Key messages

• Modelling of exposure from the source to the exposure is based on a mechanistic understanding of processes involved in the project from the source to the human exposure.  
• Source to dose modelling requires in most cases an integrated approach, meaning the considering of different exposure routes (inhalation, oral, dermal) and different sources (soil, water, air, diet, articles, product).  
• A one fit all model, covering all sources and routes, does not exist; a selection of models or model chain is to be made as function of application questions.  
• Source to dose models help to assess the relative contribution from a source to human exposure.

Overview

This project aims to develop realistic models to track how chemicals from different sources reach humans. These sources include industrial emissions, traffic pollution, contaminated soil and water, and common indoor products like construction materials and household items.

While existing models for some sources and routes are often conservative due to their use in initial screenings, there is a need for realistic external exposure models to aggregate exposure data, compare with human biomonitoring values, and conduct health impact assessments. These realistic models are crucial for policymakers to evaluate different policy or risk management options.

A key part of this project is identifying gaps in current exposure models and improving them, particularly for sources where data is lacking. The focus will be on chemicals of concern.

Case studies will target specific chemical classes consistent with PARC projects such as PFAS ↗, phthalates, flame retardants, metals, and pesticides.

Where models are absent, new ones will be developed, and existing models will be refined from screening to higher-tier models to generate realistic exposure estimates. This modelling effort will complement human biomonitoring for the general population.

The goal is to develop robust, mechanistic models and tools that are straightforward for risk assessors to use, enhancing the assessment of human chemical exposure and its health impacts. 

Achievements & Results

During the start-up phase, several meetings were organized to exchange experiences, information, and identify gaps and needs in source-to-dose modeling among partners. Inventories of realistic models for direct and indirect exposure to chemicals for the general population were created.

Two project working groups were established: one for environmental exposure and another for indoor exposure. Each group wrote a scoping document summarizing existing knowledge, previous case studies, and the complementarity of different tools within the conceptual framework.

The identification of gaps in models and data, setting of priority chemicals, products, and environmental sources, and selection of case studies was initiated. Initial steps were taken to generate a mechanistic understanding of source-to-dose exposure and translate this into a conceptual model, along with starting the inventory of existing data to parametrize the model.

Case studies are in progress, or have been completed. The case studies use a modelling approach, and show the relevance of key exposure source and routes as part of the aggregate exposure.

Policy relevance

The modelling approach and results from case studies inform policy makers on the dominant routes and sources of exposure, hence informing on adequate exposure reduction strategies.