A federal environmental public health agency said it will investigate the potential harm caused by exposure to hydrogen sulfide in the air near the sewage-tainted Tijuana River and issue recommendations to protect the public, if warranted. Following a preliminary review of available data for chemical contaminants in the air, the Agency for Toxic Substances and Disease Registry (ATSDR) determined a public health assessment was necessary. The decision is a contrast to last week’s announcement by the Environmental Protection Agency that it would not move forward with a petition from local elected officials for a potential Superfund designation because data that it reviewed from 6-7 years ago did not meet its threshold for danger. And it declined to gather fresh data, saying it would be too costly and that other efforts to improve wastewater treatment infrastructure were underway. ATSDR falls within the federal Department of Health and Human Services and is administratively overseen by the Centers for Disease Control and Prevention. Mandy Cohen, CDC director and ATSDR administrator, confirmed that the agency would take on the effort in a Jan. 7 letter to Sen. Alex Padilla and San Diego’s Congressional delegation. They had urged federal public health officials in May to examine the impacts of untreated wastewater spilling over the border from Mexico into the U.S. and impacting surrounding communities, such as Imperial Beach, Coronado and San Diego. “The CDC’s commitment to investigating the health impacts of hydrogen sulfide is an important step in addressing the public health and environmental crises that have plagued the Tijuana River Valley region for far too long,” Padilla said in a statement. “I’m glad the CDC is taking my concerns seriously, and I look forward to seeing their critical findings and recommendations in the report we requested.” Cohen said the agency would later determine whether surface water, sediment and biota data “are sufficient for public health assessment activities.” She added that the agency may find critical data gaps “that preclude us from making public health determinations for each pathway.” If so, the ATSDR would “recommend additional sampling and provide technical assistance, as needed, to fill the data gap.” The agency’s findings will be issued in a written report released to the public. If warranted, the report will also include recommendations, Cohen said. She did not specify when the investigation would commence nor how long it could take. It’s unclear what specific air data the ATSDR reviewed. The agency did not respond to a request for comment. Some available air data includes that of the San Diego County Air Pollution Control District, which deployed air monitoring equipment last year in areas such as Imperial Beach, Nestor and San Ysidro. The district also did not respond to a request for comment on whether their data was reviewed by the federal agency. Since they came online, the air monitors have repeatedly detected levels of hydrogen sulfide – one of the main chemical components of sewer gas – above the state threshold of 30 parts per billion averaging over one hour. The threshold is based primarily on nuisance as opposed to severe health effects. According to the California Air Resources Board, “if the standard were based on adverse health effects, it would be set at a much higher level.” However, the state and air pollution cops acknowledge that even at that concentration, some people, particularly sensitive groups such as children, older adults or those with respiratory issues, may be affected. More than 2,300 complaints by people who live in South County were filed last year with the air district about noxious odors. Many of them have also reported symptoms like nausea, headaches, vomiting, dizziness and exacerbated respiratory complications. While the sewage crisis has long centered around untreated wastewater from Tijuana shuttering South County shorelines, hydrogen sulfide gained significant attention last September. Local university researchers, who have been studying the health and environmental impacts of cross-border pollution, identified areas near the Tijuana River with “concerningly high” levels of the toxic gas. The county then sent its hazardous incident response team to investigate, which found elevated levels of hydrogen sulfide but not in concentrations that suggested imminent danger or a threat to public health, officials said. Months later, the air pollution control district launched an online dashboard to track hydrogen sulfide levels and an index to advise the public on what to do. The ATSDR’s investigation comes after surveys the agency and the CDC conducted last year to better assess how the sewage crisis has impacted people. Results are expected to be released soon.