title: From soil to water
title: The detachment and transport of microplastics from agricultural soil
titleType: Subtitle
Creators: name: Severe, Emilee
Publisher: name: Lancaster University
Year: 2025

description: Microplastics (MPs) are a contaminant of emerging concern found
 extensively in various ecosystems across the globe. Many questions remain
 unanswered regarding the impact MPs will have on earth’s biotic and
 abiotic systems, however, MPs have been shown to be particularly harmful
 for aquatic organisms. Rainfall-induced erosion from agricultural soils,
 is thought to be a significant source of MPs to aquatic ecosystems, though
 little research exists which quantifies the magnitude and rate of MP
 transported in these processes. There are several transport pathways MPs
 potentially follow during rainfall-induced erosion including: surface
 runoff, splash erosion and vertically into the soil with infiltrating
 rainwater. However, the majority of research investigating the movement of
 MPs have investigated either the transport of MPs in surface runoff or
 infiltration into the soil profile, but not both in tandem. Additionally,
 no research has yet explored MP transport in splash erosion processes.
 Along with investigating the transport pathways MPs follow, this thesis
 also explores properties which influence MP transport focusing on
 properties which distinguish MPs from natural soil particles specifically,
 density and aging processes. We also investigate how MP size influences
 transport as this is thought to be a significant property controlling MP
 transportation processes. This thesis uses innovative methodologies to
 investigate MP transport during rainfall-induced erosion events, focusing
 on the pathways MPs follow and how their properties influence their
 transport behaviour. It presents three rainfall simulation experiments,
 the first of which explores the differences in transport between MPs and
 sand, a proxy for natural soil particles. This experiment found that MPs
 had more rapid transport from the soil surface and distinct transport
 patterns in surface runoff and splash erosion compared to the sand
 particle. The second experiment was conducted in an agricultural field
 without vegetation and explored what transport pathways MPs of various
 size follow during a rainfall simulation. This research found that the
 influence of size on transport varied between transport pathways. The
 final experiment employed methodologies in an attempt to recreate
 environmentally relevant conditions in laboratory rainfall simulations by
 comparing the transport of aged and pristine MPs alongside the influence
 of MP-soil aggregation on transport. The result from this experiment found
 variable rates of artificial aging between polymers and that low levels of
 MP-soil aggregation do not reduce MP transport in surface runoff. Together
 the results from the research presented in this thesis are among the first
 to investigate the rate as well as the magnitude of MP transport in
 several transport pathways during rainfall-induced erosion. The knowledge
 gained in this research gives a holistic understanding of MP transport
 processes during rainfall-induced erosion and shows that soils have a high
 capacity to retain MPs but that MPs are also readily transported from soil
 in surface runoff and splash erosion processes. To mitigate the transfer
 of MPs from soil to aquatic ecosystems, policymakers should promote
 programs and initiatives that reduce soil erosion, which would not only
 limit MP emissions but also enhance soil health for farmers. Additionally,
 establishing monitoring programs in agricultural soils near riparian areas
 would greatly enhance our understanding of the MP retention in soil or
 transport into water bodies, providing critical data to inform future
 environmental policies and regulatory decisions. Efforts should be made at
 individual, community and government levels to reduce plastic consumption,
 remediate environments plastic-polluted and develop sustainable
 alternatives to conventional plastics.