Interactive Effects of Copper-Silver Mixtures at the Intestinal Epithelium of Rainbow Trout: an In-Vitro Approach.

While metals are present in mixture in the environment, metal toxicity studies are usually conducted on an individual metal basis. There is a paucity of data in the existing literature regarding specific metal-metal interactions and their effect on metal toxicity and bioavailability. Here, we studied interactions of silver-copper mixture at the intestinal epithelium using an intestinal cell line derived from rainbow trout (Oncorhynchus mykiss), the RTgutGC. Exposures were conducted in media containing different chloride concentrations (low chloride, 1 mM and high chloride, 146 mM) thus resulting in different metal speciation. Cytotoxicity was evaluated based on two endpoints, cell metabolic activity and cell membrane integrity. Silver-copper mixture toxicity was assessed using two designs: the independent action (IA) and concentration addition (CA). Metal mixture bioavailability was studied by exposing cells to 500 nM of Ag or Cu in single or mixture exposure (i.e., 500 nM of Cu plus 500 nM of Ag). We found an antagonistic effect in the low chloride medium and an additive/synergistic effect in the high chloride medium. We found that copper (Cu) dominates over silver (Ag) toxicity and bioavailability indicating a competitive inhibition when both metals are present as free metal ions in the exposure media which support our hypothesis. Our study also suggests different mechanisms of uptake of free metal ions and metal complexes. This study adds valuable information to our understanding of the role of metal speciation on metal mixture toxicity and bioavailability.