Application of Systematic Review Methods in an Overall Strategy for Evaluating Low-Dose Toxicity from Endocrine Active Chemicals (2017) / Chapter Skim
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The task specified that the committee should perform systematic reviews of animal and human studies on at least two chemicals and demonstrate how the results can be integrated and considered with other relevant data to draw conclusions about causal associations. This report describes the strategy developed by the committee and highlights the role systematic review methods play in this overall strategy.
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T These include da on specifi chemicals, information that could ha implicatio for toxici ata ic ave ons ity-testing me ethods and best practices for EACs, and in p E nformation on endocrine-r n related disease in animals and humans. Such informatio could be obtained by conducting re on o c egular survey of the scien ys ntific literatur gathering input re, from stakeholders, and collecting in d nformation ab bout human ex xposure, for eexample, thro ough biomonit toring data, exter exposure measuremen and comp rnal e nts, putational mo dels that link external and internal expo k osure.
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Investigation and Analysis The committee outlines four main options for investigation and analysis aimed at understanding the potential human health effects from exposure to EACs at low doses: targeted analysis of existing data, generation of new data or models, systematic review of evidence, and integration of evidence. The approaches used should be selected on a case-by-case basis; in some cases one approach will be sufficient while in other cases several investigative approaches might be needed to adequately answer the questions.
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As shown in Figure S-1, several options for action could be appropriate, including updating chemical assessments, continuing to monitor for new data, updating toxicity-testing designs and practices, or requiring new data or models to reduce uncertainties. The type of action that EPA takes could be influenced by additional factors, including existing policies and regulations, the size of the population at risk, the public health significance of the human health effects, and available resources.
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However, the agency will also be faced with questions about the amount and quality of evidence needed in order to justify updating test methods, and these questions might be more appropriately addressed through policy decisions. IMPLEMENTING THE STRATEGY: EXAMPLE REVIEWS In its charge to the committee, EPA requested that the committee perform systematic reviews of animal and human studies on at least two chemicals and show how the results from the animal and human evidence can be integrated to draw conclusions.
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Hazard conclusion: In utero exposure to DEHP is presume to be a rep P ed productive haazard to humans. This connclusion mean that there was sufficien animal and human evide ns nt ence to allow the committe to ee conclude that DEHP is a potentia hazard to human health Identifying the potential of a chemica to e al h h.
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PBDEs are ubiquitous in the environment, and human exposure to them has been well documented. The committee conducted its own review of available animal studies and updated a recent systematic review of human studies conducted by Lam et al., which was shared with the committee in draft form.5 The review of the human studies evaluated effects on intelligence, attention deficit/hyperactivity disorder (ADHD)
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The committee conducted an updated literature search based on this review; finding no studies with substantively new findings, the committee determined that the conclusions of the Lam et al. systematic review would form a sufficient basis for the committee's work of integrating the available evidence.
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As with phthalates, it is difficult to directly compare PBDE exposure in animal studies to that occurring in humans because the majority of animal studies report only administered doses whereas human studies rely on the measurement of PBDEs in serum or other body fluids. Estimates of human daily intakes based on measurements of PBDEs in food and dust suggest that human exposure is several orders of magnitude lower than that achieved with benchmark doses estimated from the data or the meta-analysis of the animal studies on PBDEs.
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In particular, it is essential to have expertise in the conduct of meta-analyses and benchmark dose modeling. Findings Related to Integrating Evidence The committee found comparing evidence on dose-response relationships between animal and human studies to be challenging and imprecise because animal studies often report external administered doses (usually without measures of internal dose)
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