Impact of eutrophication on arsenic cycling in freshwaters

• Published in: Water research (Oxford) 2019-03, Vol.150, p.191-199
• Main Authors: Tang, Ying, Zhang, Meiyi, Sun, Guoxin, Pan, Gang
• Format: Article
• Language: English
• Subjects: Arsenic metabolism functional genes; Arsenic volatilization; Harmful algae bloom; Organic matter; Sediment-water-air interfaces; X-ray absorption spectroscopy
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2018.11.046

Many arsenic-bearing freshwaters are facing with eutrophication and consequent algae-induced anoxia/hypoxia events. However, arsenic cycling in eutrophic waters and its impact on public health are poorly understood. Laboratory simulation experiments are performed in this study to investigate the effect of algal blooms on the cycling of arsenic in a sediment–water–air system. We found that the anoxia induced by the degradation of algal biomass promoted an acute arsenic (mostly As(III)) release within two days from sediment to both the water and atmosphere, and the release effluxes were proportional to the algae dosage. The reduction and methylation of arsenic were enhanced at the sediment–water interface, owing to the significant increase in arsenate reductase genes (arrA and arsC), and arsenite methyltransferase genes (arsM) caused by increased anoxia. The analysis of synchrotron-based X-ray absorption spectroscopy indicated that the concomitantly released natural organic matter (NOM) and sulfur (S) at the sediment–water interface reduced the As(III) release to a certain extent in the later reducing period of incubation, by forming As2S3 (43–51%) and As(III)-Fe-NOM (28–35%). Our results highlight the needs for the in-situ assessment of volatile arsenic in eutrophic freshwaters with its risk to human and animal health. [Display omitted] •Algal blooms degradation increases arsenic toxic impact to public health.•Organic matter is a sequestrator of arsenic in anoxic sediments.•Hypoxia/anoxia induced microbial changes contribute to arsenic speciation.•Volatile arsenic in algal water-sediment systems is assessed in-situ.