La Jolla researchers report evidence of a ‘global problem’: airborne ocean pollutants

Scientists at UC San Diego’s Scripps Institution of Oceanography in La Jolla have published a study indicating that pollution in the ocean is released into the air, with uncertain implications for public health.

“The bottom line is, we don’t know what the effect is yet of inhaling this cocktail that comes out of the ocean,” said the study’s principal investigator, Kimberly Prather, a professor of atmospheric chemistry at Scripps Oceanography and founding director of the National Science Foundation’s Center for Aerosol Impacts on Chemistry of the Environment.

The study, conducted in collaboration with Matthew Pendergraft, a recent doctoral graduate from SIO, and Rob Knight, director of the Center for Microbiome Innovation and a professor of pediatrics, bioengineering and computer science and engineering at UCSD, ran from January through May 2019 to determine the bacterial and chemical composition of water and air samples collected from the Tijuana Estuary region.

The Tijuana Estuary is a large wetland at the U.S-Mexico border, 20 miles south of Scripps Pier in La Jolla. The Tijuana River, which runs through the area, begins on the Mexican side of the border, “where there’s a wastewater treatment plant that sometimes gets overwhelmed,” often by rain, Prather said, sending raw sewage into the ocean and often closing beaches.

Rain also is responsible for other runoff that pollutes the ocean. San Diego County beach-goers routinely are advised to avoid the water for 72 hours after a rainstorm.

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“But people hadn’t really thought too much about the air,” Prather said.

She said atmospheric aerosols include particles “that form when waves break; you can see the spray a lot of times being broken off.”

The aerosols can float in the air for miles, like smoke from a wildfire, she said.

“The atmosphere has no walls, so once things get into the air, that can affect many more people from an inhalation perspective,” Prather said.

She said the problem “goes all up and down California, all up and down the West Coast.”

“This can be a global problem in areas where we have flooding, regions where people live near water, which is a lot of people,” she said. “Once pollutants become airborne, that just means that so many more people can be exposed to those pollutants.”

Study details

UC San Diego researchers Kimberly Prather, Matthew Pendergraft and Rob Knight (clockwise from top left) discuss their study on water and air pollution.

(Screenshot by Elisabeth Frausto)

Prather said the study tried to determine exactly what the aerosols released by the ocean contain.

Sampling air at both the Imperial Beach Pier near the north end of the Tijuana Estuary region and at Scripps Pier, researchers examined and compared chemicals they found in the air.

There were “unique signatures in Imperial Beach,” Prather said.

“The big punchline ... is [that] up to 76 percent … of the [airborne] bacteria were linked to the sewage that was detected in the Tijuana River,” Prather said.

Of the top 15 bacteria present in test samples, eight were labeled potentially infectious. Three were labeled rarely infectious.

“It was just a complete shock to find how much of the microbes in the air were traceable directly back to sewage,” Knight said.

Implications and next steps

Prather said further studies are needed to determine the impact the aerosols may have on public health.

“Some are pathogens, some are not,” she said. “We really don’t have any studies that say what would happen if you inhale these. This is a different exposure pathway than anybody has thought about before.”

Pendergraft said “more in-depth sequencing will reveal specific strains or potentially specific pathogens present.”

“We want to be able to do both epidemiological and model animal studies to try to figure out, now that we know the stuff that’s in the air, what is the impact on health in humans directly?” Knight said.

Prather said the team plans to start swabbing lifeguards, surfers and families to assess “what is physically getting into people,” along with looking at hospital records and indoor air quality.

She noted that U.S. Rep. Scott Peters (D-La Jolla) has secured congressionally directed funds for continued research. A news release indicated the money would come from the fiscal 2023 omnibus spending bill.