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

Effect of Cu/HZSM-5 sorbents with different Si/Al ratios on the adsorption and oxidation performance of H2S

This study employed a wet impregnation method to synthesize five types of Cu/HZSM-5 adsorbents with Si/Al ratios of 25, 50, 85, 200, and 300, used for the removal of H2S in low-temperature, low-oxygen environments. The impact of different Si/Al ratios on the adsorption oxidative performance of Cu30/HZSM-5-85 adsorbents was investigated. According to the performance test results, Cu30/HZSM-5-85 exhibited the highest breakthrough capacity, reaching 231.75 mg H2S/gsorbent. Cu/HZSM-5 sorbent maintains a strong ability to remove H2S even under humid conditions and shows excellent water resistance. XRD, BET, and XPS results revealed that CuO is the primary active species, with Cu30/HZSM-5-85 having the largest surface area and highest CuO content, providing more active sites for H2S adsorption. H2-TPR and O2-TPD results confirmed that Cu30/HZSM-5-85 sorbent exhibits outstanding redox properties and oxygen storage capacity, contributing to excellent oxygen transferability in the molecular sieve adsorption-oxidation process. With notable characteristics such as a large surface area, high desulfurization efficiency, and water resistance, Cu30/HZSM-5-85 sorbents hold significant importance for industrial applications.

Low level exposure to hydrogen sulfide: a review of emissions, community exposure, health effects, and exposure guidelines

Hydrogen sulfide (H2S) is a toxic gas that is well-known for its acute health risks in occupational settings, but less is known about effects of chronic and low-level exposures. This critical review investigates toxicological and experimental studies, exposure sources, standards, and epidemiological studies pertaining to chronic exposure to H2S from both natural and anthropogenic sources. H2S releases, while poorly documented, appear to have increased in recent years from oil and gas and possibly other facilities. Chronic exposures below 10 ppm have long been associated with odor aversion, ocular, nasal, respiratory and neurological effects. However, exposure to much lower levels, below 0.03 ppm (30 ppb), has been associated with increased prevalence of neurological effects, and increments below 0.001 ppm (1 ppb) in H2S concentrations have been associated with ocular, nasal, and respiratory effects. Many of the studies in the epidemiological literature are limited by exposure measurement error, co-pollutant exposures and potential confounding, small sample size, and concerns of representativeness, and studies have yet to consider vulnerable populations. Long-term community-based studies are needed to confirm the low concentration findings and to refine exposure guidelines. Revised guidelines that incorporate both short- and long-term limits are needed to protect communities, especially sensitive populations living near H2S sources.

Chronic thinner inhalation alters olfactory behaviors in adult mice

Volatile solvents exposure can result in various behavioral impairments that have been partly associated to altered adult hippocampal neurogenesis. Despite recent evidence supporting this association, few studies have been devoted to examine the impact on olfactory functioning and olfactory bulb (OB) neurogenesis, although olfactory system is directly in contact with volatile molecules. Thus, this study was designed to evaluate in adult mice the potential modifications of the olfactory functioning after acute (1 day), subchronic (6 weeks) and chronic (12 weeks) exposure to thinner vapor at both behavioral and cellular levels. Firstly, behavioral evaluations showed that chronic thinner exposure impacts on odor detection ability of treated mice but does not affect mice ability to efficiently discriminate between two different odors. Moreover, chronic thinner exposure produces impairment in the olfactory-mediated associative memory. Secondly, analysis of the effects of thinner exposure in the subventricular zone (SVZ) of the lateral ventricle and in the OB revealed that thinner treatments do not induce apoptosis nor glial activation. Thirdly, immunohistochemical quantification of different markers of adult olfactory neurogenesis showed that inhalant treatments do not change the number of proliferating progenitors in the SVZ and the rostral migratory stream (RMS), as well as the number of newborn cells reaching and integrating in the OB circuitry. Altogether, our data highlight that the impaired olfactory performances in chronically-exposed mice are not associated to an alteration of adult neurogenesis in the SVZ-OB system.

Cu/HZSM-5 Sorbent Treated by NH3 Plasma for Low-Temperature Simultaneous Adsorption-Oxidation of H2S and PH3

In this study, an NH₃ plasma-treated Cu/HZSM-5 sorbent was introduced to simultaneously remove H₂S and PH₃ in low-temperature and low-oxygen environments. The effects of the Cu loading amounts, modification methods, and plasma-treatment conditions on the adsorption-oxidation performance of the sorbents were investigated. From the performance test results, the sorbent treated by NH₃ plasma with the specific energy input (SEI, electrical input energy to the unit volume of gas) value of 1 J·mL^-1 (Cu/HZSM-5-[S1]) was identified as having the highest breakthrough capacities of 108.9 mg S·g^-1 and 150.9 mg P·g^-1 among all of the materials tested. After three times of regeneration, the sorbent can still maintain the ideal performance. The results of Fourier transform infrared (FT-IR) spectroscopy and CO₂ temperature-programmed desorption (CO₂-TPD) indicated that the NH₃ plasma treatment can introduce amino groups (functional groups) onto the sorbent surface, which greatly increases the number and strength of the basic sites on the sorbent surface. Results of N₂ adsorption/desorption isotherms and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) showed that the morphology of the sorbent changed after the plasma treatment, which exposed more active sites (copper species). In situ IR spectra showed that the amino groups are continuously consumed during the reaction process, indicating that these amino groups can help sorbents to capture gas molecules. Moreover, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses indicated that CuO is the main active species and the consumption of CuO and accumulation of the reaction products on the surface and inner pores of the sorbent are the primary reasons for the deactivation of the sorbent.

Application of adverse outcome pathway networks to integrate mechanistic data informing the choice of a point of departure for hydrogen sulfide exposure limits

Acute exposure to hydrogen sulfide initiates a series of hallmark biological effects that occur progressively at increasing exposure levels: odor perception, conjunctivitis, olfactory paralysis, "knockdown," pulmonary edema, and apnea. Although effects of exposure to high concentrations of hydrogen sulfide are clear, effects associated with chronic, low-level exposure in humans is under debate, leading to uncertainty in the critical effect used in regulatory risk assessments addressing low dose exposures. This study integrates experimental animal, observational epidemiology, and occupational exposure evidence by applying a pathway-based approach. A hypothesized adverse outcome pathway (AOP) network was developed from 34 studies, composed of 4 AOPs sharing 1 molecular initiating events (MIE) and culminating in 4 adverse outcomes. A comparative assessment of effect levels and weight of evidence identified an AOP leading to a biologically-plausible, low-dose outcome relative to the other outcomes (nasal lesions, 30 ppm versus olfactory paralysis, >100 ppm; neurological effects, >80 ppm; pulmonary edema, >80 ppm). This AOP (i.e. AOP1) consists of the following key events: cytochrome oxidase inhibition (>10 ppm), neuronal cell loss (>30 ppm), and olfactory nasal lesions (defined as both neuronal cell loss and basal cell hyperplasia; >30 ppm) in rodents. The key event relationships in this pathway were supported by moderate empirical evidence and have high biological plausibility due to known mechanistic understanding and consistency in observations for diverse chemicals.

The Scientific Basis for Occupational Exposure Limits for Hydrogen Sulphide-A Critical Commentary

OBJECTIVES

Occupational exposure limits for hydrogen sulphide (H₂S) vary considerably; three expert group reports, published from 2006 to 2010, each recommend different limits. Some jurisdictions are considering substantial reductions.

METHODS

This review assesses the scientific evidence used in these recommendations and presents a new systematic review of human studies from 2006-20, identifying 33 studies.

RESULTS

The three major reports all give most weight to two sets of studies: of physiological effects in human volunteers, and of effects in the nasal passages of rats and mice. The human studies were done in one laboratory over 20 years ago and give inconsistent results. The breathing style and nasal anatomy of rats and mice would make them more sensitive than humans to inhaled agents. Each expert group applied different uncertainly factors. From these reports and the further literature review, no clear evidence of detrimental health effects from chronic occupational exposures specific to H₂S was found. Detailed studies of individuals in communities with natural sources in New Zealand have shown no detrimental effects. Studies in Iceland and Italy show some associations; these and various other small studies need verification.

CONCLUSIONS

The scientific justification for lowering occupational exposure limits is very limited. There is no clear evidence, based on currently available studies, that lower limits will protect the health of workers further than will the current exposure limits used in most countries. Further review and assessment of relevant evidence is justified before exposure limits are set.

Case Report: Two Cases of Keratoconjunctivitis Tied to Sargassum Algae Emanations

Since 2011, considerable amounts of Sargassum algae regularly end up on beaches in the Gulf of Mexico, the Caribbean, and in the French overseas departments. We report observations of two bilateral keratoconjunctivitis associated with important functional symptomatology. There was a conjunctival hyperemia and superficial punctate keratitis. The ocular impairment would repeat at every algae ashore landing. Clinical examination, history, and time line of symptomatology onset allowed us to eliminate the classic etiologies of bilateral keratoconjunctivitis and to suggest an irritant toxic origin tied to hydrogen sulfide. This is the first description of ocular impairment tied to Sargassum algae decomposition. Their decomposition, through H2S emission, can be at the origin of bilateral keratoconjunctivitis. Ocular impairment is often at the forefront of complaints made by individuals exposed to H2S.

Use of Nasal Pathology in the Derivation of Inhalation Toxicity Values for Hydrogen Sulfide

Nasal pathology can play an important role in the risk assessment process. For example, olfactory neuron loss (ONL) is one of the most sensitive end points seen in subchronic rodent hydrogen sulfide (H₂S) studies and has been used by several agencies to derive health-protective toxicity values. Alternative methods that rely on computational fluid dynamics (CFD) models to account for the influence of airflow on H₂S-induced ONL have been proposed. The use of CFD models result in toxicity values that are less conservative than those obtained using more traditional methods. These alternative approaches rely on anatomy-based CFD models. Model predictions of H₂S delivery (flux) to the olfactory mucosal wall are highly correlated with ONL in rodents. Three major areas of focus for this review include a brief description of nasal anatomy, H₂S-induced ONL in rodents, derivation of a chronic inhalation reference concentration for H₂S, and the use of CFD models to derive alternative toxicity values for this gas.

Occupational exposure during treatment of offshore drilling waste and characterization of microbiological diversity

The exposure for workers handling and recycling offshore drilling waste are previously not described, and given the potential for exposure to hazardous components, there is a need for characterizing this occupational exposure. In this study five plants recycling offshore drilling waste with different techniques were included. Measurements were conducted in both winter and summer to include seasonal exposure variations. Altogether >200 personal air-exposure measurements for oil mist, oil vapor, volatile organic compounds (VOC), hydrogen sulfide (H₂S) and solvents were carried out respectively. Microorganisms related to drilling waste were identified in bulk samples and in stationary air measurements from two of the plants. The exposure to oil mist and oil vapor were below 10% of the current Norwegian occupational exposure limits (OEL) for all measured components. The plants using the Resoil or TCC method had a statistically significant higher exposure to oil vapor than the plant using complete combustion (p-value <0.05). No statistically significant difference was found between the different treatment methods for oil mist. The exposure to solvents was generally low (additive factor < 0.03). Endotoxin measurements done during winter showed a median concentration of 5.4 endotoxin units (EU)/m³. Levels of H₂S above the odor threshold of 0.1 ppm were measured at four plants. Both drill mud and slop water contained a high number and diversity of bacteria (2-4 × 10⁴ colony forming unit (CFU)/mL), where a large fraction was Gram-negative species. Some of the identified microorganisms are classified as potentially infectious pathogens for humans and thus might be a hazard to workers.

Does cigarette smoke exposure lead to histopathological alterations in the olfactory epithelium? An electron microscopic study on a rat model

OBJECTIVE

This study was conducted to examine the influence of smoke exposure of variable duration on the ultrastructure of and histopathologic and morphologic alterations in the olfactory epithelium.

METHODS

A total of 24 Wistar albino rats were randomly assigned to three groups and fed a standard rat chow and tap water. Experimental rats in groups I and II were exposed to cigarette smoke in a glass cabin over a period of 2 months for 5 or 15 min, respectively, four times daily; control rats (group III) were not exposed to cigarette smoke. After dissection, all tissue specimens were processed using routine procedures for TEM.

RESULTS

Groups I and II exhibited the presence of intraepithelial inflammatory cells and especially deep invaginations in the nuclear membrane of supporting cells. Extended intercellular spaces, cytoplasmic protrusions on the apical surface of supporting cells, atrophy of microvilli and olfactory neuron cilia as well as numerous electron-dense granular structures and lysosome-like structures were observed to an increasing degree from group I to group II. Particularly in group II, both supporting cells and olfactory neurons exhibited a cytoplasmic edema, mitochondrial degeneration, and numerous vacuolar structures, as well as apoptotic and minimal necrotic changes. In this group, hyperplasia of basal cells was also observed.

CONCLUSION

Our electron microscopic findings show that cigarette smoke leads to toxic degenerative changes in the rat olfactory mucosa.

Hydrogen sulphide exposure in waste water treatment

Background

The aims of this study was to assess exposure to hydrogen sulphide (H₂S) among waste water treatment workers (WWWs), and achieve a better measure of the risks of H₂S exposure than only using the eight-hour average value and the ceiling value because the exposure pattern of H₂S for WWWs is dominated by short-term peaks.

Methods

Ninety-three measurements of H₂S from 56 WWWs in three cities and three rural areas were collected. All exposure measurements were carried out from the start of the day until lunch time (sampling time 4–5 h) when most of the practical work was performed. The type of tasks and extent of flushing were registered. H₂S was measured using direct-reading instruments with logging: OdaLog L2/LL, Dräger X-am 5000 and Dräger Pac 7000 (0.1–200 ppm). Number and duration of peaks for different work tasks, seasons, places and extent of flushing were combined in an exposure index (IN), and evaluated in a mixed-model analysis, building a model aimed to predict exposure for different job tasks.

Results

Nine Percent (8 of 93) of all H₂S measurements have peaks above 10 ppm; in addition, 15% (14 of 93) have peaks of 5–10 ppm, 35% (33 of 93) have peaks of 1–5 ppm and 65% (62 of 93) have peaks of 0.1–1 ppm. 29% of the measurements of hydrogen sulphide showed no registered level > 0.1 ppm.

From the mixed-model analyses we see that exposure level, expressed as H₂S index IN, varied between places, work type, season and degree of flushing. For the work in a plant in the capital, the exposure index varied from 0.02 for working in spring doing some flushing, to 0.7 for working at the same plant in winter doing flushing more than three times or more than 10 min. Collecting sewage from cesspools in city 2 in winter doing a lot of flushing gave a hydrogen sulphide index of 230.

Conclusions

The use of a H₂S index, taking into consideration peak height, duration and number of peaks, could be a tool for exposure assessment for H₂S.

Hydrogen Sulfide Specifically Alters NAD(P)H Quinone Dehydrogenase 1 (NQO1) Olfactory Neurons in the Rat

The regions of the olfactory epithelium affected by hydrogen sulfide (H₂S) toxicity in the rat present a striking similarity with the developmental olfactory zone 1 described in the mouse. This zone which is the only region containing neurons expressing NAD(P)H quinone dehydrogenase 1 (NQO1) is involved in complex behavioral responses in rodents, and other mammals, triggered by specific olfactory stimuli. We therefore sought to determine whether (1) olfactory neurons expressing NQO1 are located in the same regions in the rats and in the mice and (2) there is an overlap between olfactory neurons expressing this protein and those affected by the toxicity of H₂S. Rats were exposed to H₂S - 200 ppm during 3 h, three consecutive days- and displayed symmetric acute segmental necrosis of the neurons and sustentacular cells of the olfactory epithelium in the dorsomedial nasal cavity. We found that expression of NQO1 in Sprague-Dawley rats spatially recapitulated that of the mouse. The degree of agreement or overlap between these two populations of neurons (necrosis vs. NQO1 expression) reached 80.2%. Although the underlying mechanisms accounted for the high sensitivity for NQO1 neurons -or the relative protection of non NQO1 neurons- to sulfide toxicity remain to be established, this observation is offering an intriguing approach that could be used to acutely suppress the pool of neural cells in olfactory zone I and to understand the mechanisms of toxicity and protection of other populations of neurons exposed to sulfide.

Environmental Toxicants-Induced Immune Responses in the Olfactory Mucosa

Olfactory sensory neurons (OSNs) are the receptor cells for the sense of smell. Although cell bodies are located in the olfactory mucosa (OM) of the nasal cavity, OSN axons directly project to the olfactory bulb (OB) that is a component of the central nervous system (CNS). Because of this direct and short connection from this peripheral tissue to the CNS, the olfactory system has attracted attention as a port-of-entry for environmental toxicants that may cause neurological dysfunction. Selected viruses can enter the OB via the OM and directly affect the CNS. On the other hand, environmental toxicants may induce inflammatory responses in the OM, including infiltration of immune cells and production of inflammatory cytokines. In addition, these inflammatory responses cause the loss of OSNs that are then replaced with newly generated OSNs that re-connect to the OB after inflammation has subsided. It is now known that immune cells and cytokines in the OM play important roles in both degeneration and regeneration of OSNs. Thus, the olfactory system is a unique neuroimmune interface where interaction between nervous and immune systems in the periphery significantly affects the structure, neuronal circuitry, and immunological status of the CNS. The mechanisms by which immune cells regulate OSN loss and the generation of new OSNs are, however, largely unknown. To help develop a better understanding of the mechanisms involved, we have provided a review of key research that has investigated how the immune response in the OM affects the pathophysiology of OSNs.

Ultrastructural changes in epithelial cells of rats exposed to low concentration of hydrogen sulfide for 50 days

Hydrogen sulfide (H₂S) and other volatile sulfur compounds (VSCs) appear mainly in the oral air of patients with halitosis. It seems that VSCs are directly involved in the pathogenesis of gingival diseases. In previous studies, short-term (7 hours-4 days), high concentrations (5-400 ppm) of H₂S applications on periodontal tissues have been evaluated in a culture medium. The aim of the present study was to investigate the potential effects of lower (equivalent to halitosis) concentrations of H₂S on rat gingival tissue for longer-term inhalation. The threshold level of pathologic halitosis perceived by humans at 250 ppb of H₂S was converted to rat equivalent concentration (4.15 ppm). Rats in the experimental (H₂S) group (n=8) were exposed to H₂S continuously but not the control rats (n=8). After 50 days, the gingival sulcular tissue samples of each rat were taken and examined using transmission electron microscope. Ultrastructural changes in the sulcular epithelia of the rat gingiva showed deformation of celullar shape, vacuolization, and disintegrity of intercelullar connection by loss of desmosomes and collagen fibrils. No basal membrane damage was observed. Inhalation of low levels of H₂S (equivalent of halitosis) in the oral environment causes ultrastructural celullar damages in rat sulcular mucosa. These results suggest that halitosis may be the potential reason for periodontal destruction in humans.

Structural changes in periodontium of rats exposed to a low concentration of hydrogen sulfide for 50 days

The aim of the present study was to investigate the effect of H2S inhalation at a low concentration (at human equivalent dose of pathologic halitosis) on rat periodontium over a long term (50 days). The threshold level of pathologic halitosis perceived by humans at 250 ppb of H2S was converted to rat equivalent concentration (4.15 ppm). Rats in the experimental (H2S) group (n = 8) were exposed to H2S continuously but not the control rats (n = 8). After 50 days, periodontal tissue samples were taken from the mandibular first molar region and examined histopathologically to determine inflammatory cell infiltration (ICI), osteoblastic activities, number of osteoclasts, and resorption lacunae.

Sulcular epithelium layer destruction was observed in the H2S group. Frequency of ICI was significantly higher in the H2S group compared to the control group ( P <0.05). The number of osteoclasts were found significantly higher in the H2S group (34.28 ± 3.28) compared to the control group (8.85 ± 1.85) ( P <0.05) and the number of resorption lacunae were also higher in the cementum tissue (6.1 ± 2.4) and alveolar bone (3.8 ± 1.5) versus their corresponding control groups (1.6 ± 0.5 and 1.4 ± 0.5, respectively) ( P <0.05). There were no statistically significant differences between the two groups with regard to osteoblastic activity. H2S inhalation induces inflammatory changes in the periodontium as well as resorption of the alveolar bone and cementum tissue in rats. These histopathologic changes in periodontal tissues support the idea that long-term H2S inhalation may have a destructive effect on periodontal tissues.

Developing effective countermeasures against acute hydrogen sulfide intoxication: challenges and limitations

Hydrogen sulfide (H2 S) is a chemical hazard in the gas and farming industry. As it is easy to manufacture from common chemicals, it has also become a method of suicide. H2 S exerts its toxicity through its high affinity with metalloproteins, such as cytochrome c oxidase and possibly via its interactions with cysteine residues of various proteins. The latter was recently proposed to acutely alter ion channels with critical implications for cardiac and brain functions. Indeed, during severe H2 S intoxication, a coma, associated with a reduction in cardiac contractility, develops within minutes or even seconds leading to death by complete electromechanical dissociation of the heart. In addition, long-term neurological deficits can develop owing to the direct toxicity of H2 S on neurons combined with the consequences of a prolonged apnea and circulatory failure. Here, we review the challenges impeding efforts to offer an effective treatment against H2 S intoxication using agents that trap free H2 S, and present novel pharmacological approaches aimed at correcting some of the most harmful consequences of H2 S intoxication.

Assessment of Potential Health Hazards During Emission of Hydrogen Sulphide from the Mine Exploiting Copper Ore Deposit - Case Study

AIM

The aim of this study was to determine hydrogen sulphide concentration emitted from the mine extracting copper ore, to evaluate potential adverse health effects to the population living in four selected villages surrounding the exhaust shaft.

MATERIALS

Maximum measured concentration of hydrogen sulphide in the emitter is 286 µg/m³. Maximum emission calculated from the results of determinations of concentrations in the emitter is 0.44 kg/h.

RESULTS

In selected villages hydrogen sulphide at concentrations exceeding 4 µg/m³ was not detected in any of the 5-hour air samples. In all locations, the estimated maximum 1-hour concentrations of hydrogen sulphide were below 1 µg/m³, and the estimated mean annual concentrations were below 0.53 µg/m³.

CONCLUSION

Any risk to the health of people in the selected area is not expected. As indicated by the available data on the threshold odour, the estimated concentrations of hydrogen sulphide may be sensed by humans.

Activating transcription factor 5 is required for mouse olfactory bulb development via interneuron

Activating transcription factor 5 (ATF5) is a stress response transcription factor of the cAMP-responsive element-binding/ATF family. Earlier, we reported that ATF5 expression is up-regulated in response to stress, such as amino acid limitation or arsenite exposure. Although ATF5 is widely expressed in the brain and the olfactory epithelium, the role of ATF5 is not fully understood. Here, the olfactory bulbs (OBs) of ATF5-deficient mice are smaller than those of wild-type mice. Histological analysis reveals the disturbed laminar structure of the OB, showing the thinner olfactory nerve layer, and a reduced number of interneurons. This is mainly due to the reduced number of bromodeoxyuridine-positive proliferating cells in the subventricular zone, where the interneuron progenitors are formed and migrate to the OBs. Moreover, the olfaction-related aggressive behavior of ATF5-deficient mice is reduced compared to wild-type mice. Our data suggest that ATF5 plays a crucial role in mouse OB development via interneuron.

Hydrogen sulfide intoxication

Hydrogen sulfide (H2S) is a hazard primarily in the oil and gas industry, agriculture, sewage and animal waste handling, construction (asphalt operations and disturbing marshy terrain), and other settings where organic material decomposes under reducing conditions, and in geothermal operations. It is an insoluble gas, heavier than air, with a very low odor threshold and high toxicity, driven by concentration more than duration of exposure. Toxicity presents in a unique, reliable, and characteristic toxidrome consisting, in ascending order of exposure, of mucosal irritation, especially of the eye ("gas eye"), olfactory paralysis (not to be confused with olfactory fatigue), sudden but reversible loss of consciousness ("knockdown"), pulmonary edema (with an unusually favorable prognosis), and death (probably with apnea contributing). The risk of chronic neurcognitive changes is controversial, with the best evidence at high exposure levels and after knockdowns, which are frequently accompanied by head injury or oxygen deprivation. Treatment cannot be initiated promptly in the prehospital phase, and currently rests primarily on supportive care, hyperbaric oxygen, and nitrite administration. The mechanism of action for sublethal neurotoxicity and knockdown is clearly not inhibition of cytochrome oxidase c, as generally assumed, although this may play a role in overwhelming exposures. High levels of endogenous sulfide are found in the brain, presumably relating to the function of hydrogen sulfide as a gaseous neurotransmitter and immunomodulator. Prevention requires control of exposure and rigorous training to stop doomed rescue attempts attempted without self-contained breathing apparatus, especially in confined spaces, and in sudden release in the oil and gas sector, which result in multiple avoidable deaths.

Neurotoxic exposure and impairment of the chemical senses of taste and smell

The chemical senses of taste and smell determine the flavor of foods and beverages, guide appropriate food intake, and warn of such environmental hazards as spoiled or poisonous food, leaking natural gas, smoke, and airborne pollutants. This chapter addresses the influences of neurotoxic exposures on human chemoreception and provides basic information on the adverse influences of such exposures on rodent epithelia. The focus of the chapter is in olfaction, given dearth of empiric research on the effects of neurotoxic chemical exposures on the sense of taste, i.e., sweet, sour, bitter, salty, and savory sensations. As will be apparent from the chapter, numerous neurotoxins--many of which are encountered in industrial workplaces--alter the ability to smell, including solvents, metals, and particulate matter. The olfactory system is particularly vulnerable to such agents since its receptors are more or less directly exposed to the outside environment. Importantly, some such agents can enter the brain via the olfactory nerve or surrounding perineural spaces, bypassing the blood-brain barrier and damaging central nervous system structures and inducing pathologic processes that appear to be similar to those seen in neurodegenerative diseases such as Alzheimer's and Parkinson's.

Short-term effects of subchronic low-level hydrogen sulfide exposure on oil field workers

OBJECTIVES

To investigate the short-term effects of low-level hydrogen sulfide (H2S) exposure on oil field workers.

MATERIALS AND METHODS

Observational study included 34 patients who work at an oil field. All patients were males with age range of 22-60 years (mean 37 years). The data were collected by systematic questionnaire about symptoms. The inclusion criteria of patients were symptoms related to inhalation of H2S gas in the oil field. The complaints should be frequent and relapsed after each gas exposure and disappeared when there was no gas exposure. Exclusion criteria were the symptoms which experienced with or without H2S exposure. The presence of H2S gas was confirmed by valid gas detector devices.

RESULTS

The most frequent presenting symptom was nasal bleeding. It was revealed in 18 patients (52.9%). This followed by pharyngeal bleeding, gum bleeding, and bloody saliva (mouth bleeding) which were encountered in five cases for each complaint (14.7%). Other less frequent presenting symptoms were tongue bleeding, bloody sputum, headache, abdominal colic, pharyngeal soreness, fatigue, and sleepiness.

CONCLUSIONS

Nasal mucosa was the most vulnerable part to H2S effect. Inhalation of H2S produced upper respiratory tract epithelial damage that led to bleeding from nose, pharynx, gum, tongue, trachea, and bronchi. There were no complaints of asthmatic attack upon exposure to low level of H2S. Sunlight had a significant role in reduction of ambient air H2S level.

Sensory irritation as a basis for setting occupational exposure limits

There is a need of guidance on how local irritancy data should be incorporated into risk assessment procedures, particularly with respect to the derivation of occupational exposure limits (OELs). Therefore, a board of experts from German committees in charge of the derivation of OELs discussed the major challenges of this particular end point for regulatory toxicology. As a result, this overview deals with the question of integrating results of local toxicity at the eyes and the upper respiratory tract (URT). Part 1 describes the morphology and physiology of the relevant target sites, i.e., the outer eye, nasal cavity, and larynx/pharynx in humans. Special emphasis is placed on sensory innervation, species differences between humans and rodents, and possible effects of obnoxious odor in humans. Based on this physiological basis, Part 2 describes a conceptual model for the causation of adverse health effects at these targets that is composed of two pathways. The first, “sensory irritation” pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing). While the first stages of this pathway are thought to be completely reversible, high or prolonged exposure can lead to neurogenic inflammation and subsequently tissue damage. The second, “tissue irritation” pathway starts with the interaction of the local irritant with the epithelial cell layers of the eyes and the URT. Adaptive changes are the first response on that pathway followed by inflammation and irreversible damages. Regardless of these initial steps, at high concentrations and prolonged exposures, the two pathways converge to the adverse effect of morphologically and biochemically ascertainable changes. Experimental exposure studies with human volunteers provide the empirical basis for effects along the sensory irritation pathway and thus, “sensory NOAEC_human” can be derived. In contrast, inhalation studies with rodents investigate the second pathway that yields an “irritative NOAEC_animal.” Usually the data for both pathways is not available and extrapolation across species is necessary. Part 3 comprises an empirical approach for the derivation of a default factor for interspecies differences. Therefore, from those substances under discussion in German scientific and regulatory bodies, 19 substances were identified known to be human irritants with available human and animal data. The evaluation started with three substances: ethyl acrylate, formaldehyde, and methyl methacrylate. For these substances, appropriate chronic animal and a controlled human exposure studies were available. The comparison of the sensory NOAEC_human with the irritative NOAEC_animal (chronic) resulted in an interspecies extrapolation factor (iEF) of 3 for extrapolating animal data concerning local sensory irritating effects. The adequacy of this iEF was confirmed by its application to additional substances with lower data density (acetaldehyde, ammonia, n-butyl acetate, hydrogen sulfide, and 2-ethylhexanol). Thus, extrapolating from animal studies, an iEF of 3 should be applied for local sensory irritants without reliable human data, unless individual data argue for a substance-specific approach.

Postnatal odorant exposure induces peripheral olfactory plasticity at the cellular level

Mammalian olfactory sensory neurons (OSNs) form the primary elements of the olfactory system. Inserted in the olfactory mucosa lining of the nasal cavity, they are exposed to the environment and their lifespan is brief. Several reports say that OSNs are regularly regenerated during the entire life and that odorant environment affects the olfactory epithelium. However, little is known about the impact of the odorant environment on OSNs at the cellular level and more precisely in the context of early postnatal olfactory exposure. Here we exposed MOR23-green fluorescent protein (GFP) and M71-GFP mice to lyral or acetophenone, ligands for MOR23 or M71, respectively. Daily postnatal exposure to lyral induces plasticity in the population of OSNs expressing MOR23. Their density decreases after odorant exposure, whereas the amount of MOR23 mRNA and protein remain stable in the whole epithelium. Meanwhile, quantitative PCR indicates that each MOR23 neuron has higher levels of olfactory receptor transcripts and also expresses more CNGA2 and phosphodiesterase 1C, fundamental olfactory transduction pathway proteins. Transcript levels return to baseline after 4 weeks recovery. Patch-clamp recordings reveal that exposed MOR23 neurons respond to lyral with higher sensitivity and broader dynamic range while the responses' kinetics were faster. These effects are specific to the odorant-receptor pair lyral-MOR23: there was no effect of acetophenone on MOR23 neurons and no effect of acetophenone and lyral on the M71 population. Together, our results clearly demonstrate that OSNs undergo specific anatomical, molecular, and functional adaptation when chronically exposed to odorants in the early stage of life.

Postnatal odorant exposure induces peripheral olfactory plasticity at the cellular level

Mammalian olfactory sensory neurons (OSNs) form the primary elements of the olfactory system. Inserted in the olfactory mucosa lining of the nasal cavity, they are exposed to the environment and their lifespan is brief. Several reports say that OSNs are regularly regenerated during the entire life and that odorant environment affects the olfactory epithelium. However, little is known about the impact of the odorant environment on OSNs at the cellular level and more precisely in the context of early postnatal olfactory exposure. Here we exposed MOR23-green fluorescent protein (GFP) and M71-GFP mice to lyral or acetophenone, ligands for MOR23 or M71, respectively. Daily postnatal exposure to lyral induces plasticity in the population of OSNs expressing MOR23. Their density decreases after odorant exposure, whereas the amount of MOR23 mRNA and protein remain stable in the whole epithelium. Meanwhile, quantitative PCR indicates that each MOR23 neuron has higher levels of olfactory receptor transcripts and also expresses more CNGA2 and phosphodiesterase 1C, fundamental olfactory transduction pathway proteins. Transcript levels return to baseline after 4 weeks recovery. Patch-clamp recordings reveal that exposed MOR23 neurons respond to lyral with higher sensitivity and broader dynamic range while the responses' kinetics were faster. These effects are specific to the odorant-receptor pair lyral-MOR23: there was no effect of acetophenone on MOR23 neurons and no effect of acetophenone and lyral on the M71 population. Together, our results clearly demonstrate that OSNs undergo specific anatomical, molecular, and functional adaptation when chronically exposed to odorants in the early stage of life.

Removal of vapor-phase elemental mercury from stack emissions with sulfur-impregnated activated carbon

This systematic review of high-quality, relevant original research articles existing in the literature was conducted to comprehensively explore the efficiency of Hg11 capture from stack emissions by sulfur-impregnated vs. virgin ACs. Our systematic overview suggested that significantly higher amounts of Hg0 are absorbed by sulfurimpregnated ACs than by virgin ones ( 1.5-32 times higher, based on the applied operational conditions). The main reason for this is because Hg11 capture by virgin ACs follows a physisorption mechanism, whereas that by sulfur-impregnated ACs occurs from a combination of physisorption of Hg11 on carbon texture and chemical reaction between Hg0 and impregnated sulfur, with subsequent formation of HgS. Temperature increased the Hg0 adsorption capacity of virgin ACs, especially when temperatures exceeded 100 oc. For sulfur-impregnated ACs, increasing the temperature up to I 00 oc increased the Hg0 adsorption capacity by enhancing the chemisorption of Hg0 capture. A further increase in temperature enhanced the efficiency of ACs that were impregnated with Sat higher temperatures (600 °C, for instance). This mainly resulted from production of stronger bonding of sulfur to carbon at higher impregnation temperatures and also from a more even distribution of sulfur in the carbon matrix. The authors of different papers reported different results with respect to whether there is an effect of initial Hg11 concentration on AC adsorption capacity. The authors of two studies could find no such etl'ect. The predominant evidence, however, favors the view that increased Hg0 adsorption capacities exist at higher inlet Hg0 concentrations. Such behavior is attributed to faster kinetics of Hg0 capture and an enhanced higher driving force at higher initial Hg0 inlet concentrations. Results from reviewed studies also indicated that the optimum SIC ratio and sulfur content are 2/1 and I 0-20%, respectively. Surface area has a less significant impact on Hg11 adsorption capacity than does sulfur content. However, at equivalent sulfur content, AC surface area also becomes an important factor, in that Hg0 adsorption capacity is accentuated at higher surface areas. We conclude from having prepared this review that sulfur-impregnated ACs have significantly greater efficiencies than virgin ACs for capturing Hg0 from stack emissions. Therefore, using them is more cost effective than using raw ACs; using them can also partly resolve the problem of high costs posed by applying carbon sorbents. In addition, the sulfur deposited in the ACs impregnated at higher temperatures is more evenly distributed in the carbon micropores and binds more strongly to the carbon matrix. Hence, sulfur-impregnated ACs can retain higher Hg0 adsorption capacities under actual stack conditions, if the temperature is at least 140 oc. Finally, since the major mechanism for Hg'l removal by sulfur-impregnated ACs is through the chemical reaction between Hg0 and S. and subsequent formation via strong bonds of HgS, the Hg'i adsorbed on ACs is quite stable and is not easily released when discharged as waste to the environment.

Formation of (FexMn(2-x))O3 solid solution and high sulfur capacity properties of Mn-based/M41 sorbents for hot coal gas desulfurization

Several MCM-41 materials were synthesized at different conditions by hydrothermal procedure using cheap and easily available industrial water glass as silica source. Fe doped manganese-based oxide/MCM-41 sorbents were prepared by a sol-gel method. The effects of loadings of metal oxide, Fe/Mn molar ratios over MCM-41 and reaction temperature on the performance of sorbent for hot coal gas desulfurization were investigated. Various techniques such as BET, XRD, XPS, LRS and HRTEM were used to characterize the sorbents. The result indicated Fe(3+) ions could occupy a position of Mn(3+) in cubic lattice of Mn2O3 and the (FexMn2-x)O3 solid solution is mainly active phase of sorbent. Moreover, the result of nine successive sulfurization-regeneration cycles of sorbent showed high sulfur adsorption capacity and endurable stability of FeMn4Ox/MCM-41 for H2S removal.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

Elevated corrosion rates and hydrogen sulfide in homes with 'Chinese Drywall'

In December 2008, the U.S. Consumer Product Safety Commission (CPSC) began receiving reports about odors, corrosion, and health concerns related to drywall originating from China. In response, a detailed environmental health and engineering evaluation was conducted of 41 complaint and 10 non-complaint homes in the Southeast U.S. Each home investigation included characterization of: 1) drywall composition; 2) indoor and outdoor air quality; 3) temperature, moisture, and building ventilation; and 4) copper and silver corrosion rates. Complaint homes had significantly higher hydrogen sulfide concentrations (mean 0.82 vs. <LOD μg/m(3), p<0.05), and significantly greater rates of copper sulfide and silver sulfide corrosion compared to non-complaint homes (Cu(2)S: 476 vs. <32 Å/30 d, p<0.01; Ag(2)S: 1472 vs. 389 Å/30 d, p<0.01). The abundance of carbonate and strontium in drywall was also elevated in complaint homes, and appears to be useful objective marker of problematic drywall in homes that meet other screening criteria (e.g., constructed or renovated in 2006-2007, reports of malodor and accelerated corrosion). This research provides empirical evidence of the direct association between homes constructed with 'Chinese Drywall' in 2006-2007 and elevated corrosion rates and hydrogen sulfide concentrations in indoor air.

Effect of precursor and preparation method on manganese based activated carbon sorbents for removing H2S from hot coal gas

Activated carbon (AC) supported manganese oxide sorbents were prepared by the supercritical water impregnation (SCWI) using two different precursor of Mn(NO(3))(2) (SCW(N)) and Mn(Ac)(2)·4H(2)O (SCW(A)). Their capacities of removing H(2)S from coal gas were evaluated and compared to the sorbents prepared by the pore volume impregnation (PVI) method. The structure and composition of different sorbents were characterized by XRD, SEM, TEM, XPS and XANES techniques. It is found that the precursor of active component plays the crucial role and SCW(N) sorbents show much better sulfidation performance than the SCW(A) sorbents. This is because the Mn(3)O(4) active phase of the SCW(N) sorbents are well dispersed on the AC support, while the Mn(2)SiO(4)-like species in the SCW(A) sorbent can be formed and seriously aggregated. The SCW(N) sorbents with 2.80% and 5.60% manganese are favorable for the sulfidation reaction, since the Mn species are better dispersed on the SCW(N) sorbents than those on the PV(N) sorbents and results in the better sulfidation performance of the SCW(N) sorbents. As the Mn content increases to 11.20%, the metal oxide particles on AC supports aggregate seriously, which leads to poorer sulfidation performance of the SCW(N)11.20% sorbents than that of the PV(N)11.20% sorbents.

Hydrogen sulfide induced disruption of Na+ homeostasis in the cortex

Maintenance of ionic balance is essential for neuronal functioning. Hydrogen sulfide (H(2)S), a known toxic environmental gaseous pollutant, has been recently recognized as a gasotransmitter involved in numerous biological processes and is believed to play an important role in the neural activities under both physiological and pathological conditions. However, it is unclear if it plays any role in maintenance of ionic homeostasis in the brain under physiological/pathophysiological conditions. Here, we report by directly measuring Na(+) activity using Na(+) selective electrodes in mouse cortical slices that H(2)S donor sodium hydrosulfide (NaHS) increased Na(+) influx in a concentration-dependent manner. This effect could be partially blocked by either Na(+) channel blocker or N-methyl-D-aspartate receptor (NMDAR) blocker alone or almost completely abolished by coapplication of both blockers but not by non-NMDAR blocker. These data suggest that increased H(2)S in pathophysiological conditions, e.g., hypoxia/ischemia, potentially causes a disruption of ionic homeostasis by massive Na(+) influx through Na(+) channels and NMDARs, thus injuring neural functions. Activation of delta-opioid receptors (DOR), which reduces Na(+) currents/influx in normoxia, had no effect on H(2)S-induced Na(+) influx, suggesting that H(2)S-induced disruption of Na(+) homeostasis is resistant to DOR regulation and may play a major role in neuronal injury in pathophysiological conditions, e.g., hypoxia/ischemia.

Myocardial and lung injuries induced by hydrogen sulfide and the effectiveness of oxygen therapy in rats

OBJECTIVE

To study myocardial and lung injuries initiated by hydrogen sulfide, and evaluate the role and effectiveness of normobaric and hyperbaric oxygen (HBO) treatment in rats.

METHODS

One hundred healthy male Wistar rats were randomly divided into five groups: A: Normal control group (no H2S); B: H2S-exposed group; C: H2S+33% oxygen treatment group; D: H2S+50% oxygen treatment group; E: H2S+HBO group. The rats in groups C, D and E were exposed to H2S in an exposure chamber (1 m3) and were made to inhale 300 ppm hydrogen sulfide for 60 min, and then they were subjected to normobaric or HBO therapy. Normobaric oxygen was at concentrations of 33% or 50%, HBO was for 100 min including compression and decompression; the rats in group A inhaled air under the same conditions. Blood was sampled immediately after the experiment for analysis of arterial blood gases, myocardial enzymes and cardiac troponin I. Lung was rapidly removed to be made into tissue homogenates and then cytochrome c oxidase activity was measured; myocardial and lung ultrastructural changes were observed by electron microscopy.

RESULTS

Arterial blood gases: partial pressure of O2 (mmHg) (Group A, 97.6 ± 8.38; B, 76.5 ± 6.95*; C, 83.2 ± 2.66*; D, 86.20 ± 10.75*; E, 93.50 ± 4.97: *p < 0.01 compared to group A) was significantly lower than that in group in all but HBO rats. For myocardial enzymes and cardiac troponin I every parameter in groups B and C was significantly higher than that in group A (p<0.01),with no difference in D and E. Cytochrome c oxidase activity (u/mg) of lung tissue was reduced compared to group A after all treatments (A, 1.76 ± 0.02; B, 0.36 ± 0.04; C, 0.50 ± 0.12; D, 0.56 ± 0.07; E, 0.68 ± 0.05 (A vs. B p < 0.01; B vs. C,D,E p < 0.05 or p < 0.01), with a graded effect of oxygen dose in C, D and E. Pathological changes: (1) Myocardium - Mitochondrial swelling and autolysis with blurred or broken cristae was observed in the myocardium of H2S-exposed group; in group E, mitochondrial structure was basically normal, and clear cristae were found. (2) Lung tissue - In H2S-exposed group, alveolar epithelial cells disappeared, vacuolization of the organelle occurred, nuclear membrane was irregular and marginal condensation of heterochromatin was present; nucleus showed relatively normal morphology in group E, although some vacuoles still persisted within them.

CONCLUSIONS

HBO therapy can effectively improve arterial oxygen partial pressure, and significantly reduce myocardial damage, as well as potentially relieve lung injury in this model. Further work in humans appears warranted.

Hydrogen Sulfide

Hydrogen sulfide is a relatively common, frequently lethal, and unique occupational hazard for which research since 1990 has uncovered many anomalies and subtleties and a previously unsuspected physiological role for the endogenous agent. The result has been uncertainty and misunderstanding, particularly for persons new to the literature. This review addresses evidence that settles past controversies, guides practical issues in evaluating human toxicity, addresses unresolved issues involving chronic exposure, and points the way to a deeper understanding of the agent and its effects.

Low-level hydrogen sulfide and central nervous system dysfunction

Forty-nine adults living in Lovington, Tatum, and Artesia, the sour gas/oil sector of Southeastern New Mexico, were tested for neurobehavioral impairment. Contributing hydrogen sulfide were (1) an anaerobic sewage plant; (2) two oil refineries; (3) natural gas/oil wells and (4) a cheese-manufacturing plant and its waste lagoons. Comparisons were to unexposed Wickenburg, Arizona, adults. Neurobehavioral functions were measured in 26 Lovington adults including 23 people from Tatum and Artesia, New Mexico, and 42 unexposed Arizona people. Participants completed questionnaires including chemical exposures, symptom frequencies and the Profile of Mood States. Measurements included balance, reaction time, color discrimination, blink reflex, visual fields, grip strength, hearing, vibration, problem solving, verbal recall, long-term memory, peg placement, trail making and fingertip number writing errors (FTNWE). Average numbers of abnormalities and test scores were adjusted for age, gender, educational level, height and weight, expressed as percent predicted (% pred) and compared by analysis of variance (ANOVA). Ages and educational attainment of the three groups were not statistically significantly different (ssd). Mean values of Lovington residents were ssd from the unexposed Arizona people for simple and choice reaction times, balance with eyes open and closed, visual field score, hearing and grip strength. Culture Fair, digit symbol substitution, vocabulary, verbal recall, peg placement, trail making A and B, FTNWE, information, picture completion and similarities were also ssd. The Lovington adults who averaged 11.8 abnormalities were ssd from, Tatum—Artesia adults who had 3.6 and from unexposed subjects with 2.0. Multiple source community hydrogen sulfide exposures impaired neurobehavioral functions.

A computational fluid dynamics approach to assess interhuman variability in hydrogen sulfide nasal dosimetry

Human exposure to hydrogen sulfide (H(2)S) gas occurs from natural and industrial sources and can result in dose-related neurological, respiratory, and cardiovascular effects. Olfactory neuronal loss in H(2)S-exposed rats has been used to develop occupational and environmental exposure limits. Using nasal computational fluid dynamics (CFD) models, a correlation was found between wall mass flux and olfactory neuronal loss in rodents, suggesting an influence of airflow patterns on lesion locations that may affect interspecies extrapolation of inhaled dose. Human nasal anatomy varies considerably within a population, potentially affecting airflow patterns and dosimetry of inhaled gases. This study investigates interhuman variability of H(2)S nasal dosimetry using anatomically accurate CFD models of the nasal passages of five adults and two children generated from magnetic resonance imaging (MRI) or computed tomography (CT) scan data. Using allometrically equivalent breathing rates, steady-state inspiratory airflow and H(2)S uptake were simulated. Approximate locations of olfactory epithelium were mapped in each model to compare air:tissue flux in the olfactory region among individuals. The fraction of total airflow to the olfactory region ranged from 2% to 16%. Despite this wide range in olfactory airflow, H(2)S dosimetry in the olfactory region was predicted to be similar among individuals. Differences in the 99 th percentile and average flux values were <1.2-fold at inhaled concentrations of 1, 5, and 10 ppm. These preliminary results suggest that differences in nasal anatomy and ventilation among adults and children do not have a significant effect on H(2)S dosimetry in the olfactory region.

Proceedings of the Hydrogen Sulfide Health Research and Risk Assessment Symposium October 31-November 2, 2000

The Hydrogen Sulfide Health Research and Risk Assessment Symposium came about for several reasons: (1) increased interest by the U.S. Environmental Protection Agency (EPA) and several state agencies in regulating hydrogen sulfide (H2S); (2) uncertainty about ambient exposure to H2S; (3) confusion and disagreement in the literature about possible health effects at low-level exposures; and (4) presentation of results of a series of recent animal bioassays. The American Petroleum Institute (API) proposed this symposium and the EPA became an early co-sponsor, with the Chemical Industry Institute of Toxicology (CIIT) and the American Forest & Paper Association (AF&PA) contributing expertise and funding assistance. The topics covered in this symposium included Animal Research, Human Research, Mode-of-Action and Dosimetry Issues, Environmental Exposure and Monitoring, Assessment and Regulatory Issues, and closed with a panel discussion. The overall goals of the symposium were to: gather together experts in H2S health effects research and individuals from governmental agencies charged with protecting the public health, provide a venue for reporting of recent research findings, identify gaps in the current information, and outline new research directions and promote research collaboration. During the course of the symposium, presenters provided comprehensive reviews of the state of knowledge for each topic. Several new research proposals discussed at the symposium have subsequently been initiated. This report provides a summary of the talks, poster presentations, and panel discussions that occurred at the Hydrogen Sulfide Health and Risk Assessment Symposium.

Gene expression changes following acute hydrogen sulfide (H2S)-induced nasal respiratory epithelial injury

Hydrogen sulfide (H2S) is a naturally occurring gas that is also associated with several industries. The potential for widespread human inhalation exposure to this toxic gas is a public health concern. The nasal epithelium is especially susceptible to H2S-induced pathology. Injury to and regeneration of the nasal respiratory mucosa occurred in animals with ongoing H2S exposure, suggesting that the regenerated respiratory epithelium under-goes an adaptive response and becomes resistant to further injury. To better understand this response, ten-week-old male Sprague-Dawley rats were exposed nose-only to either air or 200 ppm H2S for three hours per day for one day or five consecutive days. Nasal respiratory epithelial cells at the site of injury and regeneration were laser capture microdissected, and gene expression profiles were generated at three, six, and twenty-four hours after the initial three-hour exposure and at twenty-four hours after the fifth exposure using the Affymetrix Rat Genome 230 2.0 microarray. Gene ontology enrichment analysis showed that H2S exposure altered gene expression associated with a variety of biological processes, including cell cycle regulation, protein kinase regulation, and cytoskeletal organization and biogenesis. Surprisingly, our results did not show a significant change in cytochrome oxidase gene expression or bioenergetics.

The nose revisited: a brief review of the comparative structure, function, and toxicologic pathology of the nasal epithelium

The nose is a very complex organ with multiple functions that include not only olfaction, but also the conditioning (e.g., humidifying, warming, and filtering) of inhaled air. The nose is also a "scrubbing tower" that removes inhaled chemicals that may be harmful to the more sensitive tissues in the lower tracheobronchial airways and pulmonary parenchyma. Because the nasal airway may also be a prime target for many inhaled toxicants, it is important to understand the comparative aspects of nasal structure and function among laboratory animals commonly used in inhalation toxicology studies, and how nasal tissues and cells in these mammalian species may respond to inhaled toxicants. The surface epithelium lining the nasal passages is often the first tissue in the nose to be directly injured by inhaled toxicants. Five morphologically and functionally distinct epithelia line the mammalian nasal passages--olfactory, respiratory, squamous, transitional, and lymphoepithelial--and each nasal epithelium may be injured by an inhaled toxicant. Toxicant-induced epithelial lesions in the nasal passages of laboratory animals (and humans) are often site-specific and dependent on the intranasal regional dose of the inhaled chemical and the sensitivity of the nasal epithelial tissue to the specific chemical. In this brief review, we present examples of nonneoplastic epithelial lesions (e.g., cell death, hyperplasia, metaplasia) caused by single or repeated exposure to various inhaled chemical toxicants. In addition, we provide examples of how nasal maps may be used to record the character, magnitude and distribution of toxicant-induced epithelial injury in the nasal airways of laboratory animals. Intranasal mapping of nasal histopathology (or molecular and biochemical alterations to the nasal mucosa) may be used along with innovative dosimetric models to determine dose/response relationships and to understand if site-specific lesions are driven primarily by airflow, by tissue sensitivity, or by another mechanism of toxicity. The present review provides a brief overview of comparative nasal structure, function and toxicologic pathology of the mammalian nasal epithelium and a brief discussion on how data from animal toxicology studies have been used to estimate the risk of inhaled chemicals to human health.

Effects of toluene inhalation exposure on olfactory functioning: behavioral and histological assessment

Exposure to pollutant or toxic substances is known to induce adverse health effects but few studies have been devoted to study the impact on olfactory functioning although neuroreceptors in the nasal cavity are directly in contact with volatile molecules. Thus, this work was designed to evaluate in mice the potential modifications of the olfactory functioning during (1 month) and after (1 month) a prolonged toluene exposure at both sensitive/perceptive and cellular levels. Mice were exposed to 1000ppm of toluene for 5h/day, 5days/week for 4 weeks. Firstly, behavioral evaluation (T-maze test) to toluene sensitivity showed a constant decrease during all the 4 weeks of exposure (W1-W4) which continued during 2 weeks after the exposure (W5, W6). In contrast, during the last 2 weeks of the experiment (W7, W8), the sensitivity of mice to toluene went back to normal. Secondly, structural modifications, i.e. density of cells and thickness of olfactory epithelium were observed soon after the outset of exposure. The number of cells did not change at the beginning of exposure (W1, W2), decreased markedly later (W3, W4), increased significantly the first week of the recovery period (W5) and stayed stable during the following weeks (W6-W8). Concerning the thickness of neuroepithelium, the results at W1 showed a decrease followed by an increase suggesting an inflammatory process (W2, W3). In contrast, the results of W4 revealed an abrupt decrease of the thickness whereas the return to normal arose immediately at the outset of recovery period.

Adsorption of hydrogen sulfide onto activated carbon fibers: effect of pore structure and surface chemistry

To understand the nature of H2S adsorption onto carbon surfaces under dry and anoxic conditions, the effects of carbon pore structure and surface chemistry were studied using activated carbon fibers (ACFs) with different pore structures and surface areas. Surface pretreatments, including oxidation and heattreatment, were conducted before adsorption/desorption tests in a fixed-bed reactor. Raw ACFs with higher surface area showed greater adsorption and retention of sulfur, and heat treatment further enhanced adsorption and retention of sulfur. The retained amount of hydrogen sulfide correlated well with the amount of basic functional groups on the carbon surface, while the desorbed amount reflected the effect of pore structure. Temperature-programmed desorption (TPD) and thermal gravimetric analysis (TGA) showed that the retained sulfurous compounds were strongly bonded to the carbon surface. In addition, surface chemistry of the sorbent might determine the predominant form of adsorbate on the surface.

Effect of Air Pollution on Olfactory Function in Residents of Mexico City

To our knowledge there has been no study of the effect of everyday air pollution on olfactory function. It was therefore the aim of this study to compare the olfactory performance of long-term residents of Mexico City, an environment with high air pollution, with the olfactory performance of residents of the Mexican state of Tlaxcala, a region geographically similar to Mexico City but with low air pollution. Healthy volunteers [82 Mexico City subjects (MEX), 86 Tlaxcala subjects (TLX)] 20-63 years of age and balanced for age and gender between the two localities were tested for the perception of the odors of everyday beverages presented in squeeze bottles. When tested with ascending concentrations of stimuli in a three-way oddball paradigm, residents of Tlaxcala detected the odors of instant coffee and of an orange drink at significantly lower concentrations than residents of Mexico City. They also performed significantly better in discriminating between the two similar-smelling Mexican beverages horchata and atole in an oddball test. Significant differences between the two populations in overall olfactory performance were apparent in three of the four age classes (20- to 29-, 30- to 39-, and 40- to 49-year-old subjects) but not in the 50-63 years age class. About 10% of MEX subjects compared to about 2% of TLX subjects were judged to have poor olfactory function; all were from the older age classes (mean age: 48.6 years). Thus, air pollution in Mexico City appears to have a substantial impact on olfactory function even in young and middle-aged residents.

Incorporation of Tissue Reaction Kinetics in a Computational Fluid Dynamics Model for Nasal Extraction of Inhaled Hydrogen Sulfide in Rats

Rodents exposed to hydrogen sulfide (H2S) develop olfactory neuronal loss. This lesion has been used by the risk assessment community to develop occupational and environmental exposure standards. A correlation between lesion locations and areas of high H2S flux to airway walls has been previously demonstrated, but a quantitative dose assessment is needed to extrapolate dose at lesion sites to humans. In this study, nasal extraction (NE) of 10, 80, and 200 ppm H2S was measured in the isolated upper respiratory tract of anesthetized rats under constant unidirectional inspiratory flow rates of 75, 150, and 300 ml/min. NE was dependent on inspired H2S concentration and air flow rate: increased NE was observed when H2S exposure concentrations or inspiratory air flow rates were low. An anatomically accurate, three-dimensional computational fluid dynamics (CFD) model of rat nasal passages was used to predict NE of inhaled H2S. To account for the observed dependence of NE on H2S exposure concentration, the boundary condition used at airway walls incorporated first-order and saturable kinetics in nasal tissue to govern mass flux at the air:tissue interface. Since the kinetic parameters cannot be obtained using the CFD model, they were estimated independently by fitting a well-mixed, two-compartment pharmacokinetic (PK) model to the NE data. Predicted extraction values using this PK-motivated CFD approach were in good agreement with the experimental measurements. The CFD model provides estimates of localized H2S flux to airway walls and can be used to calibrate lesion sites by dose.

Respiratory tract toxicity of inhaled hydrogen sulfide in Fischer-344 rats, Sprague–Dawley rats, and B6C3F1 mice following subchronic (90-day) exposure

The goal of this study was to characterize the toxicity of hydrogen sulfide (H2S), including nasal and pulmonary effects, in adult male and female Fischer-344 and Sprague-Dawley rats and B6C3F1 mice. Animals underwent whole-body exposure to 0, 10, 30, or 80 ppm H2S for 6 h/day for at least 90 days. Exposure to 80 ppm H2S was associated with reduced feed consumption during either the first exposure week (rats) or throughout the 90-day exposure (mice). Male Fischer-344 rats, female Sprague-Dawley rats, and female B6C3F1 mice exposed to 80 ppm H2S had depressed terminal body weights when compared with air-exposed controls. Subchronic H2S inhalation did not result in toxicologically relevant alterations in hematological indices, serum chemistries, or gross pathology. Histologic evaluation of the nose showed an exposure-related increased incidence of olfactory neuronal loss (ONL) and rhinitis. ONL occurred following exposure to > or =30 ppm H2S in both sexes of all experimental groups, with one exception, male Sprague-Dawley rats demonstrated ONL following exposure to 80 ppm H2S only. A 100% incidence of rhinitis was found in the male and female B6C3F1 mice exposed to 80 ppm H2S. In the lung, exposure to H2S was associated with bronchiolar epithelial hypertrophy and hyperplasia in male and female Sprague-Dawley rats following exposure to > or =30 ppm H2S and in male Fischer-344 rats exposed to 80 ppm H2S. Our results confirm that the rodent nose, and less so the lung, are highly sensitive to H2S-induced toxicity, with 10 ppm representing the NOAEL for ONL following subchronic inhalation.