Citation:

Han, Y., Chris Knightes, D. Bouchard, R. Zepp, B. Avant, H. Hsieh, X. Chang, Brad Acrey, Matt Henderson, AND J. Spear. Simulating graphene oxide nanomaterial phototransformation and transport in surface water. Environmental Science: Nano. RSC Publishing, Cambridge, Uk, 6:180, (2019). https://doi.org/10.1039/c8en01088a

Impact/Purpose:

Engineered nanoparticles (ENPs) have been applied in essentially all areas of daily life in recent years.1-8 Among widely used ENPs, graphene-family nanoparticles (GFNs) -- including pristine graphene, graphene oxide (GO), and reduced graphene oxide (rGO) -- have become some of the fastest growing in the nanomaterials industry. The Water Quality Analysis Simulation Program (WASP) is a dynamic, spatially resolved differential mass balance fate and transport modeling framework for environmental contaminants in surface waters and sediments. The recently updated WASP (WASP8) redesigned the architecture of WASP and incorporated algorithms to simulate the fate of nanoscale and microscale emerging contaminants in surface waters (e.g., nanoparticle’s reactions, heteroaggregation). Here, we develop a fate and transport model to predict environmental exposure concentrations of GO and its major reaction phototransformation product rGO for Brier Creek, GA, using WASP8. We investigate the influence of sunlight radiation on distributions of GO and rGO in Brier Creek over a 20-year period and track the fate of these two species in the river, including the water column and sediments. Owing to the rapid production of GFNs, as well as lack of environmental models to predict GO fate in surface waters, this work aims to develop critical insights into the environmental fate of released GO and rGO in surface waters and provide valuable information for risk assessment for GO in aquatic environments.

Description:

The production of graphene-family nanoparticles (GFNs) has increased appreciably in recent years. Graphene oxide (GO) has been found to be the most toxic nanoparticle among GFNs and, to our knowledge, no studies have been conducted to model its fate and transport in the environment. Lab studies show that GO undergoes phototransformation in surface waters under sunlight radiation, resulting in formation of photoreduced GO (rGO). In this study, the recently updated Water Quality Analysis Simulation Program (WASP8) is used to simulate time-dependent environmental exposure concentrations of GO and its major phototransformation product, rGO, for Brier Creek, GA, USA under a scenario with constant loading of GO to the river for a period of 20 years. Due to the diurnal change in sunlight radiation, GO and rGO concentrations continue to vary over time, but are shown to stabilize, slightly fluctuating around a mean value in the water column in each stream segment of Brier Creek. Analysis shows that GO is the predominant nanoparticle, accounting for 99% of the total GFN mass throughout the whole river; while rGO accounts for approximately 1% of the total GFN mass throughout the whole river. Free GO and rGO remain suspended in the water column, and rGO is removed from the water column via heteroaggregation of rGO to suspended solids, resulting in appreciable accumulation of rGO in the sediment layers over time due to the settling process of suspended solids. Simulation of natural recovery after removal of the GO source suggests that free GO and rGO are the immediate contaminants of concern in the studied surface water system, while rGO heteroaggreagated with suspended solids can have a long-term ecological impact on both the water column and sediments.

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