A Novel Mechanism To Prevent H2S Toxicity in Caenorhabditis elegans

Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that can be cytoprotective, especially in conditions of ischemia/reperfusion injury. However, H2S is also toxic, and unregulated accumulation or exposure to environmental H2S can be lethal. In Caenorhabditis elegans, the hypoxia inducible factor (hif-1) coordinates the initial transcriptional response to H2S, and is essential to survive exposure to low concentrations of H2S. We performed a forward genetic screen to identify mutations that suppress the lethality of hif-1 mutant animals in H2S. The mutations we recovered are specific for H2S, as they do not suppress embryonic lethality or reproductive arrest of hif-1 mutant animals in hypoxia, nor can they prevent the death of hif-1 mutant animals exposed to hydrogen cyanide. The majority of hif-1 suppressor mutations we recovered activate the skn-1/Nrf2 transcription factor. Activation of SKN-1 by hif-1 suppressor mutations increased the expression of a subset of H2S-responsive genes, consistent with previous findings that skn-1 plays a role in the transcriptional response to H2S. Using transgenic rescue, we show that overexpression of a single gene, rhy-1, is sufficient to protect hif-1 mutant animals in H2S. The rhy-1 gene encodes a predicated O-acyltransferase enzyme that has previously been shown to negatively regulate HIF-1 activity. Our data indicate that RHY-1 has novel, hif-1 independent, function that promotes survival in H2S.

User-oriented independent analysis of the toxic load model's ability to predict the effects of time-varying toxic inhalation exposures

Toxic industrial chemicals and chemical warfare agents present an acute inhalation hazard to exposed populations. The hazardous materials consequence assessment modeling community requires toxicity models to estimate these hazards. One popular phenomenological toxicity model is the toxic load model. Although this model is only well-defined for constant-concentration exposures, several generalizations have been proposed for the case of time-varying exposures. None of them, however, were validated by experimental evidence at the time they were proposed. Accordingly, the Defense Threat Reduction Agency (DTRA) sponsored experiments to explore the effects of time-varying inhalation exposures of hydrogen cyanide (HCN) and carbon monoxide (CO) gas on rats. The experiments were designed and executed by the U.S. Army's Edgewood Chemical and Biological Center (ECBC) and the Naval Medical Research Unit Dayton (NAMRU-D) between 2012 and 2015. We conducted an independent analysis of the toxic load model's ability to predict the ECBC/NAMRU-D experimental data using an analytical methodology oriented toward hazard prediction model users. We found that although some of the proposed extensions of the toxic load model perform better than others, all of them have difficulty reproducing the experimental data. The toxic load model also has difficulty reproducing even the constant-concentration data for HCN exposures under 10 min.

A gene horizontally transferred from bacteria protects arthropods from host plant cyanide poisoning

Cyanogenic glucosides are among the most widespread defense chemicals of plants. Upon plant tissue disruption, these glucosides are hydrolyzed to a reactive hydroxynitrile that releases toxic hydrogen cyanide (HCN). Yet many mite and lepidopteran species can thrive on plants defended by cyanogenic glucosides. The nature of the enzyme known to detoxify HCN to β-cyanoalanine in arthropods has remained enigmatic. Here we identify this enzyme by transcriptome analysis and functional expression. Phylogenetic analysis showed that the gene is a member of the cysteine synthase family horizontally transferred from bacteria to phytophagous mites and Lepidoptera. The recombinant mite enzyme had both β-cyanoalanine synthase and cysteine synthase activity but enzyme kinetics showed that cyanide detoxification activity was strongly favored. Our results therefore suggest that an ancient horizontal transfer of a gene originally involved in sulfur amino acid biosynthesis in bacteria was co-opted by herbivorous arthropods to detoxify plant produced cyanide.DOI: http://dx.doi.org/10.7554/eLife.02365.001.

A comprehensive evaluation of the toxicology of experimental, non-filtered cigarettes manufactured with different circumferences

CONTEXT

Historical work indicates that cigarette circumference may affect the toxicological profile of experimental cigarettes.

OBJECTIVE

Studies were conducted to examine the effect of different cigarette circumferences on (1) selected mainstream smoke constituents including concentrations of tobacco specific nitrosamines (TSNA) in smoke and (2) mutagenicity and cytotoxicity of cigarette smoke condensate.

MATERIALS AND METHODS

Analytical chemistry, Salmonella mutagenicity and cytotoxicity assays were used to evaluate the composition and biological activity of mainstream smoke from experimental, non-filtered cigarettes manufactured with four different circumferences (17.0-27.1 mm).

RESULTS

Most smoke constituents, including TSNA, decreased with decreasing cigarette circumference; however, amounts of hydrogen cyanide increased in a non-circumference dependent manner. Mutagenicity and cytotoxicity also decreased slightly with decreasing cigarette circumference.

CONCLUSION

Cigarette circumference may have a minor role in the toxicological profile of experimental cigarettes, with a so-far-unidentified mechanism.

Genetic diversity analysis of cyanogenic potential (CNp) of root among improved genotypes of cassava using simple sequence repeat markers

Cyanogenic potential (CNp) of cassava constitutes a serious problem for over 500 million people who rely on the crop as their main source of calories. Genetic diversity is a key to successful crop improvement for breeding new improved variability for target traits. Forty-three improved genotypes of cassava developed by International Institute of Tropical Agriculture (ITA), Ibadan, were characterized for CNp trait using 35 Simple Sequence.Repeat (SSR) markers. Essential colorimetry picric test was used for evaluation of CNp on a color scale of 1 to 14. The CNp scores obtained ranged from 3 to 9, with a mean score of 5.48 (+/- 0.09) based on Statistical Analysis System (SAS) package. TMS M98/ 0068 (4.0 +/- 0.25) was identified as the best genotype with low CNp while TMS M98/0028 (7.75 +/- 0.25) was the worst. The 43 genotypes were assigned into 7 phenotypic groups based on rank-sum analysis in SAS. Dissimilarity analysis representatives for windows generated a phylogenetic tree with 5 clusters which represented hybridizing groups. Each of the clusters (except 4) contained low CNp genotypes that could be used for improving the high CNp genotypes in the same or near cluster. The scatter plot of the genotypes showed that there was little or no demarcation for phenotypic CNp groupings in the molecular groupings. The result of this study demonstrated that SSR markers are powerful tools for the assessment of genetic variability, and proper identification and selection of parents for genetic improvement of low CNp trait among the IITA cassava collection.

Assuring process safety in the transfer of hydrogen cyanide manufacturing technology

This paper outlines the critical issues to be addressed in the transfer of hydrogen cyanide (HCN) manufacturing technology to a licensee. Process safety management (PSM) is of critical importance because of the toxicity, flammability and reactivity of HCN. The critical issues are based on experience that DuPont has gained (1) while safely manufacturing hydrogen cyanide for over 50 years, and (2) while DuPont has safely licensed HCN technology to other firms at locations around the world. DuPont's HCN experience has been combined with Aker Kvaerner's project engineering experience to insure the safe transfer of HCN technology to a licensee.

Hydrogen Cyanide-Producing Rhizobacteria Kill Subterranean Termite Odontotermes obesus (Rambur) by Cyanide Poisoning Under In Vitro Conditions

The subterranean termite Odontotermes obesus is an important pest of the Indian subcontinent, causing extensive damage to major agricultural crops and forest plantation trees. Control of termites by strategies employing their parasites has limitations because they have evolved a complex social structure, immune responses, and adaptive behavior toward pathogen-infected individuals. Nonparasitic rhizobacteria that produce harmful metabolites might facilitate the biocontrol of termites. In the present investigation, three different species of hydrogen cyanide-producing rhizobacteria were tested for their potential to kill O. obesus. The three bacterial species were found to be effective in killing the termites under in vitro conditions.

Investigation of the physiological relationship between the cyanide-insensitive oxidase and cyanide production in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen which demonstrates considerable respiratory versatility, possessing up to five terminal oxidases. One oxidase, the cyanide-insensitive oxidase (CIO), has been previously shown to be resistant to the potent respiratory inhibitor cyanide, a toxin that is synthesized by this bacterium. This study investigated the physiological relationship between hydrogen cyanide production and the CIO. It was found that cyanide is produced in P. aeruginosa at similar levels irrespective of its complement of CIO, indicating that the CIO is not an obligatory electron sink for cyanide synthesis. However, MICs for cyanide and growth in its presence demonstrated that the CIO provides P. aeruginosa with protection against the effects of exogenous cyanide. Nevertheless, the presence of cyanide did not affect the viability of cio mutant strains compared to the wild-type during prolonged incubation in stationary phase. The detection of the fermentation end products acetate and succinate in stationary-phase culture supernatants suggests that P. aeruginosa, irrespective of its CIO complement, may in part rely upon fermentation for energy generation in stationary phase. Furthermore, the decrease in cyanide levels during incubation in sealed flasks suggested that active breakdown of HCN by the culture was taking place. To investigate the possibility that the CIO may play a role in pathogenicity, wild-type and cio mutant strains were tested in the paralytic killing model of Caenorhabditis elegans, a model in which cyanide is the principal toxic agent leading to nematode death. The CIO mutant had delayed killing kinetics, demonstrating that the CIO is required for full pathogenicity of P. aeruginosa in this animal model.

An internal dose model of incapacitation and lethality risk from inhalation of fire gases

A mathematical model for estimating the likelihood of incapacitation and lethality from the inhalation of toxic gases is presented. The model computes an internal dose, equal to retained toxic gas per body mass, which is used to extrapolate outcomes across species. Account is taken for ventilation changes due to species, activity, and chemical response. The internal dose is correlated with each outcome using a cumulative, log-normal, probability distribution, which allows the estimation of tolerances for any population incidence. No internal interactions of gases are modeled and probabilities are combined independently. The model compares favorably with combined gas and large animal data.

Promotion of noise-induced hearing loss by chemical contaminants

Recent studies have underscored the ability of a wide range of chemical agents to potentate noise-induced hearing loss. Given the ubiquitous nature of noise exposure particularly in many work settings, the high rate of noise-induced hearing loss, the limited degree to which auditory function can recover following damage to the inner ear, and the disparate chemical structures that appear capable of impairing hearing, this issue appears to have great public health significance. A compendium of chemicals known to potentiate noise induced hearing loss is presented along with a hypothesis that might explain at least one basis for potentiation of noise-induced hearing loss by certain chemical toxicants. The use of benchmark dose analysis to undertake a risk assessment for promotion of noise-induced hearing loss by both carbon monoxide and hydrogen cyanide is described.

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

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

A review of the volatile metabolites of fungi found on wood substrates

The holdings of eight collections of fungi have been examined for organisms isolated from wood and/or trees. Further selection of these fungi has been made according to their reported ability to produce volatile, biologically active metabolites. It is emphasized that the isolates in the collections do not necessarily produce such metabolites. The list of fungi fulfilling these conditions is slightly augmented by reports we have found in the literature, where the fungi concerned have not yet been deposited. The biochemistry of these compounds is considered with particular emphasis on their biosynthesis including that by Homo sapiens. The physiological and toxicological activity of these metabolites is reviewed especially with reference to their potential role in the complex symbioses existent in, for example, a tree. The review concludes with a discussion of areas of botany deserving increased attention in the hope that this will stimulate further work. The statements in the review are based on 173 references.

Potentiation of noise-induced hearing loss by low concentrations of hydrogen cyanide in rats

Noise-induced hearing loss is the most prevalent occupational injury in the United States despite the adoption of clear permissible exposure limits and protocols for hearing conservation. This study identifies low-level chemical asphyxiant exposure as a risk factor capable of potentiating noise-induced hearing loss. Rats were exposed to 10, 30, and 50 ppm hydrogen cyanide (HCN) alone for 3.5 h (n = 28) or in combination with 2 h octave band noise exposure (100 dB(lin); n = 28). Additional groups received noise exposure alone (n = 16) and no treatment other than placement in an inhalation chamber with clean air and quiet (n = 16). Pure tone compound action potential (CAP) thresholds were determined 4 weeks following the exposure in order to assess pure tone auditory sensitivity and permanent threshold impairment. Cochleae from an additional 13 subjects were processed for light microscopy to permit assessment of hair cell loss. The results demonstrate that the noise exposure alone impaired CAP threshold by about 10 dB, averaged between 12-40 kHz, and produced a 5% loss of outer hair cells at the base of the cochlea, but no inner hair cell loss. The combined exposure to noise and HCN caused a cyanide dose-dependent CAP threshold impairment that exceeds the noise exposure alone. This effect reached statistical significance at a HCN level of 30 ppm. Combined exposure also produced more outer hair cell loss than noise alone. HCN alone did not cause significant hearing loss or hair cell loss. A risk assessment analysis was conducted for the auditory threshold data using benchmark dose software published by the U. S. EPA (BMDS version 1.3). A continuous model showed that the data could be described by a linear function. For a benchmark response corresponding to a 5 dB increase in auditory threshold above the effect of noise alone, the lower bound on the 95% confidence interval for the benchmark dose was 9 ppm. The benchmark dose that impaired auditory threshold 10% above the effect of noise alone had a lower bound of 2 ppm. The lower bound to the HCN dose that produced a 1 SD elevation in noise-induced hearing loss was 16 ppm. These exposure levels provide a range of concentrations below to slightly above the short-term exposure limit for HCN. However, if these levels are adjusted for an 8 h time-weighted average (TWA), the resulting levels are below the permissible exposure level (PEL) for HCN.

Interaction between noise and asphyxiants: a concern for toxicology and occupational health

The article highlighted in this issue is "Potentiation of Noise-Induced Hearing Loss by Low Concentrations of Hydrogen Cyanide in Rats" by Laurence D. Fechter, Guang-Di Chen, and David L. Johnson (pp. 131-138).

Effect of cyanide concentrations on the secondary structures of protein in the crude homogenates of the fish gill tissue

The effect of cyanide concentrations on the secondary conformation of protein in the fish gill homogenate was determined using an attenuated total reflectance (ATR)/Fourier transform infrared (FT-IR) microspectroscopy. Gills from male Tilapia zillii were isolated and homogenized in pH 8.0 Tris buffer solution and subjected to FT-IR study. The results indicate that the amide I and III bands of protein in fish gill homogenate deformed markedly with the increase of cyanide concentration. The fish gill homogenate shows a maximum peak at 1650 cm(-1) in amide I band, suggesting the predominant proportion of alpha-helical conformation. Once the KCN was added into the gill homogenate, the maximum peak shifted gradually from 1650 to 1643 cm(-1) due to the random coil structure, with the increase of cyanide concentration used. Two additional shoulders at 1657 (alpha-helix) and 1627 (beta-sheet) cm(-1) also appeared gradually, implying that the cyanide can in part induce changes in protein conformation of fish gill homogenate from alpha-helix to random coil and beta-sheet conformations.

Organosulfur compounds as pre-exposure therapy for threat agents

A series of symmetric (Ar-S-S-Ar) and unsymmetric (Ar-S-S-CH2CH2NH3+Cl-) disulfides have been prepared and evaluated as potential cyanoprotective agents. Target compounds have been prepared by known methods and/or methods developed by us specifically for this program, e.g. reaction of a thiol with 2,2'-dithiobis(benzothiazole) (BT-S-S-BT) followed by reaction with a second thiol. Both 4-methoxyphenyl disulfide and 2-aminoethyl-4-methoxyphenyl disulfide hydrochloride are cyanoprotective against 2-LD50 of injected cyanide. Evaluation of both symmetric and unsymmetric related disulfides indicates that structural requirements for cyanoprotective activity are stringent and strongly suggest that protection is enzyme mediated. In addition to cyanoprotective action, initial results suggest that unsymmetric disulfides may evolve into effective antimustard agents.

Cyanide exposure affects the production and excretion of ammonia by the mudskipper Boleophthalmus boddaerti

The concentrations of ammonia in the plasma of the mudskipper Boleophthalmus boddaerti exposed to cyanide for 1-6 days were significantly greater than the respective values of the controls. This was due to an increase in the production of NH3 in the muscle and an increase in the retention of NH3 and/or NH4+ in the blood of the cyanide-exposed fish when compared to controls. Cyanide exposure significantly increased the specific activity of muscle AMP deaminase. Since adenylosuccinate synthetase and lyase were also present in the muscle, exposure to cyanide might increase the production of NH3 from the catabolism of purine nucleotides. B. boddaerti exposed to cyanide excreted significantly less ammonia than the control fish. Results indicate changes in the permeability of the epithelial surfaces of the cyanide-exposed fish to NH3 and/or NH4+. Since the tissues and organs needed time to activate the inducible cyanide detoxification mechanisms, the increase in the production of NH3 might be an important defensive mechanism for B. boddaerti during the early phase of cyanide exposure.

Exposures to carbon monoxide, hydrogen cyanide and their mixtures: interrelationship between gas exposure concentration, time to incapacitation, carboxyhemoglobin and blood cyanide in rats

Carbon monoxide (CO) and hydrogen cyanide (HCN) are generated during aircraft interior fires in sufficient amounts to incapacitate cabin occupants. For typical post-crash and in-flight fires, minimum protection periods of 5 and 35 min, respectively, have been suggested for breathing devices to protect the occupants from smoke. Relationships of blood carboxyhemoglobin (COHb) and cyanide (CN-) levels to incapacitation have not been well defined for these gases. Therefore, time to incapacitation (ti) and blood COHb and CN- at incapacitation were examined in rats exposed to CO (5706 ppm for 5-min ti; 1902 ppm for 35-min ti), HCN (184 ppm for 5-min ti; 64 ppm for 35-min ti) and their mixtures (equipotent concentrations of each gas that produced 5- and 35-min ti). Blood CO and HCN uptakes were evaluated at the two concentrations of each gas. With either gas, variation in ti was higher for the 35-min ti than the 5-min ti The COHb level reached a plateau prior to incapacitation at both CO concentrations, and COHb levels at the 5- and 35-min ti were different from each other. Blood CN- increased as a function of both HCN concentration and exposure time, but CN- at the 5-min ti was half of the 35-min ti CN- level. The HCN uptake at the high concentration was about three times that at the low concentration. In the high concentration CO-HCN mixture, ti was shortened from 5 to 2.6 min; COHb dropped from 81 to 55% and blood CN- from 2.3 to 1.1 microgram ml(-1). At the low-concentration CO-HCN mixture, where ti was reduced from 35 to 11.1 min, COHb decreased from 71 to 61% and blood CN- from 4.2 to 1.1 microgram ml(-1). Any alteration in the uptake of either gas by the presence of the other was minimal. Our findings suggest that specific levels of blood COHb and CN- cannot be correlated directly with the incapacitation onset and that postmortem blood COHb and CN- levels should be evaluated carefully in fire victims.

Nutrient content of young cassava leaves and assessment of their acceptance as a green vegetable in Nigeria

Cassava (Manihot esculenta Crantz) leaves contained a high level of crude protein (29.3-32.4% dry weight) compared to a conventional vegetable, Amaranthus (19.6%). Ash was 4.6-6.4% in cassava leaf samples but 13.1% dry weight in Amaranthus. Dietary fibre was very high in all samples (26.9-39% dry weight) while HCN-potential was low (5.1-12.6 mg/100 g dry weight). Tannin was the highest in IITA red cassava leaves (29.7 mg/g) and the lowest in Amaranthus vegetable. In vitro digestibility was very low in oven dried samples (15.6-22.7%). Blanching increased protein content (except Amaranthus) and in vitro protein digestibility but decreased ash, minerals, dietary fibre and tannin, while HCN-potential was unchanged. Grinding reduced both HCN-potential and tannin by 84 and 71% respectively while oven drying only reduced the HCN content marginally. Preference studies showed that the highest percentage of respondents (25.3%) preferred Amaranthus vegetable, followed by Celosia (17.5%), Talinum (12.4%), garden egg (11.5%), with cassava leaves as the least (0.5%). Organoleptic evaluation rated cassava leaf soup inferior to Amaranthus in terms of appearance, colour and texture but equal in terms of taste and flavour and overall acceptability.

Use of a sealed minichamber for direct observation and evaluation of the in vitro effect of cigarette smoke on sperm motility

OBJECTIVE

To determine the in vitro effect of cigarette smoke on sperm motility and survival in an attempt to find a possible association with clinical studies that had pointed to the existence of such an effect in vivo.

DESIGN

Laboratory experiments in which the effect of cigarette smoke on human sperm placed in a sealed minichamber was directly observed and determined by motion analysis.

PATIENTS

High-quality fresh semen specimens were obtained from healthy donors and used for the experimental studies.

INTERVENTIONS

Various doses of filtered and nonfiltered cigarette smoke, collected by an improvised manual smoking machine, were streamed at a rate of 2 mL/s into sealed chambers containing samples of washed spermatozoa. Evaluation of the changes in sperm motility was performed in real time by direct microscopical observation and repeated determinations by the multiple exposure photography technique until their complete immobilization.

RESULTS

Streaming of 100 mL of cigarette smoke induced a dramatic drop in sperm motility, which caused sperm immobilization in about 15 minutes. This effect showed a clear dose-response relationship either with the amounts streamed or with the time during which sperm were exposed to cigarette smoke. The harmful effect was almost the same whether sperm were exposed to filtered or nonfiltered cigarette smoke. The role of carbon monoxide and hydrogen cyanide on these findings was studied separately, and it was shown that the inhibitory effect was not due to the presence of these two important components of cigarette smoke.

CONCLUSIONS

The clear evidence of the in vitro harmful effect of crude cigarette smoke on sperm motility points to the possibility that in heavy smokers certain toxic agents may reach mature spermatozoa or their precursors via the blood stream and induce their harmful effect on sperm motility in vivo.

The development of a new small-scale smoke toxicity test method and its comparison with real-scale fire tests

A comprehensive methodology has been developed for obtaining and using smoke toxicity data for fire hazard analysis. This bench-scale method can simulate diverse fire conditions and identify extremely toxic smoke under both pre- and post-flashover conditions. However, incidence data show that most of the fire deaths in the U.S. occur outside the room of fire origin from smoke and toxic gases that are generated from a fire under post-flashover conditions. Therefore, the most relevant real-scale combustion conditions to simulate in the bench-scale apparatus would be the post-flashover conditions which are achieved by using radiant heat, a high heat flux, and correcting the bench-scale carbon monoxide (CO) results to agree with CO yields observed in real-scale post-flashover fires. The number of test animals (Fischer 344 male rats) is minimized by using the N-Gas Model to estimate the LC50 value from the chemical analysis of the smoke. The current N-Gas Model predicts the toxicity of complex fire gas mixtures based on a large data base of experimental results of individual and mixed gases that include CO, CO2, reduced O2, HCN, HCl, HBr, and NOx. The prediction is checked with a small number of animal tests and an approximate LC50 value is determined. The bench-scale results have been validated with full-scale room wall burns of a limited number of materials of widely differing characteristics chosen to challenge the system. The toxic potency values are assessed to determine if the smoke from a material or product is unusually or extremely toxic and can then be used in computations of fire hazard.

The evolution of toxic effluents in fires and the assessment of toxic hazard

Toxic hazard in fire depends upon three factors: the fire growth curve (mass loss rate of materials, kg/min) and volume dispersal (kg/m3), the yields of toxic products (e.g. kg CO/kg fuel burned) and the toxic potency of the products (exposure dose needed to cause toxic effects, e.g. lethal dose of CO in ppm.min). The first and second sets of data are obtainable from large-scale tests or small-scale tests and mathematical modelling, the third and some information on the second are derived from toxicity studies of combustion products in small-scale tests or of individual fire gases. Small-scale toxicity test data on materials expressed as lethal mass loss exposure doses (LCt50 g min m-3) can be used in Fractional Effective Dose (FED) hazard assessments, providing the decomposition conditions of the test reproduce those in the fire being examined; principally either non-flaming oxidative, early well-ventilated flaming, or vitiated post-flashover. Although bioassays are needed for a full toxicity assessment, it is now possible to predict the toxic potency of materials to some extent from analytical data alone. The suitability of the small-scale test decomposition conditions are determined in terms of non-flaming or flaming behaviour, temperature (or radiant flux), CO2/CO ratio and oxygen concentration. Existing small-scale test methods provide reasonable models for materials under non-flaming oxidative and early flaming conditions, although the data base for the latter is poor. Only the DIN 53436 method is able to model vitiated post-flashover decomposition conditions, but data for this condition are almost non-existent.

Modeling of toxicological effects of fire effluents: prediction of toxicity and evaluation of animal model

Methodology for the prediction of the toxic effects of fire effluents has made considerable progress [1,2]. As emphasized by Hartzell [2] a limiting factor has often been the availability and quality of analytical input data. The Finney model [3] was used to predict the lethal potency and would appear to have utility as a tool in reducing the number of experimental animals used in material testing. However, pilot bioassay data are indispensable to validate the prediction and to categorize fire effluents into narcosis inducing, irritant or of causing unusual or unexpected toxicity. The comparison of predicted and actually observed carboxy-hemoglobin levels is considered to be a sensitive but indirect tool to assess whether major effects on respiration occurred. All laboratory combustion toxicity methods suffer from several types of limitations. However, they might be expected to be relatable to at least some stages of actual fires. Due to a lack of a clearly defined 'generation process'--if compared with conventional inhalation toxicity studies--the classification into broad categories of relative toxic potency seemed to be more appropriate than an absolute classification scheme.

[Granulocyte metabolism in workers at a coke-processing plant]

Acid phosphatase activity examinations and nitrotetrazolium blue reduction test after latex stimulation in peripheral blood neutrophils were performed in the group of 32 coking plant workers. Reference group consisted of 150 men not exposed to any toxic substances. Neutrophils of coking plant workers, comparing with the reference group, revealed decreased activity of acid phosphatase and impaired reduction of nitrotetrazolium blue after latex stimulation. The results suggest the possibility of toxic influence of coking plant environment on the lysosomal enzymes and oxygen-dependent metabolism of neutrophils what subsequently may diminish bactericidal powers.

[Various principles of the formation of toxic gaseous pesticide degradation products in the soil]

The intensity of gaseous products of pesticides degradation in soil depends on the natural and antropogenic factors: type of soil, hydrothermal conditions, dose of the pesticide, presence in soil of other agrochemicals which can inhibit and also potentiate this process. The optimal conditions for the formation of volatile products of decay of chlororganic pesticides are created in dark chestnut and gray soils, derivatives of carbamine acids--in dark grey soil at humidity of 60-80% from the complete moisture capacity. Mineral fertilizers--ammoniacal nitrate and ammoniacal water, herbicides ronite and betanol--potentiate the decay of chlororganic pesticides, which can be used in the development of measures on soil purification from persistent pesticides.

Effects of exposure to single or multiple combinations of the predominant toxic gases and low oxygen atmospheres produced in fires

The toxicity of single and multiple fire gases is studied to determine whether the toxic effects of the combustion products from materials can be explained by the toxicological interactions (as indicated by lethality) of the primary fire gases or if minor, more obscure gases need to be considered. LC50 values for Fischer-344 rats have been calculated for the individual gases, carbon monoxide (CO), hydrogen cyanide (HCN), or decreased oxygen (O2), for 30-min exposures plus relevant postexposure periods using the NBS Toxicity Test Method. Combination experiments with CO and HCN indicate that they act in an additive manner. Synergistic effects have been found when the animals are exposed to certain combinations of CO and carbon dioxide (CO2). Five percent CO2 raised the threshold for deaths due to hypoxia and decreased the LC50 of HCN. Decreasing the O2 concentration in the presence of various mixtures of the other major fire gases increased the toxicity even further. A comparison of the concentrations of the major combustion products generated from a number of polymeric materials at their LC50 (30-min exposure plus 14-day postexposure) values with the combined pure gas results indicates that, in most cases, the observed toxicity may be explained by the toxicological interactions of the examined primary toxic fire gases. These results provide necessary information for the computer model currently being developed at the Center for Fire Research to predict the toxic hazard that people will experience under various fire scenarios.

Acute effects of carbon monoxide and cyanide on hepatic mitochondrial function

The effects of carbon monoxide and cyanide on the hepatic redox state and energy charge were investigated. Rats were used for the experiment under pentobarbital anesthesia. Immediately after laparotomy, a rat was placed in an animal chamber made of a transparent plastic box and exposed to a test gas for 3 min. Every test gas was produced in a gas chamber connected to the animal chamber with a flexible tube. HCN was produced from NaCN and H2SO4. In the CO inhalation experiment, various amounts of CO were introduced into the gas chamber. Immediately after an exposure, about 2 g liver was frozen in situ with a precooled clamp. Oozed blood from the wound surface was sampled. Concentrations of ATP, ADP, AMP, acetoacetate, and beta-hydroxybutyrate in hepatic mitochondria were determined, and the redox state and the energy charge were calculated. For cyanide as well as CO, significant negative correlations were found between the concentration in the blood and the redox state. The same held true for the energy charge. The redox state showed a slight increase at low concentrations of both gases; however, thereafter it began to decrease sharply with increases in concentrations. When concentrations of the toxicant in the blood reached certain levels, a kind of turning point, beyond which the redox state does not decrease any more, was observed. It was about 40% for HbCO and about 2.0 micrograms/ml for cyanide, and the points seemed to be related to the concentrations, beyond which cells are irreversibly damaged. On the other hand, the energy charge did not change at low concentrations. With an increase in toxicant concentrations, the energy charge decreased drastically. The rate of decrease in the energy charge became higher when blood concentrations exceeded certain levels. It was about 40% for HbCO and 2.0 micrograms/ml for cyanide. The presence of low levels of blood cyanide did not affect the relationship between the energy charge and the HbCO concentration.

Intoxication by cyanide in fires: a study in monkeys using polyacrylonitrile

It is suspected that hydrogen cyanide (HCN) may be an important factor in incapacitating fire victims, but the effects of sublethal exposures are not well characterized. Also, the incapacitating effects of fire atmospheres result from exposure to a mixture of toxic products so that the contribution from each component is difficult to determine. The mechanisms of incapacitation in monkeys exposed to the pyrolysis products of polyacrylonitrile (PAN) were compared to those resulting from low level HCN gas exposures. The physiological effects of the PAN atmospheres were almost identical to those of HCN gas alone. They consisted of hyperventilation, followed by loss of consciousness after 1-5 min, bradycardia with arrhythmias and T-wave abnormalities, and were followed by a rapid recovery after exposure. Hydrogen cyanide is considered to be the major toxic product formed by the pyrolysis of PAN. It is suggested that HCN may produce rapid incapacitation at low blood levels of cyanide in fires, while death may occur later due to carbon monoxide poisoning or other factors.

Teratogenic effects of aliphatic nitriles

Intraperitoneal injection of acrylonitrile at 1.51-2.26 mmole/kg (80-120 mg/kg) or propionitrile at 0.54-1.51 mmole/kg (30-83 mg/kg) on the morning of Day 8 of gestation in the hamster induced exencephaly, encephalocoeles, and rib fusions and bifurcations in the offspring. These doses of the aliphatic nitriles also resulted in obvious toxicity to the dams. Multiple intraperitoneal injections of sodium thiosulfate at 4.03 mmole/kg (1 gm/kg) protected both dams and embryos against toxicity. When the larger doses of either acrylonitrile or propionitrile were given in the presence of sodium thiosulfate, teratogenic effects were observed in the absence of overt signs of maternal poisoning. A survey of the literature describes many studies which demonstrate that acrylonitrile and propionitrile are converted in vivo to toxicologically significant concentrations of cyanide and that sodium thiosulfate, an established cyanide antagonist, can provide protective actions against poisoning by either acrylonitrile or propionitrile. The observations suggest that the teratogenic effects of both acrylonitrile and propionitrile are related to the metabolic release of cyanide.

A study on the combined action of CO and HCN in terms of concentration-time products

Acute toxicity at single and combined exposures of CO and HCN was studied on rats in terms of concentration-time product (ppm . min) necessary to kill animals (lethal CT). The animal was exposed individually to test gas in an animal chamber made of transparent plastics, and test gas was made in gas chamber connected to the animal chamber by a wide and short piece of plastic tube. HCN was produced by addition of NaCN solution to H2SO4 and in case of CO exposure, various amounts of pure CO were introduced. During exposure, gas samples were frequently taken. After exposure, blood sample was withdrawn from the right side of the heart. CO concentrations in the gas and blood were determined gas chromatographically. HCN in the gas sample was measured spectrophotometrically, after being absorbed into NaOH solution in a glass vessel devised by our laboratory. At single exposures, mean lethal CT for CO was 78,000 +/- 22,000 and for HCN was 4,700 +/- 940. In combined exposure, various combinations of CO and HCN were used. A fractional CT, defined as a ratio of CT to lethal CT, multiplied by 100, was calculated for each gas. A linear relationship between fractional CTs of HCN and CO was considered to show a simple additive action between the two gases. The sum of both fractional CTs averaged 100 +/- 26. On the other hand, linear relation was not observed between blood levels of the two toxicants at death.

Chronic cyanide poisoning of rainbow trout and its effects on growth, respiration, and liver histopathology

Cyanide markedly affected growth and resting metabolic rate while causing degenerative hepatic necrosis in juvenile rainbow trout (Salmo gairdneri, Richardson). This was revealed during two experiments performed in continuously renewed water at 12.5 degree C with fish fed a restricted artificial diet and exposed to assayed cyanide concentrations of 0.00, 0.01, 0.02, or 0.03 mg/L hydrogen cyanide (HCN) for 18 days. At 0.02 and 0.03 mg/L, HCN growth was reduced by 40 to 95% after 18 days. At all concentrations, cyanide caused a severe initial repression of specific growth rate, followed by a highly significant increase which was insufficient to compensate for the original repression. Previous exposure to cyanide promoted a higher resting metabolic rate during the six days following exposure, the effect increasing with cyanide concentration. At all concentrations tested, widespread cyanide-induced degenerative necrosis of hepatocytes was observed; it was more intense at higher cyanide concentrations and well established even at 0.01 mg/L HCN.

Toxicity of Saskatoon serviceberry to cattle

Saskatoon serviceberry (Amelanchier alnifolia) twigs were administered to cattle in feed rations and by intraruminal dosing to determine the toxicity of the cyanogenic shrub. When chopped twigs were fed as 75% of the diet, cattle exhibited restlessness, shivering, loss of weight, scours and shortness of breath. Low level dosing experiments indicated a rapid turnover of hydrogen cyanide in the rumen. When potential doses were increased to 5 mg hydrogen cyanide/kg (body weight) progressive stages of poisoning developed rapidly, rumen hydrogen cyanide levels were elevated for at least three hours and the increase in heart rate correlated with the rise in blood hydrogen cyanide concentration.

[Significance of hydrocyanic acid formation during fires]

Cyanide concentrations of blood samples from fire victims autopsied in the Institute of Legal Medicine, Munich, have been determined. In 25% of 48 analyzed cases cyanide concentrations from 0.52 microgram to 6.24 microgram Cyanide/ml blood have been detected. These results are compared to former studies and the higher mean level in our collective is emphasized. The importance of hydrocyanid acid in the toxicity of fire gases is evidently greater, than assumed. Hydrocyanic acid may be produced from nitrogen continaing polymers during combustion. The quote of these polymers in clothing, furniture, and also in equipment of cars is increasing. Therefore, it is necessary to take more notice of the formation of hydrocyanic acid during combustion, even though carbon monoxide is in general the main toxic agent in fire gases.

Effects of cyanogenic agents on reproduction and neonatal development in rats

A diet consisting of 50% gari (a form of cassava meal) was found to cause no significant biochemical and haematological changes in adult female rats. Although this diet caused a significant increase in their serum thiocyanate levels, there was no corresponding significant increase in the weight of their thyroid glands. The offspring of these rats had significantly lower birth weights and brain weights and never attained the same adult weights as those of the controls. Adult female rats fed a diet consisting entirely of raw cassava had significantly reduced haematological and biochemical indices. This diet also caused an increased incidence of cannibalism and a significant reduction in the frequency of pregnancy, the average number of the litter and the birth weights among these rats. In addition there was an increased incidence of neonatal deaths among the offspring which also had poor development, reduced brain weights and an increased tendency towards biting their litter-mates. Adult female rats fed diets containing 5 and 10 g cyanide/100 g laboratory diet survived for more than 3 months but never became pregnant. They developed enlarged thyroid glands and tumours of the large intestine. The relevance of these findings to the areas of the world where cyanogenic glycosides form the staple diet is discussed.

Toxic gases from fires

The major lethal factors in uncontrolled fires are toxic gases, heat, and oxygen deficiency. The predominant toxic gas is carbon monoxide, which is readily generated from the combusion of wood and other cellulosic materials. Increasing use of a variety of synthetic polymers has stimulated interest in screening tests to evaluated the toxicity of polymeric materials when thermally decomposed. As yet, this country lacks a standardized fire toxicity test protocol.