Invited Perspective: Why Systematic Reviews, Scoping Reviews, and Evidence-to-Decision Frameworks Are Critical for Transparent, Consistent, Equitable, and Science-Based Decision-Making in Environmental Health

Systematic reviews were first developed in clinical medicine to evaluate the effectiveness of interventions.¹ Systematic review methods are now increasingly being used to inform environmental health decisions, and they have a direct, long-term effect on health equity due to improved consistency, greater transparency, and reduced bias when evaluating the scientific evidence.² For example, when divergent evaluations of a body of scientific evidence lead to conflicting conclusions on the harm of an exposure or the efficacy of an intervention, these empirically based methods increase transparency and comparability of the assessments, allowing end users to identify the reason for such divergence.^3,4 US agencies and academic scientists have developed, validated, and implemented several peer-reviewed systematic review methods, including the Navigation Guide^5,6 and the National Toxicology Program (NTP) Office of Health Assessment and Translation (OHAT) systematic review handbook,⁷ both of which have been used and endorsed by the National Academies of Sciences, Engineering, and Medicine.⁸

Despite the increasing uptake of systematic reviews in environmental health, ongoing development and the use of empirically based methods is necessary to ensure these reviews contain the elements required to minimize bias when evaluating the existing literature.² At the same time, however, systematic review is simultaneously being corrupted as agencies, including the Texas Commission on Environmental Quality (TCEQ) and the US Environmental Protection Agency (EPA), as part of implementing the amended the Toxic Substances Control Act, are appropriating the term in regulatory decision-making without meeting many of the standards of an empirically based systematic review.^4,9–12 This could result in rulemakings that underestimate the true risk of harm posed by toxic chemical exposures, which could have devastating implications for vulnerable populations, including low-wealth communities of color.¹¹

As reported in this issue of Environmental Health Perspectives, Sieck et al. conducted a systematic scoping review to examine the efficacy of various exposure-reduction interventions for two classes of toxic chemicals: phthalates and bisphenols.¹³ Several members of the phthalate and bisphenol chemical classes, which have been detected in nearly 100% of people living in the United States,^14,15 are associated with serious and irreversible health harms, including reproductive and developmental toxicity.^8,16–18 Because of the known or suspected toxicity of these chemicals and their widespread exposure in the human population, international, federal, and state agencies have implemented policies over the past several decades to mitigate human exposures, especially for susceptible subpopulations, such as infants, children, and pregnant people.

Sieck et al. found that certain policy interventions (e.g., restricting the use of phthalates and bisphenol A in specific consumer products and packaging) had the most widespread, long-term impact on exposure reduction across populations in the United States, the European Union, and Asia. In addition, individual-level interventions—including a) clinical interventions that removed certain bisphenols and phthalates from medical devices and equipment, and b) dietary interventions to encourage increasing consumption of fresh produce, reducing canned food use, and switching to nonplastic beverage containers—tended to lower exposures but were more burdensome on individuals, compared with policy interventions.

Reviews that follow the steps and principles of the empirically based systematic review to ensure transparency and consistency in evidence evaluation, like that conducted by Sieck et al., are critical to inform decision-makers of potential interventions to ameliorate chemical exposures. Findings of scoping reviews should not be used as a basis for policy recommendations; however, they can inform a rigorous evaluation of intervention effects using an empirically based systematic review. However, understanding the effectiveness of different policy options is just one factor that should be accounted for in the chemical regulatory process. Other factors should include essentiality of chemical use, environmental justice, and maximization of health benefits, including evaluating to whom the benefits of a policy accrue (e.g., distributional effects).¹⁹ Each of these factors is grounded on well-established principles articulated by the Montreal Protocol (essentiality),²⁰ the US EPA (environmental justice; maximization of benefits that reduce harms),^21,22 and Executive Order 14096, “Revitalizing Our Nation’s Commitment to Environmental Justice for All” (environmental justice; feasibility and acceptability).²³

When assessing the relative merits of potential interventions, decision-makers can use evidence-to-decision frameworks to consider explicit criteria, individually and in aggregate, to develop recommendations.²⁴ However, evidence-to-decision frameworks currently used in other areas of health policymaking globally fail to adequately consider these factors of essentiality, environmental justice, and maximization of benefits that reduce harms, which may ultimately hamper effective chemical regulation and perpetuate health disparities resulting from inequitable exposures.²⁴ These disparities are amplified in communities in the United States and throughout the world that are marginalized owing to several interacting factors, including systemic racism, historical residential segregation, and geographic placement of polluting facilities.^25–27 Latinx and Black communities—and other groups with relatively higher rates of poverty and lower levels of income and educational attainment than the national average—make up the greatest proportion of the estimated 134 million people living in the US within “vulnerability zones” that surround industrial sites that manufacture, store, or use toxic chemicals.²⁸

To effectively mitigate or prevent exposures to the trillions of pounds of chemicals manufactured and imported each year,²⁹ these factors should therefore be accounted for in a consistent, transparent, and unbiased evidence-to-decision framework that can guide chemical regulation and the development of the most health-protective intervention recommendations. In addition, the scientific information used to support such a framework, such as conclusions reached through systematic review, must be free from industry influence.¹⁹

For example, if a chemical is considered essential for manufacturing a lifesaving plastic product, then identifying safer alternatives and ways to minimize exposures for those individuals at greatest risk should be the priority of those responsible for developing the recommendations.¹⁹ If safer alternatives are not readily available, recommendations should be made for developing them. Potentially toxic chemicals that are used for non-essential items—such as Bisphenol A—should be banned immediately.³⁰ In addition, nonessential items that require the use of and release potentially toxic chemicals—such as polycarbonate water bottles³¹—also should be banned.

When considering the benefits and harms of an intervention, a successful evidence-to-decision framework would account for every known human and environmental health benefit, including co-benefits that may stem from an intervention.²² This was the case for the US EPA’s 2012 Mercury and Air Toxics Standards for power plants, which significantly reduced emissions of fine particles and mercury.^32–34 In addition, the distribution of the benefits and harms of an intervention should be prioritized over the net benefits to ensure the intervention will reduce risk and disease in those subgroups that have experienced historic and persistent harms from the exposure in question.

A successful framework would also incorporate structured input from impacted communities, who can inform considerations, such as feasibility and acceptability of the intervention.¹⁹ The US government has recognized the importance of considering environmental justice and the involvement of affected communities in federal decision-making, as per Executive Order 14096, which directs agencies to “identify, analyze, and address historical inequities, systemic barriers, or actions related to any Federal regulation, policy” and “provide opportunities for the meaningful engagement of persons and communities with environmental justice concerns who are potentially affected by Federal activities.”²³

As highlighted by Sieck et al., policy interventions can be highly effective at reducing toxic chemical exposures across the human population. Given the rapidly increasing global production of chemicals and the serious health harms associated with many chemical exposures,^35,36 we believe it is critical to widely implement an evidence-to-decision framework that considers the essentiality of the chemical, environmental justice, and the distribution of the benefits and harms of an intervention so as to ensure intervention recommendations that are more equitable and health protective.

Refers to https://doi.org/10.1289/EHP11760

Conclusions and opinions are those of the individual authors and do not necessarily reflect the policies or views of EHP Publishing or the National Institute of Environmental Health Sciences.