Biomedical subjects

D E Burmaster

Publications and source records attributed to D E Burmaster.

At least 19 recordsLinked to original sources

PubMed2000

Distributions of total job tenure for men and women in selected industries and occupations in the United States, February 1996.

This article develops and fits probability distributions for the variability in projected (total) job tenure for adult men and women in 31 industries and 22 occupations based on data reported by the U.S. Department of Labor's Bureau of Labor Statistics. It extends previously published results and updates those results from January 1987 to February 1996. The model provides probability distributions for the variability in projected (total) job tenures within the time range of the data, and it extrapolates the distributions beyond the time range of the data, i.e., beyond 25 years.

Adolescent↗

PubMed2000

Fitting second-order finite mixture models to data with many censored values using maximum likelihood estimation.

Finite mixture models, that is, weighted averages of parametric distributions, provide a powerful way to extend parametric families of distributions to fit data sets not adequately fit by a single parametric distribution. First-order finite mixture models have been widely used in the physical, chemical, biological, and social sciences for over 100 years. Using maximum likelihood estimation, we demonstrate how a first-order finite mixture model can represent the large variability in data collected by the U.S. Environmental Protection Agency for the concentration of Radon 222 in drinking water supplied from ground water, even when 28% of the data fall at or below the minimum reporting level. Extending the use of maximum likelihood, we also illustrate how a second-order finite mixture model can separate and represent both the variability and the uncertainty in the data set.

Algorithms↗

PubMed1999

Human interindividual variability in parameters related to health risks.

This paper reviews existing data on the variability in parameters relevant for health risk analyses. We cover both exposure-related parameters and parameters related to individual susceptibility to toxicity. The toxicity/susceptibility data base under construction is part of a longer term research effort to lay the groundwork for quantitative distributional analyses of non-cancer toxic risks. These data are broken down into a variety of parameter types that encompass different portions of the pathway from external exposure to the production of biological responses. The discrete steps in this pathway, as we now conceive them, are: Contact Rate (Breathing rates per body weight; fish consumption per body weight) Uptake or Absorption as a Fraction of Intake or Contact Rate General Systemic Availability Net of First Pass Elimination and Dilution via Distribution Volume (e.g., initial blood concentration per mg/kg of uptake) Systemic Elimination (half life or clearance) Active Site Concentration per Systemic Blood or Plasma Concentration Physiological Parameter Change per Active Site Concentration (expressed as the dose required to make a given percentage change in different people, or the dose required to achieve some proportion of an individual's maximum response to the drug or toxicant) Functional Reserve Capacity-Change in Baseline Physiological Parameter Needed to Produce a Biological Response or Pass a Criterion of Abnormal Function Comparison of the amounts of variability observed for the different parameter types suggests that appreciable variability is associated with the final step in the process-differences among people in "functional reserve capacity." This has the implication that relevant information for estimating effective toxic susceptibility distributions may be gleaned by direct studies of the population distributions of key physiological parameters in people that are not exposed to the environmental and occupational toxicants that are thought to perturb those parameters. This is illustrated with some recent observations of the population distributions of Low Density Lipoprotein Cholesterol from the second and third National Health and Nutrition Examination Surveys.

Analysis of Variance↗

PubMed1998

A trivariate distribution for the height, weight, and fat of adult men.

Using exploratory data analysis, probability plots, scatterplots, and computer animations to rotate and visualize the data, we fit a trivariate Normal distribution to data for the height, the natural logarithm of body weight, and the body fat for 646 men between the ages of 50 and 80 years as reported by the medical staff of the U.S. Veterans Administration's "Normative Aging Study" in Boston, MA. Although these data do not include any children, women, or young men, the measurements represent the best data that we could find through a 4-year search. We believe that these data are well measured and reliable for men in the specified age range and that these data reveal an interesting statistical pattern for use in probabilistic PBPK models.

Adipose Tissue↗

PubMed1998

Lognormal distributions for skin area as a function of body weight.

This paper reanalyzes the dataset cited by the U.S. Environmental Protection Agency in its Exposure Factors Handbook that contains measurements of skin area, height, and body weight for 401 people spanning all stages of development. The reanalysis shows that a univariate model for total skin area as a function of body weight gives useful and practical results with little or no loss of reliability as compared to the Agency's bivariate model. This new result leads to a new method to develop Lognormal distributions for total skin area as a function of body weight alone.

Body Surface Area↗

PubMed1998

Lognormal distributions for total water intake and tap water intake by pregnant and lactating women in the United States.

Using probability plots and Maximum Likelihood Estimation (MLE), we fit lognormal distributions to data compiled by Ershow et al. for daily intake of total water and tap water by three groups of women (controls, pregnant, and lactating; all between 15-49 years of age) in the United States. We also develop bivariate lognormal distributions for the joint distribution of water ingestion and body weight for these three groups. Overall, we recommend the marginal distributions for water intake as fit by MLE for use in human health risk assessments.

Adolescent↗

PubMed1997

Lognormal distributions for body weight as a function of age for males and females in the United States, 1976-1980.

Based on results reported from the NHANES II Survey (the National Health and Nutrition Examination Survey II) for people living in the United States during 1976-1980, we use exploratory data analysis, probability plots, and the method of maximum likelihood to fit lognormal distributions to percentiles of body weight for males and females as a function of age from 6 months through 74 years. The results are immediately useful in probabilistic (and deterministic) risk assessments.

Adolescent↗

PubMed1996

Methodology to estimate the amount and particle size of soil ingested by children: implications for exposure assessment at waste sites.

Despite considerable efforts to improve the design of soil ingestion studies, substantial variability in daily soil ingestion rates based on different tracer estimates exists in the same subjects. The present study assessed the hypothesis that one of the unexplored causes of this intertracer variation in soil ingestion estimation was related to differences in soil tracer concentration by particle size. The study analyzed the tracer concentration in soil for children in the Anaconda, Montana soil ingestion study for the particle size fraction less than 250 microm [corrected] in diameter. Soil ingestion estimates for these children were recalculated based on the new soil concentration values and compared to previous findings (E. J. Calabrese, E. J. Stanek, P. Pekow, and R. M. Barnes, submitted, 1996) when the soil concentrations were determined for soil particle size diameter of <2 mm. The results indicated that five tracers (Al, Si, Ti, Y, and Zr) did not have their soil concentrations changed by particle size. However, for three tracers (La, Ce, and Nd) the concentration increased by two- to fourfold with the smaller particle size. Recalculation of soil ingestion estimates indicates that the soil ingestion estimates of the five tracers not varying by particle size did not change while those of the remaining three tracers were decreased by approximately 60%. The revised calculations provide a substantial improvement in intertracer estimates of soil ingestion and suggest that the children ingested soil of small particle size. These findings are of significance since they (1) identify an important potential cause of intertracer variability in soil ingestion estimates, (2) establish a new criterion for soil tracer selection, and (3) develop a method for not only providing improved soil ingestion estimates but also determining the particle size of the ingested soil. These findings offer important potential applications for risk assessment practices at contaminated sites since soil ingestion is frequently the dominant route of estimated contaminant exposure in children.

Child↗

PubMed1994

Principles of good practice for the use of Monte Carlo techniques in human health and ecological risk assessments.

We propose 14 principles of good practice to assist people in performing and reviewing probabilistic or Monte Carlo risk assessments, especially in the context of the federal and state statutes concerning chemicals in the environment. Monte Carlo risk assessments for hazardous waste sites that follow these principles will be easier to understand, will explicitly distinguish assumptions from data, and will consider and quantify effects that could otherwise lead to misinterpretation of the results. The proposed principles are neither mutually exclusive nor collectively exhaustive. We think and hope that these principles will evolve as new ideas arise and come into practice.

Computer Simulation↗

PubMed1992

Bivariate distributions for height and weight of men and women in the United States.

For the U.S. population, we fit bivariate distributions to estimated numbers of men and women aged 18-74 years in cells representing 1 in. intervals in height and 10 lb intervals in weight. For each sex separately, the marginal histogram of height is well fit by a normal distribution. For men and women, respectively, the marginal histogram of weight is well fit and satisfactorily fit by a lognormal distribution. For men, the bivariate histogram is satisfactorily fit by a normal distribution between the height and the natural logarithm of weight. For women, the bivariate histogram is satisfactorily fit by two superposed normal distributions between the height and the natural logarithm of weight. The resulting distributions are suitable for use in public health risk assessments.

Adolescent↗

PubMed1992

Monte Carlo techniques for quantitative uncertainty analysis in public health risk assessments.

Most public health risk assessments assume and combine a series of average, conservative, and worst-case values to derive a conservative point estimate of risk. This procedure has major limitations. This paper demonstrates a new methodology for extended uncertainty analyses in public health risk assessments using Monte Carlo techniques. The extended method begins as do some conventional methods--with the preparation of a spreadsheet to estimate exposure and risk. This method, however, continues by modeling key inputs as random variables described by probability density functions (PDFs). Overall, the technique provides a quantitative way to estimate the probability distributions for exposure and health risks within the validity of the model used. As an example, this paper presents a simplified case study for children playing in soils contaminated with benzene and benzo(a)pyrene (BaP).

Carcinogens, Environmental↗

PubMed1992

Lognormal distributions for water intake by children and adults.

We fit lognormal distributions to data collected in a national survey for both total water intake and tap water intake by children and adults for these age groups in years: 0 less than age less than 1; 1 less than or equal to age less than 11; 11 less than or equal to age less than 20; 20 less than or equal to age less than 65; 65 less than or equal to age; and all people in the survey taken as a single group. These distributions are suitable for use in public health risk assessments.

Adolescent↗

PubMed1992

A discussion of the U.S. EPA methodology for determining Water Quality Standards (WQS).

Based on material published by the U.S. Environmental Protection Agency (U.S. EPA) in the Federal Register for 19 November 1991, many state environmental agencies have proposed and/or adopted revisions to their State Water Quality Standards (WQS) for organic and inorganic chemicals in fresh and marine waters (see, for example, State of Connecticut, Department of Environmental Protection, Bureau of Water Management, (1992), memorandum to Interested Parties concerning the Water Quality Standards Hearing Report). Generally, many states simply republish the U.S. EPA's proposed Water Quality Criteria (WQC) as the State's proposed WQS. Many of the state WQS and federal WQC values--especially those for organic compounds regulated as human or animal carcinogens--are much more stringent than the values now in effect because the U.S. EPA's new methodology (i) for estimating exposure point concentrations, exposure doses, carcinogenic potency, and incremental lifetime cancer risk and (ii) for setting the target acceptable risk combine a series of conservative assumptions into an equally conservative set of results. In the Federal Register proposal, the U.S. EPA failed to honor its standard risk assessment methodology in that (i) it failed to perform a quantitative or even qualitative uncertainty analysis and (ii) it failed to analyze the overall degree of conservatism in the results. The U.S. EPA suggested that the analysis is suitably conservative for the average exposed adult, but it failed to consider various phenomena that make the proposed WQC far more conservative than acknowledged or intended. To focus on a central problem of manageable size, this article dissects the method by which the U.S. EPA calculates proposed WQC for organic chemicals regulated as human or animal carcinogens. Because the results for most such chemicals are driven by the pathway for the human ingestion of fish which have bioconcentrated the chemicals from the water column (as opposed to the pathway for direct ingestion of water by humans), this article focuses exclusively on the fish-to-human pathway. These considerations form the basis of general quality assurance criteria and standards.

Animals↗

PubMed1991

Trihalomethanes and maximum contaminant levels: the significance of inhalation and dermal exposures to chloroform in household water.

Our review of the literature on the importance of inhalation and dermal exposures to volatile organic compounds in household water relative to ingestion exposures sought to answer two questions. First, how well do the inhalation and dermal doses predicted by simple models, complex simulations, and measurements agree with one another? And second, what are the implications for the cancer risk from chloroform in household water? The literature yields a coherent and credible range of dose estimates: the ratio of lifetime inhalation dose to lifetime ingestion dose is probably in the range of approximately 0.6 to approximately 1.5, but may be as high as approximately 5.7; and the ratio of lifetime dermal dose to lifetime ingestion dose is probably about approximately 0.3, but may be as high as approximately 1.8. However, because the U.S. Environmental Protection Agency's (EPA's) Cancer Potency Factor (CPF) for inhalation of chloroform is much higher than the CPF for ingestion, the ratios of incremental lifetime cancer risk from inhalation of chloroform to risk from ingestion are much larger than the corresponding ratios for dose. The incremental lifetime cancer risk from chloroform by all three pathways is probably approximately 9 to approximately 21 times the ingestion risk and may be as much as approximately 79 times the ingestion risk. As the EPA reviews the drinking water standard for total trihalomethanes, it is essential that the Agency take account of all exposure pathways in estimating cancer risk.

Administration, Inhalation↗

PubMed1991

Parametric distributions for soil ingestion by children.

This note presents parameterized distributions of estimates of the amount of soil ingested by children based on data collected by Binder et al. (1986). Following discussions with Dr. Binder, we modified the Binder study data by using the actual stool weights instead of the 15 g value used in the original study. After testing the data for lognormality, we generated parameterized distributions for use in risk assessment uncertainty analyses such as Monte Carlo simulations.

Data Interpretation, Statistical↗

PubMed1991

Time- and loading-dependence in the McKone model for dermal uptake of organic chemicals from a soil matrix.

McKone has recently proposed an innovative two-layer model for dermal uptake of organic chemicals from a soil matrix that explicitly includes variables for properties of the chemical, the soil, the skin, and the exposure. In this note, we investigate the joint time- and loading-dependencies implicit in the model by using MATHEMATICA to find and plot a closed-form function for the uptake fraction for six aromatic hydrocarbons.

Computer Simulation↗

PubMed1991

Using Monte Carlo simulations in public health risk assessments: estimating and presenting full distributions of risk.

With desktop computers as powerful as mainframes were just a few years ago, analysts can now use commercial software to estimate full probability distributions for--not just point estimates of--health risks experienced by people chronically exposed to toxic chemicals at or near hazardous waste sites. Even though probability is the central concept in risk assessment, and even though probabilistic methods offer strong advantages and insights as compared to the "deterministic" methods now required by U.S. Environmental Protection Agency's guidance manuals, analysts have only begun to use probabilistic methods at Superfund sites. In this paper, we examine a simplified case study using Monte Carlo methods to estimate full distributions of public health risk. We demonstrate the use of "toggles" to isolate the contributions of different inputs, and we also offer new graphical methods to communicate the results to risk managers and concerned citizens.

Child↗

PubMed1991

A note: estimating exposure concentrations of lipophilic organic chemicals to humans via raw finfish fillets.

Although U.S. EPA and others recommend using bioconcentration factors (BCFs) suitable for estimating chemical concentrations in edible tissue, such BCFs are not often available. We present here several ways to estimate the ratio (R) of the concentrations of chemical partitioning to edible tissue (fillet) of finfish relative to the whole fish. While preliminary in nature, the ratio provides a better understanding of actual chemical dose to humans.

Animals↗