ENDOCRINE DISRUPTORS
QUESTIONS AND ANSWERS ABOUT U.S. ANIMAL TESTING OF
What does the term “endocrine disruption” mean?
Endocrine disruption refers to harmful effects on reproduction, development and/or health in
general resulting from chemically-induced interactions with the body’s hormone system. Since the
1962 publication of Silent Spring, there has been concern that chemicals in the environment could be
harmful to both wildlife populations and human health. The term “endocrine disrupter” was coined
in 1991 by former World Wildlife Fund scientist Theo Colborn, who reported that some
environmental chemicals can disrupt the body’s hormone system, and that effects of exposure during
development can be permanent and severe.
What kinds of substances have been identified as suspected endocrine
disruptors?
A range of synthetic as well as naturally occurring agents have been identified as potential endocrine
disrupters, including synthetic hormones, pesticides, compounds used in the plastics industry and in
consumer products, industrial by-products and pollutants, and even some naturally occurring
substances in plants.
What is the U.S. doing to address endocrine disruptor concerns?
In 1996, the U.S. Congress enacted the Food Quality Protection Act (FQPA),1 which introduced a
number of significant amendments to both the Federal Food, Drug and Cosmetic Act and Safe
Drinking Water Act, including a requirement that the Environmental Protection Agency (EPA)
“develop a screening program, using appropriate validated test systems and other scientifically
relevant information, to determine whether certain substances may have an effect in humans that is
similar to an effect produced by a naturally occurring estrogen, or such other endocrine effect as
[EPA] may designate.” Congress further directed that EPA “shall provide for the testing of all
pesticide chemicals” and “may provide for the testing of any other substance that may have an effect
that is cumulative to an effect of a pesticide chemical if [EPA] determines that a substantial
population may be exposed to such substance.” In practical terms, this Congressional mandate will
lead to substantial additional testing of nearly 5,000 pesticide active and other ingredients, and
possibly thousands of other high production volume chemicals and environmental contaminants.
How has EPA responded to this mandate?
Responsibility for developing a “toolbox” of validated screens and tests for the emerging testing
program has been delegated to the EPA’s Office of Science Coordination and Policy. EPA began by
establishing a multi-stakeholder Endocrine Disruptor Screening and Testing Advisory Committee
(EDSTAC) to provide the Agency with recommendations regarding:
 “Methods for chemical selection and priorities for screening”
 “A set of available, validated screening assays for early application”
1 http://www.fda.gov/opacom/laws/foodqual/fqpatoc.htm
HSUS / HSLF Fact Sheet 2
 “Ways to identify new and existing screening assays and mechanisms for their validation”
 “Processes and criteria for deciding when additional tests beyond screening would be needed
and how to validate such tests.”
In its final report to EPA in September 1998, 2 EDSTAC called for the scope of the so-called
Endocrine Disruptor Screening Program (EDSP)3 to be significantly expanded to encompass
chemical interactions with two or more additional endocrine hormones (androgen and thyroid, as
well as estrogen) in not only humans, but also in birds, fish, amphibians and invertebrates.
EDSTAC proposed a tiered testing framework to accommodate substances with differing amounts
of available data:
 Tier 1 would consist of a battery of relatively rapid, inexpensive, and largely mechanistic
screening assays, designed to detect chemical interactions with estrogen, androgen and
thyroid hormones in mammalian, amphibian and fish species
 In Tier 2, substances which appear, on weight-of-evidence, to be endocrine-active may then
be subject to multigenerational reproductive toxicity studies in up to five different
taxonomic groups.
Using the EDSTAC report as a road map, EPA established a Standardization and Validation Task
Force (which was later replaced by two similar committees4) to provide advice concerning the
scientific and technical work necessary to validate the recommended screens and tests. EPA has also
been working with other national governments through the Organization for Economic Cooperation
and Development (OECD) to validate endocrine screens and tests of international interest.5
What tests are being developed to identify endocrine disrupting substances?
Screens to detect chemical interactions with estrogen, androgen and/or thyroid hormones include the
following:
 Uterotrophic assay in rats or mice
 Hershberger assay in rats or mice
 Enhanced 28-day repeated dose toxicity study in rats
 Female and male pubertal assays in rats
 Intact male rat assay
 Amphibian metamorphosis assay
 Fish reproduction screen
 In vitro receptor-binding assays
 In vitro transcriptional/reporter gene activation assays
 In vitro steroidogenesis assays
 In vitro aromatase assays
Tests thought to provide more-definitive proof of harm to human and/or ecological health include
the following:
 2-generation reproduction study in rats
 2-generation reproduction study in birds
 2-generation reproduction study in frogs
 Fish full life-cycle test
 Mysid shrimp full life-cycle test
2 http://www.epa.gov/scipoly/oscpendo/pubs/edspoverview/finalrpt.htm
3 http://www.oecd.org/document/62/0,3343,en_2649_34377_2348606_1_1_1_1,00.html
4 http://www.epa.gov/scipoly/oscpendo/pubs/assayvalidation/edmvac.htm
5 http://www.oecd.org/document/62/0,3343,en_2649_34377_2348606_1_1_1_1,00.html
HSUS / HSLF Fact Sheet 3
How many animals are used in these screens and tests?
Tier 1 screening methods each consume between 20 and 80 animals6 (except for the in vitro methods,
which do not consume any animals), while Tier 2 reproduction/lifecycle tests each consume between
2,600 and 5,500 animals per chemical tested. It is estimated that for every chemical evaluated in
EPA’s Tier 1 battery, in excess of 360 animals will be consumed. Thus, to screen each of the roughly
5,000 pesticide chemicals as the FQPA requires would consume approximately 1.8 million animals.
Millions more could be consumed in follow-up Tier 2 testing of chemicals that yielded positive
results in Tier 1.
Won’t some of these tests already have been conducted on pesticides and
chemicals?
Yes. For most pesticide active ingredients, reproductive toxicity studies on rats, birds and
invertebrates, and lifecycle studies in fish, will already have been conducted, together with dozens of
other tests to characterize the substance’s potential toxicity.7 Thus, if a pesticide has already been
deemed safe on the basis of studies that are substantially equivalent to EDSP Tier 2 “definitive” tests
for endocrine disruption, it is highly doubtful that the results of Tier 1 screens (e.g., evidence of
binding to the estrogen receptor) or duplicate Tier 2 tests would lead to any change in the way a
pesticide or other substance is regulated.
Are animal tests accurate predictors of endocrine disrupting hazard to
people?
Not necessarily.8 A 2003 white paper commissioned by EPA documented that chemical effects on
the endocrine system can differ dramatically not only between animal species, but also between
strains of the same species.9 This raises serious doubt concerning the human relevance of test results
from rats or mice. Equally troubling are questions that have been raised as to whether OECD-run
studies to validate one or more animal tests has complied with the internationally agreed standards.10
What are some practical alternatives to animal testing?
A number of the screens that have been developed for use under the EDSP are in vitro (i.e., cell lines
and cellular components, such as isolated estrogen and androgen receptors), and could therefore
replace or reduce animal use in some cases if conducted as part of a “tiered” testing strategy (i.e., if
animal testing were undertaken only as a last resort). However, this is unlikely to be the case under
the EPA’s currently proposed “battery” approach, according to which all Tier 1 screens (animal and
non-animal) would be performed concurrently, thereby precluding any potential reduction in animal
use.
What is the status of testing under EPA’s EDSP?
In June 2007, EPA published a draft list of 73 chemicals to be subject to initial screening under the
EDSP, noting that “[t]he Tier 1 screening battery is expected to complete peer review and be ready
for use in early 2008.” Program implementation beyond this pilot phase (i.e., “the testing of all
pesticide chemicals,” per FQPA) will be left to the discretion of EPA’s Office of Pesticide Programs.
6 This estimate does not include the 270 or more mother rats and “surplus” offspring produced in for each pubertal assay,
nor the hundreds of eggs produced in the fish reproduction screens.
7 http://www.hsus.org/web-files/PDF/ARI/pesticides.pdf
8 http://www.hsus.org/animals_in_research/animal_testing/limitations-of-animal-methods.html
9 http://www.stopanimaltests.com/pdf/strain.slides.pdf
10 http://ecvam.jrc.it/publication/Esac%20statement%20on%20uterotrophic%20assay2.doc
HSUS / HSLF Fact Sheet 4
What is the Humane Society doing to help animals used in testing?
The Humane Society of the United States and Humane Society Legislative Fund are actively working
to end animal testing—permanently. We are working to promote greater reliance on available nonanimal
testing methods, and are actively supporting the vision of “twenty-first century toxicology”
articulated by the U.S. National Research Council, which would see animal tests that are decades old,
costly, slow and of dubious relevance to people replaced by ultra-modern, efficient and humanrelevant
non-animal methods.11 We are calling for a “big biology” project to meet this challenge, akin
to the Human Genome Project of the 1990s, and are forging an international, multi-stakeholder
consortium make this landmark vision a reality as quickly as possible.
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The Humane Society of the United States is the nation’s largest animal protection organization—backed by more than
10.5 million Americans. For over 50 years, HSUS has worked to reduce suffering and to create meaningful change for
animals in laboratories through public education, scientific outreach, legislative advocacy, and strategic partnerships.
Online at HSUS.org/research
The Humane Society Legislative Fund is a social welfare organization incorporated as a separate lobbying affiliate of
the HSUS. HSLF works to pass animal protection laws at the state and federal level, to educate the public about
animal protection issues, and to support humane candidates for office.
Online at HSLF.org
11 http://www.hsus.org/animals_in_research/animal_testing/hsus-projects/human_toxicology_initiative.html