Agricultural plastic, such as mulch film, is increasingly being used to cover the soil and thereby reduce the use of pesticides, water and fertilisers. Meanwhile, enough mulch film is used worldwide every year to cover the whole of the Netherlands ten times over. Some of these plastics remain in the soil and disintegrate into microplastics in the soil. These particles are between 5 millimetres and one thousandth of a millimetre in size. Van Loon studied the harmful effects of microplastics on soil life.
Springtails
His research shows that microplastics are little toxic to some soil animals, such as springtails, even when exposed to high concentrations for long periods. However, microplastics do appear to be harmful to wider soil life. At high concentrations, effects can be seen on soil acidity, water-holding capacity and density. Van Loon and his co-researchers see changes in microbial species composition and activity. In addition, the study shows harmful effects on plants already at low concentrations of microplastics. The researchers also see shifts in how the ecosystem as a whole behaves. These effects are seen at amounts of microplastics already currently measured in agricultural soils in Europe.
Direct risk to soil life
The concentrations at which Van Loon and his co-researchers found effects of microplastics on soil life and soil properties are already currently measured in agricultural soils in Europe. This means that there is a direct risk to soil life and thus to the productivity of these agricultural soils. This risk is potentially further influenced by the fact that soil may also contain other toxic substances, such as pesticides and PFAS. This study found that microplastics may also affect the toxicity of those substances.
Laboratory
For his research, Van Loon conducted experiments in the laboratory, exposing springtails, small insect-like soil animals, to microplastics in a natural soil. He did this at different concentrations of microplastics, with different species of springtails and with short- and long-term exposure. Here, he looked at springtail survival and reproduction. He also conducted tests with simulated ecosystems, where not only springtails, but also earthworms and plants were exposed to microplastics.
Van Loon will defend his thesis on 10 December.