Metabolism and dissipation kinetics of a novel protoporphyrinogen IX oxidase herbicide [oxadiargyl] in various buffered aqueous system under laboratory-simulated condition.

Present investigation was carried out using two commercial products Raft (oxadiargyl 6% EC) and Topstar (oxadiargyl 80% WP) of Oxadiargyl {5-tert-butyl-3[2,4-dichloro-5-(prop-2-ynyloxy)phenyl]-1,3,4-oxadiazol-2 (3H)-one} to investigate the persistence behavior and metabolism of the herbicide in various aqueous system under different pH condition. Half-life values revealed that alkaline hydrolysis played a dominant role in hydrolytic degradation of this compound. Q-ToF micromass study with the alkaline fractions of oxadiargyl indicated the formation of five metabolites, which was further characterized from their mass fragmentation data. The nature of metabolites formed indicated that heterocyclic oxadiazoline ring cleavage was found to be the main pathway of hydrolytic transformation of oxadiargyl.

Occurrence of heavy metals in fish: a study for impact assessment in industry prone aquatic environment around Kolkata in India.

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.

Impact assessment and decontamination of pesticides from meat under different culinary processes.

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 microg g(-1)) and organophosphorus pesticides (0.111-0.098 microg 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.

Risk assessment and chemical decontamination of an oxime carbamate insecticide (methomyl) from eggplant, Solanum melongena L.

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.

Risk assessment and decontamination of Quinalphos under different culinary processes in/on cabbage.

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).

Impact assessment of pesticide residues in fish of Ganga river around Kolkata in West Bengal.

An investigation was conducted from 2001 to 2005 for determining the residual concentration of five pesticides, viz., total-HCH, total-DDT, total-Endosulfan, Dimethoate and Malathion in fish samples collected from various points of the river Ganga. Fish samples were analyzed for pesticide residues using standard laboratory procedures by GC method. It was found that total-HCH concentration remains above the MRL values for maximum number of times in comparison to four other pesticides. The pesticide contamination to fish may be due to indiscriminate discharge of polluted and untreated sewage-sludge to the river. The pesticide contents in some places are alarming. Thus proper care, maintenance, treatment and disposal of sewage water and sludge are most vital and should be the prime thrust for the nation.

Degradation dynamics and persistence of Quinolphos and Methomyl in/on Okra (Ablemoschus esculentus) fruits and cropped soil.

Dissipation of Quinalphos (Ekalux 20 AF) and Methomyl (Lannate 12.5 L) residues were studied in/on Okra (var. Pusa Sawani) fruits and cropped soil at Baruipur, West Bengal, India. The insecticides were applied at 21 days after sowing by foliar spray at the recommended and double the recommended dose (i.e. 500 and 1,000 g a.i. ha(-1) in both the cases). Four sprays were given at 15 days interval in all the cases. The initial build-up residue on Okra fruits was to the magnitude of 3.20 and 7.50 microg g(-1) for Quinalphos, 5.61 and 8.42 microg g(-1) for Methomyl at lower and higher doses respectively. The half-lives (t(1/2)) in Okra fruit were found to be 1.25-1.43 days for Quinalphos and 0.88-0.94 days for Methomyl. The safe waiting period (T(MRL)) determined were 6.7 and 5.3 days at the lower dose of Quinalphos. The corresponding waiting period for Methomyl were 5.7 and 4.9 days. Decontamination process like washing and cooking dislodged 25.50%-81.50% residue depending on insecticides and doses, whereas 20.00%-69.60% surface residue was removed by washing alone. The residues of both insecticides in soil persisted for 6-8 days depending on dose. The half-lives in soil were found to be 1.07-1.20 days for Quinalphos and 0.97-1.25 days for Methomyl.

Degradation dynamics and dissipation kinetics of an imidazole fungicide (Prochloraz) in aqueous medium of varying pH.

Laboratory degradation studies were performed in water at pH 4.0, 7.0 and 9.2 using Prochloraz (450 EC) formulation at the concentration of 1.0 (T(1)) and 2.0 (T(2)) µg/mL. Water samples collected on 0 (2 h), 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 89.1-90.5% at pH 4.0, 84.1-88.2% at pH 7.0, and 92.4-93.8% 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. Between 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, 22.6 and 25.1 days at pH 7.0 and 15.8 and 16.6 days at pH 9.2 at T(1) and T(2) doses respectively.

Vertical migration of some herbicides through undisturbed and homogenized soil columns.

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 at doses of 10.0, 10.0 and 7.7 kg/ha, respectively. After 30 days soil samples were analyzed from each segments (i.e. 0-6, 6-12, 12-18, 18-24 and 24-30 cm) for Benthiocarb and Pendimethalin by GLC equipped with Ni(63) 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.

Fate and behavior of Benthiocarb--a herbicide in transplanted paddy under East-Indian climatic condition.

A two season field experiment was conducted to study the magnitude of Benthiocarb residue in transplanted paddy field soil of plough layer (6''), beyond the plough layer (12'') as well as in harvested straw, grain and husk. Transplanted paddy fields were treated once with Benthiocarb (Saturn 50 EC) @1500 g.a.i., 2500 g.a.i. and 3000 g.a.i.ha(-1). Irrespective of any season, the initial deposits (4 h after spraying) of Benthiocarb in 6'' soil layer were found in varying range of 4.01-4.22 ppm, 5.98-6.56 ppm and 7.47-8.19 ppm at recommended (T(1)), intermediate (T(2)) and double the recommended doses (T(3)) respectively. In paddy field soil Benthiocarb residue dissipated 70% and 90% within 3 and 30 days respectively. Irrespective of any dose and season no residues were detected in 12'' soil layer as well as in straw, grain and husk samples at harvest.