Sewage pollution flowing across the border from Tijuana into the San Diego region threatens the health not only of surfers and swimmers, but potentially those who simply breathe the air.
That is according to a study from UC San Diego’s Scripps Institution of Oceanography, published Thursday in the journal Environmental Sciences & Technology, found sewage-borne bacteria in sea spray aerosols at Imperial Beach.
“Once pollutants get into the air, it just means that so many more people could be exposed to those pollutants,” said Kim Prather, lead researcher on the study and director of the Center for Aerosol Impacts on Chemistry of the Environment at Scripps. “It goes way beyond just people going to the beach or going into the water.”
The possible health consequences are still unknown, researchers warned. Studies are ongoing and may include an epidemiological study.
Prather said her team plans to swab lifeguards, surfers and others to measure levels of respiratory exposure. Investigators also hope to examine hospital records and monitor indoor air quality.
“The bottom line is we don’t yet know the effect of inhaling this cocktail that comes out of the ocean,” she said, adding, “This is the tip of the iceberg. We’re trying to keep everyone calm.”
The study took place after rain events in early 2019, during which researchers took air and water samples along the Tijuana River, Imperial Beach Pier and Scripps Pier in La Jolla. Using DNA sequencing, the team linked up to 76% of the airborne bacteria in Imperial Beach to the heavily polluted river.
There is an established body of research that has shown that microorganisms are transferred from the ocean to the atmosphere, but this is the first study to link airborne bacteria to a known source of wastewater, said co-author Robert Knight, a professor in pediatrics, computer science, and engineering from UC San Diego.
“It was a complete shock to discover how many airborne microbes could be traced back to sewage,” he said. “We had no idea the effect would be so strong.
“Now that we know this is a real phenomenon,” he added, “we need to figure out what the implications are for human health.”
About $1.5 million has been secured by Representative Scott Peters in this year’s omnibus spending bill for Prather and her team to further explore the public health impact of airborne pollutants and potential pathogens, officials said.
Beaches as far north as Coronado were closed due to sewage contamination from Mexico on a record pace in 2022. Imperial Beach, for example, had sewage pollution warning signs along the beaches for 249 days last year. The Tijuana Sloughs, once a coveted surfing spot at the mouth of the river, has not been open since December 2021.
Swimming in sewage-contaminated water can expose beachgoers to dangerous bacteria and viruses, state public health officials said. Those who ignore the restrictions are at risk of diarrhea, fever, respiratory disease and infections.
Water contaminated with sewage carries a much higher risk of pathogens such as E. Coli, norovirus and salmonella, compared to typical urban runoff that follows rainfall events, officials said.