Effect of Microplastics and Phenanthrene on Soil Chemical Properties, Enzymatic Activities, and Microbial Communities

Abstract

Microplastic and polycyclic aromatic hydrocarbon (PAHs) pollution have received increasing attention due to their ubiquitous distribution and potential risks in soils. However, the effects of microplastics-PAHs combined pollution on soil ecosystems remain unclear. Polyethylene (PE)/polypropylene (PP) and phenanthrene (PHE) were selected as the representatives of microplastics and PAHs, respectively. A 300-day soil microcosm experiment was conducted to study the single and combined effects of PE/PP and PHE on soil chemical properties, enzymatic activities, and bacterial communities (i.e., quantity, composition, and function), using the soil agricultural chemical analysis method and 16S amplicon sequencing technology. The interactions of soil properties, enzyme activities, and flora in the presence of PE/PP and PHE were analyzed. The results showed that the addition of PE/PP and PHE slightly changed the pH, available phosphorus (AP), and microbial quantity (i.e., bacteria, actinomycetes, and mold) but considerably increased the fluorescein diacetate hydrolase (FDAse) activity. There was a significant enhancement of soil organic matter (SOM) and urease activity in PE, PP, PHE-PE, and PHE-PP amended systems. PHE, PHE-PE, and PHE-PP obviously increased the dehydrogenase/neutral phosphatase activities and available nitrogen (AN) content. PHE had little effect on the microbial community. The PE, PP, PHE-PE, and PHE-PP addition influenced the microbial community to some extent. PE/PP and PHE showed positive effects on the energy production, growth, and reproduction of soil microorganisms and then accelerated the metabolism/degradation of pollutants and membrane transport. The changes in AN and SOM induced by PE/PP and PHE were the key factors affecting soil enzyme activities. Alterations in AN, AP, and pH were mainly responsible for the increase in microbial population. The changes in the microbial community were related to soil chemical properties and enzyme activities, and SOM had a significant effect on the microbial community. The presence of different carbon sources (PE/PP and PHE) in the soil and the microbial interaction also affected the microbiota. In conclusion, the addition of single or combined pollutants of PE/PP and PHE influenced the soil chemical properties, enzymatic activities, bacterial communities, and their interaction processes, thus facilitating the adaptation of the microbial community to pollutant stress.