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To:         EDSTAC Members

From:     Penelope Fenner-Crisp, Anthony Maciorowski, Gary Timm

Subject:  Definition of "endocrine disruptor"

We have been asked to clarify the U.S. EPA position on the definition of endocrine disruptors and the unresolved language in the 5/15/97 versions of the EDSTAC Conceptual Framework related to the options for interpreting the results of Tier 2 Testing (T2T).  This memorandum provides this clarification and some background and the current Agency position.


Various terms have been used to describe the phenomenon of "endocrine disruption."  As examples, environmental estrogens, environmental hormones, endocrine disrupting chemicals, endocrine modulators, endocrine disrupters, and endocrine disruptors are all in the scientific literature. Several definitions have also been published.

Kavlock et al (1996) published the EPA definition of an endocrine disruptors as:   "an exogenous agent that interferes with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body which are responsible for the maintenance or homeostasis, reproduction, development and or behavior."

At the European Workshop on the Impact of Endocrine Disrupters on Human Health and the Environment (European Commission 1997) the following definitions emerged:

"An endocrine disrupter is an exogenous substance that causes adverse health effects in an intact organism, or its progeny, secondary to changes in endocrine function."

"A potential endocrine disruptor is as substance that possesses properties that might be expected to lead to endocrine disruption in and intact organism."

At the Baltimore plenary, EDSTAC members grappled with a definition and the following definition was discussed:

"An exogenous substance that changes endocrine function and causes [adverse] effects at the level of the organism, its progeny, and/or (sub)populations of organisms."

However, consensus was not achieved on an EDSTAC definition.  Some constituencies felt strongly that "adverse effects" should be removed from the definition, whereas other felt strongly it should be retained.

Accordingly, we have been asked to provide the current Agency position on this issue.

Current Agency Position

The Environmental Protection Agency (1997) has adopted the definition found in Kavlock et al (1997) as presented above.  Consistent with this definition, the Agency has also stated that it "...does not consider endocrine disruption to be an adverse effect per se, but rather to be a mode or mechanism of action potentially leading to other outcomes, for example carcinogenic, reproductive, or developmental effects, routinely considered in reaching regulatory decisions. Evidence of endocrine disruption alone can influence priority setting for further testing and the assessment of the results of this testing could lead to regulatory action if adverse effect are shown to occur."

The current Agency position is consistent with a broad definition of endocrine disruption that must of necessity entail research questions, but also recognizes that regulatory decision-making is generally based on adverse effects using legislatively mandated risk-based criteria.

References for Proposed Definition

Kavlock, R.J., 1996. Research needs for risk assessment of health and environmental effects of endocrine disruptors: A review of the U.S. EPA-sponsored workshop.  Environ. Health Perspect.  104:715-740.

European Commission. 1997.  European Workshop on the Impact of Endocrine Disrupters on Human Health and the Environment. Environment and Climate Research Programme, DG XII, European Commission, Report EUR 17549.

U.S. EPA. 1997. Special report on Environmental Endocrine Disruption:  An Effects Assessment and Analysis.  Office of Research and Development, EPA/630/R-96/012, Washington D.C.

Options for Interpreting the Results of T2T

You may recall that the 5/15/97 draft of the Conceptual Framework contains four options for how to interpret the results of T2T.    These options were tied to the unresolved issue regarding the definition of endocrine disruptor (i.e., whether the definition would include adverse effects). The Agency proposes the EDSTAC resolve this issue by adopting option 4.  This option basically calls for the text for this portion of what is now Chapter 3 of the Draft Report to remain silent on how the results of T2T should be interpreted.

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