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 ev er been reported, are less than 0.7 mug/L. The predominant arsenic spe cies in the well waters of the BFD area is As3+ with an average As3+/A s5+ ratio of 2.6. The methyl arsenicals, monomethylarsinic acid and di methylarsonic acid, are below detection limits (<1 mug/L), and the ins oluble suspended arsenic accounts for about 3% of the total arsenic in the water. Ultrafiltration experiments indicate that the dissolved ar senic species can be roughly divided into two main groups, one with mo lecular mass <1000 and the other with molecular mass >300 000 Da. The results obtained from the BFD area are compared with similar arsenic s tudies conducted in the United States. The importance of arsenic speci ation in environmental water studies and the possible cause of BFD are discussed.