Effects of Microplastics in Soil Ecosystems: Above and Below Ground

TLDR

Microplastics are an emerging threat to biodiversity, with soils—especially agricultural lands—acting as major sinks, yet their effects on soil ecosystems remain largely unknown. The study aimed to evaluate how PLA, HDPE, and synthetic fibers affect soil biophysical responses. The authors conducted a mesocosm experiment adding these microplastics to soil containing the earthworm *Aporrectodea rosea* and ryegrass *Lolium perenne* to assess biophysical changes. The experiment showed that PLA and HDPE microplastics, as well as synthetic fibers, reduced seed germination, inhibited ryegrass shoot growth, decreased earthworm biomass and soil pH, altered aggregate size distribution, and overall impaired key soil functions.

Abstract

Environmental contamination by microplastics is now considered an emerging threat to biodiversity and ecosystem functioning. Soil ecosystems, particularly agricultural land, have been recognized as a major sink of microplastics, but the impacts of microplastics on soil ecosystems (e.g., above and below ground) remain largely unknown. In this study, different types of microplastics [biodegradable polylactic acid (PLA)], conventional high-density polyethylene (HDPE), and microplastic clothing fibers were added to soil containing the endogeic Aporrectodea rosea (rosy-tipped earthworm) and planted with Lolium perenne (perennial ryegrass) to assess the biophysical soil response in a mesocosm experiment. When exposed to fibers or PLA microplastics, fewer seeds germinated. There was also a reduction in shoot height with PLA. The biomass of A. rosea exposed to HDPE was significantly reduced compared to control samples. Furthermore, with HDPE present there was a decrease in soil pH. The size distribution of water-stable soil aggregates was altered when microplastics were present, suggesting potential alterations of soil stability. This study provides evidence that microplastics manufactured of HDPE and PLA, and synthetic fibers can affect the development of L. perenne, health of A. rosea and basic, but crucial soil properties, with potential further impacts on soil ecosystem functioning.