Leaching of Soil Microplastics Through Meso- and Macrofuanal Community Transport (manuscript introduction)

Transport of microplastics (MPs) in terrestrial compartments has been a growing body of research in recent years, however many of these soil models do not include the realistic role that soil organisms play in terrestrial MP movement. Here, we explore, for the first time, MP transport capabilities of multiple soil species from various ecological niches to investigate complex community structure’s interaction with MPs. Soil column mesocosms were incubated for 18 weeks with 250mg LLDPE (300-600µm) placed on soil surface and introduced were communities of naturally sourced earthworms from single and combined ecological niches (anecic, epigeic and endogeic) along with further integration of the three major ecological niches of collembola (epedaphic, hemiedaphic and euedaphic). Infiltration was performed bi-weekly to simulate intermittent rainfall events and to investigate leaching potential of microplastics through the soil columns with and without the influence of organisms. Throughout the experiment MPs were counted from leachate collected every two weeks and at the end the columns were separated into 11 layers to analyze the distribution of MPs. The presence of anecic, deep burrowing, earthworms significantly increased transport of MPs through the column into the leachate, yet there was an additive effect of leached MPs with all three types of earthworms present together and an even more so when collembola were present with anecic and all earthworms together. Thus, complex community structure increases vertical transport of MPs. At the end of the experiment significantly more MPs were still present at the soil surface of treatments with no organisms and only collembola present, treatments with earthworms present had much less MPs at soil surface and more integration of MPs in each soil layer throughout the entirety of the column. This study highlights the importance of factoring in realistic communities of soil inhabitants as a driver for intensified MP movement and needs to be considered in MP transport modeling.