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Responses of soil enzyme activities to urea amendment in microplastic-impacted soils
Summary
Researchers investigated how three types of microplastics (HDPE, PP, and PET) affect key soil enzymes involved in nutrient cycling, with and without urea fertilizer. Higher microplastic concentrations significantly reduced enzyme activities by 10-34%, with PP and HDPE causing the strongest effects. While urea partially offset the enzyme inhibition at low microplastic levels, it was unable to counteract the suppression at higher concentrations, highlighting the threat microplastics pose to soil health.
Abstract This study investigates the impact of microplastics (HDPE, PP, PET) on soil enzyme activities (urease, alkaline phosphatase, β-glucosidase), which are crucial for biogeochemical cycling, and their interaction with urea, a widely used nitrogen fertilizer. Soil samples from farmland in Bursa, Turkey, were treated with microplastics at 0%, 0.5%, and 5% concentrations and urea at 0 and 20 mg/100 g, then incubated aerobically (at 28 °C and 70% field capacity) for 60 days. Enzyme activities and pH were measured at 20, 40, and 60 days, and two-way ANOVA was used for statistical evaluation. Results showed that higher microplastic concentrations (5%) significantly reduced enzyme activities, with urease decreasing by approximately 17–33%, β-glucosidase by 14–34%, and alkaline phosphatase by 10–25%. Among microplastic types, PET had the least inhibitory effect, while PP and HDPE caused stronger reductions. Urea application partially alleviated enzyme inhibition at low microplastic concentrations, enhancing activity by 15–20%, but failed to counteract suppression at higher doses. These findings highlight the disruptive impact of microplastics on soil biochemical processes, reducing nutrient cycling efficiency and compromising soil health. While urea application offers some mitigation, its effectiveness is limited in microplastic-contaminated soils. This study underscores the urgent need for integrated soil management strategies to minimize the dual threats of microplastic pollution and declining fertilizer efficiency, ensuring long-term soil sustainability.
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