Arsenic Distribution in Arsenic rich Austrian Soils

Abstract

Arsenic rich soil was collected from Gasen, a village in south eastern Austria which lies along the Strassegg electrum-arsenopyrite vein-type mineralization, and a portion of this soil was flooded in a small lysimeter. Sequential leach experiment has been conducted on the two month flooded soil (FLS) and on the `field received´ soil (FRS) in order to investigate the variation in the distribution of arsenic among the various soil fractions with a change in the soil Eh and pH. The uptake of arsenic by plants grown on the soil (Dactylis glomerata, Anthoxantum odoratum, Plantago lanceolata and Tataxacum officinale) has also been evaluated by collecting samples from various spots and determining the total arsenic content . The data indicated that in spite of the high level (~ 3000 ppm) of arsenic in Gasen it was tightly bound to the soil and not amenable to dissolution as evidenced by the necessity of stronger extractants to remove the greater proportion of the element. At the end of a two month flooding period, the Eh of the soil was observed to decrease to -14 mV from an initial value of 313 mV and the pH increased from 5.01 to 6.40. This lowering in the Eh and the increase in the pH caused an increase in the level of arsenic in the soil water of the FLS about 45 fold than in the soil water collected from the FRS. The water soluble and exchangeable forms in the FRS, generally considered to be the most mobile and immediately bio-available, accounted for only about 0.5% of the total arsenic. The total arsenic level in the plant samples was observed to be comparatively low. The mean value was 1.7 mg kg-1 and the highest values were in the 3 mg kg-1 range; where this accounted for 9% of the overall determinations. The level of arsenic in samples collected along the mineralization vein, where the soil arsenic content is high, was relatively lower than in samples collected away from the vein. Moreover, there was no observable toxic effect on the plants grown in the area.