Improving analytical methods for the extraction and analysis of biodegradable and non-biodegradable microplastics in the soil environment.

Global plastic production reached 368 million tonnes in 2019 (Plastics Europe, 2020), with the greatest demand being for packaging. Plastic waste management in many countries is mismanaged, with ~25% of post-consumer waste globally sent to landfill in 2018, this increases the likelihood of plastic ending up in the environment, raising concerns about the impact of plastic pollution on the environment. Microplastics (particles <5mm) are emerging contaminants with high risk due to their ubiquity in the environment and the as yet unknown scale of their impact on organisms and ecosystems.

Microplastics are present in all environmental compartments, but research to date has focused on marine systems, leaving a substantial knowledge gap in understanding how microplastics behave in and impact other environments, especially terrestrial ones. Terrestrial soils provide key ecosystem services (e.g. food provision and climate regulation), however these services are threatened by soil pollution including from microplastics. Soils act as a sink for microplastics, which typically enter the soil through their widespread use in agriculture. Common entry pathways include the application of microplastic containing sewage sludge as fertiliser, and the direct application of microplastics via the polymer encapsulation of pesticides and seeds. Whilst the impacts of microplastics are not fully known, it is possible that they will compromise soil health and functions.

We urgently need to understand how microplastics of different compositions and sources affect soil ecosystems, but research progress is hindered due to the lack of standardised protocols for the identification, extraction, and analysis of microplastics in the complex soil environment. Soil is high in organic matter, meaning protocols devised for aquatic samples are not feasible because more aggressive digestion steps are required to remove soil organics.

This poster looks at the extraction and analysis of microplastics from soil samples, following a generalised framework of sieving, density separation, organic digestion, and analysis. It outlines the effectiveness of each step in the soil matrix and its applicability for both biodegradable and non-biodegradable microplastics. It compares the effect of commonly used digestion solutions (e.g. Fenton’s reagent, hydrogen peroxide) on the polymers, by using Raman spectroscopy to characterise the plastics before and after treatment, and thus to assess chemical changes arising from the sample processing. Based on these results an optimal workflow is defined as the basis for evaluating the biodegradation of microplastics in soil.