(485a) Multimedia Environmental Distribution of Nanomaterials

Nanotechnology has brought about many benefits and improvements to commercial and industrial applications and products, but its potential environmental impact must also be systematically assessed. In this regard, it is essential to assess the potential exposure levels (i.e. concentrations, exposure time, etc.) of ecological receptors to engineered nanomaterials (eNMs) in order to manage risks due to possible  releases (chronic and/or accidental) of eNMs to the environment. Although a number of models have been developed to predict the multimedia environmental distribution of organics chemical contaminants, such models are not directly applicable to eNMs. For example, the concentration driving forces for transport of chemicals across environmental phase boundaries is typically constrained by equilibrium partitioning; in contrast, the transport of particulate matter is primarily driven by physical processes of driving forces that are unconstrained by equilibrium partitioning. In an effort to quantify the distribution of ENMs in the environment, “substance flow analysis” estimations have been employed in recent years as part of life cycle analysis (LCA) to assess the potential environmental impact of ENMs. Such approaches, however, are not a priori predictive and generally do not consider mechanistic descriptions of fundamental transport processes. Accordingly, in the present study, a generalized model of the multimedia environmental distribution of nanomaterials (MendNano) was developed to estimate the environmental distribution of nanomaterials subject to various release scenarios. In this model, the multimedia environment is considered as a collection of environmental compartments and subcompartments, with each compartment treated as either well-mixed (e.g. atmosphere, water), or non-uniform compartments (e.g. soil, sediment). Fundamental intermedia transport processes (e.g. dry deposition, rain scavenging, resuspension, runoff) link various compartments while considering the particle size distribution (PSD) of eNMs in both the atmospheric and aquatic compartments. In order to enable rapid “what-if?” scenario analyses, a web-based graphical user interface (GUI) was developed for the model as part of the MendNano cloud-based modeling system. The user defines the modeling scenario by specifying relevant properties of the eNM under consideration, geographical and meteorological parameters (i.e., size of regions, temperature, wind speed, rain rates, etc.), transport process parameters and source emissions (i.e., release rates, etc.). The time-evolution of eNM concentrations and mass in each environmental compartments are then calculated by solving the coupled series of differential equations and the results are displayed within the GUI. Simulations with MendNano for different geographical areas in the U.S. have shown that, when ENMs are released primarily to air the majority of their mass in the environment is accumulated in the soil and in certain cases in the soil compartment. Simulations confirmed that increased attachment efficiency of eNM to suspended solids resulted in significant increased concentration in the sediment compartment, and a modest concentration decreases for the water compartment. Additionally, for eNM with measurable solubility (e.g. Ag, ZnO), dissolution of the eNM had a significant impact in decreasing their accumulations in the water and sediment compartments. Lastly, risk indices were computed based on eNM concentrations and information from high throughput screening (HTS) of cellular toxicity studies, suggesting that ZnO, Fe₃O₄, and TiO₂ ranked high among 6 ENMs considered in the study. It is envisioned that the present multimedia analysis tool can assist regulators, industrial, and researchers in rapidly assessing the potential environmental implications of ENMs releases to the environment.