Tijuana River sewage gas identified as public health hazard

A report from the Agency for Toxic Substances and Disease Registry (ATSDR) has confirmed that exposure to certain levels of hydrogen sulfide in outdoor air near the Tijuana River poses a public health hazard. The agency found that short-term exposure to the sewer gas can cause symptoms such as headaches, nausea, coughing, and shortness of breath.

The findings are based on an analysis of over 800,000 air measurements collected between September 2024 and May 2025 at four monitoring sites in South County. The data was sourced from the San Diego County Air Pollution Control District, UC San Diego, and public health surveys. While short-term exposure is linked to immediate symptoms, the report states that long-term or chronic exposures are not expected to cause health effects beyond those symptoms.

Hydrogen sulfide is a colorless gas with a rotten egg odor, produced as a byproduct of sewage pollution that frequently crosses the U.S.-Mexico border via the Tijuana River. The ATSDR noted it cannot conclude the health impacts of exposures occurring prior to September 2024 due to insufficient data, though it acknowledged that exposures have almost certainly occurred over many years.