The contemporary world relies heavily on a massive and ever-growing inventory of chemicals. Over 160 million chemicals are known to humanity, with an estimated 350,000 individual chemicals and mixtures authorized for global production and use (Wang et al., 2020). The number of substances is continually increasing, with roughly 2,000 new chemicals authorized each year. Chemical production reached a global sales value of 5.2 Trillion Euros in 2024 (Cefic, 2025).
Chemical substances offer significant societal benefits, integrated into nearly every aspect of modern life. They are essential components in pesticides and livestock medicines that support food production, pharmaceuticals vital for human health, paints and polymers used in construction, and plastics and additives found in food packaging. Chemicals are also crucial for colours and fire retardants in textiles, and fragrances and preservatives in personal care products and cosmetics. Even after their active use, many chemicals persist, existing in landfill sites and remaining in the soils and sediments of areas with a history of chemical production or mining (Brand et al., 2018). Furthermore, many chemicals, like pharmaceuticals, are metabolised in the human body, resulting in a complex mixture of parent molecules and their metabolites being excreted.
Given their ubiquitous production, use, and disposal, the release of these chemicals into the environment—specifically indoor and outdoor air, rivers, lakes, marine waters, and soils—is an inevitable process.
Emissions occur through several key pathways:
Manufacturing activities release volatile organic chemicals into the atmosphere (Wang et al., 2013) and organic micropollutants into surface waters (Larsson et al., 2014; Anliker et al., 2022).
Agriculture is a direct source, with pesticides applied directly to soils and livestock medicines released either by treated animals at pasture or when manure and slurry are used as fertilizer on land (Boxall et al., 2003).
Wastewater systems collect pharmaceuticals, personal care products, and other down-the-drain chemicals. While some pollutants may be degraded at the treatment plant, others pass through the process into watercourses (Ashfield et al., 2025). Importantly, many chemicals absorb to the sludge during treatment and are subsequently released to soils when that sludge is applied as fertilizer (Ashfield et al., 2025).
In the indoor environment, chemicals from personal care and cleaning products, and even cooking, are released to air through sprays and volatilisation (Arata et al., 2021).
Due to the widespread nature of these emissions, it is not surprising that countless synthetic chemicals have been detected in natural environments worldwide. Scientific analysis confirms this ubiquity: a recent bibliometric study identified approximately 105,000 studies that have examined the occurrence of 19,766 individual chemicals (Muir et al., 2023). The most frequently studied classes include pharmaceuticals, pesticides, and flame retardants. A crucial realization is that chemicals never occur alone in an environmental system; rather, they exist as a complex cocktail of substances (Escher et al., 2020).
Understanding the impacts of this complex chemical pollution on human health, well-being, and ecological health is one of the major challenges facing the environmental science community. In the following topics covered in the module, you will gain an understanding of the occurrence of chemicals in the UK environment and the concerns around impacts on ecological, human and planetary health.
Recorded Lecture
Alistair Boxall, who is Professor of Environmental Science at the University of York, gives an overview of the number of chemicals in use around the world, their pathways and occurrence into/in the natural environment
Key Reading
Escher BI, Stapleton HM, Schymanski EL. (2020) Tracking complex mixtures of chemicals in our changing environment. Science. 367(6476):388-392. https://doi.org/10.1126/science.aay6636
Muir DCG, Getzinger GJ, McBride M, Ferguson PL. (2023) How Many Chemicals in Commerce Have Been Analyzed in Environmental Media? A 50 Year Bibliometric Analysis. Environ Sci Technol. 57(25):9119-9129. https://doi.org/10.1021/acs.est.2c09353
Scheringer, M., Sculz, R. (2025) The State of the World's Chemical Pollution. Annual Review of Environment and Resources 50:381-408. https://doi.org/10.1146/annurev-environ-111523-102318
Wang Z, Walker GW, Muir DCG, Nagatani-Yoshida K. (2020) Toward a Global Understanding of Chemical Pollution: A First Comprehensive Analysis of National and Regional Chemical Inventories. Environ Sci Technol. 54(5):2575-2584. https://doi.org/10.1021/acs.est.9b06379
Other Reading Materials
Anliker S, Santiago S, Fenner K, Singer H. (2022) Large-scale assessment of organic contaminant emissions from chemical and pharmaceutical manufacturing into Swiss surface waters. Water Res. 215:118221. https://doi.org/10.1016/j.watres.2022.118221
Arata C, Misztal PK, Tian Y, Lunderberg DM, Kristensen K, Novoselac A, Vance ME, Farmer DK, Nazaroff WW, Goldstein AH. (2021) Volatile organic compound emissions during HOMEChem. Indoor Air. 31(6):2099-2117. https://doi.org/10.1111/ina.12906
Ashfield, N., Li, J., Bouzas-Monroy, A., Boxall, A.B.A. (2025) Silent Side Effects: Pharmaceuticals as Contaminants of Emerging Concern. Annual Review of Environment and Resources 50:273-301. https://doi.org/10.1146/annurev-environ-111523-101837
Boxall AB, Kolpin DW, Halling-Sørensen B, Tolls J. (2003) Are veterinary medicines causing environmental risks? Environ Sci Technol. 37(15):286A-294A. https://doi.org/10.1021/es032519b
Brand, J.H., Spencer, K.L., O'shea, F.T., Lindsay, J.E. (2017) Potential pollution risks of historic landfills on low-lying coasts and estuaries. WIRES 5:e1264. https://doi.org/10.1002/wat2.1264
Cefic (2025) Facts & Figures of the European Chemical Industry. Available at: https://cefic.org/facts-and-figures-of-the-european-chemical-industry/ (accessed Oct 2025)
Larsson DG, de Pedro C, Paxeus N. (2007) Effluent from drug manufactures contains extremely high levels of pharmaceuticals. J Hazard Mater. 148(3):751-5. https://doi.org/10.1016/j.jhazmat.2007.07.008
Larsson DG. (2014) Pollution from drug manufacturing: review and perspectives. Philos Trans R Soc Lond B Biol Sci. 2014 Nov 19;369(1656):20130571. https://doi.org/10.1098/rstb.2013.0571
Wang, H., Nie, L., Li, J. et al. (2013) Characterization and assessment of volatile organic compounds (VOCs) emissions from typical industries. Chin. Sci. Bull. 58, 724–730. https://doi.org/10.1007/s11434-012-5345-2