Potential environmental implications of manufactured nanomaterials: Toxicity, mobility, and nanowastes in aquatic and soil systems

Nanotechnology has been singled out by industry and governments to become the world's largest industrial revolution, and it carries the potential to substantially benefit environmental quality through pollution prevention, treatment, and remediation. However, nanotechnology could also lead to serious environmental problems since the environmental behavior and fate of manufactured nanomaterials (MNs) are not predictable from that of chemically similar but larger compounds. The goal of this study was to develop an understanding of the potentially complex interplay between MNs and the health of organisms and ecosystems. The potential effects of MNs were evaluated by testing the hypothesis that: "chemical elements used in the production of MNs could lead to environmental dysfunctions due to: (1) the potential toxicity of these elements and their derivatives, (2) the small size driven mobility of MNs through heterogeneous porous media and ultimate contamination of aquifers, (3) their toxicity to microorganisms and the resulting negative impacts on key environmental microbial catalyzed reactions, and (4) the large surface area which would allow MNs to act as carriers/delivers of pollutants adsorbed onto them".To address this broad hypothesis, three well-established small-scale toxicity tests (i.e. the Ceriodaphnia dubia acute toxicity test, the Pseudokirchneriella subcapitata chronic toxicity test, and MetPLATE(TM)), were used. In addition, studies at the system level were conducted using a combination of column and batch experiments to investigate the transport behavior of MNs in heterogeneous porous media and the interactions of MNs with microbial-catalyzed oxidation of organic matter in sediments.Carbon (i.e. fullerenes (C60), single-walled carbon nanotubes (SWNTs)) and metal (i.e. CdSe quantum dots, and powders of the following nanometals---Ag, Cu, Co, Ni, and Al) based MNs, were used in different laboratory experiments. All tested MNs showed some degree of toxicity response to either one or more of the above three microbiotests, with nano-Cu and nano-Ag being the most toxic. The use of experimental conditions that mimic likely scenarios of MNs introduction to aquatic systems showed that the toxicity response of test model organisms to MNs under such conditions would be affected by key water quality parameters such as organic matter content and solution chemistry. Column studies of SWNTs transport in heterogeneous porous soils showed that soils characteristics and the chemical composition of MN suspensions affect transport behaviors, and that the latter can be quantitatively predicted by use of mathematical models such as the convection-dispersion equation. Finally, the use of sediment slurries spiked with either each type of MNs or pollutant (i.e. mercury) bound to MNs allowed the assessment of: (1) the impact of MNs on microbially-catalyzed oxidation of organic matter, and (2) the potential for Hg-bound to SiO2-TiO2 nanocomposites obtained from flue gas remediation studies to become available in sedimentary environments as a function of pH.Overall, these findings help shed light in the poorly studied environmental implications of MNs. However, several questions remain unanswered as these short-term laboratory investigations may not be able to predict the fate and transport of MNs on a long-term basis.