Environ. sci. Technol. 1994, 28, 877-881
Arsenic Species in Groundwaters of the Blackfoot Disease Area, Taiwan Shun-Long Chen, Shlaan I?.Dzeng, and Mo-Hslung Yang' Institute of Nuclear Science, National Tsing Hua University, Hsinchu, Taiwan, Republic of China
Kong-Hwa Chlu, Guan-Mlng Shleh, and Chlen M. Wai' Department of Chemistry, University of Idaho, Moscow, Idaho 83843
The groundwaters collected from three wells in the Blackfootdisease (BFD) area in southwest Taiwan contain, on the average, 671 i 149 r g of total dissolved arsenic/L. The arsenic contents in the well waters of Hsinchu, a city in the northwest of the island where no BFD has ever been reported, are less than 0.7 pg/L. The predominant arsenic species in the well waters of the BFD area is As3+with an average As3+/As5+ ratio of 2.6. The methyl arsenicals, monomethylarsinic acid and dimethylarsonic acid, are below detection limits (C1 pg/L), and the insoluble suspended arsenic accounts for about 3% of the total arsenic in the water. Ultrafiltration experiments indicate that the dissolved arsenic species can be roughly divided into two main groups, one with molecular mass 300 000 Da. The results obtained from the BFD area are compared with similar arsenic studies conducted in the United States. The importance of arsenic speciation in environmental water studies and the possible cause of BFD are discussed. Introduction
Blackfoot disease (BFD) is a peripheral vascular disease found in a limited area on the southwest coast of Taiwan. The BFD area consists mainly of four villages located about 20 km north of Tainan. The symptoms of BFD start with spotted discoloration on the skin of the extremities, especially the feet. The spots change from white to brown and eventually to black, hence the name BFD. The affected skin gradually thickens, cracks, and ulcerates. Amputation of the affected extremities is often the final resort to save the BFD victims. The disease, first observed in the southwest coast area of Taiwan in the 1930s and was reported to correlate with the peaking in the 1950~1, consumption of groundwater by local inhabitants (1). Outbreak of the disease increased rapidly around 1950 when the number of deep artesian wells drilled by local villagers for drinking reached a maximum. A map of the BFD area, its geological descriptions, and early investigations of arsenic in the artesian wells of this area were reported by Tseng et al. (1). The number of patients suffering from this disease has been decreasing since 1956 after purified tap water was made available to the local dwellers. In 1975, a total of 1141 BFD patients were identified in this area (2). The cause of BFD is still unknown, but it is generally attributed to the high concentrations of arsenic found in the deep well waters (1).
According to the US.Code of Federal Regulations (CFR) published in 1992,the maximum contaminant level (MCL) of arsenic in community water systems is 0.05 mg/L (3). This is also the permissible level of arsenic in bottled water according to the CFR (4). The CFR standard is actually based on the interim MCL of arsenic in drinking water 0013-938X/94/09280877$04.50/0
0 1994 American Chemlcal Soclety
recommended by the US. Environmental Protection Agency (U.S. EPA). The U.S.EPA is in the process of revising the MCL of arsenic in drinking water, and the new MCL is expected to be lower than the interim MCL value (5). The chemical form of arsenic in drinking water is not specified by the CFR, although it is well-established that the toxicity of arsenic depends on its chemical form. Arsenic is known to exist in natural waters in different oxidation states depending on the redox environment.The trivalent inorganic species arsenite is more toxic to the biological systems than the pentavalent species arsenate (6). Organoarsenicals such as monomethylarsinic acid (MMA) and dimethylarsonic acid (DMA) also exist in the natural environments, but their toxicities are lower than the inorganic arsenic species (5). Information on the distribution of arsenic species is therefore important to assess its toxicity in drinking water. The distribution of arsenic species and other trace and minor elements in well waters of the BFD area have not been reported in the literature. This information is of fundamental importance for understanding the cause of BFD and the potential hazards of arsenic in the aquatic environment. Recently, we have conducted a systematic study of arsenic species and other minor and trace elements in the well waters of a representative village (Putai) in the BFD area in southwest Taiwan for a period of 1 year. The metal contents in the well waters of the BFD area are compared with those obtained from another city in Taiwan where no BFD case has ever been reported. Correlations between the arsenic species and other elements in the well waters and the occurrence of BFD in Taiwan are discussed. Experimental Section
Reagents. Stock solutions (1000 mg/L) of arsenite, arsenate, DMA, and MMA were prepared from sodium arsenite (E. Merck), disodium hydrogen arsenate (E. Merck), sodium dimethylarsinate trihydrate (E. Merck), and disodium methylarsonate (Chem Service), respectively, and stored at 4 "C until use. Working standards for each arsenic species (usually in the range 0.1-0.8 mg/ L) were prepared fresh daily in 0.2% (v/v) sulfuric acid solution. Stock solutions of other elements were prepared from the E. Merck Titrisol standard solutions (1.000 f 0.002 g) by diluting to 1 L with deionized water. The counterion of eluent in the pairing ion chromatography (PIC) was 5 X 10-3 M tetrabutylammonium phosphate (PIC-A, Waters) in 5% methanol solution. All acids and bases used in this work were of superpure grade (E.Merck). The NIST standard reference material SRM 1643b (trace elements in water) and the ICP multi-element standard solution from E. Merck (QC 11355) were used as the references for quality control of analytical data. Sampling and Pretreatment Procedure. Groundwater samples were collected from three deep wells in the BFD endemic district, Putai, Taiwan. These wells were Envlron. Sci. Technol., Vol. 28,
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previously used by local dwellers as sources of drinking water before tap water was made available to this area. Groundwater samples were also collected from three wells in another city Hsinchu, which is about 200 km north of Putai and is the hometown of National Tsing Hua University. No BFD case has ever been reported in the Hsinchu area. Water samples were collected from the wells of these two locations every two months for 1 year (from July 1991 to May 1992). High-density polyethylene bottles were used as containers for groundwater collection. The bottles were precleaned with 10% nitric acid and then rinsed with deionized water. The well water was allowed to run through the pumping pipe for at least 10 min prior to sample collection. One liter of the collected water was filtered through a 0.45-pm Millipore membrane immediately after collection. The water was acidified by adding 2 mL of sulfuric acid and was stored at 4 "C for arsenic speciation studies. The preservation of arsenic species in water by sulfuric acid was reported in the literature (7). Another 5 L of the water was also filtered through a 0.45pm Millipore membrane, adjusted to pH
