Variability and Determinants of Wood Dust and Resin Acid Exposure during Wood Pellet Production: Measurement Strategies and Bias in Assessing Exposure–Response Relationships

Production of wood pellets is a relatively new and expanding industry in which the exposure profiles differ from those in other wood-processing industries like carpentries and sawmills where there are lower levels of wood dust. Sixty-eight personal exposure measurements of wood dust (inhalable and total dust) and resin acids were collected for 44 participants at four produc-tion plants located in Sweden. Results were used to estimate within- and between-worker var-iability and to identify uniformly exposed groups and determinants of exposure. In addition, overexposure, whether the risk of the long-term mean exposure of a randomly selected worker exceeding the occupational exposure limit is acceptably low, was calculated as well as the un-derestimation of the exposure–response relationship (attenuation). Greater variability in expo-sure between work shifts than between workers was observed with the within-worker variation accounting for 57–99 % of the total variance in the individual-based model. Several uniformly exposed groups were detected but were mostly associated with a between-worker variation of zero which is an underestimation of the between-worker variation but an indication of uni-formly exposed groups. Cleaning was identified as a work task that increases exposure slightly; so reducing workers ’ exposure during this operation is advisable. The levels of wood dust wer