Toggle Main Menu Toggle Search

Open Access padlockePrints

Environmental DNA clarifies impacts of combined sewer overflows on the bacteriology of an urban river and resulting risks to public health

Lookup NU author(s): Dr Rixia ZanORCiD, Adrian Blackburn, Dr Aom Plaimart, Dr Kishor AcharyaORCiD, Professor Claire Walsh, Dr Ross Stirling, Professor Chris Kilsby, Professor David WernerORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


There is no reference of microbiological water quality in the European Union's Water Framework Directive, adapted into English law, and consequently microbial water quality is not routinely monitored in English rivers, except for two recently designated bathing water sites. To address this knowledge gap, we developed an innovative monitoring approach for quantitative assessment of combined sewer overflow (CSO) impacts on the bacteriology of receiving rivers. Our approach combines conventional and environmental DNA (eDNA) based methods to generate multiple lines of evidence for assessing risks to public health. We demonstrated this approach by investigating spatiotemporal variation in the bacteriology of the Ouseburn in northeast England for different weather conditions in the summer and early autumn of the year 2021 across eight sampling locations that comprised rural, urban, and recreational land use settings. We characterized pollution source attributes by collecting sewage from treatment works and CSO discharge at the peak of a storm event. CSO discharge was characterized by log10 values per 100 mL (average ± stdev) of 5.12 ± 0.03 and 4.90 ± 0.03 for faecal coliforms and faecal streptococci, and 6.00 ± 0.11 and 7.78 ± 0.04 for rodA and HF183 genetic markers, for E. coli and human host associated Bacteroides, respectively, indicating about 5 % sewage content. SourceTracker analysis of sequencing data attributed 72–77 % of bacteria in the downstream section of the river during a storm event to CSO discharge sources, versus only 4–6 % to rural upstream sources. Data from sixteen summer sampling events in a public park exceeded various guideline values for recreational water quality. Quantitative microbial risk assessment (QMRA) predicted a median and 95th percentile risk of 0.03 and 0.39, respectively, of contracting a bacterial gastrointestinal disease when wading and splashing around in the Ouseburn. We show clearly why microbial water quality should be monitored where rivers flow through public parks, irrespective of their bathing water designation.

Publication metadata

Author(s): Zan R, Blackburn A, Plaimart J, Acharya K, Walsh C, Stirling R, Kilsby C, Werner D

Publication type: Article

Publication status: Published

Journal: Science of The Total Environment

Year: 2023

Volume: 889

Print publication date: 01/09/2023

Online publication date: 18/05/2023

Acceptance date: 15/05/2023

Date deposited: 05/06/2023

ISSN (electronic): 0048-9697

Publisher: Elsevier


DOI: 10.1016/j.scitotenv.2023.164282


Altmetrics provided by Altmetric


Funder referenceFunder name
BB/S009795/1Biotechnology and Biological Sciences Research Council (BBSRC)
Reece Foundation
Royal Society