Total arsenic concentrations and arsenic species present in naturally decomposing Ecklonia radiata tissues collected from various marine habitats

To investigate the release and degradation of arsenoribosides associated with the brown alga Ecklonia radiata, tissues were collected in various marine microhabitats (water column, sand intertidal, and rock platform intertidal) to establish the importance of decomposition stage and the micro-habitat in which decomposition occurs on arsenoriboside degradation. Total arsenic concentrations in E. radiata tissues varied in a similar pattern across all three sampling locations (Lake Tabourie, Burrill Lake, and Ulladulla Harbour) with concentrations in live tissues (53–124 µg As g-1 (dry mass)) greater than concentrations in tissues decomposing in the water column (28–90 µg As g-1 (dry mass)), which were in turn higher than concentrations in tissues decomposing in intertidal environments (16– 21 µg As g-1 (dry mass)). Arsenoribosides, specifically sulfonate (SO3-), phosphate (PO4-), and glycerol (Gly-) accounted for all of the arsenic extracted from live E. radiata tissues. Arsenoribosides also accounted for 100 % of the extractable arsenic species in E. radiata tissues decomposing in the water column. The proportions of arsenic species in decomposing E. radiata tissue from intertidal environments varied with sampling location and therefore micro-habitat. In rock platform-based intertidal zones (Burrill Lake and Ulladulla harbour), considerable concentrations of unextractable arsenic (10–60 %) were present plus known arsenoriboside degradation products such as dimethylarsinoylethanol (DMAE), dimethylarsenate (DMA), and arsenate (As(V)). In sand/beach-based intertidal zones, however, the vast majority of arsenic (˜95 %) was unextractable with only small concentrations of arsenoribosides and As(V) present. This study demonstrates that the release and further degradation of arsenoribosides from E. radiata tissues occurs in a two-step process with arsenoribosides released via leaching, whilst E. radiata remains suspended within the water column. Arsenoribosides are then degraded to various intermediate arsenic species once E. radiata tissues settle on intertidal environments; however, the degree of degradation varies relative to whether decomposition occurs on rock platform or sand-based environments. These results illustrate the key role of marine micro- habitats in the degradation of arsenoribosides contained within marine macro-algae.