Decadal, inter- and intra-annual variations in trace elements in Sargassum horridum (Phaeophyceae: Fucales): implication for human health risk

This study assessed temporal variability in elemental composition (As, Cd, Pb, Cu, Fe, Zn, Mn, K, C, and N), stable isotopes (δ¹³C and δ¹⁵N), and the C:N ratio in Sargassum horridum over decadal, intra-annual, and inter-annual periods. It also identified factors influencing the accumulation of toxic elements (As and Cd) and assessed potential human health risks associated with S. horridum consumption. Sampling included spring collections in 2011 and 2022 at three sites in La Paz Bay, and seasonal sampling at one representative site between 2020 and 2022. Decadal changes were evaluated using the full dataset, while inter- and intra-annual variability was assessed using the seasonal time series. The results showed significant decreases in As, Cu, Zn, K, C, and the C:N ratio from 2011 to 2022, while δ¹⁵N increased. The ANOVA revealed significant inter- and intra-annual variability and year-month interactions in elemental composition, indicating temporal variability in bioaccumulation patterns. Arsenic accumulation was mainly associated with K, N, year, and δ¹⁵N, whereas Cd was related to δ¹³C, δ¹⁵N, and Zn, suggesting different accumulation mechanisms. The human health risk assessment indicates that dietary exposure to S. horridum exceeds U.S. EPA reference dose-based safety thresholds for As, with THQ values of 0.45-1.86 (5th-95th percentiles from Monte Carlo analysis), indicating that it is unsuitable for human consumption without prior treatment to reduce arsenic content. This study enhances our understanding of elemental bioaccumulation dynamics in brown macroalgae and supports informed decisions regarding the use of S. horridum as a food resource.