Microplastics in soil act as ‘Trojan horse’ for pollutants, EU-funded study finds
An EU-funded five-year project found microplastics in soil at all 227 agricultural fields tested across 11 European countries. The particles act as a “Trojan horse” for pollutants, pesticides and bacteria, and researchers say the findings point to a global soil threat that policy has yet to address.
The project has so far resulted in 22 peer-reviewed studies. In many cases, the contamination reflected current farming practices as well as historical land use, showing that plastic pollution can persist for many years. The researchers also found that microplastics could interact with other agricultural stressors, including pesticides and veterinary drugs. One study in Switzerland found that fields with the highest levels of tire-wear particles also had the highest levels of other toxic chemicals and metals.
Microplastics can create new microbial habitats on their surfaces, known as the plastisphere. The researchers found these surfaces form a hotspot for interactions between plastics, microbes and agrochemicals. An increase in antibiotic-resistant genes was found within plastispheres when compared with controls, and pesticides appeared to amplify this effect further.
Edoardo Puglisi, a partner of the project and professor of microbiology at the Catholic University of the Sacred Heart in Piacenza, Italy, said that the smaller microplastics were, the more they tended to adsorb pollutants, microbes and DNA. He said this led to a “Trojan horse effect that can potentially increase the diffusion of pathogens and antibiotic-resistance genes”.
One study found that this Trojan horse effect can affect earthworms and soil organisms by disrupting critical processes such as nutrient cycles. Earthworms play a vital role in shaping the composition of the soil microbiome as well as the ecological functions of soils.
The research project also found that microplastics could affect plant growth and function. One study found that higher concentrations of microplastics reduced leaf area, chlorophyll content, photosynthetic efficiency and plant biomass in lettuce. When drought conditions were added, these effects became even more pronounced, with plants performing less well than under either stress alone.
Environmental assessments often consider pollutants individually, but the findings show that pollutants can behave differently when they occur together. The researchers say policy needs to recognize that plastic contamination is part of a wider picture of soil degradation and pollution.
In an effort to reduce plastic pollution, there has been an increase in the use of biodegradable plastics. However, the project found that biodegradable plastics were not automatically safer and could still degrade into microplastics, potentially causing ecological damage.
“Once these plastics fragment into the ground, they’re practically impossible to remove, acting as vectors for agrochemicals and altering critical soil ecosystems,” said Dr Esperanza Huerta Lwanga, a research associate in soil physics at Wageningen University in the Netherlands. “To protect long-term food production and soil health, policy must catch up. We urgently need standardised plastic monitoring, full manufacturer transparency, and risk assessments that evaluate through different species how microplastics interact with co-pollutants.”