Effect of combined exposure to mercury and nano/microplastics across twenty successive generations in the marine rotifer Proales similis

Mercury (Hg) and nano/microplastics (N/MPs) are widespread pollutants in coastal marine environments. The purpose of this study was to evaluate the combined toxicity of Hg and N/MPs on the marine model organism Proales similis (Rotifera). Multigenerational toxicity tests were conducted across twenty successive generations exposed to Hg (2.5 μg/L) and PE-N/MPs (250 μg/L), individually and in combination. The effects of the mixture of Hg and PE-N/MPs were measured on rotifer reproduction (three-day reproductive bioassay), feeding behavior (24 h ingestion bioassay), and Hg accumulation (24 h filtration). During individual exposure to Hg and PE-N/MPs, population growth rates (PGR) in most generations remained similar to those of the control. However, when exposed to the mixture, PGR were significantly lower than those of the control or individual exposures, especially in generations F11 to F19. In reproductive tests, PGRs in the mixture treatments declined notably compared to the control and individual exposures to Hg and PE-N/MPs. At 10 to 1000 μg/L PE-N/MPs, ingestion rates (IR) were higher than those of the control. However, when the PE-N/MPs concentration increased to 100 and 1000 μg/L in the mixture, the IR decreased significantly compared to the controls and individual exposures. The synergistic effect of the mixture of Hg and PE-N/MPs was observed in all measured endpoints. Rotifers accumulated less Hg when PE-N/MPs were present. The present study suggests that a longer-term, multigenerational exposure approach is more ecologically realistic and comprehensive for examining the ecotoxicological effects of a mixture of heavy metals and N/MPs than a single-generation approach.