Abstract
The biotransformation and detoxification mechanisms of arsenic (As) species have been active research topics because of their significance to environmental and human health. Biotransformation of As in phytoplankton has been extensively studied. However, how different growth phases of phytoplankton impact As biotransformation in them remains uncertain. This study investigated the biotransformation of As species in freshwater phytoplankton at different growth phases to ascertain at which growth phase different types of biotransformation occur. At the logarithmic growth phase, arsenate (AsV) (>90%) and arsenite (AsIII) (>80%) predominated in culture media when phytoplankton were exposed to 20 nmol L−1 and 1.0 µmol L−1 of AsV, respectively, and methylarsenic (methylAs) species were not detected in them at all. Intracellular As was mainly present in inorganic forms (iAs) at the logarithmic phase, while substantial amounts of organoarsenic (orgAs) species were detected at the stationary phase. At the stationary phase, AsV comprised the majority of the total As in culture media, followed by AsIII and methylAs, although the methylation of AsV occurred slowly at the stationary phase. Biotransformation of AsV into AsIII and As methylation inside phytoplankton cells occurred mainly at the logarithmic phase, while the biotransformation of As into complex orgAs compounds occurred at the stationary phase. Phytoplankton rapidly released iAs and methylAs species out of their cells at the logarithmic phase, while orgAs mostly remained inside their cells.
Highlights
The biotransformation and detoxification mechanisms of arsenic (As) species have been active research topics because of their significance to environmental and human health
The freshwater phytoplankton S. actus and P. duplex were quite resistant to arsenic trioxide (AsIII) toxicity, even at high concentrations (Fig. 1c,e)
These results indicate that AsV and AsIII have different levels of toxicity to different types of freshwater phytoplankton
Summary
The biotransformation and detoxification mechanisms of arsenic (As) species have been active research topics because of their significance to environmental and human health. Biotransformation of AsV into AsIII and As methylation inside phytoplankton cells occurred mainly at the logarithmic phase, while the biotransformation of As into complex orgAs compounds occurred at the stationary phase. The biotransformation of AsV into AsIII and its subsequent methylation to form methylAs species in phytoplankton has been reported in many previous studies[19,20,21,22,23]. At the stationary bloom phase, when growth is limited by limited nutrient availability, the rates of As uptake and metabolism in phytoplankton were slow, which allowed for the further biotransformation of the pentavalent AsV into the trivalent AsIII and its subsequent methylation to DMAA to occur[17]. The diversity in the biotransformation of and behavioral responses to As species by phytoplankton at different growth phases were reported in this study
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