DGT as surrogate of biomonitors for predicting the bioavailability of copper in freshwaters: an ex situ validation study.

The present report is the companion study of our previous study in which we investigated the impact of the dissolved organic matter, water cationic composition and pH on the bioavailability and the bioaccumulation of copper (Cu) in aquatic mosses (Fontinalis antipyretica). The impact had been assessed under laboratory controlled conditions and modelled using a two-compartment model calibrated under a wide range of water compositions (Ferreira et al., 2008, 2009). Herein are reported the validation stage of the abovementioned approach for contrasted geochemical field conditions. Experiments were performed with aquatic mosses that were exposed for 7d to two nominal Cu concentrations (5 and 15μgL(-1)) in a flow-through field microcosm supplied with four contrasting natural waters. At the end of the exposure period, a 6-fold difference in the bioaccumulated Cu contamination levels was found among the four deployment sites, suggesting a significant control of the water quality on the metal bioaccumulation by aquatic mosses. In parallel, the so-called 'labile' Cu concentration for the same four field conditions was determined using a DGT device (Diffusive Gradient in Thin film). By coupling these DGT measurements and a cation competition model involving Ca(2+), Mg(2+), Na(+) and H(+), the time-dependent Cu concentrations in aquatic mosses were predicted; these simulation results were compared to the actual bioaccumulation of Cu in mosses. We found that any bioaccumulation model that ignores water characteristics is not suitable to predict the Cu accumulation by aquatic mosses under various water quality conditions. Instead, we found that our approach integrating DGT measurements and cationic composition was able to reproduce the Cu bioaccumulation kinetics by aquatic mosses for a wide range of water quality conditions. In conclusion, the DGT approach was demonstrated to be a dynamic in situ measuring technique that can be used as a surrogate of bioindicators if the cationic correction is taken into account.