Total organic carbon content as an index to estimate the sorption capacity of micro- and nano-plastics for hydrophobic organic contaminants

Abstract

The worldwide existing micro- and nano-plastics (MNPs) showed high sorption capacity for hydrophobic organic contaminants (HOCs), and thus leading to change of the environmental behaviors and fates of HOCs. However, there is a lack of general index for evaluating the sorption capacity of MNPs for HOCs. Herein, we investigated the sorption of chlorobenzene, naphthalene and phenanthrene to 10 MNPs of different polymer types with and without UV-aging, respectively. It was found that the sorption was well fitted by Freundlich isotherm model with coefficients R² in the range of 0.892-1.00, and aging of most MNPs resulted in decreased sorption capacity for naphthalene and phenanthrene but slightly increased sorption capacity for chlorobenzene. More importantly, for the 8 MNPs commonly present in the environment and with measured total organic carbon (TOC) covering the range of 23.0-91.9%, the logarithm sorption constant (logK_d) values of the studied HOCs positively correlated with TOC contents of MNPs, with a good determination coefficient (R²) of 0.923 for naphthalene, 0.694 for chlorobenzene, and 0.565 for phenanthrene. Our study demonstrated that the TOC content of MNPs is a good index for estimating the contribution of total MNPs to the sorption of nonpolar HOCs in the environmental media.

Keywords: Aging; Chlorobenzene; Freundlich model; PAHs; Sorption constant.