Effect of dissolved organic matter (DOM) of contrasting origins in Cu and Pb speciation and toxicity to Paracentrotus lividus larvae

Water samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolved organic matter(DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbanceand fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pbcomplexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOMon Cu and Pb bioavailability was studied by means of theParacentrotus lividusembryo-larval bioassay.Sediment elutriates and sewage-influenced water (1) were enriched 1.4–1.7 times in DOC; (2) absorbedand reemitted more light; and (3) presented higher Cu complexation capacities (LCu) than the naturalseawater used for their preparation.LCuvaried from 0.08 M in natural seawater to 0.3 and 0.5 Min sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cucomplexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC50of0.64 M, significantly higher than the Cu EC50of natural and artificial seawater, which was 0.38 M. Theprotecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with highintensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrationsin the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and causedlittle effect on Pb EC50. This effect was contrary for both elutriates: one elutriate reduced Pb toxicity incomparisonwiththecontrolartificialseawater,whiletheotherincreasedit.UVirradiationofthesamplescaused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOMparameterswererelatedtoCuspeciationandtoxicity:goodcorrelationswerefoundbetweenDOCandCuEC50, whileLCucorrelated better with the fluorescence of marine humic substances. The present resultsstress the importanc