Thomas Schneider

Publications of Thomas Schneider

• Advanced Reach Tool (ART): development of the mechanistic model.

  Authors: Wouter Fransman, Martie Van Tongeren, John W Cherrie, Martin Tischer, Thomas Schneider, Jody Schinkel, Hans Kromhout, Nick Warren, Henk Goede, Erik Tielemans

  The Annals of occupational hygiene. 11/2011; 55(9):957-79.

  This paper describes the development of the mechanistic model within a collaborative project, referred to as the Advanced REACH Tool (ART) project, to develop a tool to model inhalation exposure forThis paper describes the development of the mechanistic model within a collaborative project, referred to as the Advanced REACH Tool (ART) project, to develop a tool to model inhalation exposure for workers sharing similar operational conditions across different industries and locations in Europe. The ART mechanistic model is based on a conceptual framework that adopts a source receptor approach, which describes the transport of a contaminant from the source to the receptor and defines seven independent principal modifying factors: substance emission potential, activity emission potential, localized controls, segregation, personal enclosure, surface contamination, and dispersion. ART currently differentiates between three different exposure types: vapours, mists, and dust (fumes, fibres, and gases are presently excluded). Various sources were used to assign numerical values to the multipliers to each modifying factor. The evidence used to underpin this assessment procedure was based on chemical and physical laws. In addition, empirical data obtained from literature were used. Where this was not possible, expert elicitation was applied for the assessment procedure. Multipliers for all modifying factors were peer reviewed by leading experts from industry, research institutes, and public authorities across the globe. In addition, several workshops with experts were organized to discuss the proposed exposure multipliers. The mechanistic model is a central part of the ART tool and with advancing knowledge on exposure, determinants will require updates and refinements on a continuous basis, such as the effect of worker behaviour on personal exposure, 'best practice' values that describe the maximum achievable effectiveness of control measures, the intrinsic emission potential of various solid objects (e.g. metal, glass, plastics, etc.), and extending the applicability domain to certain types of exposures (e.g. gas, fume, and fibre exposure).

• Advanced REACH Tool (ART): overview of version 1.0 and research needs.

  Authors: Erik Tielemans, Nick Warren, Wouter Fransman, Martie Van Tongeren, Kevin McNally, Martin Tischer, Peter Ritchie, Hans Kromhout, Jody Schinkel, Thomas Schneider, John W Cherrie

  The Annals of occupational hygiene. 11/2011; 55(9):949-56.

  This paper provides an outline of the Advanced REACH Tool (ART) version 1.0 and a discussion of how it could be further developed. ART is a higher tier exposure assessment tool that combinesThis paper provides an outline of the Advanced REACH Tool (ART) version 1.0 and a discussion of how it could be further developed. ART is a higher tier exposure assessment tool that combines mechanistically modelled inhalation exposure predictions with available exposure data using a Bayesian approach. ART assesses exposure for scenarios across different plants and sites. Estimates are provided for different percentiles of the exposure distribution and confidence intervals around the estimate. It also produces exposure estimates in the absence of data, but uncertainty of the estimates will decrease when results of exposure measurements are included. The tool has been calibrated using a broad range of exposure data and provides estimates for exposure to vapours, mists, and dusts. ART has a robust and stable conceptual basis but will be refined in the future and should therefore be considered an evolving system. High-priority areas for future research are identified in this paper and include the integration of partially analogous measurement series, inclusion of company and site-specific assessments, user decision strategies linked to ART predictions, evaluation of validity and reliability of ART, exploring the possibilities for incorporating the dermal route and integration of ART predictions with tools for modelling internal dose. ART is initially developed in the scope of REACH but is equally useful for exposure assessment in other areas.

• Classification of occupational activities for assessment of inhalation exposure.

  Authors: Hans Marquart, Thomas Schneider, Henk Goede, Martin Tischer, Jody Schinkel, Nick Warren, Wouter Fransman, Suzanne Spaan, Martie Van Tongeren, Hans Kromhout, Erik Tielemans, John W Cherrie

  The Annals of occupational hygiene. 09/2011; 55(9):989-1005.

  There is a large variety of activities in workplaces that can lead to emission of substances. Coding systems based on determinants of emission have so far not been developed. In this paper, a systemThere is a large variety of activities in workplaces that can lead to emission of substances. Coding systems based on determinants of emission have so far not been developed. In this paper, a system of Activity Classes and Activity Subclasses is proposed for categorizing activities involving chemical use. Activity Classes share their so-called 'emission generation mechanisms' and physical state of the product handled and the underlying determinants of emission. A number of (industrial) stakeholders actively participated in testing and fine-tuning the system. With the help of these stakeholders, it was found to be relatively easy to allocate a large number of activities to the Activity Classes and Activity Subclasses. The system facilitates a more structured classification of activities in exposure databases, a structured analysis of the analogy of exposure activities, and a transparent quantification of the activity emission potential in (new) exposure assessment models. The first use of the system is in the Advanced REACH Tool.

• Comparison of dust released from sanding conventional and nanoparticle-doped wall and wood coatings.

  Authors: Ismo Kalevi Koponen, Keld Alstrup Jensen, Thomas Schneider

  Journal of exposure science & environmental epidemiology. 07/2011; 21(4):408-18.

  Introduction of engineered nanoparticles (ENPs) into traditional surface coatings (e.g., paints, lacquers, fillers) may result in new exposures to both workers and consumers and possibly also a newIntroduction of engineered nanoparticles (ENPs) into traditional surface coatings (e.g., paints, lacquers, fillers) may result in new exposures to both workers and consumers and possibly also a new risk to their health. During finishing and renovation, such products may also be a substantial source of exposure to ENPs or aggregates thereof. This study investigates the particle size distributions (5.6 nm-19.8 μm) and the total number of dust particles generated during sanding of ENP-doped paints, lacquers, and fillers as compared to their conventional counterparts. In all products, the dust emissions from sanding were found to consist of five size modes: three modes under 1 μm and two modes around 1 and 2 μm. Corrected for the emission from the sanding machine, the sanding dust, was dominated by 100-300 nm size particles, whereas the mass and surface area spectra were dominated by the micrometer modes. Adding ENPs to the studied products only vaguely affected the geometric mean diameters of the particle modes in the sanding dust when compared to their reference products. However, we observed considerable differences in the number concentrations in the different size modes, but still without revealing a clear effect of ENPs on dust emissions from sanding.

• Conceptual model for assessment of inhalation exposure to manufactured nanoparticles.

  Authors: Thomas Schneider, Derk Henri Brouwer, Ismo Kalevi Koponen, Keld Alstrup Jensen, Wouter Fransman, Birgit Van Duuren-Stuurman, Martie Van Tongeren, Erik Tielemans

  Journal of exposure science & environmental epidemiology. 03/2011; 21(5):450-63.

  As workplace air measurements of manufactured nanoparticles are relatively expensive to conduct, models can be helpful for a first tier assessment of exposure. A conceptual model was developed toAs workplace air measurements of manufactured nanoparticles are relatively expensive to conduct, models can be helpful for a first tier assessment of exposure. A conceptual model was developed to give a framework for such models. The basis for the model is an analysis of the fate and underlying mechanisms of nanoparticles emitted by a source during transport to a receptor. Four source domains are distinguished; that is, production, handling of bulk product, dispersion of ready-to-use nanoproducts, fracturing and abrasion of end products. These domains represent different generation mechanisms that determine particle emission characteristics; for example, emission rate, particle size distribution, and source location. During transport, homogeneous coagulation, scavenging, and surface deposition will determine the fate of the particles and cause changes in both particle size distributions and number concentrations. The degree of impact of these processes will be determined by a variety of factors including the concentration and size mode of the emitted nanoparticles and background aerosols, source to receptor distance, and ventilation characteristics. The second part of the paper focuses on to what extent the conceptual model could be fit into an existing mechanistic predictive model for ''conventional'' exposures. The model should be seen as a framework for characterization of exposure to (manufactured) nanoparticles and future exposure modeling.

• Conceptual Model for Assessment of Inhalation Exposure: Defining Modifying Factors.

  Authors: Erik Tielemans, Thomas Schneider, Henk Goede, Martin Tischer, Nick Warren, Hans Kromhout, Martie van Tongeren, Joop Van Hemmen, John W Cherrie

  The Annals of occupational hygiene. 10/2008;

  The present paper proposes a source-receptor model to schematically describe inhalation exposure to help understand the complex processes leading to inhalation of hazardous substances. The modelThe present paper proposes a source-receptor model to schematically describe inhalation exposure to help understand the complex processes leading to inhalation of hazardous substances. The model considers a stepwise transfer of a contaminant from the source to the receptor. The conceptual model is constructed using three components, i.e. (i) the source, (ii) various transmission compartments and (iii) the receptor, and describes the contaminant's emission and its pattern of transport. Based on this conceptual model, a list of nine mutually independent principal modifying factors (MFs) is proposed: activity emission potential, substance emission potential, localized control, separation, segregation, dilution, worker behavior, surface contamination and respiratory protection. These MFs describe the exposure process at a high level of abstraction so that the model can be generically applicable. A list of exposure determinants underlying each of these principal MFs is proposed to describe the exposure process at a more detailed level. The presented conceptual model is developed in conjunction with an activity taxonomy as described in a separate paper. The proposed conceptual model and MFs should be seen as 'building blocks' for development of higher tier exposure models.

• Tools for regulatory assessment of occupational exposure: development and challenges.

  Authors: Erik Tielemans, Nick Warren, Thomas Schneider, Martin Tischer, Peter Ritchie, Henk Goede, Hans Kromhout, Joop Van Hemmen, John W Cherrie

  Journal of exposure science & environmental epidemiology. 01/2008; 17 Suppl 1:S72-80.

  REACH (Registration, Evaluation and Authorization of CHemicals) requires improved exposure models that can be incorporated into screening tools and refined assessment tools. These are referred to asREACH (Registration, Evaluation and Authorization of CHemicals) requires improved exposure models that can be incorporated into screening tools and refined assessment tools. These are referred to as tier 1 and 2 models, respectively. There are a number of candidate in tier 1 models that could be used with REACH. Tier 2 models, producing robust and realistic exposure assessments, are currently not available. A research programme is proposed in this paper that will result in a new, advanced exposure assessment tool for REACH. In addition, issues related to variability and uncertainty are discussed briefly, and some examples of tier 1 screening tools are presented. The proposed framework for the tier 2 tool is based on a Bayesian approach, and makes full use of mechanistically modelled estimates and any relevant measurements of exposure. The new approach will preclude the necessity to conduct of case-by-case exposure measurements for each chemical and scenario, since the system will allow for the use of analogous exposure data from relatively comparable scenarios. The development of the new approach requires substantial effort in the area of mechanistic modelling, database development and Bayesian statistical techniques. In this paper, the data gaps and areas for future research are identified to help realise and further improve this type of approach within REACH. A structured data collection and storage system is a central element of the research programme and the availability of this type of tool may also facilitate the sharing of exposure data down and up the supply chain. In addition, new data that are stored according to the proposed structure could enable the validation of any exposure model and thus this programme enhances the exposure assessment field as a whole.

• Combined single-drop and rotating drum dustiness test of fine to nanosize powders using a small drum.

  Authors: Thomas Schneider, Keld Alstrup Jensen

  The Annals of occupational hygiene. 01/2008; 52(1):23-34.

  A dustiness test has been developed that performs both a single-drop and a continuous rotation test using a 6-g sample. Tests were completed on pigment-grade and ultrafine TiO2, two grades ofA dustiness test has been developed that performs both a single-drop and a continuous rotation test using a 6-g sample. Tests were completed on pigment-grade and ultrafine TiO2, two grades of corundum (Aloxite), yttrium-stabilized zirconia (Y-zirconia) granules, fumed silica, goethite, talc and bentonite. The generated particles were quantified by counting and sizing at 1-s time resolution using the TSI Fast Mobility Particle Sizer and the TSI Aerodynamic Particle Sizer and by collecting the particles on a filter for weighing. The method generated reproducible amounts and size distributions of particles. The size distributions had two more or less separated size modes >0.9 microm and in addition all materials except TiO2 pigment-grade and Aloxite F1200 generated a size mode in the range from approximately 100 to approximately 220 nm. Pigment-grade TiO2 had the lowest dustiness and ultrafine TiO2 the highest dustiness as measured by particle number for both the single-drop and rotation test and as measured by mass for both tests combined. The difference was a factor of approximately 300. Three types of dust generation rate time profiles were observed; brief initial burst (talc, both grades of corundum), decaying rate during rotation period (fumed silica, TiO2 ultrafine and pigment grade, bentonite) and constant rate (Y-zirconia, goethite). These profile types were in agreement with the differences in the ratio of amount of particles generated during the single drop to the amount generated during the single-drop and rotation test combined. The ratio ranged a factor approximately 40. The new test method enables a characterization of dustiness with relevance to different user scenarios.