EFFECT OF DISSOLVED ORGANIC MATTER ON COPPER BIOAVAILABILITY TO A COASTAL DINOFLAGELLATE

Metal complexation by dissolved organic matter (DOM) is considered to decrease metal bioavailability by lowering the free metal ion concentration, therefore protecting organisms from the deleterious effects of metals (Campbell et al., 2002). In coastal lagoons like Mar Menor, with high terrestrial influence and low exchange with open sea, the levels of both DOM and metals are one or two orders of magnitude higher than in open-waters. In order to verify the free ion activity model (FIAM), copper internalization by Prorocentrum micans, a cosmopolitan dinoflagellate also present in the Mar Menor, was tested in the absence and presence of two types of DOM, commercially available fulvic acids from riverine origin (SRFA) and coastal DOM obtained by ultrafiltration (UF-DOM). The microalgae were exposed to artificial sea water enriched with increasing amounts of Cu65 isotope, at levels from 5 to 100 nM Cu, solely and in combination with DOM. After one-hour exposure, samples were centrifuged and washed and pellets were digested with nitric acid at 90ºC, following Sánchez-Marín et al (2010) and Croteau and Luoma (2005). In parallel, careful measurements of metal complexation by anodic stripping voltammetry (ASV) were performed and total Cu concentrations were measured by ICP-MS. Preliminary results show that copper internalization by the microalgae increases linearly as a function of labile Cu, both in the absence and presence of DOM, in agreement with FIAM and with labile Cu measurements performed by ASV. Future work might include testing the influence of competing metals, such as Pb or Zn, on Cu internalization, and to study Cu bioavailability in natural samples collected in the Mar Menor, in order to shed light into the factors that control Cu bioavailability in coastal lagoons