The migration and residual regularity of doxycycline and antibiotic resistance genes at different depths of sandy loam with the influence of an oversized microplastic contamination layer

• Fiber OMP was much risk than debris OMP on manure-born DOX residual in soil. • OMPs enhanced manure-born DOX migration from PCL to deeper soil. • The combination of OMP and DOX mightily increased bacteria ARGs abundance. • OMPs enhanced phage ARGs abundance increasing. • OMPs seriously enhanced phage ARG migration/residual without DOX exposure. Plastics that are larger than microplastics (MPs) in soil are always ignored in studies of environmental behavior. The soil contaminated by plastic is only included in the “soil layer” of the entire soil system, which could be called the plastic contamination layer (PCL), and a complete plastic contamination risk evaluation in the entire soil system based on the PCL is always lacking. In the present study, oversized microplastics (OMPs) and their PCL effects on the migration and residual regularity of doxycycline and bacteria/phage antibiotic resistance genes (ARGs) in complete soil systems under manuring conditions were investigated. The results showed that the OMPs greatly increased the soil DOX residual concentration in the PCL (the highest DOX concentration was 133.12 μg/kg) in a short time; moreover, the fiber OMPs could still significantly decrease DOX degradation after 56 days. The PCL also enhanced DOX migration and residual DOX from the PCL to the deeper soil. Although DOX exposure greatly increased the total abundance of potential ARG host bacteria, the combination of DOX and OMP had the highest bacterial ARG total abundance contribution proportion (34.18%). In addition, OMPs increased the absolute abundance of phage ARGs, and OMPs even enhanced phage ARG migration and residual abundance in deep soil without DOX exposure. The present study first highlights the double risks of OMPs and their PCLs during manuring, and the shape of OMPs could also cause a difference in the risks.