Evaluation of the sensory irritation potential of volatile organic chemicals from carpets-alone and in combination

Some individuals have reported burning or painful sensations in the eyes or upper respiratory tract when they enter certain indoor environments. Recently, carpets have been suggested as a potential source of organic chemicals that could contribute to this irritation. The sensations are generally termed ‘sensory irritation’ or ‘pungency’, and result from stimulation of trigeminal nerve endings. Indoor air quality is typically evaluated based on the concentrations of individual airborne materials, and rarely do concentrations of potentially offending materials exceed levels expected to cause adverse human health effects. In particular, volatile organic chemicals are measured at low levels (ppb) in the indoor environment. Sources of these organics vary considerably, but concentrations of the individual chemicals do not ordinarily exceed irritating levels. It is possible that the chemical mixture may cause effects not predicted by the present data available on individual chemicals. A list of approximately 50 chemicals identified in carpet emissions was developed for the study. Chemicals were selected from over 200, based on the highest frequency of occurrence and/or highest rate of emission. A mouse model of sensory irritation was used to examine the individual chemicals. In this model, mice are exposed to airborne chemicals by inhalation and evaluated for changes in respiratory function parameters. The model relies on chemical stimulation of the trigeminal nerve endings to elicit a response identified by a decrease in respiratory frequency and an alteration in the breathing pattern. Chemicals are compared quantitatively by measuring the airborne concentration required to elicit a 50% depression in respiratory rate (RD⁵⁰). Some of the chemicals were previously evaluated by this method, while others were recently examined. The emission chemicals tested individually to date have had RD⁵⁰ values that generally range from 100 ppm to more than 1000 ppm, indicating that human respiratory irritation would not be expected from the individual chemicals at levels measured in the indoor environment. Differences observed in timing of response from one chemical to another and experimental variability will be important considerations for mixtures testing. The potential for combinations of these emission chemicals to cause sensory irritation at low concentrations, resulting in additivity, synergy, or antagonism of the response, will be addressed. These results should have general application for assessing the risk of causing respiratory irritation in humans exposed to combinations of organic chemicals.