Sorption properties of hydrophobic organic chemicals to micro-sized polystyrene particles.

It has been reported that microplastics (MPs) have strong affinity for hydrophobic organic chemicals (HOCs) and can be ingested accidentally by aquatic organisms, posing a potential threat to the environment. To date, the sorption data used in modelling to clarify the mechanism were mostly obtained in varied sampling durations and regions from different works, which might cause inevitable deviation in modelling results. The current study aimed to illustrate the sorption properties of HOCs to the micro-sized polystyrene (PS). The sorption behaviors of HOCs to the PS were investigated at a certain pre-equilibrium status, and the theoretical analysis was taken into consideration. A bottle-shaped passive dosing system was designed to measure the concentration ratio of HOCs in different phases of the exposure suspension at a certain time (logaMP), including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) with logKow ranging from 3.17 to 10.20, between water and PS MPs with different dimensions (diameters of 100 nm, 1 µm and 2 µm, respectively). The calculated logaMP ranged from 3.73 to 8.34, and a positive correlation was found between logaMP and log1r0 (r0 is the MP radius). The results indicated that HOCs would diffuse into the PS particles, but the mass transfers inside the particles were slow and would be negligible in some environmental cases. Under theoretical considerations, the diffusion through the boundary layer of the particle was considered as the dominating process because it was fast, and the contributions of absorbed amounts on the particle surface were larger for smaller PS particles (i.e. 100-nm PS). This study could provide applicable data for further exploring the effects of micro-sized plastics on the HOCs in environmental samples.

Investigating the toxicities of different functionalized polystyrene nanoplastics on Daphnia magna.

Nanoplastics (NPs) spread widely with water and air current, and they can accumulate in aquatic organisms, even penetrating biofilms, which may cause persistent toxicity and potential hazards. This current study aimed to reveal the toxicological mechanism of different functionalized polystyrene (PS) NPs on Daphnia magna (D. magna) by investigating toxicity endpoints in individual level and biochemical level. In this study, acute toxicity, behavioral parameters and biomarker responses of D. magna was measured in the exposure of different functionalized PS NPs (plain PS, PS-p-NH2, PS-n-NH2 and PS-COOH). The results indicated that when exposed to the plain PS, ROS induction would activate MAPKs, thereby causing lethality and adverse behavior effects on D. magna; while the functionalized PS NPs were less toxic than the plain PS, especially for PS-p-NH2 which was severely flocculated after exposure, thus showing no immobilization at the investigated concentrations. Also, the antioxidant system was mainly stimulated due to the direct interaction with the cell surface receptor, which was different from the plain PS. Consequently, this work suggests significant effects of functional groups on NPs for environmental toxicity studies, and provides a better understanding of the toxicological mechanism on the toxicity of PS NPs toward D. magna.

Effect of dissolved organic matter on pre-equilibrium passive sampling: A predictive QSAR modeling study.

Pre-equilibrium passive sampling is a simple and promising technique for studying sampling kinetics, which is crucial to determine the distribution, transfer and fate of hydrophobic organic compounds (HOCs) in environmental water and organisms. Environmental water samples contain complex matrices that complicate the traditional calibration process for obtaining the accurate rate constants. This study proposed a QSAR model to predict the sampling rate constants of HOCs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and pesticides) in aqueous systems containing complex matrices. A homemade flow-through system was established to simulate an actual aqueous environment containing dissolved organic matter (DOM) i.e. humic acid (HA) and (2-Hydroxypropyl)-ß-cyclodextrin (ß-HPCD)), and to obtain the experimental rate constants. Then, a quantitative structure-activity relationship (QSAR) model using Genetic Algorithm-Multiple Linear Regression (GA-MLR) was found to correlate the experimental rate constants to the system state including physicochemical parameters of the HOCs and DOM which were calculated and selected as descriptors by Density Functional Theory (DFT) and Chem 3D. The experimental results showed that the rate constants significantly increased as the concentration of DOM increased, and the enhancement factors of 70-fold and 34-fold were observed for the HOCs in HA and ß-HPCD, respectively. The established QSAR model was validated as credible (RAdj.2=0.862) and predictable (Q2=0.835) in estimating the rate constants of HOCs for complex aqueous sampling, and a probable mechanism was developed by comparison to the reported theoretical study. MAIN FINDING OF THE WORK: The present study established a QSAR model of passive sampling rate constants and calibrated the effect of DOM on the sampling kinetics.