New model predicts how microplastics adsorb toxic PFAS

Trillions of tiny plastic pollutants known as microplastics, measuring less than five millimeters in length, have infiltrated rivers, lakes, and oceans worldwide. These minuscule particles pose a significant threat as they can easily enter the bodies of humans and animals. Even more concerning is their ability to absorb and transport toxic substances, including a newly discovered group of hazardous chemicals known as per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals.”

With thousands of different types of PFAS present in both freshwater and saltwater bodies, determining whether microplastics can absorb each specific type requires expensive, time-consuming, and labor-intensive testing methods. In light of this challenge, a team of researchers led by the University of Maine has developed an innovative model. This model aims to predict whether a particular type of microplastic is capable of adsorbing a specific kind of PFAS and at what concentration it may occur.

Dilara Hatinoglu, a Ph.D. student in civil and environmental engineering, played a central role in spearheading this project. Working in collaboration with her advisor, Onur Apul, an assistant professor of environmental engineering, and Fran├žois Perreault, an associate professor at the Arizona State University School of Sustainable Engineering and the Built Environment, they have made strides in advancing our understanding of microplastic-PFAS interactions.

Dilara Hatinoglu. Credit: University of Maine

The innovative models developed by the University of Maine-led research team have broad applicability, covering both fresh and saltwater environments. These models take into account various factors such as the type, size, shape, and ionic charge of microplastics, as well as the functional compound groups, chain length of PFAS, and solution chemistry of water including salinity, pH level, and natural organic matter. By incorporating these parameters, the models minimize the need for extensive laboratory testing and hold the potential to facilitate the development of new technologies for PFAS removal.

Dilara Hatinoglu, the driving force behind this project and a Ph.D. student in civil and environmental engineering, explains that the models can assist in modifying sorbents and designing adsorbent technologies for PFAS removal in water treatment plants. The insights gained from the models provide valuable information on the mechanisms and contributors to adsorption, guiding the development of effective solutions.

To validate their models, the UMaine-led team focused on the adsorption of 12 chemicals from the subset of PFAS called perfluoroalkyl carboxylic acids (PFCAs) by polystyrene microplastics. Their findings confirmed the accuracy of the models and shed light on various adsorption mechanisms between PFAS and microplastics. For example, polystyrene exhibited a higher capacity for adsorbing long-chain PFAS compared to short-chain ones, microplastics in saltwater showed higher PFAS adsorption than those in freshwater, and the polarizability and hydrophobicity of PFCAs were key contributing factors for their adsorption onto microplastics. These research findings were published in the journal Science of The Total Environment.

The team’s forecasting method for PFAS adsorption utilized a reconfigured version of an existing model called linear solvation energy relationships (LSER). While traditional LSER models are commonly employed for analyzing adsorption mechanics between naturally-charged organic compounds, this research marks one of the pioneering applications of LSER modeling for PFAS adsorption, considering their negative charge.

Dilara Hatinoglu is extending her previous work by developing another model to predict the adsorption of other pollutants onto microplastics, taking into account the extent of microplastic degradation. By factoring in degradation effects, the model aims to provide a more realistic representation of pollutant-microplastic interactions.

This project led by Hatinoglu is part of a broader effort involving Onur Apul, her advisor, fellow students, and researchers from Arizona State University to investigate the interactions between microplastics and various chemicals. Apul highlights the importance of interdisciplinary collaboration to address the PFAS crisis effectively, emphasizing the need to bring together talented researchers from diverse fields.

The University of Maine’s PFAS+ Initiative, which focuses on the emerging PFAS pollution crisis and its wide-ranging environmental and societal impacts, involves numerous researchers working on multiple PFAS research projects. Apul serves as the science lead and a steering committee member for this university-wide initiative.

Apul concludes that the research team aims to be at the forefront of knowledge and to align their work with the needs of Maine and the global community. Through their cutting-edge research, they strive to publish groundbreaking findings in this field, addressing the urgent challenges posed by PFAS pollution.

Source: University of Maine

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