By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Quantification of pathogens and markers of fecal contamination during storm events along popular surfing beaches in San Diego, California
Prevalence of human pathogens and indicators in stormwater runoff in Brisbane, Australia
A review on microbial contaminants in stormwater runoff and outfalls: Potential health risks and mitigation strategies
Can we swim yet? Systematic review, meta-analysis, and risk assessment of aging sewage in surface waters
A novel screening tool for the health risk in recreational waters near estuary: The Carrying Capacity indicator
Welcome to the first library of 2021! Hope all made it through the end of the year and the start of the new one intact, ideally with a sense of hope and better things ahead. With that said, we are still in the dark tunnel. COVID-19 is an ever-present reality, nowhere near a distant memory. And we are in the darkest and coldest part of the year. What I have been dreaming about is swimming in warm ocean waters. Now- I can’t do a library on the best beaches in the world. However, I can do one that ties those ocean (or fresh) waters to wastewater and stormwater. So not quite tropical blue colors and gentle breezes. Instead we have the health risks associated with swimming in waters with potential contamination resulting from aging sewage pipes, CSOs, and stormwater. Think of this as a professional vacation. Or maybe a reason to stay home.
The first paper takes us to the beautiful beaches of San Diego. Big fan of Coronado myself. Here the authors sampled water from freshwater inlets to the ocean as well as the ocean itself. Two paired sites were sampled. One watershed was highly urbanized and had a small creek and the other, the San Diego river was much larger and more diverse. The latter also includes a bird sanctuary. They tested for fecal indicator bacteria (FIB) using Polymerase Chain Reaction (PCR). My quick internet search suggests that PCR is not the best at detecting live critters from dead ones. Squirming or not, the authors found much higher pathogen counts in stormwater entering the oceans than in the water collected from the beaches. They repeatedly found evidence of human fecal matter in the stormwater even though the area has separate storm and sanitary sewers. FIB and norovirus were the most common detects though there was also the occasional Salmonella and adenovirus. They found more indicators of bird poop from the watershed with the bird sanctuary. More bacteria/ pathogens were found in the water during wet periods in comparison to dry periods. You can see just how much norovirus in the figure below.
They also found a little bit of dog associated pathogens. Who doesn’t like walking their dog by a river?
Importantly here- concentrations in the ocean were markedly lower than in the watersheds. So surfing in San Diego, even in the occasional rainstorm is not nearly as hazardous as dipping into the creek or river.
Paper #2 takes us to Brisbane, Australia where the beaches are spectacular. Here is a shot during some spectacular stormy weather back when travel was possible.
The authors of this paper stayed away from the beaches and instead sampled freshwater in the urban/ rural corridor. Sites were sampled during storm events and with regular flow. They also focused on FIB and used PCR to quantify pathogens. They also found them. More in wet periods than in dry, but E. coli and Enterococcus as well as other FIB. The authors make a big deal of the detects but they were actually less pronounced than in San Diego. They also didn’t see as marked a difference between the more rural and urban sites. Nevertheless, they conclude that their results provide evidence of leaky sewers. I just want to point out here that the beaches in Brisbane are a decent distance from the urban areas and I would still swim in them. Salt water tastes lousy so who wants to swallow it anyway!
So first two exotic locations and evidence of human pathogens present in the water. Paper # 3 is an overview/ review of this topic in general. If this does interest you past the armchair travel opportunity- this is the paper to ask for a copy of. Here the focus is also on pathogens in stormwater but it is a much broader context and considers the topic from multiple perspectives. FIB are fine, but if the bacteria come from warm blooded intestines other than the human kind, it is not clear that there is a risk. The traditional threshold for outdoor water to be considered safe for recreational use (that includes swimming) is >501 CFU/ 100 mL- that is Class D water and swimming in that would put the odds of illness at > 10%. The article points out that rural areas are a significant source of E Coli. Getting ready for this library I read one article that considered cow dung as a major source of water contamination by pathogens. They also point out that use of FIB is that they may not correlate well or survive the same as pathogens or viruses that make people ill. They talk about using microbial source tracker (MST) genes as a more sophisticated tool. By high specificity MST has been able to point a finger at aging infrastructure – leaking untreated sewage into stormwater systems. There is a big table that provides you with sources on presence of pathogens in stormwater. This table can take you around the world and in fact is where I found the first two papers in the library. There is also a discussion of different types of analysis and associated +/- s. There is also no discussion in many papers on the persistence of these pathogens. Following that, understanding actual risk can be problematic. There is a gigantic table with different references that describes pathogen found, exposure route, duration and frequency and associated risk. The paper concludes with a discussion of the efficacy of different stormwater systems at pathogen removal (short answer here is not so good).
Paper # 4- also referenced in Paper #3 is all about risk and how that changes with time of exposure. The authors use data on first order decay for different viruses and pathogens. Problems are that much of the data was conducted in the dark and decay rates will likely be altered with exposure to sunlight. Decay will also likely differ in salt versus fresh water systems. One thing absent here as well is impact of dilution on any risk. With that said, the authors used quantitative microbial risk assessment (QMRA) to come up with some estimates. Different bugs die at different rates with norovirus being the biggest concern. The authors conclude that swimming in water with 72 hour old contamination gives you a median chance of illness of less than 30/1000.
Paper #5 continues on with a focus on risk associated with swimming following CSOs. They express risk in terms of the carrying capacity (CC) of the water body in question. That is defined as the number of swimmers associated with an acceptable risk of illness. As the water gets diluted the CC capacity increases. Dilution happens both by mixing and by reduction at the source of contamination.
These days I am not quite comfortable or even allowed to get on a plane and travel to warm inviting ocean waters. I am still lucky to live near enough to salt water to take a very brief and neoprene insulated dip. Luckily, I did this a few days before the rains and winds that resulted in a power outage and placement of signs like this. As a swimmer- we still have some work to do.