British Journal of Industrial Medicine 1987;44: 133-141 Estimation of long term exposure to mixed solvents from questionnaire data: a tool for epidemiological investigations ANNE T FIDLER, E L BAKER, R E LETZ From the Occupational Health Program, Harvard School of Public Health, Boston, MA 02115, USA ABSTRACT Quantifying the exposure of construction painters to mixed organic solvents is difficult in the face of a lack of industrial hygiene data, the heterogeneity of the solvents used, and the vari- ability in work practices which influences the amount of solvents to which a worker is actually exposed. This report describes an attempt to derive an estimate of airborne solvent exposure using questionnaire responses in a population of construction and maintenance painters. This exposure index (EI) is a weighted average of the total number of gallons used a year minus the fraction which would be absorbed by a respirator, where the weights are based on the method of application (spraying, rolling, brushing) and the presence of ventilation (per cent time inside v outside). An analysis performed to determine the sensitivity of the El to variations in the values chosen for several parameters showed that the index is relatively insensitive to the underlying assumptions that we have used. One component of the El (self report of hours worked) correlated well with union payroll records. The El appears to provide a useful relative (not absolute) estimate of airborne exposure to organic solvent mixtures which may be used as a dose surrogate in epidemiological investigations. In construction and maintenance painting coatings are applied to interiors and exteriors of commercial and inidustrial buildings, as well as other structures such as tanks, vessels, and bridges. In 1977 there were in the United States about 450 000 union and non- union workers employed in this occupation, applying 8-6 billion gallons of paint composed of over 3000 different substances,' 95% of which are listed in NIOSH's Registry of Toxic Effects of Chemical Sub- stances.2 Most construction painters use a wide vari- ety of these paints throughout their working lives. The composition of paints has changed significantly over the years, causing a change in the nature of toxic exposures to those who work with these substances. By the 1960s, oil based paints had largely been replaced by those containing alkyd resins Present address: Division of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, Cincinnati, OH 45226. Accepted 14 April 1986 which, while of low toxicity in themselves, require a much higher relative solvent composition (up to 50% of the paint product). Though the popularity of water based latex paints has increased dramatically over the past 15 to 20 years, solvent paints are still widely used. About a half to a third of solvents produced in the United States are used in manufacturing surface coatings3 (M Guilleman, at international conference on organic solvent toxicity, Stockholm, Sweden, 1984). Solvent based paints consist of three components: (1) a vehicle, including solvents and resins used as binders; (2) a filler, including pigments and extenders; and (3) additives, including driers, biocidal com- pounds, and stabilisers. Each of these components may provide a hazardous exposure to those who work with paints. Of major concern are industrial organic solvents, many of which have been shown adversely to affect the functioning of the central nervous sys- temn (table 1). Several epidemiological studies have focused on workers in a variety of painting oper- ations, as these workers experience a potentially haz- ardous exposure to many different solvents. Indus- 133 copyright. on April 26, 2020 by guest. Protected by http://oem.bmj.com/ Br J Ind Med: first published as 10.1136/oem.44.2.133 on 1 February 1987. Downloaded from
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British Journal of Industrial Medicine 1987;44: 133-141
Estimation of long term exposure to mixed solventsfrom questionnaire data: a tool for epidemiologicalinvestigationsANNE T FIDLER, E L BAKER, R E LETZ
From the Occupational Health Program, Harvard School ofPublic Health, Boston, MA 02115, USA
ABSTRACT Quantifying the exposure of construction painters to mixed organic solvents is difficult inthe face of a lack of industrial hygiene data, the heterogeneity of the solvents used, and the vari-ability in work practices which influences the amount of solvents to which a worker is actuallyexposed. This report describes an attempt to derive an estimate of airborne solvent exposure usingquestionnaire responses in a population of construction and maintenance painters. This exposureindex (EI) is a weighted average of the total number of gallons used a year minus the fraction whichwould be absorbed by a respirator, where the weights are based on the method of application(spraying, rolling, brushing) and the presence of ventilation (per cent time inside v outside). Ananalysis performed to determine the sensitivity of the El to variations in the values chosen forseveral parameters showed that the index is relatively insensitive to the underlying assumptions thatwe have used. One component of the El (self report of hours worked) correlated well with unionpayroll records. The El appears to provide a useful relative (not absolute) estimate of airborneexposure to organic solvent mixtures which may be used as a dose surrogate in epidemiologicalinvestigations.
In construction and maintenance painting coatingsare applied to interiors and exteriors of commercialand inidustrial buildings, as well as other structuressuch as tanks, vessels, and bridges. In 1977 there werein the United States about 450 000 union and non-union workers employed in this occupation, applying8-6 billion gallons of paint composed of over 3000different substances,' 95% of which are listed inNIOSH's Registry of Toxic Effects of Chemical Sub-stances.2 Most construction painters use a wide vari-ety of these paints throughout their working lives.The composition of paints has changed
significantly over the years, causing a change in thenature of toxic exposures to those who work withthese substances. By the 1960s, oil based paints hadlargely been replaced by those containing alkyd resins
Present address: Division of Surveillance, Hazard Evaluations, andField Studies, National Institute for Occupational Safety and Health,Cincinnati, OH 45226.
Accepted 14 April 1986
which, while of low toxicity in themselves, require amuch higher relative solvent composition (up to 50%of the paint product). Though the popularity of waterbased latex paints has increased dramatically over thepast 15 to 20 years, solvent paints are still widely used.About a half to a third of solvents produced in theUnited States are used in manufacturing surfacecoatings3 (M Guilleman, at international conferenceon organic solvent toxicity, Stockholm, Sweden,1984).
Solvent based paints consist of three components:(1) a vehicle, including solvents and resins used asbinders; (2) a filler, including pigments and extenders;and (3) additives, including driers, biocidal com-pounds, and stabilisers. Each of these componentsmay provide a hazardous exposure to those who workwith paints. Of major concern are industrial organicsolvents, many of which have been shown adverselyto affect the functioning of the central nervous sys-temn (table 1). Several epidemiological studies havefocused on workers in a variety of painting oper-ations, as these workers experience a potentially haz-ardous exposure to many different solvents. Indus-
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trial paints used in the past contained as many aseight or ten different solvents, whereas most formu-lations in use today contain four or fewer.4 The ali-phatic and aromatic solvents are the most common insolvent based paints and in uses that require moreexpensive oxygenated solvents (alcohols, ketones, andester/ether) an equal amount of hydrocarbons is usu-ally included.3 The aromatics, although less effectivethan the aliphatics, have been decreasing in usebecause of their greater toxicity.
Modifying factors of solvent exposure
The inhaled dose of solvents-that is, the amount ofvapour inhaled that ultimately reaches the targetorgans-is dependent on several physiologicalparameters. These include pulmonary ventilationrate, diffusion of the solvent through the alveolo-capillary and tissue membranes, and solubility of thesolvent in blood and tissues.5 Solvents may also enterthe bloodstream by absorption through the skin.There, individual differences in skin permeability andprotection can also affect the total body dose.The total inhalation exposure to organic solvents
generated by workers during painting operations ismodified by several factors pertaining to work prac-tices and working conditions. The use of a respiratoris an important factor, both because of its potentiallylarge influence in reducing the amount of solventactually absorbed and because the wearing of respira-tors varies considerably and non-randomly over apopulation of painters. Spray painters (with theheaviest total exposure) often wear respirators almostall the time, thus reducing their effect exposure so thatit approaches that of those who apply paint with abrush or roller and who have a much lower total
exposure but do not wear respirators. Several types ofrespirators are currently in use, including dust masks,single and double cartridge, and airline or airhoodrespirators. Because they offer no protection againstsolvent vapours, dusts masks should be considered asconveying no protection at all.The amount of protection afforded by a respirator
to an individual is its "protection factor" (PF),defined as:
Components analysedfrom in mask sample
PF = - Components analysed
from ambient sample
Thus the PF is the percentage of the solvent that isabsorbed by the respirator. A NIOSH report whichevaluated a large number of respirators and workingconditions in paint spraying operations6 providesestimates of solvent protection factors. The type andcondition of the respirator, as well as its fit, greatlyinfluence the protection factor an individual willexperience. The average PF afforded by cartridgerespirators was approximately 65%, whereas the PFfor air supplied respirators was approximately 90%.Another problem in estimating an "average
inhalation exposure" in painting operations is theinherent difference in exposure generated by differentmethods of paint application: spraying, rolling, andbrushing. During processes in which the paint isflowed on to the surface, as in rolling and brushing, apainter is exposed to the solvent as it evaporates fromthe painted surface. Spraying, however, which pro-duces an atomisation of the paint produces anexposure to both the solvent and the paint mist. The
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Estimation of long term exposure to mixed solvents from questionnaire data
increase in exposure from spraying reflects theamount of overspray and rebound that occurs.Depending on the method of spraying and the type ofsurface being painted, the degree of overspray canrange from 5% to 90%.7 Because of this variability, itis difficult to estimate the difference in magnitude ofexposure that would result from the use of the sameamount of paint in the three types of operations,although it is agreed that by far the greatest exposureoccurs during spraying operations.
In addition to the use of respirators and thedifferential exposure generated by the different meth-ods of application, the presence of ventilation is alsoa factor of interest because of its influence on theeffective dose of solvents to an individual. A recentstudy by Riala et al reported industrial hygieneevaluations of 92 work stations at 18 sites duringmaintenance painting operations.8 Solvent naphthaconcentrations were determined by alkyd andurethane painting performed at these sites, stratifiedby method of application, room size, and presence orabsence of ventilation. Ventilation was considered tobe present if there was either mechanical or naturaldraft ventilation and was found to produce a 50-90%decrease in the ambient air solvent concentrationacross different application methods and room sizes.
Estimation of exposure: limitations of epidemiologicalstudies
The epidemiological evaluation of the neuro-behavioural effects of solvents on painters is compli-cated not only by the difficulty in measuring the effectof the exposure but also by the exposure itself. Sol-vent paints are a heterogeneous group of chemicalsthat often defy attempts to define or even categorise,often because of the lack of informative labelling ofcontainers and the failure of paint manufacturers todisclose the components of the materials. In addition,a large percentage of construction workers are notemployed for a substantial period by one employer;rather, they may work for a few days or a few monthson a job and then move to another. Therefore, thenature and amounts of paint substances to which theyare exposed vary greatly. In addition, because manypainters work on transient construction sites the col-lection of valid hygiene monitoring data is seldomfeasible.Another potential source of documentation of
exposure, biological monitoring, may be used if thetype of solvent to which the worker is exposed isknown. For example, exposure to toluene may bemonitored by urinary hippuric acid levels and styreneby mandelic acid levels.9 Paints usually contain mix-tures of organic solvents, however, many of whichhave no biological marker. Painters may use several
types of paints, even within the same day. Further-more, biological measurements reflect only currentexposures and cannot be used to assess past exposure.
Because estimating the level as well as the type ofexposure over a working lifetime is difficult manystudies have used the duration of exposure as the soleestimate of exposure.l1-15 This measure ignores theintensity and type of exposure. Furthermore, sincethe duration of exposure is highly correlated with ageand since the occurrence of neurobehaviouralimpairment increases with age, it is often difficult todistinguish solvent effects from the effects of aging.Furthermore, the use of duration as the sole measureof exposure is based on the assumption that the toxiceffects of solvents are a function of cumulativeexposure. Other models which use more precise esti-mates of exposure, incorporating terms for exposureintensity, duration, and work practices, are poten-tially more useful in epidemiological studies.
Rationale of exposure estimation technique
Frequently the only source of information regardingexposure in a population is a questionnaire completedby the worker. Recently, Mikkelsen and Brownedeveloped a measure of estimated solvent exposurebased on extended personal interviews regardingduration of exposure, application rates, materialsused, respirator use, and work conditions, includingventilation (reported at Stockholm conference, 1984).The practicalities of a large field study, taking placeeither at the workplace on "company time" or atanother site in the subjects' spare time, preclude theuse of such a time consuming instrument.
In evaluating solvent exposed industrial workersGregersen et al defined exposure on an I1 point scaleweighted by specific criteria according to differentplaces of work."6 These criteria included duration ofexposure, evaporation rates, ventilation, skin absorp-tion rates, respirator use, and toxicity of the materialsused. This type of exposure index is not directly appli-cable to the study of construction painters, as it ispartially based on industrial hygiene data that areunavailable in this population and it cannot easilyaccommodate the variability in exposure and workconditions experienced by painters. Using their indexof exposure, the dose response relation was observedwith measures of intellectual and peripheral nervefunction.
In an earlier epidemiological study of constructionpainters we evaluated the questionnaire approach toobtaining a history of solvent exposure. 7 Anexposure questionnaire was developed to determinehours worked as a painter, methods and rates ofapplication, respiratory protection, and ventilation.Union payroll records were reviewed to obtain an
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objective estimate of time worked and the nature ofthe job. In that study we found that we could obtainanswers to exposure related questions and reports ofhours worked which correlated well (r = 0.75) withsimilar data obtained from union payroll records.Thus we think that self reported work rates are an
accurate estimate of actual hours worked and are
suitable for use in calculating exposure variables.The aim of the present study was to generate a
reliable estimate of long term inhalation (or airborne)exposure to solvents from questionnaire dataobtained from a group of construction painters.
Methods
In April 1984 a health survey was undertaken of 118painters from the Boston District Council of theInternational Brotherhood of Painters and AlliedTrades (IBPAT). A solvent exposure history ques-tionnaire, derived partially from one developed byIBPAT and modified in our earlier study,'7 wasadministered to all participants. The subjects, includ-ing current and former full time and part time paint-ers, were asked to estimate their average applicationrates, percentage of time spent actually painting, andrespirator use, both over the past year and duringtheir working lifetimes.A set of computerised tests of neurobehavioural
function, chest x ray, and pulmonary function testswere also administered to the painters and to 45unexposed dry wall tapers. The results of these exam-inations will be reported elsewhere.
CALCULATION OF EXPOSURE INDEX
The inhalation exposure index (El) provides an esti-mate of the amount of solvent vapour to which aworkers is exposed by inhalation, based on individualreports of work activities, estimates of theeffectiveness of two types of respirators worn bypainters, assumptions regarding the relative airbornesolvent generation rates of three methods of paintapplication, and an adjustment factor to account forthe impact of workplace ventilation. Individuals pro-
Fidler, Baker, LetzTable 3 Estimates ofsolvent exposure among differenttypes ofpainters*
Average No gals/yearappliedt 13527 4093 1192%Absorbed by respirator 0-55 0 01 0 01Average No gals/yearavailable for inhalation 6039 4053 1188
*Painters are classified by the type of painting they do more than50% of the time.tAIl estimates refer to painters' preferred method of application-that is, estimates for sprayers pertain only to their exposure whilespraying.
vided information on paint use rates, by applicationmethod, percentage of work time spent in paint appli-cation, and amount of time worked using solventpaints in the past month, year, and over a lifetime.Details of respirator use and the availability of venti-lation were also obtained where possible.The general form of our exposure index (El) is
given by:
EIj = E E E (Tj Fmrij) (Rmj Em) ((1 - Rr) V;)ir m
where:El is the exposure indexj is the jth individuali is outdoor/indoor (1 = indoor; 2 = outdoor)r is respirator type (1 = none or dust; 2 = cartridge;
3 = airline)m is method of paint application (1 = spray; 2 = roll;
3 = brush)T is time spent painting (hours)F is the fraction of timeR is paint application rate (gallons/hour)E is a relative vapour emission factor for each method
(2 5, 1-25, 1, respectively)P is a protection factor for each type of respirator
(0, 0-65, 0 90, respectively)V is a ventilation factor relative to outdoors (1, 5,
respectively)
Table 2 Exposure indices used in sensitivity analysis
Respirator PFMethod Ventilation
Exposure index Air Cartridge Spray:roll:brush Inside:outside
Estimation of long term exposure to mixed solvents from questionnaire data
3n I * Gallons/year available for inhalation:
20 g L S | median 1254. I'
01 0
z
00 5 10 15 20 2c
Gallons / year (x 1000)
Roll3°]r0 |0 Gallons/year applied: median=2160
n20cU Gllons/year available for inhalationi20 median52044
7 0
10 15 20 25Gallons/year Cx 1000)
7
Brush60 0 Gallons / year applied: median= 600
* Gallons /year available for inhalation:50 median =600
UA
.0
3030z
20
10
00 5 10 15 20 25
Gallons/year x 1000l )Fig 1 Distributions of total paint applied and paint availablefor inhalation (total paint minus fraction absorbed byrespirator) for each of three application methods (spray, roll, brush).
Spray0 Gallons / year applied: median = 2130
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138This expression is a time weighted average, with thefirst two parameters, T and F, providing the timecomponent, the second two, R and E, related tosource strength, and the last two, P and V, providingfor source modification. Reports from each painterprovide estimates of the T, F, and R parameters foreach individual, while overall estimates of the E, P,and V parameters have been derived from previoushygiene data.
Arriving at a weighting scheme for the method ofpaint application is made difficult by the scarcity ofhygiene data reported for different types of paintingoperations. Two separate estimates made by experi-enced industrial hygienists (W A Burgess and T JSmith) gave relative exposure for spray-
ing:rolling:brushing of 10:7:6 and 10:4:2. On thisbasis the weighting scheme used in the exposure indexwas 10:5:4.
Based on reports,6 estimates of average protectionfactors (PFs) were chosen as 0-65 for cartridge and0 90 for air supplied respirators.No direct estimation of ventilation was available in
the present study but workers reported the averageamount of time during which they worked inside oroutside. The scheme used weighted the relative con-tribution of indoor and outdoor painting as 5 to 1,which is compatible with other hygiene surveys.8
For each individual the exposure index generated isa weighted average of the number of gallons a year ofsolvent based paints applied. No judgement of theamount of solvent actually absorbed is made. Becausethe E, P, and V parameters are relative, the units ofthe exposure index are equivalent gallons brushedoutdoors without a respirator. Although the exposureindex may be calculated to estimate the intensity ofexposure during any period, we have chosen to calcu-late it for the entire working lifetime as a painter;subsequent analyses are based on this lifetimeexposure index.
SENSITIVITY ANALYSISThe sensitivity of the exposure index to variations inthe values chosen for respirator protection factors orthe weighting schemes was investigated by varying thevalues used for these parameters and comparing the
Fidler, Baker, Letz
resulting indices, using simple correlation analysisand stratified analyses. The values were varied as fol-lows:
Respirator PF: cartridge = 0 65 and 0 50airline = 0 90 and 0 70
Inside:outside = 2:1; 5:1; 9:1; 1:1Eight indices representing the range of values of the
possible combinations of these terms were selectedand used in subsequent analyses (table 2).
Results
All 118 painters completed work history question-naires and were classified by the method of applica-tion which they had used for more than half the time.There were 20(16-9%) sprayers, 24(24-3%) rollers,34 (28 8%) brushers, and 40 (33 3%) who used no sin-gle method more than half the time. The sprayers hada mean age of 39 8 years (SD 10-0), 10-6 (SD 2-1)years of school, and a Hollingshead Index (parentalSES) (HI) of 53 5 (SD 12 6). Rollers had a mean ageof 46- 1 years (SD 11 -4), 10-8 (SD 2 6) years of school,and an HI of 56X8 (SD 8 4). The brushers' mean agewas 46 5 years (SD 11-7), with 11-7 (SD 2.5) years ofschool, and an HI of 55-6 (SD 12-2). The 40 remainingpainters had a mean age of 37-7 years (SD 9 9), 11-6(SD 2 1) years of school, and an HI of 52-0 (SD 11-6).The sprayers consumed more alcohol than the otherpainters: 19-4 drinks a week (SD 27-5) as opposed to11-0 (SD 11-8), 13-5 (SD 14-2), and 9-1 (SD 11 8) forrollers, brushers, and others, respectively.
In this population spray painters applied aboutfour to ten times as many gallons as rollers or brush-ers (table 3). On average, however, more than 50% oftheir total breathing zone vapour was absorbed byrespirators, whereas virtually all of the solvent vapourgenerated by rollers and brushers is available forinhalation because of the lack of respiratory protec-tion. Hence, this four to tenfold increase in totalexposure is reduced to a less than two to fivefoldincrease in inhalable exposure (table 3). All types ofpainters generally wear respirators when spraying.
Table 4 Correlation matrix ofexposure indices resultingfrom variations in parameters
Estimation of long term exposure to mixed solvents from questionnaire dataTable 5 Exposure levels ofpainters classified by three variations ofthe exposure limit
The impact of respirator use is more clearly seenwhen comparing distributions of individual paint userates with those of individual inhalable paintamounts. In spray painters the skewed distribution ofpaint use is significantly changed when respirator useis taken into account (fig 1). The distribution for paintuse and inhalable paint level are similar for rollersand brushers.The eight different exposure indices (table 2) cre-
ated to evaluate the sensitivity of the index that wasselected for final analysis (El 1) to variations in com-ponent terms were highly correlated (table 4). In par-ticular, El I was highly correlated with all other terms(r = 0-91-0 99) indicating close relative ranking abil-ity between the indices. Stratified analyses comparingthe categorisation of exposure using different indiceswas comparable among the different values chosen(table 2) for the eight indices. For example, 73-7% of118 painters were identically classified using eitherEl I or EI 3; only two individuals (1 -7%) werereclassified by more than one category. Even higheragreement was noted, 76-3%, between indices I and8, with no one reclassified by more than one category(table 5).
251
20115
1
10.
I I II I' I I IIII
60 90 120 150 180Exposure index (x 1000)
Fig 2 Frequency distribution ofexposure index(n = 118). (See textfor derivation ofEI.)
The exposure index for all 1 8 painters (fig 2)ranged from 5542 to 32 684-2 (median: 604). Theexposure index was compared among the differenttypes of painters. As expected, sprayers have the high-est value, followed by rollers and brushers (table 6).The exposure index correlated moderately well
with its component parameters (table 7). None wasobviously dominant or irrelevant in contributing tothe index. Furthermore, the lifetime exposure indexwas not correlated with the number of years workedas a painter (r = 0-01). Simply using one of the com-ponent variables only (percentage time spent spray-ing, for example) as an index of exposure, whileappealing in its simplicity and ease of use, does resultin considerable disagreement in exposure groupclassification; there is only a 44-9% agreement withten subjects (8-5%) reclassified by more than one cat-egory (table 8)By combining information on years of exposure to
paints-that is, exposure duration-with theexposure index (a measure of exposure intensity), a
intensity) is derived (table 9). Although spray paintershave worked fewer years than rollers or brushers,their intensity and cumulative exposure level was
considerably higher.
Discussion
The index of long term exposure to mixed organicsolvents presented combines information obtainedfrom painters by means of a concise questionnairewith weighting schemes established by reportedhygiene evaluations for factors that modify theexposure to an individual. These include respiratoruse, method of paint application, and presence ofventilation. Sensitivity analysis demonstrates that theexposure index is not unduly sensitive to the assump-tions underlying the constituents that reflect theseparameters. Because epidemiological studies of con-struction painters are inherently limited by a lack ofobjective hygiene data or records of paint use, theonly feasible source of information regarding the his-tory of exposure is the individual painter. Theexposure index uses this information to yield a usefulestimate of the relative ranking of individual exposureto paint solvents.The validity of the exposure index as a true mea-
sure of solvent exposure rests primarily on the issue ofself reports of painters of amounts of paints used,application rates, and other measures of exposure.
Median exposure index(intensity) 59 746 28 305 15 698
Median cumulative exposure(duration x intensity) 522 163 634467 319015
*Painters are classified by the type of painting they do more than50% of the time.
Fidler, Baker, LetzBecause most of these assess average paint use over aworking lifetime, it may often be difficult for paintersto provide a reliable and accurate estimate. It isunlikely, however, that there is a systematic differencein reporting based on health effects of the exposure,since in most instances it is the subclinical effects thatare under investigation and are, therefore, not per-ceived by the subjects.
SELECTION OF EXPOSURE MODELAs stated previously, proper modelling of exposuremust be based on clear assumptions regarding thetoxic actions of solvents on the central nervoussystem. Three potential measures-duration ofexposure, intensity of exposure, and cumulativeexposure (duration times intensity)-are presentedfor the different types of painters (table 9). It may beseen that in this study spray painters have a shortermean duration ofexposure but a much higher averagelevel of exposure, as defined by the exposure index,than either rollers or brushers. Therefore, if durationwas chosen as the exposure measure, spray painterswould compose a greater proportion of the lowerexposure categories whereas a measure of intensitywould put them in the higher exposure categories.Likewise, if a cumulative measure were used, then thepotentially different effects of duration and intensitywould mask each other. Use of a different measure ofintensity, such as an exposure index based on paintingdone in the past year, rather than a lifetime average,would provide an ability to investigate yet anothermodel of the effects of exposure.
Clearly, the key to the investigation of a doseresponse relation between exposure to organic sol-vents and neurobehavioural deficits is a valid estimateof level of exposure. Because of the unavailability ofsuch an estimate among construction workers, studieshave had to rely on the duration of the exposure as asurrogate. The exposure index presented here mayprovide an alternative which can effectively rank indi-viduals by their average long term exposure to mixedorganic solvents.Though the exposure index provides a stable sum-
mary measure of the level of solvent exposure, it hasseveral limitations. Differences in paint composition,both in type and toxicity of solvents and in percentagecomposition of solvents, preclude a direct conversionof the number of gallons to which individuals areexposed to a quantity of solvent. Also, without fur-ther information regarding the nature of paints used,it is not possible to account for the possible con-founding effects of other neurotoxic constituents suchas lead and mercury.
In addition, workers who used solvent paints in thepast experienced a somewhat higher exposure thanthey have recently because many paints contained
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Estimation of long term exposure to mixed solvents from questionnaire datamore solvents per gallon. Older painters, therefore,may show toxic effects that may appear to be due toaging but could in fact be due to their higher previousexposure which is unaccounted for by the exposureindex. The expected effect of this problem wouldappear to be small, however, because the difference inthe exposure index that would occur would be rela-tively minor by comparison with the effect of aging.Many environmental and occupational conditions
present problems similar to those faced when evalu-ating the exposure of painters; these include lack ofhygiene data, mixed exposures, and various jobclassifications or modes of exposure.The investigationof toxic waste sites and exposure of constructionworkers to asbestos are examples where an approachsimilar to the one used here would be helpful in reduc-ing a complex exposure history so that individualscould be ranked in order to investigate dose responserelations.
We are grateful to Drs James Ware and RichardMonson who reviewed the manuscript and Mr Rod-ney Wolford and staff of the International Broth-erhood of Painters and Allied Trades for their help inthe design of the questionnaire used in the study.This research was supported by the National Instituteof Environmental Sciences National Research ServiceAward 5 T32 ES 07069 from the Harvard School ofPublic Health.
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