Experimental study of interactions between five trace elements--Cu, Ag, Se, Zn, and Hg--toward their bioaccumulation by fish (Brachydanio rerio) from the direct route.

Actions and interactions between five elements--copper, zinc, silver, selenium, and methyl mercury--toward their bioaccumulation in fish (Brachydanio rerio) were studied after 12 days exposure, via the direct contamination route. The experimental approach was based on a centered composite factorial design; 43 different contamination conditions were studied simultaneously, with five concentration levels in the water for each element. Contaminated media were cyclically renewed (48 hr renewal cycle), in order to control the fish exposure conditions. Data treatment was essentially based on the multiple regression technique, applied successively to the complete factorial design (2(5) = 32 conditions) and to the centered composite design (43 conditions). Results show a complex set of actions and interactions between the elements. The most striking result is a marked interaction between silver and methyl mercury: when Ag is present in the water jointly with MeHg, it exerts a negative action on Hg bioaccumulation in the fish, at the whole organism level. Bioaccumulation of silver is also significantly influenced by the presence of Zn, Cu, and Se in the water, the action of these three elements producing an increase in the amounts of Ag in the organisms. This study corresponds to an exploratory phase in order to reveal interaction effects on the bioaccumulation processes by fish and then to set up more in-depth analysis to increase progressively the understanding of the ecotoxicological mechanisms involved.