South County communities aren’t just being exposed to sewage-linked bacteria that become airborne near where untreated wastewater spills over the U.S.-Mexico border from Tijuana. Illicit drugs and chemicals from tires and personal care products are also detectable in the air.
That’s according to a study from UC San Diego’s Scripps Institution of Oceanography, published Wednesday in the journal Science Advances, which identifies the Tijuana River as the dominant source of coastal pollution in the region.
“Often, the sewage crisis is considered a water issue — and it is — but we show that it’s in the air, too,” said Jonathan Slade, a co-author of the study and an associate professor of chemistry and biochemistry at UC San Diego.
Other study participants were Adam Cooper, the lead author and a fellow with the California Council on Science and Technology; and Kim Prather, a co-author and director of UC San Diego’s Airborne Institute. She led a different study, published in 2023 in the journal Environmental Sciences & Technology, that found sewage-linked bacteria in sea-spray aerosols at Imperial Beach. More recently, she has spearheaded efforts to monitor hydrogen sulfide, one of the primary chemical components of sewer gas, in the Tijuana River Valley and the households of many residents in affected Imperial Beach and south San Diego communities.
The Tijuana River routinely carries untreated sewage, stormwater runoff and industrial waste through the river valley and into the Pacific Ocean. Pollution has worsened in recent years due to population growth, heavy rainfall, and sediment that has damaged neglected wastewater infrastructure in Mexico and San Diego meant to treat Tijuana’s sewage. The result: beach closures and reports of illnesses not only from those who come into with polluted shorelines, but potentially those living farther inland.
Aerosols are minuscule particles emitted into the air. They can originate from human activities or natural sources.
The two studies are among the first to connect bacteria and chemicals in the wastewater that flows in the Tijuana River to the air. Both conclude that further research is necessary to understand the impacts of chronic exposure on public health and the environment.
In the newly released study, funded by state and federal grants, researchers focused on the source of the pollution and the concentrations of pollutants along the San Diego County coastline. From January to March 2020, researchers took air and water samples along the Tijuana River, Imperial Beach Pier and Scripps Pier in La Jolla.
The team found that after rainfall, levels of benzolecgonine in the waters off Imperial Beach increased when flows in the Tijuana River, a mix of untreated sewage, contaminated storm water and toxic chemicals, jumped. Concentrations of the substance in aerosols also spiked.
Benzolecgonine is a compound the body produces when processing cocaine and it is released in urine. The substance is commonly tested for in drug screens and wastewater screenings.
The researchers also detected dibenzylamine, a chemical essential for rubber production, including tires and hoses; octinoxate, an ingredient used in products to protect against UVB rays, such as sunscreens; and methamphetamine.
The study found that the pollutants were higher in the Tijuana River than in the ocean, and higher in the water and aerosols off Imperial Beach than in La Jolla. Furthermore, the report indicates that the closer one is to the river, the greater the likelihood of exposure to pollution, even though the amounts are “on the scale of tens of nanograms per hour.”
“Their concentrations, as we discussed in the paper, are likely too low to have any acute health effects,” said Slade. He added that there are potentially thousands of other wastewater chemicals in the air, but “we just didn’t have the infrastructure, the resources to really know the amounts of everything out there. This hints to the much larger issue … people living in the South Bay region, breathing in this air on the daily basis for years or decades, we have no clue to what extent this pollution’s impacting air health.”
Researchers called for increased monitoring of environmental pollutants and heightened public awareness, particularly as there are numerous other sources of wastewater and pollution issues worldwide.
“The global surge of untreated wastewater entering lakes, rivers and oceans poses a growing health threat,” Prather said in a statement. “Aerosolization of this polluted water exposes billions of people through airborne transmission, reaching far beyond those in direct and impacting countless others who inhale contaminated air that can travel for many miles.”
Most important, Prather said, is stopping the source of pollution.
“People need to be working together to stop putting this kind of pollution in the water in the first place,” she said. “The beaches can be closed, but people are still breathing that air.”
She added that their research continues and suggested that South County residents obtain and use air purifiers at home, which the San Diego County Air Pollution Control District is distributing.
The study comes as the federal Agency for Toxic Substances and Disease Registry, in collaboration with county public health experts, assesses whether chemical exposure in the river valley poses a health risk to nearby communities. After reviewing air, surface water, sediment and other environmental data collected by government groups, the agency expects to publish its findings next year, which may include recommendations to reduce or prevent harmful exposure.
San Diego State researchers are also assessing the health impacts of sewage pollution via a yearlong survey that is still open.
