Environmental Science
How Plastic Mulch Films Create Long-Term Soil Microplastic Contamination
Quick fact
A single field can accumulate up to 50 kg of microplastic per hectare each year from plastic mulch films, with residues remaining in the soil for hundreds of years.
Why this is interesting
Every year, millions of tons of plastic mulch are draped over farm fields. Why does so little of it ever get removed, and what happens to the rest?
Read the full explanation
Understanding How Plastic Mulch Films Create Long-Term Soil Microplastic Contamination
Plastic mulch films are thin sheets of polyethylene (PE) laid over soil in vegetable and berry farming. They trap heat, suppress weeds, and reduce water evaporation. Over a growing season, exposure to sunlight, fluctuating temperatures, and mechanical stress from planting or tilling causes the plastic to become brittle and fragment into tiny pieces, invisible to the naked eye—these are microplastics. Some films are collected after use, but torn fragments are easily left behind or plowed into the soil. The process is like a plastic bag left in the sun: it becomes cracked and flaky, and eventually breaks into countless tiny particles that mix into the dirt.
A deeper explanation
The mechanism begins with photodegradation: ultraviolet (UV) radiation from the sun breaks the polymer's carbon-carbon bonds, making the film brittle. Then, mechanical stress from wind and soil abrasion physically shreds the weakened film into small fragments. While some plastics are designed to photodegrade, PE films do not readily biodegrade; they merely disintegrate into smaller and smaller particles. These microplastics remain in soil, altering its physical properties (e.g., reducing bulk density) and potentially leaching additives like phthalates. Because they are persistent, they accumulate over years of repeated mulching, creating long-term contamination. Even 'biodegradable' mulches often fail to fully decompose under field conditions, leaving persistent residues. This matters because soil is a non-renewable resource, and microplastic contamination threatens soil biota, crop productivity, and possibly human health via food contamination.