The preliminary findings, which showed continued high levels of hydrogen sulfide and the presence of an even deadlier gas, hydrogen cyanide, also prompted the San Diego County Air Pollution Control District to issue what is believed to be its first advisory related to the noxious odors stemming from the cross-border crisis.
“Residents near the affected areas who notice strong odors are advised to limit outdoor physical activity,” the notice said. “Whenever possible, remain indoors, especially if you have respiratory or heart conditions, are elderly, or have young children in your household.”
Upon learning of the new readings, county officials announced they were deploying the Hazardous Incident Response Team to the same Tijuana River Valley area to conduct its own readings. These teams are typically sent to ensure an area or structure is safe for firefighters and other first responders to enter.
Sweetwater Union High and South Bay Union school districts ordered physical education classes, recess and after-school programming to move indoors and canceled sports at its campuses near the Tijuana River Valley because of “high levels of toxins in the air” from cross-border sewage pollution.
“If the heat and toxins continue to be high, we will continue these directives throughout the week,” read an alert from Berry Elementary School, located less than one mile away or about a two-minute drive from where researchers said they detected some of the highest levels of hydrogen cyanide during early morning hours Monday.
According to the U.S. Centers for Disease Control and Prevention, hydrogen cyanide (HCN) is a colorless, poisonous gas or liquid with a faint, bitter almond odor that can be a detected at 2-10 parts per million (ppm). It is used commercially for electroplating, fumigation, mining and making plastics and dyes. Exposure can lead to symptoms such as headache, nausea, vomiting and even death. Exposure thresholds only exist for workplace environments. The Occupational Safety and Health Administration, for example, sets a “permissible exposure limit” of 10 ppm over an eight-hour work shift.
A special team of firefighters from Austin, Texas, detected levels of hydrogen cyanide at 50 ppm at Saturn Boulevard near Sunset Avenue in the Tijuana River Valley, an area about a mile away from multiple elementary, middle and high schools.
The first responders, called the Robotics Emergency Deployment Team or RED Team, flew in Sunday at the request of Paula Stigler Granados, an environmental health professor at SDSU. She and other researchers from UC San Diego studying the health and environmental impacts of the sewage crisis temporarily pulled their teams from the area Friday after detecting high levels of hydrogen sulfide, a toxic gas with a strong rotten egg odor.
RED team members were asked to collect data because of their expertise in using technology, such as drones, to handle hazmat mitigation and other emergencies. The team was focused on collecting information about hydrogen sulfide and did not expect to have meters go off for hydrogen cyanide, Granados said. Levels were detected between 1.5 ppm and 50 ppm across various communities in the South Bay, particularly in Imperial Beach, Nestor and the Tijuana River Valley, she added.
Researchers and other members of a task force studying the impacts of the sewage crisis said they felt it necessary to alert state and county officials, as well as local school districts, about the preliminary findings.
County public health experts have yet to verify the data, a county spokesperson said.
The San Diego Air Pollution Control District will be tasked with interpreting the data gathered by the county’s Hazardous Incident Response Team.
Also on Monday, the South Bay task force called on the county to distribute appropriate air filters to all affected households, place signs throughout the Tijuana River Valley cautioning recreationists of toxic gas exposure and for the air district to install fully-calibrated infrastructure to monitor the air for pollution.
County officials said they and the air district will likely distribute a second round of air purifiers thanks to $160,000 in federal funding. More than 400 were provided last month.
Preliminary findings of toxic gases have also drawn the attention of members of Congress.
On Monday, the San Diego Congressional delegation reiterated calls, via a letter, to Gov. Gavin Newsom and President Joe Biden to declare a state of emergency, specifically mentioning “unhealthy levels of hydrogen sulfide and hydrogen cyanide.”
“Immediate action must be taken to respond to this imminent and serious threat to our communities from regular exposure to air and water toxins,” read their letter. “A federal emergency declaration would help residents of South San Diego get access to the air purifiers and testing equipment that they need to protect themselves against this imminent threat.”
The calls come as the Centers for Disease Control and Prevention readies its own door-to-door survey, formally known as a Community Assessment for Public Health Emergency Response, with San Diego County, to measure public health impacts of cross-border pollution.
Years of negligence and underinvestment in wastewater treatment plants by both countries have led to unprecedented levels of sewage and trash spills, impacting people’s health and local economies. Major repairs are underway on both sides of the U.S.-Mexico border, but substantive relief is still years away.
Residents and local leaders have criticized government for not issuing emergency declarations, which they say could expedite solutions. But state and federal governments have said the binational crisis does not qualify for an emergency declaration.
