Across Scotland and rUK treated sewage is used by some farmers to spread across their fields. Although this human waste has been treated, there are also hidden threats to agricultural soil within it that a report by  The James Hutton Institute has highlighted.

The report finds that microplastics, many organic contaminants and a number of pharmaceutical and personal care products—all currently applied to agricultural land in Scotland, England, and Wales—have significant potential to cause harm to our soil ecosystems.

The environment charity Fidra, explains that:

“Treated sewage sludge, also known as ‘biosolids’, are the by-product of wastewater treatment. Biosolids are applied to agricultural land as a source of crop nutrients and organic matter. In fact, England, Scotland and Wales are one of Europe’s highest agricultural users of biosolids, with 87% of the sewage sludge we produce ending up on agricultural soil. Despite treatment prior to agricultural use, biosolids contain a cocktail of potentially harmful contaminants including microplastics, pharmaceuticals, PFAS (poly or per fluorinated alkyl substances) and chemical flame retardants and there is currently no requirement to monitor or remove these unregulated pollutants from biosolids. Alarmingly, many of the unregulated persistent contaminants applied to our soils are known to have negative outcomes for human health (e.g. PFOA ) or influence the reproduction, growth and survival of soil organisms.”

The James Hutton Institute find that:

• Microplastics in sewage sludge can pose a risk to soil health after as few as two applications. Repeated application likely provides a pathway for microplastics to build up in our soils and enter our environment and water supply.
• A number of chemical contaminants are expected to exceed the safe limit for soil biota. In particular, PFAS demonstrated strong potential to accumulate in soil and pose long-term environmental risks.
• Almost half of the PPCPs tested posed a notable risk to soil health after a single application.
• The cocktail effect is likely to compound all these risks. The report emphasises that, while the impact of these chemicals is modelled on an individual basis, the reality is that a complex mixture of chemicals is highly likely to exacerbate any risks to soil or human health.

The report author Professor Rupert Hough commented:

“This new assessment builds on existing and growing scientific evidence around the risks that contaminated sewage sludge poses to the environment. Impacts on soil biota, when directly exposed to contaminants of concern, are more acute compared to impacts on humans exposed via the food chain. Further research into the long-term fate of unregulated contaminants in agricultural soils and measures to limit their release into the environment is needed.”

The report also makes seven recommendations and Fidra calls “on the Scottish and other UK Governments to further regulatory efforts to mitigate harmful contamination of our soils from contaminated sewage sludge.”

1. Adopt the Precautionary Principle: Given the persistence, bioaccumulation and emerging nature of many contaminants, the report advocates for the adoption of precautionary measures to protect soil health and the wider environment. This may involve limiting the application of sewage sludge on agricultural land until more comprehensive risk data are available and includes adopting recommendations 2 – 7.
2. Improve Wastewater Treatment: The report calls for the enhancement of wastewater treatment processes to reduce the levels of contaminants, especially microplastics, organic contaminants, and PPCPs, in sewage sludge. This includes upgrading treatment facilities and introducing stricter regulations on pollutant discharge.
3. Increase Research on Emerging Contaminants: The study emphasizes the need for further research into the environmental risks posed by unregulated microplastic and emerging chemical contaminants. More data are needed to understand the long-term impacts of these substances on soil biota and the wider environment.
4. Regular Monitoring of Contaminant Levels: The report recommends ongoing monitoring of chemical and microplastic contaminant levels in sewage sludge and agricultural soils. This will help identify trends in contamination and enable timely interventions to minimise environmental damage.
5. Develop Alternative Treatment Technologies: To address the limitations of current wastewater treatment systems, the report suggests exploring new technologies for removing persistent and other contaminants from sewage sludge.
6. Develop Enhanced Quality Standards: Encourage upstream source control solutions for reducing and/or eliminating contaminants in sewage sludge before recycling to land.
7. Improved Sludge Use in Agriculture Policies: Widen scope of regulations to enforce appropriate management strategies and best practice to ensure soil health and the wider environment are protected from a more comprehensive range of contaminants. Build in flexibility and review processes, so that regulations adapt to changes in the contamination profile in a timely manner.

 More Information :farmer guidance, farmer survey report and soil health report.

The full report can be downloaded here:

Fiona Grahame