Transgenerational effects of reduced graphene oxide modified by Au, Ag, Pd, Fe₃O₄, Co₃O₄ and SnO₂ on two generations of Daphnia magna

To evaluate the effects of surface chemical modifications on the toxicity of graphene to aquatic organisms, we investigated the transgenerational effects of six reduced graphene oxide (rGO) nanocomposites (rGO-Au, rGO-Ag, rGO-Pd, rGO-Fe₃O₄, rGO-Co₃O₄, rGO-SnO₂) on Daphnia magna over two generations. The reversibility of the effects was also assessed using recovery experiments. Physiological endpoints, including mortality, body length, neonate numbers and time of first brood, were measured to assess toxicity. The results indicated that rGO-Ag and rGO-Co₃O₄ induced higher toxicity in D. magna compared with rGO, whereas rGO-Pd induced lower toxicity in D. magna. rGO-Au, rGO-Fe₃O₄ and rGO-SnO₂ did not significantly alter the survival, growth and reproduction of D. magna compared with rGO. The different effects of the six rGO nanocomposites on D. magna were largely dependent on their specific surface area and metallic element type. In addition, the results strongly suggested the occurrence of maternal effects, which induced higher sensitivity to toxic stress and decreased ability to survive and reproduce of the offspring. However, the maternal effects were reversible in the offspring transferred to a clean medium. This study indicated that surface chemical modifications played a crucial role in altering the eco-toxicities and environmental effects of graphene materials.