Due to limitations of sampling and analytical technologies, the risk assessment of engineered nanomaterials in the environment still significantly relies on mathematical models. The Water Quality Analysis Simulation Program (WASP) is one of the most widely used water quality models throughout the world, and has recently been updated (WASP8) to include numerical algorithms for simulating the fate and transport of engineered nanomaterials in surface waters. The production of graphene oxide (GO) nanoparticles increased appreciably in recent years. GO also has been found to be the most toxic nanoparticles among graphene-based nanoparticles. Sunlight exposure induces GO phototransformation in surface waters, resulting in products that include photoreduced GO (rGO) and polycyclic aromatic hydrocarbons (PAHs). In this study, we assume that GO releases into a river located in southeastern U.S. (Brier Creek, GA) from a wastewater treatment plant at a constant loading for 20 years, and investigate the fate and transport of GO and their major phototransformation products, rGO and PAHs. We focus on three important processes on the fate and transport of GO: (1) light attenuation, (2) phototransformation, and (3) heteroaggregation. Simulation results indicate that GO dominates the GO-derived species, with the parent species accounting for 99% of the mass throughout the whole river of interest; rGO species, including free rGO and rGO aggregated to suspended solids, account for only 1%. GO and rGO are present in the water column due to their physicochemical properties and subsequent colloidal stability. Approximately 1% of rGO aggregates with suspended solids and is removed from the water column. Four major PAHs products are detected, including two anthracene derivatives, one phenalene derivative, and pyrene. Total concentrations of these three PAHs in the water column range from 0.0032 to 0.03 ng/L throughout the river. These four PAHs gradually accumulate in the sediment and highest total concentration is found to be 1.64 ng/kg. After GO stops loading in the river, rGO can be presented in water column more than 50 years due to sediment resuspension process, and PAHs can be present in the water column for more than 60 years due to pore water exchange and sediment resuspension processes. The completion of removal of rGO and PAHs from the sediment can take more than 80 years. Besides carbon-based nanomaterials, WASP8 is able to simulate metal-based nanomaterials too.

Simulating the fate and transport of graphene oxide nanoparticles and their reaction products in surface waters using the water quality analysis simulation program 8 (WASP8)

256th National Meeting (2018)

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