Extrapolation in Human Health and Ecological Risk Assessments: Proceedings of a Symposium

A symposium was conducted in April 1998 by the U.S. Environmental Protection Agency's National Health and Environmental Effects Research Laboratory (NHEERL) to explore issues of extrapolation in human health and ecological risk assessments. Over the course of three and one half days, leading health and ecology experts presented and discussed research methods and approaches for extrapolating data among taxa and across levels of biological organization, through time, and across spatial scales. The intended result of this symposium was enhanced interaction among a diverse array of scientists, policymakers, and risk assessors to promote identification of approaches for reducing the uncertainties of extrapolation in risk assessment.     

Challenges in Defining Background Levels for Human and Ecological Risk Assessments

A robust approach to defining, understanding, and tracking contaminant levels is crucial to human and ecological risk evaluation and risk management. Whether materials are present in the environment naturally (mercury, radon, nitrogen, phosphorous) and enhanced by human activities or are man-made (DDT and PCBs), the complexity of contaminant distributions and sources requires careful design and implementation of studies to characterize background. Before collection or analyses of data are initiated, an explicit definition of background appropriate to specific risk assessments is needed. Problems associated with determining background levels of contaminants in fish and seafood illustrate some challenges faced by risk assessors. Major differences in estimates of background may result from differences in sampling and analytical methods including selection of sampling locations, approaches to data analysis and synthesis, and tissues selected for analysis. Different approaches may yield background exposure or risk estimates that differ by 50% or more. Methodological transparency is essential in data collection and analysis to establish background and to ensure that data are used appropriately in both human and ecological risk assessments.     

Planning Transboundary Ecological Risk Assessments at Military Installations

Ecological risk assessments at military installations that are performed to support natural resources management objectives rely on information from the surrounding region. Stressors such as noise, ozone, and ozone precursors cross installation boundaries, and effects of urbanization and highway development are regional in scale. Ecological populations are not limited to one side of the installation boundary. Therefore, a framework for transboundary ecological risk assessment at military installations is under development. This article summarizes the problem formulation stage. Components include: (1) regional management goals such as installation Integrated Natural Resources Management Plans and land acquisition, (2) involvement of multiple stressors, and (3) large-scale assessment endpoint entities. Challenges of selecting measures of exposure include: quantifying exposure to aggregate stressors, describing land cover consistently in the region, describing rates of land-cover transition, scaling local measurements to a region, and aggregating or isolating exposures from within and outside of the installation. Measures of effect that are important to transboundary or regional ecological risk assessments at military installations are those that represent: effects at a distance from the stressor, large-scale effects, effects of habitat change or fragmentation, spatial extrapolations of localized effects, and integrated effects of multiple stressors. These factors are reflected in conceptual models.     

Consideration of Background Radiation in Ecological Risk Assessments

Background or ambient concentrations are often considered in the evaluation of potential risks to ecological receptors from exposure to hazardous chemicals in the environment. Such an evaluation may be a component of the screening or final risk management process and sets the baseline from which risks contributed by site-related activities can be addressed. Although the process for the evaluation of potential radiological risks to ecological receptors is less formalized than the chemical hazard assessment process, background remains an issue that should be addressed when considering potential site-related impacts. This paper briefly presents the ecological risk assessment approaches used to address background radionuclide concentrations at three United States Department of Defense Facilities. The concepts of total radiation dose, and tolerance and adaptation of populations to radiation are also discussed within the context of background radiation.     

Incorporating Information on Bioavailability of Soil-Borne Chemicals into Human Health Risk Assessments

Definition of the term bioavailability varies in the environmental sciences. In human health risk assessment, bioavailability is defined as the fraction of the dose of chemical delivered that is absorbed into the systemic circulation. Bioavailability can be expressed as either absolute or relative bioavailability, and both are important in calculating risks from contaminants in soils. Bioavailability of chemicals is addressed in all risk assessments, although not always in a transparent manner. Because data on bioavailability are limited, approximations and assumptions regarding chemical uptake are extensively used. The risk assessment process could benefit from new information on the bioavailability of chemicals, but there are important questions about the best means to develop this information and how it should be used. To foster discussion on these issues, three articles are presented in this issue of the journal offering different perspectives on bioavailability method development, validation, and use.     

Human Health Risk Assessment: Required Reading

Over the past 30 years, risk assessment has developed into a scientific discipline. It is critical that the next generation of risk assessors understand the history of our field, and recognize the numerous successes and failures that have taken place. This short Perspective identifies and describes specific books, monographs, and reports that are required reading for any nascent risk assessor.     

Probability Density Functions Describing 24-Hour Inhalation Rates For Use in Human Health Risk Assessments

A Monte Carlo simulation was undertaken to estimate the amount of air inhaled over a typical 24-hour period by six age groups of Canadians. The objective of the simulation was to derive probability density functions that could be used to describe inhalation rates in probabilistic health risk assessments involving airborne contaminants. The six age groups considered were those typically employed in human health risk assessments in Canada: infants (aged 0 to 6 months), toddlers (aged 7 months to 4 years), children (aged 5 to 11 years), teenagers (aged 12 to 19 years), adults (aged 20 to 59 years), and seniors (aged 60 years and older). The resulting distributions are considered equally applicable to Americans as Canadians, however, since the study relied heavily on time-activity information gathered in the USA. Existing time-activity and breathing rate studies were reviewed in order to define random variables describing probable durations that North Americans spend at various levels of activity and their probable inhalation rates while at each level of activity. These random variables were combined in a Monte Carlo simulation to empirically generate probability density functions describing 24-hour inhalation rates for each age group. The simulation suggested that most age groups' 24 hour inhalation rates can be represented with log-normal probability density functions. Arithmetic mean values and standard deviations for these distributions are as follows: approximately 9.3 ± 2.4?m³/day for toddlers; 14.6 ± 3.0?m³/day for children; 15.8 ± 3.7?m³/day for teenagers; 16.2 ± 3.8?m³/day for adults; and 14.2 ± 3.3?m³/day for seniors. The distribution of infants' 24-hour inhalation rates was found to be better represented by a normal distribution than a log-normal distribution. The mean and standard deviation for the infants' normal distribution are 2.1 ± 0.58?m³/day. Inhalation rates were also estimated separately for male and female toddlers, children, teenagers, adults and seniors. These estimates suggested that males inhale on average 8% to 27% more air than females of the same age. Because infants' activity patterns and minute volumes did not appear to be strongly correlated with gender, a single probability density function was deemed satisfactory to describe male and female infants' 24-hour inhalation rates.     

Application of the Hazard Quotient Method in Remedial Decisions: A Comparison of Human and Ecological Risk Assessments

This paper evaluates the relative roles of the human health hazard index (HI) and the ecological risk assessment hazard quotient (HQ) in remedial decision-making. Through an analysis of HI outcomes drawn from Superfund Records of Decision, the reduced importance of the HI statistic in human health risk assessments is demonstrated, and the high visibility of the ecological risk assessment (ERA) HQ for terrestrial receptors (birds and mammals) is underscored. Three HQ method limitations common to both HHRA and ERA, deriving either from the mathematical construct of the HQ (a simple binary measure, indicating that an animal's exposure either exceeds its toxicity value or does not) or from dose-response outcomes in animal trials, are reviewed. Two additional HQ limitations unique to ERA (i.e., a propensity for the HQ to easily exceed its threshold value, and a propensity for it to assume values that are unreasonably high), and deriving from the complexities of estimating bird and mammal dietary intakes of contaminants and the availability of toxicological effects information, are also identified. The paper cautions of the potential to err in concluding that terrestrial site receptors are at risk when the HQ threshold is exceeded, and regardless of the toxicological information (NOAELs, LOAELs, etc.) used. It recognizes that because other methods of terrestrial assessment are presently unavailable, HQs are sometimes, out of necessity, used to justify a remedial action. The analysis and discussion are intended to remind ecological risk assessors that the HQ is a measure of a level of concern only and not a measure of risk     

What Can Zookeepers Tell Us About Interacting With Big Cats in Captivity?

Despite the potential dangers involved, interactions between zookeepers and captive big cats are increasing. Research with other animals, particularly nonhuman primates, suggests that closer interactions can be beneficial not only for the animals and their keepers, but also for zoo visitors. This study sought to determine whether the same benefits may apply to keeper‐big cat interactions. An online questionnaire was completed by 86 keepers worldwide, assessing which types of handling (hands‐on, protected, hands‐off) they practice with their big cats, whether they practice training, and what their opinions of these methods are (through a series of rating scales and open‐ended questions). Protected contact was the most frequently used handling method among this sample, particularly with lions, tigers, and cheetahs, and training was practiced by the majority of participants with all big cat species. Participants perceived protected contact as the most beneficial handling practice for big cats, keepers, and visitors, noting how it can allow a close bond between keeper and cat, as well as its educational value for zoo visitors. Contrastingly, concerns were raised about the use of hands‐on approaches, particularly with regard to the safety of all parties involved and the potential for wrong messages to be sent to visitors. Further, training was reported to be more beneficial for each group than any handling practice, yielding similar potential benefits as protected contact. Consistent with existing information with other species, these findings will be useful in directing objective research examining the use of different handling and training methods with big cats. Zoo Biol. 32:142–151, 2013. © 2012 Wiley Periodicals, Inc.     

Use of Indicators in Ecological Risk Assessments for Persistent,Bioaccumulative Toxicants

This paper synthesizes several presentations on the use of indicators in ecological risk assessments for persistent, bioaccumulative toxicants (PBTs). The presentations were organized around two chemical case studies: (1) mercury, and (2) compounds that exhibit an Ah-receptor based mode-of-action. Presenters summarized the current practice of ecological risk assessment for these compounds and described research on known or suspected impacts. In addition, this paper addresses three special topics that apply broadly to all PBTs: (1) the convergence of ecological assessment and ecological risk assessment, (2) integration of ecological and human health risk assessment, and (3) risk assessments for population-level effects.     

Conducting Ecological Risk Assessments of Inorganic Metals and Metalloids: Current Status

Ecological risk assessment (ERA) of inorganic metals and metalloids (metals) must be specific to these substances and cannot be generic because most metals are naturally occurring, some are essential, speciation affects bioavailability, and bioavailability is determined by both external environmental conditions and organism physiological/biological characteristics. Key information required for ERA of metals includes: emissions, pathways, and movements in the environment (Do metals accumulate in biota above background concentrations?); the relationship between internal dose and/or external concentration (Are these metals bioreactive?); and the incidence and severity of any effects (Are bioreactive metals likely to result in adverse or, in the case of essential metals, beneficial effects?) — ground-truthed in contaminated areas by field observations. Specific requirements for metals ERA are delineated for each ERA component (Hazard Identification, Exposure Analysis, Effects Analysis, Risk Characterization), updating Chapman and Wang (2000). In addition, key specific information required for ERA is delineated by major information category (conceptual diagrams, bioavailability, predicted environmental concentration [PEC], predicted no effect concentration [PNEC], tolerance, application [uncertainty] factors, risk characterization) relative to three different tiered, iterative levels of ERA: Problem Formulation, Screening Level ERA (SLERA), and Detailed Level ERA (DLERA). Although data gaps remain, a great deal of progress has been made in the last three years, forming the basis for substantial improvements to ERA for metals.     

The Anna Karenina Principle Applied to Ecological Risk Assessments of Multiple Stressors

Successful ecological risk assessments are all alike; every unsuccessful ecological risk assessment fails in its own way. Tolstoy posited a similar analogy in his novel Anna Karenina: “Happy families are all alike; every unhappy family is unhappy in its own way.” By that, Tolstoy meant that for a marriage to be happy, it had to succeed in several key aspects. Failure on even one of these aspects, and the marriage is doomed. In this paper, I argue that the Anna Karenina principle also applies to ecological risk assessments involving multiple stressors. In particular, I argue that multiple stressors assessments and environmental decision making will not have a happy marriage unless the following can be achieved: (1) there must be societal and political buy-in to the assessment and decision-making process; (2) the assessment must have the latitude to consider a wide range of stressors and potential risk management options; (3) there must be a commitment to following a rigorous focusing of the assessment and to expending resources for model development and data collection; and (4) an adaptive management strategy must be adopted wherein risk management actions are undertaken, system response intensively observed and assessed, and revised management actions taken as appropriate. Failure to meet any of the above criteria for success will doom a multiple stressors assessment and prevent its use in effective decision-making.     

Framework for the Integration of Health and Ecological Risk Assessment

The World Health Organization's International Programme on Chemical Safety (IPCS), the Organization for Economic Cooperation and Development (OECD), and the U.S. Environmental Protection Agency have developed a collaborative partnership to foster integration of assessment approaches for human health and ecological risks. This paper presents the framework developed by that group. Integration provides coherent expressions of assessment results, incorporates the interdependence of humans and the environment, uses sentinel organisms, and improves the efficiency and quality of assessments relative to independent human health and ecological risk assessments. The paper describes how integration can occur within each component of risk assessment, and communicates the benefits of integration at each point. The goal of this effort is to promote the use of this internationally accepted guidance as a basis for harmonization of risk assessment.     

Framework for Human Health Risk Assessment

The views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of the USEPA. The U.S. Government has the right to retain a nonexclusive royalty-free license in and to any copyright covering this article. The U.S. Environmental Protection Agency has recognized the need to develop a framework for human health risk assessment that puts a perspective on the approaches in practice throughout the Agency. In response, the USEPA's Risk Assessment Forum has begun the process of developing a framework for human health risk assessment. This paper provides some additional background to the previous review of the framework efforts and notes the Agency's extramural efforts to begin the process of integrating and harmonizing risk assessment approaches for all human health endpoints.     

Considerations Regarding the Use of Reference Area and Baseline Information in Ecological Risk Assessments

There has been debate in the recent literature as to whether a reference assessment should be included in ecological risk assessments (ERAs) of contaminated sites, and if so, how such an evaluation can be incorporated in a way that aids in decision making. It is our view that an assessment of reference conditions can be useful in the ERA process, for both prospective and retrospective ERAs, given adequate resources and acknowledgement and understanding of the limitations and uncertainties associated with this information. Suggestions and considerations for incorporating reference area information into an ecological risk assessment are discussed.     

What Cytogenetic Studies May Tell Us about Species Diversity and Speciation of Lemurs

I discuss the contribution of cytogenetic data to studies of systematics, phylogeny and speciation of several nocturnal lemurs. I examine specific distribution in Avahi and Lepilemur and propose a chromosomal mechanism involved in speciation of these two genera. I compare the contribution of cytogenetics to that of other techniques such as mitochondrial DNA sequencing. In rare situations wherein the respective systematic conclusions are contradictory, cytogenetic evidence clearly appears to be better supported.     

Human Risk Assessment for Nonylphenol

This article presents a risk assessment for human exposure to nonylphenol (NP). We critically reviewed and assessed all relevant full-text publications based on a variety of data quality attributes. Two categories of data, environmental monitoring and biomonitoring from exposed individuals, were used to estimate human exposure to NP. Environmental monitoring data included the measurement of NP in food, water, air, and dust. From these data and estimates of human intake rates for the sources, exposures were estimated from each source and source-specific Margins of Exposure (MOEs) calculated. However, the nature of the populations studied prevented the calculation of aggregate exposure calculations from these data. Rather, the most reliable estimates of aggregate exposure to NP were those derived from biomonitoring studies in exposed individuals. Using the daily absorbed dose estimates for NP, MOEs were calculated for these populations. The MOEs were based on the use of a No-Observed-Adverse-Effect-Level (NOAEL) for sensitive toxicological endpoints of interest, that is, systemic and reproductive toxicity from continuous-feeding more than 3.5 generations (13 mg/kg/day). The MOEs were all greater than 1000 (ranging from 2863 to 8.4 × 10⁷), clearly indicating reasonable certainty of no harm for source-specific and aggregate (based on biomonitoring) exposures to NP.