Microplastics in agricultural soil could act as carriers for pollutants, pesticides, microbes and antibiotic resistance genes, potentially creating a wider threat to soil health and food production according to findings from a five year international research project.
The EU funded Minagris project which has produced 22 peer reviewed studies so far detected microplastics in all 227 agricultural fields examined across 11 European countries. Researchers said the contamination reflected both present day farming practices and historical land use, highlighting the persistence of plastic pollution in soils.
Microplastics create microbial ‘hotspots’
Researchers found that microplastics can provide surfaces for microorganisms to colonise, creating what scientists call the “plastisphere”. These surfaces can become interaction points between plastics microbes and agricultural chemicals.
One of the studies found higher levels of antibiotic resistance genes within these plastispheres compared with control samples. The researchers also observed that pesticides could intensify this effect.
Edoardo Puglisi, professor of microbiology at the Catholic University of the Sacred Heart in Piacenza, Italy, said smaller microplastic particles tend to adsorb pollutants, microorganisms and DNA more readily. He described this as a potential “Trojan horse effect”, through which plastics could contribute to the spread of pathogens and antibiotic-resistance genes.
Threats to soil organisms and plants
The research also found that microplastic contamination can interact with other environmental pressures. One study found that exposure could affect earthworms and other soil organisms potentially disrupting processes such as nutrient cycling.
Plants may also be affected. Research involving lettuce found that higher concentrations of microplastics were associated with reductions in leaf area, chlorophyll content photosynthetic efficiency and overall plant biomass.
The effects became more pronounced when plants were simultaneously exposed to drought suggesting that multiple environmental stresses can interact rather than operate independently.
‘Biodegradable’ plastics are not automatically harmless
Researchers also examined biodegradable plastics and cautioned that they should not automatically be considered environmentally safe. Such materials can break down into smaller plastic particles under certain conditions and may continue to interact with soil organisms and agricultural chemicals.
Dr Esperanza Huerta Lwanga a research associate in soil physics at Wageningen University in the Netherlands said fragmented plastics can be extremely difficult to remove from soil and may act as carriers for agrochemicals while altering soil ecosystems.
The findings suggest that environmental assessments should consider how plastics interact with other pollutants instead of evaluating each contaminant separately.
The researchers are calling for standardised monitoring of plastic contamination in agricultural soils, greater transparency from manufacturers and risk assessments that examine the combined effects of microplastics and other pollutants across different species.
With healthy soils essential for agriculture and ecosystem functioning the researchers say understanding the long term effects of persistent plastic contamination will be important for protecting food production and soil health.