Development and validation of an ELISA for metolachlor mercapturate in urine
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Alachlor
Metolachlor
A study was carried out to investigate the effects of the two acetanilide herbicides alachlor and metolachlor on
microbial activities in sandy loam soil. Effects of the herbicides on CO2 evolution were monitored for 50 d in
ambient conditions. The results showed that alachlor and metolachlor generally caused an initial decrease in
CO2 release, which subsequently increased to control level after 25 d of incubation. Both herbicides exert less effect
on CO2 evolution at lower concentrations. Fungal and bacterial populations in the soil also declined in the
presence of either herbicide at higher concentrations. Phosphatase activity was generally affected in the presence
of either herbicide except in soil treated with metolachlor at 20 ppm.
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Metolachlor
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Metolachlor
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Alachlor and metolachlor are dechlorinated and transformed into their corresponding ethane sulfonic acid (ESA) metabolites in soil. In a field-disappearance study, it was shown that alachlor ESA was formed at a faster rate and at concentrations 2-4 times higher than metolachlor ESA, conforming with the observed longer disappearance half-life of metolachlor (15.5 d) in the field as compared to alachlor (8 d). Runoff data also showed higher concentrations of alachlor ESA as compared to metolachlor ESA, even though they were applied at the same levels. Data from soil cores showed transport of the ESA compounds in soil to as far down as 75-90 cm belowthe surface, at concentrations ranging from less than 0.5 microg/L to about 50 microg/L. In contrast, no parent herbicide was detected at these depths. This observation correlates with the higher log Koc values for alachlor (3.33) and metolachlor (3.01) relative to their corresponding ESA metabolites, alachlor ESA (2.26), and metolachlor ESA (2.29).
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Abstract The leaching behaviour of the herbicide acetochlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(ethoxymethyl)acetamide] was determined as compared with two congener compounds, alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide] and metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐l‐methylethyl)acetamide]. The leaching profiles of the herbicides in columns with different types of soil and their capacity factors in reverse phase HPLC were compared. An approach for preliminary characteristic of the potential for water pollution of acetochlor is presented. The herbicide is classified as a leacher in soil and its potential for contamination of ground water is comparable with those of alachlor and metolachlor.
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Experiments were conducted in a growth chamber to study alachlor and metolachlor metabolism in soil and corn and to determine if alachlor and metolachlor and their metabolites are exuded from corn roots to the growth medium. Alachlor was more readily absorbed by corn than was metolachlor. The absorption of alachlor and metolachlor was 72 and 55%, respectively, 10 d after seedling emergence (DAE). Alachlor and metolachlor were rapidly metabolized in corn, although metabolism rates were higher with metolachlor than with alachlor. Ten similar alachlor metabolites were detected in roots and shoots. In addition, two metabolites were detected only in the shoots, and one metabolite was detected only in the roots. Metolachlor metabolism in corn produced fewer metabolites than did alachlor metabolism. At 5 DAE, 10 and 9 metabolites were detected in shoots and roots, respectively. The metabolism of alachlor and metolachlor in soil showed patterns similar to the metabolism in corn but produced fewer metabolites. One unique alachlor metabolite appeared in soil but not in corn. Roots of corn seedlings treated with 14C-alachlor or 14C-metolachlor released significant amounts of radioactivity to the surrounding growth medium 5 d after treatment. Plants treated with alachlor released more radioactivity than did plants treated with metolachlor.
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Greenhouse studies were conducted to determine the effects of herbicide, herbicide rate, genetic variability, and soil moisture content on the tolerance of corn seedlings to two chloroacetanilide herbicides. Alachlor and metolachlor were applied preemergence at 2.2, 3.4, 4.5, and 6.7 kg ha -1 to 10 Great Lakes corn hybrids. Metolachlor appeared to be less injurious at the low rate and more injurious at the high rate than alachlor. Injury among the 10 hybrids tested varied significantly. Some of the hybrids appeared to tolerate alachlor more, while others tolerated metolachlor more indicating that even in a limited number of hybrids there was a spectrum of response. Six levels ranging from 8% to 22% soil moisture were evaluated for their effect on alachlor and metolachlor injury to corn seedlings. The herbicide injury ranged from no injury at the lowest soil moisture level to about 70% at the highest soil moisture level with 4.5 kg ha -1 application rate of alachlor or metolachlor.
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Abstract Field studies were conducted during 1984, 1985, and 1987 to evaluate weed control and the relative tolerance of peanuts (Arachis hypogaea) to alachlor and metolachlor when applied at rates from 2.2 to 13.4 kg ai/ha. Both single and split preemergence, and postemergence applications were included. In 1984 and 1985, neither herbicide adversely affected yields compared to a hand-weeded control. In 1987, metolachlor at a rate of 9.0 kg/ha and alachlor at 13.4 kg/ha reduced yields. Across all years, at least a two-fold safety factor existed between the maximum registered rate and the rate necessary for peanut injury. Occurrence of injury appears to be related to rainfall. Metolachlor was slightly more mobile than alachlor in soil chromatography trials, which may be a factor in its slightly greater propensity to be injurious under certain conditions of extensive leaching and/or slow peanut emergence.
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Arachis hypogaea
Acetochlor
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The transformation of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] in aquatic systems was investigated using outdoor tank mesocosms. Metolachlor and alachlor levels and their ethane sulfonic acid (ESA) and oxanillic acid breakdown products were monitored over time under five experimental treatments (each in quadruplicate). Background water conditions were identical in all treatments with each treatment differing based on the level and type(s) of herbicide present. Treatments included a no-herbicide control, 10 μg/L metolachlor, 25 μg/L metolachlor, 25 μg/L alachlor, and 25 μg/L alachlor plus 25 μg/L metolachlor in combination. The experiment was initiated by adding herbicide(s) to the units to the target concentrations; herbicide and breakdown product levels and other chemical parameters were then monitored for 85 days. In general, metolachlor half-lives were longer than alachlor half-lives under all treatments, although the differences were not statistically significant. Metolachlor half-lives (±95% confidence limits) ranged from 33.0 d (±14.1 d) to 46.2 d (±40.0 d), whereas alachlor half-lives ranged from 18.7 d (±3.5 d) to 21.0 d (±6.5 d) for different treatments. Formation patterns of ESA were similar in all treatments, whereas oxanillic acid formation differed for the two herbicides. Alachlor oxanillic acid was produced in larger quantities than metolachlor oxanillic acid and either ESA under equivalent conditions. Our results suggest that the transformation pathways for alachlor and metolachlor in aquatic systems are similar and resemble the acetochlor pathway in soils proposed by Feng (Pestic. Biochem. Physiol. 1991, 34, 136); however, the oxanillic acid branch of the pathway is favored for alachlor as compared with metolachlor.
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Acetamide
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Granular iron metal has been found to cause the reductive dechlorination of two important chloroacetanilide herbicides, alachlor and metolachlor. Aqueous solutions (113 mL) of the herbicides were contacted with 40 g of granular cast iron (CCI coarse, 40 mesh) with mild agitation at room temperature. First-order degradation rate constants were 0.12 and 0.10 h-1 for 10 mg/L solutions of alachlor and metolachlor, respectively. A two-site, rate-limited sorption and first-order degradation model was applied to both batch data sets, with excellent agreement for alachlor and fair agreement for metolachlor. The products of the reaction were chloride (84% mass balance for alachlor and 68% for metolachlor) and dechlorinated acetanilides. Supported by GC/EIMS analysis, two sequential reactions may have occurred for alachlor, hydrogenolysis of the chloroacetyl group followed by an N-dealkylation reaction. However, only one product was confirmed by GC/FID, and the mechanism for the N-dealkylation reaction is unknown. Metolachlor was found to produce one dechlorinated product consistent with hydrogenolysis. These results are encouraging, as granular iron may be used at spill sites contaminated with these herbicides and related compounds.
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Hydrogenolysis
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