Flow Injection Hydride Generation Atomic Absorption Spectrometry for Determination of Arsenic in Water and Biological Samples from Arsenic-Affected Districts of West Bengal, India, and Bangladesh

Abstract

The increasing concern over human exposure to arsenic in West Bengal and Bangladesh has necessitated the development of a rapid method for determination of trace levels of arsenic in water and biological samples. We have developed a simple indigenous flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) system for the determination of arsenic in parts-per-billion levels in water and biological samples. The technique is fast, simple, and highly sensitive. The accuracy and precision of the method were evaluated by spiking known amounts of arsenic and analyzing different types of environmental and biological standard reference materials. The organic matter in a biological sample was destroyed by acid digestion and dry ashing technique. We analyzed thousands of tubewell water samples from the affected districts of West Bengal and Bangladesh. Most of the water samples contained a mixture of arsenite and arsenate and in none of them could we detect methylated arsenic. We also analyzed thousands of urine (inorganic arsenic and its metabolites), hair, and nail samples and hundreds of skin-scale and blood samples of people drinking arsenic-contaminated water and showing arsenical skin lesions. Quality control was assessed by interlaboratory analysis of hair samples. An understanding of arsenic toxicity and metabolism requires quantitation of individual arsenic species. The techniques we used for the determination and speciation of arsenic are (i) separation of arsenite and arsenate from water by sodium diethyldithiocarbamate in chloroform followed by FI-HG-AAS; (ii) determination of arsenite in citrate/citric buffer at pH 3 and total arsenic in water in 5 M HCl by FI-HG-AAS. Thus, arsenate is obtained from the difference; (iii) for analysis of inorganic arsenic and its metabolites in urine FI-HG-AAS was used after separation of the species with a combined cation-anion exchange column. Total arsenic in urine was also determined by FI-HG-AAS after acid decomposition. The species arsenite and arsenate are present in groundwater in about a 1:1 ratio and about 90% of the total arsenic in urine is present as inorganic arsenic and its metabolites.