Indicators for Human and Ecological Risk Assessment: A U.S. Environmental Protection Agency Perspective

Assessment of risk to public health or environmental resources requires competent characterization of stressors and corresponding effects. Because of the complexity of most stressor-response relationships, it is impossible to completely characterize all the variables, so a select set of measurements is made to reflect the most critical components. Such measurements, or indicators, are included in monitoring programs to estimate trend, stressor source, or magnitude of effects and lead to thresholds for management action or restoration. Although a wide variety of programs and program objectives exists, there are some common challenges for indicator development, including a strong link to management actions. Indicator measurements used in U.S. Environmental Protection Agency (USEPA) risk assessment activities must stem from collaboration among managers, risk assessors, scientists and stakeholders. The primary objective of the USEPA's Fifth Symposium of the National Health and Ecological Effects Research Laboratory was to improve health and ecological risk assessment through dedicated sessions that maximized interaction and discussion among these groups. Existing measurements were challenged for appropriateness, efficiency and scientific validity. Emerging science was explored for greater understanding, better interpretation, and improved methodology. A secondary objective was to uncover and exploit common indicators and supporting data for human health and ecological models.     

Annotated reference compilation: Conducting qualitative and quantitative ecological risk assessments at hazardous waste sites

As the field of ecological risk assessment (ERA) broadens, scientists from various disciplines are called upon to become assessors at hazardous waste sites. Although a United States Environmental Protection Agency (USEPA) Framework for ERAs exists, the guidance is unlike the detailed USEPA guidance available for human risk assessments. Currently, the quality of an ERA is dependent upon the assessor's scientific acumen, professional experience, and recognized reference documents. This annotated reference compilation encompasses published documents which have provided useful and important information for qualitative and quantitative ERAs.     

Metals that Drive Health-Based Remedial Decisions for Soils at U.S. Department of Defense Sites

This study was undertaken to establish which metals are most likely to drive the risk-based remedial decision-making process at those U.S. Department of Defense (DoD) sites that are affected by metals in site soils. Our approach combined queries of various databases, interviews with U.S. Environmental Protection Agency (USEPA) experts in each Region, and communication with database administrators and DoD personnel. The databases that were used were comprehensive for DoD sites, yet sometimes contained inaccuracies. Metal concentration data for various DoD facilities were screened against established regulatory criteria for both human health and ecological endpoints. Results from this analysis were compared against the information gleaned from the interviews. This preliminary analysis indicates that the five metals that most frequently exceeded risk-based screening criteria for potential human health concerns at DoD sites, in descending order of frequency, are lead, arsenic, cadmium, chromium, and antimony. The metals that most frequently exceeded ecological screening criteria, in order, are lead, cadmium, mercury, zinc, arsenic, chromium, and selenium. Although the majority of USEPA personnel interviewed indicated that human health risk, rather than ecological endpoints, generally drives remedial decision-making, the data indicated that ecological screening thresholds were exceeded more often than human health standards.     

Implementing Probabilistic Risk Assessment in USEPA Superfund Program

Application of probabilistic risk analysis to human health and ecological risk assessment is a young science. Probabilistic risk assessment (PRA), as exemplified by Monte Carlo Analysis (MCA), is more suitable to quantify the confidence or level of uncertainty in risk estimates compared with the traditional point estimate approach. Within the United States Environmental protection Agency (USEPA) the Office of Emergency and Remedial Response (OERR) is implementing PRA as part of the Superfund administrative reform activities. The OERR is completing a guidance document accompanied by a workbook. OERR is continuing its outreach effort to present PRA to the public and USEPA staff, and is organizing a training course. This paper presents an overview of the OERR's PRA implementation effort to date.     

U.S. EPA Reference Dose/Reference Concentration Methodology: Update on a Review of the Process

The U.S. Environmental Protection Agency (USEPA) has been reviewing several approaches to testing and risk assessment related to implementation of the Food Quality Protection Act (FQPA) and the Amendments to the Safe Drinking Water Act (SDWA), both signed into law in 1996. Based on recommendations from a review of issues related to children's health protection under these laws, the USEPA established the RfD Technical Panel to evaluate in depth the current reference dose (RfD) and reference concentration (RfC) process in general, and in particular with respect to how well children and other potentially sensitive subpopulations are protected. The RfD Technical Panel also was asked to consider scientific issues that have become of greater concern in RfD and RfC derivation (e.g., neurotoxicity, immunotoxicity), and to raise issues that should be explored or developed further for application in the RfD/RfC process. This paper provides the current status of the activities of the RfD Technical Panel. The Technical Panel has recommended that acute, short- term, and intermediate reference values should be set for chemicals, where possible, and that these values should be incorporated into the USEPA's Integrated Risk Information System (IRIS) Database. A review of current testing procedures is underway, including the endpoints assessed, life stages covered by exposure and outcome evaluation, and information that can be derived from current protocols on various durations of exposure. Data gaps identified for risk assessment include the types of pharmacokinetic data that should be collected, especially for developmental toxicity studies, the impact of aging on toxic responses occurring after early exposure as well as concomitant with exposure in old age, and information available on latency to response. The implications of the RfD Technical Panel's recommendations for various uncertainty factors are also being explored.     

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.     

Assessment of Carcinogenic Risk and Non-Carcinogenic Health Hazard from Exposure to Toxicants in Water from the Southwestern Coastal River System in Ghana

This study evaluated cancer risk and non-cancer human health hazard from exposure to the toxicants such as As, Cu, Pb, Zn, Mn, and CN in water from a southwestern river system in Ghana that drains through gold mining areas, using 108 water samples collected with random sampling techniques and analyzed in accordance with standard methods of chemical analysis outlined by the U.S. Environmental Protection Agency (USEPA). The concentrations of Cu and Zn were within World Health Organization and USEPA guideline values; Mn, free cyanide, As, and Pb values in most cases either exceeded USEPA and WHO values or both. The concentrations of the toxicants were used as input parameters in the cancer and non-cancer study that was conducted in line with USEPA risk assessment guidelines. The results of As cancer health risk revealed higher risk cases in two locations (Potroase and Dominase); non-cancer health risk for As was higher in 10 of the 14 locations, with other metals being of health concern at few locations in the study area. In conclusion, the findings of this study hold several policy implications as residents of mining communities still depend on these water bodies as their source of drinking water.     

Framework for Human Health Risk Assessment

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 Agency's Risk Assessment Forum has begun the long-term process of developing a framework for human health risk assessment. The framework will be a communication piece that will lay out the scientific basis, principles, and policy choices underlying past and current risk assessment approaches and will provide recommendations for integrating/harmonizing risk assessment methodologies for all human health endpoints.     

Bioavailability of Soil-borne Chemicals: A Regulatory Perspective

U.S. Environmental Protection Agency (USEPA) risk assessment guidance documents dating back to 1989 have articulated the principles for incorporating information on bioavailability into the risk assessment process. However, in the interim period both the methods for obtaining media or route specific measures of bioavailability and the corresponding guidance to incorporate these data have languished. Presently, USEPA is developing guidance to address both of these concerns. This article outlines the broad framework for systematically evaluating the role of bioavailability in site-specific risk assessment from a regulatory perspective. At the same time, in appreciation of the vast horizon of uncharted territory ahead, the focus of USEPA's draft guidance, and consequently this report, is on bioavailability adjustments for soil-borne metals. The article describes a two-stage process. The first stage outlines a paradigm for screening sites to determine if generating site-specific data on the bioavailability of a metal in soil is of technical utility and economically justifiable. The second stage focuses on the collection, analysis, and incorporation of these data into the risk assessment for decision-making purposes.     

Health Risk Assessments Based on Existing Data of Arsenic,Chromium, Lead,and Zinc in China's Air

Health risk assessments of As, Cr, Pb, and Zn in air in China were carried out from a national perspective. Concentrations of the four metals in air were gathered from published literature. Health risk assessment models recommended by the U.S. Environmental Protection Agency (USEPA) were applied to quantitatively characterize risk values of the metals by considering different age groups. Results showed that the atmospheric metal concentrations in most regions of China were lower than their inhalation reference concentrations provided by the USEPA, or limited values provided by China. Non-carcinogenic hazard values of the four metals in different regions of China were all lower than 1, indicating no or low non-carcinogenic hazard. However, the probabilities of carcinogenic risk values for As and Cr exceeding the acceptable value (1.0E-05) were 9% and 10% on a national scale, respectively. Some regions, such as Shanxi, Chongqing, Liaoning, and Shanghai, should be studied in more detail. Despite uncertainties, the results of this study provide information on the health risk of As, Cr, Pb, and Zn in air in China.     

The Value of Human Testing of Pesticides

Recently, the issue of using human volunteers as subjects for studying the potential toxicity of pesticides has received public attention through the media and subsequently in the regulatory arena. The debate has focused on whether such studies are ethical per se and if data from these investigations should be used for regulatory decisions. The precipitating event that prompted the current debate was the enactment of the Food Quality Protection Act (FQPA) of 1996. The FQPA, which amended the two laws governing the regulation of pesticides in the United States, requires the Environmental Protection Agency to reassess all of the nearly 10,000 tolerances (maximum allowable residues in food) and exemptions from tolerances that were in place when the law went into effect. When reassessing tolerances the U.S. Environmental Protection Agency (USEPA) reviews the data, including toxicology, available on each pesticide to determine if they are adequate to allow the Agency to make the necessary safety finding. Historically, it had been considered acceptable to conduct and use data from studies of exposure to chemicals (including pesticides) of human volunteers if these studies were conducted according to specific criteria as outlined in the Helsinki Declaration and Common Rule. Now this philosophy is being challenged and the USEPA is faced with answering the question of whether pesticides should be viewed as different, from an ethical standpoint, from other chemicals, and how such data should be used in the risk assessment process. The following paper makes an argument for the use of human volunteer testing of pesticides applying the logic that, if one wants to protect humans from the potential harm that may occur from eating foods containing pesticides, one must use the best possible data available. There can be little doubt that the best data for predicting the toxicity of a chemical in humans is to obtain and use human data, as long as it is obtained in an ethical manner.     

A Quantitative Ecological Risk Assessment of the Toxicological Risks from Exxon Valdez Subsurface Oil Residues to Sea Otters at Northern Knight Island,Prince William Sound,Alaska

A comprehensive, quantitative risk assessment is presented of the toxicological risks from buried Exxon Valdez subsurface oil residues (SSOR) to a subpopulation of sea otters (Enhydra lutris) at Northern Knight Island (NKI) in Prince William Sound, Alaska, as it has been asserted that this subpopulation of sea otters may be experiencing adverse effects from the SSOR. The central questions in this study are: could the risk to NKI sea otters from exposure to polycyclic aromatic hydrocarbons (PAHs) in SSOR, as characterized in 2001–2003, result in individual health effects, and, if so, could that exposure cause subpopulation-level effects? We follow the U.S. Environmental Protection Agency (USEPA) risk paradigm by: (a) identifying potential routes of exposure to PAHs from SSOR; (b) developing a quantitative simulation model of exposures using the best available scientific information; (c) developing scenarios based on calculated probabilities of sea otter exposures to SSOR; (d) simulating exposures for 500,000 modeled sea otters and extracting the 99.9% quantile most highly exposed individuals; and (e) comparing projected exposures to chronic toxicity reference values. Results indicate that, even under conservative assumptions in the model, maximum-exposed sea otters would not receive a dose of PAHs sufficient to cause any health effects; consequently, no plausible toxicological risk exists from SSOR to the sea otter subpopulation at NKI.     

Ecological Indicators in Risk Assessment: Workshop Summary

Ecological indicators can be defined as relatively simple measurements that relay scientific information about complex ecosystems. Such indicators are used to characterize risk in ecological risk assessment (ERA) and to mark progress toward resource management goals. In late 1997, scientists from the U.S. Environmental Protection Agency and from the Chemical Manufacturers Association (CMA) held a workshop to explore opportunities for collaborative research and scientific exchange on the development and application of ecological indicators. Several scientific challenges were identified as they relate to problem formulation, exposure and effects assessment, and risk characterization. Chief among these were a better understanding of multiple stressors (both chemical and non-chemical), characterization of reference sites and natural variability, extrapolation of measures to ecologically relevant scales, development of comprehensive, ecosystem-based models that incorporate multiple stressors and receptors, and a consistent system for evaluating ecological indicators.     

Noncancer Risk Assessment: A Probabilistic Alternative to Current Practice

Based on imperfect data and theory, agencies such as the United States Environmental Protection Agency (USEPA) currently derive “reference doses” (RfDs) to guide risk managers charged with ensuring that human exposures to chemicals are below population thresholds. The RfD for a chemical is typically reported as a single number, even though it is widely acknowledged that there are significant uncertainties inherent in the derivation of this number.

In this article, the authors propose a probabilistic alternative to the EPA's method that expresses the human population threshold as a probability distribution of values (rather than a single RfD value), taking into account the major sources of scientific uncertainty in such estimates. The approach is illustrated using much of the same data that USEPA uses to justify their current RfD procedure.

Like the EPA's approach, our approach recognizes the four key extrapolations that are necessary to define the human population threshold based on animal data: animal to human, human heterogeneity, LOAEL to NOAEL, and subchronic to chronic. Rather than using available data to define point estimates of “uncertainty factors” for these extrapolations, the proposed approach uses available data to define a probability distribution of adjustment factors. These initial characterizations of uncertainty can then be refined when more robust or specific data become available for a particular chemical or class of chemicals.

Quantitative characterization of uncertainty in noncancer risk assessment will be useful to risk managers who face complex trade-offs between control costs and protection of public health. The new approach can help decision-makers understand how much extra control cost must be expended to achieve a specified increase in confidence that the human population threshold is not being exceeded.     

Health risk assessment of heavy metals in groundwater of coal mining area: A case study in Dingji coal mine,Huainan coalfield,China

Heavy metals enrichment in groundwater poses great ecological risks to human beings. In the present research work, a total of 59 groundwater samples from 12 sampling points in Dingji coal mine, Huainan coalfield, were collected and measured for Cu, Pb, Zn, Cd, Ni, Mn, Cr, and Fe by inductively coupled plasma mass spectrometry (ICP-MS). The human health risk caused by heavy metals through the pathway of drinking water was evaluated and analyzed using the US Environment Protection Agency (USEPA) evaluation model. It has been found that the carcinogenic risk values were between 1.05 × 10^?5 and 3.5 × 10^?4, all exceeding the maximum acceptable level recommended by the USEPA, and the carcinogenic risk of Cr accounted for 99.67% of the total carcinogenic risk. The non-carcinogenic health risk values were all lower than the negligible level given by the USEPA, and the contribution of non-carcinogenic health risk was in the order of Cr > Zn > Cu / Pb >Mn > Fe > Cd > Ni. Among them, Cr had the largest contribution, accounting for 36% of the total non-carcinogenic risk value. In this study, the carcinogenic risk constituted 99.99% of the total health risk, indicating that the total health risk essentially consisted of carcinogenic risk. The research results suggest that much more attention should be paid to the health risk caused by Cr in the groundwater.     

Plan for an Integrated Human and Environmental Risk Assessment in the S. Domingos Mine Area (Portugal)

The need for the integration of the assessment of human and ecological risks in contaminated areas, such as derelict mines, widely increases. The risk assessment process is becoming a powerful tool to provide sound scientific bases for decision-making processes. In Portugal, the risk assessment process is in its early years and the lack of multidisciplinary teams of experts is frequently mentioned as the main obstacle to its implementation. Therefore, the majority of the reclamation actions are based on impact assessment studies that usually are characterized by few biological and toxicological considerations. In order to account for some of these constraints, the ecological risk assessment framework proposed by the U.S. Environmental Protection Agency was used to plan the assessment of human and ecological risks posed by the high concentrations of metals scattered in the vicinity of S. Domingos mine, a cuprous pyrite mine located in the Southeast Alentejo (Portugal). This study presents the problem formulation phase of the assessment. It includes all the scientific information available for the area, a conceptual model, and an analysis plan for the risk assessment process. Following a tiered approach, several tasks were planned in order to acquire chemical, toxicological, and ecological information, in order to compensate for the lack of toxicity data for site-specific species.     

Assessing Lead Risks at Non-Residential Hazardous Waste Sites

In 1996, the U.S. Environmental Protection Agency (USEPA) developed the Adult Lead Methodology (ALM) to provide an interim approach to assessing risks from non-residential exposures to lead. Because such exposures often involve occupational activities of adults, the ALM was directed at assessing soil-related lead risks to adults. Consistent with other approaches used in Superfund risk assessment, the ALM was designed to predict quasi-steady state blood lead concentrations (PbB) that might result from soil exposure. These predictions are converted to a risk estimate, expressed as the probability of exceeding a PbB level of concern. To examine the assumptions and variables in the ALM that have become available since 1996, a comparison was made of the attributes of seven alternative research models for which adequate documentation is available to understand and implement each approach. Several of these models have been used in regulatory decision-making; however, the USEPA has officially embraced none for general use. This analysis suggests that the ALM can continue to serve as a reasonable tool for assessing risks associated with non-residential exposures to soil. Under certain circumstances other models may be more applicable (i.e., for assessing acute or intensive exposures); however, the ALM is recommended for the majority of risk assessment applications.     

Adequacy Conditions for Reporting Uncertainty in Chemical Risk Assessments

Uncertainty may influence decision-making. A prerequisite for a decision to be well founded is thus that scientific experts inform decision-makers about all decision relevant uncertainty. A set of conditions is provided for adequate characterization of scientific uncertainty for the purposes of regulatory decision-making. These conditions require specification of (1) the character and degree of uncertainty about the assessment variables, (2) the possibility of reducing the uncertainty, and (3) the degree of agreement among experts. Furthermore, it is required that (4) the information covered by the previous conditions is presented in a clear and comprehensible way. The point of departure is that characterizing scientific uncertainty conceptually means specifying all potentially important possibilities that are consistent with the state of scientific knowledge. The conditions are intended to be applied to human health risk assessment of chemicals. However, the basic approach, to consider potentially important possibilities, should be useful also to environmental, and site-specific risk assessment.     

Evaluation and Spatial Diffusion of Health Risk of Persistent Organic Pollutants (POPs) in Soils Surrounding Chemical Industrial Parks in China

A case study of the cancer risk to humans posed by persistent organic pollutants (POPs) in an industrial area of China, which has a long history of contamination from many sources, is presented. Relatively great concentrations of POPs around the chemical industrial parks have the potential to be chronically carcinogenic to local people. Sixteen individual PAHs listed for priory control by the U.S. Environmental Protection Agency (USEPA), metabolites of DDTs, and isomers of HCHs were measured in soils and a human health risk assessment was conducted by use of USEPA exposure models for children and adults, respectively. Geostatistical methods were used to simulate the spatial diffusion of potential carcinogenic risk, and non-parametric Mann-Whitney U and Kruskal-Wallis tests were employed to analyze the impact of point sources on the surrounding area. The mean value of the sum of Excess Lifetime Cancer Risk (∑ELCR) exceeded the generally acceptable risk level of 1.0E-06 recommended by the USEPA for carcinogenic chemicals. The maximum ∑ELCR was 2.9E-04 for children, which was observed inside the chemical industrial parks. Contamination at the chemical industrial parks caused significant spatial diffusion of ELCR values caused by PAHs, DDT, and HCH.