Geospatial and Toxicity Assessment of Carbon Nanomaterial Releases

The growing demand and use of engineered nanomaterials (ENMs) increases the likelihood of release to the environment, especially for freshwater ecosystems. To better understand the potential risks of incorporating ENMs into... [ view full abstract ]

The growing demand and use of engineered nanomaterials (ENMs) increases the likelihood of release to the environment, especially for freshwater ecosystems. To better understand the potential risks of incorporating ENMs into current and future products, it is important to consider releases to freshwater ecosystems from the entire ENM life cycle, including synthesis, use, and end-of-life. Life cycle releases may result in direct aquatic ecosystem toxicity and indirect toxicity due to upstream energy and material consumption. While ecotoxicity studies and life cycle assessments (LCAs) exist for some ENMs, many do not account for the full life cycle or regional differences in potential release sites. Key questions remain: 1) Where are regional release pathways expected to occur for ENMs?; 2) At what rate will ENMs enter the environment and accumulate in concentration?; and 3) Are the predicted concentrations environmentally relevant?

This study introduces a novel, integrated methodology to address the aforementioned challenges by combining predictive geospatial modeling with empirical ecotoxicity assays to estimate potential ENM risks at the regional level. Because direct data on nanomaterial production and release are scarce, the predictive capacity of tools like ArcGIS can be leveraged to estimate likely ENM release patterns (manufacturing siting, regional adoption of ENM-enabled technologies, and geography of freshwater ecosystems), environmental concentrations, and potential ecological risks. The model was demonstrated using a case study of carbon nanomaterials (CNMs) used in renewable energy technologies with a geospatial focus on the Laurentian Great Lakes, the largest surface freshwater system on Earth.

Case study results show potential CNM exposure from production facilities, installation sites, and disposal sites that are within buffer zones of the Great Lakes watershed. Lakes in this region are vulnerable due to industrial discharge, landfill leachate, and chemical runoff, and the outflows are less than one percent each year, concomitantly increasing pollutant vulnerability. To link model outputs with ecosystem risk, empirical ecotoxicity assays were performed for three CNMs that have promising application in solar technologies: fullerene (C₆₀ and C₇₀) and PCBM, a functionalized form of fullerene. Acute, chronic, and generational exposure studies of Daphnia species were performed to estimate the LC50 values for each material under different release scenarios. Experimental results demonstrate that there are differences in the ecotoxicity of the materials with the highest lethal response shown for C₇₀ and the probability of a lethal response depending on organism physical contact for PCBM. These values are used with geospatial modeling results to inform the relative impacts of each CNM using the metric of freshwater ecotoxicity. 

CNM releases are at concentrations that may pose problems for aquatic ecosystems and therefore these results can be used to inform future siting of CNM production facilities, installation of energy technologies containing CNMs, or disposing of these materials at end-of-life in order to minimize risk to regional aquatic ecosystems. Using readily available geospatial data, this model can be easily adapted for other sites, making these results transferable to other freshwater ecosystems.