In this work, modification of zeolite-A was performed by ion exchange method using copper salts and the copper exchanged zeolite (CEZ) was used for removal of Arsenic (III) and Arsenic (V) from water. The adsorption capacity of zeolite-A was significantly improved after modification by copper. CEZ removes more than 98% of both As (III) and As (V) from monocomponent solutions. The material was characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD pattern shows loss in crystalline structure after copper incorporation which is evident from the decrease in intensity of characteristic peaks of zeolite-A. SEM images shows that cubical morphology characteristic of zeolite-A has been distorted after copper incorporation. Various isotherm and kinetic models were used to determine adsorption and kinetic parameters and to delineate the probable mechanism of adsorption. The data revealed that adsorption of arsenic on CEZ followed Langmuir model with maximum sorption capacity of 1.37 and 1.48 mg/g at 30 C for As (III) and As (V), respectively. CEZ effectively removes arsenic from water at wide pH range of 3-10 and in the presence of interfering ions namely phosphate, sulfate, nitrate, carbonate, and bicarbonate which is evident from tap water study. CEZ appears to be a promising adsorbent for removing arsenic from water. The water quality after treatment with CEZ also confirms that it is safe for drinking purpose and within the permissible limits as per World Health Organization guideline values and Indian drinking water standards.

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Elevated arsenic concentration in the environment and agricultural soil is a serious concern to crop production and human health. Among different detoxification mechanisms, the methylation of arsenic is a widespread phenomenon in nature. A number of microorganisms are able to methylate arsenic, but less is known about the arsenic metabolism in fungi. We identified a novel arsenic methyltransferase (WaarsM) gene from a soil fungus, Westerdykella aurantiaca. WaarsM showed sequence homology with all known arsenic methyltransferases having three conserved SAM binding motifs. The expression of WaarsM enhanced arsenic resistance in E. coli (Δars) and S. cerevisiae (Δacr2) strains by biomethylation and required endogenous reductants, preferably GSH, for methyltransferase activity. The purified WaarsM catalyzes the production of methylated arsenicals from both AsIII and AsV, and also displays AsV reductase activity. It displayed higher methyltransferase activity and lower KM 0.1945 ± 0.021 mM and KM 0.4034 ± 0.078 mM for AsIII and AsV, respectively. S. cerevisiae (Δacr2) cells expressing WaarsM produced 2.2 ppm volatile arsenic and 0.64 ppm DMA(v) with 0.58 ppm volatile arsenicals when exposed to 20 ppm AsV and 2 ppm AsIII, respectively. Arsenic tolerance in rice after co-culture with genetically engineered yeast suggested its potential role in arsenic bioremediation. Thus, characterization of WaarsM provides a potential strategy to reduce arsenic concentration in soil with reduced arsenic accumulation in crops grown in arsenic contaminated areas, and thereby alleviating human health risks.

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