovery observed at the 0.01- and 0.1-mg L−1 concentrations of Hexazinone. The reduced magnitude of impact, as well as the relative timing of response and recovery in the zooplankton as compared to the phytoplankton community, was consistent with the postulate that Hexazinone effects were secondary in nature, resulting indirectly from reductions in phytoplankton biomass and DO. The data provide evidence to suggest that chronic exposure to Hexazinone concentrations approximating 1 mg L1− or above may result in reduced primary productivity in lentic ecosystems, which may in turn cause reductions in zooplankton abundance.
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impact of Hexazinone and metsulfuron methyl on the phytoplankton community of a mixed wood boreal forest lake
Environmental Toxicology and Chemistry, 1993Co-Authors: Dean G Thompson, Stephen B Holmes, L Macdonald, David R Thomas, Keith R SolomonAbstract:The impact of two herbicides on the phytoplankton community of a typical forest lake was investigated using in situ enclosures. Chronic exposure to Hexazinone resulted in concentration-dependent depression of DO, which mirrored reductions in biomass of all dominant phytoplankton groups (Cyanophyta, Chlorophyta, Chrysophyta, Cryptophyta, and Bacilliarophyceae). Although effects observed at the lowest treatment level of Hexazinone (0.01 mg L−1) were transient, no evidence of recovery in biomass was discernible at higher test concentrations within the 77 d of investigation. In contrast, metsulfuron methyl at concentrations as high as 1.0 mg L−1 (approximately 40× the worst-case expected environmental concentration [EEC]) induced only slight transient effects and only in the Cyanophyta. For Hexazinone, 95% C.I.s (0.01-0.07 mg L−1) for nonlinear estimates of EC50 (biomass reduction) were generally an order of magnitude below the EEC for accidental overspray (0.8 mg L−1) and below the EEC estimated for drift inputs associated with aerial applications in forest vegetation management. Results of this replicated concentration-response study demonstrate substantial, statistically significant, and persistent impacts on natural phytoplankton communities chronically exposed to Hexazinone at levels >0.1 mg LT−1. In contrast, no similar effects were observed in phytoplankton communities exposed to metsulfuron methyl at levels well in excess of its EEC values.
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persistence of Hexazinone and metsulfuron methyl in a mixed wood boreal forest lake
Journal of Agricultural and Food Chemistry, 1992Co-Authors: Dean G Thompson, L Macdonald, Bozena StaznikAbstract:The persistence of Hexazinone and metsulfuron-methyl herbicides was investigated in an experiment using in situ enclosures deployed in a mixed-wood/boreal forest lake. Dissipation studies provided evidence that aqueous residues of Hexazinone may persist (DT 50 =131-280 days) under conditions typical of northern lentic systems in the mixed-wood/boreal forest. Although dissipation rates of Hexazinone differed depending upon initial concentrations (10 4 and 10 3 μg L -1 ), such differences were of little practical significance
Bozena Staznik - One of the best experts on this subject based on the ideXlab platform.
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persistence of Hexazinone and metsulfuron methyl in a mixed wood boreal forest lake
Journal of Agricultural and Food Chemistry, 1992Co-Authors: Dean G Thompson, L Macdonald, Bozena StaznikAbstract:The persistence of Hexazinone and metsulfuron-methyl herbicides was investigated in an experiment using in situ enclosures deployed in a mixed-wood/boreal forest lake. Dissipation studies provided evidence that aqueous residues of Hexazinone may persist (DT 50 =131-280 days) under conditions typical of northern lentic systems in the mixed-wood/boreal forest. Although dissipation rates of Hexazinone differed depending upon initial concentrations (10 4 and 10 3 μg L -1 ), such differences were of little practical significance
L Macdonald - One of the best experts on this subject based on the ideXlab platform.
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impact of Hexazinone and metsulfuron methyl on the zooplankton community of a boreal forest lake
Environmental Toxicology and Chemistry, 1993Co-Authors: Dean G Thompson, Stephen B Holmes, Kerrie L Wainiokeizer, L Macdonald, Keith R SolomonAbstract:The impact of Hexazinone and metsulfuron methyl herbicides on the zooplankton community of a typical boreal forest lake was investigated using in situ enclosures and a replicated multiple-treatment-level experimental design. Concentration-dependent reductions of zooplankton abundance in response to Hexazinone treatment were readily apparent, whereas metsulfuron methyl generated only marginal effects. Field-based, nonlinear regression estimates of EC50 (<6.0 mg L−1) for Hexazinone-induced reduction of zooplankton abundance suggest that abundance of various zooplankton taxa may be expected following chronic exposure to environmentally realistic concentrations of this herbicide (i.e., approximately 1 mg L−1). Time to recovery was proportional to exposure level, with definite recovery observed at the 0.01- and 0.1-mg L−1 concentrations of Hexazinone. The reduced magnitude of impact, as well as the relative timing of response and recovery in the zooplankton as compared to the phytoplankton community, was consistent with the postulate that Hexazinone effects were secondary in nature, resulting indirectly from reductions in phytoplankton biomass and DO. The data provide evidence to suggest that chronic exposure to Hexazinone concentrations approximating 1 mg L1− or above may result in reduced primary productivity in lentic ecosystems, which may in turn cause reductions in zooplankton abundance.
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impact of Hexazinone and metsulfuron methyl on the phytoplankton community of a mixed wood boreal forest lake
Environmental Toxicology and Chemistry, 1993Co-Authors: Dean G Thompson, Stephen B Holmes, L Macdonald, David R Thomas, Keith R SolomonAbstract:The impact of two herbicides on the phytoplankton community of a typical forest lake was investigated using in situ enclosures. Chronic exposure to Hexazinone resulted in concentration-dependent depression of DO, which mirrored reductions in biomass of all dominant phytoplankton groups (Cyanophyta, Chlorophyta, Chrysophyta, Cryptophyta, and Bacilliarophyceae). Although effects observed at the lowest treatment level of Hexazinone (0.01 mg L−1) were transient, no evidence of recovery in biomass was discernible at higher test concentrations within the 77 d of investigation. In contrast, metsulfuron methyl at concentrations as high as 1.0 mg L−1 (approximately 40× the worst-case expected environmental concentration [EEC]) induced only slight transient effects and only in the Cyanophyta. For Hexazinone, 95% C.I.s (0.01-0.07 mg L−1) for nonlinear estimates of EC50 (biomass reduction) were generally an order of magnitude below the EEC for accidental overspray (0.8 mg L−1) and below the EEC estimated for drift inputs associated with aerial applications in forest vegetation management. Results of this replicated concentration-response study demonstrate substantial, statistically significant, and persistent impacts on natural phytoplankton communities chronically exposed to Hexazinone at levels >0.1 mg LT−1. In contrast, no similar effects were observed in phytoplankton communities exposed to metsulfuron methyl at levels well in excess of its EEC values.
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persistence of Hexazinone and metsulfuron methyl in a mixed wood boreal forest lake
Journal of Agricultural and Food Chemistry, 1992Co-Authors: Dean G Thompson, L Macdonald, Bozena StaznikAbstract:The persistence of Hexazinone and metsulfuron-methyl herbicides was investigated in an experiment using in situ enclosures deployed in a mixed-wood/boreal forest lake. Dissipation studies provided evidence that aqueous residues of Hexazinone may persist (DT 50 =131-280 days) under conditions typical of northern lentic systems in the mixed-wood/boreal forest. Although dissipation rates of Hexazinone differed depending upon initial concentrations (10 4 and 10 3 μg L -1 ), such differences were of little practical significance
Keith R Solomon - One of the best experts on this subject based on the ideXlab platform.
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impact of Hexazinone and metsulfuron methyl on the zooplankton community of a boreal forest lake
Environmental Toxicology and Chemistry, 1993Co-Authors: Dean G Thompson, Stephen B Holmes, Kerrie L Wainiokeizer, L Macdonald, Keith R SolomonAbstract:The impact of Hexazinone and metsulfuron methyl herbicides on the zooplankton community of a typical boreal forest lake was investigated using in situ enclosures and a replicated multiple-treatment-level experimental design. Concentration-dependent reductions of zooplankton abundance in response to Hexazinone treatment were readily apparent, whereas metsulfuron methyl generated only marginal effects. Field-based, nonlinear regression estimates of EC50 (<6.0 mg L−1) for Hexazinone-induced reduction of zooplankton abundance suggest that abundance of various zooplankton taxa may be expected following chronic exposure to environmentally realistic concentrations of this herbicide (i.e., approximately 1 mg L−1). Time to recovery was proportional to exposure level, with definite recovery observed at the 0.01- and 0.1-mg L−1 concentrations of Hexazinone. The reduced magnitude of impact, as well as the relative timing of response and recovery in the zooplankton as compared to the phytoplankton community, was consistent with the postulate that Hexazinone effects were secondary in nature, resulting indirectly from reductions in phytoplankton biomass and DO. The data provide evidence to suggest that chronic exposure to Hexazinone concentrations approximating 1 mg L1− or above may result in reduced primary productivity in lentic ecosystems, which may in turn cause reductions in zooplankton abundance.
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impact of Hexazinone and metsulfuron methyl on the phytoplankton community of a mixed wood boreal forest lake
Environmental Toxicology and Chemistry, 1993Co-Authors: Dean G Thompson, Stephen B Holmes, L Macdonald, David R Thomas, Keith R SolomonAbstract:The impact of two herbicides on the phytoplankton community of a typical forest lake was investigated using in situ enclosures. Chronic exposure to Hexazinone resulted in concentration-dependent depression of DO, which mirrored reductions in biomass of all dominant phytoplankton groups (Cyanophyta, Chlorophyta, Chrysophyta, Cryptophyta, and Bacilliarophyceae). Although effects observed at the lowest treatment level of Hexazinone (0.01 mg L−1) were transient, no evidence of recovery in biomass was discernible at higher test concentrations within the 77 d of investigation. In contrast, metsulfuron methyl at concentrations as high as 1.0 mg L−1 (approximately 40× the worst-case expected environmental concentration [EEC]) induced only slight transient effects and only in the Cyanophyta. For Hexazinone, 95% C.I.s (0.01-0.07 mg L−1) for nonlinear estimates of EC50 (biomass reduction) were generally an order of magnitude below the EEC for accidental overspray (0.8 mg L−1) and below the EEC estimated for drift inputs associated with aerial applications in forest vegetation management. Results of this replicated concentration-response study demonstrate substantial, statistically significant, and persistent impacts on natural phytoplankton communities chronically exposed to Hexazinone at levels >0.1 mg LT−1. In contrast, no similar effects were observed in phytoplankton communities exposed to metsulfuron methyl at levels well in excess of its EEC values.
Xuedong Wang - One of the best experts on this subject based on the ideXlab platform.
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Modification to degradation of Hexazinone in forest soils amended with sewage sludge.
Journal of Hazardous Materials, 2012Co-Authors: Huili Wang, Chengjun Wang, Zhengti Xu, Meiping Ma, Wenwei Wang, Fan Chen, Xuedong WangAbstract:Abstract Influences of one sewage sludge on degradation of Hexazinone and formation of its major metabolites were investigated in four forest soils (A, B, C and D), collected in Zhejiang Province, China. In non-amended forest soils, the degradation half-life of Hexazinone was 21.4, 30.4, 19.4 and 32.8 days in forest soil A, B, C and D, respectively. Degradation could start in soil A and C without lag period because the two soils had been contaminated by this herbicide for a long time, possibly leading to completion of acclimation period of Hexazinone-degrading bacteria. In forest soils amended with sewage sludge, the degradation rate constant increased by 17.3% in soil A, 48.2% in soil B, 8.1% in soil C and 51.6% in soil D, respectively. The higher degradation rates (soil A and C) in non-amended soils accord with the lower rate increase in sewage sludge-amended soils. Under non-sterile conditions, biological mechanism accounted for 51.8–62.4% of Hexazinone degradation in four soils. Under sterile conditions, the four soils had the similar chemical degradation capacity for Hexazinone. In non-amended soil B, only one metabolite (B) was detected, while two metabolites (B and C) were found in sewage sludge-amended soil B. Similarly situated in agricultural soils, N-demethylation at 6-position of triazine ring, hydroxylation at the 4-positon of cyclohexyl group, and removal of the dimethylamino group with formation of a carbonyl group at 6-position of triazine ring appear to be the principal mechanism involved in Hexazinone degradation in sewage sludge-amended forest soils. These data will improve understanding of the actual pollution risk as a result of forest soil fertilization with sewage sludge.
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anaerobic biodegradation of Hexazinone in four sediments
Journal of Hazardous Materials, 2009Co-Authors: Huili Wang, Chengxia Tan, Xuedong WangAbstract:Anaerobic biodegradation of Hexazinone was investigated in four sediments (L1, L2, Y1 and Y2). Results showed that the L2 sediment had the highest biodegradation potential among four sediments. However, the Y1 and Y2 sediments had no capacity to biodegrade Hexazinone. Sediments with rich total organic carbon, long-term contamination history by Hexazinone and neutral pH may have a high biodegradation potential because the former two factors can induce the growth of microorganisms responsible for biodegradation and the third factor can offer suitable conditions for biodegradation. The addition of sulfate or nitrate as electron acceptors enhanced Hexazinone degradation. As expected, the addition of electron donors (lactate, acetate or pyruvate) substantially inhibited the degradation. In natural environmental conditions, the effect of intermediate A [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)dione] on anaerobic Hexazinone degradation was negligible because of its low level.
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influence of bovine manure on dissipation of Hexazinone in soil
Ecotoxicology and Environmental Safety, 2009Co-Authors: Huili Wang, Changjiang Huang, Minghua Zhang, Xuedong WangAbstract:The effects of bovine manure (BM) on the degradation of Hexazinone and formation of three of its major metabolites were investigated in sandy loam soil. The degradation half-life of Hexazinone was 29.6 days in unamended soil, while it decreased to 21.8 days in BM-amended soil. The major metabolites formed in unamended soil were [3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1, 3H)-dione] (metabolite A) and [3-cyclohexyl-1-methyl-1,3,5-triazine-2,4,6(1, 3, 5H)-trione] (metabolite C), while metabolite B [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1, 3H)-dione] was not detected over the entire experimental period. However, in BM-amended soil, metabolite B was detected at 20 and 40 days after incubation, suggesting that BM contributed to formation of this metabolite. N-demethylation, removal of the dimethylamino group with formation of a carbonyl group at the 6-position of the triazine ring appeared to be the principal mechanisms involved in Hexazinone metabolism in unamended soil. However, hydroxylation at the 4-positon of the cyclohexyl group as well as the above two modes were the principal pathways in BM-amended soil.
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biodegradation of Hexazinone by two isolated bacterial strains wfx 1 and wfx 2
Biodegradation, 2006Co-Authors: Xuedong Wang, Huili Wang, Sumei Zhou, Shao YangAbstract:Two Hexazinone-degrading bacterial strains were isolated from soil by enrichment culture technique, and identified as Pseudomonas sp. and Enterobacter cloacap, respectively. The two purified isolates, designated as WFX-1 and WFX-2, could rapidly degrade Hexazinone with half-lives of 3.08 and 2.95 days in mineral salts medium (hereafter referred to as MSM). In contrast, their mixed bacterial culture (herein abbreviated as MBC) was found to degrade Hexazinone, at an initial concentration of 50 mg l−1, by enhancing 2.3-fold over that when the isolates were used alone. The degradation of Hexazinone by MBC in MSM clearly decreased concomitant with the increase of initial concentration, and the level of Hexazinone that was toxic enough to totally inhibit degradation was in the range of 150–200 mg l−1. The appropriately combined conditions for Hexazinone degradation by MBC in MSM were studied, and found to be pH 5.5, 30 °C and at agitation of 120 rpm. The addition of MBC to soil had a greater impact on disappearance of Hexazinone, which nearly increased fivefold over that of the control set. As a result, findings in the present investigation provide useful information for soil and water decontamination of Hexazinone.
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degradation and metabolism of Hexazinone by two isolated bacterial strains from soil
Chemosphere, 2005Co-Authors: Xuedong Wang, Huili Wang, Chengxia TanAbstract:Abstract Two Hexazinone-degrading bacterial strains were isolated from soil by enrichment culture technique, and identified as Pseudomonas sp. and Enterobacter cloacap. The two purified isolates, designated as WFX-1 and WFX-2, could rapidly degrade Hexazinone with a half-life of 3.08 days and 2.95 days in mineral salt medium (MSM), while their mixed bacterial culture was found to degrade Hexazinone, at an initial concentration of 50 μg/ml, by enhancing 2.3-fold over that when the isolates were used alone. Two microbial metabolites (A and D) were obtained by preparative TLC and identified on the basis of the spectral data of IR, 1H NMR and HPLC–ESI–MS, but both of them were known products as they had been reported in soil and vegetation metabolites of Hexazinone. However, metabolites B and C were new degradates, whose molecular weights (MW) were 157 and 156, respectively, being reported from microbial metabolism for the first time.