Biomedical subjects

Pamela R D Williams

Publications and source records attributed to Pamela R D Williams.

9 recordsLinked to original sources

PubMed2006

VCCEP pilot: progress on evaluating children's risks and data needs.

The Voluntary Children's Chemical Evaluation Program (VCCEP) is designed to provide information to the public on children's potential health risks associated with chemical exposures. The key question of the VCCEP is whether the potential hazards, exposures, and risks to children have been adequately characterized, and, if not, what additional data are necessary. To answer this question, manufacturers or importers of 23 chemicals were asked by the U. S. Environmental Protection Agency (U.S. EPA) to sponsor their chemicals in the first tier of a pilot program. These chemicals were selected for evaluation because they have been found as contaminants in human tissue or fluids (adipose tissue, blood, breath, breast milk, or urine); food and water children may eat and drink; or air children may breathe (including residential or school air). Under the VCCEP framework, sponsoring companies agree to prepare Tier 1 hazard, exposure, and risk assessments on the individual chemicals, and identify the need for additional data. These assessment documents are submitted to the U.S. EPA and subsequently undergo review by experts in an independent peer consultation meeting that is open to the public. Following this peer consultation process, the U.S. EPA reviews each submission and makes a data-needs determination, which may include requesting further data collection or generation by the sponsor. Sponsoring companies then decide whether to volunteer for the next tier and collect or generate the requested data. The purpose of this article is to describe the VCCEP process and to review and present the key findings from the first set of chemicals that have been fully or partially evaluated under the pilot program (vinylidene chloride, decabromodiphenyl ether, pentabromodiphenyl ether, octabromodiphenyl ether, acetone, methyl ethyl ketone, decane, undecane, and dodecane). Specifically, we provide a brief summary of the sponsors' submissions, the peer consultation panels' discussions, and the U.S. EPA's data-needs decisions. Although we do not attempt to conduct independent analyses of the underlying data, we do identify a number of common themes that have emerged during implementation of the pilot program and discuss several key issues that could become important in the future. The information presented here should be useful for various parties interested in the progress of the VCCEP and the results of the initial (Tier 1) children's assessments.

Acetone↗

PubMed2005

Benzene exposures associated with tasks performed on marine vessels (circa 1975 to 2000).

In this article, we assemble and synthesize the available industrial hygiene data that describe exposure during the marine transport of benzene-containing products in the United States and abroad. A total of 25 studies were identified and summarized. The measured airborne concentrations of benzene on marine vessels were found to vary depending on several key factors, including the job task, vessel characteristics, cargo type, and sample type and duration. Despite the differences in sampling strategies and benzene content of the liquids being transported, personal time-weighted-average benzene air concentrations typically ranged from 0.2-2.0 ppm during closed loading and 2-10 ppm during open loading operations. Benzene exposures during these activities are likely due to specific short-term tasks, such as connecting and disconnecting hoses and tank gauging and sampling. Similar concentrations of benzene have been reported in the pump room during marine loading operations and during tank cleaning activities in various settings. When compared with contemporaneous occupational health standards, our review indicates that most activities performed on marine vessels from the 1970s to 1990s usually did not result in benzene exposures that exceeded these standards. The information and data presented here may be useful for quantitatively estimating or reconstructing historical exposures during the marine transport of benzene-containing cargo if details about individual's work histories in the maritime industry are available.

Air Pollutants, Occupational↗

PubMed2005

Characterizing historical industrial hygiene data: a case study involving benzene exposures at a chemical manufacturing facility (1976-1987).

This article describes how nearly 3700 air samples of benzene collected in a typical chemical manufacturing (acetic acid) facility in the United States from 1976 to 1987 were used to characterize daily time-weighted average (TWA) exposure levels. We found that those workers directly involved in manufacturing operations had likely TWA exposures to benzene of about 2.0 ppm from 1976-1981 and about 1.0 ppm from 1982-1987. These results are consistent with the improved industrial hygiene programs at chemical facilities, which often occurred following the adoption of stricter occupational exposure limits. Additionally, about 97% of all personal TWA samples had reported benzene concentrations less than 10 ppm, which was the permissible exposure limit in place prior to 1987. Because one of the primary objectives of historical workplace air sampling efforts was to understand the source of release of contaminants, a large number of short-term (typically about 1 min) area samples were also collected. Although these types of samples are often not useful for predicting human exposure without time-motion information, airborne benzene concentrations were about five- to tenfold higher for many of the short-term area samples than for the personal TWA measurements. The methodology presented here should be useful for evaluating industrial hygiene data collected after the early 1970s (after the promulgation of OSHA), and our findings support prior reports that large corporations in the United States have tended to reduce workplace exposures to airborne contaminants consistent with historical changes in occupational exposure limits.

Air Pollution, Indoor↗

PubMed2004

Health risk communication using comparative risk analyses.

The ability to communicate effectively the degree or magnitude of public exposures or health risks is essential for risk assessors and risk managers. Various guidelines exist for communicating environmental and public health risks, including recommended approaches for putting risk data into proper context. Although it remains unclear as to which approach is the most useful or appropriate under different circumstances, risk comparisons are a popular choice for conveying the significance of or providing a better perspective on a particular chemical exposure or health risk. In this paper, several different types of risk comparisons are described that are frequently used in the private and public sectors, and these are illustrated using a variety of examples from the literature. These approaches include: (1) intrachemical comparisons, (2) interchemical comparisons, (3) comparisons to background levels of risk, (4) comparisons to theoretical risks or safety levels, and (5) comparisons to other actions or activities. The primary purpose of this paper is to summarize and briefly discuss the advantages and limitations of these risk communication approaches. The evolving field of risk communication is also discussed, including ongoing research on public risk perceptions and alternative methods for communicating risk magnitudes and data uncertainties.

Communication↗

PubMed2004

The risk of MTBE relative to other VOCs in public drinking water in California.

Ongoing publicity about methyl tertiary butyl ether (MTBE) suggests that this chemical is of greater concern than other contaminants commonly found in drinking water. The purpose of this article is to evaluate the available MTBE data in context with other volatile organic compounds (VOCs) that are detected in public drinking water sources in California. We find that of the 28 VOCs with a primary maximum contaminant level (MCL) in California, 21 were found in 50 or more drinking water sources from 1985 to 2002. Over the last 10 years, the most frequently detected VOCs were chloroform, tetrachloroethylene (PCE), and trichloroethylene (TCE), which were found in about 9-15% of all sampled drinking water sources. These same chemicals were found to have the highest mean detected concentrations over the last 5 years, ranging from 13 to 15 microg/L. Many VOCs were also found to routinely exceed state and federal drinking water standards, including benzene and carbon tetrachloride. By comparison, MTBE was found in approximately 1% of sampled drinking water sources for most years, and of those drinking water sources found to contain MTBE from 1998 to 2002, over 90% had detected concentrations below California's primary MCL of 13 microg/L. Relative to the other VOCs evaluated, MTBE has the lowest estimated California cancer potency value, and was found to pose one of the least cancer risks from household exposures to contaminated drinking water. These findings suggest that MTBE poses an insignificant threat to public drinking water supplies and public health in California, particularly when compared to other common drinking water contaminants.

California↗

PubMed2003

Reconstruction of benzene exposure for the Pliofilm cohort (1936-1976) using Monte Carlo techniques.

The current cancer slope factor and occupational standards for benzene are based primarily on studies of the rubber hydrochloride (Pliofilm) workers. Previous assessments of this cohort by Rinsky et al. (1981, 1987), Crump and Allen (1984), and Paustenbach et al. (1992) relied on different assumptions about the available industrial hygiene data and workplace practices and processes over time, thereby yielding significantly different estimates of annual benzene exposures for many jobs. Given the inherent limitations and uncertainties involved in estimating historical exposures for this cohort, a probabilistic approach was used to better characterize their likely degree of benzene exposure. Ambient air exposures to benzene were based, in part, on the distribution of air sampling data collected at the Pliofilm facilities and assumptions about how workplace concentrations probably decreased over time as the threshold limit value (TLV) was lowered. The likely uptake of benzene from dermal exposures was estimated based on probability distributions for several exposure factors, including surface area, contact rate and duration, and skin absorption. The assessment also quantitatively accounts for improved engineering controls, extended work hours, incomplete Pliofilm production, and the use and effectiveness of respirators over time. All original data and assumptions are presented in this assessment, as is all new information obtained through additional interviews of former workers. Estimated benzene exposures at the 50th and 95th percentiles are reported as equivalent 8-h time-weighted average (TWA) airborne concentrations for 13 job categories from 1936 to 1965 (Akron I and II facilities) and 1939 to 1976 (St. Mary's facility). Data indicate that estimated equivalent airborne benzene concentrations for St. Mary's workers were highest for four job categories (Neutralizer, Quencher, Knifeman, Spreader), typically ranging from about 50 to 90 ppm during 1939-1946 (lower during 1942-1945), and 10 to 40 ppm during 1947-1976 at the 50th percentile. These estimates are 2-3 times greater than for other jobs in the Pliofilm process, and about 1.5 times less than those estimated at the 95th percentile. Estimates of equivalent airborne benzene concentrations for Akron I and II were about 1.5 times higher than for St. Mary's, but there is less confidence in these estimates, given the lack of industrial hygiene monitoring data for these facilities. Study results suggest that Paustenbach et al. (1992) generally over-estimated exposures for those job categories that had the highest exposure by about a factor of two to four. On the other hand, it was concluded that Rinsky et al. (1981, 1987) under-predicted benzene exposures for most jobs, and Crump and Allen (1984) both under- and overpredicted benzene exposures, depending on the specific job category and time period. The new estimates presented in this analysis incorporate what is considered to be the most likely range of plausible exposure values, and, accordingly, provide a better characterization of the potential workplace exposures for this cohort. These data could be combined with current or future mortality information to calculate a new cancer potency factor or occupational health standard for benzene.

Adult↗

PubMed2003

Data available for evaluating the risks and benefits of MTBE and ethanol as alternative fuel oxygenates.

The wide-scale use of methyl tertiary butyl ether (MTBE) in gasoline has resulted in substantial public controversy and action to ban or control its use due to perceived impacts on water quality. Because oxygenates are still required under federal law, considerable research has focused on ethanol as a substitute for MTBE. In this article, we summarize the currently available literature on the air and water quality risks and benefits of MTBE versus ethanol as alternative fuel oxygenates. We find that MTBE-fuel blends are likely to have substantial air quality benefits; ethanol-fuel blends appear to offer similar benefits, but these may be at least partially negated because of ethanol's propensity to increase emissions and ambient concentrations of some air contaminants. Releases of gasoline containing either MTBE or ethanol could have an impact on some drinking water sources, although the impacts associated with MTBE tend to relate to aesthetics (i.e., taste and odor), whereas the impacts associated with ethanol generally relate to health risk (i.e., greater exposure to gasoline constituents such as benzene). It is likely that these water quality impacts will be outweighed by the air quality benefits associated with MTBE and perhaps ethanol use, which affect a much larger population. A lack of data on environmental exposures and associated health impacts hinders the completion of a comprehensive quantitative risk-benefit analysis, and the available air and water quality data should be evaluated in a broader risk-management context, which considers the potential life-cycle impacts, costs, and feasibility associated with alternative fuel oxygenates.

Air Pollution↗

PubMed2003

Evaluation of mercury in urine as an indicator of exposure to low levels of mercury vapor.

We conducted a pooled analysis to investigate the relationship between exposure to elemental mercury in air and resulting urinary mercury levels, specifically at lower air levels relevant for environmental exposures and public health goals (i.e., < 50 microg/m3 down to 1.0 microg/m3). Ten studies reporting paired air and urine mercury data (149 samples total) met criteria for data quality and sufficiency. The log-transformed data set showed a strong correlation between mercury in air and in urine (r = 0.774), although the relationship was best fit by a series of parallel lines with different intercepts for each study R2 = 0.807). Predicted ratios of air to urine mercury levels at 50 microg/m3 air concentration ranged from 1:1 to 1:3, based on the regression line for the studies. Toward the lower end of the data set (i.e., 10 microg/m3), predicted urinary mercury levels encompassed two distinct ranges: values on the order of 20 microg/L and 30-60 microg/L. Extrapolation to 1 microg/m3 resulted in predicted urinary levels of 4-5 and 6-13 microg/L. Higher predicted levels were associated with use of static area air samplers by some studies rather than more accurate personal air samplers. Urinary mercury predictions based primarily on personal air samplers at 1 and 10 microg/m3 are consistent with reported mean (4 microg/L) and upper-bound (20 microg/L) background levels, respectively. Thus, although mercury levels in air and urine are correlated below 50 microg/m3, the impact of airborne mercury levels below 10 microg/m3 is likely to be indistinguishable from background urinary mercury levels.

Biomarkers↗

PubMedDate not supplied

Risk characterization: principles and practice.

In the field of risk assessment, characterizing the nature and magnitude of human health or environmental risks is arguably the most important step in the analytical process. In this step, data on the dose-response relationship of an agent are integrated with estimates of the degree of exposure in a population to characterize the likelihood and severity of risk. Although the purpose of risk characterizations is to make sense of the available data and describe what they mean to a broad audience, this step is often given insufficient attention in health risk evaluations. Too often, characterizations fail to interpret or summarize risk information in a meaningful way, or they present single numerical estimates of risk without an adequate discussion of the uncertainties inherent in key exposure parameters or the dose-response assessment, model assumptions, or analytical limitations. Consequently, many users of risk information have misinterpreted the findings of a risk assessment or have false impressions about the degree of accuracy (or the confidence of the scientist) in reported risk estimates. In this article we collected and integrated the published literature on conducting and reporting risk characterizations to provide a broad, yet comprehensive, analysis of the risk characterization process as practiced in the United States and some other countries. Specifically, the following eight topics are addressed: (1) objective of risk characterization, (2) guidance documents on risk characterization, (3) key components of risk characterizations, (4) toxicity criteria for evaluating health risks, (5) descriptors used to characterize health risks, (6) methods for quantifying human health risks, (7) key uncertainties in risk characterizations, and (8) the risk decision-making process. A brief discussion is also provided on international aspects of risk characterization. A number of examples are presented that illustrate key concepts, and citations are provided for approximately 100 of the most relevant papers.

Animals↗