Differential dissolution and toxicity of surface functionalized silver nanoparticles in small-scale microcosms: impacts of community complexity†
Surface functionalization can minimize nanoparticle agglomeration and expand their applications; however, these modifications can also alter particle stability, dissolution, bioavailability and toxicity. Here we investigated how silver nanoparticles (AgNPs) with different surface chemistries affect community health, and how increased trophic complexity affects the interactions between organisms and nanomaterials. We compared AgNP exposures in simple microcosms comprised of algae (Chlamydomonas reinhardtii) and bacteria (Escherichia coli) to increasingly complex microcosms containing predatory invertebrates (Daphnia magna) and developing vertebrates (Danio rerio). Each microcosm was exposed to one of three 70 nm AgNPs [polyethylene glycol (PEG–AgNP), silica (Si–AgNP), or aminated silica-coated AgNP (Ami-Si–AgNP)] at 0, 0.1, 1, and 5 mg L−1 to investigate the relative influence of surface charge, composition and dissolution on organismal uptake and toxicity. All three AgNPs released more dissolved Ag into solution when organisms were present than was measured in the same media without organisms. PEG–AgNPs had the highest overall toxicity in all scenarios, followed by Si–AgNPs, and lastly Ami-Si–AgNPs. Toxicity correlated with the amount of Ag measured in the exposure media and the amount taken up by the organisms. Our findings indicate that surface functionalization plays an important role in determining dissolution, uptake and toxicity of AgNPs. Increasing trophic complexity decreased organismal susceptibility under the same AgNP concentration exposures, likely due to the change in bioavailable Ag that each organism experienced. This implies that tests using individual species provide conservative estimates of environmental impacts, while exposure may be mitigated in more realistic multi-species scenarios like those found in nature.