NERC-NSFGEO: Unravelling the formation and impact of the plastisphere in response to environmental stresses in microplastic contaminated soils

Billions of tonnes of microplastics have accumulated in the terrestrial environment, with the slow breakdown of plastics creating a persistent threat of unknown magnitude and consequences. In soils, a plastisphere is formed on the microplastics' surface. In this unique environment, toxic byproducts of plastic degradation coupled with changes to soil surface properties can drive large shifts in microbial populations. Indeed, the plastisphere has different physical stability, pore structure and hydrophobicity to the surrounding soil, producing an altered habitat for microbes. Potential environmental consequences of the plastisphere include accentuated microbial transport (including pathogens), altered microbial diversity, decreased physical stability (erosion) and hydrophobicity (water dynamics).

Despite increased knowledge, the links between the soil physicochemical shifts and microbial processes induced by microplastics are unknown. We propose to address this knowledge gap in a multidisciplinary project between soil biophysicists, microbiologists and environmental engineers at the University of Aberdeen and soil environmental chemists at Cornell University. It builds on our recent research that unravelled how microplastic chemistry and aging as the plastic breaks down into fragments governs changes in physical properties like hydrophobicity and stability both spatially and over time. This collaboration also developed a unique DNA-tracer to explore microbial transport in microplastics-contaminated soils.

Our AIM is to link the physical and surface biogeochemical mechanisms and the microbial processes driving physical stability and water dynamics during plastisphere formation. We will first evaluate the behaviour of a range of microplastics (including biodegradable) aged in a broad range of soils on soil strength, hydrophobicity and stability to allow high throughput testing of plastisphere development (WP1). On a subset of these samples, plastisphere development will then be explored under a range of environmental factors (e.g. water, temperature and salinity), including spatial and temporal changes related to soil structure (WP2), enabling detailed changes in plastisphere properties to be unravelled. With this new knowledge, we will measure how plastisphere development impacts water dynamics and microbial transport, with modelling to predict environmental concerns (WP3).

An in-depth and holistic understanding will be achieved by deploying a range of state-of-the-art measurement techniques, some unique to our laboratories. We will apply these over multiple scales, linking processes occurring at the micron-scale plastisphere to the field via measurements and modelling. Visualisation of the plastisphere with 3D microscopy, coupled with spatial surface biogeochemical and molecular biology measurements, will piece together chemical, biological and physical drivers. Of particular interest are water and microbial transport processes, to be explored using our DNA tracers in controlled flow cells and leaching columns.

The greatest relevance of this project is exploring the impact of plastics, including new types of packaging, on the environment. Just as soil physical protection can protect carbon from decomposition, a plastisphere may enhance persistence of even biodegradable plastics. From the fundamental understanding of microplastic interactions with soils and microorganisms, poorly understood environmental risks like pathogen transport and microbial diversity shifts will be addressed. Microplastics create hot-spots with very different properties to the wider soil environment, and although microplastics may be sparse, their cumulative impact may not be hot for the environment.