Does the presence of titanium dioxide nanoparticles reduce copper toxicity? A factorial approach with the benthic amphipod Gammarus fossarum

•Nano-TiO2 mitigate copper toxicity.•Toxicity reduction by nano-TiO2 is observable at lethal and sublethal levels.•Toxicity reduction by nano-TiO2 is valid for benthic and pelagic species.•Nano-TiO2 may be considered as remediation agent.

In aquatic ecosystems, titanium dioxide nanoparticles (nano-TiO2) may adsorb co-occurring chemical stressors, such as copper (Cu). This interaction has the potential to reduce the concentration of dissolved Cu due to surface binding to the nanoparticles. The subsequent sedimentation of nano-TiO2 agglomerates may increase the exposure of benthic species towards the associated Cu. This scenario was assessed by employing the amphipod Gammarus fossarum as model species and taking advantage of a 2 × 2-factorial design investigating absence and presence of 2 mg nano-TiO2/L and 40 μg Cu/L (n = 45; t = 24 d) in darkness, respectively. Nano-TiO2 alone did not affect mortality and leaf consumption, whereas Cu alone caused high mortality (>70%), reduced leaf consumption (25%) and feces production (30%) relative to the control. In presence of nano-TiO2, Cu-induced toxicity was largely eliminated. However, independent of Cu, nano-TiO2 decreased the gammarids’ assimilation and weight. Hence, nano-TiO2 may be applicable as Cu-remediation agent, while its potential long-term effects need further attention.