This repository contains diagrams and specifications of the conceptual model for for aggregate exposure modelling developed in PARC project 6.2.1. The purpose of this conceptual model is to establish a formal consensus model for combining (human) exposure estimates to chemicals from (external) exposure models and deriving the corresponding internal exposures at some internal level. This model can be the basis for harmonization between different (external) exposure modelling tools and for establishing links between various tools. Later on, it may also serve as a basis for development of an ontology for aggregate exposure modelling.
At the present stage, this repository contains a main conceptual model diagram identifying the relevant entities and relationships, several sub-diagrams in which specific parts are worked out in more detail, and a glossary of terms and definitions of the entities of the model. This model is constructed using the established glossary of PARC AD 6.3 as a basis and alignment between the diagram and this glossary should be maintained.
Currently, the scope of the aggregate exposure conceptual model is restricted to human exposure. At a later stage, the scope could be broadened to also include environmental exposures. There is a known overlap with the following other related domains domains in PARC: human (bio)monitoring, toxicokinetic (TK) modelling (including PBK modelling), and source-to-dose modelling.
An iterative approach is proposed to design the conceptual model to ensure that it is optimized for more pragmatic use. The process is depicted in the figure below.
- Conceptual model: ideal model - logical set of nodes, edges, terminology (glossary) and their relationships
- Model suite (actual models available): It represent the pragmatic interpretation available (not necessary perfect), in the context of PARC case studies.
- Validation: Parameters, equations and data available to test performance & evaluate accuracy & precision of the models and (propagated) predictions.
You can contribute in two ways:
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Contribute in discussions by creating issues and participating in issue discussions suggesting improvements of terms/definitions and the relationships between the entities of the conceptual model.
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By updating the diagrams and vocabularies. You can edit the diagram on your local machine by cloning the git repository and editting the diagram file using the standalone draw.io app. Alternatively you can use the online diagrams.net tool for this. For the latter, use the links below the diagrams. When you want to contribute to this repository, please request membership.
** Note that in the diagram some (indirect) relationships have not been included in order to keep the diagram readable.
Aggregate exposure model: Mathematical model whose purpose is to estimate exposure at a relevant target, modelling all relevant sources and routes. If the effect is local, then in general the relevant target is an outer exposure surface, and aggregation is carried out only at exposure source level. If the effect is systemic, then aggregation is also modelled at exposure routes level, and the target is a biological matrix.
External exposure: Contact between a substance and a target that takes place in a specific exposure frequency for a defined exposure duration over an exposure period, at an external exposure surface, i.e. an exposure surface located before an absorption barrier epithelia (inner or outer surfaces) (see: exposure surface, external exposure surface).
Exposure duration: The length of time over which continuous or intermittent contacts occur between a substance and a target. For example, if an individual is in contact with an agent for 10 min, it is short term exposure. If the contact is every day for 300 days over a 1-year time period, the exposure duration is 1 year; it is long-term exposure.
Exposure event: A single event during which there is continuous contact between a substance and a target. The event is normally of a short duration (less than 24 hours). The attribute "continuous contact" in this context means that there is no interruption of the exposure.
Exposure scenario: A combination of facts, assumptions, and inferences that define a discrete situation where potential exposures may occur. These may include the exposure source, the exposed target population, and the time frame of exposure, microenvironment, and activities. Scenarios are often created to aid exposure assessors in estimating exposure (WHO/IPCS, 2004).
Exposure determinant: Exposure determinants are a broad spectrum of factors that affect/determine the exposure of an individual. Exposure determinants may be related to specific human behaviour and characteristics, substance properties, (micro-)environmental conditions, occupational processes/activities and/or Risk Management Measures (RMMs). Exposure factors form a sub-class of exposure determinants that are related to specific human behaviour and characteristics.
Exposure factor: Exposure factors are exposure parameters related to human behaviour and characteristics that help determine an individual's exposure to a substance.
Exposure pathway: The course a substance takes from its source to the exposed individual or population, or a part of that course. An exposure pathway involves in general one or several transfer mechanisms from emission sources to exposure sources, and/or between several related exposure sources (e.g., from soil to food).
External exposure estimate: Numerical estimate of an external exposure.
Exposure route: The way in which a substance reaches an external exposure surface, starting from the exposure source. These are oral ingestion, inhalation and dermal contact. Each exposure route is generally associated with a particular absorption behaviour through the absorption barriers surface that directly or indirectly separates the external exposure surfaces (outer or inner surfaces) from the internal exposure surfaces.
Exposure source: The origin of substance or a mixture for the purposes of an exposure assessment, in immediate contact with outer surfaces of exposure, to which individuals in the target population may be exposed. Examples are food, drinking water, consumer products, indoor air, outdoor air, dust and soil.
Exposure surface: A surface on a target where a substance is present. A distinction could be made between the surfaces inside the body, i.e. inner exposure surfaces, and those outside the body, i.e. outer exposure surfaces, that have in common to be located before an absorption barrier. Examples of outer exposure surfaces include the exterior of an eyeball, the skin surface, and a conceptual surface over the nose and open mouth. Examples of inner exposure surfaces include the gastrointestinal tract, the respiratory tract, and the urinary tract lining. Both outer and inner exposure surfaces can be called: external exposure surfaces. There are also exposure surfaces behind an absorption barrier the epithelia. These include, for example, urine, blood, or even specific organs. These surfaces can be called: internal exposure surfaces.
Internal exposure estimate: Numerical estimate of an external exposure.
Internal exposure: The amount of substance that passes through an absorption barrier and reaches a targeted biological matrix. These include, for example, exposure of urine, blood, or even of specific organs.
