Daphnia reproductive impacts following chronic exposure to micro- and nano-scale particles from three types of rubber

Environmental context Tyre rubber particles, from both driving and reuse of tyre rubber, are pollutants that carry toxic chemicals into the environment. We investigated the long-term effects that these particles have on small aquatic organisms and found that they drastically reduce their ability to reproduce. Continued exposure of aquatic invertebrates to tyre-related pollutants, has the potential to affect the population by inhibiting reproduction into future generations. Rationale High levels of rubber microplastics in aquatic environments are often attributed to particles from driven tyres; however, the use of recycled or crumb rubber particles in outdoor surfaces is another source. Chronic toxicity assessments with tyres are limited, and there is a need to evaluate effects of rubber particles from different sources to better understand their role in conferring toxicity. Methodology We investigated the effect of chronic exposure of Daphnia magna to micro-sized (1–20 µm, 3.13 × 104–1.25 × 105 particles mL–1) and nano-sized (<1 µm, 1.25 × 105–1.00 × 107 particles mL–1) synthetic rubber particles. These included tyre particles (TPs) and two types of rubber from recycled tyres (called recycled rubber, RR, and crumb rubber, CR). Mortality, reproduction and moulting were assessed daily, and growth was measured at the end of the exposure. Additionally, the F1 generation was reared to assess multigenerational effects. Results Chronic exposure to micro-rubber particles had severe effects, delaying, decreasing and even eliminating reproduction starting at 6.25 × 105 particles mL–1. Chronic exposure to nano-rubber particles had less severe effects, but delayed and decreased reproduction at the highest exposure level, 5.00 × 107 particles mL–1. Exposure to nano-rubber in the parental generation affected reproduction in the F1 generation. Discussion This is the first comparison of chronic and generational toxicity between different sizes and compositions of rubber particles. The reproductive affects of chronic exposure to rubber particles could have devastating impacts on populations of Daphnia. Research is needed to identify which components leached from rubber particles affect reproductive ability.