A new study of an international research group is questioning the widely accepted "free ion activity model" FIAM that assumes that the free metal ion activity reflects the chemical reactivity of the metal, i.e., the extent to what the metal reacts with binding sites on the cell membrane surface, and hence its bioavailability and toxicity. According to the results of this new study, humic acids increase dissolved lead bioavailability for marine invertebrates.
An important goal in aquatic ecotoxicology is to predict the bioavailability of dissolved metals as a function of their speciation in the environment. The widely used models, FIAM and BLM (biotic ligand model) were developed to address this challenge. According to these models, the presence of dissolved organic matter (DOM), as humic acids (HA), in natural waters is assumed to decrease dissolved metal bioavailability by binding metal ions and, therefore, decreasing the free ion concentration in solution. Although these models have been widely used in bioavailability studies, there are also a number of studies showing deviating results and questioning their general applicability to natural waters.The new study:
The new study performed by Paula Sanchez-Marín from the University of Viego, Spain, and her co-workers aimed at testing the applicability of FIAM to dissolved Pb in the presence of DOM in marine systems. Pb complexation by HA in artificial seawater was checked by means of square wave anodic stripping voltammetry (SWASV). Uptake and toxicity of this metal in the absence and presence of HA was tested using excised gills of Mytilus edulis and the Paracentrotus lividus embryo-larval bioassay respectively. Both Pb uptake by mussel gills and Pb toxicity to sea urchin larvae increased in the presence of HA, and this increase was higher at higher HA concentrations. The original study
Paula Sánchez-Marín, J. Ignacio Lorenzo, Ronny Blust, Ricardo Beiras, Humic Acids Increase Dissolved Lead Bioavailability for Marine Invertebrates
, Environ. Sci. Technol., 41/16 (2007) │5679-5684. DOI: 10.1021/es070088h Related studies
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last time updated: March 12, 2010