On January 7, 2016, the U.S. Environmental Protection Agency (EPA) announced in the Federal Register the beginning of a 45-day comment period on the peer review draft of the Guidelines for Human Exposure Assessment (draft Guidelines). According to EPA, the draft Guidelines benefit from over two decades of experience with assessments conducted by EPA programs under their respective authorities and constraints, as well as from input from external panels, including the National Academy of Sciences (NAS) and EPA’s Science Advisory Board. The draft Guidelines build on topics covered in the 1992 exposure guidelines, including planning and scoping for an assessment, data acquisition and use, modeling, and considerations of uncertainty in exposure assessment. Importantly, the draft Guidelines also include new material on planning and conducting an observational human exposure measurement study and considerations of life stages and sensitive populations in exposure assessments. EPA states that the draft Guidelines “present the most current science used in EPA exposure assessments and incorporates information about the Agency’s current policies.” Comments are due February 22, 2016.
Draft Guidelines
EPA states that the draft Guidelines’ focus is on human exposure to chemical agents (stressors) in the non-occupational environment. The exposed populations (e.g., receptors) to which the draft Guidelines refer are adults and children or other vulnerable groups within the human population. The draft Guidelines are organized in chapters, each of which explores a component of the exposure assessment process.
| ■ | Chapter 1: Introduces the draft Guidelines and discusses the purpose and scope of the document; |
| ■ | Chapter 2: Provides a general review of exposure science concepts and principles, including approaches and tools, that can be considered when planning and conducting exposure assessments. Topics include an overview of exposure science, the role of exposure assessment in the risk assessment process, concepts and types of exposure assessments, equations and input variables for estimating exposure, presentation of exposure assessment findings, and a brief history of exposure science. The draft Guidelines state that exposure characterization “is an important step in all exposure assessments,” and guidance regarding the synthesis of exposure information is presented. |
| ■ | Chapter 3: Describes a process for planning and scoping and problem formulation for an exposure assessment that builds on EPA’s 1997 Guidance on Cumulative Risk Assessment: Part I. Planning and Scoping, 2002 Lessons Learned on Planning and Scoping for Environmental Risk Assessment, and 2014 Framework for Human Health Risk Assessment to Inform Decision Making. The draft Guidelines emphasize the importance of: establishing goals and objectives; building an interdisciplinary team; developing a conceptual model; identifying assessment options, available resources, and data needs; producing an overall assessment plan; engaging and involving appropriate stakeholders; engaging and involving the community; establishing data quality objectives; and conducting peer review. |
| ■ | Chapter 4: Discusses how life stages, vulnerable groups, and populations of concern could be at increased risk for adverse health effects from environmental contaminants due to disproportionate exposure, varied responses to exposure, or both. Consistent with EPA’s 2003 Framework for Cumulative Risk Assessment, the draft Guidelines state that exposure assessors need to be aware of environmental justice issues, including unique population characteristics and sociodemographic factors that might increase exposure or predispose a life stage, vulnerable group, or population to greater risk. This chapter assembles other existing EPA guidance, along with examples of case studies, to discuss where techniques and considerations associated with life stages, vulnerable groups, and populations of concern can be applied in exposure assessments. |
| ■ | Chapter 5: Discusses data used for exposure assessments, including determining what data are needed; whether data are currently available and the quality of the available data; and when data are not available, whether data need to be developed. According to the draft Guidelines, understanding data availability, applicability, characteristics, quality issues, and limitations is critical to conducting a scientifically sound exposure assessment. This chapter discusses guidance on the assessment of data uncertainty and variability, and also emphasizes the importance of transparency and communication of findings to the risk manager/decision maker and stakeholders. |
| ■ | Chapter 6: Highlights basic concepts in modeling, including the principles of the modeling process. It provides an overview of modeling for exposure assessment, outlines the criteria for choosing appropriate models based on the goals and data quality objectives, and describes how to evaluate a model that might be useful for an exposure assessment. This chapter also includes information on modeling inventories and clearinghouses and resources that support the use of models of various levels of complexity. |
| ■ | Chapter 7: Provides details on planning an observational human exposure measurement study. The draft Guidelines state that parts of EPA use these studies to quantify people’s exposures to chemicals in their everyday environments during their normal daily activities. They involve measurements of chemical, biological, or physical agents in environmental media; collection of information about the study participants and their homes, work environments, and activities; and collection of personal exposure and biological samples. This chapter discusses the aspects surrounding planning an observational human exposure measurement study, including budget and logistical planning, establishing a study design, planning and executing both a pilot study and a full field study and the importance of conducting peer review. It also addresses ethical considerations that exposure assessors need to consider when interacting with study participants and the community. |
| ■ | Chapter 8: Considers uncertainty and variability in exposure assessments, incorporating them into planning and scoping and problem formulation (Chapter 3) and data (Chapter 5). This chapter highlights how these concepts are used in the application of models in an exposure assessment. It also provides information that exposure assessors can consider in developing communication strategies for presenting the results of uncertainty and variability analyses to interested individuals, including participants, stakeholders, and the public. |
| ■ | Chapter 9: Brings communication concepts together into a final communication strategy with more specific information. This chapter emphasizes the importance of identifying the intended audience, the types of communication products, communication strategies that might be appropriate for different exposure assessments, and related ethical considerations. |
| ■ | Chapter 10: Provides references for all cited documents. |
Next Steps
EPA states that it is seeking public comment on the draft Guidelines prior to external peer review. The draft Guidelines will undergo review during an expert peer review meeting that an independent contractor will convene, organize, and conduct. EPA will announce the date and location of the peer review meeting in a subsequent Federal Register notice. EPA will share all comments received by February 22, 2016, with the peer review panel for their consideration. According to the notice, EPA may consider comments received after the close of the comment period when it prepares the final Guidelines.
Commentary
The draft Guidelines represent EPA’s effort to incorporate developments in the risk assessment area since the first version of the guidance was released in 1992. The documents used as the primary source for this update are listed on page 1 of the draft Guidelines. The organization from the earlier version is retained for the most part in the current version. The original version consisted of seven chapters plus references. The recent version consists of nine chapters plus references. Some notable differences are chapter four, “Consideration of Lifestages, Vulnerable Groups and Populations of Concern in Exposure Assessments” and chapter seven, “Planning and Implementing an Observational Human Exposure Measurement Study.” These topics are only briefly mentioned in the original version.
The focus of the new draft Guidelines, as noted, is on human exposure to chemicals in the non-occupational environment. One could argue, however, that the updated conceptual framework accommodates occupational exposure assessments and that the same principles extend to occupational receptors.
EPA’s effort in revising the guideline appears to consist of careful editing of the older text and integration of selected material from the sources listed on page 1. On first review, there appears to be little or no new/original concepts that resulted from this integration of existing sources. Given that most if not all of the cited sources were peer reviewed when developed, one wonders whether the peer reviewers for the 2015 document will focus on science issues or subjects like organization, readability, usefulness, and related factors. Also surprising is that the revision, beyond a general discussion of the concept, does not include case studies as a way of illustrating how the newer approaches improve development or increase the utility of exposure assessments. Even if the updated guidance does not advance the science, it could be a useful source given the way it consolidates information over time and reflects the experience derived from application of these newer approaches in EPA programs, in particular those administered by the Office of Pesticide Programs, the Office of Land and Emergency Management (formerly the Office of Solid Waste and Emergency Response), and the Office of Air and Radiation.
The updated guidance effectively follows the NAS recommendation to formalize planning, scoping, and problem formulation (concepts that had been articulated earlier in several EPA guidance documents) as part of the design of EPA risk assessments. The incorporation of these elements resulted in guidance with an increased focus on characterization of the receptor (exposed population) — as opposed to sources — and a better integration of the exposure assessment component into the overall risk assessment framework. The adoption of these elements is perhaps the most significant change in the conduct of exposure assessments.
The updated version includes harmonized definitions for basic parameters, including exposure and dose. It would be helpful to include a description of the changes to these definitions relative to those found in the 1992 version to clarify these changes in the context of the subsequent section on exposure estimates. Both versions use the same equations to calculate exposure estimates except that the updated guidance refers to the outputs as exposure while the older version identifies them as dose.
On page 12, the draft Guidelines state appropriately that the “…exposure measures need to match the dose measures used in the toxicity test to enable direct comparison between the exposure of human populations and potential [suggested insertion] health outcome data,” e.g., inhalation exposure matched with inhalation test data. This statement could be expanded to make clear that exposure measures, pertinent to the exposure scenario(s) of interest, should be used to identify the most appropriate test data from a given toxicity data set or, if it is necessary to conduct testing to inform the risk assessment, to guide selection of test methods.
Chapter 4, “Consideration of Lifestages, Vulnerable Groups and Population of Concern in Exposure Assessments,” provides resources to support implementation of the receptor-based approach formalized in the updated draft Guidelines. The populations highlighted in this chapter include children, tribal groups, and socioeconomically disadvantaged groups (environmental justice). Some of the details appear to be outside the context of an exposure guidance document, such as the description of the Gini and Atkinson indices that may be more appropriate for use in the broader context of risk assessment/management considerations. The narrative in Chapter 4 is frequently dominated by detailed descriptions of the parent programs — children, tribal, and related groups. An effort should be made to streamline this chapter and bring the focus back to issues relevant to exposure assessment, specifically its role in supporting and informing risk assessment and risk management. Understanding that it is frequently difficult to dissociate the exposure narratives from the larger context of a risk assessment or risk management action, it would be helpful to include one or more case studies of EPA actions to illustrate how the combination of all these factors have been used in the risk assessment/risk management step to identify and select potential remedies for such vulnerable populations. These additions of case study or similar illustrative descriptions would help make these specialized areas of exposure more user-friendly by placing the exposure work conducted in terms of the revised framework.
Chapter 7, “Planning and Implementing an Observational Human Exposure Measurement Study,” offers a summary of methods and resources for conducting human observational studies. This chapter describes a complicated, highly regulated process. It would be useful if this chapter would include discussion of the EPA programs that are currently conducting studies of this type and briefly summarize the impetus for the study and status of such efforts. In addition, recognizing that as EPA programs use published human data to conduct risk assessments, the authors could use this chapter to alert and inform EPA assessors and others about restrictions that apply to the use of existing human data — whether submitted by a third party or publically available — in EPA programs. Typically, an ethics review focused on the conduct of the study is required to determine acceptability of publicly accessible human data. This is relevant because the latter is perhaps the more frequent and commonly used source of human data in chemical risk assessment.