The management of chemicals in commerce is a challenge for every country. The lexicon is a virtual alphabet soup of acronyms: TSCA, REACH, PFAS, VOCs, EDCs, EPA, ECHA, and EFSA, among many others.

The developed and developing worlds are striving to arrive at management approaches for chemicals that account for environmental, health, economic, and political factors. We are scientists engaged in advancing risk-based, weight-of-evidence methods to inform the complex decisions confronting policy makers, companies, and the public.

For the past several years, the Society of Environmental Toxicology and Chemistry (SETAC), the professional association for environmental professionals, has embarked on a global mission to build awareness of relevant, reliable, and practical approaches, including weight-of-evidence assessment, for characterizing chemical risks and supporting appropriate management strategies.

What is Weight-of-Evidence?

When it comes to managing the risk of chemicals, the phrase “weight-of-evidence” is frequently used, but what does it mean and why do we need it?

In short, it’s an approach for developing and combining relevant data on a chemical to provide an adequate, reliable basis for assessing its hazard and risk.

By hazard, we mean possible types of effects associated with exposures (i.e., dose-response relationships); by risk, we mean the likelihood of adverse human health and environmental effects associated with particular exposures to a chemical in the workplace and environment.

Management strategies are typically tailored to a chemical hazard, exposure, and/or risk. Developing sufficient scientific knowledge to inform these strategies involves step-wise procedures for building a weight of evidence approach concerning the hazard, exposure, and/or risk. Because of the large number of chemicals requiring assessment, there is great interest in scientific methods that begin with screening approaches and proceed as needed to more sophisticated and comprehensive analyses.

This progression is commonly organized into increasingly complex tiers.

To be reliable, the quality and adequacy of information at any level needs to be appropriate to support a determination or decision. A weight-of-evidence approach provides the needed underpinnings and the transparency necessary for communicating the information to scientists, regulators, and policy makers.

Many tools are available for assessing chemical toxicity.

Currently the emphasis is on tools that can quickly elucidate toxic mechanisms at the genomic and cellular levels. This is essential to deal with the many thousands of chemicals now in commerce as well as the thousands that will enter the marketplace in the future. Our challenge is to link such information with relevant effects on people, animals, and plants; For this, we organize information around Adverse Outcome Pathways (AOPs) which are supported and built from the available evidence.

Each type of test or measurement provides a snapshot or line of evidence on the possible impacts of a chemical, from initiation of effects as a result of exposure to ultimate health and environmental consequences.

We use formal weight-of-evidence approaches to organize, evaluate, and integrate the varied information to support a conclusion about the hazard and risk of a chemical. The weight depends on the quality and relevance of discrete pieces of information along with the nature and magnitude of effects. This type of synthesis can occur at any tier of the assessment.

A determination or decision to gather further information depends in large part on whether the weight of evidence assembled at a particular tier is adequate.

More Than 20% of Chemicals Challenging

Weight-of-evidence approaches have emerged in part due to the expanding role nonvertebrate-based bioassays play in hazard assessment—many of which look at small effects in the overall biological response to a chemical in an organism.

The approach has gained attention because of expanding chemicals management regulations in all parts of the world. In particular, there is a need to evaluate many complicated and difficult-to-test substances which presently make up approximately 21% to 25% of chemicals in commerce. These include the substances of unknown or variable chemical or biological composition (UVCBs) for which available test methods may not be adequate.

In a world where there are often disconnects between scientific information and environmental regulatory policy, we view the weight-of-evidence approaches as essential for communication. The transparency and orderliness of the methodology opens the information to wider audiences and can serve to inform regulators, policy makers, and the public about what is known and why scientists reach particular conclusions concerning hazard and risk. This information can be melded with other considerations that enter into decisions or help form views concerning the use and management of chemicals.

This column does not necessarily reflect the opinion of The Bureau of National Affairs, Inc. or its owners.

Author Information

Dr. Charles Menzie is the Global Executive Director for the Society of Environmental Toxicology and Chemistry and an internationally recognized expert on human health and ecological risk assessment.

Dr. Sarah Hughes is a Senior Ecotoxicologist for Shell Oil Company based in Houston, Texas providing expertise on the fate and effects of chemicals and contaminants to Shell’s upstream (exploration and production) and downstream (refining and chemical manufacturing) businesses.

Dr. Helena Assis is Titular Professor at Federal University of Parana, Brazil, chair of the Laboratory of Environmental Toxicology providing expertise in aquatic toxicology, past SETAC Latin America president, and a current member of the SETAC World Council.