Distribution and trophic transfer of engineered nanoparticles along aquatic food chains and related influencing factors: A review

Nanotechnology is developing rapidly and has been widely applied in chemical engineering, electronic engineering, energy sources, environmental protection and other fields. Engineered nanoparticles (ENPs) are inevitably releasing into the aquatic environment during the entire life cycle of nano-products, thus exposing to aquatic organisms, which has been well investigated in the past decade. ENPs could be internalized by different types of aquatic organisms including algae, plants, and fish. Therefore, the possible transfer of ENPs between different aquatic organisms has attracted attentions, and many important publications reported the trophic transfer of ENPs through aquatic food chains. This review first provided the internalization and distribution of ENPs in different aquatic organisms including microorganism, aquatic plants, invertebrate and fish: (1) For microorganisms, ENPs are mainly adsorbed on the cellular surface, and then be internalized, and the internalization could lead to subsequent toxicity; (2) ENPs could be taken up by the roots of aquatic plants, and then be migrated to stem and leaves by evapotranspiration; (3) ENPs were mainly located in the hepatopancreas and gut of invertebrates; (4) ENPs could be accumulated in the gill and digestive tract of fish, and then distributed into other tissues such as liver and spleen. Secondly, the research status of ENPs in aquatic food chain were summarized and analyzed. The transfer of ENPs was observed in both freshwater and marine food chains, and current investigations on freshwater food chains contributed a larger proportion than in the marine. Most of the researches proved that ENPs can transfer along the food chain, but the biomagnification was only reported in a few publications. Thirdly, the influence of water chemistry factors and ENPs properties on the transfer of ENPs via aquatic food chains was discussed. For the water chemistry factors, like light illumination, solution pH, co-existing compounds such as natural organic matter, ionic strength, and oxidation–reduction potential all altered the bioavailability of ENPs and played important roles in the trophic transfer of ENPs. For the properties of ENPs, it is observed that: (1) the metal ions which were released from metal-containing ENPs can improve the bioavailability of ENPs in aquatic organisms; (2) different coatings of ENPs brought different or opposite surface charge on the surface, thus changing the internalization and bioavailability of ENPs. For example, ENPs with positively charged surface could be easily adsorbed on the surface of aquatic organisms than the negatively charged particles; (3) different size and shape influenced the contacting area between the ENPs and organisms, and ENPs with smaller size were usually more readily enter aquatic organisms, which were deeply discussed in this review. Finally, the current researches, prospects and challenges on ENPs transfer in the aquatic food chains are addressed.