Arsenic efflux from Microcystis aeruginosa under different phosphate regimes

Phytoplankton plays an important role in arsenic speciation, distribution, and cycling infreshwater environments. Little information, however, is available on arsenic efflux fromthe cyanobacteria Microcystis aeruginosa under different phosphate regimes. Thisstudy investigated M. aeruginosa arsenic efflux and speciation by pre-exposing it to 10μM arsenate or arsenite for 24 h during limited (12 h) and extended (13 d) depurationperiods under phosphate enriched (+P) and phosphate depleted (−P) treatments.Arsenate was the predominant species detected in algal cells throughout thedepuration period while arsenite only accounted for no greater than 45% of intracellulararsenic. During the limited depuration period, arsenic efflux occurred rapidly and onlyarsenate was detected in solutions. During the extended depuration period, however,arsenate and dimethylarsinic acid (DMA) were found to be the two predominantarsenic species detected in solutions under −P treatments, but arsenate was the onlyspecies detected under +P treatments. Experimental results also suggest thatphosphorus has a significant effect in accelerating arsenic efflux and promotingarsenite bio-oxidation in M. aeruginosa. Furthermore, phosphorus depletion canreduce arsenic efflux from algal cells as well as accelerate arsenic reduction andmethylation. These findings can contribute to our understanding of arsenicbiogeochemistry in aquatic environments and its potential environmental risks underdifferent phosphorus levels.