Abstract
In order to evaluate the relative contribution of water and food to the accumulation of copper in herbivorous marine zooplankton, the accumulation and loss rates of Cu in coastal copepods (Acartia sp. and Temora sp.) were measured and applied to a kinetic bioaccumulation model. Experiments were performed to measure stable Cu uptake from the dissolved phase in field-collected copepods acclimated for 2 to 3 d to a low Cu diet. The copepods were exposed to a range of free-Cu ion concentrations ([Cu²⁺] = 10⁻¹⁴·⁸ M, 10⁻¹²·⁸ M, 10⁻⁹·⁸ M), but a significant Cu accumulation rate was only observed in copepods exposed to 10⁻⁹·⁸ M Cu²⁺. Based on the Cu uptake rate measured at 10⁻⁹·⁸ M Cu²⁺, a free ion-specific uptake rate constant of dissolved Cu of 1.1 x 10⁴ l g⁻¹ d⁻¹ was estimated. Efflux rate constants of Cu in copepods estimated from depuration experiments were 0.056 ± 0.016 and 0.076 ± 0.012 d⁻¹ in laboratory-fed and unacclimated copepods, respectively. Application of these Cu uptake and efflux parameters, and those for Cu trophic transfer from previous studies, to a kinetic bioaccumulation model shows that food is the dominant source of Cu (>75% of total accumulation) at free-Cu ion concentrations ranging from 10¹⁴·⁸ to 10⁻¹¹·⁸ M. At free-Cu concentrations ≥10⁻¹¹·⁸ M, dissolved uptake becomes a significant portion (>20%) of total Cu accumulation accounting for almost 60% of the total Cu in copepods at 10⁻⁹·⁸ M Cu²⁺. These results suggest that herbivorous marine zooplankton accumulate Cu mainly by trophic transfer, but that dissolved uptake could be important in contaminated waters.