One health wake-up call: London's river data highlights environmental perils

In a recent article published in Environment International Journal, researchers performed the largest-ever spatiotemporal monitoring of chemicals/contaminants of emerging concern (CECs) in London waterways during the coronavirus disease 2019 (COVID-19) pandemic, i.e., from 2019 to 2021. 



In the United Nations Environment Programme (UNEP) 2021, they regarded pollution as one of the greatest planetary crises after climate change and biodiversity loss.

The toxic effects of chemicals on wildlife, human, and environmental health are less clear and an impediment to achieving sustainable urban ecosystems. 

Moreover, chemical pollution is the leading cause of death worldwide, representing more fatalities (~10 million) than war, murder, alcohol use, smoking, and fatal diseases, such as malaria and acquired immunodeficiency syndrome (AIDS).

Large cities worldwide are witnessing a population surge; per a 2020 European Commission (EU) report, these might surge 68% by 2050, and their population density is high, too, which has modified their natural environment and introduced a suite of chemical products in their air, water, and land sites. As this trend continues, it will worsen urban environments even more in the coming decades.

The European Union Water Framework Directive (EU WFD) has enlisted 26 CECs, whose occurrence, fate, and effects across multiple environments are urgently needed. 

Large-scale public health interventions introduced during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic resulted in marked changes in the use of chemicals (e.g., pharmaceuticals), particularly in large cities, which likely modulated their environmental risks. 

London, the third largest city in Europe after Istanbul and Moscow, has ∼an 8.8 million residential population; thus, the potential for the Thames Basin to create CEC impacts is relatively larger than other UK regions. In addition, 57 overflow points discharge >39 million tonnes of raw sewage to the River Thames annually.

The Environment Agency (EA) started semi-quantitative chemical monitoring across England in 2019, but more spatiotemporal resolution is needed to understand CECs and their risks within London waterways. 

Previous studies reliably measured chemical concentrations; however, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and LC-high resolution accurate mass spectrometry (LC-HRMS) even more rapidly identify chemical sources in complex environmental samples from rivers and wastewater treatment plants (WWTPs) with sufficient sensitivity. 

Additionally, these methods needed fewer reagents, solvents, and consumables, reducing time and cost.

Overall, these advancements facilitated spatiotemporal scaling up of chemical monitoring programs to help prioritize CEC risks rapidly and sustainably.

About the study

In the present study, researchers executed a highly spatially-temporally resolved study in three campaigns, of which the first campaign, completed on 27 November 2019 (one day) across 29 sites spanning 60 km of the river Thames (R. Thames), fetched 84 samples.

The sampling for campaigns two and three ran from 14 October to 17 December 2020 and 5 November to 14 December 2021, respectively. In the former, the team collected 133 water samples from the R. Thames and five other rivers, R. Brent, Lee/Lea, Hogsmill, Wandle, and the Grand Union Canal over 14 days.

In the latter, the team collected 168 samples from multiple other London rivers but did not study them spatially resolved transects. However, for both these campaigns, researchers visited these sites multiple times to investigate inter-day variations.

They collected 390 samples across 2019–2021 for target compound(s) quantification, suspect screening, and prioritization of CEC risks. During quantification, the team derived measured environmental concentration (MEC) values from LC-MS/MS analysis, for each CEC substance in a sample individually and as the average of three LC-MS/MS runs.

They grouped samples from the R. Thames into a pooled matrix for separate calibrations and quantified freshwater and brackish sites separately.

For suspect screening, they selected ten samples, two from each of five freshwater bodies, based on the number and concentration of CECs and a downstream site on each water body for comparison purposes.

Furthermore, the researchers used software to screen 1,219 compounds in the Shimadzu toxicology and pesticide libraries and additional reference materials from Imperial College London.


Targeted analysis and suspect screening identified 73 and 25 (total 98 compounds), of which 66 (two-thirds) were quantifiable with MECs ranging between 3-3326 ng/L. 

The average of the total combined MECs for all substances quantified at each site across all years was 1,181 ±905 ng/L. Although MECs were relatively similar for common substances overall, their spatial resolution was much larger than in any previous study.

The top five compounds were highly variable pharmaceuticals, i.e., salicylic acid (an aspirin metabolite), carbamazepine (antipsychotic drug), clarithromycin (antibiotic), tramadol (opioid analgesic), and diclofenac (an anti-inflammatory drug) with respective MECs of 190 ±295 ng/L, 127 ±109 ng/L, 122 ±163 ng/L, 109 ±84 ng/L, and 100 ±88 ng/L. Diclofenac and clarithromycin were included in previous EU WFD Watch Lists, too.

Hierarchical cluster analysis (HCA) of all MEC data differentiated chemical signatures of treated wastewater (34 compounds) and combined sewer overflows (CSOs)/raw wastewater discharges (27 compounds) and revealed some clear groupings.

In size groupings, the first group was dominated by sampling sites on tributary rivers downstream of WWTPs/CSO discharge points.

Beverley Brook and R. Hogsmill were the most impacted sites, with temporal trends in MECs of R. Hogsmill reflecting NHS prescribing data, including for drugs used to treat COVID-19.

The NHS prescriptions of antidepressant and antipsychotic medications also increased in Greater London during the COVID-19 pandemic; however, trends in riverine MECs did not reflect those.

Moreover, these drugs presented low to insignificant risk to aquatic life, except citalopram, sertraline, and clozapine, which posed a moderate risk, with risk quotients (RQs) between one and ten. On the contrary, CECs in freshwaters, such as imidacloprid, azithromycin, and diclofenac, posed a high risk to aquatic life (all RQs ≥10). 

The second grouping had no WWTP effluent or CSO activity; thus, their contamination likely originated from surface run-off, leachate, sewer misconnections, leakages, and direct dumping.

Two main CEC groupings existed following HCA across all data, with the first grouping having 27 compounds, such as diclofenac, temazepam, and tramadol, mostly wastewater effluents. The second grouping had 39 compounds, of which 31 were drugs, and eight were pesticides. 

During the COVID-19 lockdown, daily migration to and from London and within-city movement declined by >77% and >60%, respectively, which reduced ammonia levels in WWTP influents.

In addition, in 2019, no CSOs fell in R. Thames, at least within 48 hours of sampling; however, in 2020, 11 CSOs occurred in this region.

For the 64 CECs quantifiable in the R. Thames, the average and interquartile range (IQR) of MECs declined slightly in 2020 but reverted to statistically higher levels in 2021. 

The most significant MEC decreases in R. Thames were attributable to temazepam (an antidepressant and treated effluent marker), lidocaine (an anesthetic and cocaine-cutting agent), clopidrogel (an antiplatelet drug), and acetamiprid (a neonicotinoid insecticide). 


According to the authors, this was one of the first large-scale waterways monitoring of the waterways of the Greater London area at an exceptionally high spatiotemporal resolution, which identified 98 CECs during 2019-2021.

In this way, this study laid a strong foundation for assessing the historical impact of the COVID-19 pandemic.

Journal reference:
Neha Mathur

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mathur, Neha. (2023, September 26). One health wake-up call: London's river data highlights environmental perils. News-Medical. Retrieved on July 15, 2024 from

  • MLA

    Mathur, Neha. "One health wake-up call: London's river data highlights environmental perils". News-Medical. 15 July 2024. <>.

  • Chicago

    Mathur, Neha. "One health wake-up call: London's river data highlights environmental perils". News-Medical. (accessed July 15, 2024).

  • Harvard

    Mathur, Neha. 2023. One health wake-up call: London's river data highlights environmental perils. News-Medical, viewed 15 July 2024,


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
GLP-1 drugs found to lower cancer risk in diabetes patients