Harmonizing human exposure and toxicity characterization

Abstract

The UNEP-SETAC Life Cycle Initiative has launched a project to provide global guidance and build consensus on environmental life cycle impact assessment (LCIA) indicators. Human health effects from exposure to toxic chemicals was selected as impact category due to high relevance of human toxicity impacts, past and present efforts in human toxicity assessment, and the need for further harmonization and global guidance. To address this need, an expert workshop was implemented in Utrecht in October 2016 with the aim of building a roadmap for a reliable and consistent approach for improving and harmonizing human toxicity characterization in LCIA. Building on initial work for the far-field and indoor air environments, and combining it with latest work on near-field consumer and occupational exposure assessment, dose-response and severity data, we aim at providing revised guidance on the development and use of impact factors for toxic chemicals. We propose to couple fate processes in consumer and occupational environments with existing environmental compartments and processes via a consistent and mass balance-based set of transfer fractions to quantify overall aggregated exposure to toxic substances. We propose the product intake fraction (PiF) as metric linking human intake via all exposure routes to substance mass in products. Further, for fine particulate matter, a constructed integrated exposure-response model has recently been proposed and applied to calculate marginal and average health impacts, which will serve as starting point for improving toxicity dose-response. To go beyond the additivity and linearity assumptions and to address essentiality and vulnerability, we propose to account for the fraction of population that is above a certain risk threshold for the considered disease/mode of action. We finally propose to explore the possibility to expand the endpoint coverage beyond cancer and non-cancer and to differentiate between other relevant health effects. For attributing severity to mortality (and morbidity) for cancer and non-cancer diseases to damage metrics, we will need to identify severity weights for population disease incidences expressed as disability-adjusted life years (DALY). All aspects for fate and exposure outdoors, consumer and occupational exposure, toxicity effects and dose-response, and cross-cutting issues are currently being further detailed aiming at arriving at recommended factors and global guidance within the next two years.