Redox conditions and nutrients affect the mobility of arsenic in coastal sediments

In this study, the effects of redox conditions, nitrogen (NH4+-N and NO3--N) and phosphate in the overlying water on the release of arsenic (As) in coastal sediments were investigated. The results indicated that the release of As under anaerobic conditions presented a release-dynamic equilibrium pattern. The reduction of arsenate (As(V)) to arsenite (As(III)) under anaerobic conditions was the main factor promoting the release of As. The reductive dissolution of Fe(III) oxides contributed very limited to the release; the release-remove-release pattern was observed under aerobic conditions. Although Fe(III) oxides has strong adsorption capacity for As, sulfide oxidation may be a source of As, which may continuously release As under aerobic conditions. In addition, low concentration (< 6 mg L-1) of nitrogen may stimulate anaerobic metabolism of microorganisms, resulting in reduction and dissolution of As. The low pH of high concentration (> 6 mg L-1) of nitrogen may affect the microbial community and thus decreased the concentration of As. Since the reduction of Fe(III) oxides decreased the adsorption sites, the competitive adsorption of phosphate had no significant effect on the release of As under anaerobic conditions. Totally, this study provides a new understanding of the behavior of As in coastal sediments under variable environments.

Automated summary

This study investigated the release of arsenic (As) in coastal sediments and its relationship with redox conditions, nitrogen, and phosphate in the overlying water. Under anaerobic conditions, As release showed a release-dynamic equilibrium pattern, mainly due to the reduction of As(V) to As(III). Under aerobic conditions, a release-remove-release pattern was observed. Nitrogen concentration affected anaerobic metabolism of microorganisms and the reduction of Fe(III) oxides, while phosphate had limited effect on As release.