Physiological and biochemistry responses of graphene combined with triphenyl phosphate (TPP) to <italic>Mytilus galloprovincialis</italic>

Abstract

After released into the environment, graphene nanomaterials can interact with other pollutants, due to their excellent adsorption properties. This brings changes to the environmental behavior and toxicological effects of graphene nanomaterials and other pollutants. Therefore, it is of great significance to further investigate the joint toxic effects of graphene and other pollutants. Triphenyl phosphate (TPP) is an organophosphate flame retardant and widely distributed in the Bohai sea. TPP can interact with graphene easily, as it contains three benzene rings in the molecule structure. Previous studies showed that graphene could increase the accumulation of TPP because of its hydrophobicity and durability. Due to the increasing applications of graphene and TPP, it is of great significance to study the combined toxicological effects of graphene and TPP. Marine bivalves are important model organisms to assess the effects of nanoparticles on aquatic biota, and may play a significant role in nanoparticles uptake, biotransformation and trophic transfer through food chains. The physiological response index can be used to evaluate the effects of environmental stressors on marine bivalves. These physiological parameters not only present the key processes related to energy budget, but also reflect the physiological plasticity of animals to stress environments. As a species with high tolerance and efficient accumulation of pollutants, mussel Mytilus galloprovincialis has been widely used as the bioindicator for environmental monitoring and ecotoxicological research. In this study, the physiological responses of graphene and TPP on M. galloprovincialis were explored based on the analyses of five groups, including seawater control, DMSO control, graphene (0.5 mg/L), TPP (0.5 mg/L) and graphene (0.5 mg/L) + TPP (0.5 mg/L). The antioxidant status, physiological responses and histological changes of gill and hepatopancreas tissues were measured after 14-d exposure to graphene and TPP. The oxidative stress effects of graphene and TPP on M. galloprovincialis were examined by obtaining a series of enzyme activity indicators, such as the activities of catalase (CAT), superoxide dismutase (SOD), glutathione-s-transferase (GST), glutathione peroxidase (GPx) and the content of glutathione (GSH). The key physiological parameters that characterized changes in physiological response were measured, including clearance rate (CR), ammonia excretion rate (NR), oxygen consumption rate (OR) and oxygen to nitrogen (O:N). In addition, the integrated biological response (IBR) index was also calculated to compare the toxic effects of graphene, TPP and graphene + TPP on M. galloprovincialis . The results showed that the exposure of graphene + TPP mitigated oxidative stress and tissue damage in mussels induced by graphene. Graphene had significant effects on the oxygen consumption and ammonia excretion ( P M. galloprovincialis was increased significantly after TPP exposure. Compared with the single graphene exposure, respiratory inhibition induced by graphene decreased, while oxygen-nitrogen ratio (O:N) increased after the combined exposure. It was evidenced that the combined exposure resulted in less environmental pressure on mussels compared with graphene exposure. The M. galloprovincialis was in a sub-health state after graphene and TPP exposure, and long-term continuous exposure could pose a potential threat to its population maintenance. In addition, IBR index showed that the combined exposure of graphene and TPP exhibited significantly lower stress on mussels, compared with the exposure of graphene and TPP, respectively.