Toxic Water from Tijuana River Contaminates Local Air Quality

In a significant study published on August 28, 2024, in the journal Science, researchers from the University of California San Diego, University of California Riverside, San Diego State University, and the National Science Foundation National Center for Atmospheric Research (NSF NCAR) have revealed the connection between the Tijuana River's poor water quality and local air quality issues in San Diego's South Bay region.

The study, co-authored by experts from these institutions, including UC San Diego's Rico and Prather, has identified hundreds of gases released into the air by the polluted Tijuana River and its ocean outflow, contributing to poor air quality across the region.

For over 1,300 consecutive days, beaches in San Diego's South Bay region have been closed due to poor water quality. On September 10, 2024, the Tijuana River's flow rate decreased significantly, reducing concentrations of hydrogen sulfide and other gases. This decrease was linked to the activation of a pump station in Mexico that diverted the wastewater flow, keeping it on the Mexican side of the border.

Peak concentrations of hydrogen sulfide, commonly known as "sewer gas," measured by scientists were 4,500 times what is typical for an urban area. During the study, the air quality instruments measured concentrations of hydrogen sulfide that exceeded the California Air Resources Board's one-hour standard by nearly 70 times.

From September 1-10, 2024, residents near Berry Elementary School in Nestor were exposed to levels of hydrogen sulfide that exceeded the California Air Resources Board's one-hour average air quality standard for five to 14 hours each day. Symptoms reported by residents of South Bay communities mirror those associated with exposure to hydrogen sulfide.

The San Diego Air Pollution Control District (SDAPCD) has taken steps to address this issue. They have created an online air quality dashboard showing current levels of hydrogen sulfide to help residents limit their exposure when concentrations are high. The SDAPCD also sends out alerts to all residents when hydrogen sulfide levels go above 30 ppb, a level associated with headaches, nausea, respiratory symptoms, and other adverse health effects.

In an effort to further investigate the conditions that lead to aerosolization of pollutants and pathogens, and how far they travel, UC San Diego received federal community project funding from NOAA. The researchers recommend continuing, expanding, and increasing education about a program that provides free air purifiers to help residents breathe cleaner air at night while they sleep.

SDSU researchers are continuing with a community survey which measures related health impacts. The study calls for updating air quality models globally to account for emissions from polluted waterways. By addressing these issues, the hope is to improve the health and well-being of residents in San Diego's South Bay region and beyond.

The Tijuana River has been carrying millions of gallons of untreated sewage and industrial waste across the U.S.-Mexico border for decades. The study reveals that poor water quality in the Tijuana River can lead to degraded air quality, exposing communities to toxic gases and other pollutants. This underscores the need for continued collaboration between the United States and Mexico to address this ongoing issue.