179 - Titanium dioxide nanoparticles affect mercury species bioavailability and trophic transfer from green algae to invertebrates

Mercury is a priority pollutant of global concern, which bioconcentrate, and biomagnify in aquatic food webs. A number of studies focused on mercury bioaccumulation and responses of aquatic organisms. However, these studies only rarely consider that aquatic organisms are co-exposed to mixtures of environmental pollutants. The present study explores the role of nano-sized titanium dioxide (nTiO2) on the accumulation of inorganic (IHg) and monomethyl mercury (MeHg) by green alga Chlamydomonas reinhardtii and the trophic transfer of these mercury species to invertebrate Daphnia magna. To this end the effects of three nTiO2 materials with primary particle size of 5, 15, and 20 nm at concentraions of 20 or 200 mgL-1 on IHg/MeHg accumulation by algae and daphnids were investigated. The results showed that nTiO2 adsorbed both IHg/MeHg, despite the significant aggregation and sedimentation of the formed nTiO2 aggregates. Consequently, nTiO2 decreased the cellular concentrations of mercury in microalgae and thus lessened the effects of mercury on the algal growth, enhanced generation of reactive oxygen generation and membrane damage. The influence of nTiO2 on mercury accumulation in daphnids was dependent on the exposure pathways. We have observed: (i) significant reduction of the total mercury body burden in D. magna in direct waterborne exposure to IHg/MeHg; (ii) substantial decrease of the THg in D. magna when exposed to IHg/MeHg via algal food; (iii) exposure to nTiO2 pre-treated with IHg/MeHg resulted in an increase of the THg body burden in daphnids. These effects were more pronounced for IHg than that for MeHg due to the higher adsorption capabilities of nTiO2 for IHg. Overall, the results contribute to the better understanding the role of nTiO2 on bioavailability and trophic transfer of global contaminants, such as mercury, known to bioaccumulate and biomagnify in the aquatic environment.

Authors: Vera Slaveykova, Mengting LI