Nitrates and Toxic Metals in Wild Macroalgae from Tenerife, Canary Islands: Occurrence and Assessment of the Risk to Human Health

Macroalgae are a food resource of growing interest due to their nutritional and functional value. However, their ability to bioaccumulate pollutants present in the marine environment makes it necessary to assess their food safety. The aim of this study was to determine the levels of nitrates and the toxic metals (Cd, Pb and Hg) in 44 samples from 14 species of wild macroalgae collected off the coast of Tenerife, and to assess the potential risk associated with their consumption. In terms of descriptive trends, toxic metal contents appeared higher in certain specific specimens collected from the southern part of the island, although these localised patterns are heavily influenced by species-specific bioaccumulation capacities. Gelidium spp. had the highest concentrations of Cd (0.165 mg/kg) and Pb (1.564 mg/kg), whilst Rhodymenia pseudopalmata had the highest Hg content (0.06 mg/kg). As regards nitrates, the highest concentration was recorded in Taonia atomaria (5439 mg/kg). The dietary exposure assessment, based on a daily intake of 4 g of dried seaweed, showed contribution percentages below the reference values proven by the EFSA. These results showed that, strictly under the specific consumption scenario assessed (adult population, 70 kg bw, consuming 4 g/day of dried seaweed), most analytes and macroalgal species showed low exposure levels. However, Pb exposure from Gelidium spp. warrants caution, as its nephrotoxicity margin exposure (MOE) was 7.05, below the target value 10, and therefore a potential risk cannot be entirely excluded. Potential risks may also be greater for high intake consumers or vulnerable groups, such as children regularly consuming certain species.