Scientists find bacteria and chemical compounds from coastal water pollution in sea spray aerosol along Imperial Beach, San Diego, California.
New research led by the Scripps Institution of Oceanography at UC San Diego has confirmed that coastal water pollution transfers to the atmosphere in sea spray aerosol. It can reach people beyond just beachgoers, surfers, and swimmers.
Rainfall in the US-Mexico border region causes complications in wastewater treatment. It results in untreated sewage diverting into the Tijuana River and flowing into the ocean in south Imperial Beach. This input of contaminated water has caused chronic coastal water pollution in Imperial Beach for decades. New research shows sewage-polluted coastal waters transfer to the atmosphere in sea spray aerosol formed by breaking waves and bursting bubbles. Sea spray aerosol contains bacteria, viruses, and chemical compounds from seawater.
The researchers reported their findings on March 2 in Environmental Science & Technology. The study appears amid a winter in which an estimated 13 billion gallons of sewage-polluted waters have entered the ocean via the Tijuana River. This is according to lead researcher Kim Prather, a Distinguished Chair in Atmospheric Chemistry and Distinguished Professor at Scripps Oceanography and UC San Diego’s Department of Chemistry and Biochemistry. She also serves as the founding director of the NSF Center for Aerosol Impacts on Chemistry of the Environment (CAICE).
“We’ve shown that up to three-quarters of the bacteria that you breathe in at Imperial Beach are coming from aerosolising raw sewage in the surf zone,” said Prather. “Coastal water pollution has been traditionally considered just a waterborne problem. People worry about swimming and surfing but not breathing it in, even though the aerosols can travel long distances and expose many more people than at the beach or in the water.”
How did the team test aerosol sea spray?
The team sampled coastal aerosols at Imperial Beach and water from the Tijuana River between January and May 2019. Then they used DNA sequencing and mass spectrometry to link bacteria and chemical compounds in coastal aerosol back to the sewage-polluted Tijuana River flowing into coastal waters. Aerosols from the ocean were found to contain bacteria and chemicals originating from the Tijuana River. Now the team is conducting follow-up research attempting to detect viruses and other airborne pathogens.
Prather and colleagues caution that the work does not mean people get sick from sewage in sea spray aerosol. Most bacteria and viruses are harmless. Bacteria in sea spray aerosol do not automatically mean that pathogenic or otherwise microbes become airborne. Infectivity, exposure levels, and other factors that determine risk need further investigation, the authors said.
This study involved a collaboration among three different research groups. She worked with Rob Knight and Pieter Dorrestein, both from UCSD. They sought to study the potential links between bacteria and chemicals in sea spray aerosol with sewage in the Tijuana River.
What did the tests of aerosol sea spray find?
“This research demonstrates that coastal communities are exposed to coastal water pollution even without entering polluted waters,” said lead author Matthew Pendergraft. He is a recent graduate from Scripps Oceanography who obtained his PhD under the guidance of Prather. “More research is necessary to determine the level of risk posed to the public by aerosolised coastal water pollution. These findings provide further justification for prioritising cleaning up coastal waters.”
Besides Prather, Pendergraft, Knight and Dorrestein, the research team included Daniel Petras and Clare Morris from Scripps Oceanography. Other researchers came from the UCSD School of Medicine, Department of Chemistry and Biochemistry, and the Skaggs School of Pharmacy and Pharmaceutical Science.
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