Effect Of Microplastics On Substrate Microbial Community In Constructed Wetland Influent

Potential ecological risks of the microplastics are receiving more and more attention due to its wide distribution and persistence in the environment.Relevant studies have shown that microplastics can significantly affect the wastewater treatment efficiency by changing microbial community structure and inhibiting microbial activity in water treatment systems.The occurrence of microplastics in constructed wetlands（CWs）has been reported in many previous studies,but the impact of microplastics on the purification efficiency of CWs is still unclear.Therefore in current study,synthetic wastewater with microplastics was used as the inflow of CW,and the three kinds of microplastics polyethylene（PE）,polyamide（PA）and polystyrene（PS）were used to investigate the effect of microplastics on purification efficiency of CWs,soil enzyme activities and microbial community at different exposure levels（0mg/L,1mg/L,50mg/L）.The experimental results of water quality indicators for wetland effluent indicate that long-term exposure of microplastics has a negative impact on the purification efficiency of CWs.Under low-concentration exposure,microplastics have less effect on COD removal;under high-concentration exposure,and have a significant inhibitory effect on COD removal.The order of inhibition intensity was as follows:PS>PE>PA;at various exposure levels and the impact of microplastics on NH₄⁺-N and TN removal was not evident.The inhibitory effect of the microplastics on total phosphorus removal was most significant and positively correlated with the concentration.The order of the inhibitory strength was as follows:PS>PE>PA.The outcomes of the key enzyme activities analysis in wetland soil show that long-term exposure of microplastics has an inhibitory effect on soil enzyme activities.Microplastics have a significant inhibitory effect on dehydrogenase activity where inhibitory intensity of high concentration was stronger,and the inhibition strength was as follows:PS>PE>PA.Results also reveal that microplastics have relatively slight inhibitory effect on the activities of ammonia monooxygenase and urease.The inhibitory effect of microplastic on phosphatase activity was the most significant and positively correlated with the exposure concentration.The inhibitory strength was as follows:PS>PE>PA.The change in lactate dehydrogenase relative activity shows that microplastics have caused damage to the integrity of microbial cell membranes where PS-50mg/L has the strongest damage.The inhibition of microplastics on soil dehydrogenase and phosphatase activity and the damage to microbial cell membranes resulted in a decrease in the efficiency of COD and phosphorus removal.The metagenomics analysis of the substrate microbial community showed that the structure,function and metabolism of the microbial community have changed under the long-term stress of microplastics.The species most affected by microplastics were Acidobacteria,Bacteroidetes,Verrucomicrobia,Cyanobacteria,Planctomycetes,and Armationadetes.The microbial community gene function was greatly affected by microplastics in the signal transduction mechanism,coenzyme transport and metabolism activities.Microplastics have varying degrees of influence on the abundance of functional genes related to microbial carbon,nitrogen,and phosphorus metabolism pathways.Under PS microplastic exposure,the abundance of genes related to COD and phosphorus removal was decreased most significantly,and the abundance of functional genes related to nitrogen removal was slightly affected,indicating that the decrease in abundance of functional genes was the key mechanisms for pollutant removal in CWs.The research results have made useful explorations for revealing the influence process and mechanism of microplastics on water treatment microorganisms,and provided a reference for basic analysis.