You’re reading Part IV in a 5-part series about sewage science. Catch up on Parts I, II, and III before diving into this one.
Many recent applications of wastewater-based epidemiology—including for monitoring nutrition, microbiota, and COVID-19—are still in their infancy. Scientists have yet to solve several key issues. How well does amount of food consumed correlate with the amount of biomarker excreted? What is the role of bacterial species in the microbiome of a single person? How much does the amount of SARS-CoV-2 shed in feces vary from person to person? Add onto these questions ever-present uncertainties about sewer conditions like temperature, flow rate, and the presence of other chemicals or microbes, and the rather simple concept of WBE complicates quickly.
A common problem plaguing WBE scientists might seem at first to be the easiest to solve: that of estimating population size.
Whether measuring the consumption of illicit drugs or leafy green vegetables, the results only have meaning in relation to the number of people who contributed to the sewage in the sample. But the straightforward solution of using population estimates from census data is often not the best—such estimates are frequently inaccurate and don’t account for commuters, tourists, or other day-to-day fluctuations.
“If you have a place that has a high influx of commuters, say Manhattan, that population is really different in the morning of a Monday than it is on a Saturday morning,” Dan Burgard noted. Other methods of estimating population size, like using mobile phone data, can be prohibitively expensive. But there is an alternative. “One of the things we’re working on right now is to try to use compounds in wastewater itself to help us understand how many people are in that actual population,” Burgard told me.
What Burgard means is finding a marker in sewage that can serve as a proxy for population size—preferably one that each person excretes at a similar rate and that remains relatively constant over time. In practice, these are markers of things we consume regularly: artificial sweeteners, nicotine, caffeine.
Yet, the major roadblocks to further advancing wastewater analysis might not be scientific at all, but societal.
Concerns about ethics and privacy have been around for as long as people have been analyzing sewage. In most cases, wastewater in a treatment plant comes from hundreds of thousands of flushes—that is, any data gathered is almost guaranteed to be anonymized. However, when surveying smaller populations, like a school, workplace, or prison, there are legitimate concerns that data could be used to target vulnerable groups. Phil Choi emphasized that WBE researchers adhere to a set of ethical principles to ensure that data is not used to punish or stigmatize a community. But scientists still need to address such concerns if wastewater analysis is going to be used on a larger scale.
Some cities may be reluctant to have their sewage surveilled for fear that a negative outcome— like finding high rates of illicit drug use—will tarnish their reputations. A few WBE researchers speculated that reluctance to air the “dirty laundry” of cities and communities prevents the widespread use of wastewater analysis—particularly in the US. Regardless of the reason, many WBE scientists feel frustrated by the relative lack of investment in wastewater analysis in the States, compared with well-developed programs in places like Europe and Australia.
The last and only time a government-sponsored effort took place in the U.S. was in 2006, when the Office of National Drug Control Policy began measuring cocaine metabolites in dozens of cities. But the results were never published.
“I’ve been baffled as to why it has not been embraced more wholeheartedly,” Christian Daughton said. “We have something that could be an extremely valuable tool, and we’re essentially just ignoring it.”
In the United States, wastewater analysis has typically operated on small, local scales. Some cities partner with nearby universities to analyze their sewage; others work with Biobot, which has contracts with hundreds of cities across the country. But thus far, there has been no national framework for WBE.
“Nothing has been really systemically coordinated at a national level, at least not to my knowledge,” Ryan Newton said. Although WBE is far cheaper than other survey methods, especially when it comes to COVID-19 testing, it still requires significant cost, labor, and resources. Coordinating local, state, and national efforts would make it much easier to share data and best practices—“in a much easier way than an individual academic lab that is just starting from scratch,” Newton said. Only with this investment can there be real progress on the cutting-edge ideas that could catapult the burgeoning field of wastewater-based epidemiology into the mainstream.
Putamen 