Arsenic in freshwater systems: Influence of eutrophication on occurrence, distribution, speciation, and bioaccumulation

Arsenic exists in a variety of chemical forms, and microbial metabolism results in the occurrence of thermodynamically unstable arsenite (As-III) and methylarsenic compounds in freshwaters (rivers and lakes). The inorganic forms (As-V and AsIII) and the methylated forms (methylarsonic acid; MMAA(V) and dimethylarsinic acid; DMAA(V)) are the main species of As in freshwaters while the bulk of the total dissolved As is inorganic species. Although the predominant forms of methylarsenic compounds are consistently DMAA(V) followed by MMAA(V), the DMAA(III) and MMAA(III) species have also been found in freshwaters. Several observations have revealed that phytoplankton activities are responsible for the seasonal variations of methylarsenic compounds in freshwaters. Although it was unclear if the occurrences of methylarsenic compounds were from the breakdown of larger molecules or the end-products of phytoplankton biosynthesis, recent studies have revealed that less toxic As-glutathione complexes are intermediates in the biosynthesis of organoarsenic compounds by phytoplankton. Recent studies have also revealed that eutrophication plays an important role in the production, distribution, and cycling of methylarsenic compounds in freshwaters. In this review, the recent reports on the influence of eutrophication on distribution, speciation, and bioaccumulation in freshwaters are discussed. (C) 2011 Elsevier Ltd. All rights reserved.