Chronic low-level hydrogen sulfide exposure and potential effects on human health: A review of the epidemiological evidence

Abstract

The effects of exposure to high concentrations of hydrogen sulfide (H₂S) on human health are well known. However, the potential human health hazards posed by low-level chronic environmental H₂S exposure are being debated. Accordingly, we reviewed the literature regarding the effects of chronic, environmentally-relevant H₂S exposures on human health. All human observational studies using an analytical study design (e.g. cohort, cross-sectional, case-control) to evaluate chronic-duration low-level H₂S exposure (approximately ≤ 10 ppm on average, for 1 year or more), were evaluated for a range of health outcomes. Respiratory symptoms in both adults and children were the most consistently reported symptoms on the increase. When reported, such effects appear to be temporary, given that there is no consistent evidence of pulmonary function deficit in either age group, among those chronically exposed to low H₂S concentrations. While sparse, some data also suggest potential ocular symptoms and disorders associated with chronic ambient level H₂S exposure in adults (not children), but the limited data on H₂S exposures, co-exposures and/or strong odor stimulus of H₂S, temper interpretation. Neurological symptoms and deficits have been reported in some studies, but the highest quality evidence, obtained using objective outcome measures and a reasonably detailed assessment of exposure, does not support a neurological-related risk in adults (only one study in children). For the other endpoints assessed (cardiovascular, reproductive and developmental, and carcinogenicity), the results were mixed and/or conflicting, but did not indicate a potential health hazard, although this literature has several major limitations, particularly with regard to exposure estimation and the ability to assess exposure-response.

Keywords:

• Ambient
• chronic
• developmental
• epidemiology
• environmental
• neurological
• observational
• ocular
• occupational
• pulmonary
• reproductive
• respiratory

Acknowledgements

The authors would like to thank Heather Dineen and Elizabeth DeVilbiss for their assistance provided during Summer Internships at ExxonMobil Biomedical Sciences, Inc., in collecting, reviewing and abstracting relevant literature. The authors would also like to thank Dr. John Bukowski of WordsWorld Consulting, for technical and editorial assistance in the drafting of this manuscript.

Declaration of interest

The authors are both employees of ExxonMobil Biomedical Sciences, Inc., a wholly owned subsidiary of the Exxon Mobil Corporation, a multinational energy company. Hydrogen sulfide is a by-product of crude oil production and processing, in which Exxon Mobil Corporation is engaged. The authors have not offered testimony to regulatory agencies on the health effects of chronic low-level exposure to hydrogen sulfide. The authors have not testified as experts in litigation concerning the health effects of exposure to hydrogen sulfide. The strategy for the literature review, the analyses and interpretations based on the literature, the synthesis and integration of findings, and the conclusions drawn on the professional work product of the authors, are not necessarily those of Exxon Mobil Corporation.