A critical review of the literature on hydrogen sulfide toxicity

Impact of hydrogen sulfide on carbon monoxide/heme oxygenase pathway in the pathogenesis of hypoxic pulmonary hypertension

Hypoxic pulmonary hypertension (HPH) is an important pathophysiological process of a variety of cardiac and pulmonary diseases. But the mechanisms responsible for HPH are still not fully understood. The discoveries of endogenous gas signal molecules, nitric oxide (NO), and carbon monoxide (CO), have been moving the research of HPH to a new phase. Hydrogen sulfide (H2S), which is now being considered as the third new gas transmitter, was found to be possibly involved in the pathogenesis of HPH. But whether there exists an interaction between H2S and CO has not been clear in the pathogenesis of HPH. In this study, we found that H2S was significantly decreased in the pathogenesis of HPH. However, plasma CO level and the expressions of heme oxygenase (HO-1) protein and HO-1 mRNA were significantly increased. Exogenous supply of H2S could alleviate the elevation of pulmonary arterial pressure. At the same time, plasma CO level and the expressions of HO-1 protein and mRNA in pulmonary arteries were significantly increased. Whereas, exogenous supply of propargylglycine (PPG), an inhibitor of cystathionine gamma-lyase (CSE), decreased the plasma H2S content and worsened HPH. At the same time, plasma CO level and the expressions of HO-1 protein and mRNA in pulmonary arteries were decreased. The results showed that H2S could play a regulatory role in the pathogenesis of HPH through up-regulating CO/HO pathway.

Neurobehavioral evaluation for a community with chronic exposure to hydrogen sulfide gas

In May 2000, the Agency for Toxic Substances and Disease Registry of the US government conducted a health investigation in response to community concerns regarding ambient and indoor hydrogen sulfide (H(2)S), odor, and health symptoms in Dakota City, Nebraska. The objective was to determine whether adult residents in an area with repeated exposure to H(2)S showed poorer performance on neurobehavioral tests than unexposed residents. Study participants were required to meet age (#10878;16 years of age) and length of residency (2 years) eligibility requirements. A battery of computer-assisted standardized neurobehavioral tests was administered in English or Spanish. A questionnaire was used to collect information about participants, demographic and health status. Three hundred forty-five people agreed to participate. After the exclusion of 10 persons, analyses were conducted on 335 participants; 171 residents in the target area and 164 residents in the comparison area. The two groups were comparable in demographic characteristics and various health conditions. Overall, neurobehavioral test results for the target and comparison groups were similar. Residence in the H(2)S-exposed area was associated with marginally poorer performance on a test of memory, namely, match to sample score, and a test of grip strength. However, these differences were not significant. Deficits in overall neurobehavioral performance were not associated with exposure to H(2)S in this study.

Co-worker fatalities from hydrogen sulfide

BACKGROUND

Hydrogen sulfide is a colorless, odorless gas that may cause rapid loss of consciousness and respiratory depression without warning. It has produced toxicity in workers in numerous industries and occupations.

METHODS

A review of the United States Bureau of Labor Statistics (USBLS) Census of Fatal Occupational Injuries (CFOI) for occupational deaths related to hydrogen sulfide from 1993 to 1999 was performed.

RESULTS

Fifty-two workers died of hydrogen sulfide toxicity in this 7-year period. Deaths were most commonly reported in workers who were white (85%), male (98%), and in their first year of employment with the company (48%). Common industries included waste management, petroleum, and natural gas. In 21% of cases, a co-worker died simultaneously or in the attempt to save the workers.

CONCLUSIONS

Hydrogen sulfide toxicity is uncommon, but potentially deadly. Toxicity is predominantly in new workers and co-worker fatalities occur in a significant minority of cases. Proper training and education on the warning signs of hydrogen sulfide toxicity may help reduce worker fatalities.

H2S generated by heart in rat and its effects on cardiac function

Hydrogen sulfide (H2S), which was considered as a novel gasotransmitter, is produced endogenously from L-cysteine in mammalian brain and vessels, and might be a physiological function regulator to these organs. Here, we showed that mRNA for H2S producing enzyme, cystathionine gamma-lyase, was expressed in myocardial tissues and H2S could endogenously be produced in myocardial tissues. Negative inotropic effect of H2S was proved in present study in vitro and in vivo experiments, and the effect could partly be blocked by glibenclamide, a KATP channel blocker. An intravenous bolus injection of NaHS provoked a decrease in central venous pressure. The present findings suggested that H2S could be endogenously produced by heart tissues, as a physiological cardiac function regulator, mediated by KATP channel pathway.

Hydrogen sulfide induces calcium waves in astrocytes

Hydrogen sulfide (H2S) modifies hippocampal long-term potentiation (LTP) and functions as a neuromodulator. Here, we show that H2S increases intracellular Ca2+ and induces Ca2+ waves in primary cultures of astrocytes as well as hippocampal slices. H2S increases the influx of Ca2+ and to a lesser extent causes the release from intracellular Ca2+ stores. Ca2+ waves induced by neuronal excitation as well as responses to exogenously applied H2S are potently blocked by La3+ and Gd3+, inhibitors of Ca2+ channels. These observations suggest that H2S induces Ca2+ waves that propagate to neighboring astrocytes.

The effect of antibiotics and bismuth on fecal hydrogen sulfide and sulfate-reducing bacteria in the rat

Colonic bacteria produce the highly toxic thiol, hydrogen sulfide. Despite speculation that this compound induces colonic mucosal injury, there is little information concerning manipulations that might reduce its production. We studied the effect of antibiotics and bismuth on the production of hydrogen sulfide in rats. Baseline fecal samples were analyzed for hydrogen sulfide concentration and release rate during incubation and numbers of sulfate-reducing bacteria. Groups of six rats received daily doses of ciprofloxacin, metronidazole, or sulfasalazine for one week, and feces were reanalyzed. Bismuth subnitrate was then added to the antibiotic regimens. While sulfide production and sulfate-reducing bacteria were resistant to treatment with ciprofloxacin or metronidazole, bismuth acted synergistically with ciprofloxacin to inhibit sulfate-reducing bacteria growth and to reduce sulfide production. Combination antibiotic-bismuth therapy could provide insights into the importance of sulfide and sulfate-reducing bacteria in both human and animal models of colitis and have clinical utility in the treatment of antibiotic-resistant enteric pathogens.

Cytotoxic mechanisms of hydrosulfide anion and cyanide anion in primary rat hepatocyte cultures

Hydrogen sulfide and hydrogen cyanide are known to compromise mitochondrial respiration through inhibition of cytochrome c oxidase and this is generally considered to be their primary mechanism of toxicity. Experimental studies and the efficiency of current treatment protocols suggest that H(2)S may exert adverse physiological effects through additional mechanisms. To evaluate the role of alternative mechanisms in H(2)S toxicity, the relative contributions of electron transport inhibition, uncoupling of mitochondrial respiration, and opening of the mitochondrial permeability transition pore (MPTP) to hydrosulfide and cyanide anion cytotoxicity in primary hepatocyte cultures were examined. Supplementation of hepatocytes with the glycolytic substrate, fructose, rescued hepatocytes from cyanide anion induced toxicity, whereas fructose supplementation increased hydrosulfide anion toxicity suggesting that hydrosulfide anion may compromise glycolysis in hepatocytes. Although inhibitors of the MPTP opening were protective for hydrosulfide anion, they had no effect on cyanide anion toxicity, consistent with an involvement of the permeability transition pore in hydrosulfide anion toxicity but not cyanide anion toxicity. Exposure of isolated rat liver mitochondria to hydrosulfide did not result in large amplitude swelling suggesting that if H(2)S induces the permeability transition it does so indirectly through a mechanism requiring other cellular components. Hydrosulfide anion did not appear to be an uncoupler of mitochondrial respiration in hepatocytes based upon the inability of oligomycin and fructose to protect hepatocytes from hydrosulfide anion toxicity. These findings support mechanisms additional to inhibition of cytochrome c oxidase in hydrogen sulfide toxicity. Further investigations are required to assess the role of the permeability transition in H(2)S toxicity, determine whether similar affects occur in other cell types or in vivo and evaluate whether this may provide a basis for the design of more effective therapeutic measures for hydrogen sulfide intoxication.

Homocysteine biosynthesis pathways of Streptococcus anginosus

A gene (cgs) encoding cystathionine gamma-synthase was cloned from Streptococcus anginosus, and its protein was purified and characterized. The cgs gene and the immediately downstream lcd gene were shown to be cotranscribed as an operon. High-performance liquid chromatography analyses showed that the S. anginosus Cgs not only has cystathionine gamma-synthase activity, but also expresses O-acetylhomoserine sulfhydrylase activity. These results suggest that S. anginosus has the capacity to utilize both the transsulfuration and direct sulfhydrylation pathways for homocysteine biosynthesis.

Reaction of thiols with 7-methylbenzopentathiepin

Polysulfides typically react readily with thiols, thus, reactions of endogenous cellular thiols with the polysulfide linkage in naturally-occuring pentathiepin cytotoxins are likely to be an important aspect of their biological chemistry. Here, it is reported that the reaction of thiols with the pentathiepin ring system initially produces a complex mixture of polysulfides that further decomposes in the presence of excess thiol to yield the corresponding 1,2-benzenedithiol with concomitant production of H(2)S and dimerized thiol. In this reaction, a single molecule of the pentathiepin consumes approximately six equivalents of thiol. The reaction of thiols with the pentathiepin ring system is faster than the analogous reaction involving typical di- and trisulfides.

Differences in the betaC-S lyase activities of viridans group streptococci

betaC-S Lyase catalyzes the alpha,beta-elimination of L-cysteine to hydrogen sulfide, which is one of the main causes of oral malodor and is highly toxic to mammalian cells. We evaluated the capacity of six species of oral streptococci to produce hydrogen sulfide. The crude enzyme extract from Streptococcus anginosus had the greatest capacity. However, comparative analysis of amino acid sequences did not detect any meaningful differences in the S. anginosus betaC-S lyase. The capacity of S. anginosus purified betaC-S lyase to degrade L-cysteine was also extremely high, while its capacity to degrade L-cystathionine was unremarkable. These findings suggest that the extremely high capacity of S. anginosus to produce hydrogen sulfide is due to the unique characteristic of betaC-S lyase from that organism.

Role for recombinant gamma-glutamyltransferase from Treponema denticola in glutathione metabolism

Volatile sulfur compounds, including hydrogen sulfide (H(2)S), have been implicated in the development of periodontal disease. Glutathione is an important thiol source for H(2)S production in periodontal pockets. Our recent studies have delineated a pathway of glutathione metabolism in Treponema denticola that releases H(2)S. In this pathway, gamma-glutamyltransferase (GGT) has been proposed to catalyze the first step of glutathione degradation. We have cloned the gene of GGT from T. denticola, which contains an open reading frame of 726 bp encoding a protein of 241 amino acids. Transformation of this gene into Escherichia coli led to the expression of a recombinant protein. After purification by chromatography, the recombinant protein showed enzymatic activity typical of GGT, catalyzing the degradation of Na-gamma-glutamyl-4-nitroaniline (GNA) and the hydrolysis of glutathione, releasing glutamic acid or glutamine and cysteinylglycine. L-Cysteine is not a substrate of GGT. Importantly, GNA, when added to T. denticola, was able to compete with glutathione and inhibit the production of H(2)S, ammonia, and pyruvate. This was accompanied by the suppression of hemoxidative and hemolytic activities of the bacteria. Purified GGT was inactivated by TLCK (Nalpha-p-tosyl-L-lysine chloromethyl ketone) and proteinase K treatment. However, higher enzymatic activity was demonstrated in the presence of 2-mercaptoethanol and dithiothreitol. Our further experiments showed that the addition of recombinant GGT to Porphyromonas gingivalis, a bacterium without significant glutathione-metabolizing capacity, drastically increased the utilization of glutathione by the bacterium, producing H(2)S, ammonia, and pyruvate. This was again accompanied by enhanced bacterial hemoxidative and hemolytic activities. Together, the results suggest an important role for GGT in glutathione metabolism in oral bacteria.

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.

lcd from Streptococcus anginosus encodes a C-S lyase with alpha,beta-elimination activity that degrades L-cysteine

Hydrogen sulfide is highly toxic to mammalian cells. It has also been postulated that hydrogen sulfide modifies haemoglobin resulting in haemolysis. The enzyme that produces hydrogen sulfide from L-cysteine was purified from Streptococcus anginosus. Using the N-terminal amino acid sequence of the purified enzyme, the lcd gene encoding L-cysteine desulfhydrase was cloned; the recombinant protein was then purified to examine its enzymic and biological characteristics. This L-cysteine desulfhydrase had the Michaelis-Menten kinetics K(m)=0.62 mM and V(max)=163 micro mol min(-1) mg(-1). DL-Cystathionine, L-cystine, S-(2-aminoethyl)-L-cysteine, 3-chloro-DL-alanine and S-methyl-L-cysteine were substrates for the enzyme, whereas D-cysteine, DL-homocysteine, L-methionine, DL-serine, DL-alanine, L-cysteine methyl ester, L-tryptophan, L-tyrosine and L-phenylalanine were not. These findings suggest that this L-cysteine desulfhydrase is a C-S lyase that catalyses the alpha,beta-elimination (alphaC-N and betaC-S) reaction. In addition, it is demonstrated that the hydrogen sulfide produced by this enzyme caused the modification and release of haemoglobin in sheep erythrocytes.

Two's company, three's a crowd: can H2S be the third endogenous gaseous transmitter?

Bearing the public image of a deadly "gas of rotten eggs," hydrogen sulfide (H2S) can be generated in many types of mammalian cells. Functionally, H2S has been implicated in the induction of hippocampal long-term potentiation, brain development, and blood pressure regulation. By acting specifically on KATP channels, H2S can hyperpolarize cell membranes, relax smooth muscle cells, or decrease neuronal excitability. The endogenous metabolism and physiological functions of H2S position this gas well in the novel family of endogenous gaseous transmitters, termed "gasotransmitters." It is hypothesized that H2S is the third endogenous signaling gasotransmitter, besides nitric oxide and carbon monoxide. This positioning of H2S will open an exciting field-H2S physiology-encompassing realization of the interaction of H2S and other gasotransmitters, sulfurating modification of proteins, and the functional role of H2S in multiple systems. It may shed light on the pathogenesis of many diseases related to the abnormal metabolism of H2S.

Potentially hazardous sulfur conditions on beef cattle ranches in the United States

OBJECTIVE

To analyze the sulfur content of water and forage samples from a geographically diverse sample of beef cow-calf operations in the United States and to estimate frequency and distribution of premises where forage and water resources could result in consumption of hazardous amounts of sulfur by cattle.

DESIGN

Cross-sectional study.

SAMPLE POPULATION

709 forage samples from 678 beef cow-calf operations and individual water samples from 498 operations in 23 states.

PROCEDURE

Sulfur content of forage samples and sulfate concentration of water samples were measured. Total sulfur intake was estimated for pairs of forage and water samples.

RESULTS

Total sulfur intake was estimated for 454 pairs of forage and water samples. In general, highest forage sulfur contents did not coincide with highest water sulfate concentrations. Overall, 52 of the 454 (11.5%) sample pairs were estimated to yield total sulfur intake (as a percentage of dry matter) > or = 0.4%, assuming water intake during conditions of high ambient temperature. Most of these premises were in north-central (n = 19) or western (19) states.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that on numerous beef cow-calf operations throughout the United States, consumption of forage and water could result in excessively high sulfur intake. All water sources and dietary components should be evaluated when assessing total sulfur intake. Knowledge of total sulfur intake may be useful in reducing the risk of sulfur-associated health and performance problems in beef cattle.

The origin of hydrogen sulfide in a newborn with sulfhaemoglobin induced cyanosis

This report investigated the origin of H(2)S in a newborn boy with sulfhaemoglobin induced cyanosis, who died because of multiple organ failure. Frozen material was collected and studied after death. The results suggest that enzymes had been released from deteriorating organs into the blood and abdominal fluid, and that the reaction of one of these enzymes with sulfur containing amino acids might have resulted in increased H(2)S concentrations. It is hypothesised that this release of enzymes resulted from a haemolysin produced by an invasive haemolytic Escherichia coli that was found in the blood and organs of this patient.

H(2)S-induced vasorelaxation and underlying cellular and molecular mechanisms

H(2)S is endogenously generated in vascular smooth muscle cells. The signal transduction pathways involved in the vascular effects of H(2)S have been unclear and were investigated in the present study. H(2)S induced a concentration-dependent relaxation of rat aortic tissues that was not affected by vascular denervation. The vasorelaxant potency of H(2)S was attenuated by the removal of the endothelium. Similarly, the blockade of nitric oxide synthase or the coapplication of the Ca(2+)-dependent K(+) channel blockers apamin and charybdotoxin reduced the H(2)S-induced relaxation of the endothelium-intact aortic tissues. Sodium nitroprusside (SNP)-induced relaxation was completely abolished by either 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) or NS- 2028, two soluble guanylate cyclase inhibitors. Instead of inhibition, ODQ and NS-2028 potentiated the H(2)S-induced vasorelaxation, which was suppressed by superoxide dismutase. The vasorelaxant effect of H(2)S was also significantly attenuated when Ca(2+)-free bath solution was used. Finally, pretreatment of aortic tissues with H(2)S reduced the relaxant response of vascular tissues to SNP. Our results demonstrate that the vascular effect of H(2)S is partially mediated by a functional endothelium and dependent on the extracellular calcium entry but independent of the activation of the cGMP pathway.

Correlation between oral malodor and periodontal bacteria

Volatile sulfur compounds (VSCs), including hydrogen sulfide, methyl mercaptan, and dimethyl sulfide, are primarily responsible for oral malodor. Recently, the mgl gene encoding L-methionine-alpha-deamino-gamma-mercaptomethane-lyase, which produces methyl mercaptan, was cloned from Porphyromonas gingivalis. This article discusses the mechanism and pathogenic role of the formation of VSCs by oral bacteria.

Role of glutathione metabolism of Treponema denticola in bacterial growth and virulence expression

Hydrogen sulfide (H(2)S) is a major metabolic end product detected in deep periodontal pockets that is produced by resident periodontopathic microbiota associated with the progression of periodontitis. Treponema denticola, a member of the subgingival biofilm at disease sites, produces cystalysin, an enzyme that catabolizes cysteine, releasing H(2)S. The metabolic pathway leading to H(2)S formation in periodontal pockets has not been determined. We used a variety of thiol compounds as substrates for T. denticola to produce H(2)S. Our results indicate that glutathione, a readily available thiol source in periodontal pockets, is a suitable substrate for H(2)S production by this microorganism. In addition to H(2)S, glutamate, glycine, ammonia, and pyruvate were metabolic end products of metabolism of glutathione. Cysteinyl glycine (Cys-Gly) was also catabolized by the bacteria, yielding glycine, H(2)S, ammonia, and pyruvate. However, purified cystalysin could not catalyze glutathione and Cys-Gly degradation in vitro. Moreover, the enzymatic activity(ies) in T. denticola responsible for glutathione breakdown was inactivated by trypsin or proteinase K, by heating (56 degrees C) and freezing (-20 degrees C), by sonication, and by exposure to N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK). These treatments had no effect on degradation of cysteine by the purified enzyme. In this study we delineated an enzymatic pathway for glutathione metabolism in the oral spirochete T. denticola; our results suggest that glutathione metabolism plays a role in bacterial nutrition and potential virulence expression.

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.

Interstitial fibrosis following hydrogen sulfide exposure

This case report describes a patient with interstitial fibrosis 4 years after poisoning by hydrogen sulfide. Hydrogen sulfide causes pulmonary edema and is also toxic to the nervous system. Long-term pulmonary sequelae of hydrogen sulfide poisoning has not been reported frequently in the literature.

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.

Health effects from chronic low-level exposure to hydrogen sulfide

The acute toxic effects of hydrogen sulfide have been known for decades. However, studies investigating the adverse health effects from chronic, low-level exposure to this chemical are limited. In this study, the authors compared symptoms of adverse health effects, reported by residents of two communities exposed mainly to chronic, low-levels of industrial sources of hydrogen sulfide, to health effects reported by residents in three reference communities in which there were no known industrial sources of hydrogen sulfide. Trained interviewers used a specially created, menu-driven computer questionnaire to conduct a multi-symptom health survey. The data-collection process and questions were essentially the same in the reference and exposed communities. The two exposed communities responded very similarly to questions about the major categories. When the authors compared responses of the exposed communities with those of the reference communities, 9 of the 12 symptom categories had iterated odds ratios greater than 3.0. The symptoms related to the central nervous system had the highest iterated odds ratio (i.e., 12.7; 95% confidence interval = 7.59, 22.09), followed by the respiratory category (odds ratio = 11.92; 95% confidence interval = 6.03, 25.72), and the blood category (odds ratio = 8.07; 95% confidence interval = 3.64, 21.18). Within the broader health categories, individual symptoms were also elevated significantly. This study, like all community-based studies, had several inherent limitations. Limitations, and the procedures the authors used to minimize their effects on the study outcomes, are discussed. The results of this study emphasize the need for further studies on the adverse health effects related to long-term, chronic exposure to hydrogen sulfide.

Biological monitoring: lichens as bioindicators of air pollution assessment--a review

Often as part of environmental impact studies and, above all, to obtain authorisations in accordance with prescriptions from the Ministry for the Environment (Italy), surveys and controls that use biological indicators are required. This is because such indicators are valid instruments for evaluating the quality of the air ensuing from the subject (often an industrial plant) of the Environmental Impact Assessment (EIA). In this context, this paper aims to analyse some of the theoretical aspects of biological monitoring and to provide a progress report on the use of lichens as bioindicators of air quality, with a particular eye to the situation in Italy. The object of this paper is that of pointing out the most important lines in the current state of knowledge in this field, evaluating the methodological applications and their advantages/disadvantages with respect to traditional surveying methods.

Update on sulfur-related polioencephalomalacia

Sulfur-related polioencephalomalacia is frequently associated with a high total sulfur intake by ruminants. The onset of clinical signs coincides with excessive ruminal sulfide production. Measurement of ruminal gas cap hydrogen sulfide makes it possible to identify cattle with potentially hazardous total sulfur intake. Evaluation of all potential sulfur sources is necessary to estimate total dietary sulfur concentration, which can lead to prevention strategies.

Pulmonary symptoms and spirometric values in Kangan Sour Gas Refinery workers

In this study, the author measured the frequency of symptoms and/or alterations in respiratory functions in workers of the sour gas refining industry. All workers (n = 62) were employed in the most-exposed units of the Kangan Sour Gas Refinery. The refinery is approximately 250 km east of Bushehr Port along the Persian Gulf. This cross-sectional study involved a comprehensive health questionnaire, standardized clinical examinations by physicians blinded to subjects' symptoms and concerns, and multiple spirometric values. Although gas refinery workers experienced more respiratory symptoms than the 30 controls (i.e., 37.7% vs. 23.3%, respectively), who were matched for age and smoking status, pulmonary function data were not statistically different (p > .05) between the groups. The authors concluded, therefore, that in Kangan Sour Gas Refinery workers there were no respiratory or spirometric values associated with chronic low-dose exposure to sour gas plant emissions, including hydrogen sulfide.

Occupationally related hydrogen sulfide deaths in the United States from 1984 to 1994

Alice Hamilton described fatal work injuries from acute hydrogen sulfide poisonings in 1925 in her book Industrial Poisons in the United States. There is no unique code for H2S poisoning in the International Classification of Diseases, 9th Revision; therefore, these deaths cannot be identified easily from vital records. We reviewed US Occupational Safety and Health Administration (OSHA) investigation records for the period 1984 to 1994 for mention of hazardous substance 1480 (hydrogen sulfide). There were 80 fatalities from hydrogen sulfide in 57 incidents, with 19 fatalities and 36 injuries among coworkers attempting to rescue fallen workers. Only 17% of the deaths were at workplaces covered by collective bargaining agreements. OSHA issued citations for violation of respiratory protection and confined space standards in 60% of the fatalities. The use of hydrogen sulfide detection equipment, air-supplied respirators, and confined space safety training would have prevented most of the fatalities.

Mitochondrial targets of drug toxicity

Mitochondria have long been recognized as the generators of energy for the cell. Like any other power source, however, mitochondria are highly vulnerable to inhibition or uncoupling of the energy harnessing process and run a high risk for catastrophic damage to the cell. The exquisite structural and functional characteristics of mitochondria provide a number of primary targets for xenobiotic-induced bioenergetic failure. They also provide opportunities for selective delivery of drugs to the mitochondrion. In light of the large number of natural, commercial, pharmaceutical, and environmental chemicals that manifest their toxicity by interfering with mitochondrial bioenergetics, it is important to understand the underlying mechanisms. The significance is further underscored by the recent identification of bioenergetic control points for cell replication and differentiation and the realization that mitochondria play a determinant role in cell signaling and apoptotic modes of cell death.

Abiotrophia species in early dental plaque

The most characteristic traits that distinguish Abiotrophia strains from other streptococci are nutrient requirements, satellitism and pyrrolidonyl arylamidase activity. The presence of Abiotrophia strains was studied in early dental plaque formed on sucrose-containing and sucrose-free (glucose-containing) diets. The isolates were from 0- to 3-day dental plaque formed on the buccal surface of a lower premolar in six subjects. Identification of Abiotrophia strains was based on their pyrrolidonyl arylamidase activity. They were among the predominant cultivable microorganisms isolated from diluted suspensions of early dental plaque formed on both diets. Using biochemical tests without testing for pyrrolidonyl arylamidase activity, the Abiotrophia strains would be biochemically identified as Streptococcus mitis or unidentified streptococci, and many isolates first classified as unidentified streptococci were Abiotrophia strains. Generally, identifications using partial 16S rRNA sequences confirmed the identifications obtained biochemically. However, Abiotrophia elegans and Gemella strains were biochemically identified as Abiotrophia adiacens. Abiotrophia strains produce hydrogen sulfide, which may influence the metabolism and ecology of dental plaque and act as a virulence factor in periodontal disease. They are not able to grow on tryptic soy agar. In the present study, some S. mitis strains were not able to grow on mitis salivarius agar, and some Abiotrophia strains were able to grow on this medium. These observations indicate that the use of these media for estimation of total viable counts and number of streptococci introduces systematic error in studies of microorganisms in dental plaque.

Crystal structure of cystalysin from Treponema denticola: a pyridoxal 5'-phosphate-dependent protein acting as a haemolytic enzyme

Cystalysin is a C(beta)-S(gamma) lyase from the oral pathogen Treponema denticola catabolyzing L-cysteine to produce pyruvate, ammonia and H(2)S. With its ability to induce cell lysis, cystalysin represents a new class of pyridoxal 5'-phosphate (PLP)-dependent virulence factors. The crystal structure of cystalysin was solved at 1.9 A resolution and revealed a folding and quaternary arrangement similar to aminotransferases. Based on the active site architecture, a detailed catalytic mechanism is proposed for the catabolism of S-containing amino acid substrates yielding H(2)S and cysteine persulfide. Since no homologies were observed with known haemolysins the cytotoxicity of cystalysin is attributed to this chemical reaction. Analysis of the cystalysin-L-aminoethoxyvinylglycine (AVG) complex revealed a 'dead end' ketimine PLP derivative, resulting in a total loss of enzyme activity. Cystalysin represents an essential factor of adult periodontitis, therefore the structure of the cystalysin-AVG complex may provide the chemical basis for rational drug design.

Evidence that hydrogen sulphide can modulate hypothalamo-pituitary-adrenal axis function: in vitro and in vivo studies in the rat

The gas hydrogen sulphide (H2S) is normally produced in large amounts in the central nervous system during the metabolism of sulphur-containing aminoacids. H2S was recently shown to influence long-term potentiation in the rat hippocampus; this finding suggested that the gas may act as a neuromodulator in the brain. We therefore tested the effect of the gas on the release of corticotropin-releasing hormone (CRH) from rat hypothalamic explants. CRH immunoreactivity in the incubation media was taken as a marker of peptide release. We found that the addition of NaHS to incubation media was consistently associated with a concentration-dependent decrease in KCl-stimulated CRH release, whereas basal secretion was unaffected. Increased endogenous H2S production may be also obtained using an indirect precursor of H2S formation, S-adenosyl-L-methionine (SAMe). The latter mimicked the effects of NaHS, since it reduced potassium-stimulated CRH release. In vivo, SAMe showed no effect on hypothalamo-pituitary-adrenal (HPA) function under resting conditions, but inhibited stress-related glucocorticoid increase.

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.

Fertility and developmental neurotoxicity effects of inhaled hydrogen sulfide in Sprague-Dawley rats

In this study, we examined whether perinatal exposure by inhalation to hydrogen sulfide (H2S) had an adverse impact on pregnancy outcomes, offspring prenatal and postnatal development, or offspring behavior. Virgin male and female Sprague-Dawley rats (12 rats/sex/concentration) were exposed (0, 10, 30, or 80 ppm H2S; 6 h/day, 7 days/week) for 2 weeks prior to breeding. Exposures continued during a 2-week mating period (evidence of copulation = gestation day 0 = GD 0) and then from GD 0 through GD 19. Exposure of dams and their pups (eight rats/litter after culling) resumed between postnatal day (PND) 5 and 18. Adult male rats were exposed for 70 consecutive days. Offspring were evaluated using motor activity (PND 13, 17, 21, and 60+/-2), passive avoidance (PND 22+/-1 and 62+/-3), functional observation battery (PND 60+/-2), acoustic startle response (PND 21 and 62+/-3), and neuropathology (PND 23+/-2 and 61+/-2). There were no deaths and no adverse physical signs observed in F0 male or female rats during the study. A statistically significant decrease in feed consumption was observed in F0 male rats from the 80-ppm H2S exposure group during the first week of exposure. There were no statistically significant effects on the reproductive performance of the F0 rats as assessed by the number of females with live pups, litter size, average length of gestation, and the average number of implants per pregnant female. Exposure to H2S did not affect pup growth, development, or performance on any of the behavioral tests. The results of our study suggest that H2S is neither a reproductive toxicant nor a behavioral developmental neurotoxicant in the rat at occupationally relevant exposure concentrations (< or =10 ppm).

Hemoxidation and binding of the 46-kDa cystalysin of Treponema denticola leads to a cysteine-dependent hemolysis of human erythrocytes

Cystalysin, a 46-kDa protein isolated from the cytosol of Treponema denticola, was capable of both cysteine dependent hemoxidation and hemolysis of human and sheep red blood cells. The activities were characteristic of a cysteine desulfhydrase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western immunoblotting analysis of the interaction of cystalysin with the red blood cells revealed an interaction of the protein with the red blood cell membrane. Substrates for the enzyme (including L-cysteine and beta-chloroalanine) enhanced the interaction, which occurred with both whole red blood cells as well as with isolated and purified red blood cell ghosts. SDS-PAGE and western immunoblotting employing anti-hemoglobin serum revealed that, during the hemoxidative events, the hemoglobin molecule associated with the red blood cell membrane, forming putative Heinz bodies. Spectrophotometric analysis of the hemoxidative events (cystalysin + cysteine + red blood cells) revealed a chemical modification of the native hemoglobin to sulfhemoglobin and methemoglobin. Hemoxidation also resulted in the degradation of both the red blood cell alpha- and beta-spectrin. The results presented suggest that the interaction of cystalysin with the red blood cell membrane results in the chemical oxidation of the hemoglobin molecule as well as an alteration in the red blood cell membrane itself.

Sulfhemoglobin formation in human erythrocytes by cystalysin, an L-cysteine desulfhydrase from Treponema denticola

Cystalysin, isolated from the oral pathogen Treponema denticola, is an L-cysteine desulfhydrase (producing pyruvate, ammonia and hydrogen sulfide from cysteine) that can modify hemoglobin and has hemolytic activity. Here, we show that enzymatic activity of recombinant cystalysin depends upon stochiometric pyridoxal phosphate. The enzyme was not functional as an L-alanine transaminase, and had a strong preference for L-cysteine over D-cysteine. Cystalysin preferred small alpha-L-amino acids as substrates or inhibitors and was far more active towards L-cysteine than towards the other standard amino acids that undergo pyridoxal phosphate-dependent beta-elimination reactions (serine, threonine, tryptophan and tyrosine). Cystalysin tolerated small modifications to the carboxylate of L-cysteine (i.e., the methyl and ethyl esters of L-cysteine were good substrates), but the smallest possible peptide with an N-terminal cysteine, L-cysteinylglycine, was a very poor substrate. These results, combined with the implicit requirement for a free amine for pyridoxal phosphate-dependent reactions, imply that cystalysin cannot catabolize cysteine residues located within peptides. Cystalysin has Michaelis-Menten kinetics towards L-cysteine, and there was little or no inhibition by ammonia, H2S, pyruvate and acetate. Human erythrocytes incubated with H2S or with cystalysin and cysteine primarily accumulated sulfhemoglobin and methemoglobin, along with minor amounts of choleglobin and protein aggregates. Erythrocytes retained the ability to reduce methemoglobin in the presence of H2S. Cystalysin could not modify hemoglobin when beta-chloroalanine was the substrate, indicating an absolute requirement for H2S production. Cystalysin appears to be an unregulated L-cysteine catabolizing enzyme, with the resulting H2S production being essential to the atypical hemolytic activity.

Hydrogen sulfide poisoning: clarification of some controversial issues

BACKGROUND

Hydrogen sulfide is a toxic gas about which much has been written. We discuss here several issues we believe would benefit from further clarification.

CONCLUSIONS

We conclude that: 1) Certain neurotoxic effects of exposure are probably due to a direct toxic effect on the brain, while others are almost certainly a result of hypoxia secondary to H2S-induced respiratory insufficiency; 2) pulmonary edema is a common consequence of poisoning and there is suggestive evidence of hyperactive airway responses in some individuals following brief H2S-induced unconsciousness (knockdown); 3) criteria for acceptable community levels are very different than those governing occupational standards; 4) urinary thiosulfate determinations can be useful for monitoring occupational exposure; and 5) determination of sulfide ion concentrations in blood or major organs can be useful in corroborating a diagnosis of fatal H2S toxicity, but there are many pitfalls in collecting, storing, and analyzing tissue and fluid samples.

Association of petrochemical exposure with spontaneous abortion

OBJECTIVES

To assess the association between petrochemical exposure and spontaneous abortion, a retrospective epidemiological study in a large petrochemical complex in Beijing, China was conducted.

METHODS

Plant employment records identified 3105 women who were married, were 20-44 years of age, and had never smoked. Of those, 3070 women (98.8%) reported at least one pregnancy. From this group, 2853 (93%) of the women participated in the study. According to their plant employment record, about 57% of these women workers reported occupational exposure to petrochemicals during the first trimester of their pregnancy. Trained interviewers administered a standardised questionnaire to this group of women and their husbands, collecting information on reproductive history, pregnancy outcomes, employment history, occupational exposure, smoking habits, alcohol consumption, indoor air pollution, and demographic variables. The results from the womens' first pregnancies were analysed.

RESULTS

There was a significantly increased risk of spontaneous abortion for women working in all of the production plants with frequent exposure to petrochemicals (8.8%; range of 5.8%-9.8%) compared with those working in nonchemical plants (2.2%; range of 0.0%-7.1%). Also, when a comparison was made between exposed and non-exposed groups within each plant, exposure to petrochemicals was consistently associated with an increased risk of spontaneous abortion. The overall odds ratio (OR) was 2.7 (95% confidence interval (95% CI) 1.8 to 3.9) after adjusting for potential confounders. When the analysis was performed with the exposure information obtained from the women' interview responses for (self reported) exposures, the estimated OR for spontaneous abortions was 2.9 (95% CI 2.0 to 4.0). The analysis was repeated by excluding those 452 women who provided inconsistent reports between recalled exposure and work history, and a comparable risk of spontaneous abortion (OR 2.9; 95% CI 2.0 to 4.4) was found. In analyses for exposure to specific chemicals, an increased risk of spontaneous abortion was found with exposure to most chemicals, and the results for benzene (OR 2.5; 95% CI 1.7 to 3.7), gasoline (OR 1.8; 95% CI 1.1 to 2.9), and hydrogen sulphide (OR 2.3; 95% CI 1.2 to 4.4) were significant.

CONCLUSION

An increased risk of spontaneous abortion was found associated with the exposure to petrochemicals, including benzene, gasoline, and hydrogen sulphide.

The possible role of hydrogen sulfide as an endogenous smooth muscle relaxant in synergy with nitric oxide

Hydrogen sulfide (H2S), which is well known as a toxic gas, is produced endogenously in mammalian tissues from L-cysteine mainly by two pyridoxal-5'-phosphate-dependent enzymes, cystathionine beta-synthetase and cystathionine gamma-lyase. Recently, we showed that cystathionine beta-synthetase in the brain produces H2S, and that H2S facilitates the induction of hippocampal long-term potentiation by enhancing NMDA receptor activity. Here we show that mRNA for another H2S producing enzyme, cystathionine gamma-lyase, is expressed in the ileum, portal vein, and thoracic aorta. The ileum also expresses cystathionine beta-synthetase mRNA. These tissues produce H2S, and this production is blocked by cystathionine beta-synthetase and cystathionine gamma-lyase specific inhibitors. Although exogenously applied H2S alone relaxed these smooth muscles, much lower concentrations of H2S greatly enhanced the smooth muscle relaxation induced by NO in the thoracic aorta. These observations suggest that the endogenous H2S may regulate smooth muscle tone in synergy with NO.

Cystalysin, a 46-kilodalton cysteine desulfhydrase from Treponema denticola, with hemolytic and hemoxidative activities

A 46-kDa hemolytic protein, referred to as cystalysin, from Treponema denticola ATCC 35404 was overexpressed in Escherichia coli LC-67. Both the native and recombinant 46-kDa proteins were purified to homogeneity. Both proteins expressed identical biological and functional characteristics. In addition to its biological function of lysing erythrocytes and hemoxidizing the hemoglobin to methemoglobin, cystalysin was also capable of removing the sulfhydryl and amino groups from selected S-containing compounds (e.g., cysteine) producing H2S, NH3, and pyruvate. This cysteine desulfhydrase resulted in the following Michaelis-Menten kinetics: Km = 3.6 mM and k(cat) = 12 s(-1). Cystathionine and S-aminoethyl-L-cysteine were also substrates for the protein. Gas chromatography-mass spectrometry and high-performance liquid chromatography analysis of the end products revealed NH3, pyruvate, homocysteine (from cystathionine), and cysteamine (from S-aminoethyl-L-cysteine). The enzyme was active over a broad pH range, with highest activity at pH 7.8 to 8.0. The enzymatic activity was increased by beta-mercaptoethanol. It was not inhibited by the proteinase inhibitor TLCK (N alpha-p-tosyl-L-lysine chloromethyl ketone), pronase, or proteinase K, suggesting that the functional site was physically protected or located in a small fragment of the polypeptide. We hypothesize that cystalysin is a pyridoxal-5-phosphate-containing enzyme, with activity of an alphaC-N and betaC-S lyase (cystathionase) type. Since large amounts of H2S have been reported in deep periodontal pockets, cystalysin may also function in vivo as an important virulence molecule.

Sulfide influence on polymorphonuclear functions: a possible role for Ca2+ involvement

Polymorphonuclear cells (PMN) of gingival sulcus play an important role in host defense against periodontal tissue-invading bacteria, but their phagocytic activity is conditioned by several virulence factors released by oral pathogens. In this report we have studied the influence of sulfide, a toxic bacterial metabolite, on the main PMN functions: chemotaxis, degranulation and oxidative burst. PMN exposed to sodium sulfide (up to 2 mM) used as a source of H2S showed a depression of the calcium-dependent cytoskeleton activities such as chemotaxis and azurophilic granule release induced by FMLP. No effect was observed on the calcium-independent specific granule release obtained by PMA. These data were in agreement with the sulfide inhibition of cytosolic free Ca2+ concentration [Ca2+]i increase normally induced by ionomycin. On the other hand, hydrogen sulfide was able to prime PMN for a stronger oxidative response both to calcium-dependent or calcium-independent stimulation. This finding may account for a more efficient oxidative killing under reoxygenation of the anaerobic infectious areas.

Effects of 10-ppm hydrogen sulfide inhalation in exercising men and women. Cardiovascular, metabolic, and biochemical responses

This study examined the acute effects of 10-ppm hydrogen sulfide (H2S) inhalation, a concentration equal to its occupational exposure limit, on the cardiovascular, metabolic, and biochemical responses in healthy volunteers. Fifteen men and 13 women completed two 30-minute exercise sessions at 50% of their maximal oxygen uptake, during which they inhaled medical air or 10 ppm H2S in a blind manner. Arterial and finger-prick blood samples were obtained before and during the final minute of exercise. Muscle biopsies were withdrawn from the right vastus lateralis immediately after exercise. Cardiorespiratory measurements were monitored using an automated metabolic cart interfaced with an electrocardiogram and blood pressure apparatus. A significant decrease in oxygen uptake (VO2), with a concomitant increase in blood lactate, was observed in men and women as a result of H2S exposure. No significant changes were observed in arterial blood parameters and the cardiovascular responses under these conditions. Muscle lactate, as well as the activities of lactate dehydrogenase, citrate synthase, and cytochrome oxidase, were not significantly altered by H2S exposure. However, there was a tendency for muscle lactate to increase and citrate synthase activity to decrease in both genders in the presence of H2S. It appeared that 10-ppm H2S inhalation reduced VO2 during exercise, most likely by inhibiting the aerobic capacity of the exercising muscle. These findings question the scientific validity of the current occupational exposure limit for H2S.

Calcium polysulfide overdose: a report of two cases

BACKGROUND

Calcium polysulfide or lime-sulfur solution is a common agricultural product used as a fungicide. Despite its easy availability, only two prior cases of intentional ingestion, both from Japan, have been reported in the literature.

CASE REPORTS

Two cases of calcium polysulfide ingestion are presented. In the first case severe acidosis, coma and cardiac arrest occurred. Despite aggressive supportive therapy, the patient expired. Autopsy examination revealed hemorrhagic necrosis of the gastric mucosa. The second patient also exhibited altered mental status and metabolic acidosis. He experienced liver dysfunction, rhabdomyolysis, renal dysfunction, and aspiration pneumonia. He had endoscopically proven esophageal and gastric mucosal burns which developed into esophageal strictures.

CONCLUSIONS

Calcium polysulfide ingestions cause direct caustic injury to the upper gastrointestinal tract, coma and severe metabolic acidosis.

In vivo indicators of pathologic ruminal sulfide production in steers with diet-induced polioencephalomalacia

Two groups of 3 120-160-kg Holstein steers were fed a diet high in carbohydrate and low in long fiber and either with or without added sodium sulfate. Prior to and during the course of feeding the experimental diet, the concentrations of rumen hydrogen sulfide gas and rumen fluid sulfide were determined by a simple sulfide detector tube method and by sulfide-selective electrode, respectively. Other measurements included rumen fluid pH, blood creatine kinase, and blood sulfhemoglobin. Two of the 3 steers fed the high-sulfate diet developed signs and lesions of polioencephalomalacia. Clinical signs included episodic ataxia and blunted or absent menace reaction. Increased ruminal H2S gas concentrations occurred in all 3 steers consuming the diet with added sulfate. The onset of clinical signs coincided with the onset of elevated H2S concentrations. These increases were 40-60 times the values measured in the steers consuming the diet without added sulfate. In contrast, increases in rumen fluid sulfide concentrations usually rose to 4 times that of control steers. The steers fed an identical diet but without added sulfate exhibited no signs or lesions of polioencephalomalacia and no elevations of sulfide in rumen gas or fluid. All steers had a modest decrease in rumen fluid pH associated with the transition to the concentrate diet. No significant changes were observed in any of the blood measurements of any of the steers. An additional pair of steers was fed the experimental diet with or without added sulfate to compare the ruminal H2S gas concentrations estimated by H2S detector tubes with those estimated by a different method of analysis utilizing charcoal trapping of H2S, conversion to sulfate, and measurement of the sulfate. Both methods yielded comparable estimates of H2S concentration. Overall, these data indicate that changes in rumen gas cap H2S concentrations are larger than changes in rumen fluid sulfide concentration and the estimation of rumen gas cap H2S concentration may be a practical approach to detecting pathologic increases in ruminal H2S gas. This simple, rapid, minimally invasive method should be useful for estimating the H2S content of ruminal gas under field conditions.

Effects of 10-ppm hydrogen sulfide inhalation on pulmonary function in healthy men and women

This study examined the acute effects of oral inhalation of 10-ppm hydrogen sulfide (H2S) inhalation (a concentration equal to its occupational exposure limit) on the pulmonary function in healthy men and women. Nine men and ten women consented to inhale medical air or 10 ppm H2S for 15 minutes each during cycle exercise at 50% of their maximal aerobic power. Routine pulmonary function tests were administered at rest and immediately after the two exposure conditions. The results indicated no significant changes in any of the variables derived from the flow volume loop, maximum ventilation volume, and diffusion capacity of the lung for carbon monoxide in both genders. None of the subjects experienced any signs and symptoms as a result of H2S exposure. It was concluded that oral inhalation of 10 ppm H2S at an elevated metabolic and ventilation rate does not significantly alter pulmonary function in healthy men and women.

Epidemiological study of the systemic ophthalmological effects of carbon disulfide

A total of 123 male viscose rayon workers who were exposed to carbon disulfide, and an additional 67 workers who were not exposed to any toxic agent in the working environment, underwent a thorough ophthalmological examination. The relationship between exposure and ophthalmological results was analyzed with univariate and multivariate methods. The most striking findings were strong associations between exposure and the 100-HUE color vision score and excess of microaneurysms in the exposed group. The current threshold limit value appeared to protect against these effects.

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.