Assessing Exposures to 1-chloro-4-(trifluoromethyl) Benzene (PCBTF) in U.S. Workplaces

The chemical compound 1-Chloro-4-(trifluoromethyl) benzene (CAS No: 98-56-6)—also known as PCBTF, Oxsol 100, or Parachlorobenzotrifluoride—was nominated to the National Toxicology Program (NTP) for toxicity and carcinogenicity studies (http://ntp.niehs.nih.gov/ntp/noms/support_docs/pcbtf06-0409.pdf). The nomination was based on the increasing use of PCBTF by industries and consumers, since it was exempted by the Environmental Protection Agency (EPA) as a volatile organic compound in emissions reporting on the basis of not reacting in a manner that would contribute to the formation of tropospheric ozone.(1) Although PCBTF is no longer manufactured in the United States, approximately 29 million lbs. were imported in 2012(2) and used in various applications to replace other chlorinated solvents with known environmental or human health hazards. Those applications include the automotive industry as industry-wide applications in coatings, thinners, and cleaning solvents, and repair and maintenance cleaning and as a consumer product for cosmetic stain removal and aerosol rust prevention.(3) The toxicity information on PCBTF is available from various resources(4,5) including the NTP website.(6) These studies, however, are limited to short-term toxicity, and chronic inhalation toxicity and carcinogenicity studies are unavailable. There are no Occupational Safety and Health Administration (OSHA) regulations specific to limiting occupational exposures to PCBTF. The National Institute for Occupational Safety and Health (NIOSH) has not established a time-weighted average (TWA) recommended exposure level, and the American Conference of Governmental Industrial Hygienists (ACGIH®) has not established a TWA-threshold limit value (TLV®) for PCBTF. The Occidental Chemical Corporation, which used to manufacture PCBTF in the United States, established a corporate exposure limit (CEL), which was a TWA limit of 25 ppm (185 mg/m3) for an 8-hr work-shift. The toxicological basis for setting this limit is not known to us. However, Occidental Chemical Corporation no longer manufactures or imports PCBTF into the United States. The purpose of this case study is to determine industry-wide occupational inhalation exposures using available industrial hygiene sampling methods. This information can be used to benchmark exposure concentrations that may be applied in future studies of inhalation toxicity in animal models. In addition, side-by-side samples of a pumped (active) and diffusive (passive) sorbent tubes were taken to compare concentration ratios between the active and passive sampling methods. Workplace Description Vehicle manufacturing plants Four vehicle manufacturing plants—helicopter (Plant A), aircraft (Plants B and C), and automobile (Plant C)—were recruited through personal contacts. All manufacturing plants were identified by code for confidentiality. At Plant A, PCBTF was used as a cleaning solvent to remove residual glue after upholstery removal during interior refurbishment. The cleaning work was done manually under a slotted back-draft ventilation hood. PCBTF was used during primer application prior to coating of an airplane at Plants B and C and plastic adhesive promoter application at Plant D. All painters wore airline respirators and applied the PCBTF-containing substances using spray guns under downdraft ventilation. The mixing worker at Plant C combined base (23 L with 0% PCBTF), activator (23 L with 30–60% PCBTF), and thinner (6 L with 60–90% PCBTF) to make primer. The mixing task was done under a canopy hood and the mixer wore a full facepiece air-purifying respirator. The amount of PCBTF per worker used during the specific tasks varied ranging from 0.3 to 18.5 L. Table I shows a summary of workplace description including tasks, PCBTF usage, room ventilation, local exhaust ventilation, respirator type, and the amount of PCBTF used during each task. Detailed information about job tasks and personal protective equipment was described in a supplementary file. TABLE I Summary of Workplace Description (Vehicle Manufacturing Plants) Paint manufacturing plants Three paint manufacturing plants were recruited via contacting American Coatings Association. Four tasks—pre-batch making, batch making, filling, and miscellaneous—were observed. In the pre-batch making area (Plants E and G), workers transferred PCBTF-containing materials to other containers using either a pumping system or a mechanized pouring system. Containers were partially opened to place a pumping system. No respirator was required for this task at both plants. In the batch-making area (Plants E, F, and G), each batch-maker added various chemicals in a batch container, mixed the chemicals, transferred the chemicals to other containers, and cleaned the emptied batches. The batch-making task was done in a closed system for all plants except for cleaning or partially opened to add or transfer materials. The batch-makers wore no respirators during mixing but wore dust masks (Plants E and G) and half facepiece respirators (Plant F) when manually adding materials. The filling operators (Plants E, F, and G) filled containers with final product from an automated dispenser and placed lids. No respirator was required for the filling task. Other miscellaneous tasks included lab quality control testing, cleaning, batch adjusting, color mixing, and pilot working. The workplaces for all tasks were controlled by general ventilation in addition to any local exhaust ventilation systems. Table II shows a summary of workplace description and detailed information for each task was described in a supplementary file. TABLE II Summary of Workplace Description (Paint Manufacturing Plants) METHODS Sample Monitoring At the four vehicle manufacturing plants, 28 personal and 8 area sample pairs were collected using actively pumped coconut-shell charcoal tubes (SKC 226-01, SKC Inc., Eighty Four, PA) and diffusive charcoal badges (SKC 575-001, SKC Inc.). The former represents an active sampling method (i.e., drawing air throughout the media using a pump) and the latter represents a passive sampling method (i.e., air intake by chemical diffusion). All workers sampled at the vehicle manufacturing plants handled the PCBTF-containing materials. At the three paint manufacturing plants, 64 personal and 26 area sample pairs were collected. Participants were workers who handled PCBTF and workers who did not but were in close proximity to the workers handling PCBTF. The sample size and sampling time for each task are listed in Table III. The sampling times ranged from 15 to 407 min for the vehicle manufacturing plants and 70 to 535 min for the paint manufacturing plants. Two types of sampling pumps, Pocket Pump (SKC Inc.) and Gilian LFS-113 (Sensidyne, Clearwater, FL), were used at sampling flow rates between 20 and 200 ml/min for the active sampling method. The sampling flow rates were adjusted based on anticipated concentrations, previously collected from similar workplaces. Each pump was calibrated before and after sample collection with a DryCal DC-Lite device (BIOS International Corporation, Butler, NJ) to assure the difference between pre- and post-sampling flow rates was within ±5%. The position of passive and active samplers for the personal sampling method was randomized to minimize bias from workers’ handiness (i.e., not always on the left or right of worker’s collar). All field surveys were performed between 2010 and 2012. TABLE III Air Sampling Results Using Active Sampling Method All active and passive samples were analyzed with gas chromatography/flame ionization detector according to the NIOSH Manual of Analytical Methods (NMAM) 1026(7) by the NIOSH contract laboratory. The NIOSH method has suggested a maximum of 25 ppm for a 10 L air sample with a working range between 0.024 and 9.15 ppm (0.178 to 67.8 mg/m3). Yost and Harper(8) tested passive badges at various loadings in a standard atmosphere chamber in which the test concentrations of the standard atmosphere were confirmed by means of coconut charcoal tubes for time period up to 8 hr. Those loadings were 0.012 mg (0.01×CEL), 0.123 mg (0.1×CEL), 0.505 mg (0.5×CEL), 1.10 mg (1.0×CEL), and 2.09 mg (2.0×CEL). Yost and Harper(8) showed charcoal tubes and passive badges to have a large capacity covering up to 2 times the CEL and the maximum concentration suggested by the NIOSH method. The mass concentrations of passive badges were calculated using the average sampling rate of 11.8 ml/min.(8) From each sampling site, 1–10 field blank samples were collected. In this study, sample results were not adjusted by field blank samples because almost all field blank samples (96% of 56 field blank samples) showed non-detectable masses. The limit of detection was 0.1 – 0.7 μg for both diffusive badge and charcoal tube. The limit of quantitation ranged between 0.5 – 2.5 μg for the diffusive charcoal badge and 0.5 – 3.4 μg for the charcoal tube. Three sample pairs showing at least one of each pair resulted in less than the limit of detection were excluded. None of the samples except for the three sample pairs showed less than the limit of quantitation.