Kallol Bhattacharyya

Arsenic-tolerant, arsenite-oxidising bacterial strains in the contaminated soils of West Bengal, India

As biological agents represent an affordable alternative to costly metal decontamination technologies, we isolated arsenic (As) oxidising bacteria from the As-contaminated soils of West Bengal, India. These strains were closely related to various species of Bacillus and Geobacillus based on their 16S rRNA gene sequences. They were found to be hyper-resistant to both As(V) (167-400 mM) and As(III) (16-47 mM). Elevated rates of As(III) oxidation (278-1250 μM h(-1)) and arsenite oxidase activity (2.1-12.5 nM min(-1) mg(-1) protein) were observed in these isolates. Screening identified four strains as superior As-oxidisers. Among them, AMO-10 completely (100%) oxidised 30 mM of As(III) within 24 h. The presence of the aoxB gene was confirmed in the screened isolates. Phylogenetic tree construction based on the aoxB sequence revealed that two strains, AGO-S5 and AGH-02, clustered with Achromobacter and Variovorax, whereas the other two (AMO-10 and ADP-25) remained unclustered. The increased rate of As(III) oxidation by these native strains might be exploited for the remediation of As in contaminated environments. Notably, this study presents the first correlation regarding the presence of the aoxB gene and As(III) oxidation ability in Geobacillus stearothermophilus.

Arsenic toxicity in rice with special reference to speciation in Indian grain and its implication on human health.

BACKGROUND Rice is a potentially important route of human exposure to arsenic, especially in populations with rice-based diets. However, arsenic toxicity varies greatly with species. The initial purpose of the present study was to evaluate arsenic speciation in rice. RESULTS It appeared very clear from the present study that inorganic arsenic shared maximum arsenic load in rice straw while in grains it is considerably low. As species recovered from rice grain and straw are principally As(III) and As(V) with a small amount of dimethylarsenic acid (DMA) and almost non-detectable monomethylarsonic acid (MMA) and arsenobetain (AsB). Discussion of the health risk of As in rice has largely been based on its inorganic arsenic content because these species have generally been considered to be more toxic than MMA and DMA and can be directly compared to As in drinking water, assuming equal bioavailability of inorganic As in the rice matrix and in water. The maximum dietary risk of exposure to inorganic arsenic through transplanted boro paddy in the present experiment was calculated to be almost 1706% of the provisional tolerable weekly intake for an adult of 60 kg body weight. CONCLUSION As species recovered from boro rice grain and straw are principally As(III) and As(V) with a small amount of DMA and almost non-detectable MMA and AsB. Reductions in total As load through organic amendments in boro rice grain and straw samples were manifested predominately through reduced accumulations of inorganic As species [As(III) and As(V)], between which As(V) accounted for the larger share.

Retention and release isotherm of arsenic in arsenic–humic/fulvic equilibrium study

Organic fractions from farm yard manure (FYM), vermicompost, municipal sludge, mustard cake, and surface soil of West Bengal, which was arsenic (As)-contaminated, were extracted and fractionated into fulvic and humic acid (FA and HA, respectively) fractions following standard procedures. These HA and FA samples were characterized by pH-potentiometric titrations, viscometric measurements and visible spectrophotometry. The stability constant (logK) of the complexes formed by these natural with As in aqueous phase was evaluated by the ion-exchange method. The logK values suggest that the organo-As complexes were quite stable. The release isotherm of As from the HA/FA complexes extracted from vermicompost and FYM was assayed in the presence of molybdate, nitrate, phosphate, sulfate and borate. The greatest tendency to displace As from the complexes was shown by sulfate, molybdite, and nitrate.

Study of the Suitability of Selected Extractants for Determination of Plant-Available Arsenic in Some Inceptisols of West Bengal, India

A study was conducted to assess the suitability of extractants for soil-available arsenic (As) under kharif rice (MTU-7029). Ten soil samples were collected from different locations of varying topography and land-use patterns from Nonaghata-Uttarpara of West Bengal. A pot study with MTU-7029, exposed to varying levels of arsenic (0 to 90 mg kg−1 of soil), was conducted for two successive years. Eight extractants, namely sodium bicarbonate (NaHCO3), ammonium acetate (CH3COONH4), monopotassium phosphate (KH2PO4), hydrochloric acid (HCl) + sulfuric acid (H2SO4), ammonium carbonate [(NH4)2CO3], sodium hydroxide (NaOH), malic–citric acid, and ethylenediaminetetraacetic acid (EDTA), were assessed. Soil test and crop uptake correlations revealed that 0.5 M NaHCO3 was the best extractant. In a lateral study, three soils were collected from a conventional rice field of Nonaghata-Uttarpara, Gotera, and Ghentughachi of West Bengal and sequentially extracted. The results showed that the relative abundance of As fractions were in the order of water-soluble As < Ca As < Al As < amorphous Fe As < crystalline Fe As.

Arsenic contamination in sesame and possible mitigation through organic interventions in the lower Gangetic Plain of West Bengal, India.

BACKGROUND The widespread geogenic arsenic contamination of groundwater in the Gangetic Delta of West Bengal, leading to toxicities through the food chain-principally through irrigated rice-drew due attention from researchers. Oilseeds such as sesame might be a remunerative alternative to rice and can be grown with small quantities of contaminated groundwater. RESULTS The present study was conducted to explore the efficiency of organic matter in reducing arsenic accumulation in sesame. Accumulation of total arsenic in sesame seed and available arsenic in post-harvest soils varied from 0.08 to 0.58 mg kg(-1) and from 3.87 to 8.89 kg ha(-1) , respectively. The organic manures added as soil amendment significantly reduced the accumulation (concentration) of arsenic in sesame seed to a maximum extent of 65.5% (vermicompost), 50% (phosphocompost), 42% (mustard cake) and 40% (farmyard manure (FYM)) compared with the control counterpart. The risk associated with dietary exposure to arsenic-contaminated sesame oil reached a value of 15.55% of provisional tolerable weekly intake for arsenic at the maximum accumulation of arsenic in sesame oil. CONCLUSION Substantial accumulation of arsenic in the soil-plant system was found. Risks of exposure to arsenic-contaminated oil remained considerably high. Irrigation through surface water and organic amendments both significantly reduced arsenic accumulation in sesame.

Boron Fertilization in Sunflower (Helianthus annuus L.) in an Inceptisol of West Bengal, India

This study is a synthesis of information on growth, yield, and boron-use efficiency of hybrid sunflower (cultivar Aditya) in an inceptisol (Gangetic alluvium) of West Bengal, India, under varied proportions of soil and foliar-applied boron. Foliar spray of boron (B), under all circumstances, performed better than soil application of B fertilizers with regard to sunflower seed and total dry-matter yield, B uptake, and B-use efficiencies, while 0.2 percent foliar B spray was associated with greatest B recoveries, B-use efficiencies, and sunflower seed yields in the experimental years.