Nano- and colloidal plastics in soil: input, plant uptake and risk assessment

Introduction

Plastic pollution has been identified as a key factor in soil health. Yet, information on inputs and concentrations in agricultural soil is limited to microplastics (> 1 m-5 mm) or larger particles. There is a significant gap in knowledge regarding submicron plastics, including colloidal plastics (CPs; 1-1000 nm) and nanoplastics (NPs; 1-100 nm), primarily due to a lack of analytical methods.

Importance of Submicron Plastics

This knowledge gap is critical because mainly submicron plastics harm soil biota, are taken up by plants, and thus pose a risk to human health via the food chain. As plastic pollution is on the rise, it is urgent to quantify submicron plastics in agricultural soils and assess the resulting plant uptake and contamination of our food to safeguard food production.

Project Objectives

Hence, the NanoSoil project is designed to test the following hypotheses:

1. Submicron plastics can be routinely detected using Field Flow Fractionation (FFF) with adaptations from environmental colloid tracing.
2. Agricultural practices (compost and sludge application, wastewater irrigation, plastic mulching) are main pathways for submicron plastics into soil.
3. The use of so-called biodegradable foils in agriculture contributes to submicron plastic pollution.
4. Uptake and accumulation of CPs and NPs in crops are polymer- and plant-specific, temperature- and humidity-dependent, with mainly NPs reaching edible parts.

Methodology

To quantify submicron plastics, I will:

1. Optimize a recently developed method using FFF and pyrolysis gas chromatography.
2. Use this method on soil samples from agricultural fields with known plastic input pathways for conventional and biodegradable plastics, including an Europe-wide survey and existing controlled field trials.
3. Assess plant uptake for representative crops.

Expected Outcomes

With my combined expertise in nanoparticle and plastic analysis in soil, NanoSoil will generate data that will form the basis for all future environmental fate and ecotoxicology studies of plastics and a robust risk assessment.