Structure-activity relationships of volatile organic chemicals as sensory irritants

Establishing short-term occupational exposure limits (STELs) for sensory irritants using predictive and in silico respiratory rate depression (RD50) models

Sensory irritation is a health endpoint that serves as the critical effect basis for many occupational exposure limits (OELs). Schaper 1993 described a significant relationship with high correlation between the measured exposure concentration producing a 50% respiratory rate decrease (RD50) in a standard rodent assay and the American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Values (TLVs®) as time-weighted averages (TWAs) for airborne chemical irritants. The results demonstrated the potential use of the RD50 values for deriving full-shift TWA OELs protective of irritant responses. However, there remains a need to develop a similar predictive model for deriving workplace short-term exposure limits (STELs) for sensory irritants. The aim of our study was to establish a model capable of correlating the relationship between RD50 values and published STELs to prospectively derive short-term exposure OELs for sensory irritants. A National Toxicology Program (NTP) database that included chemicals with both an RD50 and established STELs was used to fit several linear regression models. A strong correlation between RD50s and STELs was identified, with a predictive equation of ln (STEL) (ppm) = 0.86 * ln (RD50) (ppm) - 2.42 and an R2 value of 0.75. This model supports the use of RD50s to derive STELs for chemicals without existing exposure recommendations. Further, for data-poor sensory irritants, predicted RD50 values from in silico quantitative structure activity relationship (QSAR) models can be used to derive STELs. Hence, in silico methods and statistical modeling can present a path forward for establishing reliable OELs and improving worker safety and health.

Parameter Mapping Sonification of Human Olfactory Thresholds

An objective of chemical ecology is to understand the chemical diversity across and within species, as well as the bioactivity of chemical compounds. We previously studied defensive volatiles from phytophagous insects that were subjected to parameter mapping sonification. The created sounds contained information about the repellent bioactivity of the volatiles, such as the repellence from the volatiles themselves when tested against live predators. Here, we applied a similar sonification process to data about human olfactory thresholds. Randomized mapping conditions were used and a peak sound pressure, Lpeak, was calculated from each audio file. The results indicate that Lpeak values were significantly correlated with the olfactory threshold values (e.g., r_S = 0.72, t = 10.19, p < 0.001, Spearman rank-order correlation; standardized olfactory thresholds of 100 volatiles). Furthermore, multiple linear regressions used the olfactory threshold as a dependent variable. The regressions revealed that the molecular weight, the number of carbon and oxygen atoms, as well as the functional groups aldehyde, acid, and (remaining) double bond were significant determinants of the bioactivity, while the functional groups ester, ketone, and alcohol were not. We conclude that the presented sonification methodology that converts chemicals into sound data allows for the study of their bioactivities by integrating compound characteristics that are easily accessible.

Reliable prediction of sensory irritation threshold values of organic compounds using new models based on linear free energy relationships and GC×GC retention parameters

The human sensory irritation threshold (SIT) is an important biochemical parameter for the exposure assessment of organic air pollutants. First, we recalibrated the Abraham solvation models (ASMs) for 9 SIT endpoints by curating 720 individual experimental SIT values to find an accurate and parsimonious ASM variant, which exhibited root mean square error (RMSE) = 0.174-0.473 log unit. Second, we report linear free energy relationships - henceforth called partition models (PMs) - which exploit the correlations of 9 SIT endpoints with the linear combinations of partition coefficients for octanol-water and air-water systems showing RMSE = 0.221-0.591 log unit. These PMs can easily be integrated into widely used EPI-Suite™ screening tool. The explanatory and predictive performance of PMs were like parameter-intensive ASMs. Third, we present GC × GC models that are based on the retention times of the nonpolar analytes on the comprehensive two-dimensional gas chromatography (GC × GC), which successfully described the SIT variance (R²=0.959-0.996) and depicted a strong predictive power (RMSE = 0.359-0.660 log unit) for an independent set of nonpolar analytes. Taken together, PMs allow easy SIT screening of organic chemicals compared to ASMs. Unlike ASMs, our GC × GC models can be applied to estimate SIT of complex nonpolar mixtures.

Air Quality as a Key Factor in the Aromatisation of Stores: A Systematic Literature Review

Scientific literature on indoor air quality is categorised mainly into environmental sciences, construction building technology and environmental and civil engineering. Indoor air is a complex and dynamic mixture of a variety of volatile and particulate matter. Some of the constituents are odorous and originate from various sources, such as construction materials, furniture, cleaning products, goods in stores, humans and many more. The first part of the article summarises the knowledge about the substances that are found in the air inside buildings, especially stores, and have a negative impact on our health. This issue has been monitored for a long time, and so, using a better methodology, it is possible to identify even low concentrations of monitored substances. The second part summarises the possibility of using various aromatic substances to improve people’s sense of the air in stores. In recent times, air modification has come to the forefront of researchers’ interest in order to create a more pleasant environment and possibly increase sales.

Derivation of Occupational Thresholds of Toxicological Concern for Systemically Acting Noncarcinogenic Organic Chemicals

Many substances in workplace do not have occupational exposure limits. The threshold of toxicological concern (TTC) principle is part of the hierarchy of approaches useful in occupational health risk assessment. The aim of this study was to derive occupational TTCs (OTTCs) reflecting the airborne concentrations below which no significant risk to workers would be anticipated. A reference dataset consisting of the 8-h threshold limit values-Time-Weighted Average for 280 organic substances was compiled. Each substance was classified into low (class I), intermediate (class II), or high (class III) hazard categories as per Cramer rules. For each chemical, n-octanol:water partition coefficient and vapor pressure along with the molecular weight were used to predict the blood:air partition coefficient. The blood:air partition coefficient along with data on water solubility and ventilation rate allowed the prediction of pulmonary retention factor and absorbed dose in workers. For each Cramer class, the distribution of the predicted doses was analyzed to identify the various percentile values corresponding to the OTTC. Accordingly, for Cramer classes I-III, the OTTCs derived in this study correspond to 0.15, 0.0085, and 0.006 mmol/d, respectively, at the 10th percentile level, while these values were 1.5, 0.09 and 0.03 mmol/d at the 25th percentile level. The proposed OTTCs are not meant to replace the traditional occupational exposure limits, but can be used in data-poor situations along with exposure estimates to support screening level risk assessment and prioritization.

Clinical Effects, Exhaled Breath Condensate pH and Exhaled Nitric Oxide in Humans After Ethyl Acrylate Exposure

Ethyl acrylate is an irritant known to affect the upper airways and eyes. An increase of the eye blink frequency in humans was observed during exposure to 5 ppm. Studies on the lower airways are scant and our study objective was the evaluation of pH in exhaled breath condensate (EBC-pH) and nitric oxide in exhaled breath (FeNO) as markers of inflammation. Sixteen healthy volunteers were exposed for 4 h to ethyl acrylate at a concentration of 5 ppm and to sham (0.05 ppm) in an exposure laboratory. Clinical irritation symptoms, EBC-pH (at a pCO2 of 5.33 kPa) and FeNO were assessed before and after exposure. Differences after ethyl acrylate exposure were adjusted for those after sham exposure. 5 ppm ethyl acrylate induced clinical signs of local irritation in the nose and eyes, but not in lower airways. Exposure produced a subtle, but statistically significant, decrease in breathing frequency (1 breath/min; p = 0.017) and a lower EBC-pH (by 0.045 units; p = 0.037). Concerning FeNO, we did not observe significant changes compared to sham exposure. We conclude that local effects induced by 5 ppm ethyl acrylate consist of sensory irritation of eyes and nose. In addition, acute ethyl acrylate exposure to 5 ppm resulted in a net decrease of EBC-pH. Whether that can be interpreted in terms of additional lower airway irritation or already inflammatory alterations set in needs further investigations.

Human symptom responses to bioeffluents, short-chain carbonyls/acids, and long-chain carbonyls in a simulated aircraft cabin environment

Occupants of aircraft have reported an array of symptoms related to general discomfort and irritation. Volatile organic compounds (VOCs) have been suggested to contribute to the reported symptoms. VOCs are from products used, bioeffluents from people and oxidation reaction products. Thirty-six healthy, young female subjects rated symptoms and environmental quality during an eight-hour exposure to groups of compounds often present in aircraft: (i) long-chain carbonyls, (ii) simulated bioeffluents, and (iii) short-chain carbonyls/organic acids. Statistically more symptoms were identified for the simulated bioeffluents and, to a lesser extent, short-chain carbonyls/organic acids compared to a control condition, although they remained in the acceptable range. There were three temporal patterns in the environmental quality and symptom reports: (i) an adaptive response (immediate increases followed by a decline); (ii) an apparent physiological effect (increases one to three hours into the exposure that remained elevated); and (iii) no statistical differences in reported environmental quality or symptom severity compared to the control air conditions. Typical concentrations found in aircraft can cause transitory symptoms in healthy individuals questioning the adequacy of current standards. Understanding the effects on individuals sensitive to air pollutants and methods to remove the compounds causing the greatest symptom responses are needed.

An assessment of air quality reflecting the chemosensory irritation impact of mixtures of volatile organic compounds

We present a method to assess the air quality of an environment based on the chemosensory irritation impact of mixtures of volatile organic compounds (VOCs) present in such environment. We begin by approximating the sigmoid function that characterizes psychometric plots of probability of irritation detection (Q) versus VOC vapor concentration to a linear function. First, we apply an established equation that correlates and predicts human sensory irritation thresholds (SIT) (i.e., nasal and eye irritation) based on the transfer of the VOC from the gas phase to biophases, e.g., nasal mucus and tear film. Second, we expand the equation to include other biological data (e.g., odor detection thresholds) and to include further VOCs that act mainly by "specific" effects rather than by transfer (i.e., "physical") effects as defined in the article. Then we show that, for 72 VOCs in common, Q values based on our calculated SITs are consistent with the Threshold Limit Values (TLVs) listed for those same VOCs on the basis of sensory irritation by the American Conference of Governmental Industrial Hygienists (ACGIH). Third, we set two equations to calculate the probability (Qmix) that a given air sample containing a number of VOCs could elicit chemosensory irritation: one equation based on response addition (Qmix scale: 0.00 to 1.00) and the other based on dose addition (1000*Qmix scale: 0 to 2000). We further validate the applicability of our air quality assessment method by showing that both Qmix scales provide values consistent with the expected sensory irritation burden from VOC mixtures present in a wide variety of indoor and outdoor environments as reported on field studies in the literature. These scales take into account both the concentration of VOCs at a particular site and the propensity of the VOCs to evoke sensory irritation.

Estimating sensory irritation potency of volatile organic chemicals using QSARs based on decision tree methods for regulatory purpose

Volatile organic compounds (VOCs) are among the priority atmospheric pollutants that have high indoor and outdoor exposure potential. The toxicity assessment of VOCs to living ecosystems has received considerable attention in recent years. Development of computational methods for safety assessment of chemicals has been advocated by various regulatory agencies. The paper proposes robust and reliable quantitative structure-activity relationships (QSARs) for estimating the sensory irritation potency and screening of the VOCs. Here, decision tree (DT) based classification and regression QSARs models, such as single DT, decision tree forest (DTF), and decision tree boost (DTB) were developed using the sensory irritation data on VOCs in mice following the OECD principles. Structural diversity and nonlinearity in the data were evaluated through the Euclidean distance and Brock-Dechert-Scheinkman statistics. The constructed QSAR models were validated with external test data and the predictive performance of these models was established through a set of coefficients recommended in QSAR literature. The performance of all three classification and regression QSAR models was satisfactory, but DTF and DTB performed relatively better. The classification and regression QSAR models (DTF, DTB) rendered classification accuracies of 98.59 and 100 %, and yielded correlations (R(2)) of 0.950 and 0.971, respectively in complete data. The lipoaffinity index and SwHBa were identified as the most influential descriptors in proposed QSARs. The developed QSARs performed better than the previous studies. The developed models exhibited high statistical confidence and identified the structural properties of the VOCs responsible for their sensory irritation, and hence could be useful tools in screening of chemicals for regulatory purpose.

Pulmonary toxicity following exposure to a tile coating product containing alkylsiloxanes. A clinical and toxicological evaluation

CONTEXT

Coating products are widely used for making surfaces water and dirt repellent. However, on several occasions the use of these products has been associated with lung toxicity.

OBJECTIVE

In the present study, we evaluated the toxic effects of an aerosolized tile-coating product.

METHODS

Thirty-nine persons, who reported respiratory and systemic symptoms following exposure to the tile-coating product, were clinically examined. The product was analysed chemically and furthermore, the exposure scenario was reconstructed using a climate chamber and the toxicological properties of the product were studied using in vivo and by in vitro surfactometry.

RESULTS

The symptoms developed within few hours and included coughing, tachypnoea, chest pain, general malaise and fever. The physical examination revealed perihilar lung infiltrates on chest radiograph and reduced blood oxygen saturation. The acute symptoms resolved gradually within 1-3 days and no delayed symptoms were observed. By means of mass spectrometry and X-ray spectroscopy, it was shown that the product contained non-fluorinated alkylsiloxanes. The exposure conditions in the supermarket were reconstructed under controlled conditions in a climate chamber and particle and gas exposure levels were monitored over time allowing estimation of human exposure levels. Mice exposed to the product developed symptoms of acute pulmonary toxicity in a concentration-and time-dependent manner. The symptoms of acute pulmonary toxicity likely resulted from inhibition of the pulmonary surfactant function as demonstrated by in vitro surfactometry. Among these patients only a partial association between the level of exposure and the degree of respiratory symptoms was observed, which could be because of a high inter-individual difference in sensitivity and time-dependent changes in the chemical composition of the aerosol.

CONCLUSION

Workers need to cautiously apply surface coating products because the contents can be highly toxic through inhalation, and the aerosols can disperse to locations remote from the worksite and affect bystanders.

An algorithm for 353 odor detection thresholds in humans

One hundred and ninety three odor detection thresholds, ODTs, obtained by Nagata using the Japanese triangular bag method can be correlated as log (1/ODT) by a linear equation with R(2) = 0.748 and a standard deviation, SD, of 0.830 log units; the latter may be compared with our estimate of 0.66 log units for the self-consistency of Nagata's data. Aldehydes, acids, unsaturated esters, and mercaptans were included in the equation through indicator variables that took into account the higher potency of these compounds. The ODTs obtained by Cometto-Muñiz and Cain, by Cometto-Muñiz and Abraham, and by Hellman and Small could be put on the same scale as those of Nagata to yield a linear equation for 353 ODTs with R(2) = 0.759 and SD = 0.819 log units. The compound descriptors are available for several thousand compounds, and can be calculated from structure, so that further ODT values on the Nagata scale can be predicted for a host of volatile or semivolatile compounds.

A consistent and transparent approach for calculation of Derived No-Effect Levels (DNELs) for petroleum substances

The REACH legislation introduced Derived No-Effect Levels (DNELs) which are defined as 'the levels of exposure above which humans should not be exposed'. DNELs were required for several categories of petroleum substances and CONCAWE developed a consistent approach for their derivation. First, the No-Observed Effect Level from a relevant study was corrected for pattern and route of exposure to obtain a modified Point-of-Departure (POD(modified)). Subsequently, the DNEL was calculated by dividing the POD(modified) by Assessment Factors (AFs) to adjust for inter- and intraspecies differences. If substance-specific information allowed, Informed Assessment Factors (IAFs), developed by CONCAWE were utilised. When little or no substance-specific information on those differences was known, default AFs from the guidance provided by ECHA were used. Some hazard endpoints did not lend themselves to calculation of DNELs (e.g. aspiration, dermal irritation, mutagenicity). DNEL calculation was considered not appropriate if adverse effects were not observed in tests conducted at a limit dose or if meaningful dose-response curves could not be developed. However, DNELs were calculated when hazards were identified, regardless of whether or not risk characterisation was required under REACH. Examples for gasoline, Lubricating Base Oils, gas oils and bitumen are provided to illustrate CONCAWE's approach.

Odor thresholds and breathing changes of human volunteers as consequences of sulphur dioxide exposure considering individual factors

Objectives

Though sulfur dioxide (SO₂) is used widely at workplaces, itseffects on humans are not known. Thresholds are reported without reference to gender or age and occupational exposure limits are basedon effects on lung functioning,although localized effects in the upper airways can be expected.This study's aim is to determine thresholds with respect to age and gender and suggests a new approach to risk assessment using breathing reflexes presumably triggered by trigeminal receptors in the upper airways.

Methods

Odor thresholds were determined by the ascending method of limits in groups stratified by age and gender.Subjects rated intensities of different olfactory and trigeminal perceptions at different concentrations of SO₂. During the presentation of the concentrations, breathing movements were measured by respiratory inductive plethysmography.

Results

Neither age nor gender effects were observed for odor threshold. Only ratings of nasal irritation were influenced bygender. A benchmark dose analysis on relative respiratory depth revealed a 10%-deviation from baseline at about 25.27 mg/m³.

Conclusion

The proposed new approach to risk assessment appearsto be sustainable. We discuss whether a 10%-deviation of breathingdepth is relevant.

Quantitative property-property relationships for computing occupational exposure limits and vapour hazard ratios of organic solvents

Vapour Hazard Ratio (VHR) is used in solvent substitution to select the best replacement option regarding overexposure potential of solvents. However, VHR calculations are limited by the availability of Occupational Exposure Limits (OELs). The overall objective of this study was to develop quantitative property-property relationship (QPPR) approaches for computing OELs, in view of supporting the derivation of VHRs for solvents without OELs. QPPRs were developed for estimating OELs using a database of 88 solvents which have health-based Time-Weighted Average (TWA) OELs published by the American Conference of Governmental Industrial Hygienists (ACGIH). Three surrogates of biotic lipid : air partition coefficients [n-octanol : air (K(oa)), olive oil : air (K(oila)) and fat : air (K(fa))] were selected for evaluating the descriptive/predictive relationship with OELs for solvents with local modes of action. For solvents with systemic modes of action, the prediction of OEL needs to consider quantitative differences in toxicokinetics (i.e. kinetic variability factor, KVF) and toxicological potency (i.e. effective internal concentration, EIC). The n-octanol : water (K(ow)), the oil : water (K(oilw)) and the fat : water (K(fw)) partition coefficients were selected for evaluating the relationship with EICs. For local modes of action, K(oa) is the most accurate predictor of OELs [OEL (ppm) = 10(((-0.45 x log K(oa)) + 3.65)); n = 21, r²= 0.71, PRESS/SSY = 0.36, F = 45.5 with p < 0.001] and the mean (±SD) (range) of the recommended to predicted OELs was 1.04 ± 0.61 (0.2-2.5). For systemic modes of action, KVFs and EICs vary in a range from 0.73 to 41.4 µmol L⁻¹ and 1.20-848 µmol L⁻¹, respectively. K(ow) is an accurate predictor of calculated EICs [EIC (µmol L⁻¹) = 10 (((-1.16 x log K(ow)) + 3.65)); n = 27, r²= 0.88, PRESS/SSY = 0.12, F = 181 with p < 0.001] and 50% of the predicted OEL values were within a factor of two of the recommended TWA OELs. Overall, 61% and 87% of the predicted VHRs were within a factor of two and five, respectively, of the calculated VHRs. The QPPR models developed in this study represent potentially useful tools for estimating provisional OELs for solvents lacking such guideline values. These provisional OELs are developed only to support initial estimations of VHR for dealing with the challenge of solvent substitution where relative values rather than absolute values of OEL and vapour pressure guide the hygienist in making pragmatic decisions for managing occupational health hazards.

A proposal for calculating occupational exposure limits for volatile organic compounds acting as sensory irritants on the basis of their physicochemical properties

A common biological effect of exposure to workplace chemicals is sensory irritation. The ACGIH(R) threshold limit values (TLVs(R)) are developed based on data derived from industrial settings as well as experimental human and animal studies. Considering the limited amount of human data and the tendency to reduce the volume of animal testing, there is a need for an alternative method to assess sensory irritation. Nasal pungency involves transfer of a compound through the mucosa into the receptor area. This environment is inhomogeneous, being partly a hydrophobic lipid-like and hydrophilic aqueous-like area. A general equation has been developed that seems satisfactory for explaining the transfer of volatile organic compounds (VOCs) from the gaseous phase to biophases, making it possible to calculate the nasal pungency threshold (NPT). The obtained correlation between log 1/NPT and log TLV for 71 VOCs, which is based exclusively on their irritant properties, indicates that for the compounds that act through a nonreactive mechanism (alcohols, ketones, esters, ethers, aromatic and aliphatic hydrocarbons, amides) the relationship between these values differs from that calculated for compounds that act through a reactive mechanism (aldehydes, allyl compounds, aliphatic amines, benzyl halides, carboxylic acids, acrylates, and mercaptans). The correlation coefficient for nonreactive VOCs is very high (n = 46, r = 0.89), and it appears that the regression equation (log TLV = -0.422 log 1/NPT + 0.309) could be used to predict occupational exposure limits (OELs) for this group of compounds. Regarding reactive VOCs, the correlation coefficient is considerably lower (n = 25, r = 0.32), which implies that some kind of correction for their reactivity would have to be applied to calculate the OEL values.

Role of metabolic activation and the TRPA1 receptor in the sensory irritation response to styrene and naphthalene

The current study was aimed at examining the role of cytochrome P450 (CYP450) activation and the electrophile-sensitive transient receptor potential ankyrin 1 receptor (TRPA1) in mediating the sensory irritation response to styrene and naphthalene. Toward this end, the sensory irritation to these vapors was measured in female C57Bl/6J mice during 15-min exposure via plethysmographic measurement of the duration of braking at the onset of each expiration. The sensory irritation response to 75 ppm styrene and 7 ppm naphthalene was diminished threefold or more in animals pretreated with the CYP450 inhibitor metyrapone, providing evidence of the role of metabolic activation in the response to these vapors. The sensory irritation response to styrene (75 ppm) and naphthalene (7.6 ppm) was virtually absent in TRPA1-/- knockout mice, indicating the critical role of this receptor in mediating the response. Thus, these results support the hypothesis that styrene and naphthalene vapors initiate the sensory irritation response through TRPA1 detection of their CYP450 metabolites.

Temporal integration in nasal lateralization of homologous propionates

For nasal irritation from volatile chemicals, a version of Haber's rule (k = C(n)T) can model the trade-off between concentration (C) and duration of exposure (T) to achieve a fixed sensory impact, e.g. threshold-level irritation or a fixed suprathreshold intensity. The term k is a constant. The exponent, n, represents how well the system integrates over time. An exponent of 1 indicates complete temporal integration: an x-fold increase in stimulus duration exactly compensates for cutting the concentration 1/x. An exponent greater than 1 indicates incomplete temporal integration: more than an x-fold increase in duration is needed. In a previous study of homologous alcohols, n varied systematically with number of methylene units: integration became more complete as the length of the carbon chain increased. To explore the generality of this finding, we tested homologous esters that differ in the number of methylene units: n-ethyl propionate, n-propyl propionate, and n-butyl propionate. Nasal lateralization was used to measure irritation thresholds. Human subjects received a fixed concentration of a single compound within each experimental session. Stimulus duration was varied to find the briefest stimulus that caused lateralizable irritation. Concentration and compound varied across sessions. Consistent with results with n-alcohols, integration became more complete as the number of methylene units increased. Lipid solubility varies with chain length; hence, solubility in the nasal mucosa may play a role in the dynamics of irritation. Further, preliminary analyses suggest that, for data pooled across both chemical series, n varies systematically with molecular parameters related to solubility and diffusion.

A baseline inhalation toxicity model for narcosis in mammals

This paper presents the results of an analysis of the rodent inhalation literature and the development of a quantitative structure-activity relationships (QSAR) model for 4-hour LC50 as baseline toxicity to complement the baseline toxicity model for aquatic animals. We used the same literature review criteria developed for the ECOTOX database which selects only primary references with explicit experimental methods to form a high-quality database. Our literature review focused on the primary references reporting a 4-hour exposure for a single species of rodent in which the chemical had been clearly tested as a vapour and for which the exposure concentrations were not ambiguous. An expert system was used to remove reactive chemicals, receptor-mediated toxicants, and any test that produced symptoms inconsistent with non-polar narcosis. The QSAR model derived for narcosis in rodents was log LC50 = 0.69 x log VP + 1.54 which had an r(2) of 0.91, which is significantly better than the baseline toxicity model for aquatic animals. This simple model suggests that there is no intrinsic barrier to estimating baseline toxicity for in vivo endpoints in mammalian or terrestrial toxicology.

Volatile organic compounds and formaldehyde as explaining factors for sensory irritation in office environments

This study's database comprised results of volatile organic compound (VOC) measurements from 176 office buildings. In 23 of the 176 buildings, formaldehyde measurements were also conducted. It was suspected that the buildings had indoor air problems, but a walk-through inspection did not reveal any clear, abnormal contaminant sources. The 50 most abundant VOCs and their concentrations in 520 air samples were analyzed. The irritation potency was estimated for 33 out of the 50 common VOCs and their mixtures, as well as for formaldehyde. This information was used to calculate the recommended indoor air levels (RILs) for the VOCs. The RILs were considerably higher than the measured mean indoor air concentrations in the buildings. However, the RIL for formaldehyde was exceeded in most of the 23 buildings studied. According to the evaluation of irritation potency, formaldehyde was a more likely cause of sensory irritation than the mixture of common nonreactive VOCs at the concentrations that occurred in the buildings without abnormal indoor sources. Furthermore, environmental symptoms of office workers were characterized in 20 office buildings (including the database of 176 office buildings) with the aid of an indoor air questionnaire. The most frequent symptoms related to the indoor environment were involved the upper respiratory tract. However, no relationship could be shown between the reported symptoms and the occurrence of VOC and formaldehyde concentrations in these buildings. Generally, the study results indicated that formaldehyde was the more likely agent causing sensory irritation than the mixture of the common nonreactive VOCs at the concentrations occurring in the buildings without abnormal indoor sources.

Microbial volatile organic compounds

Microbial volatile organic compounds (MVOCs) are a variety of compounds formed in the metabolism of fungi and bacteria. Of more than 200 compounds identified as MVOCs in laboratory experiments, none can be regarded as exclusively of microbial origin or as specific for certain microbial species. Thus, the recognition of microbially contaminated areas by MVOC measurements is not successful with current methods. In this review, the basic physical and chemical properties of 96 typical MVOCs have been summarised. Of these, toxicological and exposure data were gathered for the 15 MVOCs most often analysed and reported in buildings with moisture and microbial damage. The most obvious health effect of MVOC exposure is eye and upper-airway irritation. However, in human experimental exposure studies, symptoms of irritation have appeared at MVOC concentrations several orders of magnitude higher than those measured indoors (single MVOC levels in indoor environments have ranged from a few ng/m(3) up to 1 mg/m(3)). This is also supported by dose-dependent sensory-irritation response, as determined by the American Society for Testing and Materials mouse bioassay. On the other hand, the toxicological database is poor even for the 15 examined MVOCs. There may be more potent compounds and other endpoints not yet evaluated.

Assessment of Upper Respiratory Tract and Ocular Irritative Effects of Volatile Chemicals in Humans

Accurate assessment of upper respiratory tract and ocular irritation is critical for identifying and remedying problems related to overexposure to volatile chemicals, as well as for establishing parameters of irritation useful for regulatory purposes. This article (a) describes the basic anatomy and physiology of the human upper respiratory tract and ocular mucosae, (b) discusses how airborne chemicals induce irritative sensations, and (c) reviews practical means employed for assessing such phenomena, including psychophysical (e.g., threshold and suprathreshold perceptual measures), physiological (e.g., cardiovascular responses), electrophysiological (e.g., event-related potentials), and imaging (e.g., magnetic resonance imaging) techniques. Although traditionally animal models have been used as the first step in assessing such irritation, they are not addressed here since (a) there are numerous reviews available on this topic and (b) many rodents and rabbits are obligate nose breathers whose nasal passages differ considerably from those of humans, potentially limiting generalization of animal-based data to humans. A major goal of this compendium is to inform the reader of procedures for assessing irritation in humans and to provide information of value in the continued interpretation and development of empirical databases upon which future reasoned regulatory health decisions can be made.

Has vertebrate chemesthesis been a selective agent in the evolution of arthropod chemical defenses?

Arthropods use a variety of chemical substances to repel potential predators, but how did they arrive at the suite of chemicals that they use? One way to explore this question is to map chemically defended arthropod species in a multidimensional "compound" space. Clustering within this space indicates species that share similar combinations of chemical compounds and can reflect a phylogenetic signal, common biochemical pathways, or both. More important for this study, clustering can help to identify allomone targets. We herein compare common arthropod allomones with known vertebrate trigeminal irritants. We argue that the degree of overlap between these two groups of compounds indicates that chemesthesis was an important determining factor in the evolution of many arthropod allomones. The multidimensional scaling methods used may also allow the identification of new irritant receptors.

A conceptual framework for predicting the toxicity of reactive chemicals: modeling soft electrophilicity

Although the literature is replete with QSAR models developed for many toxic effects caused by reversible chemical interactions, the development of QSARs for the toxic effects of reactive chemicals lacks a consistent approach. While limitations exit, an appropriate starting-point for modeling reactive toxicity is the applicability of the general rules of organic chemical reactions and the association of these reactions to cellular targets of importance in toxicology. The identification of plausible "molecular initiating events" based on covalent reactions with nucleophiles in proteins and DNA provides the unifying concept for a framework for reactive toxicity. This paper outlines the proposed framework for reactive toxicity. Empirical measures of the chemical reactivity of xenobiotics with a model nucleophile (thiol) are used to simulate the relative rates at which a reactive chemical is likely to bind irreversibly to cellular targets. These measures of intrinsic reactivity serve as correlates to a variety of toxic effects; what's more they appear to be more appropriate endpoints for QSAR modeling than the toxicity endpoints themselves.

Does Haber's law apply to human sensory irritation?

Irritation of the eyes, nose, and throat by airborne chemicals--also referred to as "sensory irritation"--is an important endpoint in both occupational and environmental toxicology. Modeling of human sensory irritation relies on knowledge of the physical chemistry of the compound(s) involved, as well as the exposure parameters (concentration and duration). A reciprocal relationship between these two exposure variables is postulated under Haber's law, implying that protracted, low-level exposures may be toxicologically equivalent to brief, high-level exposures. Although time is recognized as having an influence on sensory irritation, the quantitative predictions of Haber's Law have been addressed for only a handful of compounds in human experimental studies. We have conducted a systematic literature review that includes a semiquantitative comparison of psychophysical data extracted from controlled human exposure studies versus. the predictions of Haber's law. Studies containing relevant data involved exposures to ammonia (2), chlorine (2), formaldehyde (1), inorganic dusts such as calcium oxide (1), and the volatile organic compound 1-octene (1). With the exception of dust exposure, varying exposure concentration has a proportionally greater effect on sensory irritation than does changing exposure duration. For selected time windows, a more generalized power law model (c(n) x t = k) rather than Haber's law per se (c x t = k) yields reasonably robust predictions. Complicating this picture, however, is the frequent observation of intensity-time "plateauing," with time effects disappearing, or even reversing, after a relatively short period, depending on the test compound. The implications of these complex temporal dynamics for risk assessment and standard setting have been incompletely explored to date.

Quantitative structure-activity relationship models for prediction of sensory irritants (logRD50) of volatile organic chemicals

Quantitative classification and regression models for prediction of sensory irritants (logRD50) of volatile organic chemicals (VOCs) have been developed. Each compound was represented by the calculated structural descriptors to encode constitutional, topological, geometrical, electrostatic, and quantum-chemical features. The heuristic method (HM) was then used to search the descriptor space and select the descriptors responsible for activity. The best classification results were found using support vector machine (SVM): the accuracy for training, test and overall data set is 96.5%, 85.7% and 94.4%, respectively. The nonlinear regression models were built by radial basis function neural networks (RNFNN) and SVM, respectively. The root mean squared errors (RMS) in prediction for the training, test and overall data set are 0.4755, 0.6322 and 0.5009 for reactive group, 0.2430, 0.4798 and 0.3064 for nonreactive group by RBFNN. The comparative results obtained by SVM are 0.4415, 0.7430 and 0.5140 for reactive group, 0.3920, 0.4520 and 0.4050 for nonreactive group, respectively. This paper proposes an effective method for poisonous chemicals screening and considering.

Multiple types of sensory neurons respond to irritating volatile organic compounds (VOCs): Calcium fluorimetry of trigeminal ganglion neurons

Many volatile organic compounds (VOCs) are significant environmental irritants that stimulate somatosensory nerve endings to produce pain and irritation. We measured intracellular calcium in cultured trigeminal ganglion neurons to characterize the cellular mechanisms and chemical structural determinants underlying sensitivity to VOCs. Trigeminal neurons responded to homologous series of alcohols (C4-C7) as well as saturated and unsaturated aldehydes in a concentration dependent manner. Ranked in terms of threshold to recruit neurons by compounds of the same carbon chain length, enaldehyde<aldehyde<alcohol. Unlike aldehydes and alcohols that displayed ascending concentration curves, recruitment of neurons by enaldehydes (C4-C7) appeared to saturate, consistent with a mechanism that is restricted in its neural distribution. Using pentanol, pentanal and pentenal as model compounds, we found that many but not all cool/cold-sensitive and capsaicin-sensitive neurons responded with increases in intracellular calcium. These VOCs also stimulated other neurons that were insensitive to cooling and capsaicin. Because not all cooling- and all capsaicin-sensitive neurons responded to the model VOCs, it is highly unlikely that known nociceptive ion channels such as TRPV1 or TRPA1 mediate sensitivity to these compounds. For pentanol, pentanal and pentenal, induced calcium influx was dependent on the presence of extracellular calcium. Responses of all neurons to pentanal and pentenal were also dependent upon extracellular sodium. Responses to pentanol were variably dependent on sodium. The distribution of sensitivity suggests that VOC irritation may be mediated by an as yet unidentified mechanism(s) that is/are distributed across different modalities of neurons.

Sensory nerves, neurogenic inflammation and pain: missing components of alternative irritation strategies? A review and a potential strategy

The eyes and skin are highly innervated by sensory nerves; stimulation of these nerves by irritants may give rise to neurogenic inflammation, leading to sensory irritation and pain. Few in vitro models of neurogenic inflammation have been described in conjunction with alternative skin and eye irritation methods, despite the fact that the sensory innervation of these organs is well-documented. To date, alternative approaches to the Draize skin and eye irritation tests have proved largely successful at classifying severe irritants, but are generally poor at discriminating between agents with mild to moderate irritant potential. We propose that the development of in vitro models for the prediction of sensory stimulation will assist in the re-classification of the irritant potential of agents that are under-predicted by current in vitro strategies. This review describes the range of xenobiotics known to cause inflammation and pain through the stimulation of sensory nerves, as well as the endogenous mediators and receptor types that are involved. In particular, it focuses on the vanilloid receptor, its activators and its regulation, as these receptors function as integrators of responses to numerous noxious stimuli. Cell culture models and ex vivo preparations that have the potential to serve as predictors of sensory irritation are also described. In addition, as readily available sensory neuron cell line models are few in number, stem cell lines (with the capacity to differentiate into sensory neurons) are explored. Finally, a preliminary strategy to enable assessment of whether incorporation of a sensory component will enhance the predictive power of current in vitro eye and skin testing strategies is proposed.

Effects of 1,3-butadiene, isoprene, and their photochemical degradation products on human lung cells

Because of potential exposure both in the workplace and from ambient air, the known carcinogen 1,3-butadiene (BD) is considered a priority hazardous air pollutant. BD and its 2-methyl analog, isoprene (ISO), are chemically similar but have very different toxicities, with ISO showing no significant carcinogenesis. Once released into the atmosphere, reactions with species induced by sunlight and nitrogen oxides convert BD and ISO into several photochemical reaction products. In this study, we determined the relative toxicity and inflammatory gene expression induced by exposure of A549 cells to BD, ISO, and their photochemical degradation products in the presence of nitric oxide. Gas chromatography and mass spectrometry analyses indicate the initial and major photochemical products produced during these experiments for BD are acrolein, acetaldehyde, and formaldehyde, and products for ISO are methacrolein, methyl vinyl ketone, and formaldehyde; both formed < 200 ppb of ozone. After exposure the cells were examined for cytotoxicity and interleukin-8 (IL-8) gene expression, as a marker for inflammation. These results indicate that although BD and ISO alone caused similar cytotoxicity and IL-8 responses compared with the air control, their photochemical products significantly enhanced cytotoxicity and IL-8 gene expression. This suggests that once ISO and BD are released into the environment, reactions occurring in the atmosphere transform these hydrocarbons into products that induce potentially greater adverse health effects than the emitted hydrocarbons by themselves. In addition, the data suggest that based on the carbon concentration or per carbon basis, biogenic ISO transforms into products with proinflammatory potential similar to that of BD products.

Passive smoking, excretion of metabolites, and health effects: results of the Leipzig's Allergy Risk Study (LARS)

Over a 5-yr period, the Leipzig's Allergy Risk Study (LARS) investigated the influence of typical indoor-contaminant burdens on the development of allergies and upper respiratory tract infections in allergy-prone children. Typical indoor volatile organic compounds (VOCs) and excretion of certain VOC metabolites in urine were measured in children 3 yr of age. Data analyses were based on parent-completed questionnaires, exposure measurements, and medical examinations. Evaluation of passive smoking was of special interest. Generally, residences with a high burden of passive smoking had higher benzene concentrations than residences inhabited by nonsmokers. Obstructive bronchitis was observed more frequently in children exposed to increased concentrations of benzene, as well as toluene, styrene, and m,p-xylene. In addition, atopic symptoms were associated with excretion of certain VOC metabolites. For example, the authors found an association between eczema and exposure to toluene and between eczema and increased excretion of the toluene metabolite S-benzylmercapturic acid. The results suggest that if an association with certain health effects is to be demonstrated, evaluation of external exposures should be supplemented with evaluations of internal exposure.

Connection between chromatographic data and biological data

There are no previous references to the direct use of GLC data in the correlation of biological processes, but we show that GLC retention data can be used in the correlation of several such processes involving gaseous solutes. There are a number of reports of RP-HPLC and MEKC data being used in the correlation of biological processes, but they are mostly restricted as to the number and type of solute studied. We show that if chromatographic data are used to obtain solvation descriptors for solutes, and if these descriptors are then used in the correlation of biological processes, that this indirect connection is a much more powerful and generally applicable method than is the direct connection between chromatographic data and biological data.

Effects of methacrolein on the respiratory tract in mice

The acute respiratory effects of airborne exposure to methacrolein were studied in a recent refinement of the standard test method with mice (ASTM, 1984. American Society for Testing and Materials, Philadelphia). Irritation of the upper respiratory tract caused a concentration-dependent decrease in the respiratory rate of 2-26 ppm methacrolein. In this range, only a minor airflow limitation occurred in the lower respiratory tract, suggesting that the main effect of methacrolein is sensory irritation. During exposure, the sensory irritation response maintained the same level, i.e. no desensitisation occurred. The concentration 10.4 ppm methacrolein reduced the respiratory rate by 50% (RD50). The extrapolated threshold for the respiratory depressing effect, RD0, was 1.3 ppm. The sensory irritation effect of methacrolein was compared with results from closely related compounds in order to elucidate the mechanism of the interaction between methacrolein and the sensory irritant receptor.

WE, Green CE, Abraham MH. Solubility of the pesticide diuron in organic nonelectrolyte solvents. Comparison of observed vs. predicted values based upon Mobile Order theory

Experimental solubilities are reported at 25.0°C for diuron (also called 3-(3,4-dichlorophenyl)-1,1-dimethyl urea) dissolved in 49 different organic nonelectrolyte solvents containing ether-, chloro-, hydroxy-, ester-, methyl-, and tert-butyl-functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order theory. For the 28 nonalcoholic solvents for which predictions could be made computations show that Mobile Order theory does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 60.1%. Diuron solubilities in the alcohol solvents are used to calculate stability constants for presumed solute-solvent hydrogen bonds that are believed to occur in solution.Key words: pesticide, diuron solubilities, organic nonelectrolyte solvents, solubility predictions.

Sensory irritating potency of some microbial volatile organic compounds (MVOCs) and a mixture of five MVOCs

The authors investigated the ability/potencies of 3 microbial volatile organic compounds and a mixture of 5 microbial volatile organic compounds to cause eye and upper respiratory tract irritation (i.e., sensory irritation), with an animal bioassay. The authors estimated potencies by determining the concentration capable of decreasing the respiratory frequency of mice by 50% (i.e., the RD50 value). The RD50 values for 1-octen-3-ol, 3-octanol, and 3-octanone were 182 mg/m3 (35 ppm), 1359 mg/m3 (256 ppm), and 17586 mg/m3 (3360 ppm), respectively. Recommended indoor air levels calculated from the individual RD50 values for 1-octen-3-ol, 3-octanol, and 3-octanone were 100, 1000, and 13000 microg/m3, respectively-values considerably higher than the reported measured indoor air levels for these compounds. The RD50 value for a mixture of 5 microbial volatile organic compounds was also determined and found to be 3.6 times lower than estimated from the fractional concentrations and the respective RD50s of the individual components. The data support the conclusion that a variety of microbial volatile organic compounds may have some synergistic effects for the sensory irritation response, which constrains the interpretation and application of recommended indoor air levels of individual microbial volatile organic compounds. The results also showed that if a particular component of a mixture was much more potent than the other components, it may dominate the sensory irritation effect. With respect to irritation symptoms reported in moldy houses, the results of this study indicate that the contribution of microbial volatile organic compounds to these symptoms seems less than previously supposed.

A theoretical approach to the Ferguson principle and its use with non-reactive and reactive airborne chemicals

The Ferguson principle has been widely used in toxicology to separate or indicate possible mechanisms for acute toxic effects of chemicals. However, this principle has never been adequately tested because of the lack of a database containing a sufficient number of both types of chemicals, non-reactive and reactive, that the Ferguson principle purports to separate. Such a database is now available. In this report a theoretical framework for the Ferguson principle is presented, regarding one of the acute toxicological effects of volatile airborne chemicals: sensory irritation. Previously obtained results on series of non-reactive and reactive chemicals are then used to demonstrate that the Ferguson principle can be extended to reactive chemicals by adding chemical reactivity descriptors to the physicochemical descriptors required by the Ferguson principle. This approach can be successful, provided that specific chemical reactivity mechanisms can be identified for the reactive chemicals of concern. The findings suggest that it is possible to replace the empirical Ferguson principle by formal mechanistic equations which will provide a better foundation for the understanding of the mechanisms by which airborne sensory irritants exert their action.