Organic fertilizer facilitates the soil microplastic surface degradation and enriches the diversity of bacterial biofilm

The land-use of organic fertilizers is considered as an important sustainable method for resource utilization, which may have an impact on the microplastic behaviors in the soil. Here, a 240-d dark culture experiment was conducted to reveal the degradation and biofilm characteristics of degradable and refractory granule microplastics in soil and soil-fertilizer systems. The results indicated that microplastics generally exhibited a weak weight loss as well as a specific etiolation on the surface after the culture, especially polyvinyl-chloride and polyhydroxyalkanoates (PHA). Increase in carbon-oxygen functional groups and the changes of oxygen/carbon ratios was noticed, which implied that oxidation and degradation occurred on the surface of microplastics during the cultural process. The changes were more intense on the degradable PHA, and the fertilized-soil treatment than those of the refractory microplastics and the pure soil. Moreover, the addition of organic fertilizers enriched the community diversity of bacterial biofilm on multiple microplastic surfaces. in this regard, the animal fertilizers provide a stronger effect than the plant fertilizers. Overall, the soil, fertilizer and microplastic types affected the community structure and diversity of bacterial biofilm. The outcomes of this study would provide a theoretical basis for the utilization of organic matters for agricultural soil applications. Organic fertilization is considered effective in improving the soil fertility. It may trigger microplastic degradation in the soil by introducing rich organic matters and microbial flora in soil. The study emphasizes that supplementation of organic fertilizers into the soil can promote the degradation of microplastics, by generating and increasing the number of oxygen-containing functional groups, and altering the microplastics unsaturation in the absence of light. The application of organic fertilizer into soil can significantly improve the aggregation of microorganisms on the surface of microplastics. In this regard, the soil, fertilizer or microplastic types affect the community structure of bacterial biofilm.