Analysis of limonene as an indicator for the assessment of environmental air‐quality and health symptoms in office buildings

Abstract

Limonene, one of the most prevalent monoterpenes in indoor environment, was evaluated as an indicator of environmental air‐quality. Its association with health symptoms reported by workers was assessed from six large office‐buildings in the Midwestern USA that were identified as ‘non‐complaint’. The two‐year study from November 1996 to October 1998 focussed on monitoring 60 chemicals containing various functional groups including alcohol, aliphatic and aromatic hydrocarbons, alkene, carbonyl, ether, and halo‐hydrocarbons. Arithmetic mean of the reported number of physical symptoms was 3.4 ± 1.3 from a health symptoms‐questionnaire containing 19 items and 657 total responses. Wilcoxon‐sign and rank‐sum scores, and Kruskal‐Wallis (K‐W) tests did not indicate a significant association between the six buildings and the total number of symptoms identified by responses (K‐W χ2 = 0.5, df = 5, pH0 = 0.99) or an association between the four seasons and mean number of symptoms (K‐W χ2 = 2.7, df = 3, pH0 = 0.43). Levels of concentration of odorous or irritant chemicals including n‐butyl acetate, aliphatic hydrocarbons, aromatic hydrocarbons and formaldehyde in all six buildings were different, while limonene, pinene and n‐ethyl acetate were not significantly different (K‐W χ2 “ limonene =3.5, df = 5, p = 0. 61), suggesting a random geographical‐distribution of limonene. Wilcoxon‐sign and rank‐sum scores, and K‐W tests further indicated only indoor limonene level was significantly higher in winter (0.76 ± 0.28 ppbv) than in summer, spring or fall (0.44 ± 0.07, 0.41 ± 0.08 and 0.33 ± 0.10 ppbv respectively; K‐W χ2 = 7.1, df = 3, p = 0.07). Spearman correlation test suggested an apparent association between the mean number of symptoms with limonene (Rs = 0.48, pH0 = 0.04), sum‐aliphatics (SAL) (Rs = 0.48, pH0 = 0.04) and n‐butyl acetate (Rs = 0.51, pHo = 0.03). Limonene and pinene cause no irritation or CNS symptoms from short‐term exposures, but cause significant reduction in vital capacity at concentration ca. 8.0 x 104 ppbv in humans (F‐Filipsson et al., J. Toxicol. Environ. Health, 38, 77–88 (1993)). Limonene's oxidative product, epoxide, is known to cause upper respiratory and CNS symptoms, and dermatitis. Mean number of reported symptoms had a negative Spearman‐correlation for formaldehyde (Rs = ‐0.13, pH0 = 0.60), although it is known for its upper respiratory irritation, allergy and sensitization reaction. Limonene levels correlated least with formaldehyde. Limonene levels in the six study buildings were in the range 0.2 to 1.5 ppbv, four orders of magnitude less than the recommended exposure limit for non‐industrial indoor work‐environment, 3.0 x 104 ppbv. Random distribution of low levels limonene indoor and its positive correlation with other volatile organic compounds having different functional groups including aliphatics and esters suggest that limonene levels in indoor air should be an effective marker and an indicator of environmental air‐quality. Limonene levels also correlate with health symptoms that are positively identified with most prevalent upper respiratory health symptoms including dry, itching or irritated eyes (41%) and tired or strained eyes (37%), and headache (CNS‐symptom) (36%) reported by the workers.