Modeling human health characterization factors for indoor nanomaterial emissions in life cycle assessment: a case-study of titanium dioxide†
Life cycle assessment is used during the developmental stages of products and technologies. In the case of emerging technologies such as engineered nanomaterials there are limitations in using life cycle assessment to evaluate the direct environmental and human health impacts from emissions of nanomaterials themselves. This is due to the limited life cycle inventory data and life cycle impact assessment models currently available for describing the fate, exposure and effects of engineered nanomaterials in the environment. Specifically, current life cycle impact assessment methodologies do not include characterization factors for nanomaterials. Engineered nanomaterials may be emitted throughout the life cycle of a product, for example, in the occupational setting where there may be constant interaction between workers and large volumes of loose nano-powders. This paper presents a dynamic model that is intended for use in life cycle impact assessment methods to quantify the fate, exposure and human health effects of engineered nanomaterials. Using the case-study of nano-TiO2 emissions in the indoor workplace, nano-specific life cycle assessment characterization factors are presented. Compared to previously published steady-state models, the results of the current study demonstrate a much lower exposure potential, expressed as the ‘retained’-intake fraction of nano-TiO2 in the lung over the total emitted amount. Furthermore, the results indicate that smaller emissions lead to greater fractional deposition. Thus, an inverse relationship between the total indoor air emissions of nano-TiO2, and the resulting magnitude of the characterization factor was seen.