Significance and Consequences
Microplastics – tiny plastic particles smaller than five millimeters – are no longer just a problem for the oceans. Our soils are increasingly contaminated with microplastics as well. The consequences range from changes in soil structure to health risks for humans and animals, as microplastics can even reach our brains through the food chain.
How Does Microplastic Enter the Soil?
Microplastics enter soils in various ways:
Agriculture: The use of mulch films and plastic coverings in fruit, vegetable, and asparagus cultivation contributes significantly to contamination. Sewage sludge and compost used as fertilizers also contain large amounts of microplastics from household wastewater, cosmetics, and the abrasion of synthetic textiles.
Tire Abrasion and Waste: Microplastics enter the environment through tire abrasion, littering, and industrial emissions, eventually ending up in the soil.
Fragmentation: Larger plastic pieces in the soil are broken down into ever smaller particles through physical, chemical, and biological processes, eventually forming micro- and nanoplastics.
Effects of Microplastics on Soil
Microplastics alter the physical and chemical properties of soil:
Soil Structure: The particles affect the size and shape of soil aggregates, changing pore structure, air and water balance, and reducing soil density.
Nutrient Cycles: Microplastics can influence nutrient availability, enzyme activities, and the composition of microbial communities in the soil.
Soil Organisms: Earthworms, springtails, and other soil organisms ingest microplastics, which can impair their vitality and reproduction. Plants can also absorb the smallest particles through their roots and store them in above-ground parts.
Uptake of Microplastics by Plants and Animals
Plants: Studies show that crops like rice, corn, and wheat can absorb microplastics through their roots. The particles are stored in leaves and other plant parts, reducing photosynthetic performance and thus crop yields.
Animals: Soil organisms such as earthworms or snails ingest microplastics, further distributing them in the soil. Through the food chain, microplastics reach insects, fish, and eventually humans.
Microplastics in the Food Chain and Human Body
Food Chain: Microplastics have been detected in many foods, such as seafood, fish, sea salt, and even plant products. Humans primarily ingest microplastics through food, but also via drinking water and air.
Absorption in the Body: In the digestive tract, microplastic particles can be absorbed by intestinal cells. The smallest particles (nanoplastics) enter the bloodstream and can accumulate in various organs, including the liver, kidneys, and even the brain.
Microplastics in the Brain: How Do the Particles Get There?
Blood-Brain Barrier: Recent studies show that microplastic particles smaller than one micrometer can cross the blood-brain barrier. This occurs when endogenous molecules such as cholesterol bind to the particles, facilitating their passage through membrane barriers.
Neurological Effects: In animal studies, microplastic particles were detected in the brain just two hours after ingestion. There, they can disrupt blood flow, cause inflammation, and lead to neurological disorders such as behavioral changes and cognitive impairment.
Conclusion
Microplastics in soil are a growing environmental problem with far-reaching consequences. The particles alter soil structure, harm plants and soil organisms, and enter the human body through the food chain. Particularly concerning is the ability of microplastics to cross the blood-brain barrier and potentially cause neurological damage. Although research is still in its early stages, current findings highlight the urgency of reducing plastic input into the environment and promoting sustainable alternatives.
Author: Francesco del Orbe
