Distribution of Water-Soluble Arsenic Species in the Sub-thallus of Australian Brown Macroalgae

Abstract Algae are known to accumulate high concentrations of arsenic in different forms as inorganic or organic molecules called arsenic species. This study reports the water-soluble arsenic species in seven brown macroalgae collected from Mosquito Bay, New South Wales, Australia, during autumn 2021. The algae thalli were sectioned into four parts, i.e., holdfast, old stipe, young stipe, and blade. The total arsenic concentration and water-soluble arsenic species were measured using HPLC–ICPMS. Results indicated that arsenic concentration significantly differs between algae taxa (F 6.14 = 689, p < 0.05). Arsenic was not uniformly distributed within the thallus of individual algae. Lower parts (holdfast and old stipe) tended to have lower arsenic concentration than upper parts (young stipe and blade). Two-factor ANOVA of arsenic concentrations found a significant interaction between algae taxa and thallus section (F 1,21 = 617, p < 0.05). The main arsenic species in all samples were arsenoribosides, followed by As V and methylated arsenic. Of the four As-sugars in the samples, phosphate (PO 4 ) As-sugars were the dominant form. Monomethylarsonic acid (MA) was detected at low concentrations in all samples. Understanding the total concentration and speciation related to the uptake, fate, and forms of arsenic in marine macroalgae is critical to understanding human health risks from direct consumption. The risk of the measured inorganic arsenic in the algae taxa for human consumption was calculated using the target hazard quotient (THQ) and carcinogenic risk (CR). Values for THQ were below 1 and CR between 1 × 10 −6 and 1 × 10 −4 for all samples, indicating the low risk associated with seaweed consumption from the bay.