Biogeochemical cycle of perfluoroalkyl carboxylic acids (PFCAs) on grazing land treated with biosolids.

Per- and polyfluoroalkyl substances (PFAS) are a group of human-made chemicals that have been widely used in various industrial and consumer products for decades. They are known for their resistance to heat, water, and oil, making them valuable in applications such as non-stick cookware, firefighting foams, and water-repellent fabrics. These very characteristics are also the reason of their persistence and ecotoxicity in the environment and have earned them the moniker of “forever chemicals”.
Biosolids, also known as sewage sludge, are organic materials resulting from the treatment of domestic sewage at wastewater treatment plants. In Scotland, these biosolids are often used as fertiliser on agricultural land due to their nutrient content, and their positive effect on soil health. Wastewater treatment plants are a known point-source of anthropogenic contaminants into the environment; due to their hydrophobic nature of long-chain PFAS, PFAS in wastewaters are likely to settle in the sludge at the plant and therefore end up in biosolids. The ecological risks of environmental PFAS are currently not known and represents an emerging area of concern.
Previous work carried out in our laboratories have demonstrated that PFAS concentrations are elevated in the soil of grazing land that have been fertilised using biosolids; they have also shown that the plasma of sheep on the same farm also contains PFAS.
In this project, the PGR will investigate the source and fate of PFAS on the grazing land of the University of Glasgow ‘s Cochno Farm and Research Centre where an experimental biosolids pasture is established. The particular focus will be on perfluoroalkyl carboxylic acids and their metabolites and degradation products. Source of PFAS on the farm, biosolids, water, plastics, will be first investigated. Transfer and transformation of the PFAS will be characterised during assimilation of the biosolids pellets into the soil, during bioaccumulation in grass and through sheep metabolism and reintegration in the soil via faeces.
This is the first study of the biogeochemical cycles of PFAS on farming land; the findings of the work have the potential to inform policy on biosolids spreading but also engineering interventions to prevent public and environmental health risks.

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Paul Eynon- Lamb at Cochno Farm and Research Centre


This is a highly interdisciplinary project with a supervisory team across the environmental sciences: chemistry, engineering, endocrinology and analytical methods. The supervisors will work as a team with the PGR to truly integrate all aspects together to produce an entirely novel approach to environmental fate of PFAS. The project will have six distinct but related parts to determine the biogeochemical cycle of perfluoroalkyl carboxylic acids at Cochno farm:
1. PFAS sources: Additionally to biosolids pellets that are spread on the farm (twice a year, conventional rates), other potential sources of PFAS such as water but also farm materials will be identified and analysed and their exposure to the field characterised.
2. From pellets to soil: the interaction of the pellets with microbiological activity in the soil will be studied in detail, including the effect of microbes on the disintegration of the pellets and the potential biodegradation of the PFAS in soil.
3. From field to sheep: the concentrations of PFAS and metabolite in surface soil and grass will be studied longitudinally on both the field that receives biosolids and the control (conventionally fertilised, equivalent nitrogen) field. This will allow evaluating the exposure of the sheep through grazing.
4. From sheep to soil: the concentrations of PFAS and metabolites in sheep faeces on both fields will be studied longitudinally. This will allow evaluating the reintroduction of PFAS on the land via sheep metabolism.
5. From soil to water: adsorption experiments will be performed to measure the soil-water partition coefficients of PFAS in biosolid-amended soils to evaluate PFAS mobility in these conditions . Moreover, along these longitudinal studies, water run off on the site (which is on a slope) will also be measured for PFAS and metabolites concentrations.

Project Timeline

Year 1

0-6 months: The PGR will conduct a bibliography and will also carry out the PFAS assessment on the farm. They will familiarise themselves with the farm, sheep and land management practice to design the longitudinal studies to be ready for the Spring 2025 biosolids spreading. 6-9 months: Sampling starts and the PGR is trained in essential analytical chemistry skills and then design optimal analysis plan for samples including: pellets, soil, grass, water and faeces.
9-12 months: The PGR will spend time at Newcastle University to carry out adsorption experiments.

Year 2

12-18 months: Sampling continues and samples are analysed for the first year of sampling; the PGR will also set up lab microcosms to studies pellets disintegration and PFAS biodegradation with soil inoculum. 18-24 months: Sampling and microcosm study continue, data analysis for the first year of sampling is carried out.

Year 3

24-30 months: Sampling continues and results from the microcosm study are analysed and written up, analyses for the second year of sampling start. 30-36 months: The analyses for the second year of sampling conclude, results are analysed and written up.

Year 3.5

36-42 months: Thesis and publication write up.

& Skills

The student will learn a range of skills in the field, including non-invasive animal health monitoring, soil & faeces sample collection and sample storage techniques. They will also learn a range of skills in the laboratory including analytical chemistry, microscosm studies, sorption isotherm development. Several types of data analysis will be learned, including bioinformatic approaches and mixed-effects models to tackle data collected from the longitudinal field trials. They will also participate in active project and departmental meetings, and national/international conferences, where appropriate. All supervisors actively engage in knowledge exchange at local and national events and the student would be encouraged to participate. Both organizations also offer a range of training modules for PhD students to aid professional development, such as those in giving presentations, scientific writing, career management, and others.

References & further reading

• Kewalramani JA, Wang B, Marsh RW, Meegoda JN, Rodriguez Freire L. Coupled high and low-frequency ultrasound remediation of PFAS-contaminated soils. Ultrasonics Sonochemistry 2022, 88, 106063.
• Thangaraj SV, Kachman M, Halloran KM, Sinclair KD, Lea R, Bellingham M, Evans NP, Padmanabhan V. Developmental programming: Preconceptional and gestational exposure of sheep to a real-life environmental chemical mixture alters maternal metabolome in a fetal sex-specific manner. Sci Total Environ. 2023 Mar 15;864:161054.
• Roberts, J., McNaughtan, M., & de las Heras Prieto, H. (2023). Unwanted ingredients—highly specific and sensitive method for the extraction and quantification of PFAS in everyday foods. Food Analytical Methods, 16(5), 857-866. Advance online publication. https://doi.org/10.1007/s12161-023-02451-

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