Consumers are potentially exposed to nanomaterials during use of nano-enabled consumer products. Of particular concern is the application of nanomaterials in spray products. To investigate the exposure of the consumer to nanomaterials in these products, ConsExpo nano has been adapted from the ConsExpo model for the estimation of exposure to regular substances in spray products. It has been developed in the context of the Dutch National NanoNextNl project: “Predictive modeling of human exposure” and was updated in the EU caLIBRAte project.
During use of a consumer spray product, the nanomaterial that is released from the spray may become airborne as part of the spray aerosol or as individual particles. Exposure to a nanomaterial in an aerosol may take place via different routes, but inhalation of the aerosol is generally considered the route of most concern.
According to Braakhuis et al., (2014), the most relevant effect after inhalation exposure to nanomaterials is the induction of inflammation in the alveoli. One of the most critical determinants of this effect is both the magnitude and duration of the alveolar load of a nanomaterial. To estimate the alveolar load arising from the use of nano-enabled spray products, ConsExpo nano combines models that estimate the external aerosol concentration in indoor air, with models that estimate the deposition in and clearance of inhaled aerosol from the alveolar region.
An issue addressed in ConsExpo nano is the observation that the traditional choice of ‘mass of the substance inhaled’ as a measure of exposure is inappropriate to quantify dose-effect relations for nanomaterials. Alternative dose metrics such as total number or total surface area of the nanoparticles inhaled have been suggested, but consensus on an appropriate dose metric is currently lacking. To bridge this current knowledge gap, ConsExpo nano expresses exposure estimates in a variety of dose metrics, allowing the exposure assessor to evaluate various alternatives.
Apart from a spray scenario, ConsExpo nano features a custom scenario in which a measured air concentration is used directly as input in the tool. This makes the tool applicable simulating exposure based on monitoring data (e.g. in workplaces).
Furthermore, there is a possibility to simulate an animal hazard study with known adversed effects after inhalation exposure to the nanomaterial of interest (or a similar nanomaterial). In this way, it is possible to convert the external dose of nanomaterials to which the animals are exposed, into an internal exposure dose i.e. the alveolar load. In this way, a comparison can be made between exposure related adverse effects of the animal study and the dose that is expected after human inhalation exposure giving a first indication of the risk after that specific exposure to nanomaterials.
Update november 2019
Within the context of the caLIBRAte project, ConsExpo nano was evaluated by means of an extensive sensitivity analysis and performance test. In the latter, ConsExpo nano was tested against experimental data. Several recommendations from this evaluation have been followed and implemented in the updated version 3.0 of the ConsExpo nanotool. Added features include:
Capabilities for performing probabilistic evaluations by means of Monte Carlo simulation have been added.
For a range of parameters, probability distributions can be specified as input. Monte Carlo simulations are performed by repeatedly sampling from the input distributions, constructing a sample of the distribution of model calculations. Probabilistic calculations are a valuable tool for analyzing the effects of uncertainty and variability on the exposure evaluation.
Different normalisations of the calculated dose have been added.
Depending on the hazard information in the risk assessment, doses are more appropriately expressed in different normalisations, e.g. as dose per lung, per unit alveolar surface area, per kg body weight. Different options for normalisation of the output have been added.
Support of the use of measured data.
To characterise the particle size distribution of consumer sprays, users may bring in raw measurement data via text file input.
Currently, there is still a lack of knowledge and data on the exposure assessment and risk assessment for nanomaterials. ConsExpo nano is a “work-in-progress” online tool that is designed to reflect the current state of knowledge on exposure to nanomaterials via inhalation. The tool will be further developed to accommodate developments in the state of the science.
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