Are seaweeds suitable indicators to assess spatiotemporal patterns in critical elements concentrations? An insight on the use of seaweeds as biomonitors in Norwegian coastal areas

Rising critical element (including metals and rare earth elements plus yttrium, REY) production and use can also lead to an increasing release into the environment, therefore monitoring the concentrations of these elements in the marine environment is crucial to assess the related environmental risk. Seaweeds are, due to their high abundance, widespread distribution, sessile nature and the capacity to bioconcentrate elements considered as suitable organisms for biomonitoring of element/metal pollution. The aim of the study was to assess the suitability of brown seaweeds as biomonitoring organisms to detect spatiotemporal and source-related contamination patterns of technology critical element concentrations in the Norwegian coastal environment. We also assessed the suitability of two biomonitoring approaches through two case studies. In Case study 1 we applied passive biomonitoring using different species of naturally growing seaweeds specimens and in Case study 2 we used active biomonitoring, using cultivated specimens of a single seaweed species (Saccharina latissima) deployed at specific monitoring sites. Element concentrations were determined using ICP-MS on freeze dried seaweeds tissue samples. Relationships between element accumulation, and presence of local point-sources, environmental and biological parameters were evaluated. Results from Case study 1 indicated spatial and species-specific differences in REY concentration according to the sampling site, with seaweeds (specially Fucus spp. and Saccharina latissima) sampled in proximity to potential anthropogenic point-sources having the highest REY concentrations. Findings from Case study 2 showed a high spatiotemporal variability in element concentrations, with different elements (or element groups) exhibiting specific trends. REY behaved as a coherent group, showing similar spatiotemporal trends with accumulation being most pronounced in a freshwater impacted site. Other investigated elements exhibited various spatiotemporal trends according to different biotic and abiotic drivers. Our findings indicate that (either natural or cultivated) seaweeds can act as useful biomonitoring organisms for assessing spatiotemporal variation of the bioavailable dissolved element fraction as well as to assess the presence of local anthropogenic element sources. Furthermore, species-specific difference in element uptake and accumulation patterns exists and need to be considered for future use of biomonitoring