Copper (Cu) is by far the most studied metal concerning the effects of organic complexation on metal bioavailability, and it is widely accepted that the presence of organic matter has a protective effect on Cu uptake and toxicity, by decreasing the concentration of free metal ions. However, this idea is based in laboratory experiments either performed at higher Cu concentrations than those that are environmentally relevant, or in experiments that used synthetic chelates (such as EDTA) to control for Cu speciation. The present experimental work was designed to test if Cu bioavailability actually depends on the free ion concentration at an environmentally relevant concentration of Cu (20 nM), using both synthetic and natural samples in the absence of synthetic chelates. As synthetic samples, artificial seawater was amended with fulvic acids or Marine-DOM extracted by ultrafiltration. Natural samples were collected from a mining-impacted coastal lagoon (Mar Menor, SW Spain), presenting dissolved Cu concentrations ranging from 3.5 to 14 nM. The samples were enriched in 65Cu (15 nM) in order to study the short term internalization of Cu by the coastal dinoflagellate Prorocentrum micans. Results show that net Cu internalization by P. micans is higher than that expected on the basis of Cu speciation (either analysed by anodic or cathodic stripping voltammetry). The results are consistent and occur in all samples, both the synthetic and the natural ones, suggesting that organically complexed Cu can be accessed by marine phytoplankton. This work challenges the applicability of current bioavailability models for Cu in coastal waters

SETAC Europe 34th Annual Meeting, 5 – 9 May 2024, Seville, Spain

Peer reviewed