Cover photo credit: Surfrider Foundation and Veriditas Rising. Saturn Boulevard River Crossing.
A new study was released today in the peer-reviewed journal Science detailing emerging research from the University of California, San Diego (UCSD) and San Diego State University (SDSU) on air quality impacts to human health in South San Diego. The study’s findings confirm what many of us who live and work in the area know - this crisis continues to get worse and those bearing the brunt of the public health impacts are continuing to suffer each day that passes without immediate solutions in place to stop the flow of polluted water (and air!) through our neighborhoods, watershed and coast.
The university-led air quality study focused on field data gathered during summer and fall of 2024, when toxic flows of contaminated water across the US/Mexico border surged to tens of millions of gallons per day despite there being no rain to dilute the pollution. These severely polluted flows caused hydrogen sulfide (H2S) to aerosolize, or be released from the water into the air in gaseous form, at certain points in the Tijuana River. The study measured high levels of H2S that were unsafe for human health in and around the Tijuana River Valley. H2S is a toxic, colorless gas with a rotten egg smell that is most commonly produced when organic matter in sewage breaks down. It serves as a key indicator of wastewater contamination in the environment and often signals the presence of other dangerous contaminants.
Particularly problematic during the study (and continues today) was a turbulent hotspot at the Saturn Boulevard River Crossing in the San Diego neighborhood of Nester. During the night, when daytime breezes dropped and stagnant air dominated, researchers measured spikes in H2S levels near this hotspot that peaked at 4,500 parts per billion (ppb)— alarmingly higher than typical urban levels (<1 ppb) and the chronic health exposure limit of 7.3 ppb established by the California Office of Environmental Health Hazard Assessment.
At one point during the research period, measurements were so high that carbon monoxide alarms were going off in people’s homes and student investigators were pulled from the field out of concern for their safety. This was swiftly followed by a press conference where researchers shared their preliminary findings openly with the public because of the immense threat to public health. Immediately after the frenzy of press coverage that followed and the political pressure it created, transboundary flows were diverted from the main river channel by the Mexican government and this reduced the overnight flows from approximately 80 million gallons per day (MGD) to less than 5 MGD. The diversion of contaminated water in the main river channel caused both H2S measurements and odor complaints from residents to decrease by about 95%. Visit the UCSD website for a full summary of the study, but key findings include:
One of the most impactful findings of this study is to show with scientific evidence that poor water quality can drastically affect air quality in frontline communities. The Tijuana River and other polluted waterbodies can serve as dangerous sources of hydrogen sulfide and other toxic gases in the air. Turbulent water flows and wind patterns can carry air contaminants far beyond the river’s edge. It’s no wonder that pediatricians and urgent care doctors working in San Diego South Bay have testified at public meetings and forums that they are seeing kids from Imperial Beach and the Nestor area with headaches, nausea and wheezing symptoms when there is a sewage smell in the air. Exposure to H2S and other air pollutants could help account for many of the long-term health symptoms, including respiratory and gastrointestinal issues, headaches, fatigue, skin infections, nausea, and anxiety, reported in the household health study conducted by the Centers for Disease Control and Prevention and the County of San Diego in October, 2024. Not only is the water unsafe to enter, but this study has confirmed that the air can also be unsafe to breathe when sewage and pollution levels in the Tijuana River are high. Effective short-term strategies that are needed now include diverting contaminated water away from neighborhoods and providing more local air quality monitoring to inform and protect affected residents.
The paper also draws attention to the demographic disparities in the impacted communities of Imperial Beach, Nestor, and San Ysidro compared to more affluent communities in San Diego County where air pollution problems have been dealt with more swiftly and effectively. In addition to the social stressors that impacted communities endure, environmental pollution leads to cumulative impacts on the local economy, health, and overall quality-of-life. Such prolonged exposure without adequate protection or timely intervention highlights a clear environmental injustice that would likely not be tolerated in more affluent or less marginalized communities.
Get Involved!
The findings of this study clearly demonstrate that we can no longer wait to see infrastructure solutions in place. We need everyone to stand up, raise your voice, and demand better from our elected leaders.
Sign our petition (if you haven't yet). Ask the Trump Administration to declare a national emergency to solve this dire public health crisis immediately and completely, whilst providing the needed relief to the people living in the neighborhoods most affected by this long-standing and unsafe pollution.
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