Sorption behavior of polycyclic aromatic hydrocarbons on biodegradable polylactic acid and various nondegradable microplastics: Model fitting and mechanism analysis

The main objective of this study was to gain more detailed knowledge of how four selected polycyclic aromatic hydrocarbons (PAHs) interact on six nondegradable types of microplastics (MPs) and one biodegradable plastic (BP) in two water matrices. The results were evaluated using the popular Freundlich and Langmuir isotherm models, as well as a new modified mathematical model. The modified mathematical model was developed to additionally elucidate the adsorption mechanism, to investigate transfer kinetics of PAHs and to predict the variation of adsorption rate and capacity as a function of time. The adsorption kinetics of selected PAHs onto MPs and biodegradable plastic were described best by the pseudo-second order kinetic model ( R 2 = 0.810–0.999), implying that chemisorption is possibly the adsorption mechanism. The results of the adsorption isotherm study also indicated that adsorption of PAHs on selected types of microplastics was best described by the Langmuir model, implying that adsorption of PAHs is more dominant on powdered types of MPs in both synthetic and real water matrices. On the other hand, the lowest adsorption affinity was achieved for adsorption of PAHs on polylactic acid, indicating that this type of biodegradable plastic would have significantly less impact on the transport and distribution of PAHs through environment. • Non-degradable and biodegradable MPs adsorption of so far unexamined PAHs • Mathematical model developed to investigate mass transfer kinetics of PAHs on MPs • MPs properties are the most important factor determining adsorption rate of PAHs. • Adsorption affinity of PLA for PAHs is lower than of non-degradable MPs.