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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 ...

The Ogosta Valley downstream the town of Chiprovtsi, NW Bulgaria, was subject to long-lasting contamination with arsenic and other toxic elements due to mining and ore-processing activities in the second half of the last century. Although the exploitation of lead-silver and iron ores was ceased in the end of the 90`s, the soil in particular sections of the Ogosta?s river floodplain remained highly contaminated with arsenic, lead and other heavy metals. Arsenic mobilization and transport in the vadose zone is highl...