Culture-dependent study of arsenic-reducing bacteria in deep aquatic sediments of Bengal Delta.

Biogeochemical release of soil-bound arsenic (As) governs mobilization of the toxic metalloid into the groundwater. The present study has examined AsV-reduction ability of bacteria from anoxic aquatic sediments that might contribute to arsenic mobilization in the Bengal Delta. Arsenic-reducing bacteria from deep layers of pond sediment were enriched and isolated in anaerobic environments and AsV reduction was assessed in culture medium. The pond sediment enrichments harboured AsV-reducing bacteria belonging to the phyla Firmicutes and Proteobacteria with dominance of Paraclostridium benzoelyticum and P. bifermentans. Among total 17 isolates, the respiratory reductase genes were not detected by the most common primers and only 3 strains had arsenic reductase ArsC gene suggesting involvement of resistance and some unknown mechanisms in AsV reduction. Presence of high levels of organic matter, As, and As-reducing bacteria might make deep aquatic sediments a hot spot of As mobilization and aquifer contamination.

Ground water arsenic contamination in West Bengal, India: a risk of sub-clinical toxicity in cattle as evident by correlation between arsenic exposure, excretion and deposition.

Arsenic contamination of ground water in West Bengal, India, is a great concern for both human and livestock populations. Our study investigated and correlated the arsenic concentration in the drinking water, urinary excretion and deposition of total arsenic in hair of cattle at an arsenic contaminated zone in West Bengal. The results of our study indicated that the average concentration of arsenic in tube well water in contaminated villages ranged from 0.042 to 0.251 ppm and a statistical significant (p < 0.01) difference was seen when compared to samples from a non-contaminated zone. The arsenic concentration in urine and hair of cattle ranged between 0.245-0.691 ppm and 0.461-0.984 ppm, respectively. A close relationship was found between the total arsenic in drinking water urinary excretion (r² = 0.03664, p < 0.05) and the arsenic concentration in hair (r² = 0.03668, p < 0.05). Our findings indicate that quantification of arsenic concentration in cattle urine and hair can serve as biomarkers for both present and past exposure in cattle population.