Aging of nanosized titanium dioxide modulates the effects of dietary copper exposure on Daphnia magna – an assessment over two generations.

Nanosized titanium dioxide (nTiO 2) is widely used in products, warranting its discharge from various sources into surface water bodies. However, nTiO 2 co-occurs in surface waters with other contaminants, such as metals. Studies with nTiO 2 and metals have indicated that the presence of natural organic matter (NOM) can mitigate their toxicity to aquatic organisms. In addition, "aging" of nTiO 2 can affect toxicity. However, it is a research challenge, particularly when addressing sublethal responses from dietary exposure over multiple generations. We, therefore exposed the alga Desmodesmus subspicatus to nTiO 2 (at concentrations of 0.0, 0.6 and 3.0 mg nTiO 2 /L) in nutrient medium aged for 0 or 3 days with copper (Cu) at concentrations of 0 and 116 µg Cu/L and with NOM at concentrations equivalent to 0 and 8 mg total organic carbon (TOC) per litre. Subsequently, the exposed alga was fed to Daphnia magna for 23 days over two generations and survival, reproduction and body length were assessed as endpoints of toxicity. In parallel, Cu accumulation and depuration from D. magna were measured. The results indicate that the reproduction of D. magna was the most sensitive parameter in this study, being reduced by 30% (at both parental (F 0) and filial (F 1) generations) and 50% (at F 0 but not F 1) due to the dietary Cu exposure in combination with nTiO 2 for 0 and 3 days aging, respectively. There was no relationship between the effects observed on reproduction and Cu body burden in D. magna. Moreover, D. magna from the F 1 generation showed an adaptive response to Cu in the treatment with 3.0 mg nTiO 2 /L aged for 3 days, potentially due to epigenetic inheritance. Unexpectedly, the presence of NOM hardly changed the observed effects, pointing towards the function of algal exopolymeric substances or intracellular organic matter, rendering the NOM irrelevant. Ultimately, the results indicate that the transferability of the impacts observed during the F 0 to the responses in the F 1 generation is challenging due to opposite effect directions. Additional mechanistic studies are needed to unravel this inconsistency in the responses between generations and to support the development of reliable effect models. • nTiO 2 aging controls dietary Cu effects on D. magna over two generations. • Impairments in reproduction were not explained by Cu body burden. • NOM did not substantially affect response variables. • Effect assessment over more than two generations is recommended. [ABSTRACT FROM AUTHOR]