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Pesticide Action
Network Updates Service (PANUPS) Atrazine: Possible Cause of
Global Decline in Frogs?
Atrazine, the most commonly used
herbicide in the U.S. and possibly the world, causes an array of sexual
abnormalities including hermaphrodism (the development of both male and
female sex organs) according to a new study published in the Proceedings
of the National Academy of Sciences. The results may provide the key to
a global mystery. The U.S. Environmental Protection Agency (EPA) is now
in the process of evaluating the ecological impacts of atrazine, and we
are encouraging the public to send in comments (see below). For the last decade, scientists
have documented a worldwide collapse in frog populations, and some believe
that as many as 20 species are now extinct. Perhaps most surprising, frog
populations have collapsed even in very remote, pristine areas. While
the declines are well documented, the cause is a mystery; suggested culprits
have included global climate change, habitat destruction, toxics, predation
from introduced species and diseases. Now University of California at
Berkeley researcher Tyrone Hayes may have found a key cause that would
explain much of the decline. Atrazine, is used in over 80 countries,
and where it is used it is almost invariably found in streams, ponds and
lakes. In the U.S., it is found in virtually all waterways. "[It]
can be found in rain water, snow runoff, and ground water. There seems
to be no atrazine-free environment," says author Hayes. The reason
for this is simple: in addition to being widely used, it is also highly
mobile and persistent in the environment. The EPA estimates that the average
half-life of atrazine in aquatic environments is 167 days, and in the
cold waters of Lake Michigan, it is 31 years. Atrazine flows downstream
from farms where it is applied and is also picked up by winds and carried
to remote areas. The EPA notes that atrazine "was detected in more
than 60% of weekly rainfall samples taken in 1995 from agricultural and
urban sites in Mississippi, Iowa and Minnesota." While widespread atrazine pollution
in the U.S. is well documented, U.S. pesticide manufacturers have long
claimed that it is of little concern because the amounts normally found
in the environment produce few obvious effects in laboratory studies.
However, traditional toxicological studies use very high concentrations
of atrazine and look for gross abnormalities. Hayes's low-dose study,
documented subtle sexual abnormalities missed by traditional high-dose
atrazine studies. The results of the study, if confirmed, may pave the
way to a major rethinking of how toxicological assessments are done in
the United States. Atrazine is a known endocrine
disruptor. Endocrine disruptors cause developmental harm in extremely
low doses by interfering with hormonal triggers at key points in the development
of an organism. Hayes' study shows significant sexual abnormalities
at just 0.1 parts per billion (ppb)--30 times lower than levels
allowed by the EPA for drinking water and 120 times lower than the 12
ppb EPA guideline for the protection of aquatic life. The ubiquity of atrazine in the
environment combined with an explanation of how very low concentrations
might cause harm to frog populations could provide a key piece of information
to unravel the mystery surrounding the decline of frog populations worldwide.
The EPA periodically re-assesses
chemicals and is currently finalizing the ecological risk assessment for
atrazine. Though this document is supposed to consider all the major ecological
impacts, developmental impacts on frogs like those shown by Hayes'
paper are not considered in their risk assessment model. In fact, impacts
on amphibians are entirely ignored in their model, which only looks at
mammals, birds, fish, aquatic invertebrates and plants. The EPA's
conclusions, based on this flawed assessment are that "potential
effects [are] likely to be greatest where concentrations recurrently or
consistently exceed 10 to 20 ppb"--100 to 200 times the concentrations
where significant sexual abnormalities were observed in Hayes' study.
Though Hayes' results are mentioned elsewhere in the assessment,
these risk assessment models are expected to form the basis of any EPA
regulatory action. * Write the EPA and urge them
to include the developmental impacts of atrazine on amphibians in their
risk assessment models. The EPA's "Environmental Fate and Effects
Revised Risk Assessment" for atrazine states that: "One of the
most important steps in problem formulation is the selection of the endpoints
upon which the ecological risk assessment is to be based." By excluding
developmental impacts on frogs, this document fails to accurately assess
the likely impacts of continued atrazine use. Comments should reference the
docket number (OPP-34237C) in the subject and must be received by EPA
on or before July 5, 2002. Comments can be sent via email or mail. Email: opp-docket@epa.gov Public Information and Records
Integrity Branch, Document Number in Subject Line:
OPP-34237C Background information on atrazine
can be found on the EPA's atrazine re-registration Web page at: http://www.epa.gov/pesticides/reregistration/atrazine/ For further information on the
EPA assessment of atrazine see: http://www.epa.gov/oppsrrd1/reregistration/atrazine/efed_redchap_22apr02.pdf For further chemical information
on atrazine see: http://www.pesticideinfo.org/PCW/Detail_Chemical.jsp?Rec_Id=PC35042 For further information on frog
declines see: http://dlp.cs.Berkeley.edu/aw/declines/ Sources: "Feminized Frogs: Herbicide disrupts sexual groups," Science News Online, April 20, 2002, Vol. 161, No. 16, http://www.sciencenews.org/20020420/fob1.asp; Hayes, T.B., et al. 2002. "Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses." Proceedings of the National Academy of Sciences, Vol. 99:5476-5480, April 16, 2002, http://www.pnas.org/cgi/content/full/99/8/5476; "Popular weed killer demasculinizes frogs, disrupts their sexual development, UC Berkeley study shows," UC Berkeley press release, April 15, 2002; "Amphibian Declines: An Issue Overview" jointly published by the Federal Taskforce on Amphibian Declines and Deformities (TADD), Partners in Amphibian and Reptile Conservation (PARC), the Declining Amphibian Populations Task Force (DAPTF), and the Amphibian Conservation Alliance (ACA), http://elib.cs.berkeley.edu/aw/declines/declines.pdf; and "Reregistration Eligibility Science Chapter for Atrazine, Environmental Fate and Effects Chapter," April 22, 2002, http://www.epa.gov/oppsrrd1/reregistration/atrazine/efed_redchap_22apr02.pdf. Contact: PANNA. |
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