Interaction of biosolids-derived dissolved organic matter with microplastics: EEM analysis

Composted biosolids are commonly used in agricultural lands as organic amendments. However, biosolids application also exposes the soil to pollution risk from various contaminants including microplastics (MPs). The MPs inevitably interact with the dissolved organic matter (DOM), which is the most active fraction of the soil organic matter. The physiochemical properties of the DOM, which vary based on the organic matter origin, are one of the key factors influencing these interactions. The majority of studies on DOM-MP interactions employ commercially available humic and fulvic acid as the DOM source and may not accurately represent the polydisperse nature of DOM released from organic amendments used in agricultural fields. The motivation for this study stems from recognizing the knowledge gap in understanding the interaction between the naturally occurring DOM in the soil and the MPs. It is imperative to investigate these interactions to determine consequential changes in DOM composition and to evaluate the fate and cotransport with other pollutants in the soils. For this purpose, we conducted adsorption experiments with various concentrations of biosolids-derived DOMs and different MP particles. We used the Excitation-Emission matrix (EEM) obtained by fluorescence spectroscopy to study the changes in the DOM due to its adsorption on the MPs. PARAFAC modeling of the EEMs was used to identify the preferential binding affinity of distinct fluorescent DOM components to the MPs. The results of the adsorption experiment and the EEM analysis will be presented and discussed.Keywords: microplastics, dissolved organic matter, biosolids, adsorption, fluorescence spectroscopy, EEM