High levels of sewage contamination released from urban areas after storm events: A quantitative survey with sewage specific bacterial indicators

Abstract

BackgroundPast studies have demonstrated an association between waterborne disease and heavy precipitation, and climate change is predicted to increase the frequency of these types of intense storm events in some parts of the United States. In this study, we examined the linkage between rainfall and sewage contamination of urban waterways and quantified the amount of sewage released from a major urban area under different hydrologic conditions to identify conditions that increase human risk of exposure to sewage.Methods and findingsRain events and low-flow periods were intensively sampled to quantify loads of sewage based on two genetic markers for human-associated indicator bacteria (human Bacteroides and Lachnospiraceae). Samples were collected at a Lake Michigan estuary and at three river locations immediately upstream. Concentrations of indicators were analyzed using quantitative polymerase chain reaction (qPCR), and loads were calculated from streamflow data collected at each location. Human-associated indicators were found during periods of low flow, and loads increased one to two orders of magnitude during rain events from stormwater discharges contaminated with sewage. Combined sewer overflow (CSO) events increased concentrations and loads of human-associated indicators an order of magnitude greater than heavy rainfall events without CSO influence. Human-associated indicator yields (load per km2 of land per day) were related to the degree of urbanization in each watershed. Contamination in surface waters were at levels above the acceptable risk for recreational use. Further, evidence of sewage exfiltration from pipes threatens drinking water distribution systems and source water. While this study clearly demonstrates widespread sewage contamination released from urban areas, a limitation of this study is understanding human exposure and illness rates, which are dependent on multiple factors, and gaps in our knowledge of the ultimate health outcomes.ConclusionsWith the prediction of more intense rain events in certain regions due to climate change, sewer overflows and contamination from failing sewer infrastructure may increase, resulting in increases in waterborne pathogen burdens in waterways. These findings quantify hazards in exposure pathways from rain events and illustrate the additional stress that climate change may have on urban water systems. This information could be used to prioritize efforts to invest in failing sewer infrastructure and create appropriate goals to address the health concerns posed by sewage contamination from urban areas.

Host Specificity and Sensitivity of Established and Novel Sewage-Associated Marker Genes in Human and Nonhuman Fecal Samples

“…Quantitative data for the concentrations of sewage-associated marker genes in human and nonhu-man fecal samples provide important information with regard to the ability to detect their presence in environmental waters. Because the concentrations of sewageassociated marker genes are relatively consistent in sewage (3,26,40), concentrations in environmental waters can be compared with the concentrations in untreated sewage to obtain information on the amount of sewage present immediately after a contamination event.…”

“…Urbanization and extreme weather events such as floods and wet/dry weather overflows result in an increased amount of sewage being discharged into water bodies (3,(25)(26)(27). Sewage-contaminated water bodies are potential public health hazards and can cause severe illnesses to humans due to the presence of infectious pathogens (28).…”

Molecular Analyses of Fecal Bacteria and Hydrodynamic Modeling for Microbial Risk Assessment of a Drinking Water Source

“…The primers were chosen amongst other Salmonella specific primers due to their superior performance in real-time PCR. Although presence of Salmonella in the tributary Björkaån could be due to e.g., agricultural runoff [9,47], the finding in infiltrated groundwater was not expected. It is possible that migrating birds or other wild animals residing close to the infiltration ponds and the water extraction wells caused the occurrence of Salmonella spp.…”

“…However, in most countries with developed water supply systems, increased levels of contamination are often linked to failures in water piping systems or drinking water treatment plants [5,6]. Storms and heavy rainfalls resulting in discharges of wastewater and runoff from livestock or wildlife into rivers and lakes can also increase microbial contamination [7][8][9].…”

Short-term effects of natural stream discharge on the water quality trends along two small urban streams – a pilot study

“…The surface water quality is furthermore impacted by the local weather conditions (Bhurtun et al, 2019)". For example, big storm (i.e., heavy precipitation) events may cause increased nutrient release from a major urban area into the associated streams, which may further yield far-reaching indirect effects on biogeochemical cycles and biodiversity trends along urban streams (e.g., Grimm et al, 2005;Olds et al, 2018). This is particularly important for small urban streams (characterized by small sizes and high degree of imperviousness), which exhibit a faster and stronger stream discharge response (Chen & Chang, 2014;Yang et al, 2016).…”