From a heavy metal perspective, is macroalgal biomass from Madeira Archipelago and Gran Canaria Island of eastern Atlantic safe for the development of blue bioeconomy products?

Macroalgae are considered a valuable source of several compounds with nutritional, nutraceutical, cosmeceutical, and pharmaceutical applications. They are also used for crop fertilization and biofortification by introducing important minerals into the soil essential for crop productivity. At the same time, however, they are known bio-accumulators of some heavy metals. In this work, we assessed the content of 7 minerals considered as heavy metals in 25 macroalgae samples, comprising 4 greens, 9 reds and 12 browns, from Madeira Archipelago, Portugal, for their potential use as blue bioeconomy products. These heavy metals included zinc (Zn) with concentrations that ranged from 1.95 – 242.65 mg kg −1 dw, nickel (Ni, 0.6 – 34.78 mg kg −1 dw), copper (Cu, 0.42 – 7.98 mg kg −1 dw), chromium (Cr, 0.47 – 45.74 mg kg −1 dw), cadmium (Cd, 0.1 – 2.58 mg kg −1 dw), lead (Pb, 0.05 – 2.79 mg kg −1 dw) and mercury (Hg, 0.03 – 8.49 µg kg −1 dw). We also analysed 22 samples of beach-cast macroalgae from Gran Canaria Island, Spain, collected from November 2016 to November 2019. The same heavy metals were assessed with their concentrations that ranged as follows: Zn (11.41 – 42.20 mg kg −1 dw), Ni (3.17 – 17.78 mg kg −1 dw), Cu (1.85 – 4.20 mg kg −1 dw), Cr (6.08 – 37.98 mg kg −1 dw), Cd (0.02 – 0.11 g kg −1 dw), Pb (0.16 –5.42 mg kg −1 dw) and Hg (3.59 – 31.00 µg kg −1 dw). These concentrations are all within the normal ranges reported in earlier studies in low industrialized areas, except for the brown algae Gongolaria abies-marina and Sargassum vulgare with high mean (± SD) Cd concentration (1.91 ± 0.36 and 1.75 ± 0.07 g kg −1 dw respectively). Our results suggest that most of the biomass prospected in these localities covered in the present study would be a viable source of materials for the development of a blue economy industry with emerging products following the European Union directives.