The Global Landscape of Occupational Exposure Limits--Implementation of Harmonization Principles to Guide Limit Selection.

Occupational exposure limits (OELs) serve as health-based benchmarks against which measured or estimated workplace exposures can be compared. In the years since the introduction of OELs to public health practice, both developed and developing countries have established processes for deriving, setting, and using OELs to protect workers exposed to hazardous chemicals. These processes vary widely, however, and have thus resulted in a confusing international landscape for identifying and applying such limits in workplaces. The occupational hygienist will encounter significant overlap in coverage among organizations for many chemicals, while other important chemicals have OELs developed by few, if any, organizations. Where multiple organizations have published an OEL, the derived value often varies considerably-reflecting differences in both risk policy and risk assessment methodology as well as access to available pertinent data. This article explores the underlying reasons for variability in OELs, and recommends the harmonization of risk-based methods used by OEL-deriving organizations. A framework is also proposed for the identification and systematic evaluation of OEL resources, which occupational hygienists can use to support risk characterization and risk management decisions in situations where multiple potentially relevant OELs exist.

Ambient particulate matter, C-reactive protein, and coronary artery disease.

This article is a review of the scientific literature with respect to fine particulate matter (PM), 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, and coronary artery disease (CAD). The association between air pollution and respiratory diseases has been extensively investigated for decades; however, the role of air pollution in exacerbating heart disease has only recently become a focus of attention. It has been shown that for every 10-microg/m(3) increase in fine PM in the air, there appears to be a 2.1% increase in the number of deaths related to ischemic heart disease. PM has been linked to increased levels of systemic inflammation biomarkers such as C-reactive proteins (CRP). Daily variation of ambient pollution is correlated with rises and falls in CRP levels. Increased CRP levels have been associated with increased morbidity and mortality in individuals with CAD. Seventy-five percent of patients with elevated CRP levels have reportedly experienced a major cardiac event despite low-density lipoproteins (LDL) levels that were below the threshold recommended for pharmacological intervention. HMG CoA reductase inhibitors (statins) have been shown to cause a reduction in coronary events by lowering LDL levels. However, recently it has been shown that statins have the effect of lowering CRP levels. This may explain why individuals with normal lipid levels may benefit from statin therapy. Ambient PM exposure levels and its effects on CRP are risk factors associated with coronary events and should be considered as a target for the treatment of CAD.

Identification and screening evaluation of key historical materials and emission sources at the Oak Ridge Reservation.

In 1991, the State of Tennessee initiated a Health Studies Agreement with the U.S. Department of Energy. It included independent studies of possible adverse health effects in people living near the Oak Ridge Reservation resulting from releases of chemicals and radionuclides since 1942. A Dose Reconstruction Feasibility, the first of a planned sequence of initiatives to evaluate the potential for health effects, included application of screening methods to focus subsequent dose reconstruction and epidemiologic efforts on the materials and emission sources that have historically been most important. The feasibility study produced a history of operations that likely generated off-site releases from the X-10, K-25, Y-12, and S-50 plants, based on reviews of classified and unclassified records and interviews of active and retired workers. The availability of environmental monitoring and research data that would support dose reconstruction was also characterized. Quantitative emission and environmental contamination data were used to identify those materials and plant activities that should receive the highest priority in further health studies. Plausible exposure pathways were identified, and screening methods were used to identify the most important pathways and past activities that appear to be associated with the greatest health hazards. The materials and activities shown to have the highest potential for public health hazards are as follows: 1) The release of radioiodine [likely over 3.7 PBq (100,000 Ci)] to the air from radioactive lanthanum ("RaLa") processing at X-10 (now Oak Ridge National Laboratory) from 1944 through 1956; 2) The release of 137Cs and other radionuclides in liquid wastes from chemical separation activities at X-10; 3) The release of mercury to the air, soil, and surface waters from Y-12 lithium enrichment operations between 1950 and 1963. About 11,000,000 kg of mercury were handled at Y-12, and 910,000 kg were reported lost or unaccounted for; and 4) The release of polychlorinated biphenyls (PCBs) from machining oils, electrical equipment, and other sources in the Oak Ridge area. Based on the findings of the study, the Oak Ridge Health Agreement Steering Panel called for a dose reconstruction for radioiodine, mercury, PCBs, and radionuclides released from White Oak Creek and research into opportunities for analytic epidemiologic studies to identify adverse health effects in exposed populations.

Past radionuclide releases from routine operations at Rocky Flats.

The Colorado Department of Public Health and Environment sponsored a study to reconstruct contaminant doses to the public from operations at the Rocky Flats nuclear weapons facility. This analysis of routine releases of plutonium and uranium, the principal radioactive materials used at the plant, was part of the Colorado Department of Public Health and Environment study. Historical radionuclide monitoring and data handling practices are characterized and uncertainties are quantified. Estimates of the annual release of plutonium and uranium are provided for the period from 1953 to 1989. Off-site airborne concentrations and deposition of plutonium and uranium associated with the releases are estimated, along with the highest doses for off-site populations. The predicted effective doses from the routine release of plutonium and uranium from Rocky Flats for a person residing near the plant boundary between 1953 and 1989 are very small.

Plutonium releases from the 1957 fire at Rocky Flats.

The Colorado Department of Public Health and Environment sponsored a study to reconstruct contaminant doses to the public from the Rocky Flats nuclear weapons plant. This analysis of the September 1957 fire in a plutonium fabrication building that breached the building air filtration system is part of the Colorado Department of Public Health and Environment study. The plutonium release from this fire is estimated using environmental data collected around the time of the fire and an air dispersion model. The approximate upper bound on the total plutonium release from the fire is 1.9 GBq (0.05 Ci), with an uncertainty of about two orders of magnitude. Off-site air concentrations and deposition of plutonium resulting from the approximate upper-bound release are estimated. The highest predicted off-site effective dose resulting from the approximate upper-bound release is about 13 microSv (1.3 mrem).

Plutonium release from the 903 pad at Rocky Flats.

The Colorado Department of Public Health and Environment (CDH) sponsored a study to reconstruct contaminant doses to the public from operations at the Rocky Flats nuclear weapons plant. This analysis of the accidental release of plutonium from the area known as the 903 Pad is part of the CDH study. In the 1950's and 1960's, 55-gallon drums of waste oil contaminated with plutonium, and uranium were stored outdoors at the 903 Pad. The drums corroded, leaking contaminated oil onto soil subsequently carried off-site by the wind. The plutonium release is estimated using environmental data from the 1960's and 1970's and an atmospheric transport model for fugitive dust. The best estimate of total plutonium release to areas beyond plant-owned property is about 0.26 TBq (7 Ci). Off-site airborne concentrations and deposition of plutonium are estimated for dose calculation purposes. The best estimate of the highest predicted off-site effective dose is approximately 72 microSv (7.2 mrem).

Field evaluation of a sampling and analytical method for environmental levels of airborne hexavalent chromium.

Hexavalent chromium, Cr(VI), has been classified as a human respiratory carcinogen. Airborne Cr(VI) emissions are associated with a number of industrial sources including metal plating, tanning, chromite ore processing, and spray painting operations; combustion sources such as automobiles and incinerators; and fugitive dusts from contaminated soil. There has been considerable interest within industry and the regulatory community to assess the potential cancer risks of workers exposed to Cr(VI) at levels substantially below the threshold limit value (TLV) of 50 micrograms/m3. To date, only the workplace sampling and analytical method (National Institute for Occupational Safety and Health [NIOSH] Method 7600) has been validated for measuring airborne Cr(VI), and it can accurately measure concentrations only as low as 500 ng/m3. This paper describes the field evaluation of a sampling and analytical method for the quantitation of airborne Cr(VI) at concentrations 5000 times lower than the current standard method (as low as 0.1 ng/m3). The collection method uses three 500-mL Greenberg-Smith impingers in series, operated at 15 Lpm for 24 hr. All three impingers are filled with 200 mL of a slightly alkaline (pH approximately 8) sodium bicarbonate buffer solution. The results of validation tests showed that both Cr(VI) and trivalent chromium, Cr(III), were stable in the collection medium and that samples may be stored for up to 100 days without appreciable loss of Cr(VI). Method precision based on the pooled coefficient of variation for replicate samples was 10.4%, and method accuracy based on the mean percent recovery of spiked samples was 94%. Both the precision and accuracy of the impinger method were within NIOSH criteria. This method could be used to measure ambient concentrations of Cr(VI) in the workplace caused by fugitive emissions from manufacturing processes or chromium-contaminated soils at workplace concentrations well below the current TLV (50 micrograms/m3) or permissible exposure limit (100 micrograms/m3).

The current practice of health risk assessment: potential impact on standards for toxic air contaminants.

Since the Bhopal incident, the public has placed pressure on regulatory agencies to set community exposure limits for the dozens of chemicals that may be released by manufacturing facilities. More or less objective limits can be established for the vast majority of these chemicals through the use of risk assessment. However, each step of the risk assessment process (i.e., hazard identification, dose-response assessment, exposure assessment, and risk characterization) contains a number of pitfalls that scientists need to avoid to ensure that valid limits are established. For example, in the hazard identification step there has been little discrimination among animal carcinogens with respect to mechanism of action or the epidemiology experience. In the dose-response portion, rarely is the range of "plausible" estimated risks presented. Physiologically based pharmacokinetic (PB-PK) models should be used to understand the difference between the tissue doses and the administered dose, as well as the difference in target tissue concentrations of the toxicant between rodents and humans. Biologically-based models like the Moolgavkar-Knudson-Venzon (MKV) should be developed and used, when appropriate. The exposure assessment step can be significantly improved by using more sensitive and specific sampling and analytical methods, more accurate exposure parameters, and computer models that can account for complex environmental factors. Whenever possible, model predictions of exposure and uptake should be validated by biological monitoring of exposed persons (urine, blood, adipose) or by field measurements of plants, soil, fish, air, or water. In each portion of an assessment, the weight of evidence approach should be used to identify the most defensible value. In the risk characterization, the best estimate of the potential risk as well as the highest plausible risk should be presented. Future assessments would be much improved if quantitative uncertainty analyses were conducted. Procedures are currently available for making future assessments. By correcting some of these shortcomings in how health risk assessments have been conducted, scientists and risk managers should be better able to identify scientifically appropriate ambient air standards and emission limits.