bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative Potency of Chemical Carcinogens in Rodents
Authors: Gaylor David W. , Chen James J.
Published: May 2006

Extensive carcinogenesis data compiled by Gold et al.(1) for 770 compounds tested in 2944 chronic bioassays in animals provided an opportunity to compare cancer rates across animal species for a wide variety of compounds administered by various routes of exposure. The comparisons in this paper are restricted to the most frequently tested species: rats, mice, and hamsters. When sufficient experimental data exist, Gold et al.1’ provide estimates of the TD50 (the chronic dose rate expressed in mg/kg body weight/day which halves the actuarially adjusted percentage of tumor‐free animals at the end of a standard lifetime experiment). Since the current practice generally is to base risk assessments upon the data set producing the highest cancer risk, the ratio of the minimum TD50's provides a measure of the relative potency between two species for each compound administered to animals by the same route. The geometric means of the ratios of minimum TD50's for rats: mice are 1/2.2 and 1/1.3 for diet and gavage, respectively. A mean ratio for rats: mice of 1/1.48 is obtained for compounds administered in the diet when the tumor site is the liver for both species. In general the minimum TD50 is lowest for the rat and highest for the hamster. Although limited data are available for inhalation studies, this route of administration resulted in the poorest agreement between rats and mice. In general, comparisons of minimum TD50's across the three rodent species are generally within a factor of 100 for a wide variety of compounds.
Errors in Estimates of Smoking‐Related Deaths Derived from Nonsmoker Mortality
Authors: Sterling Theodor D. , Weinkam James J.
Published: May 2006

A number of recent analyses have computed present and future costs associated with a risk by estimating what would happen if the risk were absent. Two sources of bias are associated with this approach: (1) differences in confounding factors between present risk avoiders and risk takers, and (2) the difficulty of selecting an unbiased sample of risk avoiders. A staff memo from the Office of Technology Assessment used this approach to estimate mortality due to smoking. Numbers of deaths and age at death distributions of U.S. smokers and nonsmokers for all causes, all cancers, lung cancers, heart disease, and cerebrovascular lesions are used to assess the accuracy of these estimates. Large errors in the OTA estimates are found. Conditions are discussed that might help reduce errors from this approach.
Uncertainty about Probability: A Decision Analysis Perspective
Authors: Howard Ronald A.
Published: May 2006

The issue of how to think about “uncertainty about probability” is framed and analyzed from the viewpoint of a decision analyst. The failure of nuclear power plants is used as an example. The key idea is to think of probability as describing a state of information on an uncertain event, and to pose the issue of uncertainty in this quantity as uncertainty about a number that would be definitive: it has the property that you would assign it as the probability if you knew it. Logical consistency requires that the probability to assign to a single occurrence in the absence of further information be the mean of the distribution of this definitive number, not the median as is sometimes suggested. Any decision that must be made without the benefit of further information must also be made using the mean of the definitive number's distribution. With this formulation, we find further that the probability of r occurrences in n exchangeable trials will depend on the first n moments of the definitive number's distribution. In making decisions, the expected value of clairvoyance on the occurrence of the event must be at least as great as that on the definitive number. If one of the events in question occurs, then the increase in probability of another such event is readily computed. This means, in terms of coin tossing, that unless one is absolutely sure of the fairness of a coin, seeing a head must increase the probability of heads, in distinction to usual thought. A numerical example for nuclear power shows that the failure of one plant of a group with a low probability of failure can significantly increase the probability that must be assigned to failure of a second plant in the group.
An ALARA Approach to the Radiological Control of Foodstuffs Following an Accidental Release
Authors: Lombard Jacques , Coulon René , Despres Alain
Published: May 2006

This article presents a methodology based on two complementary approaches, thus allowing a selection of maximal concentration in foodstuffs for determining appropriate countermeasures. The first approach is based on a minimal and maximal per capita intervention level and takes into account the annual intake of each product. The second one is based on a cost‐benefit analysis, comparing the advantages of a countermeasure concerning those products presenting a contamination higher than a given maximal concentration (in terms of reduction of cost of the detriment associated with the risk), with its drawbacks (in terms of cost of the products) in order to select the “ALARA” maximal concentration. This second approach is used as a complement to the first one. The results obtained through these two approaches are given for four products (milk, meat, fresh vegetables, and corn) and two nuclides (Cs‐137 and I‐131). These are presented for various scenarios: one or various products contaminated by one or various radionuclides. It is concluded that these two approaches are complementary, the first one being related to individual risk and the second to collective risk. Therefore, these approaches are both of interest in the context of the elaboration of modalities for the radiological control of foodstuffs following an accidental release and both methods may be useful for determining appropriate countermeasures.
A Stochastic Two‐Stage Model for Cancer Risk Assessment. II. The Number and Size of Premalignant Clones
Authors: Dewanji Anup , Venzon David J. , Moolgavkar Suresh H.
Published: May 2006

Mathematical expressions are derived, under different dosing patterns, for the number and size of premalignant clones within the framework of a two‐mutation model for carcinogenesis, which has previously been shown to be consistent with a large body of epidemiologic and experimental data.
A Health‐Based Approach for Evaluating Soil at Depth Contaminated by Hazardous Waste: Utilizing the AALsoil contact Criterion1
Authors: Reynolds Stephen D. , Hadley Paul W. , Sedman Richard M.
Published: May 2006

Contaminated soil at depth can pose a threat to public health upon excavation. Following the excavation of contaminated soils, toxicants which once resided at depth become available for exposure due to direct contact. A scenario is developed that describes the excavation and redistribution of soil to the surface. Based on typical excavations occurring in a residential setting in California, soil to a depth of 10 feet is considered available for future exposure due to direct contact. The capabilities of various earthmoving equipment were employed to establish that the average toxicant level in 12 cubic yards of soil is the appropriate measure for evaluating contaminated soil at depth. This allows the evaluation of future risk to public health due to direct contact exposures following the excavation of contaminated soils at depth.

Direct contact exposures can result if soil contamination initially at depth is excavated and distributed to the soil surface. The evaluation of future exposure to soil at depth due to direct contact should be a component of many hazardous waste site investigations.

A scenario that accounts for the excavation and redistribution of soil at depth has been established. The manner in which soil would be handled by earthmoving equipment typically employed for residential construction activities, established 12 yd3 of soil as a reasonable and appropriately conservative minimum amount of soil to be placed uniformly over a 1000 ft2 area. In California, 10 ft is the maximum depth to which soil on a residential property is likely to be excavated.

In the absence of overriding site‐specific considerations, the appropriate sampling objective for evaluating future direct contact exposures to soil contamination initially at depth is to determine average levels of toxicants in subsurface soils within 10 ft of the existing ground surface. Results of such sampling are amenable to interpretation as described in the California Site Mitigation Decision Tree(1) to determine if contamination initially at depth could present a future risk to public health.
Routes of Chloroform Exposure and Body Burden from Showering with Chlorinated Tap Water
Authors: Jo Wan K. , Weisel Clifford P. , Lioy Paul J.
Published: May 2006

While there is an awareness of the need to quantify inhalation exposure from showers, the potential for dermal exposure to organic contaminants in showers has not been appreciated or explored. To establish routes of environmental exposure from showers, comparisons of the concentration of chloroform in exhaled breath after a normal shower with municipal tap water were made with those after an inhalation‐only exposure. The postexposure chloroform breath concentrations ranged from 6.0–21 μg/m3 for normal showers and 2.4 to 10 μg/m3 for inhalation‐only exposure, while the pre‐exposure concentrations were all less than the minimum detection limit of 0.86 μg/m3. According to an F‐test, the difference between the normal shower and the inhalation‐only exposures was considered significant at a probability of p= 0.0001. Based on the difference, the mean internal dose due to dermal exposure was found to be approximately equal to that due to the inhalation exposure. The effect of the showering activities on the concentration of chloroform shower air was examined by comparing air concentrations during a normal shower with the air concentrations obtained when the shower was unoccupied. The F‐test showed that there is no significant difference between the two sets of data.
Assessment of Population Exposure and Carcinogenic Risk Posed by Volatile Organic Compounds in Indoor Air
Authors: Stolwijk Jan A.J.
Published: May 2006

A number of air pollutants are being found in low concentrations in indoor and outdoor air. Several studies have measured these concentrations for a large number of compounds in hundreds of residences. The concentrations range over several orders of magnitude over time and space. The log‐normal distributions that are found make it possible to assess the impact on the health of populations, especially for genotoxic effects for which a threshold concentration is not expected to exist. Spreadsheets can be constructed which incorporate the unit risk of a substance for cancer, the distribution of concentrations of the substance in the population, and the size of the population into an assessment of the expected excess cases of cancer that can be attributed to the population exposure to such a toxicant. This approach allows for the evaluation of population risk for different substances as found in different environments, and for the evaluation of the relative efficacy of different strategies for population risk reduction.
Nonstop Flying Is Safer Than Driving
Authors: Sivak Michael , Weintraub Daniel J. , Flannagan Michael
Published: May 2006

The relative safety of driving and flying is important in many situations that involve selecting a mode of transportation. The traditional view, that flying via scheduled airlines is safer than driving, has recently been challenged by Evans et al.(1) They concluded that for a low‐risk driver it is safer to drive on rural interstate highways (the safest roads) than to fly if the trip length is less than 602 miles. We reestimated the fatality probabilities for flying by taking into account that the risk of flying is dependent on the number of nonstop segments flown, but, for all practical purposes, is independent of the length of the trip. Our calculations indicate that, for average or high‐risk drivers, it is always safer to fly than to drive. Furthermore, even for a low‐risk driver, nonstop flying is safer than driving on rural interstate highways for a trip distance of more than 303 miles; the corresponding breakeven distances for flights that involve two and three segments are 606 and 909 miles, respectively.
Sampling Strategies for Toxic Air Contaminants
Authors: Rao S. Trivikrama , Ku Jia‐Yeong , Rao K. Shankar
Published: May 2006

Annual concentrations of toxic air contaminants are of primary concern from the perspective of chronic human exposure assessment and risk analysis. Despite recent advances in air quality monitoring technology, resource and technical constraints often impose limitations on the availability of a sufficient number of ambient concentration measurements for performing environmental risk analysis. Therefore, sample size limitations, representativeness of data, and uncertainties in the estimated annual mean concentration must be examined before performing quantitative risk analysis. In this paper, we discuss several factors that need to be considered in designing field‐sampling programs for toxic air contaminants and in verifying compliance with environmental regulations. Specifically, we examine the behavior of SO2, TSP, and CO data as surrogates for toxic air contaminants and as examples of point source, area source, and line source‐dominated pollutants, respectively, from the standpoint of sampling design. We demonstrate the use of bootstrap resampling method and normal theory in estimating the annual mean concentration and its 95% confidence bounds from limited sampling data, and illustrate the application of operating characteristic (OC) curves to determine optimum sample size and other sampling strategies. We also outline a statistical procedure, based on a one‐sided t‐test, that utilizes the sampled concentration data for evaluating whether a sampling site is in compliance with relevant ambient guideline concentrations for toxic air contaminants.
Perceived Risk, Stigma, and Potential Economic Impacts of a High‐Level Nuclear Waste Repository in Nevada
Authors: Slovic Paul , Layman Mark , Kraus Nancy , Flynn James , Chalmers James , Gesell Gail
Published: May 2006

This study investigates the potential impacts of the proposed nuclear waste repository at Yucca Mountain, Nevada, upon tourism, retirement and job‐related migration, and business development in Las Vegas and the state. Adverse impacts may be expected to result from perceptions of risk, stigmatization, and socially amplified reactions to “unfortunate events” associated with the repository (major and minor accidents, discoveries of radiation releases, evidence of mismanagement, attempts to sabotage or disrupt the facility, etc.). The conceptual underpinnings of risk perception, stigmatization, and social amplification are discussed and empirical data are presented to demonstrate how nuclear images associated with Las Vegas and the State of Nevada might trigger adverse economic effects. The possibility that intense negative imagery associated with the repository may cause significant harm to Nevada's economy can no longer be ignored by serious attempts to assess the risks and impacts of this unique facility. The behavioral processes described here appear relevant as well to the social impact assessment of any proposed facility that produces, uses, transports, or disposes of hazardous materials.
Scheduling Updates of Probabilistic Risk Assessments: The Arkansas Nuclear One‐Unit 1 Experience
Authors: Paula Henrique M. , Guthrie Vernon H. , Campbell David J.
Published: May 2006

This paper presents the results of a study that identified how often a probabilistic risk assessment (PRA)should be updated to accommodate the changes that take place at nuclear power plants. Based on a 7‐year analysis of design and procedural changes at one plant, we consider 5 years to be the maximum interval for updating PRAs. This conclusion is preliminary because it is based on the review of changes that occurred at a single plant, and it addresses only PRAs that involve a Level 1 analysis (i.e., a PRA including calculation of core damage frequency only). Nevertheless, this conclusion indicates that maintaining a useful PRA requires periodic updating efforts. However, the need for this periodic update stems only partly from the number of changes that can be expected to take place at nuclear power plants–changes that individually have only a moderate to minor impact on the PRA, but whose combined impact is substantial and necessitates a PRA update. Additionally, a comparison of two generations of PRAs performed about 5 years apart indicates that PRAs must be periodically updated to reflect the evolution of PRA methods. The most desirable updating interval depends on these two technical considerations as well as the cost of updating the PRA. (Cost considerations, however, were beyond the scope of this study.)
Physiologically Based Liver Modeling and Risk Assessment
Authors: Robinson Peter J.
Published: May 2006

Because of the inherent complexity of biological systems, there is often a choice between a number of apparently equally applicable physiologically based models to describe uptake and metabolism processes in toxicology or risk assessment. These models may fit the particular data sets of interest equally well, but may give quite different parameter estimates or predictions under different (extrapolated) conditions. Such competing models can be discriminated by a number of methods, including potential refutation by means of strategic experiments, and their ability to suitably incorporate all relevant physiological processes. For illustration, three currently used models for steady‐state hepatic elimination—the venous equilibration model, the parallel tube model, and the distributed sinusoidal perfusion model—are reviewed and compared with particular reference to their application in the area of risk assessment. The ability of each of the models to describe and incorporate such physiological processes as protein binding, precursor‐metabolite relations and hepatic zones of elimination, capillary recruitment, capillary heterogeneity, and intrahepatic shunting is discussed. Differences between the models in hepatic parameter estimation, extrapolation to different conditions, and interspecies scaling are discussed, and criteria for choosing one model over the others are presented. In this case, the distributed model provides the most general framework for describing physiological processes taking place in the liver, and has so far not been experimentally refuted, as have the other two models. These simpler models may, however, provide useful bounds on parameter estimates and on extrapolations and risk assessments.
High Risk or Low: How Location on a “Risk Ladder” Affects Perceived Risk
Authors: Sandman Peter M. , Weinstein Neil D. , Miller Paul
Published: May 2006

Efforts to explain risk magnitude often rely on a “risk ladder” in which exposure levels and associated risk estimates are arrayed with low levels at the bottom and high ones at the top. Two experiments were conducted to test the hypothesis that perceived threat and intended mitigation vary with the location of the subject's assigned level on the risk ladder. Subjects were New Jersey homeowners, asked to assume a particular level of radon or asbestos contamination in their homes, to read a brochure explaining the risk, and then to complete a questionnaire. Both studies found that the difference between an assigned level one‐quarter of the way up the ladder and the same level three‐quarters of the way up the ladder significantly affected threat perception; the effect on mitigation intentions was significant in only one of the studies. Variations in assigned risk also affected threat perception and mitigation intentions. Variations in test magnitude (e.g., 15 fibers per liter vs. 450 fibers per cubic foot, roughly equivalent risks) had no effect, nor did the distinction between radon and asbestos affect the dependent variables. These findings suggest that communicators can design risk ladders to emphasize particular risk characteristics.
An Approach for Balancing Health and Ecological Risks at Hazardous Waste Sites
Authors: Suter II Glenn W. , Cornaby Barney W. , Hadden Charles T. , Hull Ruth N. , Stack Mark , Zafran Fred A.
Published: May 2006

Human health and ecological risks must be balanced at hazardous waste sites in order to ensure that remedial actions prevent unacceptable risks of either type. Actions that are designed to protect humans may fail to protect nonhuman populations and ecosystems or may damage ecosystems. However, there is no common scale of health and ecological risk that would allow comparisons to be performed. This paper presents an approach to addressing this problem based on classifying all risks (i.e., health and ecological risks due contaminants and remediation) as insignificant (de minimis), highly significant (de manifestis), or intermediate. For health risks the classification is based on standard criteria. However, in the absence of national guidance concerning the acceptability of ecological risks, new ecological criteria are proposed based on an analysis of regulatory precedents. Matrices and flow charts are presented to guide the use of these risk categories in remedial decision making. The assessment of mercury contamination of the East Fork Poplar Creek is presented as an example of the implementation of the approach.
An Exact Analysis of the Multistage Model Explaining Dose‐Response Concavity
Authors: Cox Louis Anthony
Published: May 2006

The traditional multistage (MS) model of carcinogenesis implies several empirically testable properties for dose‐response functions. These include convex (linear or upward‐curving) cumulative hazards as a function of dose; symmetric effects on lifetime tumor probability of transition rates at different stages; cumulative hazard functions that increase without bound as stage‐specific transition rates increase without bound; and identical tumor probabilities for individuals with identical parameters and exposures. However, for at least some chemicals, cumulative hazards are not convex functions of dose. This paper shows that none of these predicted properties is implied by the mechanistic assumptions of the MS model itself. Instead, they arise from the simplifying “rare‐tumor” approximations made in the usual mathematical analysis of the model. An alternative exact probabilistic analysis of the MS model with only two stages is presented, both for the usual case where a carcinogen acts on both stages simultaneously, and also for idealized initiation‐promotion experiments in which one stage at a time is affected. The exact two‐stage model successfully fits bioassay data for chemicals (e.g., 1,3‐butadiene) with concave cumulative hazard functions that are not well‐described by the traditional MS model. Qualitative properties of the exact two‐stage model are described and illustrated by least‐squares fits to several real datasets. The major contribution is to show that properties of the traditional MS model family that appear to be inconsistent with empirical data for some chemicals can be explained easily if an exact, rather than an approximate model, is used. This suggests that it may be worth using the exact model in cases where tumor rates are not negligible (e.g., in which they exceed 10%). This includes the majority of bioassay experiments currently being performed.
Gender Differences in Risk Perception: Effects Differ in Stressed vs. Non‐Stressed Environments
Authors: Greenberg Michael R. , Schneider Dona F.
Published: May 2006

Contrary to previous reports that women are more concerned about environmental risks than men, we hypothesized that men and women residing in neighborhoods stressed by multiple hazards would demonstrate similar concerns about local environmental conditions. Analysis of a national data base and an aggregate of ten local data bases found greater female than male concern about local technological, behavioral, and land use hazards in good neighborhoods, but, as expected, not in stressed ones. We urge analysts to conduct more studies in stressed neighborhoods in order to better understand the perspective of those who live with environmental risks.
Reanalysis of Dose‐Response Data from the Iraqi Methylmercury Poisoning Episode
Authors: Crump Kenny , Viren John , Silvers Abraham , Clewell III Harvey , Gearhart Jeff , Shipp Annette
Published: May 2006

Applying a hockey stick parametric dose‐response model to data on late or retarded development in Iraqi children exposed in utero to methylmercury, with mercury (Hg) exposure characterized by the peak Hg concentration in mothers’hair during pregnancy, Cox et al. calculated the “best statistical estimate” of the threshold for health effects as 10 ppm Hg in hair with a 95% range of uncertainty of between 0 and 13.6 ppm.(1)A new application of the hockey stick model to the Iraqi data shows, however, that the statistical upper limit of the threshold based on the hockey stick model could be as high as 255 ppm. Furthermore, the maximum likelihood estimate of the threshold using a different parametric model is virtually zero. These and other analyses demonstrate that threshold estimates based on parametric models exhibit high statistical variability and model dependency, and are highly sensitive to the precise definition of an abnormal response. Consequently, they are not a reliable basis for setting a reference dose (RfD) for methylmercury. Benchmark analyses and statistical analyses useful for deriving NOAELs are also presented. We believe these latter analyses—particularly the benchmark analyses—generally form a sounder basis for determining RfDs than the type of hockey stick analysis presented by Cox et al. However, the acute nature of the exposures, as well as other limitations in the Iraqi data suggest that other data may be more appropriate for determining acceptable human exposures to methylmercury.
Intuitive Toxicology. II. Expert and Lay Judgments of Chemical Risks in Canada
Authors: Slovic Paul , Malmfors Torbjörn , Krewski Daniel , Mertz C. K. , Neil Nancy , Bartlett Sheryl
Published: May 2006

This study is a replication and extension in Canada of a previous study in the United States in which toxicologists and members of the public were surveyed to determine their attitudes, beliefs, and perceptions regarding risks from chemicals. This study of “intuitive vs. scientific toxicology” was motivated by the premise that different assumptions, conceptions, and values underlie much of the discrepancy between expert and lay views of chemical risks. The results showed that Canadian toxicologists had far lower perceptions of risk and more favorable attitudes toward chemicals than did the Canadian public. The public's attitudes were quite negative and showed the same lack of dose‐response sensitivity found in the earlier U.S. study. Both the public and the toxicologists lacked confidence in the value of animal studies for predicting human health risks. However, the public had great confidence in the validity of animal studies that found evidence of carcinogenicity, whereas such evidence was not considered highly predictive of human health risk by many toxicologists. Technical judgments of toxicologists were found to be associated with factors such as affiliation, gender, and worldviews. Implications of these data for risk communication are briefly discussed.
Exposure of Contractors to Chemical Pollutants During the Maintenance Shut‐Down of a Chemical Plant
Authors: Hery Michel , Diebold François , Hecht Gérard
Published: May 2006

The exposure of employees of different contracting firms to chemical pollutants was assessed during the five‐week biennial maintenance shut‐down of an isocyanate (TDI) synthesis plant. This assessment was mainly based on personal sampling, but work‐related constraints occasionally required that area samples be used instead. Many tasks were carried out during the shut‐down procedure (dismantling of reactors, installation of insulation, refection of kilns, cleaning, painting, electricity, etc.), thereby causing the employees of the contracting firms to be exposed to different kinds of pollutants, including products used or manufactured in the process (solvents, TDI and its synthesis intermediates), and products specific to the contractors’ activity (welding fumes, crystalline silica, mineral fibers of heat insulation). The highest level of exposure (mainly to TDI) was found for the mechanical engineering activities undertaken during the dismantling of reactors and for cleaning activities. It was demonstrated that there was much variability in day‐to‐day exposure levels, and occasionally in the exposure levels encountered during a given shift. Cases of concomitant exposure to TDI (mainly short‐term exposures) and other pollutants due to simultaneous activities from different tasks in the same area (co‐activity) were also observed. Both the need for, and limitations of personal protective equipment (mainly respiratory) are stressed. Special emphasis is put on the responsibility of the owner of the facilities in helping the contractors in the organization of a health and safety policy.
A Nonidentifiability Aspect of the Two‐Stage Model of Carcinogenesis
Authors: Hanin Leonid G. , Yakovlev Andrej Yu.
Published: May 2006

This paper discusses identifiability of the two‐stage birth‐death‐mutation model of carcinogenesis. It is shown that the homogeneous version of the model is nonidentifiable; the same is all the more evident for its nonhomogeneous versions. This result implies that the model parameters cannot be uniquely estimated from time‐to‐tumor observations.
Efficient Treatment of Uncertainty in Numerical Optimization
Authors: Galambos J. D. , Holmes J. A.
Published: May 2006

We have combined the methods of probabilistic risk analysis and optimization to devise a technique suitable for the efficient treatment of uncertainties (or the effects of random fluctuations) in the design and analysis of mathematically describable processes. The key step is the approximation, by a multivariable Taylor series expansion, of the influence of random variables on the objective function. Statistical averaging of this expansion leads to a description of the objective function in terms of the moments of the random variables. Knowledge or estimation of these moments allows the optimization to be carried out using standard calculus based techniques. An example is treated with three variations to illustrate the use of this technique for nonlinear sets of equations and objective functions. The method presented here is applicable to process models in manufacturing, systems analysis, and risk analysis.
An Alternative Exact Solution of the Two‐Stage Clonal Growth Model of Cancer
Authors: Hoogenveen Rudolf T. , Clewell Harvey J. , Andemen Melvin E. , Slob Wout
Published: May 2006

The approximate solution of the two‐stage clonal expansion model of cancer may substantially deviate from the exact solution, and may therefore lead to erroneous conclusions in particular applications. However, for time‐varying parameters the exact solution (method of characteristics) is not easy to implement, hampering the accessibility of the model to nonmathematicians. Based on intuitive reasoning, Clewell et al. (1995) proposed an improved approximate solution that is easy to implement whatever time‐varying behavior the parameters may have. Here we provide the mathematical foundation for the approximation suggested by Clewell et al. (1995) and show that, after a slight modification, it is in fact an exact solution for the case of time‐constant parameters. We were not able to prove that it is an exact solution for time‐varying parameters as well. However, several computer simulations showed that the numerical results do not differ from the exact solution as proposed by Moolgavkar and Luebeck (1990). The advantage of this alternative solution is that the hazard rate of the first malignant cell can be evaluated by numerically integrating a single differential equation.
A Comparison of Regulatory Implications of Traditional and Exact Two‐Stage Dose‐Response Models
Authors: Chiu Weihsueh A. , Hassenzahl David M. , Kammen Daniel M.
Published: May 2006

We compare the regulatory implications of applying the traditional (linearized) and exact two‐stage dose‐response models to animal carcinogenic data. We analyze dose‐response data from six studies, representing five different substances, and we determine the “goodness‐ of‐fit” of each model as well as the 95% confidence lower limit ofthe dose corresponding to a target excess risk of 10‐5 (the target risk doseTRD). For the two concave datasets, we find that the exact model gives a substantially better fit to the data than the traditional model, and that the exact model gives aTRD that is an order of magnitude lower than that given by the traditional model. In the other cases, the exact model gives a fit equivalent to or better than the traditional model. We also show that although the exact two‐stage model may exhibit dose‐response concavity at moderate dose levels, it is always linear or sublinear, and never supralinear, in the low‐dose limit. Because regulatory concern is almost always confined to the low‐dose region extrapolation, supralinear behavior seems not to be of regulatory concern in the exact two‐stage model. Finally, we find that when performing this low‐dose extrapolation in cases of dose‐response concavity, extrapolating the model fit leads to a more conservative TRD than taking a linear extrapolation from 10% excess risk. We conclude with a set of recommendations.
Fundamentals of Health Risk Assessment. Use, Derivation, Validity and Limitations of Safety Indices
Authors: Putzrath Resha M. , Wilson James D.
Published: May 2006

We investigated the way results of human health risk assessments are used, and the theory used to describe those methods, sometimes called the “NAS paradigm.” Contrary to a key tenet of that theory, current methods have strictly limited utility. The characterizations now considered standard, Safety Indices such as “Acceptable Daily Intake,”“Reference Dose,” and so on, usefully inform only decisions that require a choice between two policy alternatives (e.g., approve a food additive or not), decided solely on the basis of a finding of safety. Riskis characterized as the quotient of one of these Safety Indices divided by an estimate of exposure: a quotient greater than one implies that the situation may be considered safe. Such decisions are very widespread, both in the U. S. federal government and elsewhere. No current method is universal; different policies lead to different practices, for example, in California's “Proposition 65,” where statutory provisions specify some practices. Further, an important kind of human health risk assessment is not recognized by this theory: this kind characterizes risk as likelihood of harm, given estimates of exposure consequent to various decision choices. Likelihood estimates are necessary whenever decision makers have many possible decision choices and must weigh more than two societal values, such as in EPA's implementation of “conventional air pollutants.” These estimates can not be derived using current methods; different methods are needed. Our analysis suggests changes needed in both the theory and practice of human health risk assessment, and how what is done is depicted.
A Risk Assessment Method for Biological Introductions
Authors: Harris Adrian R. , Correll Raymond L. , Adkins Paul G.
Published: May 2006

This article describes an application of a method for assessing risks associated with the introduction of an organism into a new environment. The test organism was a binucleate Rhizoctonia fungal isolate that has potential for commercial development as a biological control agent for damping‐off diseases in bedding plants. A test sample of host plant species was selected using the centrifugal phylogenetic host range principles, but with an emphasis on economic species. The effect of the fungus on the plant was measured for each species and expressed on a logarithmic scale. The effects on weights of shoots and roots per container were not normally distributed, nor were the effects on the number of plants standing (those which survived). Statements about the effect on the number standing and the shoot weight per container involved using the observed (empirical) distribution. This is illustrated with an example. Problems were encountered in defining the population of species at risk, and in deciding how this population should be formally sampled. The limitations of the method are discussed.
Ethical Issues in Risk Communication: Continuing the Discussion*
Authors: Johnson Branden B.
Published: May 2006

Proposed in this article is one possible framework for classifying multiple types of ethical issues in risk communication research and practice to help continue a discussion initiated in 1990 by Morgan and Lave. Some of the questions that each stage of the process for planning risk communication strategies appears to pose for ethics are discussed (e.g., selecting issues to be communicated, knowing the issue, dealing with constraints). Also discussed briefly are some issues raised by the possibility that risk communicators aspire to the status of a profession. The purpose is to foster discussion rather than issue a conclusive statement on the topic, because its very nature makes a definitive pronouncement indefensible.
Critical Radionuclide/Critical Pathway Analysis for the U.S. Department of Energy's Savannah River Site
Authors: Jannik G. Timothy
Published: May 2006

Many different radionuclides have been released to the environment from the Savannah River Site (SRS) during the facility's operational history. However, as shown by this analysis, only a small number of the released radionuclides have been significant contributors to potential doses and risks to off‐site people. This article documents the radiological critical contaminant/critical pathway analysis performed for SRS. If site missions and operations remain constant over the next 30 years, only tritium oxide releases are projected to exceed a maximally exposed individual (MEI) risk of 1.0E‐06 for either the airborne or liquid pathways. The critical exposure pathways associated with site airborne releases are inhalation and vegetation consumption, whereas the critical exposure pathways associated with liquid releases are drinking water and fish consumption. For the SRS‐specific, nontypical exposure pathways (i.e., recreational fishing and deer and hog hunting), cesium‐137 is the critical radionuclide.
Statistical Evaluation of Population Data for Calculation of Radioactive Material Transport Accident Risks
Authors: Mills G. Scott , Neuhauser K. Sieglinde
Published: May 2006

Calculation of accident dose‐risk estimates with the RADTRAN code requires input data describing the population likely to be affected by the plumeof radioactive material (RAM) released in a hypothetical transportation accident. In the existing model, population densities within 1/2 mile (0.8 km)of the route centerline are tabulated in three ranges (Rural, Suburban, andUrban). These population densities may be of questionable validity since the plume in the RADTRAN analysis is assumed to extend out to 120 km from thehypothetical accident site. We present a GIs‐based population model which accounts for the actual distribution of population under a potential plume, and compare accident‐risk estimates based on the resulting population densities with those based on the existing model. Results for individual points along a route differ greatly, but the cumulative accident risks for a sample route of a few hundred kilometers are found to be comparable, if not identical. We conclude, therefore, that for estimation of aggregate accident risks over typical routes of several hundred kilometers, the existing, simpler RADTRAN model is sufficiently detailed and accurate.
Economic Impact of Accelerated Cleanup on Regions Surrounding the U.S.DOE's Major Nuclear Weapons Sites
Authors: Greenberg Michael , Solitare Laura , Frisch Michael , Lowrie Karen
Published: May 2006

The regional economic impacts of the U.S. Department of Energy's accelerated environmental cleanup plan are estimated for the major nuclear weapons sites in Colorado, Idaho, New Mexico, South Carolina, Tennessee, and Washington. The analysis shows that the impact falls heavily on the three relatively rural regions around the Savannah River (SC), Hanford (WA), and Idaho National Engineering and Environmental Laboratory (ID) sites. A less aggressive phase‐down of environmental management funds and separate funds toinvest in education and infrastructure in the regions helps buffer theimpacts on jobs, personal income, and gross regional product. Policy options open to the federal and state and local governments are discussed.
Restorative dental care of children participating in a school based plaque control programme in London
Authors: Sainsbury Robert H. , Ashley Frank P.
Published: May 2006

Abstract The effect of a school based plaque control programme on restorative dental treatment was investigated over a 4‐yr period. The programme consisted of fortnightly visits to a hygienist during term time for oral hygiene reinforcement and prophylaxis during the first 3 yr. The subjects were girls aged 11–12 yr at baseline and all attended the same school; the present study was concerned with the subjects in both the experimental and control groups who attended the dentist based in the school for restorative care (n= 147 for the first year falling to 108 for the 4‐yr period). During the first year, the subjects treated from the experimental group received significantly fewer restorations than the subjects treated from the control group. This significant difference was not seen in the subsequent 3 yr and the mean number of restorations provided over the 4‐yr period in the experimental and control groups respectively was 5.45 and 6.67. The corresponding 4 yr DFS increments for these groups were 5.56 and 5.52. The anomalous first finding appeared to have been due more of decayed surfaces being present in the control group at baseline. The results for restorative care generally confirmed the ineffectiveness of the programme in preventing caries and the relatively low caries increments reflect the reductions in caries experience occurring in similar communities during the period of the study.
Sugar consumption and caries risk in schoolchildren with low caries experience
Authors: Szpunar Susan M. , Eklund Stephen A. , Burt Brian A.
Published: May 2006

Abstract This paper assesses the risk from sugar consumption in a population of schoolchildren with low caries experience. It relates eight different measures of sugar consumption to the occurrence of any DMFS increment, and, separately, to approximal and pit‐and‐fissure DMFS. The data are from a 3‐yr longitudinal study of 429 children, initially aged 11–15, residing in non‐fluoridated rural communities in Michigan, USA. All children completed at least three dietary interviews, were present for baseline and final dental examinations, and had a parent or guardian provide questionnaire information on residence history, use of fluoride and dental services, and family history. Results indicated that a higher proportion of total energy intake from sugars increased the probability of caries on all surfaces, and a higher total intake of sugars was also associated with total caries increment. No relationship, however, was found between DMFS increment and the frequency of eating high sugar foods. Each additional 5 g of daily sugars intake was associated with a 1% increase in the probability of developing caries, and those whose energy intake from sugars was 1 SD above the mean had 2.0 times the risk of developing approximal caries than did children whose energy intake from sugars was 1 SD below the mean.
Comparing dental utilization of U.S. Army soldiers with their employed civilian cohorts
Authors: Chisick Michael C.
Published: May 2006

Abstract In fall 1992, a random, worldwide sample of 5474 enlisted and 4036 officer, active duty, U.S. Army personnel was surveyed on dental utilization. Overall survey response rate was 62%. After weighting the data to reflect the population, dental utilization rates of military personnel were compared with their employed civilian cohorts in the U.S. population. Results show that, regardless of race or gender, over 80% of U.S. Army personnel have seen a dentist within the past year. Controlling for age, gender, and race, active duty U.S. Army personnel have dental utilization rates that greatly exceed their employed civilian cohorts. The results suggest that access barriers to dental care present in the civilian population, especially for minorities, are greatly diminished in the U.S. Army. The results suggest that access to free care may be a potent stimulus to utilization of dental services among military or civilian personnel. Further, access to free denial care should be emphasized in recruiting and retaining U.S. military personnel.
Dental caries in Namibia – the first national survey
Authors: Schier Manfred , Cleaton‐Jones Peter
Published: May 2006

Abstract This paper reports findings on dental caries in the first national survey in Namibia, the second largest country on the Southern African subcontinent. In 1991. a total of 208l individuals, representing 0.15% of the Namibian population, 764 12‐yr‐olds, 736 15‐yr‐olds and 581 35–44‐yr‐olds were examined to determine their oral health. Caries was diagnosed using WHO criteria by a single calibrated dentist. At 12 yr between 37% and 81% of the subjects examined were caries‐free, at 15 yr between 25% and 66%, and in the age class 35–44 yr 6–44% were caries‐free. Mean DMFT at 12 yr was 0.40–1.74 and at 15 yr 0.92–3.05; mean DFT at 35–44 yr was 1.36–3.93. Females had significantly more caries than males and there were significant differences between urban, peri‐urban and rural areas. The caries prevalence and experience is nevertheless low and within the WHO target for the year 2000 at 12 yr of age.
Dentists' variability in restorative decisions, microscopic and radiographic caries depth
Authors: Lewis Donald W. , Kay Elizabeth J. , Main Patricia A. , Pharoah Michael G. , Csima Adele
Published: May 2006

Abstract Restorative and dental caries depth decisions were recorded for 5168 unrestored approximal tooth surfaces by 17 dentists who worked in the school dental clinics of the North York (Ontario) Public Health Department. Each dentist examined 15 pairs of experimental bitewing radiographs for which true caries depth had previously been determined by microscopy of the sectioned teeth following production of the radiographs. The dentists independently recorded their restorative decisions and radiographic caries depth perceptions. The relationship between the variation in the dentists' restorative decisions and their perceptions of caries depth based on a re‐reading of the bitewings on the one hand, and true caries depth on the other was also examined. The percentages of total variability in each dentist's restorative decisions attributable to radiographic and to microscopic caries depth were estimated using regression analyses. Large variations were found among the 17 dentists' distributions of overall restorative and depth decisions. The relationship between microscopic caries depth and the dentists' restorative decisions was, understandably, less strong than that of the dentists' radiographic perceptions of caries depth and restorative decisions. Relative to true caries depth, high numbers of false positive and false negative restorative decisions were made. Overall, 50% of the variability in the dentists' restorative decisions was explained by their perceptions of radiographic caries depth; however, among individual dentists, the range was from 29% for one dentist to 69% for another. A much lower percentage of the overall restorative variation was explained by microscopic depth, 18%. Like the findings of the only two previous European studies that quantified the role of radiographs on clinical decisions, this study demonstrated that dentists' perceptions of dental caries depth using bitewing radiographs play a major but variable role in their restorative decisions for approximal tooth surfaces.