Elizabeth P. Sauer
Steven R. Corsi
Melinda J. Bootsma
Alexandria B. Boehm
Susan K. Spencer
Mark A. Borchardt
Sandra L. McLellan
2018
<p><span>Despite modern sewer system infrastructure, the release of sewage from deteriorating pipes and sewer overflows is a major water pollution problem in US cities, particularly in coastal watersheds that are highly developed with large human populations. We quantified fecal pollution sources and loads entering Lake Michigan from a large watershed of mixed land use using host-associated indicators. Wastewater treatment plant influent had stable concentrations of human </span><i>Bacteroides</i><span> and human </span><i>Lachnospiraceae</i><span> with geometric mean concentrations of 2.77 × 10</span><sup>7<span> </span></sup><span>and 5.94 × 10</span><sup>7<span> </span></sup><span>copy number (by quantitative PCR) per 100 ml, respectively. Human-associated indicator levels were four orders of magnitude higher than norovirus concentrations, suggesting that these human-associated bacteria could be sensitive indicators of pathogen risk. Norovirus concentrations in these same samples were used in calculations for quantitative microbial risk assessment. Assuming a typical recreational exposure to untreated sewage in water, concentrations of 7,800 copy number of human </span><i>Bacteroides</i><span> per 100 mL or 14,000 copy number of human </span><i>Lachnospiraceae</i><span> per 100 mL corresponded to an illness risk of 0.03. These levels were exceeded in estuarine waters during storm events with greater than 5 cm of rainfall. Following overflows from combined sewer systems (which must accommodate both sewage and stormwater), concentrations were 10-fold higher than under rainfall conditions. Automated high frequency sampling allowed for loads of human-associated markers to be determined, which could then be related back to equivalent volumes of untreated sewage that were released. Evidence of sewage contamination decreased as ruminant-associated indicators increased approximately one day post-storm, demonstrating the delayed impact of upstream agricultural sources on the estuary. These results demonstrate that urban areas are a diffuse source of sewage contamination to urban waters and that storm-driven release of sewage, particularly when sewage overflows occur, creates a serious though transient human health risk.</span></p>
application/pdf
10.1525/elementa.301
en
University of California Press
Sewage loading and microbial risk in urban waters of the Great Lakes
article