The ongoing issue of wastewater flowing from the Tijuana River poses a serious threat not just to beaches in Southern California, but it also releases significant amounts of toxic gases into nearby communities.
These waterways, which start in Baja California, emit hydrogen sulfide—often referred to as “sewer gas” because of its rotten egg smell.
During a press conference on Wednesday, a local resident expressed distress over the serious respiratory issues and health problems affecting the community, stating they are often left sleep-deprived.
Plazor, an atmospheric chemist at the Scripps Institute of Oceanography, pointed out that residents have felt like they were being poisoned, but their concerns went unheard.
This comment was directed at those living in the southernmost area of San Diego County, including Imperial Beach, which is directly affected by contaminated wastewater flowing through the Ocean Plume and the Tijuana River.
The pollution stemming from inadequate treatment processes in Tijuana contains both pathogens and toxic substances, leading to beach closures and impacting naval operations for years.
Recently, EPA administrator Lee Zeldin and his Mexican counterpart signed a memorandum aimed at tackling the issue. Zeldin highlighted last Thursday the expansion of a U.S. wastewater treatment facility that deals with some of Tijuana’s waste through international agreements.
Although many studies on the pollution typically concentrate on direct water contact, researchers have cautioned that contaminants can aerosolize and spread much further than just the riverbanks.
Once airborne, these pollutants can travel significant distances, posing inhalation risks to a larger number of people, Plazor noted.
This means that residents don’t necessarily have to be directly at the beach to be affected; the contaminants could spread throughout all of San Diego County.
It’s not feasible to simply ask people to “stop breathing” when the beach is closed, Plazor added.
The cross-border sewage crisis has been a longstanding issue for nearly a century, but recent findings have drawn connections between river pollution and airborne emissions.
A pivotal moment came in 2023 when Prather and her team used genomic technology to trace up to 76% of airborne bacteria found at Imperial Beach back to the Tijuana River.
This May, researchers published findings identifying various aerosolized wastewater compounds, including illicit drugs and chemicals from tires and personal care products that are present in local air and water.
The latest research aimed to validate the longstanding concerns of residents who have reported unpleasant odors and several health issues, often feeling dismissed. Plazor recalled how residents specifically complained about the unbearable smell in the summer of 2024.
Shifting focus from wet weather to the dry season, Plazor and her colleagues sought to measure gas emissions rather than just liquid pollutants.
Prather noted, “There’s industrial waste from various sources, including raw sewage flowing steadily into the Pacific.”
The research team, utilizing data on airborne contaminants along with local odor complaints, pinpointed river sections that could be hotspots for gas emissions.
Using a mobile air quality lab, they measured concentrations of hydrogen sulfide, the notorious “sewer gas,” as a way to track water contamination.
Their findings revealed that during drought conditions, hydrogen sulfide emissions surged, reaching significantly higher levels at night compared to typical urban averages.
Interestingly, the majority of these gases originated inland rather than from the coast, as explained by Plazor.
What took researchers by surprise was a notable drop in odor reports after a sharp decrease in wastewater discharge, from almost 80 million gallons daily to under five. They suggested this reduction strengthens the idea that turbulent areas of the Tijuana River are major sources of both odor and hydrogen sulfide emissions.
Plazor recalled that team members donned protective gear for personal safety while monitoring the situation.
During the announcement on Wednesday, scientists admitted a prior misreport regarding the presence of cyanide gas in the air, which was later retracted after further investigation revealed false positives for hydrogen cyanide.
Paula Stigler Granados, an environmental health scientist, stressed the importance of sharing the data they had initially collected, emphasizing a responsibility to public health.
Prather affirmed that their hydrogen sulfide readings were accurate and were recorded using a continuous air quality monitoring device, not a first responder sensor.
Overall, the researchers stressed the need to consider how turbulent river areas influence local air quality, as traditional models often overlook these contaminated waterway emissions.
The high hydrogen sulfide levels near the river corroborate many long-standing community reports and highlight the disproportionate environmental burdens faced by marginalized groups.
Researchers concluded that effective maintenance, oversight, and collaborative leadership are essential to ensure much-needed protection and justice for the communities affected by this environmental crisis.
In the short term, Prather recommended that residents wear masks near the river and prioritize purifying indoor air. The ultimate solution, she argued, should focus on preventing discharges into the river.
“We must act quickly,” Plazor insisted. “No one should have to breathe in this toxic mixture.”
