Environmental Fate Modeling of Nanoplastics in a Salinity Gradient Using a Lab-on-a-Chip: Where Does the Nanoscale Fraction of Plastic Debris Accumulate?

• Published in: Environmental science & technology 2021-03, Vol.55 (5), p.3001-3008
• Main Authors: Venel, Zélie, Tabuteau, Hervé, Pradel, Alice, Pascal, Pierre-Yves, Grassl, Bruno, El Hadri, Hind, Baudrimont, Magalie, Gigault, Julien
• Format: Article
• Language: English
• Subjects: Agglomeration; Aggregates; Colloids; Concentration gradient; Contaminants in Aquatic and Terrestrial Environments; Continuums; Earth Sciences; Environment models; Environmental Monitoring; Environmental Sciences; Estuaries; Geochemistry; Interfaces; Lab-on-a-chip; Lab-On-A-Chip Devices; Mangrove swamps; Microfluidics; Microplastics; Physics; Plastic debris; Plastic pollution; Plastics; Pollutants; Saline environments; Salinity; Salinity effects; Sciences of the Universe; Swamps; Water Pollutants, Chemical - analysis; Water pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.0c07545

The aim of this study is to demonstrate how the flow and diffusion of nanoplastics through a salinity gradient (SG), as observed in mangrove swamps (MSPs), influence their aggregation pathways. These two parameters have never yet been used to evaluate the fate and behavior of colloids in the environment, since they cannot be incorporated into classical experimental setups. Land–sea continuums, such as estuaries and MSP systems, are known to be environmentally reactive interfaces that influence the colloidal distribution of pollutants. Using a microfluidic approach to reproduce the SG and its dynamics, the results show that nanoplastics arriving in a MSP are fractionated. First, a substantial fraction rapidly aggregates to reach the microscale, principally governed by an orthokinetic aggregation process and diffusiophoresis drift. These large nanoplastic aggregates eventually float near the water’s surface or settle into the sediment at the bottom of the MSP, depending on their density. The second, smaller fraction remains stable and is transported toward the saline environment. This distribution results from the combined action of the spatial salt concentration gradient and orthokinetic aggregation, which is largely underestimated in the literature. Due to nanoplastics’ reactive behavior, the present work demonstrates that mangrove and estuarine systems need to be better examined regarding plastic pollution.