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Ann. occup. Hyg., Vol. 46, Supplement 1, pp. 71–75, 2002© 2002 British Occupational Hygiene Society

Published by Oxford University PressDOI: 10.1093/annhyg/mef613

Pneumoconiosis and Exposure to Quartz-containing Dust in the Construction IndustryE. TJOE NIJ1*, P. BORM2, D. HÖHR2 and D. HEEDERIK1

*Author to whom correspondence should be addressed.

1Division of Environmental and Occupational Health, Institute for Risk Assessment Sciences, Utrecht University, PO Box 80176, 3508TD Utrecht, The Netherlands; 2Department of Particle Toxicology, Institute for Environmental Medicine, PO Box 103751, D-40028 Düsseldorf, Germany

Construction workers are potentially at risk for pneumoconiosis due to exposure to highlevels of quartz-containing dust. Studies on quartz and dust exposure in the constructionindustry are scarce and little is known about the toxic potency. An additional problem is thepotential heterogeneity of the toxic potency due to differences in materials used in thisindustry. In this study we have made an attempt to characterize dust and quartz exposure aspart of a cross-sectional study on pneumoconiosis among construction workers. Constructionworkers (n = 1335) were studied for quartz dust-related radiographic abnormalities and lungfunction changes. Full shift personal respirable exposure measurements (n = 68) wereperformed for certain job titles included in the cross-sectional study. For a more precise char-acterization of the dust, several samples were studied by scanning electron microscopy andX-ray diffraction. A mixed dust type of pneumoconiosis (ILO category ≥1/1, irregular opac-ities) was observed in 2.9% of the construction workers studied. Exposure measurementsshowed quartz levels between 0.002 and 3.77 mg/m3. SEM analysis showed that most particlesconsisted of silica and that dusts sampled during different tasks had different size distribu-tions. In all samples, particle size ranged from 200–300 nm to 5–10 mm. The risk for pneu-moconiosis among construction workers is evident, but a clear-cut exposure–responserelationship is hard to define because of heterogeneity in dust exposure levels, heterogeneityin composition of the dusts and possible modification of the toxicity of quartz by other factorspresent in the dusts.

Keywords: construction industry; exposure; pneumoconiosis; quartz; SEM

INTRODUCTION

Quartz is known to cause silicosis in several occupa-tional groups exposed to it. Silicosis is an importantcause of morbidity and mortality among constructionworkers (Bang et al., 1995; Sullivan et al., 1995).Among populations exposed to mineral dust withhigh quartz content there is a rather steep dose–response relationship (Fig. 1). When the averagequartz content is lower, silicosis is associated withmuch higher levels of cumulative exposure.

A health effects study among 1335 constructionworkers showed a prevalence of pneumoconiosis(ILO category ≥1/1, irregular opacities) of 2.9%(E. Tjoe Nij, A. Burdorf, J. Parker, M. Attfield andD. Heederik, unpublished data) and an associationbetween radiographic abnormalities and duration of

exposure (Fig. 2). Persons with radiographic abnor-malities had no history of asbestos exposure.

To calculate an exposure–response relationship forquartz exposure among construction workers, cumu-lative quartz exposure for individuals had to be esti-mated. Exposure data in the construction industry isscarce and not aimed at assessing job-specific fullshift exposure. Task-specific exposure assessmentsusually show high exposure levels (Hallin, 1983;Riala, 1988; Chisholm, 1999; Thorpe et al., 1999;Nash and Williams, 2000; Lumens and Spee, 2001).Little is known about the toxic potency of dust gener-ated during construction work. An additionalproblem is the potential heterogeneity of the toxicpotency of quartz due to differences in the matrix andsurface (Donaldson and Borm, 1998; Clouter et al.,2001). In this study we have made an attempt tocharacterize dust and quartz exposure as part of across-sectional study on pneumoconiosis amongconstruction workers.

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72 E. Tjoe Nij et al.

MATERIALS AND METHODS

Full shift (6–8 h) personal respirable exposuremeasurements (n = 68) were performed on 34 indi-viduals with certain job titles included in the cross-sectional study. The following specialized tasks wereincluded in the measurements: concrete drilling,recess milling, cleaning of construction sites, tuckpointing, inner wall construction and demolition.Personal air sampling for respirable dust was con-ducted using Dewell–Higgins cyclones, connectedto Gilian Gilair5 portable pumps at a flow rate of1.9 l/min. After gravimetric determination of dust onthe filters, α-quartz was determined by infraredspectroscopy (NIOSH method 7602) (Eller andCassinelli, 1994). Variance components were calcu-lated using random effect nested ANOVA.

For a more precise characterization of the dust,several samples were studied by scanning electronmicroscopy (SEM). For the SEM images inhalabledust was sampled with IOM sampling heads oncoated polycarbonate filters. Particles sizes weredetermined and images were produced using aPhilips 515 scanning electron microscope equippedwith elemental dispersive X-ray analytics (EDAX).

RESULTS

Group average exposures (arithmetic and geomet-ric mean) and variance components for respirabledust and quartz are shown in Table 1. Quartz expos-ure levels exceeded the MAC value (0.075 mg/m3,8 h time-weighted average) in all measured groups,except in the background group. The average quartzcontent of the respirable dust was 12%.

The between and within worker variance compon-ents (bwR95 and wwR95) were large for both dust andquartz exposure for the whole group. The largebetween worker component for repirable quartz(bwR95 = 600) indicates a large difference betweenoccupational sub-groups. Analysis by sub-group,however, showed a higher within worker component,indicating that the exposure for a given subject variedto a great extent from day to day. A crude estimate ofcumulative exposure was calculated for the wholegroup, leaving out the exposure measurements for thebackground group and cleaners, because they werenot involved in the study population. This resulted ina group-based cumulative exposure of 5.7 mg/m3 yr(Fig. 1).

SEM analysis showed that most particles consistedof silica and that dusts from different tasks haddifferent size distributions. SEM images from twoconstruction worker operations are shown. Duringrecess milling (Fig. 3) angular α-quartz particles of5–10 µm were generated. A small number of particleswere 200–300 nm in diameter. Many aggregates ofsmaller particles were seen.

During removal of mortar from between bricks(Fig. 4) particles consisting of silica and calcium(diameter 5 µm) were generated. Larger particlescontained a lot of calcium, which is the majorelement in cement. During the removal of mortar themajority of particles generated were 200–300 nm indiameter, although some were <100 nm.

In the dust samples generated during pile topcrushing many particles with sharp edges were seen.A high silica content was observed in these particles.Most of the other particles consisted mainly of silica,but calcium and aluminium were also present. The

Table 1. Respirable dust (mg/m3) and respirable quartz (mg/m3) by construction worker sub-group and within and between worker variation

N, number of workers measured; n, number of measurements; GSD, geometric standard deviation; bwR95, between worker ratio of the 97.5th and 2.5th percentiles of the log normally distributed exposure; wwR95, within worker ratio of the 97.5th and 2.5th percentiles of the log normally distributed exposure.

Group N n Respirable dust (mg/m3) Respirable quartz (mg/m3)AM(min–max)

GM(GSD)

bwR95(GSD)

wwR95(GSD)

AM(min–max)

GM(GSD)

bwR95(GSD)

wwR95(GSD)

Total 34 68 2.2(0.1–11.5)

1.1 (3.5) 31 (2.4) 38 (2.5) 0.35(0.002–3.77)

0.086 (6.6) 600 (5.1) 47 (2.7)

Tuck pointers 4 10 3.5(0.6–8.0)

2.2 (2.9) 1 (1.0) 69 (2.9) 0.56(0.089–1.65)

0.35 (2.8) 1 (1.0) 110 (3.3)

Recess millers/ concrete workers

8 14 2.8(0.2–11.5)

1.4 (3.4) 12 (1.9) 62 (2.9) 0.84(0.028–3.77)

0.31 (5.3) 47 (2.7) 174 (3.7)

Demolition workers

10 22 2.4(0.2–9.4)

1.4 (3.1) 25 (2.3) 21 (2.2) 0.25(0.038–1.26)

0.14 (2.7) 14 (2.0) 20 (2.1)

Inner wall constructor

2 4 2.1(0.6–4.0)

1.5 (2.5) 1 (1.0) 57 (2.8) 0.043(0.016–0.084)

0.036 (2.0) 1 (1.0) 25 (2.3)

Construction site cleaners

6 12 1.0(0.1–2.5)

0.5 (3.7) 8 (1.7) 114 (3.4) 0.032(0.002–0.097)

0.017 (3.6) 55 (2.8) 29 (2.4)

Background exposed group

4 6 0.3(0.1–0.4)

0.2 (1.8) 10 (1.8) 3 (1.3) 0.005(0.002–0.015)

0.003 (2.4) 22 (2.2) 8 (1.7)

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Quartz-containing dust in the construction industry 73

number of particles of 200–300 nm in this samplewas large (∼40%).

DISCUSSION AND CONCLUSIONS

The high levels of quartz-containing respirabledust measured during construction work and the radio-logical abnormalities found on chest X-rays areindicative of a silicosis risk. Exposure measurementsamong construction workers revealed that the day-to-day variance especially is very large, which makesthe calculation of a cumulative exposure estimate forindividuals for risk assessment purposes inaccurate.A dose–response relationship is difficult to estimate,not only due to variation in quartz exposure levels,but also because of differences in the biologicalactivity of quartz-containing dusts from differentsources of exposure. In the construction trade quartzdust is generated by working with a variety of highenergy electrical tools on different quartz-containingmaterials, resulting in dusts with different charac-teristics. The variations in the biological activity ofquartz are presumably caused by factors that modifyquartz toxicity (Donaldson and Borm, 1998; Fubini,1998; Borm and Donaldson, 1999).

When risk estimates were calculated using cumu-lative exposure, based on the measurements describedabove, the trend was comparable to other studies,but risk estimates were smaller and statistical sig-nificance was only reached for the highest exposuregroup. Nevertheless, the overall results were includedin Fig. 1. Calculation of accurate estimates of cumu-lative exposure is complicated for constructionworkers, because of the large day-to-day varianceand differences in composition of the respirable dusts

Fig. 1. Prevalence of pneumoconiosis (profusion category ≥1/1) in relation to cumulative quartz exposure in studies where the average quartz level of dust was ∼30% (filled squares) (Theriault et al., 1974; Hnizdo and Sluis-Cremer, 1993; Ng and Chan, 1994; Steenland and Brown, 1995) and in studies were the average quartz content was <20% (filled diamonds) (Muir et al., 1989; Graham

et al., 1991; Tornling et al., 1992; Kreiss and Zhen, 1996; Abrons et al., 1997; Hughes et al., 1998; Love et al., 1999). A crude estimate of construction worker cumulative exposure and prevalence is included (filled circles) (Tjoe Nij et al., 2002).

Fig. 2. Relative risk of pneumoconiosis (profusion category ≥1/1) in relation to years worked in the construction industry.

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74 E. Tjoe Nij et al.

(size and shape of particles) and because onlyconstruction worker sub-groups with potential quartzdust exposure participated in the survey. A largernumber of exposure measurements and a bettercharacterization of the toxicological properties ofdusts from construction sites are needed to assess thebiological effective dose.

Acknowledgements—The construction workers who partici-pated in the study and their employers are acknowledged fortheir participation. The quartz analyses were funded by the

National Institute for Occupational Health and Safety in theConstruction industry (Arbouw).

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Fig. 4. SEM images from dust generated during tuck pointing (removing mortar between bricks) and element analysis of one

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