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Prediction of vertical transport of microplastics: Shape- and aging-dependent drag models

Journal of Hazardous Materials 2024 4 citations

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Shape- and aging-dependent drag models for microplastic settling were developed using pristine and UV-aged PET and PS particles, with average errors of about 10% and carbonyl index incorporated to account for the effect of aging on vertical transport velocity.

The prediction of vertical transport of microplastics (MPs) is essential for understanding their multidimensional transport, fate, and environmental risks, but drag models applicable to aging MPs are currently understudied. In this study, pristine and UV-aged polyethylene terephthalate (PET) and polystyrene (PS) MPs were used for settling experiments. Combining physicochemical properties and transport data, a shape-dependent drag model based on the Corey shape factor was optimized with average errors of 9.73 % and 10.42 % and coefficients of determination of 0.6878 and 0.8359 for predicting the settling terminal velocities (u) for PET and PS MPs, respectively. Meanwhile, aging-dependent drag models were constructed by incorporating the carbonyl index as functional forms of the newly defined aging index, which can be used to differentiate the effects of shape and aging characteristics on the vertical transport of MPs. These aging-dependent models showed better predictive abilities with average errors of 3.97 % and 4.56 % in predicting u for PET MPs, and of 5.89 % and 6.91 % for PS MPs. Additionally, the drag models in this study improved applicability to predict vertical transport of environmentally-collected weathered MPs. With the continuous improvement of the transport database of diverse MPs, this study is expected to provide scientific support for predicting the environmental behaviors of MPs and formulating targeted pollution control strategies.

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