Selenium speciation in waters: role of dissolved polysaccharides on the mobilization process.

The paper deals with the study of selenium speciation in a water system where antropic contribution could be relevant (Tiber river). The speciation at natural levels was determined before, inside, after the city of Rome by a previously defined method: the tetravalent state is prevalent in the anthropized zone while the highest oxidation state is predominant outside. The study of the storage effects (on a whole sample) and the distribution (fate) of the selenium contribution were also carried out. The study showed how in polluted waters the fraction of dissolved organic matter able to bind Se(IV) highly affects the mobility of selenium in the matrix. Polysaccharide species show this property, so they are be very probably responsible for the adsorption of selenium on particulate and stabilize this form against oxidation.