Ashim Chowdhury

Impact of pesticides use in agriculture: their benefits and hazards

Impact of pesticides use in agriculture: their benefits and hazards

Impact of pesticides on soil microbiological parameters and possible bioremediation strategies

Intensive agriculture is spectacularly successful since last couple of decades due to the inputs viz; fertilizers and pesticides along with high yielding varieties. The mandate for agriculture development was to feed and adequate nutrition supply to the expanding population by side the agriculture would be entering to into new area of commercial and export orientation. The attention of public health and proper utilization natural resources are also the main issues related with agriculture development. Concern for pesticide contamination in the environment in the current context of pesticide use has assumed great importance [1]. The fate of the pesticides in the soil environment in respect of pest control efficacy, non-target organism exposure and offsite mobility has been given due consideration [2]. Kinetics and pathways of degradation depend on abiotic and biotic factors [6], which are specific to a particular pesticide and therefore find preference. Adverse effect of pesticidal chemicals on soil microorganisms [3], may affect soil fertility [4] becomes a foreign chemicals major issue. Soil microorganisms show an early warning about soil disturbances by foreign chemicals than any other parameters.But the fate and behavior of these chemicals in soil ecosystem is very important since they are degraded by various factors and have the potential to be in the soil, water etc. So it is indispensable to monitor the persistence, degradation of pesticides in soil and is also necessary to study the effect of pesticide on the soil quality or soil health by in depth studies on soil microbial activity.The removal of metabolites or degraded products should be removed from soil and it has now a day’s primary concern to the environmentalist. Toxicity or the contamination of pesticides can be reduced by the bioremediation process which involves the uses of microbes or plants. Either they degrade or use the pesticides by various co metabolic processes.

Photodegradation of metsulfuron methyl in aqueous solution

Metsulfuron methyl (1) was effectively degraded by ultra violet light in aqueous solution. About 50% of 1 was degraded within 15 hours. A new metabolite (2) of metsulfuron methyl was isolated and characterised along with phenyl sulfonamide (3) and an unidentified photometabolite (4). The pathway of photodegradation of metsulfuron methyl has been proposed.

Laboratory simulated dissipation of metsulfuron methyl and chlorimuron ethyl in soils and their residual fate in rice, wheat and soybean at harvest

Two sulfonylurea herbicides, metsulfuron methyl (Ally 20 WP) and chlorimuron ethyl (Classic 25 WP) were evaluated for their dissipation behaviour in alluvial, coastal saline and laterite soils under laboratory incubated condition at 60% water holding capacity of soils and 30 °C temperature was maintained. In field study herbicides were applied twice for the control of grasses, annual and perennials broad leaves weeds and sedges in rice, wheat and soybean to find out the residual fate of both the herbicides on different matrices of respective crops after harvest. Extraction and clean up methodologies for the herbicides were standardized and subsequently analyzed by HPLC. The study revealed that the half-lives of metsulfuron methyl and chlorimuron ethyl ranged from 10.75 to 13.94 d irrespective of soils and doses applied. Field trials with rice, wheat and soybean also revealed that these two herbicides could safely be recommended for application as no residues were detected in the harvest samples.

Effect of novaluron on microbial biomass, respiration, and fluorescein diacetate-hydrolyzing activity in tropical soils

The aim of this study was to assess the potential harmful effects of novaluron on soil microbiological parameters in clay loam alluvial soil (Typic udifluvent) and coastal saline soil (Typic endoaquept) under controlled laboratory tests. The applications of novaluron were made at or above the recommended rates, which includes field rate (FR), two times (2FR), and ten times (10FR) the FR. The laboratory incubation study was carried out at 60% of maximum water holding capacity of soils and at 30°C. Novaluron application rate even up to 10FR resulted in a short-lived and transitory toxic effect on soil microbial biomass C and fluorescein diacetate-hydrolyzing activity. Microbial metabolic quotient changed but for a short period. It can be concluded that novaluron had a transient and negligible harmful effect on the soil microbiological parameters studied at higher rates than those usually used in the field.

Butachlor Degradation in Tropical Soils: Effect of Application Rate, Biotic-Abiotic Interactions and Soil Conditions

The degradative characteristics of butachlor (N-Butoxymethyl-2-chloro-2′,6′-diethyla- cetanilide) were studied under controlled laboratory conditions in clay loam alluvial (AL) soil (Typic udifluvent) and coastal saline (CS) soil (Typic endoaquept) from rice cultivated fields. The application rates included field rate (FR), 2-times FR (2FR) and 10-times FR (10FR). The incubation study was carried out at 30°C with and without decomposed cow manure (DCM) at 60% of maximum water holding capacity (WHC) and waterlogged soil condition. The half-life values depended on the soil types and initial concentrations of butachlor. Butachlor degraded faster in AL soil and in soil amended with DCM under waterlogged condition. Microbial degradation is the major avenue of butachlor degradation from soils.

Imidacloprid in Processed Tea and Tea Liquor

Imidacloprid is a newly introduced broad-spectrum chloronicotinyl insecticide and will find its way in agricultural production, particularly in Asia. However, information on the fate of imidacloprid in crop plants is lacking. The degradation of imidacloprid in processed CTC tea and tea liquor was investigated in the present study in which imidacloprid was applied at recommended application rate (30.0 g a.i./ha) and twice the recommended application rate (60.0 g a.i./ha) for three consecutive seasons. Imidacloprid was rapidly dissipated in processed tea following first order reaction kinetics at all application rates and had half-lives of 0.91∼1.16 d with the residue in tea liquor found to be below detectable limit on 3rd day samples. The study revealed that imidacloprid is safe for human consumption and will not pose any residual toxicity problem.

INFLUENCE OF BIOTIC-ABIOTIC FACTORS ON THE DEGRADATION OF NOVALURON IN TROPICAL SOIL

In this study, the degradation of novaluron (benzoylphenyl urea insect growth regulator) was investigated under controlled laboratory conditions in clay loam alluvial and coastal saline soils of West Bengal, India. The application rates were field rate (FR); 2FR and 10FR. The incubation study was carried out at 30 °C and 60% of maximum water holding capacity of both the soils. Degradation of novaluron in both the soils followed first order reaction kinetics at all application rates under non-sterile and sterile conditions. The half-lives of novaluron in non-sterilized soils ranged from 17.0–17.8 days (alluvial soil) and 11.4–12.7 days (coastal saline soil), while the values in case of the sterilized soils were 53.7–59.0 days (alluvial soil) and 28.9–29.8 days (coastal saline soil) respectively. The novaluron degradation patterns were found to be highly influenced by soil types, application rates, and biotic abiotic factors. Abiotic factors strongly influenced novaluron degradation in both the soils. Biotic degradation was higher in alluvial soil compared to the coastal saline soil.

Stimulation of heterotrophic dinitrogen fixation in barley root association by the herbicide pendimethalin and its metabolic transformation by Azotobacter SPP

Abstract Pendimethalin [N-(l-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzamine] at normally applied concentrations stimulated root associated nitrogen fixation activity of young barley seedlings in a neutral alluvial loam soil, as measured by excised-root acetylene reduction assay. From 3- to 7-fold increases in excised root C2H2-reduction activity (ARA) were obtained with 3–5 kg a.i. ha−1 at 15–35 days age of seedlings. The stimulatory response declined with age of seedlings and higher concentrations of the herbicide. Root-associated aerobic and microaerophilic N2-fixing bacterial populations registered a highly significant increase corresponding to the stimulatory response of root ARA to the herbicide but not as much in soil. Isolates ofAzolobacter vinelandu and Azospirillum lipaferum obtained from herbicide-treated barley rhizosphere showed in vitro tolerance to high concentrations of the herbicide in N-free media. The Azolobacler isolate utilized pcndimethalin as a C source (o fix N2 in pure culture with equal efficiency to that with mannitol. The isolate mctabolically-degraded pendimcthalin to several products including the N-dcalkylated product. 2.6-dinitro-3,4-dimcthylbenzamine. The property of herbicide utilization for N2 fixation was also available in an A. chrootoccum isolate without prior exposure to the herbicide.

Studies on the photodegradation of pendimethalin in solvents and in Kalyani soil

Abstract In a laboratory study on the photodegradation of pendimethalin (1) in solvents and in Kalyani soil, N-propy1–3,4-dimethy1–2,6-dinitroaniline (3) has been identified as one of the photometabolite along with two other unknown photometabolites.