Modelling the time profiles of organic solvent concentrations for occupational exposure assessment purposes

Confronted by variable exposure scenarios characterized by intermittent concentration peaks, our study aimed to develop methods and determine mathematical functions reproducing organic solvent concentration profiles in order to assess health risks.

Two similar repetitive decanting tasks using either formalin or toluene (TOL) were studied at a teaching hospital pathology laboratory. Real-time air monitoring performed in the immediate vicinity of pollutant sources over a 1-year period identified intermittent concentration peaks. In order to describe these specific exposure profiles, two different methods were used. In a first descriptive approach, concentration peaks were either assimilated to an equivalent series of rectangle functions or described by a mathematical bell-shaped function. As an alternative approach, a model based on the schedule of decanting tasks was constructed. To this end, a time-varying emission function was incorporated into three deterministic exposure models of increasing complexity (well-mixed room, two-zone, spherical turbulent diffusion) and field-derived emission parameters were estimated by fitting model outputs to measured concentration profiles.

Real-time measurements revealed highly variable concentration profiles, consisting of 1-8 peaks ranging from 5 to 220 s per decanting task, and average concentrations within peaks varying over 1-2 orders of magnitude. Acceptable fits were obtained by both descriptive approaches. The tested emission function seemed relevant in reproducing intermittent pollutant releases. Only advanced models (two-zone and diffusion) gave satisfying fits within assigned input parameter ranges. Average emission rate estimates varied in the range 10-47 mg min(-1) for formaldehyde and 360-1780 mg min(-1) for TOL, depending on the model tested.

Both descriptive approaches and deterministic models accurately reproduced the patterns of measured concentration peaks. However, only deterministic models provided an understanding of the relations between pollutant releases, air movements, and the resulting concentrations and may thus be recommended for exposure variability assessment purposes.