Arsenic efflux from Microcystis aeruginosa under different phosphate regimes

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