Waterborne nickel bioaccumulation in Gammarus pulex: Comparison of mechanistic models and influence of water cationic composition

Abstract

The biodynamic and saturation models offer promising lines of enquiry to predict the bioaccumulation of metals by aquatic organisms. However, in order to construct these models, the accumulation strategies have to be defined for each metal/organism couple in controlled conditions. This study aims at modelling the waterborne bioaccumulation of Ni and the influence of the water's geochemical properties on this process in a crustacean that is widely distributed in Europe, Gammarus pulex. In the laboratory, G. pulex was exposed to several Ni concentrations (from 0.001 to 100 mg L(-1)) in aquatic microcosms. Our results show that G. pulex is very tolerant to Ni (LC50(48 h)=477 mg L(-1) Ni). Time course experiments enabled the construction of a biodynamic model by determining the uptake (k(u)) and elimination (k(e)) rate constants. When the exposure concentration exceeded 1 mg L(-1) Ni, the metal uptake reached a maximum due to a limited number of binding sites for Ni. Therefore, the organism's maximal capacity to accumulate the metal (B(max)) and the half-saturation constant (K) were determined to establish the saturation model. We showed that the two models are comparable for the lowest exposure concentrations (<1 mg L(-1) Ni), with k(u)/k(e)=B(max)/K. Then, the bioaccumulation of Ni was recorded in waters exhibiting various concentrations of three major ions (Na(+), Mg(2+) and Ca(2+)). Only Ca had an inhibitory effect on the Ni uptake. This study reports for the first time the bioaccumulation of Ni in G. pulex. Because of its high tolerance to Ni and its high capacity to accumulate this metal, this crustacean could be used as an indicator of Ni bioavailability in freshwaters.

Modelling copper bioaccumulation in Gammarus pulex and alterations of digestive metabolism

“…The ratio I max /K corresponds to k umax that is the maximal uptake rate. As detailed in Lebrun et al (2011), the saturation model was constructed by combining Eqs. (2) and (3), which allowed the calculation of Cu bioaccumulation at the steady state as follows:…”

“…Pools of 5 gammarids were sampled at 0.5, 1, 2 and 5 days for each exposure condition. Before being frozen at -20°C, gammarids were rinsed with 2 and 0.5 mM EDTA, then twice with ultrapure waters for 1 min, so as to remove the metal potentially adsorbed on the organisms (Lebrun et al 2011).…”

“…Saturation kinetics model was used to analyse the uptake rate data as a function of Cu concentration in water (Lebrun et al 2011):…”

“…Nevertheless, competitions for the same transport sites may occur between free metals and major ions found in freshwaters, leading to a decrease in metal uptake (Bourgeault et al 2010;Komjarova and Blust 2009). In G. pulex, increasing concentrations of Ca in water inhibits the uptake of Ni and Cd (Lebrun et al 2011;Pellet et al 2009). This is an evidence of the necessity to integrate water's chemical parameters affecting metal bioavailability into bioaccumulation models in order to improve their predictions.…”

“…Indeed, gammarids are widely distributed in European freshwaters and known as ecosystem engineers by facilitating the litter decomposition (Schaller et al 2010). Furthermore, efficient accumulations of metals, essential or not, has been reported in G. pulex or G. fassarum (Geffard et al 2010;Lebrun et al 2011). Because metal accumulations in gammarids can induce sublethal alterations at physiological, biochemical and behavioural levels, these amphipods are also suitable candidates for the development of exposure biomarkers (Dedourge-Geffard et al 2009;Felten et al 2008).…”