New research has shown that farmlands across Europe are potentially the biggest global reservoir of microplastics due to the high concentrations found in fertilizers derived from sewage sludge.
A team of researchers from Cardiff University and the University of Manchester has estimated that between 31,000 and 42,000 tonnes of microplastics are applied to European soils annually, mirroring the concentration of microplastics found in ocean surface waters.
Wastewater treatment plants remove microplastics from municipal sewage flow, with the resulting bulk of microplastics being concentrated within generated sewage sludge. The sludge is frequently recycled back onto agricultural land as accepted practice in many European countries as a sustainable and renewable source of fertilizer.
Microplastics spread onto farmland will eventually be transported back into the natural watercourse by means of surface water run-off or infiltration to groundwater. Microplastics, less than 5 mm in size, pose a significant threat to wildlife as they are easily ingested and can carry contaminants, toxic chemicals, and hazardous pathogens, potentially impacting the whole food chain.
The new research involved analyzing samples from the Nash Wastewater Treatment Plant in Newport, South Wales, which treats the combined sewage from a population of 300,000. The analysis revealed that the treatment plant was 100% effective in removing large microplastic particles, 1-5 mm in size, from incoming sewage that would otherwise be released into the aquatic environment. Each gram of sewage sludge created through this process, however, was then found to contain up to 2 microplastic particles, amounting to around 1% of its total weight.
The data was then used to assess the impact across Europe using figures from the European Commission and Eurostat on the use and application of sewage sludge as fertilizer across the continent. As the researchers did not analyze microplastics that are less than 1 mm in size, the overall concentrations are likely to be a lot higher than their estimates.
“Our results highlight the magnitude of the problem across European soils and suggest that the practice of spreading sludge on agricultural land could potentially make them one of the largest global reservoirs of microplastic pollution,” said the lead author of the study James Lofty, from Cardiff University’s School of Engineering.
“At present, there is currently no European legislation that limits or controls microplastic input into recycled sewage sludge-based on the loads and toxicity of microplastic exposure,” he continued. “Efforts should be made to increase standardized monitoring of microplastic concentrations in sewage sludge and agricultural soils, which would provide a more accurate picture of contamination levels in soils across Europe.”