Abstract
Phytoplankton plays an important role in arsenic speciation, distribution, and cycling in freshwater environments. Little information, however, is available on arsenic efflux from the cyanobacteria Microcystis aeruginosa under different phosphate regimes. This study investigated M. aeruginosa arsenic efflux and speciation by pre-exposing it to 10 µM arsenate or arsenite for 24 h during limited (12 h) and extended (13 d) depuration periods under phosphate enriched (+P) and phosphate depleted (−P) treatments. Arsenate was the predominant species detected in algal cells throughout the depuration period while arsenite only accounted for no greater than 45% of intracellular arsenic. During the limited depuration period, arsenic efflux occurred rapidly and only arsenate was detected in solutions. During the extended depuration period, however, arsenate and dimethylarsinic acid (DMA) were found to be the two predominant arsenic species detected in solutions under −P treatments, but arsenate was the only species detected under +P treatments. Experimental results also suggest that phosphorus has a significant effect in accelerating arsenic efflux and promoting arsenite bio-oxidation in M. aeruginosa. Furthermore, phosphorus depletion can reduce arsenic efflux from algal cells as well as accelerate arsenic reduction and methylation. These findings can contribute to our understanding of arsenic biogeochemistry in aquatic environments and its potential environmental risks under different phosphorus levels.
Highlights
Arsenic (As), ubiquitous throughout global environments [1, 2], is toxic to multicellular organisms being a group 1 carcinogen as specified by the International Agency for Research on Cancer (IARC)
M. aeruginosa was able to recuperate under different phosphate regimes after arsenate or arsenite pre-exposure, the cyanobacteria showed a greater recovery potential in +P media than in 2P media, indicating that toxic mechanisms of arsenic at low concentrations were associated with ambient phosphorus concentrations
It should be noted that only arsenate was detected in media under +P treatments over the extended depuration period, but it was similar to what was found in 2P media over the limited depuration period
Summary
Arsenic (As), ubiquitous throughout global environments [1, 2], is toxic to multicellular organisms being a group 1 carcinogen as specified by the International Agency for Research on Cancer (IARC). Elevated arsenic concentrations in freshwater severely impact safe drinking water provisions [5, 6] but have lately raised public concern on food safety [7, 8]. Inorganic arsenic species make up the bulk of total dissolved arsenic in freshwater [9] in nonionic trivalent (arsenite) and ionic pentavalent (arsenate) forms [10]. Arsenite has a high affinity for sulfhydryl groups of the amino acid cysteine (Cys), affecting many key metabolic processes such as fatty acid metabolism and glutathione production. Arsenate is a phosphate analogue and can substitute phosphate in adenosine triphosphate (ATP), affecting cell nucleotide synthesis and energy homeostasis [11]
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