The effects of microplastics on aquatic ecosystems have been researched intensively by scientists and engineers since its discovery in 2004 by researchers at the University of Plymouth, yet research on its effect on soil and land ecosystems has only recently taken shape. Scientists from the Norwegian Institute for Water Research noted this knowledge gap and have conducted the first detailed study of microplastics in sewage sludge used as fertilizer for agricultural purposes, yet the implications of this study is still under investigation. Of particular interest in the research of microplastics is its interaction with biota, or living organisms.
Current research on the effects of microplastics in soil has turned towards life forms existing within its layers, particularly worms. Researchers from Anglia Ruskin University in the United Kingdom have discovered that worms, particularly the species called the rosy-tipped earthworm (Apporrectodea rosea), lose their body weight when placed in the soil with microplastics. Their procedure involved placing earthworms in two different types of soil, one loaded with a plastic called high-density polyethylene (HDPE) commonly used for plastic bags and bottles, and the other without any plastic at all. After 30 days in their respective soil types, the worms in the set-up with HDPE were found to have lost 3% of its original body weight, while those found in the set-up without any plastic at all were found to have gained around 5% of its original body weight. The main reason for the weight loss is still unclear, according to the main author of the study, Bas Boots, an associate lecturer of biology at the same university. The best explanation, however, that the researchers can provide is that the microplastics affect how the worms digest their food. These plastics accumulate in their system, effectively blocking about any absorption of nutrients. This leads to the stunting of their growth.
Other studies on the link between microplastics and earthworms have been done before. Scientists from Germany have published in the scientific journal Nature how worms can serve as agents for transporting microplastics from the top soil down below the surface. The experiments buried microplastics in two different patches of soil. One patch had earthworms (Lumbricus terrestris), while the other patch had no earthworms. After 21 days, it was found that the patch with earthworms had significantly transported the microplastics down the soil by around 10 cm as a result of its movement. Another scientist from Germany has published in Science how earthworms have been found to eat microplastics, contributing to its transport from the surface down to the depths of the soil.
This discovery has very big implications for agriculture because of the importance of earthworms in production. They help aid in boosting the nutrients in the soil by digesting organic material and excreting large amounts of nitrogen and phosphorus in the process. These two elements are very good fertilizers used by plants to increase its capacity. In fact, earthworms have been found to improve farm productivity by 25–30% when introduced into the soil. As such, developments regarding the presence of microplastics in the soil should be closely monitored because the biggest consequence that can arise from this problem is the lowering of food security in the next few years.