Short-term effects of polyethene and polypropylene microplastics on soil phosphorus and nitrogen availability

Microplastics are an emerging threat to soils, but little is known about their effects on soil nitrogen (N) and phosphorus (P) cycling. In this study, a three-month soil incubation experiment has been conducted to analyze the effects of polyethene (PE) and polypropylene (PP) microplastics in sizes of 0-1 mm and 1-5 mm on soil available phosphate, nitrate, and ammonium contents under different fertilization regimes. Soil phosphorus and nitrogen availability were continuously determined in-situ by ion-exchange membrane method during the incubation. Microplastic surface chemical composition and the specific surface area were analyzed by FTIR and BET, respectively. The 16s rRNA sequencing of soil bacterial communities as well as soil pH have been determined after the incubation. The results showed that the presence of microplastics could significantly (P < 0.05) decrease soil available phosphate content from 122.61 mg P L-1 to 63.43 mg P L-1. The addition of PP microplastics could significantly increase soil available ammonium content from 0.94 mg N L-1 to 1.53 mg N L-1. Since microplastics had undetectable specific surface area and limited effects on soil microorganisms, adsorption and microorganism alteration functions might not be the main drivers of microplastic effects on soil phosphorus and nitrogen.