Variability of task-based dermal exposure measurements from a variety of workplaces.

Introduction: The RISKOFDERM project collected task-based estimates of potential dermal exposure from a wide range of industries and services from around Europe. A formal statistical analysis was carried out to explore the main components of variability in dermal exposure levels. The central research question was to what extent dermal exposure levels could be explained by generic grouping variables like 'exposure scenarios' and 'dermal exposure operation units' (DEOs) (grouping of scenarios on the basis of similarity in exposure patterns).

Methods: Mixed effect linear models were used to estimate variance components of potential dermal exposure for DEOs or scenarios and for factories, workers and time. In addition within- and between-worker variance components were estimated for single groups of workers performing a specific scenario in a specific location with potential dermal exposure to a specific agent.

Results: Variability in potential dermal exposure is very large. Differences in geometric mean potential dermal exposure can range over 3-5 orders of magnitude both for DEOs and scenarios. The range depends on how dermal exposure is expressed (amount or rate). Both DEOs and scenarios explain a considerable amount of variability, but large differences in dermal exposure still existed within DEOs and scenarios. In contrast, between-worker variability in mean potential dermal exposure is minimal for a given scenario carried out within a specific location with exposure to a particular agent. Temporal variability, however, is considerable, most likely due to the event-based nature of the dermal exposure process.

Conclusion: The classification of tasks in DEOs and scenarios has proven to be useful since large differences in average dermal exposure estimates exist between DEOs and between scenarios. However, large differences also exist between scenarios within a DEO and even within a scenario. These differences are governed by local conditions determined by the actual handling of the agent, the agent's physical and chemical properties, its intrinsic toxicity, control measures taken and training and attitude of workers. For the time being, actual dermal exposure measurements and a better understanding of actual determinants of dermal exposure seem to be a necessity in order to evaluate dermal exposure hazards properly.