Researchers studying the health and environmental impacts of the cross-border sewage crisis said Friday they are temporarily pulling their teams collecting air and water samples in southern San Diego County communities because of “concerningly high” levels of hydrogen sulfide, a toxic gas. According to emails between researchers from UC San Diego and San Diego State University, the decision came late Friday morning from Kim Prather, director of the Center for Aerosol Impacts on Chemistry of the Environment at UC San Diego and principal investigator on a 2023 study about sewage in waters off Imperial Beach becoming airborne. “As you know, I feel strongly about solving this problem, but cannot in good conscience continue to put my own people at this level of risk,” she wrote to members of a task force studying the impacts of the sewage crisis. Moments later, Prather advised her team to stay in hotels outside South County. Prather said her team, which collects data around the clock, found levels of hydrogen sulfide — one of the main chemical components of sewer gas — to be persistently and dramatically above the state standard throughout the night and into the early morning hours Friday. The rotten egg odors characteristically associated with the gas were especially unbearable Thursday, according to her team and numerous reports from the public, who said odors infiltrated their air conditioners and their carbon monoxide alarms went off late at night or early in the morning. Prather said it was no coincidence that reports came in during a heatwave. In fact, Thursday was the county’s hottest day in four years. “Heat is trapping these gases,” said Prather. “Wind makes air cleaner but when you don’t have high wind and you do have high heat, the pollutants, or smells, can get trapped close to the ground and go into people’s houses. And that’s what we’re feeling right now.” Additionally, the International Boundary and Water Commission, which treats some of Tijuana’s sewage from San Ysidro, reported Thursday that a wastewater pipeline leak in Mexico was detected late Wednesday night, sending larger volumes of untreated sewage into San Diego via the Tijuana River. The federal agency said Friday repairs were expected to be completed over the weekend. In collaboration with UCSD, San Diego State University has also had teams collecting samples in South Bay, particularly in neighborhoods closest to the Tijuana River. Paula Stigler Granados, an environmental health professor at SDSU, said she was also pulling her teams from gathering data at least through the duration of the heatwave, which is forecast through Monday night across Southern California. Teams consisting of dozens of university staff, students and engineers have been using personal protective gear, such as gas masks and rubber boots, in the field. But Granados said teams are considering sending out drones to pull air samples “so that we don’t have to get as close.” Researchers are urging the public to do what they can to protect themselves from exposure. Prather suggested people could change the filters in their HVAC systems or obtain air purifiers that have the capability to filter out gasses like hydrogen sulfide. And, if possible, stay with family and friends living outside of impacted communities at least until the end of the heatwave. “No one should have to breathe this air, but there are ways to clean it; there are solutions,” she said. Prather, Granados and their teams are gathering data as part of a local task force studying the link between poor water quality and air quality near where millions of gallons of sewage and chemicals spill over into the U.S. from Tijuana and how it affects people who are exposed daily. The group’s expected yearlong work recently began with the launch of air monitoring across communities such as Imperial Beach, Nestor and Otay Mesa West. Their preliminary data indicates that “hotspots,” or areas with higher concentrations of wastewater gases, tend to be the closest to the Tijuana River. The task force will also soon launch a community health survey asking people to report any symptoms and exposure they had in recent weeks. They would then recruit people with reported illnesses and study their cases closely to identify what got them sick. To date, their on-the-ground work is the most comprehensive effort in the South Bay region measuring the effects of the sewage crisis on local health and the environment. Their work comes as the Centers for Disease Control and Prevention readies their 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. Researchers called Friday on county and state health agencies to take immediate action, including exploring whether a temporary shelter or cooling centers could be offered to South Bay residents. When asked for comment, the state and county did not address whether they would take immediate action on the matter, but said they were collaborating and meeting regularly to support the region. Their latest meeting was Friday, where the public health officials discussed Prather’s data on hydrogen sulfide climbing above state thresholds. A county spokesperson said the agencies agreed to request that the San Diego County Air Pollution Control District bring on a consultant with expertise in the matter.