Biosolids pose a threat to healthy waters

Biosolids are nutrient rich, organic solid or semi-solid materials recovered from wastewater processing and their management is a growing challenge.

Wastewater includes everything that is flushed down toilets and drains from households, businesses, and some industries and institutions. In Canada, 86% of homes are served by wastewater treatment plants (WWTPs), with millions of cubic metres of wastewater ending up at these facilities every day1. At these plants, wastewater gets processed to remove pathogens, nutrients, and some contaminants, with the processed liquid effluent being discharged into the environment. 

Treating wastewater is crucial in mitigating water pollution as it can contain human and organic waste, nutrients, pathogens, microorganisms, suspended solids, and chemicals from homes and some industries2. There are three basic levels of wastewater treatment, and most municipal Canadian WWTPs use primary and secondary levels which can remove ~90% of suspended solids and coliform bacteria from wastewater3.

Simplified levels of wastewater treatment

➔ Primary treatment: Physical and/or chemical processes are used to remove a portion of suspended solids and organic matter.

➔ Secondary treatment: Biological processes and secondary settlement are used to remove suspended solids and organic matter.

➔ Tertiary treatment: Advanced physical, chemical, and/or biological processes are used to remove specific substances including nutrients and some contaminants of concern.

Much of the wastewater treatment process relies on the separation and removal of solids from water. These solids contain much of the nutrient-rich organic materials as well as those contaminants that bind to particles. The separated byproduct of the wastewater treatment process is called sewage sludge – and after further processing4 5, is referred to as biosolids.

What are biosolids?

Biosolids are nutrient rich, organic solid or semi-solid materials recovered from wastewater processing. The global production of biosolids is ~125 million tonnes annually, with this value increasing with population growth and subsequent demand for more WWTPs6. In British Columbia alone, enough biosolids are produced every year to cover a football field 25m deep (~38,000 dry tonnes)7.

Biosolids can be considered either a waste product or a resource, and their management is becoming an increasing challenge for many countries. In North America, biosolids are often applied as a fertilizer in horticulture, agro-forestry operations or in reclamation projects, with their high nutrient content facilitating plant and tree growth8 9

In Canada, biosolids management is guided by the framework established in the Approach for the Management of Municipal Biosolids under the Canadian Council of Ministers of the Environment (CCME). This framework promotes the sound management and beneficial use of biosolids, to capitalize on the high nutrient, organic material, and energy content of this by-product of liquid waste. ‘Beneficial use’ includes composting, certain land applications, and combustion for energy production10. Regulations for processing, management, and use of biosolids vary among Canadian provinces and territories, and even among municipalities.

The regulation of biosolids in British Columbia (BC)11

➔ Biosolids are regulated in BC under the Organic Matter Recycling Regulation (OMRR) under the Environmental Management and Public Health Acts.

➔ Biosolids can be classified as Class A or B, depending on the extent of treatment, and attaining safe levels of fecal coliforms and metals.

➔ Class A biosolids are subject to more stringent quality criteria and greater treatment, and therefore have less land application restrictions compared to Class B biosolids, given they are considered comparably “lower risk”.

➔ Biosolids may be mixed with organic materials, such as sand, wood chips or yard waste, to produce compost or biosolid growing medium; these may be sold for use in landscaping and agriculture (i.e. Nutrifor, OgoGrow).

The land application of biosolids is less prevalent in other parts of the world. Some countries like the Netherlands and Switzerland have imposed strict regulations and/or outright bans on land application because of environmental and human health concerns. In place of land application, countries may choose to landfill or incinerate their biosolids, or use technologies to capture energy12

Mounting concerns about the safety of biosolid application

There are mounting concerns that the term ‘beneficial uses’ may not fully capture the safety of land based biosolids applications, as risks to the health of the environment and/or human health are poorly understood. These concerns emanate from an increasing number of reports on the diverse suite of contaminants found in biosolids.

The following types of contaminants have been documented in biosolids13 14 15 16 17 18 19 20 21 22:

  • Pharmaceuticals and personal care products (medications, anti-microbial, anti-fungal, anti-bacterial agents, and synthetic musks (fragrances))
  • Recreational and/or illicit drugs
  • Detergents and surfactants 
  • Flame retardants
  • Microplastics
  • Hydrocarbons and other petrochemicals
  • Pathogens
  • Metals

Contaminants end up in biosolids because current wastewater treatment facilities are typically only designed to address nutrients, pathogens and suspended solids. Many contaminants survive WWTP processes and end up in liquid effluent and/or in biosolids. Biosolids are a particular sink for those contaminants that are persistent and ‘particle-active’ (lipophilic or hydrophobic), with many being toxic at relatively low concentrations23 24 25.

Missing the mark: contaminants in biosolids

Biosolids destined for land use in BC must be processed to meet regulatory criteria for fecal coliform and metals26. There is no other legal requirement to monitor biosolids for any other classes of contaminant prior to their land application as a fertilizer. 

A wide range of concentrations of different contaminants of concern have been reported in biosolids27 28 29. In Canada, anti-microbial and bacterial agents (e.g. triclocarban and triclosan), antibiotics (e.g. azithromycin, carbamazepine, sulfamethoxazole), synthetic musks (e.g. galoxolide, tohalide), and prescription pharmaceuticals (e.g. estradiols) have been reported in biosolids30 31 32. Although the concentrations of some of these contaminants are often low, the quantities applied are large. In 2021, the United States Environmental Protection Agency (US EPA) estimated that over 1.96 million dry tonnes of biosolids were land applied in the USA33. The cumulative impacts of repeated applications are not well understood but could be significant, with biosolid-amended environments becoming an environmental reservoir for a multitude of contaminants.

The fate of contaminants after land application

The limited assessment of contaminants in biosolids in BC and lack of monitoring after application is problematic. In addition to the potential for adverse effects in the lands they are applied to, contaminants in biosolids are free to move into aquatic environments or the atmosphere after biosolid application. Land application of biosolids is not only a terrestrial issue…it has potentially important consequences for aquatic ecosystems.

Biosolids as a source of wider contamination

➔ PFAS – these “forever chemicals” are extremely persistent in the environment, and have been detected in groundwater and surface runoff34 35 36.

➔ Microplastics, steroid hormones, pharmaceuticals, and personal care products have been documented in surface runoff from areas of biosolid application37 38 39 40.

➔ Microplastics and dust containing contaminants including PFAS have been found to be transported by wind up to 10 km from biosolid applications41 42.

The fate of biosolid contaminants following land application depends on a number of factors including soil properties, physicochemical properties of the contaminant, application method, and environmental variables of the geographic area where application occurred43 44. Generally, the risk of contaminant migration is highest immediately after biosolid application, with the concentrations in runoff are proportional to the quantity of biosolids applied and the intensity of the precipitation event45 46 47. Climate change and weather events have the potential to affect the transport, fate, and risks associated with biosolid contaminants, highlighting the need for an upgraded evaluation of biosolid risks associated with severe and variable precipitation and flooding events.

A threat to healthy waters

Biosolid-amended lands are a reservoir for a wide variety of contaminants of concern, with strong potential for contaminants to move into adjacent waters. Many of the contaminants reported in biosolids possess endocrine-disrupting properties, which can, at low doses, negatively affect fish through changes to their physiology, behaviour, and reproduction48 49 50. Microplastics are also commonly found in biosolids, and they also have demonstrated potential to elicit negative effects on fish51 52.

The cursory requirements for biosolid screening prior to ‘beneficial use’ in BC underscores the significant unknowns regarding risks to the receiving environment. This, combined with limited understanding of fate and effects in the environment in and around areas of application, raise the spectre of undocumented impacts to aquatic ecosystems in BC.

Four small salmon swimming near the bottom of the water.
Photo by Fernando Lessa.
The water being blown into the air by a killer whale is reflecting as pink and yellow.
Photo by Miles Ritter.

Moving forward with biosolids: greener options

We are falling short on safeguarding our environment with current biosolid regulations and practices in BC. To align with the CCME Approach, which “promotes the beneficial use of valuable resources such as nutrients, organic matter, and energy contained within municipal biosolids”, we provide options for future biosolids management which would allow for ‘beneficial use’ but with reduced risk of environmental impact.

Option 1: Implement high-resolution contaminant monitoring in biosolids destined for land application

Monitoring should be frequent and must move beyond the current basic screening (fecal coliforms and metals) by targeting some of the other current and emerging contaminants of concern. The list of target contaminants may be derived from studies in WWTPs. Improved monitoring can then be used in human and ecological risk assessments to inform if application is safe and if so, to guide application.

Option 2: Clean up biosolids through source control initiatives and local regulations

Source control initiatives and municipal bylaws are routinely used to reduce or eliminate contaminants from entering the waste stream and ending up in biosolids. Many initiatives already exist, and jurisdictions should maintain and enforce these programs. These initiatives may be supplemented by new programs targeting emerging contaminants of concern. 

Option 3: Inform federal policies and regulations

Use new data from contaminants of concern in WWTPs and in biosolids to inform the national regulation of chemicals under the Canadian Environmental Protection Act (Chemical Management Plan) and other relevant laws and policies. 

Option 4: Focus on energy capture from biosolids

Biosolids can be used as a combustible fuel alternative in power plants, and the ash byproduct of incineration can be used as a component in cement manufacturing53. Emerging technologies including pyrolysis and gasification are becoming more common and can be used to produce process gas which can be converted to energy, with lower emissions compared to incineration54. The byproducts of pyrolysis and gasification can also be used as a soil amendment in place of biosolids, with some research suggesting these byproducts are less contaminated compared to biosolids55

Option 5: Take individual action

As individuals, we can do our part to clean up biosolids by reducing the release of harmful products in our homes and gardens. Find out more about source control programs that are relevant to you, such as BC’s Medications Return Program. Apply best practices at home by using green detergents and soaps, designing a sustainable yard and garden, and installing filters on laundry machines to reduce microfiber pollution from clothing.


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  10. Canadian Council of Ministers of the Environment. (2012). CANADA-WIDE APPROACH FOR THE MANAGEMENT OF WASTEWATER BIOSOLIDS.
  11. Ibid. Ministry of the Environment and Climate Change Strategy, n.d.
  12. Ibid. Environmental Dynamics Inc., 2017.
  13. Ibid. US EPA, 2016.
  14. Hydromantis Inc., University of Waterloo, & Trent University. (2010). Emerging substances of concern in biosolids: Concentrations and effects of treatment processes. Government of Canada and Canadian Council of Ministers of the Environment.
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  25. Langdon, K. A., Warne, M. S. J., & Kookana, R. S. (2010). Aquatic hazard assessment for pharmaceuticals, personal care products, and endocrine-disrupting compounds from biosolids-amended land. Integrated Environmental Assessment and Management, 6(4), 663–676.
  26. Ibid. Ministry of the Environment and Climate Change Strategy, 2016.
  27. Ibid. Kumar et al., 2022.
  28. Ibid. Langdon et al., 2010.
  29. BC Ministry of the Environment and Climate Change Strategy. (2020). Biosolids sampling project.
  30. Ibid. Bright & Healey, 2003.
  31. Ibid. Land Resource Consulting Services, 2016.
  32. Ibid. BC Ministry of the Environment and Climate Change Strategy, 2020.
  33. Ibid. US EPA, 2016.
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  35. Gottschall, N., Topp, E., Edwards, M., Payne, M., Kleywegt, S., & Lapen, D. R. (2017). Brominated flame retardants and perfluoroalkyl acids in groundwater, tile drainage, soil, and crop grain following a high application of municipal biosolids to a field. The Science of the Total Environment, 574, 1345–1359.
  36. Washington, J. W., Yoo, H., Ellington, J. J., Jenkins, T. M., & Libelo, E. L. (2010a). Concentrations, distribution, and persistence of perfluoroalkylates in sludge-applied soils near Decatur, Alabama, USA. Environmental Science & Technology, 44(22), 8390–8396.
  37. Gray, J. L., Borch, T., Furlong, E. T., Davis, J. G., Yager, T. J., Yang, Y.-Y., & Kolpin, D. W. (2017). Rainfall-runoff of anthropogenic waste indicators from agricultural fields applied with municipal biosolids. The Science of the Total Environment, 580, 83–89.
  38. Yang, Y.-Y., Gray, J. L., Furlong, E. T., Davis, J. G., ReVello, R. C., & Borch, T. (2012). Steroid Hormone Runoff from Agricultural Test Plots Applied with Municipal Biosolids. Environmental Science & Technology, 46(5), 2746–2754.
  39. Topp, E., Monteiro, S. C., Beck, A., Coelho, B. B., Boxall, A. B. A., Duenk, P. W., Kleywegt, S., Lapen, D. R., Payne, M., Sabourin, L., Li, H., & Metcalfe, C. D. (2008). Runoff of pharmaceuticals and personal care products following application of biosolids to an agricultural field. Science of The Total Environment, 396(1), 52–59.
  40. Naderi Beni, N., Karimifard, S., Gilley, J., Messer, T., Schmidt, A., & Bartelt-Hunt, S. (2023). Higher concentrations of microplastics in runoff from biosolid-amended croplands than manure-amended croplands. Communications Earth & Environment, 4(1), Article 1.
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  46. Ibid. Washington et al., 2010a.
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  48. Ibid. Brodin et al., 2014.
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  53. Ibid. Environmental Dynamics Inc., 2017.
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  55. Thoma, E. D., Wright, R. S., George, I., Krause, M., Presezzi, D., Villa, V., Preston, W., Deshmukh, P., Kauppi, P., & Zemek, P. G. (2022). Pyrolysis processing of PFAS-impacted biosolids, a pilot study. Journal of the Air & Waste Management Association (1995), 72(4), 309–318.

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