Show summary
This report presents a risk assessment of organic contaminants in sewage sludge
and sewage-sludge-based products used on agricultural land in Norway, under
current and alternative fertiliser regulations and management practices. It
identifies a limited number of substances of concern for soil health, aquatic
organisms, animal health, and human health, and provides a scientific basis for
evaluating circular economy, organic fertilisers, and the safe recycling of
bioresources in agriculture.
Background and purpose
The Norwegian fertiliser regulations was revised in 2025 to support reduced pollution, better
utilisation of nutrients, fulfilment of international obligations, simplification, and facilitation of
nutrient recycling. In Norway, 50 to 60 per cent of sewage sludge is used on agricultural land,
compared with around 40 per cent in the EU. Norway has many small wastewater treatment
plants and a long tradition of using treated sludge in agriculture. At the same time, incineration
is less common in Norway than in many other European countries, partly because Norwegian
wastewater treatment largely relies on chemical phosphorus precipitation (chemical
separation of phosphorus).
In recent years, new products based on sewage sludge have been developed, such as pellets,
biochar and struvite (a fertiliser product recovered from wastewater that makes it possible to
recycle phosphorus and nitrogen for agricultural use).
At the same time, knowledge about organic contaminants in sewage sludge has increased. On
this basis, the Norwegian Food Safety Authority asked VKM to assess the risks associated with
organic contaminants in sewage sludge and sludge-based products.
Terms of reference and scope
VKM was tasked with identifying organic contaminants in sewage sludge and assessing which
substances were relevant to include in the risk assessment. The assignment also covered
products made from sludge, such as biochar, ash and struvite.
Risks were to be assessed for the use of sludge on agricultural land over a period of up to 100
years. If current practice could lead to undesirable effects, alternative application rates and
uses were also to be evaluated. In addition, less stringent rules for use in the cultivation of
vegetables and on grassland used for mowing and grazing were to be assessed.
The assessment covered possible effects on soil-dwelling organisms, aquatic organisms,
livestock and humans. Combined effects of multiple substances were not assessed in detail.
Methods and scenarios
The risk assessment was based on data for more than 1,000 organic contaminants measured in
Norwegian sewage sludge. For some pharmaceuticals that had not been analysed, levels were
estimated using consumption data and modelling. Substances were prioritised based on
occurrence, properties, degradation, mobility and toxicity.
A model was developed to calculate how organic contaminants may accumulate and spread in
soil, water and plants over time. The calculations were used to assess exposure for soil- and
water-dwelling organisms, livestock and humans. The model accounted for climate and soil
conditions in five regions in Norway.
A wide range of scenarios for the use of sewage sludge and sludge-based products in the
cultivation of cereals, potatoes, vegetables and grass were assessed. These included current
practice, reduced application rates, use every ten years and annually, different intervals
between application and cultivation or grazing, and the use of pellets, biochar, struvite and
liquid digestate from sewage sludge. The effects of thermal hydrolysis were also assessed.
Summary of main findings
Norwegian monitoring data show that municipal sewage sludge contains many different
organic contaminants, but levels vary widely between treatment plants and regions. The levels
of several legacy pollutants, such as PCBs, PAHs and PBDEs, have decreased over time but are
still present in sludge and remain relevant because they degrade slowly and can accumulate in
the environment. PFAS are regularly detected, particularly PFOS and other long-chain PFAS.
Pharmaceuticals and newer industrial chemicals often occur at low levels but with large
variation. Several substances found at the highest concentrations are linked to cosmetics and
personal care products.
The different sludge-based products have different risk profiles. Pellets are expected to pose
roughly the same or slightly lower risk than dewatered sludge. Struvite contains very low levels
of organic contaminants and was consistently associated with low risk. Biochar is distinctive in
that pyrolysis reduces many organic contaminants, but there is still uncertainty related to the
possible formation of new compounds and how residues may be bound or released over time.
For soil-dwelling organisms, the assessment showed that current practice may pose a long
term risk for some substances. After quality assessment of the data, 19 organic substances
showed potential risk, including certain pharmaceuticals, cosmetic-related substances, plastic
related compounds, PAHs and PFOS.
Lower application rates reduced risk but did not eliminate it. For some persistent substances,
annual application could result in a higher cumulative load than application every ten years.
For aquatic organisms, under current practice one substance exceeded the risk threshold, the
pharmaceutical fenbendazole, but the assessment is uncertain. In scenarios with less stringent
conditions or alternative uses, several substances were considered capable of posing a risk to
the aquatic environment.
For livestock, the calculations generally showed low levels of individual substances in feed
rations. Risk was highest for grazing animals, as soil ingestion is an important exposure
pathway, and with the use of liquid digestate from sewage sludge, direct intake may also
contribute. Delayed grazing after application of products was found to reduce exposure. At the
same time, some substances, particularly bisphenols and certain pharmaceuticals, are
highlighted as relevant to animal health, and combined effects cannot be ruled out.
For humans, current use of sewage sludge is generally assessed to pose relatively low risk to
food safety for most of the substances examined. At the same time, an increase in organic
contaminants in agricultural soil is undesirable. The report highlights PFAS, PCBs, dioxins,
PAHs, PBDEs, siloxanes, bisphenol A, octocrylene and several pharmaceuticals as important for
food safety, because dietary exposure to some of these substances is already considered
undesirable or of concern. For individuals with high consumption of locally caught freshwater
fish, exposure is generally assumed to be limited, but for some individuals it may be relevant.
Main conclusion
Norwegian data show that sewage sludge contains many organic contaminants, but levels vary
widely. Most substances appear to pose low risk to soil-dwelling and aquatic organisms, and
low health risk to livestock and humans. Some persistent substances may give rise to concern
over time.
Struvite was consistently associated with low risk, while pellets, biochar, sewage sludge and
liquid digestate from sewage sludge have more complex risk profiles. For humans and
livestock, risk is generally low under current practice, but certain groups of substances are
undesirable because the overall burden is already high or of concern.
The report concludes that some substances should be prioritised for further investigation and
follow-up.
In summary: VKM concludes that most organic contaminants in sewage sludge pose low risk,
but that some organic contaminants may give rise to concern over time. This particularly
applies to persistent substances that can accumulate in soil. The report therefore highlights
the need for further investigation through the collection of more data and knowledge to
support future risk assessments.