Federal Study Confirms Toxic Hydrogen Sulfide Levels Threaten San Diego Air Quality
A U.S. health agency report found that hydrogen sulfide from the Tijuana River has reached concentrations that pose a public-health hazard for residents of San Diego’s South Bay.
A federal health assessment released by the U.S. Department of Health’s Agency for Toxic Substances and Disease Registry confirmed that hydrogen sulfide emissions from the Tijuana River are reaching levels hazardous to public health in San Diego’s South Bay. Monitoring data showed the odor threshold of.5 ppb was surpassed in 93% of 30-minute samples across four sites, with a record 3,021 ppb recorded at the Leon Avenue station in September 2024.
The agency warned that such concentrations can trigger headaches, nausea, eye irritation and respiratory congestion. County Supervisor Paloma Aguirre, who represents the affected neighborhoods, said the report validates years of resident complaints about sick-making air. UC San Diego atmospheric chemist Kimberly Prather noted that polluted water is turning into polluted air, affecting a broad area.
The agency’s recommendations call for halting cross-border sewage discharges and reducing hydrogen sulfide to below.5 ppb. In response, San Diego County’s Board of Supervisors approved the Capture and Clean Initiative, which will construct a sewage-treatment system on the U.S. side and replace failing infrastructure, while also distributing 14,500 free air purifiers to locals.
Why it matters
The findings confirm that toxic gas from cross-border sewage is endangering residents’ health and prompt urgent remediation actions.
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