Chemical food safety of seaweed: Species, spatial and thallus dependent variation of potentially toxic elements (PTEs) and techniques for their removal

The increasing interest in seaweed as a food resource in Western societies raises concerns about associated potentially toxic elements (PTEs), including arsenic, cadmium, mercury, lead, and iodine. Hence, this study examined variation in PTEs by including samples of four different species (Ulva lactuca, Palmaria palmata, Alaria esculenta, and Saccharina latissima) from Ireland, as well as of a single species (S. latissima) from three different harvest sites and with different thallus parts analyzed from a single harvest site. Comparing different species from the Irish site, U. lactuca showed the overall lowest PTE levels, while S. latissima and A. esculenta had notably higher levels of arsenic (105±3 and 57.9±5.5 mg kg-1 DW, respectively) and cadmium (0.839±0.046 and 1.03±0.05 mg kg-1 DW, respectively), and S. latissima had highest iodine levels (2480±210 mg kg-1 DW). Lead was higher in P. palmata and U. lactuca but below maximum limits. Further analysis of S. latissima from three sites (Ireland, Norway, Sweden) showed site-specific variations in inorganic arsenic (0.192–9.69 mg kg-1 DW), lead (0.0751–0.269 mg kg-1 DW), and cadmium (0.554–1.16 mg kg-1 DW). Saccharina latissima from the Swedish site exhibited uneven PTE distribution in tissue of different age. In terms of tolerable intake levels, iodine and cadmium posed most concern for seaweed consumption. After processing, total ash content decreased, leading to reductions in total arsenic (61.1%), inorganic arsenic (92.4%), lead (49.4%), and iodine (72.8%). Cadmium and mercury were difficult to remove. This study offers insights into the chemical food safety of seaweed, both pre- and post-processing, for introduction into expanding European markets.