Personal exposure to asbestos and respiratory health of heavy vehicle brake mechanics

Abstract

Asbestos brake linings and blocks are currently used in heavy vehicle brake repair shops (BRSs) in Bogotá, Colombia. Some brake products are sold detached from their supports and without holes, requiring manipulation before installation. The aim of this study was to assess asbestos exposures and conduct a preliminary evaluation of respiratory health in workers of heavy vehicles in BRSs. To estimate asbestos exposures, personal and area samples were collected in two heavy vehicle BRSs. Each shop was sampled during six consecutive days for the entire work shift. Personal samples were collected on 10 workers including riveters, brake mechanics, and administrative staff. Among workers sampled, riveters had the highest phase contrast microscopy equivalent (PCME) asbestos concentrations, with 8-h time-weighted average (TWA) personal exposures ranging between 0.003 and 0.157 f/cm3. Respiratory health evaluations were performed on the 10 workers sampled. Three workers (30%) had circumscribed pleural thickening (pleural plaques), with calcifications in two of them. This finding is strongly suggestive of asbestos exposure. The results of this study provide preliminary evidence that workers in heavy vehicle BRSs could be at excessive risk of developing asbestos-related diseases.

INTRODUCTION

Asbestos-containing products are still used in low- and middle-income countries, where occupational regulations tend to be scarce.1, 2 Chrysotile is the type of asbestos with the most extended use worldwide.3, 4 All types of asbestos, including chrysotile, are classified as carcinogenic to humans.5

Brake mechanics have been identified as an occupational group potentially exposed to asbestos fibers and there is an ongoing debate about whether brake mechanics are at excessive risk of developing asbestos-related diseases. Lemen6 concluded that the manipulation processes of asbestos-containing brake products can release asbestos fibers, and that short chrysotile fibers found in brake products increase the risk of disease.6 Other studies have concluded that heavy vehicles brake mechanics are exposed to asbestos concentrations in compliance with the US Occupational Safety and Health Administration personal exposure limit (US OSHA PEL) of 0.1 f/cm3, and that they are not at excessive risk of developing asbestos-related diseases.7, 8, 9, 10, 11 All these studies were conducted in high-income countries, especially in the United States.

The working conditions and potential asbestos exposures of brake mechanics working in heavy vehicle brake repair shops (BRSs) located in low- and middle-income countries may be different from those reported in studies conducted in high-income countries. In a study conducted with brake mechanics in Iran, it was found that mechanics were exposed to extremely high fiber concentrations12 determined using phase contrast microscopy (PCM). In a previous study conducted in Colombia, we found that the manipulation of asbestos-containing brake linings is a very common practice in passenger vehicle BRSs.13 This study identified that riveters are the workers in charge of attaching the brake linings to the supports, and perform a lengthy manipulation process during this task.13 The study concluded that although riveters were exposed to asbestos concentrations in compliance with the US OSHA PEL based on phase contrast microscopy equivalent (PCME) concentrations, these workers were exposed to extremely high asbestos concentrations based on assessment using transmission electron microscopy (TEM).13

The relationship between asbestos exposure and respiratory disease has been studied for many years.14 Because of confounding factors, understanding the pathogenesis of lung carcinomas, mesothelioma, and asbestosis is complex.15 Although some studies have suggested that chrysotile is less harmful compared with amphiboles,14 there is robust evidence showing an excess mortality risk because of lung cancer, all cancers, and non-malignant respiratory diseases in chrysotile-exposed workers, even for those exposed to low concentrations.16

Asbestos-containing brake pads, brake linings, and brake blocks are still commercialized in Colombia. Brake linings are used for both passenger and heavy vehicles (i.e., with important differences in size and thickness), whereas brake blocks are exclusively used for heavy vehicles. Many brake blocks and linings are commercialized detached from their supports and without holes. For this reason, they are subject to manipulation processes in order to attach them to the supports.

Colombia is a unique setting to assess occupational exposures to asbestos because asbestos regulations are recent. In November 2011, the first Colombian regulation regarding occupational exposures to asbestos was issued (i.e., Resolution 007/2011). Resolution 007/2011 adopts the asbestos threshold limit value (TLV) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) as the Colombian permissible limit value (PLV).17 The asbestos TLV is set at 0.1 f/cm3 for a TWA of 8 h. In the United States, OSHA establishes an 8 h PEL of 0.1 f/cm3, and a short-term exposure limit for 30 min (US OSHA STEL) of 1 f/cm3.

This paper extends our previous work in passenger vehicle BRSs by assessing asbestos exposures in two heavy vehicle BRSs. Asbestos exposures in heavy duty vehicle BRSs are expected to be different than passenger vehicle BRSs because of differences in the manipulations performed and the size of the brake products. In addition, we have added a preliminary respiratory health component to the assessment of workers of these BRSs.

MATERIALS AND METHODS

In 2012, two asbestos sampling campaigns of six consecutive days were conducted in two heavy vehicle BRSs located in Bogotá, Colombia. Respiratory health was evaluated in 10 workers of these BRSs. As an exploratory study, the BRSs and workers evaluated were selected by convenience. Because the evaluation of respiratory health was preliminary and exploratory, no control group was formally established. This is discussed in more detail in the Discussion section. For the interpretation of the results of the workers analyzed in the current study, information in the literature18, 19, 20 describing the prevalence of pleural plaques in populations non-exposed to asbestos was used.

A structured questionnaire, based on the US OSHA Medical Questionnaire,21 was translated and culturally adapted by members of our research team to collect information from the workers. This information included brake products used, manipulation procedures, and general characteristics of the shops. In addition, a specific set of questions regarding riveters’ occupational history were part of the questionnaire.

Ethics Committees of the two institutions directly involved on the sampling campaigns and respiratory health evaluations (i.e., Universidad de Los Andes and Fundación Neumológica Colombiana, respectively) approved the methods and study design. All workers signed an informed consent. To participate in the study, workers were required to have health insurance.

Asbestos Exposure Campaigns

BRS1 was sampled between 16 and 21 January 2012, and BRS2 was sampled between 30 January and 4 February 2012. Personal samples were collected on riveters, brake mechanics, and administrative staff. Area samples and quality control samples were collected as well.

Workers were instructed to maintain their regular daily activities and working procedures without modifications. The full shift was divided into shorter partial-period sampling windows as a strategy to prevent filter overloading. Brake mechanics and administrative staff had at least two partial-period personal samples collected daily. For riveters, several personal samples were collected during the entire work shift, including short-term personal samples (i.e., 30 min) collected during the manipulation of brake products.

Samples were collected and analyzed following NIOSH methods 7400 (ref.22) and 7402.23 Personal and area samples were collected using AIRChek XR5000 pumps (SKC, Eighty Four, PA, USA) connected to 25-mm MCE filters, with 0.45 μm pore size, mounted on 25-mm sampling cassettes equipped with 50-mm conducting extension cowls (SKC Preloaded Cassette, SKC). Samples were collected at a flow rate of 2 LPM measured at the beginning and at the end of each sampling window using a Defender 510 High or 520 High BIOS International Calibrator (BIOS International, Butler, NJ, USA) following standard procedures. To determine regulatory compliance, personal PCME concentrations were compared against both the Colombian and the US OSHA standards. PCME concentrations were estimated correcting PCM concentrations with the fraction of asbestos fibers to total fibers (f/F) reported by TEM Method 7402.23, 24 Using asbestos fiber counts, TEM asbestos concentrations were also estimated.

In Colombia, brake mechanics have on average longer work shifts (i.e., 540 min) than the traditional 480 min per day stipulated in the standard. The Colombian regulation determines that in these cases the PLV should be adjusted using Eqs. (1) and (2):

Where PLVc is the corrected PLV, and CF is a correction factor calculated using Eq. (2).

Where hd is the number of hours worked per day.

The adjusted PLV for a 9 h work shift is 0.083 f/cm3. PCME 9 h TWA asbestos concentrations were calculated for comparison purposes against the adjusted Colombian standard. When the work shift exceeded 8 h, and for comparison purposes against the US OSHA PEL, the worker’s 8 h TWA exposure was estimated using the worst partial-period sampling windows, following the recommendations of the US OSHA Technical Manual.25

When work shifts were <8 or 9 h (i.e., depending on the standard analyzed), full-shift TWAs were calculated assuming that the concentration during the unsampled time was 0 f/cm3. This assumption was made because in these cases, the worker was not longer in the BRS (e.g., Saturday’s work shifts finished at 1500 h). Samples analyzed by PCM that had concentrations below the limit of detection (LOD) were not analyzed by TEM, preventing us from estimating PCME concentrations. In these cases, the same assumption of 0 f/cm3 was made for these sampling windows. A sensitivity analysis to determine the impact of this assumption is described in the Results section.

For samples that were overloaded with particulate matter, two radically different assumptions were made to estimate TWA concentrations. One assumption assigned 0 f/cm3 for sampling windows that were overloaded. As this assumption could underestimate the TWA concentration, a second assumption was made assigning to the overloaded sampling windows the TWA PCME concentration of the remaining sampling windows of the same work shift.

Manipulation zones and office facilities area samples were collected at a respiratory height of 1.5 m. In BRS1, area samples were also collected at the warehouse. Area samples were only analyzed by PCM. During sampling campaigns, temperature and relative humidity were recorded using a HOBO U10 Temperature Relative Humidity Data Logger U10-003 (ONSET, Bourne, MA, USA).

Blank samples were collected each sampling day, and background samples were collected during one or two nights of the sampling days.

Asbestos counts and identification was done by an American Industrial Hygiene Association (AIHA)-certified laboratory (Forensic Analytical Laboratories, Hayward, CA, USA). Samples were analyzed using a Philips CM12 TEM (Philips, Eindhoven, The Netherlands). Counting of fibers with length >5 μm was conducted at a magnification of × 2500. A magnification of × 10,000 was used to determine fiber dimension and countability of fibers close in length to 5 μm. The accelerating voltage used was 100 keV. An Energy Dispersive X-ray (EDXA) (Evex NanoAnalysis System IV, Princeton, NJ, USA) was also used.26 In the Supplementary Material a discussion regarding quality control strategies applied in this study on laboratory analysis of air samples is explained.

All activities were recorded in activity diaries during the entire sampling campaigns. Asbestos concentrations and exposure results were communicated to BRS owners and workers.

Respiratory Health Evaluation

Respiratory health evaluation was performed at Fundación Neumológica Colombiana (FNC) facilities by pulmonologist expert on occupational diseases. Health evaluation results were personally communicated to each worker. The evaluation included:

  • Clinical evaluation (interview and physical examination) conducted by a pulmonologist. A detailed interview was performed looking for respiratory symptoms, exposures, and potential causes of pulmonary and pleural disease.

  • Pulmonary function tests (PFTs): Flow-volume curve with bronchodilator and carbon monoxide diffusing capacity (DLCO) were performed in a Vmax Encore 22D (Care Fusion, San Diego, CA, USA) according to the American Thoracic Society (ATS) and the European Respiratory Society (ERS) standards.27 DLCO results were adjusted to Bogota’s elevation (2640 m).28 Airflow obstruction was defined as a FEV1/FVC ratio less than the lower limit of normal using Crapo’s reference values.29

  • Chest X-ray and CT scans: Chest X-rays were taken using a Duodiagnost X-ray equipment (Phillips, Andover, MA, USA) and ILO (International Labor Office) criteria. Scans were taken using a CT Scanner with hardware version Somaton Sensation 64, and software version Syngo CT 2006A VB20B (Siemens, Erlangen, Germany). Chest X-rays were interpreted independently by a pulmonologist certified by NIOSH as a ILO B reader, and by a radiologist. CT scans were interpreted independently by two experienced radiologists using previously described criteria.30 Any lack of concordance in the interpretation was resolved by consensus.

  • Tuberculin skin tests (TSTs), using monopuncture intradermal technique (Mantoux): TSTs were performed in workers with evidence of pleural (circumscribed (plaques) or diffuse thickening or calcification) or parenchymal abnormalities. Results were interpreted based on the TST quantitative value established by ATS.31, 32

RESULTS

Sampled Population General Characteristics

Workers sampled in BRS1 included one riveter (R1), one auxiliary riveter (R2), one brake mechanic (W1), one secretary (W2), one warehouseman (W3), and the owner of the shop (W4). Workers sampled in BRS2 included two riveters who also work as brake mechanics (R3 and R4), one secretary/warehousewoman (W5), and the owner of the shop (W6).

Table 1 summarizes the information collected with the adapted structured questionnaire, including the demographic characteristics and occupational and non-occupational risk factors of workers sampled. Of the 10 workers, 2 were females. The mean age of sampled workers was 40 (±9.8) years, and 8 out of 10 workers reached high school educational level. Of the 10 workers, 4 were current smokers (R1, R2, R4, and W3) and 2 were former smokers (W1 and W4). Workers did not have additional history of asbestos exposure with previous employers, and two workers (W3 and W4) were riveters in the past in the BRS where they currently work. Only 1 of the 10 workers used respiratory protection.

Table 1 Demographic characteristics and risk factors for workers sampled.

Description of Heavy Vehicle Brake Product Manipulation Activities

Based on the working practices recorded in activity diaries, the steps involved in the manipulation process of brake products were identified (Figure 1). Brake mechanics that do not directly manipulate asbestos-containing brake products only performed steps 1–3 in Figure 1. Riveters perform the other manipulation steps identified in Figure 1.

Figure 1
figure1

Steps involved in the manipulation process of heavy vehicle brake linings or blocks.

The use of either brake linings or brake blocks depended on the size of the wheel. Larger wheels tend to use brake blocks. The initial step in the preparation of brake products included the removal of the old brake lining (or block) from the original support (i.e., shoe). When brake products were commercialized without holes, the manipulation process included drilling and countersinking the brake product, and then riveting it to the support. When the brake blocks were previously holed from factory, it was only necessary to rivet them to the support. Based on what was observed in these heavy vehicle BRSs, beveling and grinding brake products were less common activities compared with passenger vehicle BRSs.13 If the edges of the brake linings or blocks extended beyond the support’s borders, they were reduced by using either an electric circular saw or an emery disc followed by grinding the brake products’ edges.

In BRS1, the riveter occasionally manipulated asbestos and non-asbestos brake pads, and small asbestos and non-asbestos brake linings for emergency brakes. The manipulation processes on brake pads were similar to those conducted on brake linings or blocks. When necessary, brake pads were cut with an emery disc and the edges were ground until the pads fitted the brake shoe. The manipulation processes on small linings were similar to those described in a previous study of passenger vehicle BRS.13

Description of the BRSs Sampled

Both BRSs that participated in this study worked with heavy vehicles. They prepared brake products exclusively for the vehicles repaired at their facilities, and used asbestos- and non-asbestos-containing brake linings and blocks. Characteristics of the BRSs sampled are shown in Table 2.

Table 2 Description of heavy vehicle brake repair shops (BRSs) sampled.

Airborne Sample Results

A total of 235 air samples were collected during the 12 sampling days, including 115 personal samples, 44 short-term personal samples, 61 area samples, 3 background samples, and 12 blanks.

PCME 8 h and 9 h TWA personal samples for riveters are presented in Table 3 (a detailed description of the results of all the personal samples collected is included in Supplementary Tables S1 and S2). Riveter 1 (R1) was exposed to asbestos concentrations exceeding the US OSHA PEL and the Colombian standard in 5 of the 6 days sampled. All other riveters were exposed to asbestos concentrations in compliance with the Colombian and US OSHA standards. Riveter 4 (R4) in BRS2 had personal 8 h TWA concentrations in compliance but above the US OSHA PEL action level (0.05 f/cm3) in 3 of the 6 sampled days. Chrysotile fibers were the only type of asbestos fibers identified.

Table 3 Phase contrast microscopy equivalent (PCME) TWA personal samples for riveters.

All riveters had sampling windows with PCM concentrations below the LOD. Most of the samples that had concentrations below the LOD were collected during non-manipulation activities, except for 4 short-term personal samples (i.e., samples R1–day 6–a, R3–day 2–c, R3–day 4–b, and R4–day 4–e shown in Table 5). To determine the potential impact of assuming 0 f/cm3 for samples below the LOD, a sensitivity analysis was conducted using half the PCM LOD instead of assuming zero. The sensitivity analysis showed that using half the PCM LOD did not result in new TWA PCME concentrations above the occupational standard. For TWA concentrations that exceeded the standard of 0.1 f/cm3, the results show a negligible impact of this assumption on the TWA concentrations. For TWA concentrations below 0.1 f/cm3, using half the PCM LOD to estimate 8 h TWA concentrations could lead to larger TWA estimations; however, in these cases, the concentrations were so small that the actual concentration change was negligible as well. The sensitivity analysis described above is included in Supplementary Table S3.

Table 5 Short-term transmission electron microscopy (TEM) and phase contrast microscopy equivalent (PCME) asbestos concentrations and related activities.

Three of the samples collected on R1 and one sample collected on R3 were overloaded (i.e., see footnote “c” in Table 3). Two methods were used in these cases to estimate TWA concentrations. One method assumed that the concentration in overloaded sampling windows was 0 f/cm3 (i.e., this assumption was applied in all the TWA estimations showed in all the tables). The other method assumed that the concentration in overloaded sampling windows was the average concentration of the remaining sampling windows of that work shift. A sensitivity analysis of these assumptions is presented in Table 4.

Table 4 Comparison of TWA phase contrast microscopy equivalent (PCME) asbestos concentrations using two estimation approaches for overloaded samples.

As expected, assuming 0 f/cm3 underestimates TWA concentrations. However, sample R3–day 1, which was the only sample in compliance among the four samples analyzed in Table 4, did not change from compliance to non-compliance of the regulatory standards after using a different assumption.

Table 5 describes the manipulation activities performed by riveters, and the short-term asbestos concentrations associated with these activities. The largest TEM and PCME short-term asbestos concentrations were associated with complete manipulation activities (i.e., manipulation that included beveling and grinding, on top of unriveting, drilling, countersinking, and riveting). Manipulation activities that performed all but beveling and grinding (i.e., unriveting, drilling, countersinking, and riveting) were associated with the second highest short-term concentrations, followed by exposures during cleaning activities. For short-term samples that exceeded 30 min, the TWA was estimated using the entire sampling time. All short-term exposures were in compliance with the US OSHA STEL (1 f/cm3). However, several PCME 30 min asbestos concentrations were >50% of the US OSHA STEL, and some 30 min samples had TEM concentrations of >1 f/cm3 (i.e., recognizing that TEM concentrations cannot be used to determine regulatory compliance).

A summary of the results of PCME personal samples for both 8 h TWA and 30 min samples for each type of worker is presented in Table 6. As riveters were the workers with the highest exposures, personal concentrations of other workers were grouped together in one category (i.e., other workers). Other workers were exposed to 8 h TWA PCME asbestos concentrations in compliance with both the Colombian and the US OSHA standards.

Table 6 Phase contrast microscopy equivalent (PCME) personal statistics summary for both brake repair shops (BRS) sampled.

For area samples, most of the PCM concentrations were below the LOD, including samples collected close to the manipulation equipment. PCM concentrations for area samples (i.e., including manipulation area, office facilities, and warehouse) ranged from <0.003 to 0.020 f/cm3. The highest PCM area concentration was collected at the manipulation area of BRS2.

All blank filters were analyzed by both PCM and TEM and had no fibers detected. Background samples had PCM concentrations below the LOD and were not analyzed by TEM. Four samples were considered suspect because of flow drift above 5%. Flow drift for these samples ranged between 5.03% and 8.8%. Two of these samples were area samples and the other two were personal samples of riveter 1 (R1–day 4, Table 3) and worker 5 (W5). This is important because the sample of R1 was used in the TWA estimation of one of the non-compliance days of this worker. The suspect sample of this day was collected over 106 min, and the PCME concentration of this sample was 0.058 f/cm3.

During sampling days, air temperature was 20 °C in both the manipulation area and office facilities in BRS1, and relative humidity was 53% and 57% in each microenvironment, respectively. In BRS2, air temperature was 22 °C at the manipulation area and 21 °C at the office facility, and relative humidity was 50% and 52% in each microenvironment, respectively.

Respiratory Health Evaluation of Workers Sampled

Table 7 summarizes the results of the respiratory evaluation of the 10 workers. All chest X-rays were normal. CT scans were abnormal in 4 of 10 subjects; some of them had more than one abnormality. Of the three subjects with pleural calcifications (R2, W3, and W4), two had circumscribed pleural thickening (plaques). In these three subjects, the TST was negative. We found two mild abnormalities in PFT, but the four subjects with abnormal CT scan had normal PFT.

Table 7 Respiratory health evaluation of workers sampled.

Table 8 shows detail information of smoking status and imaging results for each worker sampled. Two subjects had mild alteration of pulmonary function; W2 had obstructive defect, and R4 had decreased diffusing capacity (i.e., detailed information regarding pulmonary function results is presented in Supplementary Table S4). All the subjects with CT abnormalities had normal PFT. Based on the questionnaire, W5 reported recurrent acute bronchitis, and W4 reported untreated high blood pressure, self-reported conditions that cannot be directly associated with asbestos exposure.

Table 8 Smoking history and imaging results of workers sampled.

Based on information collected with the structured questionnaire, the occupational history of the three subjects with pleural calcifications and negative TST was as follows: R2 has been working as an auxiliary riveter over the past 4 years, and had previously worked as full-time riveter for 3 years. W3 reported working as riveter for 2 years, and in the past 7 years had worked as a warehouseman. W4 has been working in BRS over the past 15 years, and at the beginning of this job he worked as a riveter for 4 months.

DISCUSSION

This study showed that 3 out of 10 workers of two heavy vehicle BRSs located in Bogotá (Colombia) had pleural calcifications and circumscribed thickening, strongly suggestive of asbestos exposure. The three workers who had pleural calcifications and circumscribed thickening are current or former riveters.

This study included an exploratory analysis of the respiratory health of a population potentially exposed to chrysotile asbestos that work in BRSs. There are limited number of studies that address respiratory health in occupational groups with these characteristics. Taking into consideration issues associated with exposure to radiation derived from chest X-ray and CT scans, and the exploratory character of this study, a formal control group of workers non-exposed to asbestos was not established. However, our results can be contextualized in relation with the prevalence of pleural plaques in the general population reported in the literature that ranges from 0.02% to 7.5%,18, 19, 20 and in men can go up to 12.8%.20 These values are below the percentage found in the current study. Furthermore, because tuberculosis can cause pleural thickening and plaques, TSTs were performed in all the workers who had imaging evidence of pleural plaques. The three workers with pleural calcifications had a negative TST result. Although this finding does not completely rule out tuberculosis, it is strongly suggestive that the pleural plaques could be related with asbestos exposure. Moreover, no other causes of pleural diseases were identified in the clinical evaluation. Recognizing that the sample size of workers evaluated is small (n=10), this finding is important because of the high apparent prevalence (30%) of pleural calcifications, and because these workers were exclusively exposed to chrysotile. Furthermore, imaging evaluation included both chest X-ray and CT scans, and some studies have shown that CT scans are better for the detection of pleural plaques.18, 33, 34 Several samples collected in the BRSs where these mechanics currently work exceeded both the US OSHA and Colombian occupational standards. To the best of our knowledge, this is the first study to analyze simultaneously asbestos exposures and respiratory health of brake mechanics and riveters of heavy vehicle BRSs in low- and middle-income countries.

This study documented that riveters working in the heavy vehicle BRSs sampled have to perform manipulation activities of asbestos-containing brake products, and in some cases this manipulation resulted in asbestos exposures not in compliance with the US OSHA and Colombian standards. In other cases, the exposures exceeded the US OSHA action level. Thus, riveters could be at excessive risk of developing asbestos-related diseases. This is aggravated because of the high prevalence of smoking observed in this group of workers. Smoking has a synergistic effect with asbestos exposure in the risk of developing lung cancer.35

Manipulation activities are required because brake products are commercialized detached from their supports and in most cases without holes. Grinding and beveling, which were some of the manipulation activities identified in the current study, have been identified in previous studies as opportunities of exposure because of the release of asbestos fibers.6, 36

A study similar in design to the current study conducted on passenger vehicle BRSs13 found that all the workers were exposed to concentrations in compliance with the US OSHA PEL and US OSHA STEL. Recognizing that the sample size in both studies in terms of the number of BRSs and workers sampled is small, the results suggest that riveters who work in heavy vehicle BRSs appear to be at higher risk for overexposure compared with workers in passenger vehicle BRSs.

Our findings differ from the results of several studies conducted in high-income countries that have concluded that brake mechanics are not at excessive risk of developing asbestos-related diseases.7, 8, 9, 10, 11 However, brake mechanics in high-income countries do not routinely manipulate asbestos-containing brake products to the extent observed in this study.

High exposure concentrations in BRSs were reported in a study conducted in Iran. Brake mechanics analyzed worked in both passenger vehicle and heavy vehicle shops, and were exposed to a mean PCM concentration of 0.46 f/cm3.12 PCM concentrations reported in the Iran study were higher compared with the results of the current study. Unfortunately, the Iran study did not estimate PCME concentrations.

Although short-term personal samples of the current study were in compliance with the US OSHA STEL, some TEM short-term personal concentrations were >1 f/cm3. The higher TEM concentrations provide additional support to the conclusion that brake mechanics could be at excessive risk of developing asbestos-related diseases.

Interestingly, some short-term personal samples collected during the manipulation of non-asbestos-containing brake products detected the presence of asbestos fibers (i.e., R1–day 2–b and R1–day 4–b; Table 5). This result could have two potential explanations: first, labels were incorrect and the brake products did in fact have asbestos fibers; second, as the manipulation equipment was covered with dust and fibers from previous manipulation activities, the manipulation process may have resuspended fibers exposing the worker. A similar event was observed in passenger vehicle BRSs.13

The elevated personal asbestos concentrations identified for R1 occurred despite the fact that a local ventilation system was constantly operated during the manipulation activities. Thus, a false expectation of safety may have been created for this worker. It was strongly recommended that the ventilation design and performance be revaluated and that major improvements should be implemented.

Although asbestos concentrations were high, only four samples were overloaded. This highlights the importance of designing a proper sampling strategy in heavily polluted occupational environments. Although the number of overloaded samples was small, their impact on exposure underestimation can be important. Because of this, strategies to include overloaded samples in TWA estimations have to be considered, as it was discussed in the Results section of this study.

Administrative staff spend most of their work shifts at the office facilities and the warehouse that are microenvironments where no manipulation activities are performed. Although they were exposed to asbestos fibers, all administrative workers and brake mechanics who do not manipulate brake products had personal asbestos exposures in compliance with the standards. The maximum 8 h TWA PCME concentration for non-riveter workers was 0.017 f/cm3.

Asbestos-related diseases were not diagnosed in any of the workers evaluated in this study. Reports of pulmonary diseases on brake repair workers exclusively exposed to chrysotile asbestos are scarce.4, 33, 37, 38 Furthermore, some authors report that brake mechanics are not at excessive risk of developing asbestos-related diseases.36, 39 Previous studies have shown that asbestos-exposed brake mechanics can have functional abnormalities including restrictive impairment with decreased forced vital capacity and total lung capacity.37 This was not the case for the workers sampled in the current study. Erdinç et al.37 reported that pulmonary function loss was higher on asbestos-exposed workers who also smoke.37 As smoking is common in the workers sampled, including riveters, these workers should be followed-up closely.

Imaging evaluations showed that 3 workers (30%) had pleural thickening with calcifications that are considered markers of asbestos exposure,34, 35, 40 and can occur in 20–60% of occupationally exposed workers.35 A fourth worker also had these CT features, but was positive in the TST that can confound this finding. Similar pleural abnormalities have been recently described in a study of 103 French brake mechanics that reported 5 cases (4.9%) with pleural thickening.33 However, none of the workers evaluated in the current study had interstitial compromise (i.e., asbestosis), as reported in the French study. Brake mechanics in the French study were exposed to chrysotile, similar to the workers sampled in the current study. Both studies used CT scans that are the most accurate method to detect pleural thickening.33, 34 Recognizing that there is an important difference in sample size between the two studies (i.e., the current study only evaluated 10 workers), the prevalence of pleural thickening in Bogotá is higher than the results obtained in the French study.33 Manipulation activities performed by the riveters of Bogotá, and the use of non-appropriate respiratory protection, could help explain this difference.

As chrysotile was the only type of asbestos found, and workers sampled did not have other occupational history of asbestos exposure, this study provides additional information regarding personal exposures of workers exclusively exposed to chrysotile.4, 16, 41

This study, combined with the results presented in a previous study of our research group,13 could help inform current efforts to reconstruct historical asbestos exposures of brake mechanics. Nevertheless, additional efforts are needed to characterize asbestos exposures, not only for brake mechanics, but also for other occupations that use and manipulate asbestos-containing products.

This study has a number of weaknesses. The principal limitation is the small sample size in terms of numbers of shops and workers sampled. The small sample size may limit the generalizability of the data. We have visited a number of other BRSs in Bogotá (Colombia) and the shops sampled are typical of the city in terms of size, manipulation activities, and amount of work. Although the number of shops and workers sampled is small, their exposure characterization is extensive, with a total of 235 samples collected during the assessment campaigns. In addition, these results are important because very few assessments of BRSs in developing countries have been published. As a result, this paper is a significant contribution to the literature, highlighting the important public health problem of asbestos and brake repairs in low- and middle-income countries.

In conclusion, this study identified the deplorable working conditions of a group of heavy vehicle brake mechanics, something previously observed in passenger vehicle brake mechanics.13 It also identified the presence of asbestos exposure pulmonary markers in a large percentage of the riveters evaluated. The “controlled or safe use” of asbestos and asbestos-containing products has been argued to justify the use of this material. The results of this study suggest that the “controlled or safe use” of asbestos is not always achieved. These results may be found in other low- and middle-income countries, and because of this, the authors highlight the urgent need of additional studies to identify the risks resulting from the ongoing use of asbestos worldwide.

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Acknowledgements

We thank the owners, administrative staff, brake mechanics, and riveters from the BRSs sampled. We also thank the Research Vice-presidency, the School of Engineering, and the Department of Civil and Environmental Engineering from Universidad de Los Andes for their financial support. The collaboration received from the staff of Fundación Neumológica Colombiana and the Radiology Department in Fundación Cardioinfantil in Bogotá is also greatly appreciated. Finally, we thank Forensic Analytical Laboratories for the analysis of the samples. All the equipment used to assess exposure was acquired with the financial support of the Department of Civil and Environmental Engineering from Universidad de Los Andes. Laboratory analysis and respiratory health evaluations were performed with the financial support of the Research Vice-presidency, the School of Engineering, and the Department of Civil and Environmental Engineering from Universidad de Los Andes.

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Correspondence to Juan P Ramos-Bonilla.

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The authors declare no conflict of interest.

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Supplementary Information accompanies the paper on the Journal of Exposure Science and Environmental Epidemiology website

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Cely-García, M., Torres-Duque, C., Durán, M. et al. Personal exposure to asbestos and respiratory health of heavy vehicle brake mechanics. J Expo Sci Environ Epidemiol 25, 26–36 (2015). https://doi.org/10.1038/jes.2014.8

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Keywords

  • brake mechanics
  • riveters
  • chrysotile
  • Colombia
  • pleural plaques
  • pleural thickening

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