SAN DIEGO (CNS) - Pollution from the Tijuana River makes its way into the air and decreases air quality as far north as La Jolla, according to a study released Wednesday by UC San Diego researchers.
The paper's lead author, Adam Cooper, collected samples from the air and water at various points along the coast of San Diego County, including the U.S.-Mexico border, Imperial Beach and Scripps Institution of Oceanography in La Jolla. The study was published in Wednesday's edition of Science Advances.
Cooper graduated UCSD last spring with a doctorate in chemistry. He collected the samples in 2020 as part of a field study with Professor of Atmospheric Chemistry Kimberly Prather's lab.
Although the samples are now several years old, the paper's authors say the findings are still relevant because little has changed in how sewage release from the river is processed.
"The Tijuana River region is a very dynamic environment with implications for public health, environmental policy and international relations between the United States and Mexico," Cooper said. "Ours is one of the most comprehensive studies to date investigating water-to-air transfer of these pollutants."
The 120-mile Tijuana River flows from Baja California into the United States and discharges millions of gallons of wastewater -- including sewage, industrial waste and runoff -- into the Pacific Ocean every day.
The study looked at two aspects of wastewater pollution: the source and the concentration of pollutants along the San Diego County coastline.
Assistant Professor of Chemistry and Biochemistry Jonathan Slade's lab analyzed the collected samples by searching for a compound they knew came from sewage -- a chemical produced when people use cocaine and excrete it in urine.
That chemical -- benzoylecgonine or BZG -- spiked in Imperial Beach ocean water after rainfall and in the air when choppy sea spray aerosolized it. Other chemical compounds that behave in a fluid environment similarly, such as methamphetamine; octinoxate, a UV filter used in sunscreen; and dibenzylamine, a compound used in tire manufacturing, were also analyzed.
Concentrations of these chemicals were highest in the Tijuana River itself, and petered out the more northerly the samples were taken from.
Although the amounts of some pollutants, like cocaine, were minuscule, others were more prominent, like octinoxate, which can break down into more toxic components.
"It's been shown that octinoxate can degrade DNA when exposed to light," Slade said. "And if it's in these tiny aerosols we're breathing in, it can get deep into our lungs and pass into our bloodstream. That's very concerning, especially considering the high levels at which we found it in the air."
The tiny amount of pollutants caused by aerosolized spray can cause health problems. Many residents have complained of respiratory illness, insomnia and headaches, and several San Diego beaches have been closed almost continuously for the last three years because of high levels of bacteria from wastewater runoff.
"The solutions to the cross-border sewage crisis aren't constrained by technical challenges," Cooper said. "They're constrained by political challenges and policy issues. We have to motivate decision-makers to make the right investments."
Slade and Cooper said the need for more research, better infrastructure and cross-border collaboration is imperative to draw any conclusions about the detrimental effects on the environment or human health.
"Often the sewage crisis is considered a water issue -- and it is -- but we show that it's in the air too. Truthfully, we don't yet know the acute health effects," Slade said. "But the numbers we report can be incorporated into models to help us better understand what we're breathing in and how much we're exposed to."
The authors said the impact of sunscreen and degrading tires impacted air quality along the coast.
"Although our study focuses on the Tijuana River, there are other notable sources of wastewater and pollution run-off in Southern California, including wastewater treatment outfalls, the San Diego River and the Los Angeles River," Slade said, who also noted that "turbulence in rivers and streams may aerosolize wastewater, requiring further study."
Around 80% of all global wastewater is untreated, according to the authors. Of the portion that is treated, many plants remove bacteria, but not chemical pollutants.
"The global surge of untreated wastewater entering lakes, rivers and oceans poses a growing health threat," Prather said. "Aerosolization of this polluted water exposes billions of people through airborne transmission, reaching far beyond those in direct contact and impacting countless others who inhale contaminated air that can travel for many miles.
"We are continuing our studies in this region to better understand the short and long-term health impacts of inhaling this newly identified source of airborne pollution."
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