NRDC Recommends Improvements to Chemical Risk Assessment Methods

Chemical Risk Assessment: 

Readers following efforts to improve chemical management and control in the United States may be interested in a recent National Resources Defense Council (NRDC) White Paper, Strengthening Toxic Chemical Risk Assessments to Protect Human Health.  In the White Paper, NRDC reaches several conclusions in reliance on National Academy of Sciences (NAS) findings that significant improvements in both chemical testing and risk assessment are needed to protect people from toxic chemicals.  NRDC emphasizes the need to address the following:

  • the range of human exposures and vulnerabilities,
  • data gaps and uncertainties, and
  • impacts of exposure to multiple chemicals.

NRDC also argues that risk assessment should not presume that a zero effect exposure level exists, unless there are sufficient data to support this assumption.

Each of NRDC’s points is discussed further below.

Citing the NAS findings, NRDC concludes that differences among human exposures and individual vulnerabilities are important determinants of risk.  NRDC therefore recommends that risk assessment consider vulnerable individuals and those who are more highly exposed.  NAS had noted that a broad variety of factors, including nutrition, health status, and psychosocial stress, can increase and individual’s vulnerability to toxic chemicals, and these factors—and their variability—need to be incorporated into risk assessments so that adequate measures can be employed to protect public health.  NRDC also cites an NAS recommendation that risk assessments incorporate analyses that address the uncertainty and variability inherent in a risk assessment—including uncertainty and variability in the measurement of chemical releases into the environment, environmental fate and transport, exposure assessment, dose-response assessment, and risk characterization.  

To address data gaps and uncertainties, NRDC stresses the need for agencies to develop robust risk assessments by updating default factors and assumptions.  It cites the NAS recommendation that agencies update risk assessment protocols based on the best current science.  NAS had identified significant missing default assumptions.  For example, most chemicals are not tested for their potential interference with the hormone systems that govern growth and development, learning, and behavior; the assumption being that chemicals have no effect on hormones—an implicit default assumption that may or may not be true.  And, NRDC noted, allowing such assumptions does not protect health.

NRDC emphasizes the need to address the impacts of multiple chemical exposures.  It faults risk assessment methodologies that focus on only single chemical exposure, rather than endeavoring to model the actual complexity of the world.  NRDC relies on a NAS finding that stressed the need for cumulative risk assessments that address the combined risks posed by aggregate exposure to multiple agents or stressors.  

And finally, the NRDC challenges the standard assumption that there is a safe level of exposure to most chemicals.   NRDC notes that NAS recommends risk assessments assume that all exposures, even low level, are associated with some level of risk, unless there are sufficient data to the contrary.  NRDC explains that science has found many examples of chemicals that increase the risk of various non-cancer health effects—such as reproductive harm and neurological effects—at low doses, without any scientifically-identifiable threshold.

For more information see the NAS reports: