Health Effects of Hydrogen Sulfide Exposures: A Review of the Evidence Pertaining to Low Level Exposures

Abstract

BACKGROUND AND AIM: Hydrogen sulfide (H2S) is a toxic gas well-known for its acute health risks in occupational settings and long considered a nuisance in community settings. Less is known about the health effects of chronic, low-level exposures (10 ppm). We review the health effects of chronic exposure to H2S at low concentrations that are relevant in community, and often occupational, settings. METHODS: We focus on the peer-reviewed epidemiological literature since 2004. Taking an interdisciplinary approach, we contextualize epidemiological studies with peer-reviewed toxicological, experimental, and exposure assessment studies as well as agency guidelines and standards. We examine all sources of H2S emissions, geothermal and industrial, yet limit the exposure route of interest to inhalation. RESULTS:Chronic exposure to H2S at levels below 10 ppm was associated with odor aversion, irritation, and harmful ocular, nasal, respiratory, and neurological effects. Exposure to an annual mean concentration between 7 and 27 ppb was associated with an increased prevalence of harmful neurological effects. Among people exposed to mean concentrations as low as 0.3 ppb, a slight increase of H2S as little as 1 ppb may be associated with increased eye irritation, nasal irritation, and respiratory effects. Few studies considered vulnerable and susceptible populations. In epidemiological studies, the strength of association between low-level H2S exposure and adverse health effects was primarily limited by exposure measurement error and confounding by co-pollutants. CONCLUSIONS:Long-term, community-based epidemiological studies with robust objective exposure assessment are needed. Still, the evidence linking chronic exposure to H2S in the ppb range with negative health effects, especially considering potential effects on sensitive populations, suggests that more stringent guidelines and standards are needed to protect communities. KEYWORDS: air pollution, long-term exposure, environmental epidemiology, exposure assessment