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Modeling the Environmental Fate of Graphene Oxide and Its Phototransformation Products in Brier Creek Watershed Using the Water Quality Analysis Simulation Program 8 (WASP8)
Citation:
Han, Y., Chris Knightes, D. Bouchard, R. Zepp, H. Hsieh, X. Chang, AND J. Spear. Modeling the Environmental Fate of Graphene Oxide and Its Phototransformation Products in Brier Creek Watershed Using the Water Quality Analysis Simulation Program 8 (WASP8). 2017 AGU Fall Meeting, New Orleans, LA, December 11 - 15, 2017.
Impact/Purpose:
Poster presented at the 2017 AGU Fall Meeting session: Hydrology and Water Quality Models: Advances and Applications in Watershed Planning and Management.
Description:
The production of graphene-family nanoparticles (GFNs) appreciably increased in recent years. Among GFNs, graphene oxide (GO) is one of the most highly studied members due to its inexpensive synthesis cost compared to graphene, its stability in aqueous media and its broad application. However, GO also has been found to be the most toxic among GFNs. Lab studies showed that GO undergoes phototransformation in surface waters, resulting in products that include reduced GO (rGO) and polycyclic aromatic hydrocarbons (PAHs). Due to technical and analytical limitations, it is still difficult to conduct in-situ measurement of GO and rGO concentrations released in the environment, and it is of utmost importance to establish a model that can predict their environmental exposure concentrations in the environment. In this study, we develop a fate and transport model to predict time-dependent environmental exposure concentrations of GO for the Brier Creek Watershed in the GA coastal plain. We investigate the influence of sunlight radiation on the distribution of GO and its phototransformation products in the watershed over a 20-year period using the most updated Water Quality Analysis Simulation Program (WASP8). Flow rate, sediment transport data and sunlight radiation data are input into WASP8, and WASP8 is used to internally calculate a GO phototransformation rate and productions of rGO and PAHs. Heteroaggregation coefficients of GO and rGO with suspended solids were measured in an EPA laboratory, and then input into WASP8. GO and rGO concentrations in the watershed are calculated by WASP8. Mass fraction results show that GO is the predominant species among GO derived species, which account for 99% of the mass throughout the whole watershed of interest, while rGO species, including free rGO and rGO heteroaggregated to suspended solids, only account for 1%. We also found that almost all free GO and rGO are present in water column due to their extremely low settling velocity. rGO can be precipitated through heteroaggregation processes and predominantly accumulate in sediment. The identification of the exact PAHs species generated during GO phototransformation and simulation of PAHs concentrations in both water column and sediment using WASP8 are useful tools to facilitate the risk assessment of PAHs in watersheds.
