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.