Arsenic species and their health risks in intertidal macroalgae in response to seasonal variations

This study investigated the total arsenic (TAs) content and arsenic formation of three macroalgae, including Ulva lactuca (U. lactuca) in the Chlorophyta and Mazzaella japonica (M. japonica) and Neohodomela munita (N. munita) in the Rhodophyta, in different seasons. The results showed that TAs concentrations ranged from 6.4 to 13.7 mg kg^-1 in M. japonica, 4.9 to 21.7 mg kg^-1 in N. munita, and 0.7 to 20.3 mg kg^-1 in U. lactuca, indicating significant seasonal variations in arsenic content. Arsenic content is higher in cold seasons (October 2022 and February 2023) and lower in hot seasons (July 2022 and July 2023). Additionally, arsenic speciation varied among different macroalgae, the content of arsenic betaine (AsB) in U. lactuca is relatively high, while the glycerol arsenide (AsS-OH) content in the Rhodophyta, such as the M. japonica and the N. munita, is also high, and the N. munita has a high content of inorganic arsenic As^V. Human exposure to toxic arsenic via macroalgae consumption was assessed using estimated daily intake (EDI) and target hazard quotient (THQ). Most macroalgae posed low health risks, but N. munita presented significant risks in warmer seasons due to high inorganic arsenic (IAs) content. Continuous monitoring and further research on climate impacts on arsenic in macroalgae are necessary to understand long-term consumption risks.