The Effect of Microplastics on the Depuration of Hydrophobic Organic Contaminants in Daphnia Magna: A Quantitative Model Analysis

Abstract

Microplastics are emerging pollutants that can absorb large amounts of hydrophobic organic contaminants (HOCs). However, no biodynamic model has yet been proposed to estimate their effects on HOC depuration in aquatic organisms, where the HOC concentrations are time-varying. In this work, a microplastics-inclusive biodynamic model was developed to estimate the depuration of HOCs via microplastics ingestion. Several key parameters of the model were redefined to determine the dynamic HOC concentrations. Through the parameterized model, relative contributions of dermal and intestinal pathways can be distinguished. Moreover, by studying the depuration of polychlorinated biphenyl (PCB) in Daphnia magna (D. magna) with different sizes of microplastics, the model was verified and the vector effect of microplastics was confirmed. Results showed that microplastics contributed to the elimination kinetics of PCBs because of the fugacity gradient between the ingested microplastics and the biota lipids, especially for the less hydrophobic PCBs. The intestinal elimination pathway via microplastics would promote overall PCB elimination, contributing 37‒41% and 29‒35% to the total flux in the 100 nm and 2 μm polystyrene (PS) microplastics suspensions, respectively. Moreover, the contribution of microplastic ingestion to overall HOC elimination may increase as microplastic size decreases in water, implying that microplastics may protect organisms from HOC risks to some extent. To sum up, this work demonstrated that the proposed biodynamic model is capable of estimating the dynamic depuration of HOCs for aquatic organisms, with results that can shed light on better understanding the vector effects of microplastics.

Keywords: depuration, biodynamic model, HOCs, microplastics, intestinal elimination