The potential of TiO₂ nanoparticles as carriers for cadmium uptake in Lumbriculus variegatus and Daphnia magna

The use of engineered nanoparticles (e.g. in industrial applications and consumer products) is increasing. Consequently, these particles will be released into the aquatic environment. Through aggregation/agglomeration and sedimentation, sediments are expected ultimately to be sinks for nanoparticles. Both in the water phase and in the sediments engineered nanoparticles will mix and interact with other environmental pollutants, including metals. In this study the toxicity of cadmium to two freshwater organisms, water column crustacean Daphnia magna and sediment oligochaete Lumbriculus variegatus, was investigated both in the absence and presence of titanium dioxide (TiO2) nanoparticles (P25 Evonic Degussa, d: 30nm). The uptake of cadmium in sub-lethal concentrations was also studied in the absence and presence of 2mg/L TiO2 nanoparticles. Formation of larger nanoparticles aggregates/agglomerates was observed and sizes varied depending on media composition (358±13nm in US EPA moderately hard synthetic freshwater and 1218±7nm in Elendt M7). TiO2 nanoparticles are potential carriers for cadmium and it was found that 25% and 6% of the total cadmium mass in the test system for L. variegatus and D. magna tests were associated to suspended TiO2 particles, respectively. μXRF (micro X-ray fluorescence) analysis confirmed the uptake of TiO2 in the gut of D. magna. For L. variegatus μXRF analysis indicated attachment of TiO2 nanoparticles to the organism surface as well as a discrete distribution within the organisms. Though exact localisation in this organism was more difficult to assess, the uptake seems to be within the coelomic cavity. Results show that the overall body burden and toxicity of cadmium to L. variegatus was unchanged by addition of TiO2 nanoparticles, showing that cadmium adsorption to TiO2 nanoparticles did not affect overall bioavailability. Despite facilitated uptake of cadmium by TiO2 nanoparticles in D. magna, resulting in increased total cadmium body burden, no change in toxicity was observed.