California’s 120-Mile sewage river is polluting the air—Not just the water

San Diego, California – A new study from UC San Diego reveals that pollutants from the Tijuana River aren’t just contaminating local waters—they’re also degrading air quality as far north as La Jolla.

Published on Wednesday in Science Advances, the study reveals that wastewater flowing from Baja California into San Diego County is being aerosolized by ocean waves and transported into the atmosphere through sea spray, exposing coastal communities to chemical pollutants.

Adam Cooper, the study’s lead author and a recent UCSD chemistry Ph.D. graduate, collected air and water samples from the U.S.-Mexico border to La Jolla in early 2020. The work was part of a collaborative field study with Professor Kimberly Prather’s atmospheric chemistry lab and Professor Jonathan Slade’s chemistry group.

“The Tijuana River region is a very dynamic environment with implications for public health, environmental policy and international relations,” said Cooper. “Our study is one of the most comprehensive to date examining how waterborne pollutants make their way into the air.”

The 120-mile river discharges millions of gallons of sewage, industrial waste and stormwater runoff into the Pacific Ocean daily, creating an environmental crisis decades in the making. The research identified airborne traces of illicit drugs, personal care products and industrial chemicals in aerosols along the coast, particularly after rainfall and in areas with heavy wave activity.

One marker chemical used was benzoylecgonine, a stable metabolite of cocaine excreted in human urine. Its presence in both ocean water and air indicated sewage contamination. Researchers found the highest concentrations in Imperial Beach, tapering off toward La Jolla. Other pollutants detected included methamphetamine, octinoxate (a common sunscreen ingredient), and dibenzylamine (used in tire production).

“It’s been shown that octinoxate can degrade DNA when exposed to light,” said Slade. “If it’s in the aerosols we’re breathing, it can enter our lungs and bloodstream. That’s deeply concerning.”

Though the quantities detected—often in nanograms—were small, researchers emphasized that chronic exposure could pose health risks. Residents in southern coastal communities have long reported respiratory issues, headaches and insomnia, and many beaches have faced extended closures due to bacterial contamination.

“The sewage crisis isn’t just a water issue—it’s airborne too,” Slade added.

Cooper, now a science policy fellow with the California Council on Science and Technology, stressed that the primary obstacles to resolving the crisis are political, not technical. “We need investments in infrastructure and cross-border cooperation,” he said.

The authors call for further research to better understand the health effects of long-term exposure and to improve pollution mitigation strategies both locally and globally.