Scalable low-cost processes for arsenic removal from holopelagic Sargassum spp: Performance of soaking and pressing treatments

Massive stranding of holopelagic Sargassum spp. across the Caribbean have raised major environmental and socio-economic concerns, while also offering opportunities for biomass valorisation. However, the high content of inorganic arsenic (iAs), the most toxic arsenic fraction, remains a critical barrier to their use in agriculture or animal feed. This study investigates the feasibility of simple, low-cost treatments for reducing arsenic concentrations in Sargassum biomass, with a particular focus on iAs removal. Mechanical pressing (1.5–3.2 bar), with or without pre-soaking and mixing–rehydration steps, was evaluated alongside soaking treatments at different temperatures (20–60 °C). Pressing resulted in limited arsenic removal, whereas pre-soaking greatly enhanced efficiency. Soaking at 20 °C reduced total arsenic and iAs by 42% and 54%, respectively, with further improvements at higher temperatures, reaching up to 66% and 70% removal at 60 °C. Final iAs concentrations decreased to approximately 10 mg kg −1 . Importantly, no apparent loss of phenolic compounds was observed under these conditions. Although higher removal efficiencies have been reported using high-temperature treatments (e.g., 90 °C), such approaches involve greater energy costs and may compromise the preservation of valuable bioactive compounds. To the best of our knowledge, this study provides one of the first systematic evaluations of treatment strategies specifically targeting iAs reduction in holopelagic Sargassum . These findings highlight the potential of simple soaking-based processes as scalable pre-treatment options, while emphasizing the need for additional processing steps to meet stricter regulatory thresholds for certain applications.