Assimilation efficiencies and elimination rates of trace metals accumulated by trophic pathway in Gammarus fossarum

Abstract

To improve the assessment of metal toxicity in aquatic organisms, it is important to consider the different uptake pathways (i.e. trophic or dissolved). The bioaccumulation of dissolved metals such as Cd and Zn is beginning to be well described in gammarids. But there are very few data concerning the contribution of the diet route, and its related toxicokinetic parameters. Among these, the assimilation efficiency is an essential parameter for the implementation of models considering the trophic pathway. This study aims to estimate the assimilation efficiencies and elimination rates of two type of food, i.e. alder leaves and larvae of chironomids, contaminated by three metals (Ag, Cd and Zn) of major concern for the Water Framework Directive (WFD). The pulse-chase-feeding method was used. Gammarids were fed with alder leaves or chironomid larvae previously contaminated with ^110mAg, ¹⁰⁹Cd or ⁶⁵Zn, for a short period of time (1 to 5 hours), followed by an elimination phase of 14 days. At different time steps, the gammarids were placed alive on the gamma detector to quantify individually the whole-body concentrations of ^110mAg, ¹⁰⁹Cd or ⁶⁵Zn. Our results indicate that: i) Cd has the highest assimilation efficiency (44% for leaves and 34% for larvae), followed by Zn (14% for leaves and 9% for larvae) and Ag (5% for leaves); ii) for Cd and Zn, the AE were higher when gammarids were fed with leaves than with larvae; iii) the elimination rates of metals seem to depend more on the food matrix than the metal assimilated; and thus iv) the biological half-life calculated from the k_es is 5.1 days for Ag, between 4.9 and 13 days for Cd and between 3.8 and 13 days for Zn.