Occurrence and chemical form of arsenic in marine macroalgae from the east coast of Australia

Arsenic concentrations were measured in thirteen macroalgal species from Sydney, Australia. Brown macroalgae contained, on average, more arsenic (range, mean ± s.e.: 5-173 μg g^-1, 39 ± 4 μg g^-1) than either green (0.12-30.2 μg g^-1, 10.7 ± 0.7 μg g^-1) or red macroalgae (0.11-16.9 μg g^-1, 4.3 ± 0.3 μg g^-1). Despite the overlap in arsenic concentrations between different macroalgal species, inter-species arsenic variation was apparent with arsenic concentrations following the order brown > green > red macroalgal species. It was concluded that the main contribution to the variation in arsenic concentration was from natural variability expected to occur between individuals of any species as a result of physiological differences. Most of the arsenic compounds in macroalgae (70-108%) could be extracted using methanol/water mixtures, with 38-95% of the arsenic compounds present in characterizable forms. All macroalgal species contained arsenoribosides (9-99%). The distribution of arsenoribosides followed a general pattern; glycerol-arsenoriboside and phosphate-arsenoriboside were common to all macroalgal species. Sulfonate-arsenoriboside and sulfate-arsenoriboside were found in brown macroalgal species and one red macroalgal species. Six macroalgal species contained high concentrations of inorganic arsenic (14.2-62.9%) and four species contained high concentrations of dimethylarsinic acid (13.3-41.1%). The variation in the distribution of arsenic compounds in marine macroalgal species appears to be related to taxonomic differences in storage and structural polysaccharides.