Microplastics in soil pose global threat by acting like ‘Trojan horse’ to deliver toxins

The research also uncovered that microplastics can interact with other agricultural stressors, such as pesticides and veterinary drugs. In one Swiss study, fields with the highest levels of tyre-wear particles also exhibited the highest concentrations of toxic chemicals and metals. Microplastics create new microbial habitats on their surfaces, known as the plastisphere, which serve as hotspots for interactions between plastics, microbes, and agrochemicals. This environment was found to increase antibiotic-resistant genes, an effect further amplified by pesticides.

Edoardo Puglisi, a project partner and professor of microbiology, explained that smaller microplastics tend to adsorb more pollutants, microbes, and DNA, enhancing the "Trojan horse effect" that can potentially spread pathogens and antibiotic-resistance genes. This phenomenon can disrupt critical soil processes like nutrient cycles, impacting earthworms and other soil organisms vital for soil health. Furthermore, the research indicated that microplastics can negatively affect plant growth, with higher concentrations reducing leaf area, chlorophyll content, photosynthetic efficiency, and plant biomass in lettuce. These effects were amplified when combined with drought conditions.

The findings underscore the need for policy changes, as current environmental assessments often overlook the combined effects of co-occurring pollutants. The researchers advocate for a broader recognition of plastic contamination as part of overall soil degradation. They also noted that biodegradable plastics are not inherently safer, as they can still break down into microplastics and cause ecological harm. Esperanza Huerta Lwanga, a research associate, emphasized the difficulty of removing microplastics once they enter the soil and their role as vectors for agrochemicals, altering soil ecosystems. She called for standardized plastic monitoring, manufacturer transparency, and risk assessments that consider the interaction of microplastics with co-pollutants across different species to protect long-term food production and soil health.