Impacts of Microplastics on the Soil Biophysical Environment

Soils
are essential components of terrestrial ecosystems that experience
strong pollution pressure. Microplastic contamination of soils is
being increasingly documented, with potential consequences for soil
biodiversity and function. Notwithstanding, data on effects of such
contaminants on fundamental properties potentially impacting soil
biota are lacking. The present study explores the potential of microplastics
to disturb vital relationships between soil and water, as well as
its consequences for soil structure and microbial function. During
a 5-weeks garden experiment we exposed a loamy sand soil to environmentally
relevant nominal concentrations (up to 2%) of four common microplastic
types (polyacrylic fibers, polyamide beads, polyester fibers, and
polyethylene fragments). Then, we measured bulk density, water holding
capacity, hydraulic conductivity, soil aggregation, and microbial
activity. Microplastics affected the bulk density, water holding capacity,
and the functional relationship between the microbial activity and
water stable aggregates. The effects are underestimated if idiosyncrasies
of particle type and concentrations are neglected, suggesting that
purely qualitative environmental microplastic data might be of limited
value for the assessment of effects in soil. If extended to other
soils and plastic types, the processes unravelled here suggest that
microplastics are relevant long-term anthropogenic stressors and drivers
of global change in terrestrial ecosystems.