Temporal and spatial variation in hydrogen sulfide (H2S) emissions during holopelagic Sargassum spp. decomposition on beaches

BACKGROUND

Since 2011, over 30 tropical Atlantic nations have experienced substantial landings of holopelagic Sargassum spp. Its decomposition results in the production of hydrogen sulfide (H2S), which, in elevated concentrations, can pose a threat to human health. This study aims to enhance our understanding of the temporal and spatial variability in H2S emissions during the decomposition of Sargassum on beaches. The primary objective is to assess potential exposure risks for local populations, tourists, and cleanup workers.

METHODS

H2S levels were monitored using a SENKO sensor (SGTP-H2S; limit of detection 0.1-100 ppm; resolution 0.1 ppm) at four distances from Sargassum accumulation points of (0, 10, 30, and 40 m) in Puerto Morelos, Mexico, during 2022 and 2023.

RESULTS

Elevated concentrations of H2S were detected beneath the Sargassum piles, with 23.5% of readings exceeding 5 ppm and occasional spikes above 100 ppm. Above the piles, 87.3% of the measurements remained below 2 ppm, and the remainder fell between 2.1 and 5.2 ppm. At 10 m from the shoreline, 90% of measurements registered below 0.1 ppm, and the remaining 10% were below 2 ppm. Readings at 30 and 40 m consistently recorded levels below 0.1 ppm. H2S concentrations positively correlated with Sargassum pile height, the temperature beneath the piles, and wind speed.

CONCLUSIONS

Our findings suggest no immediate and significant exposure risk for residents or tourists. However, Sargassum cleanup workers face a higher exposure risk, potentially encountering concentrations above 5 ppm for nearly one-fourth of the working time.

Respiratory and nervous system effects of a hydrogen sulfide crisis in Carson, California

BACKGROUND

In October 2021, many residents in Carson, California experienced malodors, headaches, and respiratory symptoms. Hydrogen sulfide (H2S), a toxic odorous gas, was measured in Carson at concentrations up to 7000 parts per billion (ppb) and remained above California's acute air quality standard of 30 ppb for about a month. Research on how low- and medium-level H2S exposure affects the respiratory and nervous systems has yielded conflicting results, and few studies have examined the effects of subacute H2S exposure.

METHODS

We calculated daily rates of emergency department (ED) visits with various respiratory and nervous systems diagnosis codes in Carson area ZIP codes (≤6 km from event's epicenter) and in Los Angeles County ZIP codes >15 km from event's epicenter (control area). Using controlled interrupted time series, we compared ED visit rates during the month of the H2S crisis in Carson to the predicted rates had the incident not occurred, based on 2018-2021 ED trends, and controlling for ED visit rate changes in the control area.

RESULTS

We observed a 24 % increase in ED visit rate for all respiratory system diseases (rate ratio = 1.24, 95 % CI: 1.16, 1.32), a 38 % increase for asthma (RR = 1.38, 95 % CI: 1.26, 1.50), a 26 % increase for acute upper respiratory infections (RR = 1.26, 95 % CI: 1.13, 1.38), a 21 % increase for dizziness (RR = 1.21, 95 % CI: 1.04, 1.38), and a 25 % increase for migraines and headaches (RR = 1.25, 95 % CI: 1.13, 1.36) in the Carson area during the first month of the H2S event compared to the expected rates.

CONCLUSIONS

This H2S crisis was associated with increased ED visit rates for multiple respiratory and nervous system outcomes. Reducing H2S exposure and improving to response during H2S episodes may improve public health.

The Ying and Yang of Hydrogen Sulfide as a Paracrine/Autocrine Agent in Neurodegeneration: Focus on Amyotrophic Lateral Sclerosis

Ever since its presence was reported in the brain, the nature and role of hydrogen sulfide (H2S) in the Central Nervous System (CNS) have changed. Consequently, H2S has been elected as the third gas transmitter, along with carbon monoxide and nitric oxide, and a number of studies have focused on its neuromodulatory and protectant functions in physiological conditions. The research on H2S has highlighted its many facets in the periphery and in the CNS, and its role as a double-faced compound, switching from protective to toxic depending on its concentration. In this review, we will focus on the bell-shaped nature of H2S as an angiogenic factor and as a molecule released by glial cells (mainly astrocytes) and non-neuronal cells acting on the surrounding environment (paracrine) or on the releasing cells themselves (autocrine). Finally, we will discuss its role in Amyotrophic Lateral Sclerosis, a paradigm of a neurodegenerative disease.

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.

Estimation of sulfur fate and contribution to VSC emissions from lakes during algae decay

Algae decay is an important process influencing environmental variables and emissions of volatile sulfur compounds (VSCs) in eutrophic lakes. However, effects of algae decay on VSC emissions from eutrophic lakes as well as fate of algae-derived sulfur remain poorly understood. In this study, simulated algae-sediment systems were used to explore the flow and distribution of sulfur during algae decay. VSCs including hydrogen sulfide (H₂S), methanethiol (CH₃SH), carbon disulfide (CS₂) and dimethyl sulfide ((CH₃)₂S) were detected during algae decay, which increased with algae biomass and eutrophic levels in lakes. During algae decay, the highest H₂S, CH₃SH and (CH₃)₂S emission rates of 10.45, 21.82 and 43.26 μg d^-1 occurred in the first 1-2 days, respectively, while the highest CS₂ emission rates were observed between days 8 and 11. The maximum emissions of H₂S and CS₂ from algae decay were estimated at 0.51 and 0.35 mg m^-2 d^-1 in Lake Taihu, accounting for 1.57% and 0.69% of the total H₂S and CS₂ emissions of in situ, respectively. Algae decay could significantly increase the contents of total sulfur and total carbon in sediments by 2.90%-21.11% and 4.23%-45.05%, respectively. The VSC emissions during algae decay could be predicted using the multiple regression models with the contents of total carbon, total nitrogen and sulfur-containing compounds in sediments. Partial least squares path modelling demonstrated that algae decay had a low direct effect on VSC emissions with a strength of 0.06, while it had a significant influence on environmental variables with a strength of 0.63, which could affect VSC emissions with a strength of 0.85, indicating VSC emissions from eutrophic lakes were affected by the environmental variables rather than the direct influence of algae decay. These findings illustrated the mechanisms of VSC emissions during algae decay and provided insights into VSC control and mitigation for eutrophic lakes.

Identification of volatile sulfur odorants emitted from ageing wastewater biosolids

Volatile sulfur compounds (VSCs) are important sources of unpleasant odours in biosolid emissions. However, the study of VSCs may be limited by complications in their gas phase measurements due to reactivity, transformations and varying reported odour detection thresholds. A range of methods were used to quantitatively analyse VSCs in wastewater biosolid emissions. VSCs were identified in aged biosolid emissions by gas chromatography (GC) with a sulfur chemiluminescence detector (SCD) and mass spectrometry coupled with olfactory detection port (MS/O). In total, 10 VSC's were identified with two volatile organic sulfur compounds (VOSCs), allyl methyl sulfide and methyl propyl sulfide being reported for the first time in biosolid emissions. The emission patterns of different VSCs varied as the biosolids aged. Initially, the median concentrations of H₂S, dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), methanethiol (MeSH) and ethanethiol (EtSH) were orders of magnitude greater than their reported odour detection threshold, suggesting they would contribute to the odorous impact of the biosolids. The maximum H₂S value was equal to 59.9 × 10³ μg/m³ and was at least one magnitude higher compared to VOSCs, such as dimethyl disulfide (DMDS) (3.8×10³ μg/m³), DMS (4.53 × 10³ μg/m³), EtSH (2.83 × 10³ μg/m³) and MeSH (3.25 × 10³ μg/m³). Among the identified VSCs, H₂S was the prominent odorant in terms of the magnitude and the frequency of detection, both initially as well as throughout storage. However, DMTS should be considered as a high priority or key odorant due to its odour activity value (OAV) and frequency of detection (sensorially detected in more than 75% of samples, with an OAVs higher than 1).

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.

Experimental study on volatile sulfur compound inhibition using a single-chamber membrane-free microbial electrolysis cell

Odor emissions from sewer systems and wastewater treatment plants have attracted much attention due to the potential negative effects on human health. A single-chamber membrane-free microbial electrolysis cell was proposed for the removal of sulfides in a sewer system. The feasibility of the use of volatile sulfur compounds and their removal efficiency in liquid and headspace gas phases were investigated using synthetic wastewater with real sewer sediment and Ru/Ir-coated titanium electrodes. The results indicate that hydrogen sulfide and volatile organic sulfur compounds were effectively inhibited in the liquid phase upon electrochemical treatment at current densities of 1.55, 2.06, and 2.58 mA/cm², and their removal rates reached up to 86.2-100%, except for dimethyl trisulfide, the amount of which increased greatly at 1.55 mA/cm². In addition, the amount of volatile sulfur compounds in the headspace decreased greatly; however, the total theoretical odor concentration was still high, and methanethiol and ethanethiol greatly contributed to the total strength of the odor concentration due to their low odor threshold concentrations. The major pathway for sulfide removal in the single-chamber membrane-free microbial electrolysis cell is biotic oxidation, the removal rate of which was 0.4-0.5 mg/min, 4-5 times that of indirect electrochemical oxidation.

Estimating exposure to hydrogen sulfide from animal husbandry operations using satellite ammonia as a proxy: Methodology demonstration

Husbandry trace gases that have climate change implications such as carbon dioxide (CO₂), methane (CH₄) and ammonia (NH₃) can be quantified through remote sensing; however, many husbandry gases with health implications such as hydrogen sulfide (H₂S), cannot. This pilot study demonstrates an approach to derive H₂S concentrations by coupling in situ and remote sensing data. Using AMOG (AutoMObile trace Gas) Surveyor, a mobile air quality and meteorology laboratory, we measured in situ concentrations of CH₄, CO₂, NH₃, H₂S, and wind at a southern California university research dairy. Emissions were 0.13, 1.93, 0.022 and 0.0064 Gg yr^-1; emission factors (E_F) were 422, 6333, 74, and 21 kg cow^-1 yr^-1, respectively, for the 306 head herd. Contributing to these strong E_F were spillway emissions from a grate between the main cowshed and the waste lagoon identified in airborne remote sensing data acquired by the hyperspectral thermal infrared imager, Mako. NH₃ emissions from the Chino Dairy Complex, also in southern California, were calculated from Infrared Atmospheric Sounding Interferometer (IASI) satellite data for 2008-2017 using average morning winds, yielding a flushing time of 2.7 h, and 8.9 Gg yr^-1. The ratio of E_F(H₂S) to E_F(NH₃) for the research dairy from AMOG data were applied to IASI NH₃ emissions to derive H₂S exposure concentration maps for the Chino area, which ranged to 10-30 ppb H₂S for many populated areas. Combining remote sensing with in situ concentrations of multiple emitted gases can allow derivation of emissions at the sub-facility, facility, and larger scales, providing spatial and temporal coverage that can translate into exposure estimates for use in epidemiology studies and regulation development. Furthermore, with high fidelity information at the sub-facility level we can identify best practices and opportunities to sustainably and holistically reduce husbandry emissions.

Emerging pharmacological tools to control hydrogen sulfide signaling in critical illness

Hydrogen sulfide (H2S) has long been known as a toxic environmental hazard. Discovery of physiological roles of H2S as a neurotransmitter by Kimura and colleagues triggered an intensive research in the biological roles of H2S in the past decades. Manipulation of H2S levels by inhibiting H2S synthesis or administration of H2S-releasing molecules revealed beneficial as well as harmful effects of H2S. As a result, it is now established that H2S levels are tightly controlled and too much or too little H2S levels cause harm. Nonetheless, translation of sulfide-based therapy to clinical practice has been stymied due to the very low therapeutic index of sulfide and the incomplete understanding of endogenous sulfide metabolism. One potential strategy to circumvent this problem is to use a safe and stable sulfide metabolite that may mediate effects of H2S. Alternatively, endogenous sulfide levels may be controlled using specific sulfide scavengers. In this review article, the role of endogenous H2S production and catabolism will be briefly reviewed followed by an introduction of thiosulfate and H2S scavengers as novel pharmacological tools to control H2S-dependent signaling.

Photopaper as a Tool for Community-Level Monitoring of Industrially Produced Hydrogen Sulfide and Corrosion

Scientific instrumentation driven by academic, military, and industrial applications tends to be high cost, designed for expert use, and "black boxed". Community-led citizen science (CLCS) is creating different research instruments with different measurement goals and processes. This paper identifies four design attributes for CLCS tools: affordability, accessibility, builds community efficacy and provides actionable data through validating a community method for monitoring the neurotoxic and corrosive gas Hydrogen Sulfide (H2S). For $1 per sample, the semi-quantitative method provides an affordable and easily interpretable data for communities to compare H2S concentrations and silver corrosion in their home environments to those in a major municipal sewage treatment plant. H2S is a leading cause of workplace injury in the U.S. and commonly found in oil and gas production, sewage treatment plants, and concentrated animal feeding operations (CAFOs). Communities neighboring such sources tend to be socio-economically marginalized with little access to scientific or political resources. Consequently, health risks and material degradation from corrosion are well studied in workplaces while community exposures are under-studied. Existing commercial H2S detection methods are prohibitively expensive for low-income communities and often require the support of professional scientists. This paper describes a simple and inexpensive semi-quantitative H2S measurement method that uses photopaper. Photopaper passively measures H2S as its silver halide layer linearly reacts with H2S between concentrations of 60 ppb to 1 ppm, discoloring the paper from white to brown. We develop a colorimetric scale for this discoloration for visual estimation of H2S concentration and overall corrosion. The scale is based on comparing silver sulfide (Ag2S) measured by Purafil Corrosion Classification Coupons (CCCs) and H2S concentrations measured with the industry standard tool a Jerome Meter to silver and sulfur bound to the photopaper as measured with X-Ray Fluorescence (XRF). We conduct our validation studies in a major municipal sewage treatment plant to provide real-world occupational benchmarks for comparison to community results. This community science method is affordable, accessible, designed to build collective efficacy and to create actionable data to flag the need for follow-up research.

Hydrogen sulfide intoxication induced brain injury and methylene blue

Hydrogen sulfide (H₂S) remains a chemical hazard in the gas and farming industry. It is easy to manufacture from common chemicals and thus represents a potential threat for the civilian population. It is also employed as a method of suicide, for which incidence has recently increased in the US. H₂S is a mitochondrial poison and exerts its toxicity through mechanisms that are thought to result from its high affinity to various metallo-proteins (such as - but not exclusively- the mitochondrial cytochrome c oxidase) and interactions with cysteine residues of proteins. Ion channels with critical implications for the cardiac and the brain functions appear to be affected very early during and following H₂S exposure, an effect which is rapidly reversible during a light intoxication. However, during severe H₂S intoxication, a coma, associated with a reduction in cardiac contractility, develops within minutes or even seconds leading to death by complete electro-mechanical dissociation of the heart. If the level of intoxication is milder, a rapid and spontaneous recovery of the coma occurs as soon as the exposure stops. The risk, although probably very small, of developing long-term debilitating motor or cognitive deficits is present. One of the major challenges impeding our effort to offer an effective treatment against H₂S intoxication after exposure is that the pool of free/soluble H₂S almost immediately disappears from the body preventing agents trapping free H₂S (cobalt or ferric compounds) to play their protective role. This paper (1) presents and discusses the neurological symptoms and lesions observed in various animals models and in humans following an acute exposure to sub-lethal or lethal levels of H₂S, (2) reviews the potential interest of methylene blue (MB), a potent cyclic redox dye - currently used for the treatment of methemoglobinemia - which has potential rescuing effects on the mitochondrial activity, as an antidote against sulfide intoxication.

H2S promotes a glycometabolism disorder by disturbing the Th1/Th2 balance during LPS-induced inflammation in the skeletal muscles of chickens

Hydrogen sulfide (H₂S) is a common environmental pollutant. In humans, H₂S enters the body and is transported to different tissues and organs, inducing various types of damage such as chronic inflammatory reactions. Glucose metabolism disorders have been shown to be closely associated with chronic inflammation. The goal of the present study was to investigate the effects and mechanisms of H₂S on glycometabolism disorders and chronic inflammatory responses. A chronic inflammation model in the skeletal muscles of chickens was induced using lipopolysaccharide (LPS), after which the animals were exposed to exogenous H₂S. Subsequently, the glucose metabolism and the pathways associated with chronic inflammation were analyzed. The pathological analysis showed that significant inflammatory injury to skeletal muscles occurred after animals exposed to H₂S. The Th1/Th2 ratio imbalance was exacerbated after exposure to H₂S with IFNγ downregulated and IL-1, IL-4, and IL-6 upregulated. In addition, the level of IκBα was suppressed and induced the expression of NF-κB, significantly activating the inflammatory pathway, while the expression of heat shock proteins was elevated. In addition, glucose metabolism factors were analyzed. IRS1 phosphorylation was inhibited in animals exposed to H₂S, and the expression of insulin-like growth factor (IGF) signaling pathway-related factors was upregulated to promote insulin resistance, causing glucose metabolism disorders. The results of this study revealed that H₂S can trigger changes in the ratio of Th1/Th2 to produce more proinflammatory cytokines that disturb the insulin signaling pathway, causing glycometabolism disorders during the inflammatory response in the skeletal muscles of chickens.

Gaseous signaling molecules and their application in resistant cancer treatment: from invisible to visible

Multidrug resistance (MDR) in cancer remains a critical obstacle for efficient chemotherapy. Many MDR reversal agents have been discovered but failed in clinical trials due to severe toxic effects. Gaseous signaling molecules (GSMs), such as oxygen, nitric oxide, hydrogen sulfide and carbon monoxide, play key roles in regulating cell biological function and MDR. Compared with other toxic chemosensitizing agents, GSMs are endogenous and biocompatible molecules with little side effects. Research show that GSM modulators, including pharmaceutical formulations of GSMs (combined with conventional chemotherapeutic drugs) and GSM-donors (small molecules with GSMs releasing property), can overcome or reverse MDR. This review discusses the roles of these four GSMs in modulating MDR, and summarizes GSMs modulators in treating cancers with drug resistance.

Exogenous hydrogen sulfide promotes hepatocellular carcinoma cell growth by activating the STAT3-COX-2 signaling pathway

The effects of hydrogen sulfide (H₂S) on cancer are controversial. Our group previously demonstrated that exogenous H₂S promotes the development of cancer via amplifying the activation of the nuclear factor-κB signaling pathway in hepatocellular carcinoma (HCC) cells (PLC/PRF/5). The present study aimed to further investigate the hypothesis that exogenous H₂S promotes PLC/PRF/5 cell proliferation and migration, and inhibits apoptosis by activating the signal transducer and activator of transcription 3 (STAT3)-cyclooxygenase-2 (COX-2) signaling pathway. PLC/PRF/5 cells were treated with 500 µmol/l NaHS (a donor of H₂S) for 24 h. The expression levels of phosphorylated (p)-STAT3, STAT3, cleaved caspase-3 and COX-2 were measured by western blot assay. Cell viability was detected by Cell Counting kit-8 assay. Apoptotic cells were observed by Hoechst 33258 staining. The expression of STAT3 and COX-2 messenger RNA (mRNA) was detected by semiquantitative reverse transcription-polymerase chain reaction. The production of vascular endothelial growth factor (VEGF) was evaluated by ELISA. The results indicated that treatment of PLC/PRF/5 cells with 500 µmol/l NaHS for 24 h markedly increased the expression levels of p-STAT3 and STAT3 mRNA, leading to COX-2 and COX-2 mRNA overexpression, VEGF induction, decreased cleaved caspase-3 production, increased cell viability and migration, and decreased number of apoptotic cells. However, co-treatment of PLC/PRF/5 cells with 500 µmol/l NaHS and 30 µmol/l AG490 (an inhibitor of STAT3) or 20 µmol/l NS-398 (an inhibitor of COX-2) for 24 h significantly reverted the effects induced by NaHS. Furthermore, co-treatment of PLC/PRF/5 cells with 500 µmol/l NaHS and 30 µmol/l AG490 markedly decreased the NaHS-induced increase in the expression level of COX-2. By contrast, co-treatment of PLC/PRF/5 cells with 500 µmol/l NaHS and 20 µmol/l NS-398 inhibited the NaHS-induced increase in the expression level of p-STAT3. In conclusion, the findings of the present study provide evidence that the STAT3-COX-2 signaling pathway is involved in NaHS-induced cell proliferation, migration, angiogenesis and anti-apoptosis in PLC/PRF/5 cells, and suggest that the positive feedback between STAT3 and COX-2 may serve a crucial role in hepatocellular carcinoma carcinogenesis.

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.

Remote sensing and in situ measurements of methane and ammonia emissions from a megacity dairy complex: Chino, CA

Methane (CH₄) and ammonia (NH₃) directly and indirectly affect the atmospheric radiative balance with the latter leading to aerosol generation. Both have important spectral features in the Thermal InfraRed (TIR) that can be studied by remote sensing, with NH₃ allowing discrimination of husbandry from other CH₄ sources. Airborne hyperspectral imagery was collected for the Chino Dairy Complex in the Los Angeles Basin as well as in situ CH₄, carbon dioxide (CO₂) and NH₃ data. TIR data showed good spatial agreement with in situ measurements and showed significant emissions heterogeneity between dairies. Airborne remote sensing mapped plume transport for ∼20 km downwind, documenting topographic effects on plume advection. Repeated multiple gas in situ measurements showed that emissions were persistent on half-year timescales. Inversion of one dairy plume found annual emissions of 4.1 × 10⁵ kg CH₄, 2.2 × 10⁵ kg NH₃, and 2.3 × 10⁷ kg CO₂, suggesting 2300, 4000, and 2100 head of cattle, respectively, and Chino Dairy Complex emissions of 42 Gg CH₄ and 8.4 Gg NH₃ implying ∼200k cows, ∼30% more than Peischl et al. (2013) estimated for June 2010. Far-field data showed chemical conversion and/or deposition of Chino NH₃ occurs within the confines of the Los Angeles Basin on a four to six h timescale, faster than most published rates, and likely from higher Los Angeles oxidant loads. Satellite observations from 2011 to 2014 confirmed that observed in situ transport patterns were representative and suggests much of the Chino Dairy Complex emissions are driven towards eastern Orange County, with a lesser amount transported to Palm Springs, CA. Given interest in mitigating husbandry health impacts from air pollution emissions, this study highlights how satellite observations can be leveraged to understand exposure and how multiple gas in situ emissions studies can inform on best practices given that emissions reduction of one gas could increase those of others.

Association between Daily Hydrogen Sulfide Exposure and Incidence of Emergency Hospital Visits: A Population-Based Study

BACKGROUND

The adverse health effects of high concentrations of hydrogen sulfide (H2S) exposure are well known, though the possible effects of low concentrations have not been thoroughly studied. The aim was to study short-term associations between modelled ambient low-level concentrations of intermittent hydrogen sulfide (H2S) and emergency hospital visits with heart diseases (HD), respiratory diseases, and stroke as primary diagnosis.

METHODS

The study is population-based, using data from patient-, and population-registers from the only acute care institution in the Reykjavik capital area, between 1 January, 2007 and 30 June, 2014. The study population was individuals (≥18yr) living in the Reykjavik capital area. The H2S emission originates from a geothermal power plant in the vicinity. A model was used to estimate H2S exposure in different sections of the area. A generalized linear model assuming Poisson distribution was used to investigate the association between emergency hospital visits and H2S exposure. Distributed lag models were adjusted for seasonality, gender, age, traffic zones, and other relevant factors. Lag days from 0 to 4 were considered.

RESULTS

The total number of emergency hospital visits was 32961 with a mean age of 70 years. In fully adjusted un-stratified models, H2S concentrations exceeding 7.00μg/m3 were associated with increases in emergency hospital visits with HD as primary diagnosis at lag 0 risk ratio (RR): 1.067; 95% confidence interval (CI): 1.024-1.111, lag 2 RR: 1.049; 95%CI: 1.005-1.095, and lag 4 RR: 1.046; 95%CI: 1.004-1.089. Among males an association was found between H2S concentrations exceeding 7.00μg/m3, and HD at lag 0 RR: 1.087; 95%CI: 1.032-1.146 and lag 4 RR: 1080; 95%CI: 1.025-1.138; and among those 73 years and older at lag 0 RR: 1.075; 95%CI: 1.014-1.140 and lag 3 RR: 1.072; 95%CI: 1.009-1.139. No associations were found with other diseases.

CONCLUSIONS

The study showed an association between emergency hospital visits with HD as primary diagnosis and same day H2S concentrations exceeding 7.00μg/m3, more pronounced among males and those 73 years and older than among females and younger individuals.

Exogenous hydrogen sulfide exerts proliferation, anti-apoptosis, angiopoiesis and migration effects via activating HSP90 pathway in EC109 cells

Hydrogen sulfide (H2S) participates in diverse physiological and pathophysiologic processes of cancer both in vitro and in vivo. We have previously reported the proliferation/anti-apoptosis/angiogenesis/migration effects of exogenous H2S on liver cancer and glioma via amplifying the activation of NF-κB and p38 MAPK/ERK1/2-COX-2 pathway. However, the effects of H2S on EC109 esophageal cells remain unclear. The present study demonstrated the effects of exogenous H2S on cancer cell growth via activating HSP90 pathways in EC109 esophageal cells. EC109 esophageal cells were treated with 400 µmol/l NaHS (a donor of H2S) for 24 h. The expression levels of HSP90, bcl-2, caspase-3, bax and MMP-2 were detected by western blot assay. Cell viability was detected by Cell Counting Kit-8 (CCK-8). The migration rate was analyzed using a Transwell migration assay and ImageJ software. NaHS promoted cell proliferation, as evidenced by an increase in cell viability. In addition, NaHS treatment reduced apoptosis, as indicated by the increased bcl-2 expression and decreased cleaved caspase-3 and bax expression. Importantly, exposure of NaHS increased the expression of MMP-2, the migration rate and expression of VEGF. Notably, co-treatment of EC109 cells with NaHS and GA (an inhibitor of HSP90 pathway) largely suppressed the aforementioned NaHS-induced effects. The findings of the present study provided novel evidence that HSP90 pathway was involved in NaHS-induced cancer cell proliferation, anti-apoptosis, angiopoiesis and migration in EC109 esophageal cells.

Hydrogen Sulfide--Mechanisms of Toxicity and Development of an Antidote

Hydrogen sulfide is a highly toxic gas—second only to carbon monoxide as a cause of inhalational deaths. Its mechanism of toxicity is only partially known, and no specific therapy exists for sulfide poisoning. We show in several cell types, including human inducible pluripotent stem cell (hiPSC)-derived neurons, that sulfide inhibited complex IV of the mitochondrial respiratory chain and induced apoptosis. Sulfide increased hydroxyl radical production in isolated mouse heart mitochondria and F₂-isoprostanes in brains and hearts of mice. The vitamin B₁₂ analog cobinamide reversed the cellular toxicity of sulfide, and rescued Drosophila melanogaster and mice from lethal exposures of hydrogen sulfide gas. Cobinamide worked through two distinct mechanisms: direct reversal of complex IV inhibition and neutralization of sulfide-generated reactive oxygen species. We conclude that sulfide produces a high degree of oxidative stress in cells and tissues, and that cobinamide has promise as a first specific treatment for sulfide poisoning.

Effect of environmental exposure to hydrogen sulfide on central nervous system and respiratory function: a systematic review of human studies

BACKGROUND

Assessment of the health effects of low-level exposure to hydrogen sulfide (H2S) on humans through experiments, industrial, and community studies has shown inconsistent results.

OBJECTIVE

To critically appraise available studies investigating the effect of H2S on the central nervous system (CNS) and on respiratory function.

METHODS

A search was conducted in 16 databases for articles published between January 1980 and July 2014. Two researchers independently evaluated potentially relevant papers based on a set of inclusion/exclusion criteria.

RESULTS

Twenty-seven articles met the inclusion criteria: 6 experimental, 12 industry-based studies, and 10 community-based studies (one article included both experimental and industry-based studies). The results of the systematic review varied by study setting and quality. Several community-based studies reported associations between day-to-day variations in H2S levels and health outcomes among patients with chronic respiratory conditions. However, evidence from the largest and better-designed community-based studies did not support that chronic, ambient H2S exposure has health effects on the CNS or respiratory function. Results from industry-based studies varied, reflecting the diversity of settings and the broad range of H2S exposures. Most studies did not have individual measurements of H2S exposure.

DISCUSSION

The results across studies were inconsistent, justifying the need for further research.

Exogenous hydrogen sulfide promotes C6 glioma cell growth through activation of the p38 MAPK/ERK1/2-COX-2 pathways

Hydrogen sulfide (H2S) participates in multifarious physiological and pathophysiologic progresses of cancer both in vitro and in vivo. We have previously demonstrated that exogenous H2S promoted liver cancer cells proliferation/anti‑apoptosis/angiogenesis/migration effects via amplifying the activation of NF-κB pathway. However, the effects of H2S on cancer cell proliferation and apoptosis are controversial and remain unclear in C6 glioma cells. The present study investigated the effects of exogenous H2S on cancer cells growth via activating p38 MAPK/ERK1/2-COX-2 pathways in C6 glioma cells. C6 glioma cells were treated with 400 µmol/l NaHS (a donor of H2S) for 24 h. The expression levels of phosphorylated (p)-p38 MAPK, total (t)-p38 MAPK, p-ERK1/2, t-ERK1/2, cyclooxygenase-2 (COX-2) and caspase-3 were measured by western blotting assay. Cell viability was detected by Cell Counting Kit-8 (CCK-8). Apoptotic cells were observed by Hoechst 33258 staining assay. Cell proliferation was directly detected under fully automatic inverted microscope. Exposure of C6 glioma cells to NaHS resulted in cell proliferation, as evidenced by an increase in cell viability. In addition, NaHS treatment reduced apoptosis, as indicated by the decreased apoptotic percentage and the cleaved caspase-3 expression. Importantly, exposure of the cells to NaHS increased the expression levels of p-p38 MAPK, p-ERK1/2 and COX-2. Notably, co-treatment of C6 glioma cells with 400 µmol/l NaHS and AOAA (an inhibitor of CBS) largely suppressed the above NaHS-induced effects. Combined treatment with NaHS and SB203580 (an inhibitor of p38 MAPK) or PD-98059 (an inhibitor of ERK1/2) resulted in the synergistic reduction of COX-2 expression and increase of caspase-3 expression, a decreased number of apoptotic cells, along with decreased cell viability. Combined treatment with NS-398 (an inhibitor of COX-2) and NaHS also resulted in the synergistic increase of caspase-3, a decreased in the number of apoptotic cells and the decrease in cell viability. The findings of the present study provide novel evidence that p38 MAPK/ERK1/2-COX-2 pathways are involved in NaHS-induced cancer cell proliferation and anti-apoptosis in C6 glioma cells.

Hydrogen sulfide and traffic-related air pollutants in association with increased mortality: a case-crossover study in Reykjavik, Iceland

OBJECTIVES

To study the association between daily mortality and short-term increases in air pollutants, both traffic-related and the geothermal source-specific hydrogen sulfide (H₂S).

DESIGN

Population-based, time stratified case-crossover. A lag time to 4 days was considered. Seasonal, gender and age stratification were calculated. Also, the best-fit lag when introducing H₂S >7 µg/m(3) was selected by the Akaike Information Criterion (AIC).

SETTING

The population of the greater Reykjavik area (n=181,558) during 2003-2009.

PARTICIPANTS

Cases were defined as individuals living in the Reykjavik capital area, 18 years or older (N=138,657), who died due to all natural causes (ICD-10 codes A00-R99) other than injury, poisoning and certain other consequences of external causes, or cardiovascular disease (ICD-10 codes I00-I99) during the study period.

MAIN OUTCOME MEASURE

Percentage increases in risk of death (IR%) following an interquartile range increase in pollutants.

RESULTS

The total number of deaths due to all natural causes was 7679 and due to cardiovascular diseases was 3033. The interquartile range increased concentrations of H₂S (2.6 µg/m(3)) were associated with daily all natural cause mortality in the Reykjavik capital area. The IR% was statistically significant during the summer season (lag 1: IR%=5.05, 95% CI 0.61 to 9.68; lag 2: IR%=5.09, 95% CI 0.44 to 9.97), among males (lag 0: IR%=2.26, 95% CI 0.23 to 4.44), and among the elderly (lag 0: IR%=1.94, 95% CI 0.12 to 1.04; lag 1: IR%=1.99, 95% CI 0.21 to 1.04), when adjusted for traffic-related pollutants and meteorological variables. The traffic-related pollutants were generally not associated with statistical significant IR%s.

CONCLUSIONS

The results suggest that ambient H₂S air pollution may increase mortality in Reykjavik, Iceland. To the best of our knowledge, ambient H₂S exposure has not previously been associated with increased mortality in population-based studies and therefore the results should be interpreted with caution. Further studies are warranted to confirm or refute whether H₂S exposure induces premature deaths.

Exogenous hydrogen sulfide exerts proliferation/anti-apoptosis/angiogenesis/migration effects via amplifying the activation of NF-κB pathway in PLC/PRF/5 hepatoma cells

Hydrogen sulfide (H2S) takes part in a diverse range of intracellular pathways and hss physical and pathological properties in vitro and in vivo. However, the effects of H2S on cancer are controversial and remain unclear. The present study investigates the effects of H2S on liver cancer progression via activating NF-κB pathway in PLC/PRF/5 hepatoma cells. PLC/PRF/5 hepatoma cells were pretreated with 500 µmol/l NaHS (a donor of H2S) for 24 h. The expression levels of CSE, CBS, phosphosphorylate (p)-NF-κB p65, caspase-3, COX-2, p-IκB and MMP-2 were measured by western blot assay. Cell viability was detected by cell counter kit 8 (CCK-8). Apoptotic cells were observed by Hoechst 33258 staining assay. The production level of H2S in cell culture medium was measured by using the sulfur-sensitive electrode method. The production of vascular endothelial growth factor (VEGF) was tested by enzyme-linked immunosorbent assay (ELISA). Our results showed that the production of H2S was dramatically increased in the PLC/PRF/5 hepatoma cells, compared with human LO2 hepatocyte cells group, along with the overexpression levels of CSE and CBS. Treatment of PLC/PRF/5 hepatoma cells with 500 µmol/l NaHS (a donor of H2S) for 24 h markedly increased the expression levels of CSE, CBS, p-IκB and NF-κB activation, leading to COX-2 and MMP-2 overexpression, and decreased caspase-3 production, as well as increased cell viability and decreased number of apoptotic cells. Otherwise, the production level of H2S and VEGF were also significantly increased. Furthermore, co-treatment of PLC/PRF/5 hepatoma cells with 500 µmol/l NaHS and 200 µmol/l PDTC for 24 h significantly overturned these indexes. The findings of the present study provide evidence that the NF-κB is involved in the NaHS-induced cell proliferation, anti-apoptisis, angiogenesis, and migration in PLC/PRF/5 hepatoma cells, and that the PDTC against the NaHS-induced effects were by inhibition of the NF-κB pathway.

Determination of VOSCs in sewer headspace air using TD-GC-SCD

The management of odorous emissions from sewer networks has become an important issue for sewer operators resulting in the need to better understand the composition of volatile organic sulfur compounds (VOSCs). In order to characterise the composition of such malodorous emissions, a method based on thermal desorption (TD) and gas chromatography coupled to sulfur chemiluminescence detector (GC-SCD) has been developed to determine a broader range of VOSCs, hydrogen sulfide (H2S), methanethiol (MeSH), ethanethiol (EtSH), dimethyl sulfide (DMS), carbon disulfide (CS2), ethylmethyl sulfide (EMS), 1-butanethiol (1-BuSH), dimethyl disulfide (DMDS), diethyl disulfide (DEDS), and dimethyl trisulfide (DMTS). Parameters affecting the chromatographic behaviour of the target compounds were studied (e.g., temperature program, carrier gas velocity) as well as the experimental conditions affecting the adsorption/desorption process (temperature, flow and time). Optimised extraction of VOSCs samples was achieved under adsorption temperatures of less than -20°C, and a desorption flow rate of ~6 ml/min. Active collection on the cold trap enabled a small gas volume of 50-100ml to be sampled for all analytes without breakthrough. Calibration curves were derived at different TD loading volumes with determined linearity ranging between 0.09 ng and 60.1 ng. The method detection limits (MDLs) were in the range of 0.10-5.26 μg/m(3) with TD recoveries higher than 66% and reproducibility (relative standard deviation values) between 1.8% and 6.1% being obtained for all compounds. The VOSCs characterisation at different sewerage collection sites in Sydney, Australia (for seasonal, weekly and diurnal) showed that six of the ten targeted compounds were consistently detected at all sample events. Diurnal patterns of VOSCs investigated were clearly observed with the highest concentration occurring after 12 pm (noon) for H2S and MeSH. The consecutive 5 day analysis showed no significant difference in the targeted VOSCs concentrations and demonstrated the suitability of the method for routine sewer VOSCs emission measurements.

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.

The effects of acute hydrogen sulfide poisoning on cytochrome P450 isoforms activity in rats

Hydrogen sulfide (H2S) is the second leading cause of toxin related death (after carbon monoxide) in the workplace. H2S is absorbed by the upper respiratory tract mucosa, and it causes histotoxic hypoxemia and respiratory depression. Cocktail method was used to evaluate the influences of acute H2S poisoning on the activities of cytochrome P450 isoforms CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19, and CYP2C9, which were reflected by the changes of pharmacokinetic parameters of six specific probe drugs, bupropion, metoprolol, midazolam, phenacetin, omeprazole, and tolbutamide, respectively. The experimental rats were randomly divided into two groups, control group and acute H2S poisoning group (inhaling 300 ppm for 2 h). The mixture of six probes was given to rats by oral administration and the blood samples were obtained at a series of time points through the caudal vein. The concentrations of probe drugs in rat plasma were measured by LC-MS. The results for acute H2S poisoning and control groups were as follows: there was a statistically significant difference in the AUC and C max for bupropion, metoprolol, phenacetin, and tolbutamide, while there was no statistical pharmacokinetic difference for midazolam and omeprazole. Acute H2S poisoning could inhibit the activity of CYP2B6, CYP2D6, CYP1A2, and CYP2C9 in rats.

Chronic ambient hydrogen sulfide exposure and cognitive function

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

A liquid crystal-based passive badge for personal monitoring of exposure to hydrogen sulfide

A new liquid crystal (LC)-based passive dosimeter badge for personal monitoring of exposure to hydrogen sulfide (H2S) gas is reported. When a thin film of LC supported on a surface functionalized with lead perchlorate Pb(ClO4)2 (the LC sensor) is exposed to H2S, the orientation of LC molecules in the film changes from perpendicular to parallel. This reorientation induces a change in the appearance of the LC film when viewed between crossed polarizers. A H2S dosimeter was fabricated by pairing a LC sensor with a glass substrate forming a headspace between the two surfaces, to control diffusion of H2S across the LC film. When the dosimeter is exposed to H2S, a bright front appears as a function of exposure time. An algorithm has been developed to correlate this response length and exposure dose. The dosimeters are functionally stable when subjected to extreme temperature and humidity fluctuations, and are immune to a number of potentially interfering chemicals, except mercaptans. These dosimeters detect H2S at 0.2 ppm TWA (8 hr) with ±20% overall accuracy. The dosimeters were used to monitor the personal exposure of personnel working in an oil refinery. The TWA concentrations measured by the LC-based dosimeters correlate strongly with the NIOSH 1063 method that uses a sorbent tube and a pump followed by laboratory analysis. Thus, the LC-based dosimeters can provide a sensitive tool for on-site assessment of personal exposure to H2S in different environments.

Associations of ambient hydrogen sulfide exposure with self-reported asthma and asthma symptoms

BACKGROUND

Whether long-term, low-level hydrogen sulfide (H2S) gas is a cause of health effects, including asthma, is uncertain. Rotorua city, New Zealand, has the largest population exposed, from geothermal sources, to relatively high ambient levels of H2S. In a cross-sectional study, the authors investigated associations with asthma in this population.

METHODS

A total of 1637 adults, aged 18-65 years, were enrolled during 2008-2010. Residences and workplaces were geocoded. H2S exposures at homes and workplaces were estimated using city-wide networks of passive H2S samplers and kriging to create exposure surfaces. Exposure metrics were based on (1) time-weighted exposures at home and work; and (2) the maximum exposure (home or work). Exposure estimates were entered as quartiles into regression models, with covariate data.

RESULTS

Neither exposure metric showed evidence of increased asthma risk from H2S. However, some suggestion of exposure-related reduced risks for diagnosed asthma and asthma symptoms, particularly wheezing during the last 12 months, emerged. With the maximum exposure metric, the prevalence ratio for wheeze in the highest exposure quartile was 0.80 (0.65, 0.99) and, for current asthma treatment, 0.75 (0.52, 1.08). There was no evidence that this was caused by a "survivor effect".

CONCLUSIONS

The study provided no evidence that asthma risk increases with H2S exposure. Suggestions of a reduced risk in the higher exposure areas are consistent with recent evidence that H2S has signaling functions in the body, including induction of smooth muscle relaxation and reduction of inflammation. Study limitations, including possible confounding, preclude definitive conclusions.

Mitochondrial adaptations to utilize hydrogen sulfide for energy and signaling

Sulfur is a versatile molecule with oxidation states ranging from -2 to +6. From the beginning, sulfur has been inexorably entwined with the evolution of organisms. Reduced sulfur, prevalent in the prebiotic Earth and supplied from interstellar sources, was an integral component of early life as it could provide energy through oxidization, even in a weakly oxidizing environment, and it spontaneously reacted with iron to form iron-sulfur clusters that became the earliest biological catalysts and structural components of cells. The ability to cycle sulfur between reduced and oxidized states may have been key in the great endosymbiotic event that incorporated a sulfide-oxidizing α-protobacteria into a host sulfide-reducing Archea, resulting in the eukaryotic cell. As eukaryotes slowly adapted from a sulfidic and anoxic (euxinic) world to one that was highly oxidizing, numerous mechanisms developed to deal with increasing oxidants; namely, oxygen, and decreasing sulfide. Because there is rarely any reduced sulfur in the present-day environment, sulfur was historically ignored by biologists, except for an occasional report of sulfide toxicity. Twenty-five years ago, it became evident that the organisms in sulfide-rich environments could synthesize ATP from sulfide, 10 years later came the realization that animals might use sulfide as a signaling molecule, and only within the last 4 years did it become apparent that even mammals could derive energy from sulfide generated in the gastrointestinal tract. It has also become evident that, even in the present-day oxic environment, cells can exploit the redox chemistry of sulfide, most notably as a physiological transducer of oxygen availability. This review will examine how the legacy of sulfide metabolism has shaped natural selection and how some of these ancient biochemical pathways are still employed by modern-day eukaryotes.

The therapeutic potential of hydrogen sulfide: separating hype from hope

Hydrogen sulfide (H(2)S) has become the hot new signaling molecule that seemingly affects all organ systems and biological processes in which it has been investigated. It has also been shown to have both proinflammatory and anti-inflammatory actions and proapoptotic and anti-apoptotic effects and has even been reported to induce a hypometabolic state (suspended animation) in a few vertebrates. The exuberance over potential clinical applications of natural and synthetic H(2)S-"donating" compounds is understandable and a number of these function-targeted drugs have been developed and show clinical promise. However, the concentration of H(2)S in tissues and blood, as well as the intrinsic factors that affect these levels, has not been resolved, and it is imperative to address these points to distinguish between the physiological, pharmacological, and toxicological effects of this molecule. This review will provide an overview of H(2)S metabolism, a summary of many of its reported "physiological" actions, and it will discuss the recent development of a number of H(2)S-donating drugs that show clinical potential. It will also examine some of the misconceptions of H(2)S chemistry that have appeared in the literature and attempt to realign the definition of "physiological" H(2)S concentrations upon which much of this exuberance has been established.