Exposure assessment is "the determination of the emissions, pathways and rates of movement of a substance and its transformation or degradation in order to estimate the concentrations/doses to which human population or the environmental compartments are or may be exposed" (Van Leeuwen and Vermiere, 2007). A hazardous chemical does not pose a risk if the exposure of this chemical is below a safe threshold. Exposure assessment is therefore essential to decide if the identified hazard effectively implies a risk or not. Exposure can be determined via modelling or monitoring. During the exposure assessment, it is important to identify all risk management measures (for modelling or monitoring and input parameters (for modelling) that are relevant. Examples are wastewater treatment or ventilation that might significantly impact the final exposure values and thus the potential risk that will be determined later.
Environmental Exposure Modelling
There are various models available for modelling environmental exposure to chemicals (see below). The exposure models predict the environmental concentration of a chemical based on the physicochemical properties of the chemical (water solubility, vapour pressure, etc.), its behaviour in the relevant environmental compartment(s) (degradation, transport, transformation, etc.), and/or the concentration of the chemical released (amount, periodicity, etc.). The predictions are based on the statistics and correlations between various model parameters. The final exposure estimate depends on the model that is used and its input parameters. It is, as such, critical to select a model that is suited for the chemical of concern (metal vs organics) and the purpose of the assessment (single compartment vs multi-compartment models). Important to keep in mind when modelling environmental metal exposure:
- Metals are naturally occurring elements and thus always present in the environment
- Some metals are essential elements and thus a prerequisite for life
- Metal cannot (bio)degrade but only transform
- Parameters such as Kow or vapour 0 pressure are not relevant for most metals and metal compounds.
Risk Management of Complex Inorganic Materials, Violaine Verougstraete, 2018
The Specific Environmental Release Factors (SPERCS) for metals and metal compounds provide a more realistic approach to characterise the environmental releases from manufacture, processing and downstream uses of the metal (compounds) in the EU. A database consisting of more than 1,300 (1993-2010), site-specific measured release factors to air and water of 18 different metals (and their compounds), from various EU Member States was compiled. The metal SPERCs can be used as an advanced tier instrument in environmental safety assessments, increasing the realism of the estimates while keeping a sufficient level of conservatism.
The DU scaling tool (originally initiated by EURAS) allows downstream users to carry out compliance checking with the environmental Exposure Scenario (ES) of metals. It is based on the spreadsheet version of EUSES. In the registrant-interface, the generic default Operational Conditions (OCs) and Risk Management Measures (RMMs) can be entered.
It also allows the DU to enter bioavailability-corrected PNECs (Predicted No Effect Concentrations), for those metals for which relevant models are available. The resulting risk characterisation ratios allow the DU to assess safe use. In this way, the DU scaling tool enables the DU to check compliance with the Exposure Scenario if his Operational Conditions or Risk Management Measures differ from those in the Exposure Scenario.
TICKET-UWM, is a tool created to assess the environmental fate of complex inorganic materials in the aquatic environment. It is a software application that models metals and organics transport in a well-mixed lake with an underlying sediment layer (Farley et al., 2005; Farley et al., 2011). TICKET-UWM simultaneously considers the effects of chemical speciation on metal partitioning, transport and bioavailability in the lake water column and underlying sediments. The user can now assess the dynamic response of a lake to a continuous or instantaneous load of a metal. The metal source can be specified as a soluble salt subject to instantaneous dissolution or as a powder/massive which dissolves according to a user-specified kinetic expression and rate.
Framework for Metals Risk Assessment (US EPA, 2007), Chp. 5.2 Aquatic ecological Risk assessment for metals - Characterization of Exposure (5; 2-11); Chp.6.2 Terrestrial Ecological Risk assessment for Metals - Characterization of Exposure (6; 2- 8)
The Framework for Metals Risk Assessment is a science-based document that addresses the special attributes and behaviours of metals and metal compounds to be considered when assessing their human health and ecological risks. The document describes basic principles to be considered in assessing risks posed by metals and is intended to foster consistency on how these principles are applied across the Agency’s programmes and regions when conducting these assessments.
Chp 5. Aquatic ecological Risk assessment for metals
5.2. Characterisation of exposure (5-2)
- Background levels (5-2)
- Forms of metals (5-3)
- Exposure Pathway Analysis (5-4)
- Fate and transport of metals (5-5)
- Toxicokinetics and toxicodynamics (bioavailability and bioaccumulation issues) (5-6)
- Aqueous phase (5-6)
- Sediment phase (5-8)
- Dietary phase (5-9)
- Bioaccumulation and trophic transfer (5-11)
Chp 6. Terrestrial Ecological Risk assessment for Metals
6.2 Characterisation of exposure (6-1)
- Natural occurrence of metals (6-1)
- Forms of metals (6-3)
- Exposure routes (6-3)
- Soil transport and fate models (6-3)
- Toxicokinetics/toxicodynamics (6-4)
- Bioavailability (6-4)
- Bioaccumulation (6-5)
- Soil invertebrate exposure (6-6)
- Plant exposure (6-7)
- Wildlife exposure (6-8)
MERAG is an environmental risk assessment guidance targeting metal substances, therefore taking metal specificities into account contrary to most of the other risk assessment guidances.The critical concepts are presented in a series of nine independently reviewed MERAG fact sheets. It is hoped that these latest concepts will enable regulators and scientists to create new or adapt local, national or regional risk assessment systems accordingly.
REACH Guidance Environmental risk assessment for metals and metal compounds(ECHA, Chp.2. Exposure assessment p.12-35; July 2008)
The REACH Guidance on information requirements and chemical safety assessment targets Environmental Risk Assessment for metals and metal compounds. This official document published on ECHA’s website has been based on the MERAG fact sheets.
This document contains guidance on REACH explaining the REACH obligations and how to fulfil them.
2.1 General introduction (11)
- Guidance for the local exposure assessment (12)
- Guidance for the regional exposure assessment (14)
2.2 Metal-specific aspects in exposure modelling (15)
- Adjusting multimedia fate models for metals (15)
- Modelling adsorption/desorption processes (17)
2.3 Guidance on metal-specific aspects in selecting measured data (23)
- Introduction (23)
- Data selection and handling (24)
- Determination of natural background and historical contamination (26)
- Guidance on how to handle natural background concentrations and historical contamination (29)
2.4 Guidance on the incorporation of bioavailability in the exposure assessment (32)
- Introduction (32)
- Guidance on the use of the’ ecoregion driven approach’ (35)
- Bioavailability and toxicity
- Bioconcentration and bioaccumulation
- Trophic transfer
- Basic chemistry of metals/metalloids
- Soils as a charged medium
- Metal/metalloid partitioning between solid and solution phases in soil
- Metal/metalloid speciation
- Natural occurrence of metals in soil- background
Deriving Site-Specific Water Quality Criteria Safe Thresholds for metals based on Bioavailability to Aquatic Organisms (ICMM presentation at APEC, Philippines, 2015)
Risk Management of Complex Inorganic Materials: A practical Guide (Violaine Verougstraete, 2018, Chp.2.3, 3.3, 4.3,13.5)
The aim of this publication is to facilitate the hazard identification as part of risk assessment and management of complex inorganic materials around the world by providing accessible and specific guidance on their assessment. This book explains the main characteristics of inorganic complex materials affecting their hazard and risk assessment and management, including their source and main uses, also covering hazard and exposure assessment, risk characterisation and risk management.
It is an essential reference for regulators involved in risk assessment and risk management, industry experts charged with compliance of chemicals management programme requirements, consultants preparing chemicals management files for companies and regulators, and academics involved in research on complex inorganic materials.
Table of Contents:
- General introduction
- Sources of Exposure to inorganic complex materials
- Mechanisms Underlying Toxicity of Complex Inorganic Materials
- Principles of risk Assessment and Management of Complex Inorganic Materials
- Main characteristics of relevance for the assessment of complex inorganic materials
- Data needs, availability, sources and reliability
- Environmental Toxicity assessment of complex inorganic materials
- Human Health Toxicity assessment of complex inorganic materials
- Specific methodologies/tools to support assessment
- Hazard assessment of ores and concentrates
- Risk assessment of exposure to inorganic substances of UVCBs during manufacturing (recycling) of metals
- Risk assessment for manufacture and formulation of Inorganic Pigments (manufacturing and use)
- Risk assessment of alloys (manufacturing, use, end of life)
- Emerging tools in the assessment of metals: Current Applicability