ARSENIC SPECIES IN GROUNDWATERS OF THE BLACKFOOT DISEASE AREA, TAIWAN

The groundwaters collected from three wells in the Blackfoot disease (BFD) area in southwest Taiwan contain, on the average, 671 +/- 149 mug 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 mug/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 (<1 mug/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 <1000 and the other 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.