The known “knowns” and known “unknowns”: Mapping uncertainty in regard to the potential human and environmental health risks of manufactured nanoparticles

As the number of products containing nanoscale materials continues to rise, questions still remain on the potential risks associated with their use and exposure in both our homes and environment. There are already over 500 nanotechnology-based consumer products on the market, while at the same time the scientific knowledge on the risks associated with nanoscale materials is still in its infancy. Although uncertainty and severe knowledge gaps surrounding potential negative impacts from exposure to nanomaterials are apparent and a corresponding understanding of the nature of uncertainty is fundamental for risk assessors and regulators, not much work has been done on this thus far. In this study we systematically map the scientific uncertainty by locating the areas of uncertainty through an in-depth analysis of governmental reports and scientific reviews dealing with the human health and environmental risks of nanomaterials. Once the locations of uncertainty were identified, we estimated the level and the sensitivity of the uncertainty. The study shows that significant knowledge gaps exist not only in terms of documenting potential (eco)toxicological effects, but also in terms of characterizing exposure and nanoparticles behaviour even in simple test systems. For example, uncertainty related to testing strategies and environmentally realistic exposure scenarios, including establishing, developing and standardising reference materials, monitoring and detection equipment and estimating human and environmental exposure concentrations, impedes a successful risk characterisation of engineered nanoparticles according to several reports. These issues ultimately lead to significant challenges in performing human and environmental risk assessments and present a daunting task for regulators. We recommend that increased efforts are made by risk assessors and regulators to estimate the sensitivity of these knowledge gaps while simultaneously ensuring that the “right” scientific questions are addressed in order to effectively prioritise resources to reduce uncertainty most pertinent to an accelerated risk analysis of nanomaterials.