Effect of environmental exposure to hydrogen sulfide on central nervous system and respiratory function: a systematic review of human studies

Background: Assessment of the health effects of low-level exposure to hydrogen sulfide (H2S) on humans through experiments, industrial, and community studies has shown inconsistent results. Objective: To critically appraise available studies investigating the effect of H2S on the central nervous system (CNS) and on respiratory function. Methods: A search was conducted in 16 databases for articles published between January 1980 and July 2014. Two researchers independently evaluated potentially relevant papers based on a set of inclusion/exclusion criteria. Results: Twenty-seven articles met the inclusion criteria: 6 experimental, 12 industry-based studies, and 10 community-based studies (one article included both experimental and industry-based studies). The results of the systematic review varied by study setting and quality. Several community-based studies reported associations between day-to-day variations in H2S levels and health outcomes among patients with chronic respiratory conditions. However, evidence from the largest and better-designed community-based studies did not support that chronic, ambient H2S exposure has health effects on the CNS or respiratory function. Results from industry- based studies varied, reflecting the diversity of settings and the broad range of H2S exposures. Most studies did not have individual measurements of H2S exposure. Discussion: The results across studies were inconsistent, justifying the need for further research.