Effects of Inhalative Exposure to Dioxins in Wood Preservatives on Cell-Mediated Immunity in Day-Care Center Teachers

The study investigated the effects of chronic inhalative low-level exposure to dioxins in day-care centers containing wood treated with preservatives on (1) the number of peripheral CD4 and CDS cells and the CD4:CD8 ratio in peripheral blood and (2) the delayed-type hypersensitivity reaction of the skin (Multitest Mérieux). The study population consisted of 221 exposed and 189 unexposed employees of day-care centers in or near Hamburg. A status of decreased skin test reagibility was operationalized as hypoergy I (score <5 mm), hypoergy II (≤ 1 positive reaction), and anergy (no positive reaction). Taking the fading during postexposure time into account, a surrogate for the dioxin burden based on the concentration of dioxins in indoor air (measured using the 2,3,7,8-TCDD TEF followed by the Federal Republic of Germany) was modeled. No effect was found regarding the number of CD4 cells, CD8 cells, and CD4:CD8 ratio. However, some evidence for an increasing dose-response relationship between inhalative exposure to dioxins and the risk of hypoergy and anergy was found, both in the total study population and among subjects with a short postexposure time (≤ 6 months). Subjects with a short postexposure time and a dioxin burden >0.6 pg/m3 had a significantly higher risk of hypoergy than unexposed subjects (hypoergy I: OR = 9.51, 95% CI = 1.9-42.02; hypoergy II: OR = 2.92, 95% CI = 1.14-7.5). It is concluded that a suppressive effect of inhalative exposure to dioxins in wood preservatives on human cell-mediated immunity cannot be ruled out.