Laboratory experiment was conducted to understand the persistence behavior of tetraconazole in three soils of West Bengal (alluvial, red lateritic, and coastal saline) and also in water maintained at three different pH (4.0, 7.0, and 9.2) conditions. Processed soil samples (100 g) were spiked at two treatment doses: 2.5 μg/g (T 1 ) and 5.0 μg/g (T 2 ). Double distilled buffered water (200 ml) was spiked at two treatment doses: 1.0 μg/ml (T 1 ) and 2.00 μg/ml (T 2 ). The tetraconazole dissipation followed first-order reaction kinetics and the residual half-life ( T 1/2 ) values in soil were found to be in the range of 66.9–77.2 days for T 1 and 73.4–86.0 days for T 2 . The persistence increased in the order red lateritic > new alluvial > coastal saline. Interestingly, the red lateritic soil exhibited the lowest pH (5.56) and organic carbon (0.52 %) content as compared to other two soils. However, the dissipation of tetraconazole in case of water was not pH dependant. The T 1/2 values in water were in the range of 94 to 125 days. The study indicated the persistent nature of tetraconazole in soil and water.

Laboratory degradation studies were performed in water at pH 4.0, 7.0 and 9.2 using methomyl (Lannate 12.5 L) formulation at the rates of 1.0 (T1) and 2.0 (T2) µgmL-1. Water samples collected on 0 (2 h), 3, 7, 15, 30, 45, 60 and 90 days after treatments were processed for residue analysis of methomyl by HPLC equipped with Photo Diode Array Detector. In 60 days, dissipation was 84-87% at pH 4.0, 71-77% at pH 7.0, and 91-93% at pH 9.2 in both treatments showing very little effect of pH on dissipation. The half-life periods observed were 20.76 and 22.13 days at pH 4.0, 27.87 and 28.67 days at pH 7.0 and 15.84 and 16.54 days at pH 9.2 at T1 and T2 doses respectively.

Methomyl, S-methyl (EZ)-N-(methylcarbamoyloxy)thioacetimidate, is a systemic insecticide chosen for the management of shoot and fruit borer, Leucinodes orbonalis G. Codex Alimentarious Commission has proposed a maximum residue limit (MRL) of 0.2 mg kg − 1 of methomyl, and there is a need to validate this value on eggplant. First + first-order model can explain the nonlinear dissipation pattern of methomyl conveniently in comparison to first-order kinetics. The preharvest intervals (PHI) of 27.3 and 35.3 days as obtained from first + first-order model for single and double doses would bring down the methomyl residue below MRL in actual practice. The respective half-lives were 6.6 and 7.8 days. On the other hand, first-order model suggests methomyl dissipated with a half-life value around 5 days and proposed PHIs of 6.57 and 8.57 days for single and double doses, which was far from reality. Hence, five different decontamination agents were chosen for the decontamination of methomyl from eggplant. Safety factors such as theoretical maximum daily intake and maximum permissible intake were used to evaluate risk assessment to human health. A 3-day waiting period for the both doses, following conventional agricultural practice and processing factor could not ensure sufficient margin of safety. Subjecting the data to a processing factor of 60% could not bring the residues below the proposed MRL by Codex. Methomyl is not found appropriate and effective for application in eggplant. Either the proposed MRL needs to be revised or good agricultural practice involving methomyl for plant protection in eggplant cultivation is questioned.

A high-pressure thin-layer chromatography (HPTLC) method for quantitative analysis of nicotine in Nicotiana sp. was developed using a methanol extract of leaves and stems and TLC plates (silica gel 60 GF254) with spot visualization under ultraviolet (UV) light. Scanning at 235 nm in the absorption-reflection mode produced linear calibration curves in the range of 2 to 25 μg, with a correlation coefficient of 0.991. The average recovery rate was 95% (CV % 1.35). From the present study, the lower limit of detection was 0.08 μg spot−1 for the nicotine. The validity of the method was confirmed by comparing the UV spectra of the tobacco plant samples with standards within the same Rf window.

A study was conducted during November 2005-October 2006 for determining the heavy metal contamination in surface water and sediments and giving prime thrust to determine the heavy metal concentrations fish samples collected from various points of the river Ganga at different time interval. Fish samples (viz., Channa marulius and Aorichthys seengala) were analyzed for heavy metals using standard laboratory procedures by AAS method. In impact points the annual average values for Cu, Cr, Cd, Pb and Zn were 0.15, 0.04, 0.03, 0.02 and 0.29 ppm, respectively. The concentrations of heavy metals in the riverine water collected from middle point had the order Zn > Cu > Cr > Cd > Pb. The data indicated that copper was maximally accumulated in the riverine sediments whereas least annual average concentration was obtained for lead. The trend of accumulation suggested deposition was maximum for zinc and minimum for cadmium in the muscles of both fish species. Only zinc has shown some significant seasonal variation in relation to metal deposition in fish muscles (minimum in monsoon and maximum in summer). The heavy metal contamination to fish may be due to indiscriminate discharge of polluted and untreated sewage sludge to the river. The heavy metal contents in fish at some places are alarming.

Quinalphos 20 AF was applied at the rate of 500 and 1,000 g a.i. ha − 1 in cabbage for two consecutive seasons and the samples harvested at intervals of 0 (3 h after application), 2, 4, 6, 8, and 10 days interval after application. The calculated half-life values were 1.27–1.38 days and 1.12–1.24 days for cabbage heads and cropped soil, respectively. The calculated safe waiting period based on field dissipation study was 5.28–6.7 days, which indicated its persistence nature. Thus, to reduce the safe waiting period, efforts were made to decontaminate the Quinalphos residue from cabbage head by various household preparations (viz. washing, cooking, washing plus cooking, salt water dipping, dipping in boiled salt water, dipping in detergent solution, and dipping in boiled detergent solution). Statistical analysis of the data using Duncan’s multiple range test revealed that various household processing substantially reduced the residue of Quinalphos in cabbage heads in the range of 27.72–75.01% irrespective of any dose and seasons, but none were able to satisfactorily bring down the residue below the tolerance level of 0.05 mg kg − 1.

A two season (2005-2007) study on persistence of propineb (Propineb 70% WP) was undertaken in Tomato (at two locations) following the application at two doses 2.0 and 4.0 kg a.i ha -1 . More than 92% of the initial residues dissipated within 10 days after application irrespective of doses, seasons and locations. The residue was detectable up to 15 days after application. Assuming first order kinetics the half-life values varied from 2.11 to 2.64 days. The safe waiting periods of 7 days are recommended for Tomato.

A two season study (Season-I: October, 2005 January, 2006 and Season-II: October, 2006 January, 2007) on the persistence of propineb (Propineb 70% WP) was undertaken with potatoes at two different locations having two different types of soil: new alluvial and old alluvial, respectively. Two dosage rates were applied: 2.5 and 5.0 kg ai ha-1 twice with a 15-day interval. More than 94% of the initial residues of propineb in the potato tubers dissipated within 15 days after application irrespective of dose, season and location. The residue was detectable up to 20 days after the last application of the fungicide. Assuming first order kinetics, the half-life values varied from 2.59 to 3.48 days. A safe waiting period of 10 days is recommended for potatoes.

A laboratory experiment was conducted by using three herbicides, two from dinitroaniline group and one from thiocarbamate group to know their degree of downward movement (leachability) through soil columns and their contribution in ground water contamination. Soil columns were loaded with Pendimethalin, Benthiocarb and Oryzalin @ 10.0, 10.0 and 7.7 kg a.i. ha-1, respectively. After 30 days soil samples were analyzed from each segments (i.e. 0-6, 6-12, 12-18, and 18-24 and 24-30 cm) for Benthiocarb and Pendimethalin by GLC equipped with Ni63 electron capture detector (ECD) and for Oryzalin by HPLC coupled with UV-VIS detector. The results obtained in the present study reveal that the residues of the three herbicides under investigation were predominantly confined to the upper soil layer (0-6 cm). Comparatively, low mobility of these herbicides in soils could be due to strong adsorption of these chemical to soil colloids.

Impact of pesticides use in agriculture: their benefits and hazards

Chlorpyriphos 20 EC was applied at the rate of 500 g a.i. ha -1 in Cabbage heads and the samples harvested at intervals of 0 (2 hours after application), 1 and 7 days after application. The calculated half-life value and safe waiting period (8.75 and 45.29 days respectively), indicated its longer persistence. Thus, to reduce the safe waiting period, efforts were made to decontaminate the Chlorpyriphos residue from Cabbage head by various household preparations (viz. washing, cooking, washing plus cooking, salt water dipping, dipping in boiled salt water, dipping in detergent solution and dipping in boiled detergent solution). Statistical analysis of the data using Duncan´s Multiple Range Test revealed that various household processing substantially reduced the residue of Chlorpyriphos in Cabbage heads in the range of 27.89-73.32 % but none were able to satisfactorily bring down the residue below the tolerance level of 0.05 mg kg -1 .

One pre-emergent application of oryzalin 40% SC herbicide and one hoeing was found to control maximum pests of cabbage crop. By following proper date of sowing of cabbage crop and controlling the weeds, no pest including insect and diseases was observed to attack the crop. During the period of controlling weeds of cabbage crop neither insect pest nor any fungal attack was observed during the period of this study. The insects and diseases were thus below economic threshold value.

A total of 75 animals between 1.5 and 8 years old were randomly selected for the study. Of these, 57.8% were cross-bred animals and the rest were non-descript. Moreover, 61.8% of the animals under study were brought for slaughter from local sources and the rest from farm houses. Samples collected from five districts revealed contamination with traces of organochlorine pesticides (0.01–0.22 μg g − 1) and organophosphorus pesticides (0.111–0.098 μg g − 1). In general, all the raw meat samples possessed dichlorodiphenyltrichloroethane at the highest level. Contamination was highest in cow meat samples and lowest in chicken samples. No particular district-wise trend was obtained for the pesticides selected for analysis. Subsequent decontamination study revealed that cooking is the best option in reducing pesticide load in raw meat samples. Cooked chicken is the safest foodstuff for consumption.

Laboratory degradation studies were performed in water at pH 4.0, 7.0 and 9.2 using Prochloraz (450 EC) formulation at the rates of 1.0 (T-1) and 2.0 (T-2) mu g/mL. Water samples collected on 0 (2h),3,7,15,30,45,60 and 90 days after treatments were processed for residue analysis of Prochloraz by HPLC-UV detector. In 60 days, dissipation was 89.12-90.53% at pH 4.0,84.10-88.17% at pH 7.0, and 92.35-93.81% at pH 9.2 in both treatments. The results indicate that at pH 7.0 the degradation of Prochloraz was much slower as compared to other two. Among pH 4.0 and 9.2 the degradation of compound is little faster at pH 9.2. The half-life periods observed were 18.35 and 19.17 days at pH 4.0, 22.64 and 25.08 days at pH 7.0 and 15.84 and 16.63 days at pH 9.2 at T-1 and T-2 doses respectively.

A field study was carried out to investigate persistence and dissipation kinetics of Trifluralin (48 EC) applied pre emergently in Green gram (Variety T-44) @ 1 Kg ai ha-1 (T1) and 2 Kg ai ha-1 (T2) for the control of broad leaf weeds during kharif 2006. The dissipation on 90 days was around 71.56 - 64.55% in T1 and T2. Kinetics studies revealed that dissipation of Trifluralin residues followed first order kinetics. The half life values observed were 60.21 days in T1 and 75.56 days in T2. Irrespective of any dose no residues were detected in cropped soil as well as plant samples at harvest.