DETERMINATION OF ARSENIC(III) FOR THE INVESTIGATION OF THE MICROBIAL OXIDATION OF ARSENIC(III) TO ARSENIC(V)

Recent evaluations of acute and chronical toxicity of arsenic resulted in a reduction of the standard value for total arsenic from 40 mu g/L to 10 mu g/L in drinking water which will be valid in Germany after a transition period as from January 1996. Arsenic is well known as subs tance of deep groundwaters, mainly of geogenic origin and normally fou nd as As(III) or AS(V) As(V) is well removable by flocculation and fil tration after adding iron salts. As(III), however, has to be oxidized first to As(V). Therefore, it is important for treatment techniques to be able to distinguish between As(III) and As(V). A modified determin ation of As(III) using flow injection analysis was installed and optim ized in order to investigate whether As(III) may be oxidized to As(V) by bacteria in natural waters. The results showed that at 4 degrees C, no As(III)-oxidation was observed within 14 days. At loom temperature , however, in the bacteria-containing samples, an As(III)-oxidation wa s found starting after 3 to 7 days. After 14 days, no As(III) was left over In contrast, in the sterile samples, no As(III)oxidation could b e observed within 14 days. These results demonstrated that microbial p rocesses influence the oxidation of As(III) to As(V) in natural waters .