Applicability of surface sampling and calculation of surface limits for pharmaceutical drug substances for occupational health purposes

Within the context of Occupational Hygiene (OH), surface sampling has been employed as a method to assess surface levels of Active Pharmaceutical Ingredients (APIs). There are potentially a number of reasons surface samples are collected including assessing potential health risks, housekeeping and cleaning effectiveness. There are no internationally accepted standards relating to collecting or interpreting surface samples for OH purposes. In the past, surface sampling results have been applied not only for estimating risks due to dermal contact, but also for other routes of exposure (e.g. inhalation, ingestion, etc). In this publication, we provide a decision tree to support the decision and value of performing surface sampling. For scenarios without conceivable skin exposure due to applied risk mitigation measures or for substances that do not penetrate the skin, surface sampling may not be needed. If the workers' health is determined to be at risk for systemic effects via skin, we propose to use the skin Permitted Daily Exposure (PDE_skin), a safe skin dose independent of the exposure scenario that takes into consideration skin absorption properties of substances. For the purpose of OH monitoring, the likelihood of dermal exposure has to be understood before taking any samples, using both the PDE_skin to calculate the surface limit and appropriate validated monitoring method for the surface.