Effects of biosolids spreading on soils and streams

Supervisors: Prof. Lee Brown, Dr Laura Carter and Prof. Paul Kay (Leeds), Dr Martin Wilkes (Essex )

Project overview: The application of sewage sludges or “biosolids” to farmland as organic fertilizers is practiced around the world. In the UK, an estimated 3.6M Tonnes of biosolids are applied annually to 150,000 ha of farmland1, but there is capacity and a desire for this to expand further given the increasing costs of synthetic fertilisers in addition to government policies promoting circular economy practices. However, a wide range of chemically complex contaminants has been found in biosolids, including perfluoroalkyl and polyfluoroalkyl substances (PFAS), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), nitrosamines, antibiotics, pharmaceuticals, personal care products and pesticides2,3. Extensive landspreading of biosolids therefore potentially creates novel environmental and public health risks and whilst recent policy debates around river water quality declines have focused intensively on sewage overflows4, diffuse pollution from agriculture accounts for a larger percentage of ecological status classification failures in UK rivers. Biosolids are likely to be an under-appreciated source of chemical and biological pollutants contributing to these outcomes5,6. Whilst the complexity of pollutant mixtures contained within biosolids is relatively well understood3, few studies have documented concerns such as excess nutrient effectse.g.7 and elevated PFAS in biosolid amended soils e.g.8,9. Landspreading practices might therefore need to be evaluated as we gain increased knowledge of pollutant transport through the landscape, and effects on soil/aquatic biodiversity and ecosystem functioning.


Biosolids use in agriculture. (Left) – biosolids delivery pile; (Centre) landspreading onto soils; (Right) crops grown in biosolid amended soils. Centre image from https://www.flickr.com/photos/cityofgeneva/4111259626/ 

Increasing knowledge of biosolid effects in the environment is required urgently in the UK to inform new policy and practice. The Sludge (Use in Agriculture) Regulations 1989 (SUiAR) set standards for testing biosolids and specified precautions that must be taken after landspreading. Additionally, in 1998 a consortium of UK water companies and food retailers entered into the voluntary “Safe Sludge Matrix” agreement to phase out the use of untreated sewage, heavily restrict the use of conventionally treated biosolids, and set minimum harvest intervals after the spreading of “enhanced” treated (99.9999% reduction in pathogens; salmonella absent) biosolids on cropland. In 2020, the Environment Agency stated its aim to bring landspreading into Environmental Permitting (England & Wales) Regulations by mid-2023, partly due to the emergence of new chemical hazards in the decades since SUiAR and the Safe Sludge Matrix were introduced10. However, UK standards for testing contaminants in biosolids remain limited to just six heavy metals. This compares poorly with 352 unregulated pollutants identified in biosolids by the US EPA11, leaving significant uncertainties over the risks to environmental health. The UK lags behind other EU countries in managing biosolid threats; for example, in Germany a ban on landspreading of biosolids from larger sewage treatment plants came into effect in 2017 and the Netherlands halted virtually all agricultural use of biosolids as early as 1995. The UK Government response to a recent Environmental Audit Committee inquiry on Water Quality in Rivers also recommended “independent evaluation of the potential risks to human health and the environment of spreading sewage sludge, with all the pollutants it contains, on farmland” (Paragraph 128)12.

Project aims: The main aim of the PhD is to increase knowledge of the environmental effects of biosolid spreading on land, to contribute to the evidence base that is needed to drive future changes in UK policy and practice. The project offers multiple options for enquiry, such as studies of soil chemical properties, soil ecology, water quality in receiving rivers, and freshwater biodiversity responses, and will be tailored by the successful applicant in line with their skills/interests following a detailed review of the literature. Studies will be designed comparing ‘control’ sites (with no landspreading) against agricultural systems where biosolid applications are already taking place (e.g. using the existing SPADE network https://environment.leeds.ac.uk/geography-research-river-basin-processes-management/dir-record/research-projects/1776/spade-soil-pollution-assessment-delivery )

Benefits: The successful candidate will benefit from inter-disciplinary training in aquatic ecosystem and soil science as part of the River Basin Processes and Management. Training at Leeds deals fully with the elements described in the Joint Research Centre statement on skills training for research students. PhD students take modules provided by the staff development unit (e.g. starting your PhD, small group teaching) and a 15-week faculty-training course (covering elements such as planning, critical reading and writing, oral presentations, writing research papers). Students present results and receive constructive feedback from peers in a Research Support Group, from colleagues in the River Basins research group, and at a university postgraduate research day. The student will also benefit from being part of water@leeds, the largest interdisciplinary water centre in any UK university, which runs multiple postgraduate activities.

The nature of the project means that the student will be trained in project specific research methods including literature reviews, field work techniques (chemistry, ecology, hydrology), laboratory soil/water quality/taxonomic analysis, and modelling/statistics for analysing data, both internally and at external workshops. An additional important part of the training will be to attend national and international conferences to present results and gain feedback. The student will be expected to submit papers for publication in international journals during the project.

Indicative references

  1. assuredbiosolids.co.uk/wp-content/uploads/2019/01/Biosolids-Agric-Good-Practice-Guidance-January-2019.pdf
  2. comptox.epa.gov/dashboard/chemical-lists/BIOSOLIDS;
  3. Materials to Land Phase 2, 2017 Environment Agency report https://s3.documentcloud.org/documents/6941365/EA-Materials-to-Land-report.pdf
  4. https://www.gov.uk/government/news/largest-overhaul-of-sewer-system-to-tackle-storm-sewage-discharges
  5. Whelan et al. 2022. Sci Total Environ. 10.1016/j.scitotenv .2022.157014
  6. https://publications.parliament.uk/pa/cm5802/cmselect/cmenvaud/74/report.html
  7. https://www.mdpi.com/2571-8789/6/1/9
  8. https://www.sciencedirect.com/science/article/pii/S004896972103521X
  9. https://www.sciencedirect.com/science/article/pii/S0169772221000516
  10. https://www.gov.uk/government/publications/environment-agency-strategy-for-safe-and-sustainable-sludge-use/environment-agency-strategy-for-safe-and-sustainable-sludge-use
  11. https://www.epa.gov/sites/default/files/2018-11/documents/_epaoig_20181115-19-p-0002.pdf
  12. https://committees.parliament.uk/work/891/water-quality-in-rivers/publications/