A new study finds pollutants from the water are mirrored in San Diego’s air, with particles from drugs and other chemicals detectable.

The pollution from the Tijuana River mouth isn’t only creating health hazards for swimmers, it’s affecting the air we breathe, according to a new study from researchers at UC San Diego and its Scripps Institution of Oceanography.

The 120-mile Tijuana River flows from Baja California, Mexico into the US just south of Imperial Beach, discharging millions of gallons of wastewater, including sewage, industrial waste and runoff, into the Pacific Ocean every day.

San Diego Coastkeeper

The river is the dominant source of coastal pollution in the region, leading to the nonprofit environmental group American Rivers naming the Tijuana River the second most endangered river in the US.

The pollution often leads to beach closures in Imperial Beach north to Coronado due to sewage contamination, and has spurred activism and advocacy at the national level for change.

The new UCSD study, published May 28 in Science Advances, examined how pollutants in wastewater travel and are transmitted in the atmosphere through coastal aerosols. Researchers found that a mixture of illicit drugs, drug metabolites, and chemicals from tires and personal care products aerosolize from wastewater and are detectable in both air and water.

Aerosols and contaminants

When aerosols are inhaled, they “enter deep into your body,” said Kimberly Prather, co-corresponding author, distinguished chair in atmospheric chemistry and distinguished professor at UCSD’s Scripps Oceanography and department of chemistry and biochemistry. “They can get all the way into your bloodstream [and] brain.”

The work, ongoing in Imperial Beach and San Diego’s South Bay region since 2017 with the field work for this particular paper conducted during 2020, showed the Tijuana River pollution gets trapped in the surf zone.

UCSD/Scripps Institute of Oceanography

The white bubbles that form at wave breaks are aerosolization, said Prather, also the founding co-director of UCSD’s Airborne Institute. 

When those bubbles rupture, the contaminants “get released into the air in much higher relative concentrations than you would expect,” she said.

Humans drink about two liters of water per day but inhale 11,000 liters of air per day, Prather said. “This is the number one way that this pollution from the water is actually making its way into your body, even if you’re not at the beach. … The beaches can be closed, but people are still breathing that air.”

Using genomic tracing, researchers were able to show that up to 76 percent of the bacteria in the air around the Tijuana River mouth comes from its pollution, she said.

What’s in the air

UCSD/Scripps Institute of Oceanography

The researchers tracked and quantified wastewater chemicals such as illicit and pharmaceutical drugs, personal care products, plastics, herbicides and pesticides in the river, with sampling locations included as far south to the Mexican border and as far north as the Scripps Pier in La Jolla.

The collections were taken around precipitation events, with the team operating under the hypothesis stormwater runoff would influence water pollution, leading to more air pollution, said Jonathan Slade,  co-corresponding author and UCSD associate professor of chemistry and biochemistry.

Researchers found octinoxate, used as a UV filter in sunscreens and illicit drugs including methamphetamine, cocaine and heroin, Slade said, along with drug metabolates and pharmaceutical drugs like erythromycin.

Industrial chemicals like dibenzylamine, used in rubber tire manufacturing, and pesticides and herbicides were also present.

There were higher concentrations of pollutants found closer to the river mouth, with lesser concentrations farther north to Scripps Pier.

This is the first study on this wide an array of chemicals transferred due to aerosolization, Prather said. 

“We understand that process now a little bit better based on this study.” 

Health impacts

Some of the drug concentrations “are likely too low to have any acute health effects,” Slade said, noting concentrations of methamphetamine in water are at a level that can lead to addictive behavior in fish. 

But humans “would have to stand at the beach and breathe in for 100 years in order to inhale the equivalent to one dose,” said Adam Cooper, lead author and science and policy technology fellow with the California Council on Science and Technology.

“We expect many of the health effects to be more chronic in nature, rather than acute, more long-term than short-term,” Cooper said.

However, “it’s not just one compound at a time you’re breathing in,” he added. “It’s this complicated soup of thousands of chemical compounds, bacteria, viruses, all at the same time.”

Compounds like octinoxate were found at the highest rates, Slade said, at levels similar to what a worker would be exposed to at a wastewater treatment plant, necessitating the use of personal protective equipment like masks.

“Studies have shown that when octinoxate is exposed to light and DNA, it can damage DNA,” Slade said. “That’s really important.”

Scientists don’t currently have the infrastructure and the resources to yet understand the effects of chronic, long-term exposure.

“That’s a subject for future research,” Slade said. 

What can we do now?

UCSD/Scripps Institute of Oceanography

Slade noted he himself doesn’t “want to spend more than a few hours” in the South Bay breathing the air.

“When we’re there, … especially when we’re near the river hotspot, we wear respirators,” Prather said, advising people in the immediate vicinity to use air filters at home.

“There are ways to protect yourself,” she said, also calling for better education.

The most important action to take, Prather said, is to reduce the source of the pollution, called source control. She praised recent efforts for federal funding and advocacy to address the contamination.

“The best control is to never … let it out in the first place.”

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