Natural DOM affects copper speciation and bioavailability to bacteria and ciliate.

This study aimed to investigate the influence of natural dissolved organic materials (DOM) on copper speciation (total dissolved, particulate, and free Cu2+ ions) and bioavailability during a two-level experimental microbial food chain. Bacteria were used as the first trophic level, and Paramecium caudatum (protozoan) as the second. The organisms were obtained from a freshwater reservoir and kept under controlled laboratory conditions. Three experimental treatments were performed: exposure of the organisms to copper in the absence of DOM, exposure to DOM in the absence of copper, and exposure to both copper and DOM. Freshwater medium containing natural DOM and copper at a total dissolved concentration of 1.8 x 10(-6) mol L(-1) was furnished to bacteria, which was further used as food to the protozoan. The results showed that after bacterial growth, DOM concentration decreased as quantified by total organic carbon determinations. At the same time, free Cu2+ ions concentration increased in the medium. A lower copper concentration was detected in both microorganisms in the presence of DOM. We conclude that natural DOM reduced copper accumulation in the organisms on the first and second trophic levels, thus reducing the entrance of copper into the aquatic microbial food chain.