How water chemistry determines the risk of metallic engineered nanoparticles in aquatic ecosystems: nAg and nZnO case study

Abstract

The dispersion of nAg and nZnO engineered nanoparticles (ENPs) in water was investigated through the dissolution and agglomeration analysis over a 14 days exposure period. Before testing, the ENPs were in the nanoscale: 40-60 and 10-130 nm for nAg and nZnO respectively. Dynamic light scattering revealed that introduction of ENPs into water resulted in significant particle growth, even reaching um range in certain instances. ICP-OES analysis indicated limited dissolution which was concentration dependent, however more favourable for nZnO. Using a free floating duckweed candidate; we observed induction of oxidative stress following a multiple biomarker endpoint analysis after plants were exposed to the ENPs. Our results siggest a systematic compromise of biological defence mechanisms by ENPs, revealing a crucial toxicity route by ENPs towards higher aquatic plants. We then detail the importance of water abiotic parameters in, (a) influencing the ENPs surface charge potential, (b) driving the ENPs growth, (c) limiting the generation of metal ionic species, and, (d) determining the overall risk by ENPs towards aquatic biota. We suggest that informed understanding or evaluation of ENPs potential harm towards aquatic biota basically lies on detailed and suitable characterisation of both water and ENPs physico-chemical parameters. We close by listing crucial aspects when evaluating nanotechnology risks towards aquatic ecosystems.