Bioaccumulation and biotransformation of arsenic by the brown macroalga Sargassum patens C. Agardh in seawater: effects of phosphate and iron ions

The toxicity and bioaccumulation and biotransformation potential of inorganic arsenic (IAs) species As(V) and As(III) were investigated using Sargassum patens under laboratory culture for 7 days. Algal chlorophyll fluorescence decreased with increasing As(V) and As(III) concentrations, being significantly affected by As(III) treatments. Higher As(III) concentration negatively affected growth rate, and P and Fe limitation greatly enhanced IAs toxicity. The extracellular, intracellular, and total bioaccumulation of As(III) and As(V) varied significantly depending on initial concentrations and addition of P and Fe. P and Fe availability suppressed intracellular As accumulation in As(V) medium but not in As(III) medium. In P-rich (10 μmol L−1) medium, intracellular As was reduced by 4.7% and 9.9% when As(V) in the medium was constant (4.0 μmol L−1), under Fe-limited (0 μmol L−1) and Fe-rich (10 μmol L−1) conditions, respectively. However, the Fe-rich condition positively affected extracellular As accumulation from both As source. Extracellular As increased by 43.5% and 38.8% in P-limited + Fe-rich cultures with 4.0 μmol L−1 of As(V) and As(III), respectively. Algae exhibited greater absorption and adsorption to As(V) than to As(III). The reduced metabolites of As(III) (3.5 to 4.9% of the total As) and oxidized metabolites of As(V) (2.0 to 3.7% of the total As) were recorded as biotransformed species from coexisting media containing As(V) and As(III) at a constant 4.0 μmol L−1, respectively. Both P and Fe had significant influences on the variation in behaviors of IAs. This information is vital in terms of As research in marine ecosystems.