Degradation Of Metolachlor Research Articles

Persistence of metolachlor, atrazine and deethylatrazine in soil and its simulation by deterministic models

Abstract Laboratory and field experiments were carried out on a loam soil and a sandy loam soil to study the persistence of metolachlor, atrazine and deethylatrazine in soil under Spanish conditions of maize cultivation. Herbicide levels in soil were studied for about 90 days at two different soil depths: 0–10 cm and 10–20 cm. Field half‐lives varied from 23 to 57 days for atrazine and from 22 to 42 days for metolachlor in the first layer. The highest deethylatrazine level in the first layer was 8% of the initial atrazine concentration. Maximum concentration in the second layer ranged from 5% to 17% for atrazine, from 3.5% to 31% for metolachlor and from 0.75% to 4.5% for deethylatrazine, in the conditions studied. Results were compared with outputs of two versions of the simulation model LEACHMV3: LEACHP and LEACHA. Laboratory assays were performed at different conditions to determine the atrazine and metolachlor degradation rates and the formation and disappearance rate of deethylatrazine, which were used in the computer programs. LEACHP predicted the herbicide persistence in soil with reasonable accuracy in the studied fields. Values from LEACHA model were also in agreement with the experimental data for these herbicides in one field, but in the other field, under a higher irrigation, this model overestimated the residues of these herbicides in the first layer.

Environmental Behavior of Acetamide Pesticide Stereoisomers. 2. Stereo- and Enantioselective Degradation in Sewage Sludge and Soil

The degradation of five acetamide pesticides (alachlor, acetochlor, metalaxyl, metolachlor and dimethenamid) with different types of stereoisomerism (axial- and/or C-chirality) was studied in soil and sewage sludge using chiral high-resolution gas chromatography/mass spectrometry (HRGC/MS). Overall degradation rates in both media were in the order of alachlor > acetochlor > dimethenamid > metolachlor > metalaxyl. The results indicated the degradation of metalaxyl, metolachlor, and dimethenamid to be stereo- and/or enantioselective, particularily with respect to C-chirality. For acetochlor (axial-chiral), the results were inconclusive due to interference in the detection of this compound. Metalaxyl showed different enantioselectivity in the two media with the 1'S-(+)-enantiomer faster degraded in sewage sludge and the fungicidal more active 1'R-(-)-enantiomer faster degraded in soil. α-Hexachlorocyclohexane (α-HCH) and its enantioselective degradation were used as an internal control to confirm biotic action in the sewage sludge. Surface water (lakes, drainage canal) and rain contained detectable quantities (2-120 ng/L) of some of these pesticides. The peak area ratios in all but one sample (drainage canal) were close to those of the technical products, indicating little if any biological degradation.

Effects of the safeners CGA 154281, oxabetrinil and fenclorim on uptake and degradation of metolachlor in corn (Zea mays L.) seedlings

Summary. The influence of three crop safeners on the uptake and degradation of 14C‐metolachlor was investigated in two corn varieties. Following application of herbicide and safener together to seedling shoots the concentrations of non‐metabolized 14C‐metolachlor in the tissues was found to be lower in the tolerant variety LG 9 than in the susceptible variety 211A. The difference between varieties was due to differences in both uptake and degradation of 14C‐metolachlor.Following shoot application most of the radioactivity was retained in the coleoptile and the mesocotyl. Two hours after application 95% of the herbicide had been degraded in coleoptiles and mesocotyls, whereas approximately 20% of non‐metabolized 14C‐metolachlor was present in the enclosed developing shoot leaves. In both corn varieties the safener CGA 154281 caused a substantial lowering of tissue levels of parent 14C‐metolachlor. This was primarily due to an enhanced degradation. Glutalhione‐S‐transfer‐ase (GST) enzyme activity in shoot tissues was found to be enhanced in both varieties by CGA 154281. Oxabetrinil and fenclorim were less effective than CGA 154281 both in reducing tissue levels of non‐metabolized 14C‐metolachlor and in enhancing GST activity in either variety.

The Degradation and Bioactivity of Metolachlor in the Soil

In bioassays, rice (Oryza sativaL.) recovery from metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] injury tended to be slower in flooded rice, but was not significantly different from the recovery rate in a nonflooded rice. In soils treated with 1 ppm (w/w) metolachlor and incubated in constant-temperature chambers, the half-life of metolachlor was shorter at 40 C than at 30 C. The degradation rate of metolachlor was not significantly correlated with declining moisture potentials in the range of −30 to −80 kPa. The CO2evolution from metolachlor-treated soil was negatively correlated with incubation time and positively correlated to declining moisture levels. In a field study, metolachlor, as determined by bioassay, was mobile in a Taloka silt loam soil profile. After being incorporated to 7.5 cm, it became evenly distributed in the top 15 cm of the soil profile within 18 days. Metolachlor adsorption was positively correlated with clay and organic carbon content.

Degradation of Three Acetanilide Herbicides in Soil

The persistence of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and propachlor (2-chloro-N-isopropylacetanilide) in soil was examined under laboratory and field conditions using sorghum (Sorghum vulgarePers. ‘NB280S′) or annual ryegrass (Lolium multiflorumLam.) as bioassay species. In laboratory studies, degradation rate of alachlor and propachlor was greater at 50 and 80% than at 20% field capacity at 20 C. Degradation of metolachlor was greater at 80 than at 20% field capacity. Degradation rate of alachlor and metolachlor at 50% field capacity was greater at higher temperatures. Propachlor degradation rate varied with temperature. Under irrigated, cropped field conditions, the order of persistence was metolachlor > alachlor > > propachlor.

Simulation of the persistence of atrazine, linuron and metolachlor in soil at different sites in the USA

Summary:The effects of soil temperature and soil moisture content on the rates of degradation of atrazine, linuron and metolachlor were measured in the laboratory in soil from different sites in the USA. Persistence of the herbicides was measured in the same soils in the field during the summers of 1978 and 1979. Weather records from the different sites for the periods of the field experiments were used in conjunction with appropriate constants derived from the laboratory data in a computer program to simulate persistence in the field. There was a general tendency for the model to overestimate the observed soil residues. For example, with atrazine, 40 of the 48 measured residues were lower than those predicted by the model; seven were more than 30% below and two were more than 50% below. With metolachlor, 16 of the 48 measured residues were more than 30% below those predicted and six were more than 50% below; almost identical results were obtained with linuron. When the model overestimated late‐season residues by a large amount, the discrepancies between predicted and observed data were usually apparent from early in the experiment. Possible reasons for the discrepancies are discussed.