An odor, described as a “rotten egg” smell, often fills Imperial Beach resident Rosie Montaño’s home.
“It’s to the point where, I mean, you’re breathing it,” she says. “… You’re just like ‘Oh my god!’”
That stench is attributed to hydrogen sulfide – a product of decaying human wastes emanating from sewage in the nearby Tijuana River. And Montaño, 44, is among hundreds or thousands of area residents inhaling the olfactory fallout from a Tijuana pollution crisis that also has contaminated and closed the Pacific shores of Coronado and Imperial Beach.
According to the San Diego County Air Pollution Control District, hydrogen sulfide levels in Imperial Beach frequently exceed 30 parts per billion – the safety threshold established by the California Office of Health Hazard Assessment.
This week, a new University of California San Diego study, published by Science Advances on May 28, reports that pollutants in the contaminated river wastewater — including illicit drugs, drug metabolites, and chemicals from tires and personal care products — have become aerosolized and are detectable in both water and air.
Through spatial analyses, researchers found that most measured chemicals, such as octinoxate and methamphetamine, concentrate in aerosols near the Tijuana River, potentially exposing local populations to tens of nanograms per hour via inhalation, the study says.
“No one knows the health effects of breathing this chemical soup — hundreds to thousands of pollutants becoming airborne and traveling miles to Coronado and beyond,” said Kimberly Prather, professor of atmospheric chemistry at UC San Diego and Scripps Institution of Oceanography, who co-authored the study and has spent years researching the air pollution impacts of the Tijuana River.
According to the study, residents in Imperial Beach are inhaling concentrations of prominent pollutants, like octinoxate, comparable to measurements made directly above wastewater treatment plant vats.
“This study is shocking as it is validating for those of us who live this crisis every day,” said Imperial Beach Mayor Paloma Aguirre in a statement. “It confirms what we’ve been saying for years: the sewage pollution flowing through the Tijuana River isn’t just in the ocean — it’s literally in the air families here are breathing. This study shows with science what working people all know – that the air in South County is more polluted than in La Jolla. That’s not just unjust — it’s unbelievable and unacceptable. We are not second-class communities. We are working people who deserve the same clean air and safe environment as every other neighborhood in this country.”
Sampling data from 2020 still pertinent
Adam Cooper, the paper’s lead author, told UC San Diego Today: “Ours is one of the most comprehensive studies to date investigating water-to-air transfer of these pollutants.”
The UCSD article says even though the samples were taken in 2020, the findings are still relevant because little has changed in how sewage release from the river is processed. It also said the EPA has not formally reviewed the paper.
Samples of air and water were collected between January 24, 2020 and March 14, 2020, at various coastal locations in San Diego County, including: Border Field State Park, the Tijuana River, Imperial Beach, Silver Strand, and the Scripps Institution of Oceanography in La Jolla, California, during periods of increased transboundary flows.
To determine which chemical species measured in collected aerosols came from the river, researchers used benzoylecgonine, a widely used and robust tracer for tracking sewage pollution in water bodies to trace wastewater pollutants transferred from water into coastal aerosols, the study says.
“Benzoylecgonine is nonvolatile, stable in the environment, and concentrates in surface waters,” it continues. “Therefore, detecting benzoylecgonine in aerosol samples directly indicates air masses strongly influenced by aerosols from wastewater transferred into the air.”
The study focused on 12 chemicals expected in sewage, wastewater, and runoff.
Among the pollutants examined, researchers found that methamphetamine; octinoxate, a UV filter used in sunscreen; and dibenzylamine, a compound used in tire manufacturing, behaved similarly to the tracer.
According to the study, there is increased airborne exposure to all measured compounds in Southern San Diego compared to La Jolla because sewage pollution in water and air is concentrated near the Tijuana River outflow.
The study estimates the following onshore mass transfer of airborne contaminants based on the airborne concentrations of each compound: a median-to-max transfer of ~1 to 10 g of dibenzylamine, ~10 to 100 g of methamphetamine, and ~100 to 1000 g of octinoxate to air over the 1 km Imperial Beach coast per day.
“The study found methamphetamine, cocaine residue, tire chemicals and toxic compounds from sunscreen floating through the air in South County — chemicals being inhaled by children, workers and families every single day,” added Aguirre. “No American should have to breathe meth-laced sea spray and call that normal.”
An ‘unbearable’ reality
Thousands of South County residents have voiced concerns about air quality in a survey conducted last year, whose results were released earlier this year. In that report, 72% of households reported a foul odor indoors, outdoors and in their neighborhood during the prior month. More than 69% said the smell was strongest after dark.
“Early health surveys near the border show clear effects,” added Prather. “We urgently need expanded studies to understand the risks of inhaling this potentially toxic mix.”
“The Cays and the Shores know these smells and exposures,” agreed Coronado resident Laura Wilkinson Sinton, who co-founded a Stop the Sewage advocacy group with other women in Coronado to bring attention to the crisis. “We need them [County Health officials Department] to further fund … research to measure and then mitigate these dangers to Coronado citizens and families. Silver Strand Elementary school is right in the pathway. This is urgent.”
This year, American Rivers, an environmental advocacy organization, named the Tijuana River the No. 2 most endangered river in the nation following its listing as No. 9 in 2024.
Coronado Mayor John Duncan said his concern for air quality issues related to the raw sewage flows prompted him to seek a position on the San Diego County Air Pollution Control District board in March.
“I am grateful for the UCSD study of its effect on our air quality,” Duncan said in a statement. “I agree with the conclusion of the study, further scientific study is warranted as to the effects of the airborne contaminants on people. … This confirms the current urgency to continue to push for full resolution of the crises immediately.”
EPA Administrator Lee Zeldin visited San Diego in April. Last month he announced the fast-tracked construction of the South Bay International Wastewater Treatment Plant.
Last week, U.S. Senator Cory Booker joined a San Diego delegation on a tour of the polluted area.
“No one should be forced to breathe toxic air and swim in sewage. What I saw and smelled today in South San Diego County is unconscionable – it would never be tolerated in Malibu or Mar-a-Lago and it shouldn’t be tolerated here,” Booker said in a statement on May 29. “I’m taking what I saw here back to Washington to help make sure this community’s fight for clean air and water is heard and answered.”
Meanwhile, residents like Montaño, a mother of eight, are left to deal with a public health crisis they cannot escape.
“There’s no remedy. And then if you go into your house and you’re still smelling it,” said Montaño, who chuckled as if in disbelief, “there’s not much you can do about that, you know? Because you’re closing your windows and it’s like … that’s bad.”
“Even though you have air humidifiers and all that, it still gets through. It’s just, it’s unbearable,” she added.
