Greg Sirianni

Biological versus ambient exposure monitoring of creosote facility workers.

Traditional methods for monitoring occupational creosote exposure have focused on inhalation. However, there is evidence that dermal exposure contributes importantly to total systemic dose, as measured by biological monitoring methods. This study was conducted to further characterize the relationships between inhalation and dermal exposures to creosote, and to compare traditional ambient exposure monitoring versus biological monitoring in 36 creosote-exposed wood treatment workers. Full-shift personal air samples were obtained, along with post-shift and next-day urine measurements for 1-hydroxypyrene. There was little or no correlation between airborne measures and urinary 1-hydroxypyrene (r2 = 0.05 to 0.35). More than 90% of 1-hydroxypyrene could be attributed to dermal exposure. These data indicate that traditional monitoring methods may be inappropriate for creosote workers, raising concerns about the adequacy of methods currently mandated by the Occupational Safety and Health Administration.

Comments on the Diesel Exhaust in Miners Study

We are writing in response to four recent articles describing the historical reconstruction of diesel exhaust exposures in underground mines (Diesel Exhaust in Miners Study or DEMS) for use in epidemiological analyses of exposure–response relationships between mining-associated diesel exposure and health effects, e.g. lung cancer (Coble et al., 2010; Stewart et al., 2010; Vermeulen et al., 2010a,b). We have particular concerns about the estimation of historical respirable elemental carbon (REC) levels for underground miners. Those estimates were back extrapolated using historical carbon monoxide (CO) area measurements and estimated levels of historical ‘adjusted horsepower (HP)’ of diesel fleets to estimate levels of CO as surrogates of diesel exhaust (DE). As discussed below, those measures are at best imprecise and may not be valid measures of DE. Accordingly, we have concerns about the validity of the articles’ conclusions, which we believe are insufficiently justified. The following communication briefly describes those concerns. 1. Measurements of CO by colorimetric tubes are imprecise and may be unreliable. The historical reconstruction relied on CO data obtained in the DEMS survey, a 1994 Feasibility study, and a compilation of MSHA data from 1976 to 2001 (MIDAS). In the DEMS and Feasibility studies, CO measurements were obtained using long-term (i.e. 8 h) colorimetric tubes. The MIDAS surveys used short-term colorimetric tubes (i.e. 5–15 min) or gas chromatography, but the numbers determined by each of those methods were not described. The precision of CO colorimetric tubes is limited, especially at low exposure levels. Prior to the NIOSH certification program, colorimetric and length-ofstain detector tubes were considered ‘inaccurate’ (Perkins, 1997). Early studies reported that over the range from 25 to 100 p.p.m., all commercially available CO detector tubes were worse than –25% of the true value, while only some brands yielded results within –50% of the true value (Morgenstern et al., 1970). CO tubes are currently required to yield results –35% the true value at 12.5 p.p.m., but precision and accuracy decline as concentrations approach the limit of their recommend use ( 5 p.p.m.). Because of imprecision, inaccuracy, and observer variability, historical and current authorities agree that CO colorimetric tubes should only be used to detect the presence of CO and for range finding purposes, not for quantitative measurements (WHO, 1976; Stern and Mansdorf, 1999; Todd, 2003) and that after CO detection ‘a more accurate . . . method’ should be used (Lodge, 1988). In 1976, the year MIDAS surveys began, WHO recommended that detector tubes only be used ‘for estimating the concentration of CO at concentrations above 5 mg/ m, (i.e. 4.35 p.p.m.) (WHO, 1976). Accordingly, it is notable that the great majority of CO measurements in the DEMS reports were below 4.35 p.p.m.. We are also concerned by a table footnote indicating that some CO values were ‘corrected for measurement technique (detector tube versus bistable)’, but the reports described neither the method for and effects of such ‘correction’, nor the number of samples so ‘corrected’. Thus, the CO measurements are subject to still further uncertainty. 2. The majority of CO measurements were below the recommended range for use of colorimetric tubes. The reports do not describe the actual CO measurements across the seven mines, but summary statistics were provided for samples obtained at the underground production face. Across the seven mines in the DEMS survey, the geometric means of CO samples ranged from 0.8 to 4.5 p.p.m.. Among historical production face CO measurements, the geometric means across all mines grouped by decade ‘typically’ ranged from 1 to 3 p.p.m..

Particle Size Distribution and Particle Size-Related Crystalline Silica Content in Granite Quarry Dust

Previous studies indicate that the relationship between empirically derived particle counts, particle mass determinations, and particle size-related silica content are not constant within mines or across mine work tasks. To better understand the variability of particle size distributions and variations in silica content by particle size in a granite quarry, exposure surveys were conducted with side-by-side arrays of four closed face cassettes, four cyclones, four personal environmental monitors, and a real-time particle counter. In general, the proportion of silica increased as collected particulate size increased, but samples varied in an inconstant way. Significant differences in particle size distributions were seen depending on the extent of ventilation and the nature and activity of work performed. Such variability raises concerns about the adequacy of silica exposure assessments based on only limited numbers of samples or short-term samples.

HORMESIS: IMPLICATIONS FOR CANCER RISK ASSESSMENT

Current guidelines for cancer risk assessment emphasize a toxicants “mode of action”, rather than its empirically derived dose-response relationship, for determining whether linear low-dose extrapolation is appropriate. Thus, for reasons of policy, demonstration of hormesis is generally insufficient to justify a non-linear approach, although it may provide important insights into the actions of toxicants. We evaluated dose-response characteristics of four carcinogens reported to have hormetic dose-response curves: cadmium chloride; ionizing radiation; PAHs; and, 2,3,7,8-TCDD. For each, the study that documented hormesis in one organ also provided evidence of non-hormetic dose-responses in other organs or non-hormetic responses for seemingly similar carcinogens in the same species and organs. Such inconsistency suggests toxicologic reasons that the finding of hormesis alone is not sufficient to justify use of non-linear low-dose extrapolations. Moreover, available data in those examples are not sufficient to know whether hormesis is a property of the toxicants, the target organ, or the exposed species. From the perspectives of cancer risk assessment, the greatest informational value of hormesis may be that it provokes mechanistic studies intended to explain why hormesis occurs.

Studies of Self-Pollution in Diesel School Buses: Methodological Issues

Considerable interest has focused on levels of exhaust emissions in the cabins of diesel-powered school buses and their possible adverse health effects. Significantly different policy and engineering issues would be raised if compelling evidence found that in-c-cabin contamination was due to self-pollution from bus emissions, rather than ambient pollution, neighboring vehicles, and/or re-entrained road dust. We identified 19 reports from 11 studies that measured diesel exhaust particulate in the cabins of 58 school bus of various type. Studies were evaluated in light of their experimental design, their data quality, and their capacity to quantify self-pollution. Only one study had a true experimental design, comparing the same buses with and without emission controls, while four others used intentional tracers to quantify tailpipe and/or crankcase emissions. Although definitive data are still lacking, these studies suggest that currently available control technologies can nearly eliminate particulate self-pollution inside diesel school buses.

Observations on the suitability of the aethalometer for vehicular and workplace monitoring.

Abstract A field study was undertaken to evaluate the suitability of the aethalometer, an instrument capable of performing near-real-time measurement of low-level (10–1000 ng/m3) airborne combustion products, for vehicular and workplace monitoring. Several technical limitations were identified: (1) there was no ready means for external calibration of optical measurements; (2) airflow rates were unstable; (3) effective range of concentrations was limited; and (4) the aethalometer demonstrated sensitivity to movement and vibration. Unless addressed, these limitations will restrict future uses of the aethalometer for vehicular and workplace monitoring.

How clean is "clean"? Regulations and standards for workplace clothing and personal protective equipment.

Objective: To compile current regulations and advisory recommendations on cleanliness of worker clothing and personal protective equipment and to evaluate the adequacy of criteria for determining whether cleanliness has been achieved. Methods: Systematic review of information provided by federal agencies (eg, OSHA, MSHA, and NIOSH), nongovernmental advisory bodies (eg, ACGIH, AIHA, and ANSI), and manufacturers of protective clothing and equipment. Results: We identified an array of terms describing “cleanliness” and the processes for achieving “cleanliness” that were almost never defined in regulations and recommendations. We also found a general lack of criteria for determining whether cleanliness and/or sterility have been achieved. Conclusions: There is need to harmonize cleanliness-related terminology, establish best practices for equipment cleaning and sterilization, implement a signage systems to provide equipment-specific cleaning instructions, and adopt objective criteria for determining what is “clean.”