Influence of the exposure concentration of dissolved cadmium on its organotropism, toxicokinetic and fate in Gammarus fossarum

Information on the relationship between the exposure concentrations of metals and their biodistribution among organs remained scarce in invertebrates. The objective of this study was to investigate the effects of Cd con-centration on the organotropism, toxico-kinetic and fate of this metal in different organs of gammarids exposed to dissolved radioisotope Cd-109. Gammarids male were exposed for 7 days to three environmental Cd concen-trations (i.e. 4, 52 and 350 ng.L-1) before being placed in depuration conditions (i.e. uncontaminated water). At several sampling times, Cd concentrations were determined by Cd-109 gamma-counting in water, caeca, cephalon, gills, intestine and remaining tissues. Bioconcentration Factors (BCF) and Cd relative proportions in organs were calculated to assess the exposure concentration effect on the bioaccumulation capacities. The dependance of the organ-specific kinetic parameters to Cd water concentrations were estimated by fitting nested one-compartment toxico-kinetic (TK) models to both the accumulation and depuration data, by Bayesian inference. Then, for each Cd concentrations, the metal exchanges among organs over time were formalized by a multi-compartments TK model fitted to all organ data simultaneously. Our results highlighted that, at the end of the exposure phase, BCF and Cd relative proportions, in each organ, were not significantly modulated by water concentrations. Kineti-cally, Cd accumulation rates in all organs (except intestines) were depended on the exposure concentration, but not the elimination rates. The in vivo management of Cd (i.e. metal exchanges among organs) remained quali-tatively unchanged according to exposure concentration. All these results also highlighted key role of that organs in the management of Cd: bioconcentration by caeca, storage by gills and main entry pathway by intestine. This study shows the interest of implementing TK approaches to test the effect of environmental factors on bio-accumulation, inter-organ exchanges and fate of contaminants in invertebrate body to enhance the under-standing of the toxicity risk.

Automated summary

This study aimed to investigate the effects of Cd concentration on organotropism, toxico-kinetics, and fate of Cd in gammarids. The results showed that Cd concentration did not significantly modulate the bioconcentration capacity and Cd distribution in different organs. However, Cd accumulation rates in organs (except intestines) were dependent on the exposure concentration. The in vivo management of Cd among organs remained qualitatively unchanged according to exposure concentration. This study highlights the importance of implementing toxico-kinetic approaches to enhance the understanding of the toxicity risk of contaminants in invertebrates.