Hydrogen sulfide gas (H2S) has an obnoxious odor at very low concentrations and is thus responsible for considerable annoyance and concern in communities near H2S sources such as wastewater treatment plants.  Human health data, however, do not clearly indicate that ambient concentrations (less than 1 ppm) are hazardous.  Several regulatory or scientific organizations have derived standards or guidelines for H2S exposure for different populations, and these values vary considerably.  Cambridge Environmental has examined some of the reasons for the differences, and suggests that community exposures may best be evaluated in light of the acute minimal risk level of 70 ppb derived by the Agency for Toxic Substances and Disease Registry (ATSDR).

The full text of Cambridge Environmental’s analysis is available here.