Ganga-Meghna-Bramhaputra basin is one of the major arsenic-contaminated hotspot in the world. To assess the level of severity of arsenic contamination, concentrations of arsenic in irrigation water, soil, rice, wheat, common vegetables, and pulses, intensively cultivated and consumed by the people of highly arsenic affected Nadia district, West Bengal, India, were investigated. Results revealed that the arsenic-contaminated irrigation water (0.318-0.643 mg l -1 ) and soil (5.70-9.71 mg kg -1 ) considerably influenced in the accumulation of arsenic in rice, pulses, and vegetables in the study area. Arsenic concentrations of irrigation water samples were many folds higher than the WHO recommended permissible limit for drinking water (0.01 mg l -1 ) and FAO permissible limit for irrigation water (0.10 mg l -1 ). But, the levels of arsenic in soil were lower than the reported global average of 10.0 mg kg -1 and was much below the EU recommended maximum acceptable limit for agricultural soil (20.0 mg kg -1 ). The total arsenic concentrations in the studied samples ranged from <0.0003 to 1.02 mg kg -1 . The highest and lowest mean arsenic concentrations (milligrams per kilogram) were found in potato (0.654) and in turmeric (0.003), respectively. Higher mean arsenic concentrations (milligrams per kilogram) were observed in Boro rice grain (0.451), arum (0.407), amaranth (0.372), radish (0.344), Aman rice grain (0.334), lady's finger (0.301), cauliflower (0.293), and Brinjal (0.279). Apart from a few potato samples, arsenic concentrations in the studied crop samples, including rice grain samples were found not to exceed the food hygiene concentration limit (1.0 mg kg -1 ). Thus, the present study reveals that rice, wheat, vegetables, and pulses grown in the study area are safe for consumption, for now. But, the arsenic accumulation in the crops should be monitored periodically as the level of arsenic toxicity in the study area is increasing day by day.

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The presence of arsenic in irrigation water and in paddy field soil were investigated to assess the accumulation of arsenic and its distribution in the various parts (root, straw, husk, and grain) of rice plant from an arsenic effected area of West Bengal. Results showed that the level of arsenic in irrigation water (0.05-0.70 mg l -1 ) was much above the WHO recommended arsenic limit of 0.01 mg l -1 for drinking water. The paddy soil gets contaminated from the irrigation water and thus enhancing the bioaccumulation of arsenic in rice plants. The total soil arsenic concentrations ranged from 1.34 to 14.09 mg kg -1 . Soil organic carbon showed positive correlation with arsenic accumulation in rice plant, while soil pH showed strong negative correlation. Higher accumulation of arsenic was noticed in the root (6.92 ± 0.241-28.63 ± 0.225 mg kg -1 ) as compared to the straw (1.18 ± 0.002-2.13 ± 0.009 mg kg -1 ), husk (0.40 ± 0.004-1.05 ± 0.006 mg kg -1 ), and grain (0.16 ± 0.001-0.58 ± 0.003 mg kg -1 ) parts of the rice plant. However, the accumulation of arsenic in the rice grain of all the studied samples was found to be between 0.16 ± 0.001 and 0.58 ± 0.003 mg kg -1 dry weights of arsenic, which did not exceed the permissible limit in rice (1.0 mg kg -1 according to WHO recommendation). Two rice plant varieties, one high yielding (Red Minikit) and another local (Megi) had been chosen for the study of arsenic translocation. Higher translocation of arsenic was seen in the high yielding variety (0.194-0.393) compared to that by the local rice variety (0.099-0.161). An appreciable high efficiency in translocation of arsenic from shoot to grain (0.099-0.393) was observed in both the rice varieties compared to the translocation from root to shoot (0.040-0.108).

Spent pot liner (SPL), a hazardous solid waste produced at cell houses of aluminum smelters, is a potential source of fluoride pollution. Leachates collected from SPL disposal sites were found to contain fluoride at considerable concentration levels (up to 575 mgIL). This paper reports a study of selective fluoride removal following laboratory-prepared, ion-exchange treatment. Spent pot liner leachates were pretreated with lime to bring the fluoride level down to approximately 10 mgIL for economic and effective working of the ion exchanger. The detailed ion-exchange treatment study for removal of fluoride was carried out on synthetic SPL leachates and the optimum treatment thus developed was applied on natural SPL leachates.Bench-scale studies were carried out at various flow rates and pHs and in the presence of other ions commonly available in the SPL leachates. The prepared exchanger reduced the level of fluoride from approximately 10 mglL to less than I mgIL. Results indicate that the extraction was 100% up to 6-mUmin flow rate through the ion exchanger and it works efficiently in the pH range of 7 to 10. There is no effect of the other ions present in leachates on removal of fluoride. The exchanger has good capacity to exchange and can be recharged by eluting fluoride sorbed on the exchanger using two molar hydrochloric acid. Water Environ. Res., 71,36 (1999).

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Microorganisms influence the fate of metals in environment. Increasing anthropogenic and geogenic activity had increase the risk of arsenic pollution and this has forced the future research area to involve microbes-metal toxicity to achieve bioremediation. The present study deals with the role of arsenite transforming bacteria and incorporates them into remediation design. Sample was collected from Haringhata in Nadia district which is a known arsenic contaminated zone. Out of six isolated bacteria one bacterium revealed as arsenic tolerant bacteria which shows molecular similarity with Brevibacillus brevis from 16s rRNA studies. It can tolerate upto 1000 mg/L of arsenite and 500 mg/L of arsenate. Both the arsenic species has toxic effects on its protein concentration. The strains can tolerate upto a certain limit after that their growth ceased. This strain can accumulate and also transform arsenite to arsenate. The transformation capacity of strain was assessed qualitatively and quantitatively. The strain can transform 90% of arsenite to arsenate. But the transformation capacity only reveals as detoxification mechanism and has no relation with their respiration. Morphological biochemical and molecular identification was done. As arsenate is absorbed into iron oxyhydroxides and get immobilize thus a remediation mechanism can be designed with this strain.

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The study examined the impact of raking and fish bioturbation on modulating phosphorus (P) concentrations in the water and sediment under different trophic conditions. An outdoor experiment was set to monitor physicochemical and microbiological parameters of water and sediment influencing P diagenesis. A pilot study with radioactive P was also performed under the agency of raking and bacteria (Bacillus sp.). Raking was more effective in release of P under unfertilized conditions by significantly enhancing orthophosphate (35%) and soluble reactive phosphate (31.8%) over respective controls. Bioturbation increased total and available P in sediments significantly as compared to control. The rates of increase were higher in the unfertilized conditions (17.6-28.4% for total P and 12.2 to 23.2% for available P) than the fertilized ones (6.5-12.4% for total P and 9.1 to 15% for available P). The combined effects of raking and bioturbation on orthophosphate and soluble reactive phosphate were also stronger under unfertilized state (54.5 and 81.8%) than fertilized ones (50 and 70%). The tracer signature showed that coupled action of introduced bacteria and repeated raking resulted in 59.2, 23 and 16% higher counts of radioactive P than the treatments receiving raking once, repeated raking and bacteria inoculation, respectively. Raking alone or in sync with bioturbation exerted pronounced impact on P diagenesis through induction of coupled mineralization and nutrient release. It has significant implication for performing regular raking of fish-farm sediments and manipulation of bottom-grazing fish to regulate mineralization of organic matter and release of obnoxious gases from the system. Further, they synergistically can enhance the buffering capacity against organic overload and help to maintain aquatic ecosystem health.