Since 1988 we have analyzed 140 150 water samples from tube wells in all 19 districts of West Bengal for arsenic; 48.1% had arsenic above 10 microg/L (WHO guideline value), 23.8% above 50 microg/L (Indian Standard) and 3.3% above 300 microg/L (concentration predicting overt arsenical skin lesions). Based on arsenic concentrations we have classified West Bengal into three zones: highly affected (9 districts mainly in eastern side of Bhagirathi River), mildly affected (5 districts in northern part) and unaffected (5 districts in western part). The estimated number of tube wells in 8 of the highly affected districts is 1.3 million, and estimated population drinking arsenic contaminated water above 10 and 50 microg/L were 9.5 and 4.2 million, respectively. In West Bengal alone, 26 million people are potentially at risk from drinking arsenic-contaminated water (above 10 microg/L). Studying information for water from different depths from 107 253 tube wells, we noted that arsenic concentration decreased with increasing depth. Measured arsenic concentration in two tube wells in Kolkata for 325 and 51 days during 2002-2005, showed 15% oscillatory movement without any long-term trend. Regional variability is dependent on sub-surface geology. In the arsenic-affected flood plain of the river Ganga, the crisis is not having too little water to satisfy our needs, it is the crisis of managing the water.

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The toxicity of nanomaterials can sometimes be attributed to photogenerated reactive oxygen species (ROS), but these ROS can also be scavenged by nanomaterials, yielding opportunities for crossover between the properties. The morphology of nanomaterials also influences such features due to defect-induced properties. Here we report morphology-induced crossover between pro-oxidant activity (ROS generation) and antioxidant activity (ROS scavenging) of MgO. To study this process in detail, we prepared three different nanostructures of MgO (nanoparticles, nanoplates, and nanorods) and characterized them by HRTEM. These three nanostructures effectively generate superoxide anions (O2 •–) and hydroxyl radicals (•OH) at higher concentrations (>500 μg/mL) but scavenge O2 •– at lower concentrations (40 μg/mL) with successful crossover at 200 μg/mL. Nanorods of MgO generate the highest levels of O2 •–, whereas nanoparticles scavenge O2 •– to the highest extent (60%). Photoluminescence studies reveal that such crossover is based on the suppression of F2+ and the evolution of F+, F2 +, and F2 3+ defect centers. The evolution of these defect centers reflects the antibacterial activity of MgO nanostructures which is initiated at 200 μg/mL against Gram-positive S. aureus ATCC 29737 and among different bacterial strains including Gram-positive B. subtilis ATCC 6633 and M. luteus ATCC 10240 and Gram-negative E. coli ATCC K88 and K. pneumoniae ATCC 10031. Nanoparticles exhibited the highest antibacterial (92%) and antibiofilm activity (17%) against B. subtilis ATCC 6633 in the dark. Interestingly, the nitrogen-centered free radical DPPH is scavenged (100%) by nanoplates due to its large surface area (342.2 m2/g) and the presence of the F2 + defect state. The concentration-dependent interaction with an antioxidant defense system (ascorbic acid (AA)) highlights nanoparticles as potent scavengers of O2 •– in the dark. Thus, our findings establish guidelines for the selection of MgO nanostructures for diverse therapeutic applications.

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Since 1988, water samples from 140,150 tubewells were analyzed for arsenic (As) in all 19 districts of West Bengal. In 9 districts, As has been found above the national standard (50 µg/L) and in 5 districts, between 10 and 50 µg/L. From Bangladesh, 50,515 tube-well water samples were analyzed from all 64 districts. Arsenic was present above 10 µg/L in 60 districts and in 50 districts, above 50 µg/L. Other than urine As speciation, 39,000 biological samples were analyzed from both patients and non-patients, 83% of the samples had As above normal level. Arsenical skin lesions were identified in 13,118 people, screening 114,841 from West Bengal and Bangladesh. About 6.1% of 5,000 children in Bangladesh and 1.7% of 14,000 in West Electronic supplementary material The online version of this article (http://dx.

The effectiveness of arsenic removal plants (ARPs) to provide safe water was evaluated based on a study of 577 ARPs out of 1900 installed in 5 arsenic-affected districts of West Bengal, India. Out of 577, 145 (25.1%) were found in defunct condition. Both raw and filtered water from 305 ARPs were analyzed for total arsenic concentration. Forty-eight ARPs were installed despite raw water arsenic concentrations below the Indian standard (50 µg/L) and in 22 cases even below the WHO guideline value (10 µg/L). Among the 264 ARPs having raw water arsenic above 50 µg/L, 140 (53.1%) and 73 (27.7%) failed to remove arsenic below the WHO guideline value and Indian standard, respectively. The highest arsenic concentration in treated water was 705 µg/L. Analysis of 217 treated water samples for iron showed that 175 (80.6%) failed to remove iron below 300 µg/L. The treated water became coloured on standing 6 to 8 h, for 191 (44.2%) ARPs and 25 (5.8%) produced bad-odoured water. Overall, the study showed that 475 (82.3%) of the ARPs were not useful. The reasons for ineffectiveness and poor performance of these ARPs include improper maintenance, sand gushing problems, a lack of user-friendliness and absence of community participation. A comparative study of ARPs in two different blocks (Domkol in Murshidabad district and Swarupnagar in North 24 Parganas) showed that 39 (80%) and 38 (95%) ARPs, respectively, were not useful. Further study in Gram Panchayet Kolsur, Deganga block, North 24 Parganas, showed that 14 (87.5%) ARPs were not useful. Proper watershed management with active participation from the villagers is urgently required for successful mitigation.

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