The desorption mechanism of dissolved organic matter on pollutants and the change of biodiversity during sediment dredging.

Sediment dredging is an effective means to control the endogenous pollution of lakes, which could significantly change the concentration and composition of organic matter, especially dissolved organic matter (DOM) in the lake. DOM is particularly important for the release of endogenous pollutants, which will inevitably bring an impact on aquatic biodiversity. Nevertheless, in recent research little attention has been paid to the desorption mechanism of DOM on pollutants and the change of biodiversity during dredging. This study investigated the physicochemical properties of DOM in the sediment by taking a sediment dredging project in Dianchi Lake in China for example. The correlations of DOM properties with the desorption behavior of nitrogen (N), phosphorus (P), cadmium (Cd), lead (Pb) and the biodiversity of aquatic organisms were analyzed. The results show that the aromaticity and humification of DOM were improved after dredging, and the high molecular weight DOM was degraded into low molecular weight substance. The desorption amount of N, P and heavy metals (Cd, Pb) were decreased as the pH values increased. Moreover, NH4+-N promoted the release of Pb2+ from DOM, while the release of PO43--P was inhibited. Correlation analysis shows that the physicochemical properties of DOM exactly affected the release of N, P, Cd and Pb. It was easier to desorb pollutants with low aromaticity and humification of DOM, leading to a decrease in the diversity of aquatic organisms. This study identified the desorption mechanism of endogenous pollutants in DOM and the ecological risk to aquatic organisms, providing a theoretical basis for the prevention and control of water pollution.

The distribution and risk of microplastics discharged from sewage treatment plants in terrestrial and aquatic compartment.

Many microplastics (MPs) were produced in daily life, which would enter sewage treatment plants (STPs) with the wastewater. Although the STPs has a good interception effect on these MPs, there will still be a part of MPs entering the environment with the effluent and sludge treatment, causing a certain ecological risk. This study investigated the abundance, characteristics and retention of MPs in different STPs, as well as the ecological risks caused by MPs entering the environment. The abundance of MPs in influent and effluent was ranged from 2.02 to 2.50 items L-1 and 0.27-0.48 items L-1, respectively. The abundance of MPs in dewatered sludge and sediment of Lake Dianchi was ranged from 3.719-6.949 × 103 items (kg Ds)-1 and 1.84-5.23 × 103 items (kg Ds)-1, respectively. So roughly 80% of the MPs were trapped and transferred into the dewatered sludge. The observed colors of MPs were transparent, black, blue, red, pale brown, green and gray, and their main species were polypropylene (PP) and polyethylene (PE). To further evaluate the ecological risks of MPs, the oyster mushroom was cultivated in a medium supplemented with MPs. It was found that MPs could be absorbed by oyster mushrooms with a 7-11% of absorption rate, the fibers were widely distributed in the stipes and the pileus. This study had theoretical significance for exploring the distribution of MPs in STPs and clarifying the ecological risk posed by MPs in the environment.

Cytotoxicity and pro-inflammatory effect of polystyrene nano-plastic and micro-plastic on RAW264.7 cells.

Numerous studies have shown that exposure to micro- or nano-plastics led to the cell viability and function of macrophages in the intestine tissue might be one possible mechanism. This study investigated the cytotoxicity and pro-inflammatory effect of 80 nm polystyrene-nano-plastic (PS-NP) and 3 µm PS-micro-plastic (PS-MP) on mouse macrophages RAW264.7 cells. Our results showed that exposure to PS-NP or PS-MP induced apoptosis of cells at 5 or 10 µg/mL, respectively. Besides, PS-NP enhanced the secretion of inflammatory cytokines (Tumor necrosis factor-α, Interleukin-6 and Interleukin-10) with the lowest effective concentration (LOEC) of 1, 0.01, and 0.01 µg/mL, respectively. PS-MP enhanced secretion of TNF-α and IL-10 with the LOEC of 1 and 0.01 µg/mL, respectively. We further studied the possible mechanisms of the effects of PS-NP or PS-MP on RAW264.7 cells. We found they might cause cytotoxicity and inflammatory effects by producing reactive oxygen species and nitric oxide in the cells. Accordingly, our results demonstrated that PS-NP and PS-MP had cytotoxicity and pro-inflammatory effect on macrophages, which might further lead to intestinal inflammation. Moreover, we revealed that the PS-NP had more potent adverse impacts on macrophages than PS-MP.