Effects of metal nanoparticles on freshwater rotifers may persist across generations

Nanotechnology has become one of the fastest growing industries in the current century because nanomaterials (NMs) are present in an ever-expanding range of consumer products increasing the chance of their release into natural environments. In this study, the impacts of two metal nanoparticles (Ag-NPs and CuO-NPs) and their equivalent ionic forms (Ag⁺ and Cu²⁺) were assessed on the lentic freshwater rotifer Brachionus calyciflorus and on its ability to adapt and recover through generations. In our study, Ag-NPs and CuO-NPs inhibited the rotifer population growth rate and caused mortality at low concentrations (< 100 μg L^-1). Ag-NPs and CuO-NPs decreased in the medium when organisms were present (48 h exposure: 51.1 % and 66.9 %, respectively), similarly Ag⁺ and Cu²⁺ also decreased from medium in presence of the organisms (48 h: 35.2 % and 47.3 %, respectively); although the metal concentrations removed from the medium were higher for nanoparticles than metal ions, metal ions showed higher effects then their respective nanoparticle forms. Rotifer populations exposed for 4 generations to the toxicants were able to recover the population growth rate, but some rotifers showed developmental delay and inability to reproduce even after the removal of the toxicants. Intracellular accumulation of reactive oxygen species as well as plasma membrane damage were found in the rotifers at concentrations corresponding to EC₁₀ (Ag-NPs = 1.7 μg L^-1, Ag⁺ = 4.5 μg L^-1, CuO-NPs = 46.9 μg L^-1, Cu²⁺ = 35 μg L^-1) of the population growth rate. Our results showed, for the first time, that effects of metal nanoparticles and metal ions on rotifer populations may persist along several generations. This should be taken into account when assessing risks of metal nanoparticles in freshwaters.