title: Development of an equation based on physicochemical properties of plastic and polycyclic aromatic hydrocarbons (PAH) to predict plastic-water partition coefficients (log Kp-w) for PAHs
Creators: name: Gottschling, Michael
Publisher: name: UNSPECIFIED
Year: 2024

description: Understanding the sorption behaviour of pollutants onto the surface of plastic particles is crucial to evaluate the ecotoxicological impact of microplastics in the environment. Especially in the aquatic milieu, plastic-water partition coefficients (log Kp-w) is one of the important parameters to quantify and compare the adsorption of pollutants on different plastic materials. Log Kp-w for a variety of pollutants have been determined in the laboratory or in the field experiments. log Kp-w values for pollutants with low water solubility are, however, often not available or estimated using a mathematical equation based on physicochemical properties of sorbates such as molar mass (MW), ocatnol-water partition coefficient (log Kow) or water solubility (log Cwsat). Such equations are developed mostly only for polyethylene (PE).
In this dissertation, an equation was established to predict log Kp-w values for three widely used plastics, namely, low density polyethylene (LDPE), polypropylene (PP) and polyethylene terephthalate (PET) as well as a commonly known biodegradable polybutylene succinate (PBS). 
First, log Kp-w values of naphthalene, fluorene and phenanthrene were derived on a set of small laboratory scale experiments using four plastics and the Freundlich isotherm. In addition, plastic properties were determined in the laboratory, which were combined with PAH properties to establish a number of equations for the prediction of log Kp-w. From these equations, the most appropriate and robust equation was selected using statistical tools, including two-dimensional correlation coefficient and root mean square error (RMSE). Finally, the validity of this equation was evaluated by comparing predicted log Kp-w values using the equation with the log Kp-w values that are available in the literature. 
In the process of the development of an equation, it was confirmed that two plastic properties (crystallinity = Xc, density = ρ) and one PAH property (aqueous solubility = log Cwsat) are significant variables to understand the sorption behavior of PAHs on plastics in the aqueous environment. The major outcome of this work is the development of a universal equation for four important polymers to predict log Kp-w for PAHs based on these plastic and PAH properties:
log K(p-w) of PAH = (-1.85 * log⁡Cw^sat + 1.00) * Xc * ρ + 2.50. 
A transferability of this equation to previously published log Kp-w was performed. The result showed that 93.0 % (93 out of 100 published values), 91.7% (11 out of 12 published values), 100 % (2 out of 2 published values) and 50% (2 out of 4 published values) of the log Kp-w of LDPE, PP, PBS, and PET, respectively, were found to be within the limits of this equation. 
The procedure for the development of the equation in this work as well as the equation itself can be utilized as a basis for i) the further optimization of the equation based on log Kp-w values actually determined in the laboratory and in the field, ii) the prediction of log Kp-w for untested combinations of a pollutant and a polymer and iii) prediction of ecotoxicological effects of microplastics in the aquatic milieu.