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Arsenic transformation in marine macroalgae Granchinho, Sophia Catarina Reineke

Abstract

A high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) system was utilized for the determination of arsenate (As(V)), arsenite (As(III)), monomethylarsonate (MMA), dimethylarsinate (DMA) and arsenosugars X - XIII. In marine algae and in a marine fungus, the system was used to study pathways for the biotransformation of arsenicals. Fucus gardneri, Nereocystis luetkeana and Fusarium oxysporum melonis were grown in media enriched with arsenicals. Arsenosugars in the algae were identified by comparing the retention times with the organoarsenic compounds previously identified in oyster tissue standard reference material (NIST-1566a) and Fucus sample standard (IAEA-140/TM). Two HPLC columns and two mobile phase conditions were used. Arsenate, when added to Fucus gardneri under different environmental conditions, was reduced to As(III) and methylated to DMA and several different arsenosugars. The amount of arsenic species varied depending on the environmental condition. High levels of salinity and high levels of phosphate resulted in lower amounts of the arsenic species compared to low levels of salinity and phosphate. The presence or absence of antibiotics in the medium did not result in any major changes in the amount of arsenic species produced. This may indicate that the presence of more complex arsenicals in environmental algae samples is dependent on symbiotic interactions between the algae and its surroundings, rather than resulting from independent synthesis by the algae. The bull kelp Nereocystis luetkeana reduced and methylated As(V) to DMA. Significant amounts of more complex arsenic species, such as arsenosugars, were not observed in the cells or medium. The bioaccumulation and biomethylation of arsenic species by Nereocystis was found to be different than Fucus gardneri. The Fusarium fungus, which grows with Fucus gardneri in a parasitic relationship produces arsenite and DMA when incubated with arsenate. The amounts, however, were about 1000 times lower than produced by Fucus. Water soluble arsenic species were determined in a variety of marine algae collected from two sampling areas in British Columbia. Arsenate, MMA and arsenosugars X , XII and XIII were the predominant species extracted from the samples. The total arsenic content was determined by ICP-MS and the water content was determined by freeze-drying for all the samples collected. It was found that the kelp samples contained the highest amounts of total arsenic as well as the highest water content. The extraction efficiency varied between samples.

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