Neuropsychological effects of occupational exposures to carbon disulfide and hydrogen sulfide

A comprehensive review of treatments for hydrogen sulfide poisoning: past, present, and future

Hydrogen sulfide (H₂S) poisoning remains a significant source of occupational fatalities and is the second most common cause of toxic gas-induced deaths. It is a rapidly metabolized systemic toxicant targeting the mitochondria, among other organelles. Intoxication is mostly acute, but chronic or in-between exposure scenarios also occur. Some genetic defects in H₂S metabolism lead to lethal chronic H₂S poisoning. In acute exposures, the neural, respiratory, and cardiovascular systems are the primary target organs resulting in respiratory distress, convulsions, hypotension, and cardiac irregularities. Some survivors of acute poisoning develop long-term sequelae, particularly in the central nervous system. Currently, treatment for H₂S poisoning is primarily supportive care as there are no FDA-approved drugs. Besides hyperbaric oxygen treatment, drugs in current use for the management of H₂S poisoning are controversial. Novel potential drugs are under pre-clinical research development, most of which target binding the H₂S. However, there is an acute need to discover new drugs to prevent and treat H₂S poisoning, including reducing mortality and morbidity, preventing sequalae from acute exposures, and for treating cumulative pathology from chronic exposures. In this paper, we perform a comprehensive review of H₂S poisoning including perspectives on past, present, and future.

Hunting for Toxic Industrial Chemicals: Real-Time Detection of Carbon Disulfide Traces by Means of Ion Mobility Spectrometry

Sensitive real-time detection of vapors produced by toxic industrial chemicals (TICs) represents a stringent priority nowadays. Carbon disulfide (CS₂) is such a chemical, being widely used in manufacturing synthetic textile fibers and as a solvent. CS₂ is simultaneously a very reactive, highly flammable, irritant, corrosive, and highly toxic compound, affecting the central nervous system, cardiovascular system, eyes, kidneys, liver, skin, and reproductive system. This study was directed towards quick detection and quantification of CS₂ in air, using time-of-flight ion mobility spectrometry (IMS); photoionization detection (PID) was also used as confirmatory technique. Results obtained indicated that IMS can detect CS₂ at trace levels in air. The ion mobility spectrometric response was in the negative ion mode and presented one product ion, at a reduced ion mobility (K₀) of 2.25 cm² V⁻¹ s⁻¹. Our study demonstrated that by using a portable, commercial IMS system (model Mini IMS, I.U.T. GmbH Berlin Germany) one can easily measure CS₂ at concentrations of 0.1 ppm_v (0.3 mg m⁻³) in the negative ion mode, which is below the lowest threshold value of 1 ppm_v given for industrial hygiene. A limit of detection (LOD) of ca. 30 ppb_v (0.1 mg m⁻³) was also estimated.

Changes of median nerve conduction velocity in rayon manufacturing workers: A 6-year cohort study

Objectives:

We conducted a 6-year cohort study to evaluate the relationship between carbon disulfide (CS₂) exposure and reductions in the motor and sensory nerve conduction velocity (MCV and SCV) of the median nerve.

Methods:

Study subjects at baseline included 432 exposed workers and 402 unexposed workers. Among the exposed workers, 145 workers terminated CS₂ exposure during the follow-up period (ex-exposed workers). MCV and SCV were measured at baseline and followed up. CS₂ personal exposure concentration was measured two times a year during a 6-year follow-up period and mean (range) CS₂ exposure concentrations (ppm) were 5.96 (0.8-16.0) and 3.93 (0.6-9.9) in the exposed and ex-exposed workers, respectively.

Results:

Reductions in MCV during the follow-up period did not differ among the exposed, ex-exposed, and unexposed workers. Reduction in SCV (m/s) of the exposed workers (-4.47±3.94) was significantly larger than that of the unexposed (-3.38±3.97) and ex-exposed workers (-3.26±3.79). For SCV reduction, a partial multiple regression coefficient of (ex-exposed workers) / (unexposed workers) was significantly positive (+0.915, p < 0.01) after adjustment for confounding variables.

Conclusions:

This cohort study showed that 6-year CS₂ exposure around a mean level of 6 ppm did not affect MCV reduction but induced significant SCV reduction beyond the influence of aging. The effect of CS₂ on SCV around a mean exposure level of 4 ppm may be reversible, since it disappeared in the ex-exposed workers after CS₂ exposure cessation for a mean period of 4.1 years.

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.

Chronic ambient hydrogen sulfide exposure and cognitive function

BACKGROUND

Exposures to hydrogen sulfide gas (H2S) have been inconclusively linked to a variety of negative cognitive outcomes. We investigated possible effects on cognitive function in an urban population with chronic, low-level exposure to H2S.

METHODS

Participants were 1637 adults, aged 18-65 years from Rotorua city, New Zealand, exposed to ambient H2S from geothermal sources. Exposures at homes and workplaces were estimated from data collected by summer and winter H2S monitoring networks across Rotorua in 2010/11. Metrics for H2S exposure at the time of participation and for exposure over the last 30 years were calculated. H2S exposure was modeled both as continuous variables and as quartiles of exposure covering the range of 0-64 ppb (0-88 μg/m(3)). Outcomes were neuropsychological tests measuring visual and verbal episodic memory, attention, fine motor skills, psychomotor speed and mood. Associations between cognition and measures of H2S exposure were investigated with multiple regression, while covarying demographics and factors known to be associated with cognitive performance.

RESULTS

The consistent finding was of no association between H2S exposure and cognition. Quartiles of H2S exposure had a small association with simple reaction time: higher exposures were associated with faster response times. Similarly, for digit symbol, higher H2S exposures tended to be marginally associated with better performance.

CONCLUSION

The results provide evidence that chronic H2S exposure, at the ambient levels found in and around Rotorua, is not associated with impairment of cognitive function.

Neurobehavioral and clinical effects in workers exposed to CS2

OBJECTIVES

Diffuse vascular encephalopathy, parkinsonism and peripheral polyneuropathy (PNP) due to CS(2) exposure are known since long. Data concerning low exposure are sparse. The current study aimed to evaluate whether the decrease of exposure below the threshold limit value (TLV) of 31 mg/m(3) results in an absence of neurological health effects using the same health outcomes as in the first study.

METHODS

The study was conducted in a group of workers of a viscose rayon plant and a control group (CG, n=66). The exposed group was divided into two groups, according to the average CS(2) exposure being below (EG1; n=60) or above 31 mg/m(3) (EG2; n=25). If the current TLV seemed insufficient to prevent effects, the analysis was repeated with three subgroups (10, >10 to 30, >30 mg/m(3)) to estimate the NOEL. Every participant filled in the neurotoxicity symptom checklist (NSC-60) and the Q16. Clinical neurological examination, computer-assisted neurobehavioral tests (NES) and neurophysiological examinations (nerve conduction velocities and electromyography (EMG)) were performed.

RESULTS

Sensorimotor complaints (NSC-60) were significantly worse in both EG1 and EG2 compared to CG (p=0.032) and both exposure groups had a higher proportion of positional tremor compared with CG (p=0.046). Finger tapping in the dominant and non-dominant hand (NES) was worse in EG1 and EG2 compared with CG (both p<0.001). A significant increase in sural nerve SCV, a significant decrease in sural nerve SNAP amplitude and duration and sympathetic skin response (SSR) amplitude, and higher prevalence of EMG abnormalities and PNP was also found in both EG1 and EG2 (p<0.003). All effects remained significant after controlling for possible confounding factors. Further analysis suggested that even average CS(2) exposures of 10 mg/m(3) could still cause effects on positional tremor, finger tapping dominant and non-dominant hand, sural nerve amplitude, SSR amplitude and EMG abnormalities.

CONCLUSIONS

An excess of psychomotor slowing, tremor and PNP was found in workers on average exposed to CS(2) concentrations below 31 mg/m(3). Data suggest that even average exposures as low as 10 mg/m(3) can cause the deleterious effects. This indicates that the current TLV insufficiently protects against neurological effects and, as a consequence, should be lowered.

Chemicals and gases

This article covers the major chemicals and gases that are considered to be of the most clinical relevance to the primary care provider. The reader is referred to other comprehensive textbooks of toxicology and occupational medicine for a complete discussion of the numerous additional products found in the workplace that may result in occupational exposure.