South Karelia Air Pollution Study: daily symptom intensity in relation to exposure levels of malodorous sulfur compounds from pulp mills.

In a longitudinal study, we assessed the relation between daily exposure to ambient air malodorous sulfur compounds from pulp production and experience of symptoms in a small population living in the vicinity of a pulp mill. Special emphasis was laid on exposure-response pattern, where the intensity of the symptoms of interest was assessed in six consecutive questionnaires after three predefined levels of exposure to malodorous sulfur compounds [total reduced sulfur (TRS)] (reference: daily mean < 10 micrograms/m3, medium exposure: 10-30 micrograms/m3 high exposure: > 30 micrograms/m3). The study population included 81 adults, who responded to the baseline questionnaire (response rate 81%). The outcomes of interest were eye, respiratory, and central nervous symptoms. The mean daily intensity of the outcome symptoms, but not of control symptoms, was significantly higher on days of medium and high exposure compared with the reference days (paired t test). The probability ratios between experiencing more or fever symptoms during the medium and high exposure compared with reference days were increased for all the symptoms of interest with a consistent exposure response pattern. The probability ratios were for eye symptoms 3.17, 95% confidence intervals (CI) 1.21 to 7.47 (medium exposure), and 5.0, 95% CI 1.66 to 12.65 (high exposure); for nasal symptoms 3.13, 1.25 to 7.25 (medium), and 8.50, 3.19 to 18.64 (high); and for pharyngeal symptoms 2.0, 0.92 to 4.14 (medium) and 5.20, 1.95 to 11.99 (high). The results suggest that relatively low daily levels of malodorous sulfur compounds (TRS > 10 micrograms/m3) cause exposure-related short-term adverse effects.