TREXMO: a new tool to assess occupational exposure
Choosing the best modelling tool
One of the current issues with risk assessment is defining the most suited data-modelling tool for a substance and its use in order to obtain exposure values and, consequently, risk ratios as precise as possible. The European Chemicals Agency, ECHA’s technical guide R14 indicates the scope of these tools. It can however be difficult to differentiate them. Indeed, depending on the model used, the calculated exposure values may highlight a variability in the results, which may lead to an incorrect risk interpretation. This variability comes, for the most part, from the heterogeneity of input parameters exploitable and attributable to each model for the substance’s use.
TREXMO, an answer to the homogeneity issue
To solve this problem, the Institute for Work and Health in Lausanne, and the Geneva University elaborated a modelling tool: TREXMO (TRanslation of EXposure MOdels). This tool gathers simultaneously the six tools recommended by ECHA, namely ART v.1.5, Stoffenmanager® version 4.0 (Schinkel et al. 2010), ECETOC TRA v.3, MEASE v.1.02.01, EMKG-EXPO-TOOL and EASE v.2.0. TREXMO allows to obtain and compare the exposure values generated by the 6 models for various evaluated contributing scenarios. This way, from a unique web interface in which the models’ input parameters are filled in, TREXMO assigns to each model the parameters necessary for its functioning.
This function, specific to TREXMO, enables the harmonisation and homogenisation of input parameters used in exposure assessment and, in this way, it can increase the reliability of exposure values given for each model. This tool has several advantages:
- it limits the variability of results obtained with different users,
- it reduces the uncertainty linked to the input parameters choice to be used in each model
Thus, TREXMO offers a particularly reliable exposure estimation.
The tool allows for a considerable gain in time by proposing an exposure value for each available model. The results’ analysis offers a critical perspective on the reliability of the various models according to the studied substances and conditions of use.
Risk assessment, a key issue for REACH
According to REACH Regulation (EC) No 1907/2006, risk assessments may be required to demonstrate a controlled use of substances in order to ensure a better protection for humans and the environment. It is specifically the case for the registration of a substance manufactured or imported at more than 10 tonnes per year or in the case of authorisation dossiers.
By definition, risk is the occurrence probability of a harmful effect resulting from the exposure to a danger. Risk assessment is carried out through two steps:
- the evaluation of a substance’s danger in order to identify harmful effects linked to its intrinsic properties
- the evaluation of human or environmental exposure arising from this substance’s use
In particular, the inhalation and dermal exposure assessment for workers when they manipulate a substance is a primordial step in human health risk assessment. Various data-modelling tools were created from exposure scenarios and are representative of the real conditions of use of a substance on industrial premises. They enable the generation of exposure values for substances for each of the tasks carried out (contributing scenarios) by workers along the considered industrial process. Exposure values calculated via these tools are then compared to threshold values or excess risk. Potential risks are then concluded for the use of a substance in a specific industrial context, taking into account the risk management measures implemented on the premises to protect workers’ health.
Modelling tools are divided into two categories. They vary in the calculated values’ precision and the complexity of the input parameters to be provided for the models. Regarding the data-modelling tools to assess inhalation exposure, several Tier 1 tools (ECETOC Target Risk Assessment (TRA), EMKG-EXPO-TOOL, etc.) allow the quick generation of exposure values with little information on the substance’s conditions of use (screening). The Tier 2 tool (Advanced REACh Tool (ART)), provides more precise exposure values but requires more input information to get them.
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