Cellular location of K, Na, Cd and Zn in the moss Pseudoscleropodium purum in an extensive survey

The aim of the present study was to determine if use of the Sequential Elution Technique (SET) improves interpretation of data on the total concentrations of elements in the moss Pseudoscleropodium purum, obtained in a regional network, by providing information about the cellular location, bioavailability and temporal representativeness of different elements. In total, 147 sites located at the vertices of a 15 × 15 km network were sampled. The total, extra- and intracellular concentrations of K, Na, Cd and Zn were determined and the spatial structure was analysed by use of robust variograms. The percentage of intracellular K was high (85%) compared with that of the extracellular K (15%), whereas those of the extra and intracellular Na and Cd were similar, both close to 50%. Zinc comprised a higher percentage of extracellular metal (61%). Spatial structure was clearly observed in both the total and intracellular concentrations of Na and in the total and extracellular concentrations of Zn. These results demonstrated that use of the SET improves interpretation of the total concentrations of elements, with differences between the elements that are metabolically regulated and those that possibly are not. Despite problems regarding particles deposited on the moss surface, the extracellular concentration of elements may provide information about the potential risks associated with possible solubilization of these particles and their posterior absorption. However, the intracellular concentration, which is not influenced by the presence of particles on the moss surface, provides more realistic toxicological information, as it may be related to metabolic processes in the moss. We therefore recommend prioritizing the use of the intracellular fraction when using mosses in environmental monitoring networks.

Research Highlights
► SET improves interpretation of metal moss concentration in an extensive survey.
► Extracellular concentration may provide information about the potential risks.
► Intracellular concentration provides more realistic toxicological information.
► In biomonitoring networks, we recommend the use of the intracellular fraction.