Precipitation contributes to alleviating pollution of rubber-derived chemicals in receiving watersheds: Combining confluent stormwater runoff from different functional areas.

The release of rubber-derived chemicals (RDCs) in road surface runoff has received significant attention. Urban surface runoff is often the confluence of stormwater runoff from specific areas. However, the impact of precipitation on RDCs contamination in confluent stormwater runoff and receiving watersheds remains poorly understood. Herein, we investigated the profiles of RDCs and their transformation products in confluent stormwater runoff and receiving rivers affected by precipitation events. The results showed that 34 RDCs are ubiquitously present in confluent stormwater runoff and surface water, with mean concentrations of 1.03-2749 and 0.28-436 ng/L, respectively. The most dominant target compounds in each category were N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 6PPD-quinone, 2-benzothiazolol, and 1,3-diphenylguanidine. Total RDCs concentrations in confluent stormwater runoff decreased spatially from industrial areas to business districts to college towns. A significant decrease in RDCs levels in surface water after rainfall was observed (P < 0.01), indicating that precipitation contributes to alleviating RDCs pollution in receiving watersheds. To our knowledge, this is the first report of N,N'-ditolyl-p-phenylenediamine quinone (DTPD-Q) levels in surface waters in China. The annual mass load of ∑RDCs reached 72,818 kg/y in confluent stormwater runoff, while 38,799 kg/y in surface water. The monitoring of confluent stormwater runoff is an efficient measure for predicting contamination loads from RDCs in rivers. Risk assessment suggested that most RDCs posed at least medium risks to aquatic organisms, especially 6PPD-quinone. The findings help to understand the environmental fate and risks of RDCs in the confluent stormwater runoff and receiving environments after precipitation events.

[Sorption Characteristics and Site Energy Distribution Theory of Typical Estrogens on Microplastics].

Microplastics (MPs) and estrogens are high-profile emerging contaminants at present, and MPs might become the carrier of estrogens in the environment and induce combined pollution. To study the adsorption behavior of polyethylene (PE) microplastics to typical estrogens, the adsorption isothermal properties of the six estrogens[estrone (E1), 17α-estradiol (17α-E2), 17ß-estradiol (17ß-E2), estriol (E3), diethylstilbestrol (DES), and ethinylestradiol (17α-EE2)] in single-solute and mixed-solute systems were studied through batch equilibrium adsorption experiments, in which the PE microplastics before and after adsorption were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Then, the site energy distribution theory of the adsorption of six estrogens on PE microplastics was further analyzed based on the Freundlich model. The results showed that the adsorption process of selected estrogens with two concentrations (100 µg·L-1 and 1000 µg·L-1) on PE were more consistent with the pseudo-second order kinetic model. The increase in initial concentration reduced the equilibrium time of adsorption and increased the adsorbing capacity of estrogens on PE. In the single system (one estrogen) or mixed system (six estrogens) with different concentrations (10 µg·L-1-2000 µg·L-1), the Freundlich model showed the best fitting effect for the adsorption isotherm data (R2>0.94). The results of isothermal adsorption experiments and XPS and FTIR spectra showed that the adsorption of estrogens on PE in the two systems was heterogeneous adsorption, and hydrophobic distribution and van der Waals forces were the principal factors in the process of adsorption. The occurrence of C-O-C (in only the DES and 17α-EE2 systems) and O-C[FY=,1]O (in only the 17α-EE2 system) indicated that the adsorption of synthetic estrogens on PE was affected slightly by chemical bonding function, but no obvious effects were observed for natural estrogens. The results of site energy distribution analysis showed that, compared with the single system, the adsorption site energy of each estrogen shifted to the high-energy region in its entirety in the mixed system, and the site energy increased by 2.15%-40.98%. The energy change in DES was the most significant among all of the estrogens, indicating its competitive advantage in the mixed system. The above results of this study can provide some reference for the study of adsorption behavior, mechanism of action, and environmental risks under the coexisting condition of organic pollutants and MPs.