Evaluation of Hydrogen Sulfide in Outdoor Air Environmental Contamination in the Tijuana River

In May 2024, the Centers for Disease Control and Prevention (CDC)/Agency for Toxic Substances and Disease Registry (ATSDR) received a petition from members of the California congressional delegation to investigate the public health impacts of Tijuana wastewater contamination, both in the Tijuana River and in the surrounding communities of Imperial Beach, Coronado, and San Diego. The congressional delegation requested that CDC/ATSDR assess the presence of contaminants in the communities’ water, soil, and air. CDC/ATSDR was also asked to investigate any potential connection between these contaminants and the reported increases in gastrointestinal illnesses and other symptoms.

In July 2024, the CDC/ATSDR director responded that ATSDR would start the petition process to investigate specific environmental health concerns. ATSDR gathered air, surface water, sediment, and biota data from federal, state, local, and academic partners, determining that there were enough data to accept the petition. On January 7, 2025, the CDC/ATSDR director notified the congressional delegation that ATSDR would conduct a public health assessment of hydrogen sulfide in the air [CDC/ATSDR 2025]. ATSDR will release the findings of the public health assessment activities in two reports. This is the first, focusing on potential exposures to contaminants in air in the Tijuana River Valley. A second report will address other potential exposure pathways, like surface water, sediment, and soil. In this health consultation, ATSDR evaluated exposures to air contaminants via outdoor air in the Tijuana River Valley following the agency’s public health assessment (PHA) process, as summarized in Appendix A, and detailed in ATSDR’s Explanation of ATSDR’s PHA Process [ATSDR 2022].