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(P296) Arsenic Uptake, Metabolism and Toxicity in Tolerant and Sensitive Freshwater Microalgae.
Stauber, Jenny*,1, Levy, Jacqueline1,2, Adams, Merrin1, Kirby, Jason3, Maher, William3, Jolley, Dianne2, 1 CSIRO Centre for Advanced Analytical Chemistry, Sydney, NSW, Australia2 Department of Chemistry, University of Wollongong, Wollongong, NSW, Australia3 Science and Design, University of Canberra, Canberra, ACT, Australia
ABSTRACT- Mining activities have led to the widespread leaching of arsenic into soils, groundwaters and surface waters. Although microalgae are important components of wetland systems proposed to remediate surface waters, very little is known about the mechanisms of tolerance of microalgae to arsenic. The transformations, uptake and toxicity of arsenic in two tropical freshwater microalgae (axenic) were compared using HPLC-ICPMS. Both chlorophytes Chlorella sp. and Monoraphidium arcuatum were insensitive to As(III), with concentrations of up to 17 and 3 mg/L respectively having no effect on algal cell division rate over 72 h. Chlorella sp. was also tolerant to As(V), with a 72-h EC50 of 27 mg/L. In contrast, M. arcuatum was sensitive to As(V) (72-h EC50 of 0.2 mg/L), and sensitivity increased as the concentration of phosphate in the bioassay medium decreased. In this species, arsenate (100 g/L) was reduced to arsenite, either in the medium (to reduce arsenate uptake) or intracellularly, followed by efflux of arsenite from the cells. Some arsenite was also methylated to monomethylarsonic acid and dimethylarsinic acid, and the arsenosugar phosphate arsenoriboside was also detectable. At higher arsenate concentrations (200 g/L), this detoxicifation process was insufficient, resulting in a toxic response by M. arcuatum. Arsenate reduction was probably coupled to glutathione oxidation, leading to a lowering of the ratio of oxidised to reduced glutathione, and subsequent inhibition of cell division. In contrast, no arsenosugars were detected in the tolerant species, nor was arsenite detectable in the bioassay medium. The different pathways of arsenic detoxification in these species and arsenic transformation in a simple freshwater food chain (algae and cladocerans) were further investigated to help manage risks posed by arsenic in freshwater systems.
Key words: arsenic, microalgae, metabolism, arsenosugars
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