Metal(oid)s in Ulva: should we be worried?

Ulva spp. are promising food resources owing to their nutritional richness and beneficial properties. However, it accumulates potentially toxic trace elements, raising health safety concerns and proving useful for biomonitoring studies. In response to this concern, this review, conducted in collaboration with the EU-COST Action CA 20106 network, critically analysed 176 peer-reviewed papers to evaluate metal(oid) accumulation in Ulva. This study revealed substantial variability in the essential and non-essential element content due to environmental conditions, geographic regions, morphological forms, and analytical methods used in both wild and cultivated Ulva. The analysis was based on gross morphology (tube or foliose) rather than species-level identification. The identification of toxic forms, such as methylmercury and inorganic arsenic, remains limited, highlighting the need for element speciation to more accurate assess safety. Based on these findings, the review identified and outlined key areas requiring attention to ensure the safe and effective use of Ulva. Standardised analytical protocols are needed to improve consistency and comparability across studies and to enable accurate detection of toxic element forms. Improved taxonomic resolution, using molecular tools, is essential for distinguishing species-specific accumulation patterns. Expanding research into understudied geographic regions will help capture global variability in environmental influences on trace element uptake. Finally, standardised cultivation parameters are crucial to control elemental composition in farmed Ulva and to ensure its suitability for human consumption and commercial applications.