In this guest blog for CHEM Trust, Francesca Bevan, policy & advocacy manager for chemicals at the Marine Conservation Society, shares the important messages from their new report: Sewage sludge: Why we need to stop pollution at source
Pollution, both chemical and plastic, has been cited as one of the main direct drivers of the current biodiversity crisis. Stopping pollution at source is essential to protecting the health of our oceans.
Wastewater treatment is often thought of as a way to prevent contaminants reaching the environment. However, during wastewater treatment a solid material called sewage sludge is produced. This sludge, once treated, is often spread on agricultural land as a fertiliser. It contains high levels of nutrients such as nitrogen and phosphorus and is a good source of organic matter.
Unfortunately, it also contains chemicals such as PFAS and microplastics which have been captured during wastewater treatment, but are not removed during sludge treatment. In fact, in the UK, treated sludge is estimated to contain 69 – 80% of the microplastics which enter the wastewater treatment works, and from the sludge spread on land, nearly all of the microplastics are transported to aquatic environments.
Aside from the physical impacts caused by microplastic pollution, they may also release harmful chemicals that are contained within or are absorbed to their surface. As well, chemicals like PFAS, have been shown to cause problems with marine wildlife, with PFAS contamination linked to impacts on the immune, blood, kidney and liver functions in bottlenose dolphins.
In the UK around 3.5 million tonnes of sewage sludge is spread to agricultural land (which is around 87 % of the sludge produced in the UK). Although this is a relatively large amount of sludge it is only applied to a comparatively small amount of agricultural land, approximately 1.3 % of UK farmland. Aside from agricultural uses, incineration, land reclamation and industrial uses are among the other disposal routes for sludge.
Stopping pollution at source: allowing for a safe and clean circular economy
The use of sewage sludge on agricultural land is itself a good example of the circular economy. However, it also highlights the need for a safe and clean circular economy, free from harmful chemicals. This cannot be achieved while persistent pollutants like PFAS remain in circulation.Their extreme persistence means that in a circular system they will just continue to build up and accumulate in the environment.
There is also emerging concern around the ‘mixtures effect’, where organisms are exposed to a wide range of different chemicals simultaneously. There is an increasing amount of evidence showing that the toxicity of a mixture of chemicals is not equal to the sum of its parts, and most worryingly that mixture toxicity could happen at levels below the toxicity of the individual single chemicals. Sewage treatment works are, in theory, an optimum place for the mixing to occur. Thus, providing a product, via the sludge, which contains a multitude of different pollutants, thereby resulting in subsequent exposure once spread.
What should we be doing with sewage sludge?
Preventing contaminants from entering wastewater systems must be the priority, as it is the most effective and sustainable option to reduce contaminants within sludge. However, particularly in the short-term, contaminants entering wastewater systems will be unavoidable due to historic legacy and essential uses. Therefore, regulatory limits that reflect the modern composition of wastewater, must be set for a wider range of chemicals and microplastics within treated sludge, if it is to be applied to agricultural land.
This would ensure that contaminants from sludge are not simply transferred to farmland and then ultimately the rivers and ocean. It would also prevent farmers being blamed for environmental contamination from a product they are supplied with.
If sludge is too contaminated to meet these new limits, innovation in treatment and alternative uses may be required and should be achieved by remaining as high in the waste hierarchy as possible.
What needs to be done to help stop pollution at source?
The following recommendations for stopping pollution at source in the UK are a selection from all asks presented in our report.
- The upcoming UK Chemicals Strategy should take into account the 12 key asks proposed by NGOs, including phasing out the use of PFAS and other very persistent chemicals.
- The UK Government needs to ensure UK REACH remains aligned with EU REACH, including all recent and upcoming restrictions such as the restriction on intentionally added microplastics.
- Environmental monitoring needs to be extended to include a wider range of emerging contaminants to provide a more accurate picture of the contamination of the environment.
- Governments should introduce thresholds for a wider range of contaminants than those currently required to be monitored in treated sewage sludge (biosolids) applied to land – including chemicals and microplastics. Thresholds should be based on health and environmental impact, applying the precautionary principle.
Dr Francesca Bevan, MCS policy & advocacy manager for chemicals said:
“Despite undergoing treatment, sewage sludge is still contaminated with microplastics and synthetic chemicals. When treated sludge is spread onto agricultural land, the contaminants are released into the environment, and may subsequently end up in the ocean. Pollution from a variety of sources is impacting the functioning of marine ecosystems, negatively impacting wildlife throughout the food chain. Therefore, emphasis has to be on stopping pollution at source as soon as possible.”
Full report: Sewage sludge: Why we need to stop pollution at source. MCS, June 2021, 9p.
MCS blog: Sewage sludge: Why we must stop pollution at source. MCS, July 2021.
Educational animation (1’15”): Microfibres, chemicals and washing machines: the problem with sewage sludge. MCS, July 2021.