Axenic cultures of the microalgae species, Dunaliella tertiolecta and Phaeodactylum tricornutum were grown at arsenic (As) concentrations typically found in uncontaminated marine environments (∼2 µg L−1) under different phosphorus concentrations. D. tertiolecta accumulated higher arsenic concentrations (mean: 13.7±0.7 µg g−1 dry mass) than P. tricornutum (mean: 1.9±0.2 µg g−1 dry mass). Media phosphorus concentrations (0.6–3 mg/L) had little influence on microalgae growth rates or arsenic accumulation. Arsenic was present as lipid bound (29–38%; 4.2–9.5%), water-soluble (20–29%; 26–34%) and residue bound (41–45%; 57–69%) arsenic species in D. tertiolecta and P. tricornutum respectively. Hydrolysed lipids contained mostly glycerol arsenoribose (OH- ribose), dimethylarsinate (DMA) and inorganic arsenic (As(V)) moieties. Water-soluble species of microalgae were very different. D. tertiolecta contained inorganic arsenic (54–86%) with variable amounts of DMA (7.4–20%), arsenoriboses (5–25%) and traces of methylarsonate (MA) (∼1%). P. tricornutum contained mostly DMA (32–56%) and phosphate arsenoribose (PO4-ribose, 23–49%) and small amounts of OH-ribose (3.8–6.5%) and As(V) (9–16%). Both microalgae contained an unknown cationic arsenic species. The residue fractions of both microalgae contained predominately inorganic arsenic (99–100%). These results show that at natural seawater arsenic concentrations, both algae take up substantial amounts of inorganic arsenic that is complexed with structural elements or sequestered in vacuoles as stable complexes. A significant portion is also incorporated into lipids. Arsenic is metabolised to simple methylated species and arsenoriboses.

The cycling of arsenic in marine inter-tidal and estuarine algae was examined by measuring total arsenic concentrations and arsenic species in marine inter-tidal and estuarine algae from the south-east coast, NSW, Australia. A range of elements required for metabolism in photosynthetic organisms were also measured to determine if any relationship between these elements and arsenic concentrations occurred. Total arsenic concentrations varied between classes of algae: red macro algae, 4.3–24.7 µg g−1; green macro algae, 8.0–11.0 µg g−1; and blue green algae, 10.4–18.4 µg g−1. No significant relationships were found between arsenic concentrations and concentrations of iron, cobalt, copper, manganese, molybdenum, magnesium, phosphorus and zinc. Distinct differences between algal classes were found for the proportion of arsenic species present in the lipid and water-soluble fractions, with green algae having a higher proportion of arsenic in lipids (19–44%) than red inter-tidal (5–34%) or estuarine algae (10–24%). Acid hydrolysis of lipid extracts revealed dimethyl arsenic, glycerol arsenoribose and two unknown cation based arsenolipids. Within water-soluble extracts, red macro algae and blue green algae contained a greater proportion of arsenic as inorganic and simple methylated arsenic species compared with green macro algae, which contained predominantly glycerol arsenoribose. Arsenobetaine, arsenocholine and tetramethyl arsonium ion were also present in some water-soluble extracts, but are not normally identified with algae and are probably due to the presence of attached microscopic epiphytes. Residue extracts contained predominantly inorganic arsenic, most likely associated with insoluble constituents of the cell. Marine algae contained lipids with arsenic moieties that may be precursors for arsenobetaine. Specifically, the presence of dimethylated arsenoribose-based arsenolipids can transform to arsenobetaine via intermediates previously identified in marine organisms. Copyright © 2007 John Wiley & Sons, Ltd.

The leaves of four angiosperm species, the mangrove Avicennia marina , the samphire Sarcocornia quinqueflora , the seablight Suaeda australis and the seagrass Posidonia australis , were sampled from three locations from the south-east coast of NSW. Mean total arsenic concentrations (mean ± SD) in dry mass for all locations were A. marina (0.38 ± 0.18 to 1.2 ± 0.7 µg g −1 ), S. quinqueflora (0.13 ± 0.06 to 0.46 ± 0.22 µg g −1 ), S. australis (0.03 ± 0.06 to 0.05 ± 0.03 µg g −1 ) and P. australis (0.34 ± 0.10 to 0.65 ± 0.26 µg g −1 ). Arsenic concentrations were significantly different between species and locations but were consistently low compared with marine macroalgae species. Significant relationships were found between arsenic and iron concentrations for A. marina, S. quinqueflora and P. australis and a negative relationship between arsenic and zinc concentrations for S. quinqueflora . No relationship between arsenic and phosphorus concentrations was found in this study. Angiosperms contained predominantly inorganic arsenic in the water-extractable and residue fractions with minor concentrations of DMA in the water-soluble fraction. P. australis also contained dimethylated glycerol and phosphate arsenoriboses. The presence of arsenobetaine, arsenocholine, trimethylated glycerol arsonioribose and an unknown cation in P. australis is most likely due to the presence of epiphytes on fronds. There is no evidence to suggest that angiosperms produce arsenobetaine as arsenic is mostly present as inorganic arsenic. In conclusion, marine angiosperms only accumulate low arsenic concentrations and uptake appears to be dependent on iron uptake but not phosphorus uptake. Marine angiosperms mainly cycle inorganic arsenic with little biomethylation of arsenic occurring. Copyright © 2007 John Wiley & Sons, Ltd.