The speciation of arsenic in the environment is among others controlled by reduction, methylation and oxidation processes and therefore influenced by the prevailing redox conditions. In this study we have analyzed sediments taken from La Coru#xF1;a estuary in the north west of Spain. Inorganic (trivalent and pentavalent) and the organic (MMA and DMA) arsenic speciation is related to Eh, Fe and Mn load. The various of the arsenic species concentration and other parameters was analyzed at different depths in some of the sampling points. Low arsenic concentrations (1#x2013;10 #x3BC;g#xB7;g#x2013;1) were found. In spite of oxidising conditions (Eh values between 31#x2013;96 mV), most of the samples showed a higher As(V) percentage than As (III). Principal component analysis was made to see a sample groups and the results showed that speciation depends on reducing conditions (Eh and Mn).
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