Annals of Occupational Hygiene Advance Access originally published online on March 24, 2005
Annals of Occupational Hygiene 2005 49(5):443-451; doi:10.1093/annhyg/mei007
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© 2005 British Occupational Hygiene Society Published by Oxford University Press
Original Article |
An Experimental Study to Investigate the Feasibility to Classify Paints According to Neurotoxicological Risks: Occupational Air Requirement (OAR) and Indoor Use of Alkyd Paints
Food & Chemical Risk Analysis, TNO Quality of Life, PO Box 360, 3700 AJ Zeist, The Netherlands
* Author to whom correspondence should be addressed. Tel: +31 30 6944914; fax: +31 30 6944926; e-mail: brouwer{at}chemie.tno.nl
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ABSTRACT |
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 TOPFOOTNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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The concept of occupational air requirement (OAR), representing the quantity of air required to dilute the vapor concentration in the work environment resulting from 1 l product to a concentration below the occupational exposure limit (OEL), was considered to have potential to discriminate between paints that can and cannot be used safely. The OAR is a simple algorithm with the concentration of volatile organic compound (VOC) in the paint, a discrete evaporation factor and the neurotoxicological effects-based OEL. Conceptually, OAR categories of paints for construction and maintenance applications could be identified that can be applied manually without exceeding OELs with no appreciable room ventilation. Five painters volunteered in an exposure study aimed at testing the OAR approach in practice. Total exposure to VOC was assessed in 30 experiments during the application of 0.5 l of paint in a defined ‘standard indoor paint job’. Fifteen paints were prepared, reflecting differences in solvents (percentage, volatility, toxicity) with a range of OAR levels from 43 to 819 m3/l. Exposure was assessed by personal air sampling (PAS). In addition, real-time air monitoring was performed. All tests were conducted at minimum ventilation rate (
0.33 h–1). PAS results were expressed as percentage of the nominal OEL and ranged from 8 to 93% for high solids and from 38 to 168% for conventional paints. In general, higher VOC contents resulted in higher exposure. High volatile paints showed a statistically significant faster increase of VOC concentration with time compared with paints containing low volatile solvents. A significant relationship between OAR value and exposure was observed (R2 = 0.73). The experiments indicate that OAR-based classification of paints predicts and discriminates risk levels for exposure to neurotoxic paint-solvents in indoor painting fairly well.
Keywords: indoor exposure • paint composition • risk classification • VOC
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INTRODUCTION |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Long-term and/or high exposure to volatile organic compounds (VOCs) has been associated with chronic neurotoxic effects, i.e. chronic toxic encephalopathy (CTE); however, the exposure–effect relationship is not fully understood (ECETOC, 1997
). The Netherlands introduced new legislation in 1999 in an attempt to prevent CTE, where high-VOC content products have to be substituted by low-VOC content products such as water-based products (SZW, 1998). All stakeholders, i.e. Ministry of Social Affairs and Employment, The Dutch Solvent Industry, the Dutch Association of Paint and Printing Ink Manufacturers, and the Paint Shops and Painters Association agreed that a flexible alternative for rigid substitution should be explored and the condition for paint for specific uses, i.e. VOC contents <120 g/l, should be made more specific. For some decades now in Norway and Denmark paint products are labeled according to a classification system that combines paint composition, intrinsic hazard of paint components, e.g. VOCs, likelihood of VOCs to evaporate, resulting in exposure (Norwegian State Pollution Control Authority (1998). In both systems the underlying occupational air requirement (OAR) value represents the quantity of air required to dilute the vapor concentration in the work room resulting from 1 l product to a concentration below the occupational exposure limit (OEL). A simple algorithm with concentration of solvent in the paint (g/l), evaporation factor (f), and OEL of the solvent is used to calculate the OAR [equation (1)].
 | (1) |
- OAR: occupational air requirement (m3/l)
- C: concentration of VOCs in product (g/l)
- f: evaporation factor category (0, 0.3, 0.7 or 1.0)
- OEL: occupational exposure limit (mg/m3)
- C: concentration of VOCs in product (g/l)
The evaporation factors are derived from the film evaporation rates as determined by the ASTM D3539-87 (ASTM, 1996) or the vapor pressures according to a classification proposed by the Norwegian State Pollution Control Authority (1998), and presented in Table 1.
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The OAR approach as incorporated in the Danish and Norwegian systems has proven to have great potential for use in the classification of paints for construction and maintenance applications, i.e. to identify OAR categories of paints that can be applied without exceeding OELs with no appreciable room ventilation (Zock et al., 1998
). However, so far no exposure data have been generated to evaluate the concept of the OAR. An experimental study was conducted and aimed at (i) investigating the relationship between OAR and exposure during the application of a series of paints, (ii) exploring the relevance of the OAR parameters and (iii) investigating the ability of OAR labeling to give guidance to select paints that can be used safely in view of neurotoxicological risk. |
MATERIALS AND METHODS |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Study design
A semi-experimental study was conducted, where exposure to volatile (organic) solvents was assessed for a defined ‘standard indoor paint task’, i.e. application of 0.5 l of paint by brushing on a surface area of
6 m2 in an unventilated room of 50 m3 (SER, 1997). This standard indoor paint task was interpreted by defining an unventilated room as a room with an air exchange rate <0.2 h–1, and application of 0.5 l of paints to both sides of a door and a door frame. After drying for at least 3 x 24 h the objects were reused (maximum 3 times). Fifteen (experimental) alkyd paints were prepared by the Dutch Association of Paint Manufacturers (VVVF) according to a designed grid reflecting differences in solvent content [percentage, volatility (three categories) and toxicity (aliphatic and/or aromatic hydrocarbons)]. Five professional qualified painters volunteered in two sets of experiments; each of the subjects conducted several times the ‘standard indoor paint task’ with different paints, resulting in duplicate exposure data for each type of paint. The study protocol was approved by the Medical Ethics Committee, and all test subjects volunteered to participate in the study. Prior to the study the test subjects were informed in writing about the objects and the methods of the study and an informed consent form was completed. Prior to each replicate the test subjects were provided with clean work clothing and respiratory protection.
Experimental paints
Two types of experimental paints were included, i.e. high-solid paints (A-type, n = 6), and conventional paints (B-type, n = 9). On average the solvent content of the experimental paints was 175 g/l for high-solid paints and 350 g/l for conventional paints (B1–B6). Additionally, three conventional paints were prepared with solvent contents of 390 g/l and 447 g/l. All paints contained a skimming agent (2-butanone-oxim) in a concentration of 0.4% (w/w) for high-solid paints and 0.2% (w/w) for conventional paints. The A-type of paints could be prepared using neat VOC-mixtures, representing different evaporation (f) factors: A1, D25; A2, D25 + 20% Xylenes; A3, D40; A4, WS; A5, D60 and A6, SSH. The same solvent mixture of the B-type paints of the first set of experiments, i.e. B1 through B6, appeared to be dominated by the solvent mixture of the alkyd resin. Therefore, the three other conventional paints were prepared, i.e. B7–B9, to get paints with a higher f factor and with higher OAR values. Prior to the experiments, the solvent mixtures for paint composition were analyzed for contents of C8–C12 napthene and paraffin, xylene and other aromatic compounds. In addition, the solvent content and density of all paints were determined. Based on both the blend data and the results of the chemical analyses, the OEL (derived for neurotoxicological effects) and the OAR values for each paint were calculated. The OAR values ranged from 43 to 300 m3/l for high-solid paints (A-type) and from 224 to 819 m3/l for conventional paints (B-type). Details on VOC mixtures and paints are given in Tables 2 and 3, respectively.
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Exposure assessment
Inhalation exposure to solvents during the actual application of the paint was assessed by personal air sampling using an air sampling pump (flow rate
250 ml/min) and a heavy weight (800/200 mg) charcoal adsorption tube over consecutive intervals of 15 min. Breathing zone concentration of 2-butanone-oxim was assessed using silicagel adsorption tubes. In addition, real-time air monitoring was performed during the application in the breathing zone of the test subject. A photo ionization detector (PID)-type (Mini-RAE) equipped with a 10.6 eV bulb and a photo-acoustic infrared detection (PAIRD) device (B&K, type 1302) were used for the measurement of ‘total’ hydrocarbon-concentration and xylenes, respectively. Response times were 2 s and 150 s for PID and PAIRD, respectively. After application, but not earlier than 30 min after beginning the application, the painter left the room and personal sampling changed into stationary sampling, i.e. charcoal tube sampling, and the inlet of the PID and PAIRD devices were placed on a fixed location between the painted surfaces. The sampling period was 60 min. PID and PAIRD were calibrated for iso-butylene and device responses were expressed as iso-butylene equivalents. Prior to the start of the painting, a tracer gas (SF6) was generated in the test room and the concentrations were monitored by the PAIRD monitoring device during the experiment to determine the air exchange rate.
Charcoal tubes were extracted with 5 ml CS2 and analyzed for C8 through C12 n-aliphatic hydrocarbon groups, xylene isomers, aromatic hydrocarbons, and expressed as total aliphatic hydrocarbons, total aromatic hydrocarbons (C9–C11) and xylenes, since these hydrocarbons have different OELs. An aliquot of 1 µl of the sample was injected splitless in a Carlo Erba 5360 type GC, provided with a CP-Sil-5-CB and a CP-Wax-52–CB column (Chrompack 50 m x 0.32 mm x 1.2 µm), and detected by flame ionization detectors (FID). Injection portal temperature and detection temperatures were 250 and 300°C, respectively. He gas was used as carrier at 120 kPa. 2-Ethylnaphthalene (20.5 µl/ml extract) was used as an internal standard. Over the range of spike levels the recoveries ranged from >80 to <120%, with the exception of naphthalene (26%). The results for naphthalene were adjusted for low recovery. The coefficient of variation was <8% in all cases. Between-days variation was 10%. The limit of quantification (LOQ) differed between the individual components, but was 110 µg/tube and 46 µg/tube for sum aliphatic hydrocarbons and sum aromatic hydrocarbons, respectively.
Silicagel tubes were extracted with 5 ml methanol. 2-Butanone-oxime was detected by FID and calculated using CP-Wax-52–CB column calibration curves. The LOQ was 2.1 µg/tube.
Statistical analysis
All data were transferred to a spreadsheet program and the SAS system for Windows (version 8.2; SAS Institute, Cary, NC, USA) was used for statistical analysis. To enable the comparison of exposure to different VOC mixtures during the jobs, time-weighed average (TWA) sum aliphatic hydrocarbons and TWA sum aromatic hydrocarbons concentrations were expressed as percentages of the OELs, i.e. 1200 mg/m3 and 200 mg/m3, respectively, and summed to form relative exposures. Significant differences between high-solid paints and conventional paints for duration of application and surface area painted were tested on both sides with the Student's t-test (
= 0.05). The differences between increases of hydrocarbon concentration in the experimental room as determined by PAIRD during application for paints with different evaporation factors were tested by comparison of regression coefficients and the room concentrations at the end of the experiments.
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RESULTS |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Details of experimental parameters for both test series are listed in Table 4. The duration of the actual application of B-type paints during series 1 is listed; however painters were not allowed to leave the room earlier than 30 min. They were asked to continue brushing for the remaining time. During the second set of experiments both the surface area and the air exchange rates were considerably higher than for the first set of experiments for conventional paints.
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The differences in the surface area painted and the duration of application were statistically significant between high-solid and conventional paints. These observations suggest that the differences result from the higher viscosity of the conventional paints. This was supported by the experience during application as reported by the painters.
Temperatures at the start of the experiments ranged from 18.1 to 24.0°C, whereas end-temperatures ranged from 20.4 to 25.2°C. During the paint tasks a linear increase of temperature from 1.0 to 1.5°C was observed. During all experiments RH was <85%.
Based on the ratio of total aliphatic and total aromatic hydrocarbons as recovered from the charcoal tubes and as determined in the paints, the composition of the vapor seems to be quite similar compared with the composition of the paint. Based on the results for each consecutive 15-min charcoal tube interval within each experiment this seems to be valid for the entire duration of the paint task.
Personal air sampling results, i.e. TWAs over the duration of the task with a minimum of 30 min, were expressed as percentage of the nominal concentration of the OEL and ranged approximately from 8 to 93% for high solids, and from 38 to 168% for conventional paints. The B7–B9 types of conventional paint showed the highest concentrations during and following application. Figure 1 illustrates the TWA-relative exposure during the task.
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In general, the duplicate samples gave similar results (maximum difference <20%), indicating a possible slight between-subject and/or within-paint variation.
For several paint types, i.e. A2, A4, B2, B4, some of the periods observed during the task showed VOC-concentrations up to 140% OEL, while the overall period revealed concentrations below OEL. Figure 2 illustrates the variation in TWA-relative exposure over different periods for the high-solid paints (A types). During experiments with paint type B7–B9 short time relative exposure exceeded two to three times the nominal concentration of the OEL.
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Linear regression analysis revealed a strong relation between the OAR value of the paints and the TWA concentration (OEL percentage) during the task. For both paint types 73% of the differences in relative exposure could be explained by the differences in OAR values.
Vapor emission profiles, resulting from PID and PAIRD real-time air monitoring, show a strong increase of the vapor concentration during the actual application, a slight increase during the first period after the painter left the experimental room followed by a slight decrease. These profiles indicate that the highest vapor concentration occurred after the actual application when the painter had left the room; however this might to some extent also be related to the different sampling location, i.e. breathing zone versus a location in the surroundings of the painted surfaces, and the absence of air movements caused by the painter. Total hydrocarbon measurements during experiments with high-solid paints by PAIRD revealed similar results compared with PID-detection. The exposure profiles also show a (statistically significant) higher increase of vapor concentrations of the paints containing the most volatile solvents (evaporation factor (f) = 1), i.e. A1 and A2, compared with other paint types with lower f-values (Table 5). Moreover, for equilibrium room concentrations after the job the same sequence of evaporation factors was observed. In a combined plot of the average hydrocarbons concentration determined by charcoal tube sampling of each individual experiment over different time periods and the real-time monitoring, a remarkable good fit between the two measurement methods can be observed for A1, A3 and A5 paints, whereas an agreement, that is not so good, is observed for the paints, that contained aromatic hydrocarbons (Fig. 3). Different response to aromatic hydrocarbons of the PAIRD device compared with aliphatic hydrocarbons may be responsible for this.
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2-Butanone-oxim, present as skimming agent in all paints, was detected in all samples. During application the concentration in the breathing zone varied from 2.7 to 5.5 mg/m3 (GM = 4.2; GSD = 1.2; n = 12) for high-solid type of paints. The concentration during the application of conventional paints was slightly less than half the level of the high solids (GM = 1.5; GSD = 1.5; n = 20, including duplicates of B1 and B2 paints), reflecting the difference in concentration of 2-butanone-oxim in the paints, 0.4% w/w for high solids and 0.2% w/w for conventional paints, respectively.
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DISCUSSION |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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During the second series, two conventional paints of the first test series (B1 and B2) were also a part of the series. Since the results for these paints in the second set were quite similar with the results in the first set, it was concluded that there was no evidence to show that the different environmental conditions, i.e. air exchange rate and subject related parameters had affected exposure in such a way, that both test series were not comparable.
The solvent content of conventional types of paint that were prepared for the first test series (B1–B6) was dominated by the solvents of the alkyd resin (Uralac AD47Q-65), i.e. D40 and xylene residue. Therefore, no distinction could be made between paints based on the f-value, since 63% of the solvent in the paints was D40 (f = 0.7).
Also, there was a difference between total solvent content of the paints based on the formula and based on the determination of the non-volatile substances in the paint samples. Since the formula always gave a lower estimate, it is indicated that there are other ‘diffuse’ sources of solvents, e.g. in additives. For a reliable calculation of the OAR, the exact quantity of all substances, i.e. all VOCs, should be known.
In contrast to OEL and the VOC contents, the evaporation factor f represents a discrete variable in the OAR algorithm, since it indicates categories of evaporation. The influence of f was shown clearly for the high-solid paints, where pure categories of evaporation could be distinguished (Fig. 3). Both the slope of the concentration–time profiles and the level of the TWA–concentration following application were significantly different for all three categories of f-factors (Table 5). In addition, the differences between the classes of evaporation were demonstrated by the results of the different personal air sampling PAS over the period of application (Fig. 2).
The concentration of VOC in the paint has been demonstrated to affect the relative exposure. In the first series of experiments the B types of paint (conventional paints) contained twice the concentration of VOC compared with the high-solid types (A). Application of the B types resulted in higher relative exposure compared with the corresponding A types of paints (identical indices, Fig. 1), though the composition was not similar, as it should have been. For the second set of experiments a similar effect was observed, the paint with the highest VOC content (B9) showed higher relative exposure compared with B8, where only the VOC content was somewhat lower. The plots of relative exposure and OAR values as shown in Fig. 1 suggest, however, that the evaporation parameter might be slightly undervalued in the OAR algorithm, as f = 1 types of paints with lower OAR, result in higher relative exposures, e.g. A2 versus A4, and B7 versus B8 and B9. This might be associated with the fact that f is a discrete variable, whereas concentration and OEL are continuous variables in the OAR algorithm.
The type of VOC determines both the evaporation category f and the OEL. Within the same class of f-factor, the presence or absence of aromatic hydrocarbons affects the OEL of the mixture (and thus the OAR of the paint product) strongly. This can be illustrated most clearly for the high-solid paints. Substitution of 20% of the aliphatic hydrocarbons by aromatic hydrocarbons resulted in a decrease of the OEL (and an increase of the OAR of the paint) by 50, 33 and 42%, respectively for A2 compared with A1, A4 compared with A3, and A6 compared with A5. During the application of the paints containing aromatic hydrocarbons an increase of relative exposure was observed compared with the similar non-aromatic paint types of 45, 37 and 37%.
The use of concentration limits equal to 8-h TWA threshold limit values as OEL values in the calculation of the OAR implies that the risk approach, i.e. the ratio of relative exposure and OEL, is conservative. Actual duration of tasks will be <8 h. Implicitly the 8-h TWA threshold limit value has been adopted as a surrogate ceiling value. In addition, the OAR approach results in conservative estimates of exposure/risk since in the conceptual relative exposure model that the OAR algorithm represents, the (theoretical) ventilation necessary to prevent exposure above the OEL exceeds far the actual ventilation during application. For example, for paints that result in exposures just below 100% OEL, i.e. A2 and B2, the actual ventilation during the job was 25 times lower than the required ventilation derived from the OAR algorithm.
The observation that the ratio between aliphatic and aromatic hydrocarbons vapors that were trapped by the adsorbent tubes only slightly differs over time and from the VOC ratios in the paints is important for the robustness of the OAR approach, i.e. prediction of relative exposure to vapors calculated from the composition of VOCs in the paints.
Based on the observations discussed previously, it is concluded that the results indicate that all OAR parameters, i.e. f, the concentration VOC in the paint and the OEL are relevant, and OAR values calculated according to the OAR algorithm relate to relative exposure during brush application of paints under similar conditions. This outcome is somewhat surprising, since such a relatively simple algorithm including the pseudo-exposure parameters, i.e. VOC contents of the paint and f, was not intended to predict relative exposure for such a complex process as exposure during painting. Painting involves two distinct processes, (i) adding paint to a surface and (ii) drying of the paint, where compounds evaporate from paint to indoor air or breathing zone of the painter (van Veen et al., 1999). Therefore, apart from the paint composition the indoor air concentration will be determined by the application rate, the surface area of the paint film layer on the surface and the thickness of the film layer. Van Veen et al. (1999) used a two- compartment system to describe the painted surface. The upper compartment includes the surface of the paint in contact with air, so evaporation can occur. The lower compartment includes the portion that entered the wooden material, being potentially an important rate-limiting process. Exchange between the two layers is given by a diffusion-dependent exchange rate. Both Van Veen et al. (1999) and Bjerre (1989) developed mathematical indoor exposure models to predict solvent concentration from evaporation of solvents for paints based on the variables room volume, air exchange rate, application rate (mass of solvent and surface painted in unit time), surface area to be painted and evaporation rates. These models, i.e. the Painting Model and Maler Ekspositions Model (MEM 1), are relatively complex compared with the OAR algorithm, and have been shown to predict indoor hydrocarbon concentration and painter breathing zone concentration rather accurately in experimental conditions.
Since no or very limited differences of the above mentioned parameters for all but the paint composition factor were accepted during the present experiments, the observed association between relative exposure and paint composition only indicates the relevance of paint composition as determinant of exposure.
For the specific ‘standard paint task’ the relation between relative exposure and OAR can be considered as a task-specific risk parameter that makes it possible to derive a ‘cut-off’ OAR value. This relation is illustrated in Fig. 4 by the regression line and the 95% confidence interval the upper- and lower limits. If an acceptable level of relative exposure (in terms of OEL percentage) has been set, the relationship enables to establish a cut-off or limit value of OAR. Fig. 4 suggests that for the present specific task, paint products that have OAR values <275 m3/l could be applied safely, i.e. the VOCs exposure will not exceed OEL with 95% confidence. However, the reliability of the calculated OAR depends on the reliability of the OAR parameters. Therefore, precise product composition should be known and scientifically sound OELs should be available.
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The OAR approach uses the addition rule to establish OELs for mixtures, since OELs used the ones derived for similar neurotoxicological effects. Therefore, the OAR values given here do not necessarily reflect the ‘total risk’ of the paint during application. Inclusion of other effects, e.g. carcinogenicity, should mean that another VOC present as skimming agent, i.e. 2-butanone-oxime, would have been included in the OAR calculations. Based on the OEL (35 mg/m3, SER, 2004
) OAR values would increase substantially, especially for the high solids, since the concentration of 2-butanone-oxim in these types of paints was twice the concentration in conventional paints. The use of the addition rule for OELs based on different toxicological endpoints, however, is not acceptable. It can be recommended though to consider an additional classification of the (alkyd and/or water-based paint) products according to other risks by assigning an OAR value for all identified health effects, and to label products according to the highest OAR value. For the conditions of the experiments, the OAR approach proved to be a useful tool for the classification of alkyd paints based on neurotoxicological risks. The approach might be transposed to other products that are used in similar scenarios, i.e. similar application techniques and application rates, and VOC exposure resulting from similar evaporation processes (film layers on substrates). However, the relationship between ‘risk’ and OAR should be known for all (specific) tasks that are distinguished, in order derive ‘cut-off’ points for safe use of the products for the given scenario.
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ACKNOWLEDGEMENTS |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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The study was jointly sponsored by the Dutch Ministry of Social Affairs and Employment, The Dutch Association of Chemical Industries (VNCI), the Dutch Association Paint Printing Ink Manufactures (VVVF) and the Paint Shops and Painters Association (Bedrijfschap Schilders), which representatives participated in the Advisory Committee. E. van de Beemd is acknowledged for his work as a liaison officer. Sjaak de Vreede and Luco Ravensberg are acknowledged for their assistance during the experiments and the chemical analysis, respectively. The authors also acknowledge the painters who participated in the study.
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FOOTNOTES |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Present addresses: Royal Dutch Navy, Occupational Health Services, PO Box 20702, 2500 ES, The Hague, The Netherlands. 
Achmea Arbo, Occupational Health Services, PO Box 309, 8000 AH, Zwolle, The Netherlands.
Received May 27, 2004; in final form February 14, 2005
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REFERENCES |
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TOPFOOTNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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ASTM (1996) Standard test methods for evaporation rates of volatile liquids by shell-film evaporometer D3539-87. American Society for Testing and Materials, West Conshohocken, PA, USA.
Bjerre A. (1989) Assessing exposure to solvent vapor during the application of paints, etc. Model calculations versus common sense. Ann Occup Hyg;33:507–517.
CEFIC/HSPA (1997) Hydrocarbon Solvents Procedures Association: assigning occupational exposure limits to hydrocarbon solvents, a recommended approach. Brussels, Belgium: CEFIC.
ECETOC (1997) Occupational exposure limits for hydrocarbon solvents. Special Report no. 13. Brussels, Belgium: European Centre for Ecotoxicology and Toxicology of Chemicals.
NSPCA (1998) Guidelines for Norwegian Regulations concerning labelling, sale etc. of chemical substances and products which may involve a hazard to health and for Regulations concering marking/labelling of flammable and explosive goods. Oslo, Norway: Norwegian State Pollution Control Authority.
SER (1997) Advies OPS [Advice on Chronic Toxic Encephalopathy], 97/33, Annex 6. The Hague, The Netherlands: Sociaal Economische Raad Den Haag.
SER (2004) Nationale MAC-lijst [Dutch Occupational Exposure Limit Values]. The Hague, The Netherlands: Sociaal Economische Raad, Available from: http://www.ser.nl
SZW (1998) Ontwerp-regeling tot Wijziging van de Arbeidsomstandighedenregeling Betreffende Werkzaamheden met Vluchtige Organische Stoffen [Draft Directive on Labor Conditions for Use of VOCs]. ARBO/MIL/98/00670, Directie Arbeidsomstandigheden. The Hague, The Netherlands: Ministry of Social Affairs and Employment.
Veen van M, Fortezza F, Bloemen HJTH, Kliest JJ. (1999) Indoor air exposure to volatile compounds emitted by paints: experiment and model. J Exp Anal Environ Epidem; 9:569–574.[CrossRef]
Zock JP, Stouten JTh.J, van Hemmen JJ. (1998) Occupational Air Requirement (OAR) en vervanging van oplosmiddelen voor verf en verfproducten. TNO rapport V98. 1241, Zeist, The Netherlands.
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