Interactions between TiO2 nanoparticles and cadmium: consequences for uptake and ecotoxicity

As a consequence of the increasing use of engineered nanoparticles in e.g. industrial applications and consumer products, these particles will be released into the aquatic environment. They will be present in the water phase where they are likely to form aggregates/agglomerates. Through sedimentation, the sediments are expected to be a sink for nanoparticles. Both in the water phase and in sediments they will mix and interact with other environmental pollutants, including heavy metals. In this study the toxicity of cadmium to three relevant freshwater species, green algae Pseudokirchneriella subcapitata, crustacean Daphnia magna and sediment organism Lumbriculus variegatus, was investigated both in the absence and presence of TiO2 nanoparticles. Also uptake of cadmium in D. magna and L. variegatus was investigated in tests where organisms were exposed to cadmium in sublethal concentrations in the absence and presence of 2mg/L TiO2 nanoparticles (P25 Evonic, d: 30 nm). Mass balances for cadmium in the test systems were determined. A high degree of sorption of cadmium onto TiO2 particles was found, which makes TiO2 nanoparticles potential carriers for cadmium. The observed toxicity was higher than expected based on water phase cadmium concentrations, and results shows that adsorbed fraction of cadmium is bioavailable.