Scientists from Brno reveal risks of bioplastics in agriculture
Are bioplastics and plant-based materials safer than conventional plastics? Scientists from Mendel University in Brno have been investigating one type of bioplastic, and their findings are alarming. Even plastics marketed as eco-friendly, can negatively affect the soil, causing an overgrowth of microorganisms, which then compete with plants for vital nutrients.
The scientists focused on a specific bioplastic commonly used in cosmetics as a substitute for scrubs. However, it is also increasingly used in packaging for gradual-release fertilizers and biodegradable mulch films. Martin Brtnický from Mendel University’s soil ecology research group explains the motivation for the study:
"Conventional plastics are bad for the environment. That is a well-known fact. But we are interested in the effect that degradable plastics have on soil and plants. We are studying this in pots, using poly-3-hydroxybutyrate as an example.”
To test the effects of this bioplastic, researchers mixed it into soil and planted lettuce and corn in different groups of pots. Some pots contained soil with varying concentrations of the plastic powder, ranging from 0.1% to 10%, while others were left untreated as controls for comparison. The plants were observed over an eight-week period, and the experiments were repeated multiple times to ensure reliable results.
The findings were striking. At the lowest concentration, the bioplastic had little impact. But with just 1% of plastic in the soil, lettuce growth was reduced to a tenth of its normal size. At 5% and 10%, lettuce plants barely grew. Corn performed slightly better but still saw significant effects, with a 20% reduction in growth at just 1% plastic concentration.
So why do degradable plastics affect plants this way? According to researcher Jiří Holátko, the answer lies in the high carbon content of these materials:
“We analyse the treated soil samples with an optical spectrophotometer to measure carbon dioxide levels. The results show that as the concentration of degradable plastic increases, so does carbon dioxide production. This indicates a surge in microorganisms in the soil.”
The carbon from microplastics encourages an overgrowth of bacteria and fungi in the soil, disrupting its natural balance. This overgrowth reduces the amount of organic matter—known as humus—in the soil, which is vital for its fertility. At the same time, both plants and microorganisms require essential nutrients like nitrogen and phosphorus to survive, explains scientist Jiří Kučerík:
“Degradable plastics create a nutrient imbalance. Microorganisms overgrow due to the added carbon and then compete with plants for nitrogen and phosphorus, reducing plant growth.”
Despite these concerns, the researchers see promise in degradable plastics as an alternative to conventional plastics. They plan to explore how these materials could be modified to benefit soil health rather than harm it, making them a truly eco-friendly option for the future.
