Current Chemical Exposures Among Ontario Construction Workers

ABSTRACT

Current occupational exposures to chemical agents were assessed as part of an epidemiological study pertaining to the cancer and mortality patterns of Ontario construction workers. The task-based exposure assessment involved members from nine construction trade unions. Air samples were taken using personal sampling pumps and collection media. A DustTrak direct-reading particulate monitor was also employed. Exposure assessments included measurements of airborne respirable, inhalable, total, and silica dust; solvents; metals; asbestos; diesel exhaust and man-made mineral fibers (MMMF). In total, 396 single- or multi-component (filter/tube), 798 direct-reading, and 71 bulk samples were collected. The results showed that Ontario construction workers are exposed to potentially hazardous levels of chemical agents. The findings are similar to those reported by other researchers, except for silica exposure. In our study, silica exposure is much lower than reported elsewhere. The difficulty associated with assessing construction workers’ exposures is highlighted.

MATERIALS AND METHODS

Literature searches were conducted on published sources of information regarding occupational exposures for construction workers. Initial meetings were held with local business managers of various trade unions in Ontario where knowledgeable union members were asked to describe relevant exposures from both current and retrospective points of view. The research group reviewed collective agreements and consulted information sources at the CSAO and on the Internet. In consultation with major stakeholders, a list was compiled summarizing the important exposure factors for each trade.

Study sites were selected on the basis of convenience. An industrial hygienist visited each site in advance of sampling in order to familiarize himself with the process, hazards, and potential exposures, and assess the feasibility of carrying out an industrial hygiene sampling campaign. Potential contaminants and related processes were identified. Available material safety data sheets (MSDS) were consulted, and a date(s) arranged for sampling. Based on the initial site assessment, appropriate sampling methodologies were employed as listed in Table I.

While on site, prospective subjects were approached and informed of the nature and purpose of the study. They were asked to wear air sampling equipment and advised that participation was voluntary. Air samples were collected using SKC air sampling pumps, Models 52, 224-PCXR3, 224-PCXR4, 224PCXR7, 224-43XR, 224-44XR, and Pocket Pump (SKC Inc., Eighty Four, PA) connected to appropriate sampling media via Tygon tubing. If they agreed, they were shown how to wear the instrument and how to operate it.

All pumps were calibrated before and after sampling with a DryCal DC-Lite Calibrator (BIOS International Corp., Pompton Plains, NJ) to ensure that air flow did not change significantly during sampling (±5%). In some cases, due to short duration of activities, it was not possible to re-calibrate after each filter was changed. Sampling volume was deemed acceptable if the daily pre- and postcalibration were within the 5 percent tolerance limits. In the event sample tampering was suspected, because it was not possible to observe the operation continuously, the sample was considered spoiled and excluded from the data set.

A direct-reading instrument was employed as a means of evaluating multiple exposures to the same agent on site and for those trades where traditional task-based sampling did not yield meaningful results because of the task duration being too small. A DustTrak Aerosol Monitor, Model 8520 (TSI Inc., Shoreview, MN) was used. It operates based on the light-scattering principle. The instrument was factory-calibrated for the respirable fraction of standard test dust (ISO 12103-1, A1). It is an active sampling instrument containing a pump operating at 1.7 L per minute. Depending upon the particle size of the aerosol being studied, different inlets are used. Thoracic particulates were estimated using a PM 10 inlet, which has a median cutoff of 10 µm. Respirable particulates were evaluated using a 10-mm nylon cyclone connected by Tygon tubing to the PM 10 inlet. The cyclone is designed so the respirable dust fraction meets the 4 µm (50%) cutoff criteria. Diesel particulate matter was estimated using a 1 µm inlet and impactor.

Before and after each sampling day, the DustTrak was zerochecked to ±0.001 mg/m3 using a special filter. The flow was checked using the rotameter supplied with the instrument. The DustTrak has a data logging feature, which allows the user to collect specific information regarding sampling duration and average, minimum, and maximum aerosol concentrations. A 10-second data logging interval was used. The major benefits of using the DustTrak were that it allowed us to measure short duration high-exposure tasks with reasonable accuracy and permitted evaluation of changes in working conditions instantaneously. It also offered the flexibility to roam around each site to measure short-term exposures for multiple trades.

To verify the accuracy of the DustTrak, side-by-side sampling with the traditional sampling method was performed. During its use, the inlet to the instrument was held near the worker’s breathing zone until an acceptable sample was collected. If the instrument could not be held near the breathing zone for safety reasons, it was placed in the general work area close to the worker. At the end of each sample period, which would last from one minute to several hours, the average, minimum, and maximum readings and sample duration were noted in logbook along with a description of the task performed. Bulk samples of interest were collected to document the presence of materials on-site and to provide supplementary information.

RESULTS

In total, 396 single or multi-component (filter/tube), 798 direct-reading, and 71 bulk samples were collected at the workplaces listed in Table II. Twenty of the 396 single- or multicomponent samples were not included due to various sampling complications such as pump failure, breakthrough, and tampering. Bulk samples were analyzed for silica, lead, or fiber content and type depending upon the samples. The results of the air sampling are presented in Table III, which describes measured task-based exposures for each of the trades. The minimum and maximum task-based sample concentrations presented are values that were detectable, unless otherwise noted. Since refractory ceramic fibers (RCF) have a lower TLV than other MMMFs, they have been identified separately in the tables.

Data were analyzed using statistical package MINITAB version 12. Figures 1 to 6 illustrate concentration distributions of respirable dust, total dust, and respirable MMMF by task and trade. Box plots illustrate the statistical range of data between the 25th and 75th percentiles, with whiskers extending out showing the general range of all data. The numerical value shown at the center of each box plot is the median value. The width of each box is proportional to the square root of the number of observations in the box.

Outliers, specific data outside of the statistical range, are shown as a diamond symbol. Outliers were predetermined automatically by the statistical analysis package used. In the box plot function, MINITAB considers any observation 1.5 to 3 times away from the middle 50 percent of data as a possible outlier. No observations were greater than 3 times away from the middle 50 percent of data in any of our plots, which would otherwise have been noted with a different symbol. Numerical values of outliers may or may not be shown. Outliers not shown on the graphs are noted as required.

The results of the DustTrak aerosol monitor are presented in Table IV. The results of our side-by-side sampling between gravimetric respirable dust and DustTrak respirable dust are shown in Figure 7.
