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STUDY OF THE FORMS OF ARSENIC IN WATER AND BOTTOM SEDIMENTS

Elena Demenchuk

Abstract

This paper presents the geochemical forms of arsenic that are present in bottom sediments of rivers and surface waters under various oxidative conditions. In summer, in the rivers with the high anthropogenic load the redox potential of bottom sediments varies from 78 mV to 255 mV (at a temperature of 16-20?C), which corresponds to oxidative and mixed oxidative-reductive conditions. It is shown that under these conditions arsenic is present in the form of insoluble arsenous acid, partially ionized arsenic acid and arsenous acid that adsorbed on hydrated iron oxide with a ratio of the forms of about 15:65:25. With rising temperature above 22?C in shallows, the redox potential can reduce to 25-60 mV due to a decrease of the dissolved oxygen content. In this conditions the content of immobile form of As (III) could increase. In winter was noticed the changing of the redox conditions toward oxidative ones (the potential value varies up to 320-340 mV), and the ratio of arsenic forms varies in the direction of increasing mobile forms As (V). The assessed value of the background concentrations of As in river bottom sediments and surface waters of the rivers which flow into Vistula (Kaliningradsky) Bay has been of about 3.5 В± 0.3 mg/kg and 2,5В±0.4 mkg/dm3 respectively.

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