Brain damage caused by hydrogen sulfide: a follow-up study of six patients

Effects of hydrogen sulfide on neurobehavioral function

BACKGROUND

Nineteen hydrogen sulfide (H2S)-exposed patients were compared with 202 unexposed subjects. This 1997-to-2001 case-referent series was compared with 16 previous (1991-1996) case-referent patients.

METHODS

New patients were bystanders of H2S exposure and none had been unconscious. In contrast, 13 members of the prior group were exposed at work and 7 had been unconscious. The three groups were compared on the basis of 8 physiologic and 12 psychological measurements. Observed measurements were compared with predicted ones after adjusting for age, sex, educational attainment (years), and other significant factors (observed/predicted x 100).

RESULTS

The new group performed poorly compared with unexposed controls and were similar to the first group on balance, reaction time, color discrimination, visual performance, hearing, Culture Fair, digit symbol, vocabulary, verbal recall, peg placement, trail making A and B, and information.

CONCLUSION

H2S impairments associated with H2S were similar in 19 workers (44% had been unconscious) and in 16 bystanders who had not been unconscious.

Assay methods and biological roles of labile sulfur in animal tissues

Sulfur is a chemically and biologically active element. Sulfur compounds in animal tissues can be present in two forms, namely stable and labile forms. Compounds such as methionine, cysteine, taurine and sulfuric acid are stable sulfur compounds. On the other hand, acid-labile sulfur and sulfane sulfur compounds are labile sulfur compounds. The sulfur atoms of labile sulfur compounds are liberated as inorganic sulfide by acid treatment or reduction. Therefore, the determination of sulfide is the basis for the determination of labile sulfur. Determination of sulfide has been performed by various methods, including spectrophotometry after derivatization, ion chromatography, high-performance liquid chromatography after derivatization, gas chromatography, and potentiometry with a sulfide ion-specific electrode. These methods were originally developed for the determination of sulfide in air and water samples and were then applied to biological samples. The metabolic origin of labile sulfur in animal tissues is cysteine. The pathways of cysteine metabolism leading to the formation of sulfane sulfur are discussed. Finally, reports on the physiological roles and pathological considerations of labile sulfur are reviewed.

Olfactory mucosal necrosis in male CD rats following acute inhalation exposure to hydrogen sulfide: reversibility and the possible role of regional metabolism

Hydrogen sulfide (H2S) is a potent inhibitor of cytochrome oxidase (CO) and is associated with dysosmia and anosmia in humans and nasal lesions in exposed rodents. An improved understanding of the pathogenesis of these lesions is needed to determine their toxicological relevance. We exposed 10-week-old male CD rats to 0, 30, 80, 200, or 400 ppm H2S for 3 hours/day for 1 or 5 days consecutively. The nose was histologically examined 24 hours after H2S exposure, and lesion recovery was assessed at 2 and 6 weeks following the 5-day exposure. A single 3-hour exposure to > or = 80 ppm H2S resulted in regeneration of the respiratory mucosa and full thickness necrosis of the olfactory mucosa localized to the ventral and dorsal meatus, respectively. Repeated exposure to the same concentrations caused necrosis of the olfactory mucosa with early mucosal regeneration that extended from the dorsal medial meatus to the caudal regions of the ethmoid recess. Acute exposure to 400 ppm H2S induced severe mitochondrial swelling in sustentacular cells and olfactory neurons, which progressed to olfactory epithelial necrosis and sloughing. CO immunoreactive cells were more frequently observed in regions of the olfactory mucosa commonly affected by H2S than in regions that were not. These findings demonstrate that acute exposure to >80 ppm H2S resulted in reversible lesions in the respiratory and olfactory mucosae of the CD rat and that CO immunoreactivity may be a susceptibility factor for H2S-induced olfactory toxicity in the rat.

Hydrogen sulfide exposure without loss of consciousness: chronic effects in four cases

Adverse effects of acute exposure to hydrogen sulfide (H2S) are well documented, but long-term effects of occupational exposure to low levels of the gas are not. To evaluate effects of such exposure we performed physical, neurologic, psychiatric, and chemosensory (smell and taste) examinations of four workers who were present but did not lose consciousness when the gas was accidentally released at a construction site. None of the four workers tested positive for functional problems, but all met diagnostic criteria for at least three, and up to eight, H2S-induced neuropsychiatric clinical disorders and from zero to two subclinical disorders. All four had abnormal P300 evoked responses (electrical neurophysiologic tests of brain waves). Our data indicate that exposures to even relatively low concentrations of H2S are hazardous. A rigorous epidemiologic investigation of persons who work with H2S is warranted.

Imaging of the olfactory system

The olfactory system consists of the primary olfactory nerves in the nasal cavity, the olfactory bulbs and tracts, and numerous intracranial connections and pathways. Diseases affecting the sense of smell can be located both extracranially and intracranially. Many sinonasal inflammatory and neoplastic processes may affect olfaction. Intracranially congenital, traumatic, and neurodegenerative disorders are usually to blame for olfactory dysfunction. The breadth of diseases that affect the sense of smell is astounding, yet the imaging ramifications have barely been explored.

Mental retardation in Down syndrome: a hydrogen sulfide hpothesis

Mental retardation is progressive in Down syndrome: individuals are born with normal intelligence which starts to decline linearly within the first year. This phenomenon can be observed with phenylalanine in patients with phenylketonuria, therefore it is compatible with metabolic intoxication. The toxic compound could be hydrogen sulfide. The amount of the compound is probably increased in Down syndrome by increasing active cystathionine beta synthase. This heuristic hypothesis requires further investigation.

Noxious gas exposure in the outback: two cases of hydrogen sulfide toxicity

Two cases of toxicity from industrial exposure to hydrogen sulfide are presented. Both patients had neurological effects with loss of consciousness and amnesia along with respiratory symptoms and signs. Both were treated with hyperbaric oxygen therapy in addition to standard resuscitative techniques with rapid improvement. Sodium nitrite and hyperbaric oxygen therapy are suggested specific treatments. The literature and the two case reports support the use of hyperbaric oxygen therapy in the treatment of acute hydrogen sulfide toxicity. Hyperbaric oxygen therapy has also been reported to have a role in the prevention of both short- and long-term neurological toxicity.

Neurotoxicological effects associated with short-term exposure of Sprague-Dawley rats to hydrogen sulfide

Although hydrogen sulfide (H2S) is a known neurotoxic hazard, only a limited number of experimental animal studies have examined its neurochemical or behavioral effects. Our aim was to determine if short-term inhalation exposure of rats to H2S would result in altered brain catecholamnine levels or impaired learning and memory. Three groups of adult male CD rats were tested; two groups were exposed by nose-only inhalation (0, 30, 80, 200, or 400 ppm H2S) and one group was exposed by whole-body inhalation (0, 10, 30, or 80 ppm H2S) for 3 h per day forfive consecutive days. The first group (n = 10 rats per concentration) was tested immediately following each daily nose-only H2S exposure for spatial learning with a Morris water maze. Core body temperatures were also monitored in these animals during and after the last H2S exposure. The second group of rats (n = 10 rats per concentration) was tested for spontaneous motor activity immediately following the fifth exposure. These rats were then euthanized and striatal, hippocampal, and hindbrain catecholamnine levels determined. A third group of rats (n = 5-7 rats per concentration) was pretrained on a multiple fixed- interval (FI) schedule and exposed whole-body. Daily performance on the FI schedule was compared for the week pre-exposure, for the exposure week immediately following daily exposures, and for the week postexposure. We observed significant reductions in motor activity, water maze performance, and body temperature following exposure only to high concentrations (> or = 80 ppm) of H2S. Exposure to H2S did not affect regional brain catecholamine concentrations or performance on the FI schedule. Additional studies using other measures of behavior and longer-term exposure to H2S may be required to more definitively address conditions under which H2S exposure results in behavioral toxicity.

Effects of repeated hydrogen sulphide (H2S) exposure on learning and memory in the adult rat

The effects of repeated exposure (125 ppm) of hydrogen sulphide (H2S) on learning and memory in the rat were investigated. A 16-arm radial arm maze (RAM) was used to examine neurobehavioural functioning in a series of three experiments. Experiment 1 involved training animals on a complex spatial maze task, prior to a 5-week period of exposure to H2S or a control gas mixture. Rats were tested for maze retention after each 5-day exposure period. It was determined that repeated H2S exposure had no effect on memory for a previously learned spatial task. Experiment 2 was conducted to determine whether H2S interferes with the acquisition of a novel spatial task. Naïve animals received daily maze training and exposure (H2S or control) sessions over an extended 11-week period (48 sessions). The results indicated that the groups were comparable on four of five measures of maze performance. H2S animals were impaired in their ability to find all of the reinforcers prior to the end of a trial, suggesting that H2S had an effect on performance rate, but not acquisition of the maze task. Finally, Experiment 3 was conducted to determine what role proactive interference might play in H2S-related brain impairment. Animals from the preceding experiment were trained on a new reversed contingency maze task. H2S animals made more overall arm entries than controls, suggesting that H2S may impair learning by increasing the animals' susceptibility to interference from irrelevant stimuli. The prefrontal cortex was discussed as a potential target site of H2S. The pathophysiological mechanisms underlying the effect of H2S on normal brain function have yet to be identified.

Fatal methane and cyanide poisoning as a result of handling industrial fish: a case report and review of the literature

The potential health hazards of handling industrial fish are well documented. Wet fish in storage consume oxygen and produce poisonous gases as they spoil. In addition to oxygen depletion, various noxious agents have been demonstrated in association with spoilage including carbon dioxide, sulphur dioxide, and ammonia. A fatal case of methane and cyanide poisoning among a group of deep sea trawler men is described. Subsequent independent investigation as a result of this case led to the discovery of cyanides as a further potential noxious agent. This is thus the first case in which cyanide poisoning has been recognised as a potentially fatal complication of handling spoiled fish. The previous literature is reviewed and the implications of the current case are discussed.

Basal ganglia neurotoxins

The epidemiology, clinical features, pathology, and mechanisms of action of basal ganglia neurotoxins are reviewed. Manganese, cyanide, hydrogen sulfide, methanol, carbon monoxide, 3-nitropropionic acid, MPTP, and annonaceae alkaloids are discussed. The probable mechanism of action for almost all basal ganglia neurotoxins is inhibition of mitochondrial function with destruction of the pallidum and putamen. MPTP produces selective loss of dopaminergic neurons because of selective uptake of a toxic metabolite in dopaminergic neurons. The basis for selective vulnerability of the putamen and pallidum is unknown.

Olfactory neuron loss in adult male CD rats following subchronic inhalation exposure to hydrogen sulfide

Dysosmia and anosmia are reported to occur following human exposure to hydrogen sulfide (H2S) gas. The clinical association between H2S exposure and olfactory dysfunction in humans necessitates evaluation of the nasal cavity and olfactory system in experimental animals used to study H2S toxicity. The purpose of this study was to subchronically expose 10-week-old male CD rats to relatively low concentrations of H2S and to histologically evaluate the nasal cavity for exposure-related lesions. Rats (n = 12/group) were exposed via inhalation to 0, 10, 30, or 80 ppm H2S 6 h/d and 7 d/wk for 10 weeks. Following exposure to 30 and 80 ppm H2S, a significant increase in nasal lesions limited to the olfactory mucosa was observed. The lesions, which consisted of olfactory neuron loss and basal cell hyperplasia, were multifocal, bilaterally symmetrical, and had a characteristic rostrocaudal distribution pattern. Regions of the nasal cavity affected included the dorsal medial meatus and the dorsal and medial portions of the ethmoid recess. The no observed adverse effect level for olfactory lesions in this study was 10 ppm. For perspective, the American Conference of Governmental Industrial Hygienists threshold limit value (TLV) recommendation for H2S is currently 10 ppm (proposed revision: 5 ppm), so the concentrations employed in the present study were 3 and 8 times the TLV. These findings suggest that subchronic inhalation exposure to a relatively low level of H2S (30 ppm) can result in olfactory toxicity in rats. However, because of differences in the breathing style and nasal anatomy of rats and humans, additional research is required to determine the significance of these results for human health risk assessment.

Long-term effects on the olfactory system of exposure to hydrogen sulphide

OBJECTIVE

To study chronic effects of hydrogen sulphide (H2S) on cranial nerve I (nervi olfactorii), which have been only minimally described.

METHODS

Chemosensations (smell and taste) were evaluated in eight men who complained of continuing dysfunction 2-3 years after the start of occupational exposure to H2S. Various bilateral (both nostrils) and unilateral (one nostril at a time) odour threshold tests with standard odorants as well as the Chicago smell test, a three odour detection and identification test and the University of Pennsylvania smell identification test, a series of 40 scratch and sniff odour identification tests were administered.

RESULTS

Six of the eight patients showed deficits of various degrees. Two had normal scores on objective tests, but thought that they continued to have problems. H2S apparently can cause continuing, sometimes unrecognised olfactory deficits.

CONCLUSION

Further exploration into the extent of such problems among workers exposed to H2S is warranted.

Hydrogen sulfide in parenteral amino-acid solutions

We have previously reported appreciable concentrations of hydrogen sulfide (H2S) in paediatric amino-acid solutions, apparently formed from cysteine during the production process. Since manufacturers assured us of their aim to reduce the contents of the potentially toxic H2S in these solutions, we determined whether lower amounts have been achieved 2 years after our first report. Median H2S content of 13 paediatric amino-acid solutions was 22.8 microg/l (range: not detectable to > 280 microg/l which is comparable to the amounts previously found. Median H2S content of 8 special solutions for renal and hepatic disorders was 15.8 microg/l (range not detectable to > 280 microg/l). We conclude that manufacturers should make further efforts to reduce H2S amounts in parenteral amino-acid solutions.

Effects of repeated exposures of hydrogen sulphide on rat hippocampal EEG

Exposure to high levels of hydrogen sulphide (H2S) in humans has been associated with a number of respiratory and neurological symptoms. Acute toxicity following exposure to high concentrations is well-documented, however, there is little scientific information concerning the effects of exposure to low concentrations. The effects of low levels of H2S on electroencephalographic (EEG) activity in the hippocampus and neocortex were investigated on the freely moving rat (Sprague-Dawley). Hippocampal electrodes were implanted in the dentate gyrus (DG) and CA1 region. Activity was recorded for 10 min just prior to H2S exposure in the presence of air (pre-exposure). Rats were exposed to H2S (25, 50, 75, or 100 ppm) for 3 h/day; data was collected during the final 10 min of each exposure. The total power of hippocampal theta activity increased in a concentration-dependent manner in both DG and CA1; repeated exposures for 5 consecutive days resulted in a cumulative effect that required 2 weeks for complete recovery. The effects were found to be highly significant at all concentrations within subjects. Neocortical EEG and LIA (Large Amplitude Irregular Activity) were unaffected. The results demonstrate that repeated exposure to low levels of H2S can produce cumulative changes in hippocampal function and suggest selectivity of action of this toxicant.

Occupational fatality and persistent neurological sequelae after mass exposure to hydrogen sulfide

Exposure to hydrogen sulfide (H2S) has been associated with death as well as survival following coma with or without hypoxic brain damage. The release of H2S at a beachfront construction site led to the emergency evaluation and treatment of 37 people, with six admissions and one death. At least one victim, who underwent extensive therapy with hyperbaric oxygen, developed persistent neurological sequelae. Despite increased awareness of the potentially life-threatening consequences of exposure to H2S, significant poisoning continues to occur, even in workplaces where the hazards are well-known and can be avoided. Recommended therapy includes nitrites, hyperbaric oxygen, and supportive care, but documentation of efficacy is lacking. Because patients with chronic neurological sequelae after acute H2S exposure continue to be reported, we suggest that any survivor of H2S poisoning who presents in coma or who manifests objectively verifiable evidence of neurotoxicity on physical examination or lab testing should undergo baseline and annual neurological and neuropsychological testing for at least five years. This approach could standardize and enhance our knowledge of, and ability to detect, the subtle but permanent alterations of central nervous system function that follow H2S exposure.

Hydrogen sulfide and reduced-sulfur gases adversely affect neurophysiological functions

Hydrogen sulfide (H2S) above 50 parts per million (ppm) causes unconsciousness and death. Lower doses of H2S and related gases have been regarded as innocuous, but the effects of prolonged exposure have not been studied. This study was designed to determine whether people exposed to sulfide gases as a result of working at or living downwind from the processing of "sour" crude oil demonstrate persistent neurobehavioral dysfunction. Thirteen former workers and 22 neighbors of a refinery complained of headaches, nausea, vomiting, depression, personality changes, nosebleeds, and breathing difficulties. Their neurobehavioral functions and a profile of mood states (POMS) were compared to 32 controls, matched for age and educational level. The exposed subjects' mean values were statistically significantly abnormal compared to controls for two-choice reaction time, balance (as speed of sway), color discrimination, digit symbol, trail-making A and B, and immediate recall of a story. Their POMS scores were much higher than those of controls. Visual recall was significantly impaired in neighbors, but not in exworkers. It was concluded that neurophysiological abnormalities were associated with exposure to reduced sulfur gases, including H2S from crude oil desulfurization.

Case report: profound neurobehavioral deficits in an oil field worker overcome by hydrogen sulfide

A 24-year-old oil well tester was rendered semiconscious by hydrogen sulfide (H2S). He received oxygen and was hospitalized but released in 30 minutes. The next day, nausea, vomiting, diarrhea, and incontinence of urine and stool led to rehospitalization. These problems and leg shaking, dizziness, sweating, trouble sleeping, and nightmares prevented his return to work. A physical examination, chest x-ray, and pulmonary function tests were normal 39 months after the episode but vibration sense was diminished. Two choice visual reaction times were delayed. Balance was highly abnormal (5 to 6 cm/sec) with eyes closed. Blink reflex latency was slow (R-1 17.5 msec versus normal 14.3 msec). Numbers written on finger tips were not recognized. Verbal and visual recall were impaired but overlearned memory was intact. Cognitive functions measured by Culture Fair, block design, and digit symbol were impaired. Perceptual motor was slow. Scores for confusion, tension-anxiety, depression, and fatigue were elevated and vigor was reduced. Forty-nine months after exposure his reaction time, sway speed, and color vision had not improved. His recall and his cognitive, constructional, and psychomotor speeds had improved but remained abnormal. These deficits are most likely due to H2S. Similar testing of other survivors is recommended.