Impacts of Sediment Organic Matter Content and pH on Ecotoxicity of Coexposure of TiO2 Nanoparticles and Cadmium to Freshwater Snails Bellamya aeruginosa

The environmental factors are expected to affect the ecotoxicity of heavy metals in the presence of engineered nanoparticles (NPs) in aquatic ecosystems. However, in sediment scenario, little is known regarding their impacts on the ecotoxicity of co-exposure of sediment-associated heavy metals and NPs. This study evaluated the impacts of different levels of organic matter (OM) (4.8-11.6%) and pH (6-9) on the ecotoxicological effects of co-exposure of sediment-associated titanium dioxide nanoparticles (TiO2-NPs) and cadmium (Cd) to a freshwater gastropod Bellamya aeruginosa. The burdens of Ti and Cd and biomarkers of DNA damage, Na+/K+-ATPase, lipid peroxidation (LPO), and protein carbonylation (PC) in the hepatopancreas were determined following 21 days of exposure. At background level of OM (4.8%) in sediments, TiO2-NPs significantly promoted Cd accumulation in low-Cd treatments (5 mg/kg) but did not promote Cd accumulation in high-Cd treatments (25 mg/kg). At the relatively higher OM levels (7.1 and 11.6%), TiO2-NPs significantly enhanced Cd accumulation and toxicity as evidenced by aggravated DNA damage, decreased Na+/K+-ATPase activities, and increased LPO and PC levels. Moreover, Cd burdens in both low-Cd and high-Cd treatment were positively correlated with corresponding Ti burdens, indicating TiO2-NPs partially acted as carrier of Cd. At all pH levels, in low-Cd treatments, TiO2-NPs did not affect Cd accumulation, LPO, and PC levels but significantly enhanced DNA damage and slightly facilitated the inhibition of Na+/K+-ATPase activities. In high-Cd treatments, only at pH 9, TiO2-NPs significantly enhanced Cd accumulation and toxicity. Our results implied that interaction between TiO2-NPs and OM or pH significantly affected the accumulation and toxicity of Cd in B. aeruginosa, but the underlying mechanisms need further investigation. Additionally, it should be noted that the potential ecological risk of co-exposure of NPs and coexisting pollutants might be closely species-specific and related to environmental media.