Given the possibility of disease transfer by sewage, researchers recently set out to determine what happens when wastewater leaks into waterways. They followed the journey of wastewater in Tijuana, Mexico, as it traveled from estuary to ocean, chasing down a question with critical public health implications: If the virus gets into the ocean, can it be carried into the atmosphere in sea spray?
What they discovered proved to be the first finding of SARS-CoV-2 in a body of water that's not the wastewater of treatment plants. The implications of this finding are not yet certain and, for now, not cause for alarm.
Kimberly Prather, a professor and atmospheric chemist at the University of California San Diego, led the research. Prather presented her team's early results Monday during a virtual meeting of the American Chemical Society. The research is on-going and has not yet been peer-reviewed.
Prather and her colleagues' aim is investigating whether SARS-CoV-2, which causes Covid-19, travels from a Tijuana sewage plant into the ocean environment. The plant in question is a known contaminant — it dumps tens to hundreds of millions of sewage into the Tijuana River, which flows into an estuary, which flows into the ocean.
Sewage already has an effect on the atmosphere — the microbes that humans add to the environment get trapped in the surf zone and change the composition of seawater and the surrounding air.
"We see a lot of viruses and bacteria — basically a lot of things that are present in sewage — in the air near San Diego," Prather explained.
In general, that can have public health implications: "Once it gets in the air, then a lot more people can breathe it," Prather said.
To explore whether SARS-CoV-2 is among the contaminants, Prather's team took water samples from the three water bodies in question, analyzed, and discovered:
- SARS-CoV-2 is present in Tijuana River water (6 negative detections, 27 positive)
- SARS-CoV-2 is present in the estuary that leads to the ocean (11 negative, 2 positive)
- SARS-CoV-2 is present, at least in one suspected case, in the ocean (44 negative, 1 positive)
- SARS-CoV-2 is not present in sea spray (90 negative, 0 positive)
The sea spray finding is good news, Prather said: "We don't see it getting out and getting into the sea spray — at least not at our limits of detection."
Crucially, the presence of SARS-CoV-2 refers only to the virus's RNA being detected. That does not mean that the virus is infectious. In fact, Prather suspects it is not.
"We hope it's not — we know that sunlight can kill this virus," Prather said. Her team's next step is to determine how long the virus can survive and remain infectious in the environment.
The journey of a microbe — A goal of Prather's lab is to understand how the ocean's microbes contribute to the marine atmosphere. The findings help illuminate how tiny networks of life shape our environment and even alter the rate of climate change.
That all begins with a comprehension of how microbes travel.
"Microbes don't want to be in the ocean, so they sit on the very top surface of the ocean," Prather explained. "And so when waves crash, they launch large amounts of whatever's sitting on the surface."
In separate studies, Prather's team is looking at the natural microbes like phytoplankton. They set up a micro-ocean in a lab to mimic the water's chemistry, biology, and physics — like crashing waves — to better understand how microbes shape the environment. The gases let off by microbes interact with the air, changing cloud formation, and in turn, atmospheric temperature.
Prather's SARS-CoV-2 announcement pertains to an ongoing examination of the "extra microbes we see in the air," including viruses and bacteria, and their health implications. The study is funded by the US National Science Foundation.
Moving forward, the researchers will continue to investigate the virus that causes Covid-19 in coastal waters near sewage outflow, with the hope determining whether there are "hot spots" where certain strains of viruses and bacteria are concentrated. They plan to assess how the virus interacts with environmental conditions like water flow and wind, and monitor its ability to infect.