Assessing the impact of arsenite and arsenate on Sarcodia suae: a tale of two toxicities.

Inorganic arsenic (iAs), which predominantly occurs as arsenite (As³⁺) and arsenate (As⁵⁺) in natural water, is primarily accumulated by seaweed in marine environments. However, the detailed mechanisms through which As³⁺ and As⁵⁺ affect the physiological processes of these organisms remain largely unknown. This study focused on evaluating the toxicological effects of As³⁺ and As⁵⁺ on the seaweed Sarcodia suae. Exposure to As³⁺ and As⁵⁺ resulted in IC₅₀ values of 401.5 ± 9.4 μg L^-1 and 975.8 ± 13 μg L^-1, respectively. Morphological alterations and a reduction in phycoerythrin content were observed, particularly under As³⁺ exposure, with increased lipid peroxidation as evidenced by higher malondialdehyde levels. Exposure to As³⁺ also elevated the production of superoxide radicals, while decreasing hydrogen peroxide levels specifically in the presence of As³⁺. The induction of antioxidative enzyme activities, namely superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase was observed, signaling an adaptive response to iAs-induced oxidative stress. Moreover, levels of the antioxidants ascorbate and glutathione were elevated post-exposure, especially in response to As³⁺. Additionally, bioaccumulation of arsenic was significantly higher in the As³⁺ compared to As⁵⁺. Collectively, the data suggest that As³⁺ imposes greater adverse effects and oxidative stress to S. suae, which responds by adjusting its antioxidative defense mechanisms to mitigate oxidative stress.