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 and 0.27-0.48 items L, respectively. The abundance of MPs in dewatered sludge and sediment of Lake Dianchi was ranged from 3.719-6.949 × 10 items (kg Ds) and 1.84-5.23 × 10 items (kg Ds), 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.