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

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.

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.

Poly(3-Methylthiophene) Thin Films Deposited Electrochemically on QCMs for the Sensing of Volatile Organic Compounds

Poly(3-methylthiophene) (PMeT) thin films were electrochemically deposited on quartz crystal microbalance QCM transducers to investigate their volatile organic compound (VOC) sensing properties depending on ambient conditions. Twelve different VOCs including alcohols, ketones, chlorinated compounds, amines, and the organosphosphate dimethyl methylphosphonate (DMMP) were used as analytes. The responses of the chemical sensors against DMMP were the highest among the tested analytes; thus, fabricated chemical sensors based on PMeT can be evaluated as potential candidates for selectively detecting DMMP. Generally, detection limits in the low ppm range could be achieved. The gas sensing measurements were recorded at various humid air conditions to investigate the effects of the humidity on the gas sensing properties. The sensing performance of the chemical sensors was slightly reduced in the presence of humidity in ambient conditions. While a decrease in sensitivity was observed for humidity levels up to 50% r.h., the sensitivity was nearly unaffected for higher humidity levels and a reliable detection of the VOCs and DMMP was possible with detection limits in the low ppm range.

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.

Volatile organic compound conversion by ozone, hydroxyl radicals, and nitrate radicals in residential indoor air: Magnitudes and impacts of oxidant sources

Indoor chemistry may be initiated by reactions of ozone (O₃), the hydroxyl radical (OH), or the nitrate radical (NO₃) with volatile organic compounds (VOC). The principal indoor source of O₃ is air exchange, while OH and NO₃ formation are considered as primarily from O₃ reactions with alkenes and nitrogen dioxide (NO₂), respectively. Herein, we used time-averaged models for residences to predict O₃, OH, and NO₃ concentrations and their impacts on conversion of typical residential VOC profiles, within a Monte Carlo framework that varied inputs probabilistically. We accounted for established oxidant sources, as well as explored the importance of two newly realized indoor sources: (i) the photolysis of nitrous acid (HONO) indoors to generate OH and (ii) the reaction of stabilized Criegee intermediates (SCI) with NO₂ to generate NO₃. We found total VOC conversion to be dominated by reactions both with O₃, which almost solely reacted with d-limonene, and also with OH, which reacted with d-limonene, other terpenes, alcohols, aldehydes, and aromatics. VOC oxidation rates increased with air exchange, outdoor O₃, NO₂ and d-limonene sources, and indoor photolysis rates; and they decreased with O₃ deposition and nitric oxide (NO) sources. Photolysis was a strong OH formation mechanism for high NO, NO₂, and HONO settings, but SCI/NO₂ reactions weakly generated NO₃ except for only a few cases.

A proposal for calculating the no-observed-adverse-effect level (NOAEL) for organic compounds responsible for liver toxicity based on their physicochemical properties

OBJECTIVES

Both environmental and occupational exposure limits are based on the no-observed-adverse-effect level (NOAEL), lowest-observed-adverse-effect level (LOAEL) or benchmark dose (BMD) deriving from epidemiological and experimental studies. The aim of this study is to investigate to what extent the NOAEL values for organic compounds responsible for liver toxicity calculated based on their physicochemical properties could be used for calculating occupational exposure limits.

MATERIAL AND METHODS

The distribution coefficients from air to the liver (log K(liver)) were calculated according to the Abraham solvation equation. NOAEL and LOAEL values for early effects in the liver were obtained from the literature data. The descriptors for Abraham's equation were found for 59 compounds, which were divided into 2 groups: "non-reactive" (alcohols, ketones, esters, ethers, aromatic and aliphatic hydrocarbons, amides) and "possibly reactive" (aldehydes, allyl compounds, amines, benzyl halides, halogenated hydrocarbons, acrylates).

RESULTS

The correlation coefficients between log-log K and log NOAEL for non-reactive and reactive compounds amounted to r = -0.8123 and r = -0.8045, respectively, and were statistically significant. It appears that the Abraham equation could be used to predict the NOAEL values for compounds lacking information concerning their liver toxicity.

CONCLUSIONS

In view of the tendency to limit animal testing procedures, the method proposed in this paper can improve the practice of setting exposure guidelines for the unstudied compounds.