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Synopsis of the study
Using Human Data in Risk Assessment
To Protect Public Health*
by
Michael Dourson
Toxicology Excellence for Risk Analysis
Melvin Andersen
Colorado State University
Linda Erdreich
Exponent
Judith MacGregor
Toxicology Consulting Services
The use of human data in the assessment
and management of risk was studied. Although the use of such data has a
long and successful history with environmental contaminants and the
development of drugs and commercial chemicals, recent deliberations within
the Environmental Protection Agency (EPA) have questioned this practice in
part. Specifically, we evaluate the degree to which animal data change
risk estimates derived from human data by comparing human-based Reference
Doses (RfDs) and Reference Concentrations (RfCs) from EPA's Integrated
Risk Information System with similar risk values estimated from animal
data.
Human-based risk values are lower than animal derived values for 27% of
the comparisons when precision is considered (defined as with uncertainty
spanning perhaps an order of magnitude). Without considerations of
precision, human based risk values are lower than corresponding
animal-based values for 39% of the RfD and RFC comparisons. Furthermore,
for 10 out of 43 possible comparisons, insufficient animal data are
readily available or data are inappropriate to estimate either RfDs or
RfCs.
At the outset a series of questions were asked regarding the use of human data for risk assessment, as follows:
- Is information from human studies the best way to judge the
potential health risk from chemicals in our environment?
The answer is perhaps given best by the many health organizations that address this question. For example, Health Canada, IPCS and U.S. Agencies that we discussed each prefers the use of human data rather than animal data in the development of risk values. Based on our analysis we also agree. The use of human data has led to the estimation of risk values that are often lower than animal-based risk values. Especially in these cases, the use of these human-based risk values is better protective of public health.
- Should public health agencies strive to resolve the ethical
questions and identify criteria to foster the conduct of human studies
that might lead to better protection of public health?
We hope that the answer to this question is a resounding yes. Our analysis, although limited, suggests a high percentage of comparisons where the exclusive use of animal data would lead to risk values that do not protect public health. Moreover, in many cases the animal data were recognized as having greater limitations than the existing human data, as reflected in generally larger uncertainty factors than those used with existing human data.
- Should scientists ignore available human data that might suggest
a lower or higher risk value?
The obvious answer here is no. Protecting public health is why we all do this work. However, it seems reasonable for scientists and regulatory agencies to further evaluate the use of human data in the development of risk values. Perhaps new criteria could be developed so that such data can be used with greater confidence.
* This synopsis was provided by Michael Dourson. To access the full text of the paper, which has been submitted to Toxicological Sciences for possible publication but is currently available on the Toxicology Excellence for Risk Analysis web site, go to http://www.tera.org/, select the "News" button, and look for the paper's title. An outline of the study (in HTML) and the human data interim results (in PDF) are also available.
Posted August 3, 2000.
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