Sensory and cognitive effects of acute exposure to hydrogen sulfide

Abstract

Background: Some epidemiologic studies have reported compromised cognitive and sensory performance among individuals exposed to low concentrations of hydrogen sulfide (H2S).

Objectives: We hypothesized a dose-response increase in symptom severity and reduction in sensory and cognitive performance in response to controlled H2S exposures.

Methods: In separate exposure sessions administered in random order over three consecutive weeks, 74 healthy subjects [35 females, 39 males; mean age (+/- SD) = 24.7 +/- 4.2; mean years of education = 16.5 +/- 2.4], were exposed to 0.05, 0.5, and 5 ppm H2S. During each exposure session, subjects completed ratings and tests before H2S exposure (baseline) and during the final hour of the 2-hr exposure period.

Results: Dose-response reduction in air quality and increases in ratings of odor intensity, irritation, and unpleasantness were observed. Total symptom severity was not significantly elevated across any exposure condition, but anxiety symptoms were significantly greater in the 5-ppm than in the 0.05-ppm condition. No dose-response effect was observed for sensory or cognitive measures. Verbal learning was compromised during each exposure condition.

Conclusions: Although some symptoms increased with exposure, the magnitude of these changes was relatively minor. Increased anxiety was significantly related to ratings of irritation due to odor. Whether the effect on verbal learning represents a threshold effect of H2S or an effect due to fatigue across exposure requires further investigation. These acute effects in a healthy sample cannot be directly generalized to communities where individuals have other health conditions and concomitant exposures.

Keywords: acute exposure; cognitive; hydrogen sulfide; sensory; symptoms.

Figure 1

Controlled environment facility: technician and exposure stations.

Figure 2

Timeline of events during each exposure session. Abbreviations: CS, contrast sensitivity vision test; Guess, exposure guess questionnaire; NES, Continuous Performance, Simple Reaction Time, Finger Tapping, Symbol Digit Substitution; Sym, symptom.

Figure 3

Mean anxiety symptom severity at each time point across exposure conditions. Post, postexposure. Change from 70 min to 80 min; 0.05 vs. 5 ppm: p = < 0.0001. Change from 70 min to 100 min; 0.05 vs. 5 ppm: p = 0.01. Change from 70 min to 120 min: 0.05 vs. 5 ppm; p = 0.03. Change from 70 min to 165 min: 0.05 vs. 5 ppm: p = 0.02; 0.5 vs. 5 ppm: p = 0.04. Error bars represent SE.

Figure 4

Mean total number of words recalled from List A over 5 trials on the AVLT. Change from baseline to during exposure: p < 0.0001.