Metabolism of metolachlor by fungal cultures.

Metabolism of metolachlor was studied using a mixed fungal culture isolated from a metolachlor-acclimated field soil. The culture rapidly degraded metolachlor with a half-life of 3.5 days in broth. Aspergillus flavus and A. terricola purified from the mixed culture also metabolized metolachlor effectively. Five metabolites obtained were identified by co-chromatography on HPLC by comparing with authentic standards and by GC-MS. Hydrolytic dechlorination, N-dealkylation, and amide bond cleavage appeared to be the dominant transformations involved in the metabolism. Metabolites, 6-methyl 2-ethyl acetanilide and 6-methyl 2-ethyl aniline, identified in this study are new metabolites of metolachlor being reported from any mixed or pure microbial cultures. The mixed culture could degrade 99% of metolachlor at a fortification level as high as 100 microg mL(-)(1).

Identification of impurities in technical anilofos and their effect on transplanted rice.

Seven impurities, namely, isopropylaniline (III), isopropylacetanilide (V), isopropylchloroacetanilide (VII), oxoanalogue (VIII), dithiodimer (IX), monothiodimer (X), and mercaptoacetanilide (XI), have been identified from technical anilofos. The quantification of each impurity was carried out by comparison with authentic samples of known concentration by GC and HPLC. The structure of authentic samples (synthesized and isolated) was established on the basis of NMR, IR, and MS spectral data. Bioassay of all the detected impurities along with three possible contaminants was carried out on transplanted rice under laboratory conditions. The oxo compound (VIII) was found to have an inhibitory effect on transplanted rice at 1 microg/g of soil.

Metolachlor persistence in laboratory and field soils under Indian tropical conditions.

Metolachlor [2-chloro-N-(2-methoxy-1-methylethyl)-2'-ethyl-6'- methyl acetanilide] dissipation under both field and laboratory conditions were studied during summer season in an Indian soil. Metolachlor was found to have moderate persistence with a half-life of 27 days in field. The herbicide got leached down to 15-30 cm soil layer and residues were found up to harvest day of the sunflower crop in both 0-15 cm and 15-30 cm soil layers. Metolachlor was found to be more persistent in laboratory studies conducted for 190 days. The rate of degradation was faster in soil under flooded partial anaerobic conditions as compared to aerobic soil with a half-life of 44.3 days. In aerobic soil, metolachlor was very stable with only 49% dissipation in 130 days. Residues remained in both the soils up to the end of the experimental period of 190 days.

Analysis of flufenacet in soil, wheat grain and straw by gas chromatography.

An analytical procedure for detecting residues of a new herbicide, flufenacet, in soil, wheat grain and straw by gas chromatographic method using various solvents and extraction methods was standardized. The best results were obtained when samples fortified with flufenacet and were extracted with acetone-0.2 M HCl (95:5) using a horizontal shaker for soil and Soxhlet extractor for plant samples. The clean up was done by partitioning with dichloromethane. The GC equipped with an electron-capture detector and a column packing of HP-1 as stationary phase and nitrogen as a carrier gas at a flow-rate of 15 ml min(-1) was used. Temperatures of oven, injector and detector were adjusted at 190, 210 and 270 degrees C, respectively. The retention time of flufenacet was 2.07 min. The herbicide recoveries ranged between 81 to 100% from the three matrices.

New gas chromatographic method for residue determination of dithiopyr in soil, wheat grain and straw.

A gas chromatographic method has been developed for a new pyridine herbicide, dithiopyr, utilising an electron capture detector. The method makes use of a column (10 m x 0.534 mm I.D.; 1 microm film thickness) containing HP-1 with nitrogen as a carrier gas at a flow rate of 15 ml min(-1) at temperatures of 190, 210, 270 degrees C for oven, injector port and detector, respectively. Soil, wheat grain and straw samples fortified with dithiopyr were extracted with acetone-0.2 M HCl (95:5) and cleaned up by partitioning with hexane. The technique has a sensitivity of 0.05 microg ml(-1) and the recovery of dithiopyr from soil, wheat grain and straw ranged between 80 and 99%.

Gas chromatographic analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans.

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans are toxic compounds formed during natural processes and human activities. The extraction and clean-up for these compounds from various environmental and biological sources has been described. The gas chromatographic analysis of polychlorinated dibenzo dioxins/furans with different columns and detectors has been reviewed. The advantages of using a mass detector in the analysis are discussed.

Organochlorine insecticide residues in agricultural soils of the indo-gangetic plain.

Multiple residues of organochlorine insecticides were monitored in the agricultural fields near Farrukhabad in the vicinity of the River Ganga in northern India for one year (1991-1992). Almost all soil samples were found to be contaminated with residues of hexachlorocylohexane (HCH) and dichlorodiphenyl-trichloroethane (DDT). Residues of aldrin and endosulfan were also detected in a large number of samples. Heptachlor residues were scarcely detected. Alpha-HCH, pp'-DDT and alpha-endosulfan were found to dominate over the other isomers/metabolites of HCH, DDT and endosulfan, respectively. The average concentration of dieldrin was more than that of aldrin. The concentrations of residues progressively increased up to a depth of 1 m.

Microbial degradation of pendimethalin.

Microbial degradation of pendimethalin (N-(1-Ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline) in vitro was studied. Fusarium oxysporum and Paecilomyces varioti, two soil fungi, in culture media degraded pendimethalin to two metabolites namely N-(1-Ethylpropyl)-3, 4-dimethyl-2-nitrobenzene-1, 6-diamine (II) and 3,4-Dimethyl-2, 6-dinitroaniline (IV). Rhizoctonia bataticola, another soil fungus, decomposed pendimethalin yielding only the latter metabolite (IV). Fungal decomposition of pendimethalin involved nitro reduction and dealkylation.