Derk H. Brouwer

Conceptual model for assessment of dermal exposure.

Dermal exposure, primarily to pesticides, has been measured for almost half a century. Compared with exposure by inhalation, limited progress has been made towards standardisation of methods of measurement and development of biologically relevant exposure measures. It is suggested that the absence of a consistent terminology and a theoretical model has been an important cause of this lack of progress. Therefore, a consistent terminology based on a multicompartment model for assessment of dermal exposure is proposed that describes the transport of contaminant mass from the source of the hazardous substance to the surface of the skin. Six compartments and two barriers together with eight mass transport processes are described. With the model structure, examples are given of what some existing methods actually measure and where there are limited, or no, methods for measuring the relevant mass in a compartment or transport of mass. The importance of measuring the concentration of contaminant and not mass per area in the skin contaminant layer is stressed, as it is the concentration difference between the skin contamination layer and the perfused tissue that drives uptake. Methods for measuring uptake are currently not available. Measurement of mass, concentration, and the transport processes must be based on a theoretical model. Standardisation of methods of measurement of dermal exposure is strongly recommended.

Potential release scenarios for carbon nanotubes used in composites

The expected widespread use of carbon nanotube (CNT)-composites in consumer products calls for an assessment of the possible release and exposure to workers, consumers and the environment. Release of CNTs may occur at all steps in the life cycle of products, but to date only limited information is available about release of CNTs from actual products and articles. As a starting point for exposure assessment, exploring sources and pathways of release helps to identify relevant applications and situations where the environment and especially humans may encounter releases of CNTs. It is the aim of this review to identify various potential release scenarios for CNTs used in polymers and identify the greatest likelihood of release at the various stages throughout the life-cycle of the product. The available information on release of CNTs from products and articles is reviewed in a first part. In a second part nine relevant release scenarios are described in detail: injection molding, manufacturing, sports equipment, electronics, windmill blades, fuel system components, tires, textiles, incineration, and landfills. Release from products can potentially occur by two pathways; (a) where free CNTs are released directly, or more frequently (b) where the initial release is a particle with CNTs embedded in the matrix, potentially followed by the subsequent release of CNTs from the matrix. The potential for release during manufacturing exists for all scenarios, however, this is also the situation when exposure can be best controlled. For most of the other life cycle stages and their corresponding release scenarios, potential release of CNTs can be considered to be low, but it cannot be excluded totally. Direct release to the environment is also considered to be very low for most scenarios except for the use of CNTs in tires where significant abrasion during use and release into the environment would occur. Also the possible future use of CNTs in textiles could result in consumer exposure. A possibility for significant release also exists during recycling operations when the polymers containing CNTs are handled together with other polymers and mainly occupational users would be exposed. It can be concluded that in general, significant release of CNTs from products and articles is unlikely except in manufacturing and subsequent processing, tires, recycling, and potentially in textiles. However except for high energy machining processes, most likely the resulting exposure for these scenarios will be low and to a non-pristine form of CNTs. Actual exposure studies, which quantify the amount of material released should be conducted to provide further evidence for this conclusion.

Harmonization of Measurement Strategies for Exposure to Manufactured Nano-Objects; Report of a Workshop

The present paper summarizes the outcome of the discussions at the First International Scientific Workshop on Harmonization of Strategies to Measure and Analyze Exposure to (Manufactured) Nano-objects in Workplace Air that was organized and hosted by the Netherlands Organization for Applied Scientific Research (TNO) and the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) (Zeist, The Netherlands, December 2010). It reflects the discussions by 25 international participants in the area of occupational (nano) exposure assessment from Europe, USA, Japan, and Korea on nano-specific issues related to the three identified topics: (i) measurement strategies; (ii) analyzing, evaluating, and reporting of exposure data; and (iii) core information for (exposure) data storage. Preliminary recommendations were achieved with respect to (i) a multimetric approach to exposure assessment, a minimal set of data to be collected, and basic data analysis and reporting as well as (ii) a minimum set of contextual information to be collected and reported. Other issues that have been identified and are of great interest include (i) the need for guidance on statistical approaches to analyze time-series data and on electron microscopy analysis and its reporting and (ii) the need for and possible structure of a (joint) database to store and merge data. To make progress in the process of harmonization, it was concluded that achieving agreement among researchers on the preliminary recommendations of the workshop is urgent.

Conceptual model for assessment of inhalation exposure to manufactured nanoparticles

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 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.

Stoffenmanager Nano version 1.0: a web-based tool for risk prioritization of airborne manufactured nano objects.

Stoffenmanager Nano (version 1.0) is a risk-banding tool developed for employers and employees to prioritize health risks occurring as a result of exposure to manufactured nano objects (MNOs) for a broad range of worker scenarios and to assist implementation of control measures to reduce exposure levels. In order to prioritize the health risks, the Stoffenmanager Nano combines the available hazard information of a substance with a qualitative estimate of potential for inhalation exposure. The development of the Stoffenmanager Nano started with a review of the available literature on control banding. Input parameters for the hazard assessment of MNOs were selected based on the availability of these parameters in, for instance, Safety Data Sheets or product information sheets. The conceptual exposure model described by Schneider et al. (2011) was used as the starting point for exposure banding. During the development of the Stoffenmanager Nano tool, the precautionary principle was applied to deal with the uncertainty regarding hazard and exposure assessment of MNOs. Subsequently, the model was converted into an online tool (http://nano.stoffenmanager.nl), tested, and reviewed by a number of companies. In this paper, we describe the Stoffenmanager Nano. This tool offers a practical approach for risk prioritization in exposure situations where quantitative risk assessment is currently not possible. Updates of this first version are anticipated as more data become available in the future.

Control Banding Approaches for Nanomaterials

Control banding (CB) has been developed as a pragmatic tool to manage the risk resulting from exposure to a wide variety of potentially hazardous substances in the absence of firm toxicological and exposure information. Currently, the CB approach is applied for emerging risks such as nanoparticles, by the development of various CB-based tools. Six of these are compared. Despite their similarity, i.e. combining hazard and exposure into control or risk bands, the structure, the applicability domains, and the assignment of the hazard and exposure bands, show differences that may affect the consistency of the resulting outcome amongst the various CB tools. The value of the currently available CB tools for nanomaterials can be enhanced by transparently elucidating these differences for user consideration during the selection of a tool for a specific scenario of application.

Occupational Exposure to Nano-Objects and Their Agglomerates and Aggregates Across Various Life Cycle Stages; A Broad-Scale Exposure Study

BACKGROUND Occupational exposure to manufactured nano-objects and their agglomerates, and aggregates (NOAA) has been described in several workplace air monitoring studies. However, data pooling for general conclusions and exposure estimates are hampered by limited exposure data across the occupational life cycle of NOAA and a lack in comparability between the methods of collecting and analysing the data. By applying a consistent method of collecting and analysing the workplace exposure data, this study aimed to provide information about the occupational NOAA exposure levels across various life cycle stages of NOAA in the Netherlands which can also be used for multi-purpose use. METHODS Personal/near field task-based exposure data was collected using a multi-source exposure assessment method collecting real time particle number concentration, particle size distribution (PSD), filter-based samples for morphological, and elemental analysis and detailed contextual information. A decision logic was followed allowing a consistent and objective way of analysing the exposure data. RESULTS In total, 46 measurement surveys were conducted at 15 companies covering 18 different exposure situations across various occupational life cycle stages of NOAA. Highest activity-effect levels were found during replacement of big bags (<1000-76000 # cm(-3)), mixing/dumping of powders manually (<1000-52000 # cm(-3)) and mechanically (<1000-100000 # cm(-3)), and spraying of liquid (2000-800000 # cm(-3)) showing a high variability between and within the various exposure situations. In general, a limited change in PSD was found during the activity compared to the background. CONCLUSIONS This broad-scale exposure study gives a comprehensive overview of the NOAA exposure situations in the Netherlands and an indication of the levels of occupational exposure to NOAA across various life cycle of NOAA. The collected workplace exposure data and contextual information will serve as basis for future pooling of data and modelling of worker exposure.

A Road Map Toward a Globally Harmonized Approach for Occupational Health Surveillance and Epidemiology in Nanomaterial Workers.

Objective: Few epidemiological studies have addressed the health of workers exposed to novel manufactured nanomaterials. The small current workforce will necessitate pooling international cohorts. Method: A road map was defined for a globally harmonized framework for the careful choice of materials, exposure characterization, identification of study populations, definition of health endpoints, evaluation of appropriateness of study designs, data collection and analysis, and interpretation of the results. Results: We propose a road map to reach global consensus on these issues. The proposed strategy should ensure that the costs of action are not disproportionate to the potential benefits and that the approach is pragmatic and practical. Conclusions: We should aim to go beyond the collection of health complaints, illness statistics, or even counts of deaths; the manifestation of such clear endpoints would indicate a failure of preventive measures.

Assessment of dermal exposure during airless spray painting using a quantitative visualisation technique

The range of dermal exposure to non-volatile compounds during spray painting was studied in a semi-experimental study involving three enterprises and 12 painters. A fluorescent tracer was added to the paint and deposition of the tracer on clothing and uncovered parts of the skin was assessed using video imaging and processing techniques. A container (volume 36 m(3)) was sprayed with a colourless laquer (varnish) containing 66.7 mg/l fluorescent whitening agent. All painters sprayed the outside of the container. Nine painters repeated the painting a second time and five also sprayed the inside of the container. The painters wore white Tyvek coveralls, but no gloves. Duration of spraying the outside ranged from 4 to 21 min with a mean of 10 min and the amount of paint sprayed ranged from 3.0 to 12.8 l (mean 6.6 l). The mass of tracer deposited on the coverall ranged from 2.2 to 471 microg (90th percentile 256 microg), whereas, mass deposited on skin (i.e. the hands, wrists, and face) ranged from 0.01 to 52 microg tracer (90th percentile 20 microg). The quantity of tracer on the coverall was three times higher after spraying the inside of the container compared to spraying the outside, whereas the quantity on the skin was similar in both cases. On average 10% of the surface area of the coverall and skin was exposed during spraying the outside. Exposures, expressed in units of mass per area exposed were slightly higher for skin compared to coverall. In this study, deposited mass of tracer was correlated with an alternative exposure metric, i.e. surface area exposed multiplied by the duration of exposure, which has been proposed as a surrogate for uptake. Using a quantitative fluorescent tracer technique, it could be demonstrated that body parts which showed the lowest mass of tracer had the highest exposure as mass per surface area. Compared to other techniques which only determine mass, the ability to identify and quantify the actual surface area exposed is a clear advantage of the quantitative fluorescent tracer technique.

Pesticide exposure and blood endosulfan levels after first season spray amongst farm workers in the Western Cape, South Africa

The study investigated serum endosulfan changes resulting from occupational exposure to the pesticide on farms. Eight applicators and 17 non-applicators were tested (serum endosulfan, anthropometry, short exposure questionnaire) before and after the first day of seasonal spraying. Task-based job exposure matrix (JEM) estimates were calculated. Mean baseline serum endosulfan (530 ± 0.05 μ g/L) was high. Increases in post-spraying endosulfan levels (IPSE) were higher in applicators (mean = 60 ± 90 μ g/L) than in non-applicators (mean = 3.5 × 10− 6± 90.0 μ g/L) adjusting for age (β = 54.0, p = 0.162, R2 = 0.22). There was a weak positive relationship between IPSE and JEM estimates. IPSE occurred in applicators and non-applicators and were higher in applicators. The validity of the JEM weightings and characterization of other routes of pesticide exposure require further investigation.