Enhanced bioaccumulation and biotransformation of As in coral reef organisms surrounding a marine shallow-water hydrothermal vent system

Abstract

The marine shallow-water hydrothermal system in Tutum Bay, Ambitle Island, Papua New Guinea discharges as much as 1.5kg of arsenic (As) per day into a coral reef ecosystem. Despite the amount of As released, coral reef organisms do not seem to be affected. We investigated the uptake and bioaccumulation of geothermally-derived inorganic As by the soft coral Clavularia sp., the calcareous algae Halimeda sp., and the sea squirt Polycarpa sp., by measuring the total As concentration (TAs) in tissues from each organism and comparing it to the same type of organism collected from a nearby control site. All organisms collected from the hydrothermal area displayed distinctly higher (2 to 20 times) TAs compared to the control site. Concentrations were typically higher in samples collected closer to the focused hydrothermal venting, which is the first direct evidence for enhanced bioaccumulation of As in organisms living within an area of hydrothermal influence. To assess As biotransformation to organoarsenicals, anionic and cationic As species were determined by IC-ICP-MS in methanol/water tissue extracts. The concentrations of several of the organoarsenic species were much higher at the hydrothermal vent site compared to the control site, and several organoarsenic species were present only in the hydrothermal samples, including some unidentifiable species. While intriguing, these speciation results cannot be interpreted robustly due to poor extraction efficiencies. Future researchers should attempt to improve the extraction efficiency to closer to 100%, which would allow a more accurate description of As biosynthesis pathways for the marine organisms living in these environments.