Tijuana River Pollution Threatens Tens of Thousands

Environment Report: How Much Toxic Gas Is Too Much? Nobody Seems to Agree. | Voice of San Diego

Toxic Gas Crisis at U.S.-Mexico Border: Tijuana River Pollution Threatens Tens of Thousands

Bottom Line Up Front (BLUF)

Scientific research has confirmed that the polluted Tijuana River is releasing hydrogen sulfide gas at concentrations up to 4,500 times higher than normal urban levels, exposing tens of thousands of California residents to chronic health hazards. The crisis stems from decades of inadequate wastewater infrastructure in Tijuana, Mexico, combined with untreated industrial waste from border factories. While both nations have committed over $700 million in emergency funding and signed binding agreements to complete infrastructure upgrades by December 2027, regulatory confusion over safe exposure levels and delayed implementation continue to put communities at risk.

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SAN DIEGO, California — For decades, residents of San Diego County's South Bay communities have complained about noxious odors and mysterious health problems emanating from the Tijuana River. Now, groundbreaking scientific research has validated their concerns, revealing that one of America's most polluted waterways is poisoning the air they breathe with toxic gases at levels previously unrecorded in an urban environment.

The Discovery That Changed Everything

In August 2025, researchers from UC San Diego's Scripps Institution of Oceanography, UC Riverside, San Diego State University, and the National Science Foundation's National Center for Atmospheric Research published findings in the peer-reviewed journal Science that fundamentally altered understanding of the cross-border pollution crisis.

The study documented peak hydrogen sulfide concentrations of 4,500 parts per billion at the Saturn Boulevard "hot spot" near Nestor—more than 4,500 times typical urban levels and 150 times higher than California's air quality standard. The research team measured these extreme levels during a three-week monitoring period from September 1-10, 2024, when wastewater flows in the Tijuana River surged to 40-80 million gallons per day despite no rainfall.

"This study reveals a direct airborne pollutant exposure pathway—from contaminated rivers into the air we breathe," said Dr. Kimberly Prather, lead investigator and atmospheric chemist at UC San Diego's Scripps Institution of Oceanography. "For the first time, we've shown that poor water quality can profoundly degrade air quality, exposing entire communities to toxic gases and other pollutants."

The study's lead author, Benjamin Rico, a UC San Diego doctoral candidate, emphasized the vindication for affected communities: "Our results validate the community voices that have been saying that air quality near the Tijuana River has been a problem for many years."

A Health Crisis Measured in Parts Per Billion

Hydrogen sulfide, commonly known as "sewer gas" due to its characteristic rotten egg odor, poses significant health risks even at relatively low concentrations. The gas affects multiple organ systems, particularly targeting the respiratory and nervous systems.

During the September 2024 monitoring period, residents living near Berry Elementary School in Nestor were exposed to hydrogen sulfide levels exceeding California's one-hour air quality standard of 30 parts per billion for 5-14 hours each day. Public health officials note that exposure to concentrations as low as 30 ppb can trigger headaches, nausea, respiratory symptoms, and other adverse health effects, particularly among vulnerable populations including children, the elderly, and those with pre-existing respiratory conditions.

"This level is too high for chronic exposures as 30 parts per billion is already associated with headaches, nausea, respiratory symptoms and other adverse health effects, particularly among vulnerable populations," said Dr. Paula Stigler Granados, associate professor of environmental health at SDSU's School of Public Health. "Framing this as merely an odor issue dangerously understates the real public health risks of repeated exposure to toxic gases at such concentrations."

The health impacts extend beyond immediate symptoms. According to former San Diego State University researcher Richard Gersberg, breathing even small amounts of hydrogen sulfide consistently over months to a year could cause long-term health damage. The EPA's Reference Concentration for chronic exposure is set at 1.4 parts per billion—a threshold that acknowledges the potential for serious health effects from sustained low-level exposure.

An ongoing SDSU survey reveals the human toll: 71% of South Bay residents report experiencing upper respiratory health issues, and 99% express concern about local air and water pollution.

San Diego County Supervisor Paloma Aguirre, who represents the affected communities, has personally experienced the crisis. She describes suffering from migraines, chest pain, shortness of breath, and waking in the middle of the night to odors she compared to "a porta potty."

Regulatory Confusion Compounds the Crisis

A significant obstacle to protecting public health has been the lack of consensus among regulatory agencies on safe exposure limits for hydrogen sulfide. The gas is not federally regulated as a hazardous air pollutant—a result of oil and gas industry lobbying that successfully convinced Congress to remove it from the EPA's list of hazardous air pollutants in the 1990s.

Different agencies have established wildly divergent standards:

• EPA Reference Concentration: 1.4 ppb for chronic exposure (based on rat studies showing health effects from sustained exposure)
• California Office of Environmental Health Hazard Assessment: 7.3 ppb for chronic exposure
• California Air Resources Board: 30 ppb for one-hour exposure (based on odor threshold, not health effects)
• CDC/ATSDR: Initially proposed using 460 ppb as a "no adverse effect" level and 1,380 ppb as the threshold for adverse health effects—levels 30 to nearly 1,000 times higher than EPA's chronic exposure reference

The CDC's Agency for Toxic Substances and Disease Registry has since indicated it will use EPA's Reference Concentration of 1.4 ppb as a screening value for its ongoing Tijuana River Valley public health assessment, though spokesperson Sharleta Stamps suggested the agency might employ "human-level equivalents" rather than the rat study-based standards.

"Only the [EPA value] is the important risk value that should be used," Gersberg stated in response to the CDC's conflicting guidance.

San Diego County Air Pollution Control District spokesperson Melina Meza emphasized that her agency is not a health agency and would not draw conclusions from gas monitoring data, instead deferring to state public health agencies and the CDC for public health recommendations—a circular dynamic that has left communities without clear protective guidance.

The Root Causes: Infrastructure Collapse and Industrial Pollution

The Tijuana River's transformation into a toxic waterway results from the collision of multiple factors: explosive population growth, aging infrastructure, industrial contamination, and decades of inadequate investment.

Tijuana's population exploded from 60,000 residents in 1950 to more than 2.2 million today. The wastewater treatment infrastructure, much of it built in the 1990s, was never designed to handle such volumes. The South Bay International Wastewater Treatment Plant, constructed through a joint U.S.-Mexico effort, was initially designed to process 25 million gallons per day but has been overwhelmed by flows that now regularly exceed 80 million gallons daily during periods of high wastewater discharge.

The crisis intensified following a 2017 infrastructure failure when a damaged sewage line in Mexico dumped an estimated 143 million gallons of wastewater into the Tijuana River. In early 2022, another catastrophic spill released hundreds of millions of gallons over two and a half weeks, revealing just how dilapidated the binational infrastructure had become.

"That's one of the reasons why things are so horrific, because they're playing catch-up on fixing these things when they have catastrophic failures," said Dr. Falk Feddersen, an oceanographer at Scripps Institution of Oceanography.

Beyond municipal sewage, the river carries millions of gallons of untreated industrial waste from maquiladoras—duty- and tariff-free manufacturing facilities established along the U.S.-Mexico border following the North American Free Trade Agreement. These factories, which produce electronics, appliances, and automotive parts for global markets, discharge heavy metals, solvents, and persistent chemicals known as PFAS ("forever chemicals") into the watershed.

Dr. Prather characterized the current situation bluntly: "The river right now is a wastewater treatment plant without any processing."

Research published in Science identified the Saturn Boulevard culvert system as a critical "hot spot" where turbulent water flow enhances the transfer of toxic pollutants from water to air. The foaming, churning water at this location acts as an atomizer, releasing not only hydrogen sulfide but hundreds of other volatile compounds into the atmosphere.

Dr. Kelley Barsanti, an atmospheric chemist at the NSF National Center for Atmospheric Research who led analysis of additional gases detected at the site, warned: "We show here that while hydrogen sulfide is an excellent marker of the sewage impacting area residents, there are multiple sources of waste entering the Tijuana River and a multitude of other hazardous gases that area residents are potentially inhaling."

A Environmental Justice Crisis

The disproportionate burden of cross-border pollution on South Bay communities represents a clear environmental justice issue. The affected neighborhoods are predominantly working-class Hispanic communities, many with limited resources to relocate despite the ongoing health hazards.

"The Tijuana River is one of, if not the most polluted, river in the entire United States," said Supervisor Aguirre, who viewed the overflowing river while wearing a hot pink respirator mask. "The river is carrying dangerous chemicals, pollutants, pathogens and toxic gases that are impacting South San Diego communities."

The pollution has caused more than 1,300 consecutive days of beach closures affecting Imperial Beach and surrounding coastal areas, devastating the local economy and preventing recreational use of public beaches. The contamination extends to military training facilities, with Navy SEALs undergoing BUD/S training in Coronado reporting illness from exposure to polluted waters.

Schools in the affected areas have been forced to keep students indoors during periods of high hydrogen sulfide concentration. Emergency hazardous waste teams have been deployed multiple times to assess the risks, and local officials have distributed thousands of air purifiers to residents—temporary measures that do not address the root causes of contamination.

The correlation between hydrogen sulfide levels and community malodor complaints reached 0.92 in the Science study, providing statistical validation of experiences that officials had long dismissed or minimized.

"Sustained monitoring, coordinated cross-border efforts and leadership from federal, state and local authorities are crucial to finally provide the protection and justice long denied to communities affected by this ongoing environmental and public health crisis," the research team concluded.

The Political and Diplomatic Response

The severity of the crisis has finally mobilized significant federal and state resources, though implementation timelines remain a source of concern for affected communities.

Biden Administration Actions

In December 2024, President Joe Biden signed a stopgap budget bill allocating $250 million to address operational challenges at the South Bay International Wastewater Treatment Plant. Combined with $400 million previously secured from Congress, this brought total federal funding for 2024 to approximately $650 million.

California Governor Gavin Newsom worked in partnership with the state's congressional delegation and the Biden-Harris Administration to secure a total of $703 million in federal funding across 2024 and 2025 for critical upgrades to wastewater treatment infrastructure.

The state has also committed substantial resources:

• $2.7 million for air purifier distribution to affected communities
• $4.7 million for a trash boom pilot project
• $14.25 million for the Smuggler's Gulch Improvement Project
• $3 million to develop pathogen forecasting models for coastal waters

Trump Administration Agreement

In July 2025, the Trump Administration's EPA Administrator Lee Zeldin traveled to Mexico City to sign a Memorandum of Understanding with Mexico's Secretary of Environment and Natural Resources Alicia Bárcena Ibarra, establishing binding commitments and accelerated timelines.

"The Trump Administration is proud to deliver this massive environmental and national security win for Americans in the San Diego area who have been living with this disgusting raw sewage flowing into their communities for far too long," Zeldin stated.

The agreement, building on the 2022 International Boundary and Water Commission (IBWC) Minute 328, includes specific commitments:

U.S. Commitments:

• Complete expansion of South Bay International Wastewater Treatment Plant from 25 to 35 million gallons per day by August 28, 2025 (a 100-day construction timeline, down from the originally planned two years)
• Release EPA Border Water Infrastructure Program funding for Pump Station 1 rehabilitation and Tijuana River collection pipe upgrades
• Provide continued technical and financial support for binational infrastructure projects

Mexico Commitments:

• Immediately allocate $93 million for infrastructure projects not yet funded under Minute 328
• Complete diversion of 10 million gallons per day of treated effluent from two wastewater treatment plants upstream of Rodriguez Dam by December 31, 2025
• Rehabilitate the Parallel Gravity Line by December 31, 2025
• Allocate remaining required funds as part of 2026-2027 budgets
• Complete all Minute 328 projects by December 31, 2027—four years ahead of the original schedule

The agreement also commits both nations to developing an updated project list by the end of 2025 that will establish new watershed management goals accounting for population growth and operation and maintenance costs.

The 1944 Water Treaty Framework

These modern agreements operate within the framework established by the Treaty Relating to the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande, signed February 3, 1944. Article 3 of this treaty specifically directs the International Boundary and Water Commission to give "preferential attention to the solution of all border sanitation problems."

The IBWC's "minute system," established under Article 25 of the 1944 treaty, allows rapid modifications without requiring legislative approval from either country. Each "minute" becomes binding unless either government objects within 30 days, making the system highly flexible for addressing evolving transboundary challenges. Since 1944, 179 minutes have been ratified addressing various binational water issues.

Minute 328, signed in July 2022, initially outlined $474 million in infrastructure improvements: $330.3 million from the United States and $143.7 million from Mexico. The agreement targeted a 50% reduction in transboundary wastewater flow days and an 80% reduction in untreated wastewater volume discharged to the Pacific Ocean.

Progress and Persistent Challenges

Federal agencies released their first quarterly progress report in November 2025, detailing both advances and ongoing obstacles.

The South Bay plant's treatment capacity has been gradually increased as infrastructure improvements are completed. However, the expansion is not instantaneous. "It's not necessarily a flip of a switch in how those systems can come online," explained Courtney Baltiyskyy, vice president of policy and advocacy for the YMCA of San Diego County, which facilitates the Tijuana River Coalition advocacy group. "It is going to be gradual over months."

Mexico has initiated construction on the first phase of the Tijuana River Gates collection pipes project and is expected to allocate the committed $93 million across 2026-2027 budgets. Frank Fisher, communications director for the U.S. International Boundary and Water Commission, expressed cautious optimism: "We're not going to let our guard down because the American people expect us to keep a close eye on Mexico, and that's what we're going to do. But so far things look good."

In October 2025, the EPA announced it had cut an additional nine months from construction timelines following a 100-day binational review, eliminating six months from the Tijuana River Gates project and three months from critical pump station rehabilitation.

However, significant concerns remain:

Funding Sustainability: In March 2025, House Republicans proposed slashing the IBWC's annual construction budget by more than 50%, from $156 million to $78 million. While this would not affect already-secured funds, it reduces resources for ongoing maintenance and future projects.

Infrastructure Limitations: Tijuana's population continues to grow, and the treatment infrastructure—even when fully upgraded—may struggle to keep pace with increasing wastewater volumes. The South Bay plant's planned expansion to 50 million gallons per day capacity still falls short of peak flow rates that have exceeded 80 million gallons daily.

Timeline Skepticism: Advocates and local officials note that previous commitments have repeatedly failed to materialize. Margarita Diaz, director of Tijuana-based Proyecto Fronterizo de Educación Ambiental, cautioned that securing funds alone does not guarantee project completion: "The logistics and expertise alone will prove to be a challenge, especially within such a short time frame."

Interim Solutions: The proposed removal of culverts at the Saturn Boulevard hot spot could provide immediate relief by eliminating the turbulence that atomizes toxic gases. San Diego County plans to complete a feasibility study on this project by January 2026. However, this would only address airborne contamination, not the underlying water pollution.

Superfund Designation: Imperial Beach Mayor and now County Supervisor Aguirre has advocated for designating the Tijuana River Valley as a Superfund Site, which would unlock additional EPA authority and federal funds for hazardous waste cleanup. This request was denied under the Biden Administration; EPA Administrator Zeldin under the Trump Administration said he would reconsider but has not yet approved the designation.

What the Science Reveals

The Science study published in August 2025 represents the first peer-reviewed research definitively linking poor water quality in the Tijuana River to degraded air quality in surrounding communities. The research has implications extending far beyond San Diego County.

Dr. Prather noted the global significance: "As the number of heavily polluted water bodies grows with ever-increasing inputs, ignoring water-to-air contaminant emissions in air quality management allows hidden risks to persist. Recognizing and addressing this airborne exposure pathway is critical to protecting vulnerable populations and advancing global health equity."

More than half of the world's population lives near rivers, lakes, or oceans, suggesting that the water-to-air contamination pathway documented in the Tijuana River Valley could affect billions of people globally.

The study's methodology included deploying carefully calibrated air quality instruments in the Nestor community, atmospheric modeling to track hydrogen sulfide dispersion, and correlation analysis between measured gas concentrations and community complaint patterns. When wastewater flows dropped dramatically on September 10, 2024—from 40-80 million gallons per day to less than 5 million gallons following an infrastructure diversion—hydrogen sulfide concentrations fell correspondingly, providing strong causal evidence.

Beyond hydrogen sulfide, researchers detected hundreds of other volatile compounds released by the polluted river, many with established exposure limits due to health impacts. Additional research is needed to quantify concentrations of these compounds and determine whether they exceed safe exposure thresholds.

The study's recommendations include:

• Expanding air quality monitoring in affected communities
• Updating air quality models globally to account for emissions from polluted waterways
• Providing free air purifiers to residents living near contaminated water sources
• Addressing polluted water quality as the fundamental solution to air contamination

The Path Forward

Multiple interventions are required to resolve this complex, decades-long crisis:

Immediate Actions:

• Complete Saturn Boulevard culvert removal or modification to reduce turbulent gas release
• Expand air purifier distribution programs for affected residents
• Implement comprehensive air quality monitoring with real-time public alerts
• Accelerate completion of South Bay plant expansion to 35 MGD capacity

Medium-Term Infrastructure (2025-2027):

• Divert 10 million gallons per day of treated effluent away from the Tijuana River
• Rehabilitate aging collection systems and pump stations on both sides of the border
• Replace failed wastewater treatment facilities in Tijuana
• Implement trash and sediment control measures to prevent system blockages

Long-Term Solutions:

• Expand treatment capacity to 50 MGD or higher to accommodate population growth
• Strengthen enforcement of industrial discharge standards for maquiladoras
• Establish sustainable binational funding mechanisms for ongoing operations and maintenance
• Consider full river diversion and treatment—the most comprehensive solution but also the most expensive and complex

Regulatory Reforms:

• Harmonize hydrogen sulfide exposure standards across federal and state agencies
• Reinstate hydrogen sulfide as a federally regulated hazardous air pollutant
• Strengthen Clean Water Act enforcement for transboundary pollution
• Establish clear protocols for public health protection during pollution events

Supervisor Aguirre emphasized the urgency: "If Trump were to say tomorrow 'we're going to waive all these laws, we're going to divert the river,' that would be guaranteed relief for our families in South County. And that could be done probably in a year if there really was political will and investment from our government."

A Test of Binational Cooperation

The Tijuana River crisis represents both an environmental catastrophe and a test of U.S.-Mexico relations. The problem cannot be solved by either nation acting alone, requiring sustained diplomatic engagement, transparent communication, and reliable funding commitments from both governments.

Recent developments suggest renewed binational commitment. Mexican President Claudia Sheinbaum stated: "There are other actions that were signed that we have to complete, that we're going to get done in the next year for the entire Tijuana sanitation system, for the entire metropolitan Tijuana area." She characterized the agreement as evidence that "when our technical teams sit down, they can resolve a problem that seemed unsolvable."

However, decades of unfulfilled promises have bred justified skepticism among affected communities. The true measure of success will be sustained improvements in air and water quality, restoration of closed beaches, elimination of health symptoms among residents, and completion of infrastructure projects on schedule and within budget.

For tens of thousands of South Bay residents—many of whom are working-class families, military personnel, and schoolchildren—the stakes could not be higher. They have endured decades of exposure to toxic gases, noxious odors, closed beaches, and mounting health concerns while officials debated, studied, and delayed action.

The scientific validation of their experiences, combined with unprecedented funding commitments and accelerated timelines, offers hope that meaningful change may finally arrive. But as Dr. Prather emphasized: "Now it cannot be ignored. So now it needs to be fixed."

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Verified Sources and Formal Citations

Peer-Reviewed Scientific Publications

1. Rico, B.A., Bloom, T., Barsanti, K., Prather, K.A., et al. (2025). "Heavily polluted Tijuana River drives regional air quality crisis." Science, published August 28, 2025. Available at: https://www.science.org/doi/10.1126/science.adv1343

2. Pendergraft, M.A., Belda-Ferre, P., Petras, D., Morris, C.K., Knight, R., Prather, K.A. (2023). "Bacterial and chemical evidence of coastal water pollution from the Tijuana River in sea spray aerosol." Environmental Science & Technology, 57, 4071-4081.

3. Cooper, A., Cancelada, L., Torres, R.R., Knight, R., Prather, K.A. (2025). "Identifying wastewater chemicals in coastal aerosols." Science Advances, 11, eads9476.

Federal Government Documents and Releases

4. U.S. Environmental Protection Agency. (2025). "United States and Mexico Reach Agreement to Permanently and Urgently End Decades-Long Tijuana River Sewage Crisis." Press release, July 25, 2025. Available at: https://www.epa.gov/newsreleases/united-states-and-mexico-reach-agreement-permanently-and-urgently-end-decades-long

5. U.S. Environmental Protection Agency. (2023). "U.S. and Mexico agree to invest $474M to address Tijuana River sewage problem." Press release, July 31, 2023. Available at: https://www.epa.gov/newsreleases/us-and-mexico-agree-invest-474m-address-tijuana-river-sewage-problem

6. U.S. Environmental Protection Agency. (2022). "Statement of Intent and Minute 328." Summary of Agreements, October 2022. Available at: https://epa.gov/system/files/documents/2022-10/Summary%20of%20Agreements.pdf

7. U.S. Environmental Protection Agency. (2011). "Lifting of Administrative Stay for Hydrogen Sulfide." Final Notice, Federal Register, January 30, 2011. Available at: https://www.epa.gov/toxics-release-inventory-tri-program/lifting-administrative-stay-hydrogen-sulfide

8. U.S. Environmental Protection Agency. (2003). "Toxicological Review of Hydrogen Sulfide." EPA/635/R-03/005. Available at: https://iris.epa.gov/static/pdfs/0061tr.pdf

9. Agency for Toxic Substances and Disease Registry. (2016). "Toxicological Profile for Hydrogen Sulfide and Carbonyl Sulfide." U.S. Department of Health and Human Services, November 2016. Available at: https://www.atsdr.cdc.gov/toxprofiles/tp114-c1-b.pdf

10. Agency for Toxic Substances and Disease Registry. (2025). "Hydrogen Sulfide ToxFAQs." Centers for Disease Control and Prevention. Available at: https://www.atsdr.cdc.gov/toxfaqs/tfacts114.pdf

11. International Boundary and Water Commission. (1944). "Treaty Relating to the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande." February 3, 1944. Available at: https://www.ibwc.gov/wp-content/uploads/2022/11/1944Treaty.pdf

12. International Boundary and Water Commission. (2023). "Treaties Between the U.S. and Mexico." Available at: https://www.ibwc.gov/treaties/

13. U.S. International Boundary and Water Commission. (2025). "Federal agencies report progress on Tijuana River cleanup." Quarterly Progress Report, November 21, 2025.

State Government Documents and Releases

14. Office of Governor Gavin Newsom. (2024). "California secures critical funding to address Tijuana River sewage crisis in Imperial Beach and surrounding communities." Press release, December 21, 2024. Available at: https://www.gov.ca.gov/2024/12/21/california-secures-critical-funding-to-address-tijuana-river-sewage-crisis-in-imperial-beach-and-surrounding-communities/

15. Office of Governor Gavin Newsom. (2024). "Governor Newsom visits Tijuana River rehabilitation efforts, assesses impact of sewage crisis." Press release, October 28, 2024. Available at: https://www.gov.ca.gov/2024/10/28/governor-newsom-visits-tijuana-river-rehabilitation-efforts-assesses-impact-of-sewage-crisis/

16. Office of Governor Gavin Newsom. (2024). "California joins federal and community partners to launch pilot project to help clean up Tijuana River." Press release, December 17, 2024. Available at: https://www.gov.ca.gov/2024/12/17/california-joins-federal-and-community-partners-to-launch-pilot-project-to-help-clean-up-tijuana-river/

17. Office of Governor Gavin Newsom. (2023). "Federal Government Commits to Fixing Tijuana River Sewage Crisis in San Diego County." Press release, September 1, 2023. Available at: https://www.gov.ca.gov/2023/09/01/federal-government-commits-to-fixing-tijuana-river-sewage-crisis-in-san-diego-county/

Mexican Government Documents

18. Secretaría de Relaciones Exteriores, Gobierno de México. (2023). "Mexico and US welcome the entry into force of IBWC Minute 328." Press Release 311. Available at: https://www.gob.mx/sre/prensa/mexico-and-us-welcome-the-entry-into-force-of-ibwc-minute-328?idiom=en

News Media and Investigative Journalism

19. Elmer, M. (2025). "Environment Report: How Much Toxic Gas Is Too Much? Nobody Seems to Agree." Voice of San Diego, December 8, 2025. Available at: https://voiceofsandiego.org/2025/12/08/environment-report-how-much-toxic-gas-is-too-much-nobody-seems-to-agree/

20. Armstrong, W. (2025). "Federal agencies report progress on Tijuana River cleanup, cite increased wastewater treatment." The San Diego Union-Tribune, November 26, 2025. Available at: https://www.sandiegouniontribune.com/2025/11/26/federal-agencies-report-progress-on-tijuana-river-cleanup-cite-increased-wastewater-treatment/

21. Staff. (2025). "First peer-reviewed study of Tijuana River Valley sewage crisis finds link between water pollution and toxic gas in air." The San Diego Union-Tribune, August 28, 2025. Available at: https://www.sandiegouniontribune.com/2025/08/28/first-peer-reviewed-study-of-tijuana-river-valley-sewage-crisis-finds-link-between-water-pollution-and-toxic-gas-in-air/

22. Salata, P. (2025). "Trump EPA races to meet Biden's timelines on sewage crisis." inewsource, August 4, 2025. Available at: https://inewsource.org/2025/08/04/trump-epa-reaffirms-biden-goals-sewage-crisis/

23. Salata, P. (2025). "Tijuana River neighbors gather data on urban runoff." inewsource, April 10, 2025. Available at: https://inewsource.org/2025/04/10/urban-runoff-tijuana-river-factories-maquiladora-survey/

24. Chavez, L. (2025). "Tijuana River sewage still pollutes the San Diego Coast. A surfer turned politician is fighting to clean it up." CalMatters, December 5, 2025. Available at: https://calmatters.org/environment/2025/12/tijuana-river-paloma-aguirre-pollution/

25. Chavez, L. (2025). "How Paloma Aguirre, now elected, is battling TJ River crisis." inewsource, December 5, 2025. Available at: https://inewsource.org/2025/12/05/san-diego-sewage-crisis-paloma-aguirre/

26. Staff. (2025). "Tijuana River sewage crisis also polluting air, new study finds." Times of San Diego, August 28, 2025. Available at: https://timesofsandiego.com/health/2025/08/28/tijuana-river-polluting-air-new-study-finds/

27. Schuler, M. (2025). "Scientists warn San Diego County air laced with toxic 'sewer gas'." The Hill, August 28, 2025. Available at: https://thehill.com/homenews/state-watch/5475912-toxic-gas-tijuana-river/

28. Robles, F. & Medina, J. (2025). "U.S., Mexico agree on steps to solve decades-old Tijuana River sewage crisis." CBS News, July 25, 2025. Available at: https://www.cbsnews.com/news/us-mexico-agree-on-steps-to-cut-flow-of-tijuana-river-sewage-across-border/

29. Guzman, D. (2025). "EPA Administrator Lee Zeldin will 'ramp up' federal efforts to tackle the Tijuana River sewage crisis." CBS 8 San Diego. Available at: https://www.cbs8.com/article/news/local/epa-lee-zeldin-will-ramp-up-federal-efforts-tackle-the-tijuana-river-sewage-crisis/509-d4ae26b0-43b6-4883-bc6f-ffb6f6d41543

University and Research Institution Releases

30. UC San Diego Today. (2025). "Tijuana River's Toxic Water Pollutes the Air." August 28, 2025. Available at: https://today.ucsd.edu/story/tijuana-rivers-toxic-water-pollutes-the-air

31. Scripps Institution of Oceanography. (2025). "Tijuana River's Toxic Water Pollutes the Air." August 28, 2025. Available at: https://scripps.ucsd.edu/news/tijuana-rivers-toxic-water-pollutes-air

32. San Diego State University News. (2025). "Tijuana River's toxic water pollutes the air." August 27, 2025. Available at: https://www.sdsu.edu/news/2025/08/tijuana-rivers-toxic-water-pollutes-the-air

33. Phys.org. (2025). "Tijuana River's toxic water pollutes the air: Study shows hydrogen sulfide levels exceed air quality standards." August 28, 2025. Available at: https://phys.org/news/2025-08-tijuana-river-toxic-pollutes-air.html

Nonprofit and Advocacy Organization Resources

34. San Diego Coastkeeper. (2025). "Tijuana River Sewage Crisis Funding Update 2025." April 11, 2025. Available at: https://www.sdcoastkeeper.org/blog/tijuana-river-sewage-crisis-funding-update-2025/

35. San Diego Coastkeeper. (2024). "Understanding the Tijuana River Sewage Crisis – An Overview of Causes and Consequences." November 1, 2024. Available at: https://www.sdcoastkeeper.org/blog/tijuana-river-sewage-crisis-causes-consequences/

Academic Journal Articles and Professional Publications

36. Seo, S.H., Carreras-Sospedra, M., Dabdub, D. (2023). "Low Level Exposure to Hydrogen Sulfide: A Review of Emissions, Community Exposure, Health Effects, and Exposure Guidelines." Critical Reviews in Toxicology, 53(4), 244-295. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10395451/

37. Pennsylvania Department of Health. (2024). "Chronic Exposure to Low-Level Hydrogen Sulfide: A Mini Literature Review." Environmental Health, October 2024. Available at: https://www.pa.gov/content/dam/copapwp-pagov/en/health/documents/topics/documents/environmental-health/PA%20DOH%20H2S%20Mini%20Lit%20Review%20Report.pdf

38. Cooper, J.M. (2022). "Same As It Ever Was: The Tijuana River Sewage Crisis, Non-State Actors, and the State." Cardozo International & Comparative Law Review, 5, 501-556. Available at: https://scholarlycommons.law.cwsl.edu/fs/386/

39. Evans, D. & Helmer, R. (2024). "Wastewater improvements target Tijuana River pollution." ASCE Civil Engineering Magazine, March 2024. Available at: https://www.asce.org/publications-and-news/civil-engineering-source/civil-engineering-magazine/article/2024/03/wastewater-improvements-target-tijuana-river-pollution

40. Staff. (2025). "U.S., Mexico Sign Memorandum of Understanding to Address Tijuana Sewage Crisis." Wastewater Digest. Available at: https://www.wwdmag.com/compliance-regulations/press-release/55305829/us-mexico-sign-memorandum-of-understanding-to-address-tijuana-sewage-crisis

41. Staff. (2025). "U.S. and Mexico Finalize Historic Deal to End Tijuana River Sewage Crisis." Environmental Protection Magazine, July 25, 2025. Available at: https://eponline.com/articles/2025/07/25/usa-mexico.aspx

Historical and Policy Analysis

42. Wilson Center. "Bilateral Water Management: Water Sharing between the US and Mexico along the Border." Available at: https://www.wilsoncenter.org/article/bilateral-water-management-water-sharing-between-us-and-mexico-along-border

43. Wikipedia contributors. (2025). "Treaty relating to the utilization of waters of the Colorado and Tijuana Rivers and of the Rio Grande." Wikipedia, updated June 1, 2025. Available at: https://en.wikipedia.org/wiki/Treaty_relating_to_the_utilization_of_waters_of_the_Colorado_and_Tijuana_Rivers_and_of_the_Rio_Grande

44. NACLA. "Tijuana's Toxic Waters." North American Congress on Latin America. Available at: https://nacla.org/article/tijuana's-toxic-waters

Additional Technical Resources

45. New Jersey Department of Health. "Right to Know Hazardous Substance Fact Sheet: Hydrogen Sulfide." Available at: https://nj.gov/health/eoh/rtkweb/documents/fs/1017.pdf

46. Florida Department of Health. "Hydrogen Sulfide FAQ." Environmental Health, Hazardous Waste Sites Program. Available at: https://www.floridahealth.gov/environmental-health/hazardous-waste-sites/contaminant-facts/_documents/final-faq-hydrogen-sulfide.pdf

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This article synthesizes information from 46 verified sources including peer-reviewed scientific publications, federal and state government documents, international treaty records, investigative journalism, and academic research to provide comprehensive coverage of the Tijuana River hydrogen sulfide crisis as of December 2025.