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Feminizing Frogs

Short answer: Atrazine is a weedkiller widely used on US corn, sorghum and sugarcane.

In 2002, Tyrone Hayes's lab at UC Berkeley reported that male African clawed frogs (Xenopus laevis) raised in water with as little as 0.1 parts per billion of atrazine developed gonadal abnormalities, including hermaphroditism, and smaller larynxes. A 2010 study from the same lab found that exposed genetic males were demasculinized, and about 10% developed into functional females that laid eggs. Other labs, including studies funded by the manufacturer, did not consistently reproduce these effects. In 2007, the US EPA weighed 36 studies and concluded that atrazine does not produce consistent, reproducible effects on amphibian gonadal development. A 2010 review by Rohr and McCoy found fairly consistent sublethal effects on fish and amphibians, such as on metamorphosis and immune measures. The EU hasn't allowed atrazine since 2004, largely because of groundwater limits. The US still permits it, and in 2024 the EPA set its aquatic level of concern at 9.7 µg/L, based on aquatic plant communities.

VideoWrite-up5 sources
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What should you know about Feminizing Frogs?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Hayes's 2002 study reported effects in frogs at 0.1 parts per billion of atrazine.

    DD-679-F01 · Write-up · Exhibit B (The 2002 study)

  2. The EPA's 2007 review found no consistent, reproducible gonadal effects.

    DD-679-F02 · Write-up · Exhibit D (A contested result)

Video transcript: Feminizing Frogs: A Weedkiller vs. Frog Hormones

DID YOU KNOW? Atrazine a widely used herbicide, has been linked to significant effects on amphibians, particularly frogs. Studies have shown that exposure to atrazine, even at low concentrations, can disrupt endocrine function leading to abnormal sexual development such as hermaphroditism, demasculinization of males, and reduced fertility. It can also interfere with growth, immune function, and behavior. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 20.6s Reel ·

Video coming soonFeminizing Frogs · Instagram Reel
Feminizing Frogs: A Weedkiller vs. Frog Hormones Instagram Reel · · 20.6s

The write-up

A weedkiller vs. frog hormones. Lab studies link atrazine to intersex frogs; regulators disagree.

  1. Exhibit A

    The herbicide

    Atrazine is one of the most widely used weedkillers in the US, mainly on corn, sorghum and sugarcane. Runoff carries it into streams and ponds.

  2. Exhibit B

    The 2002 study

    Hayes and colleagues reported that male African clawed frogs (Xenopus laevis) raised in water with as little as 0.1 ppb of atrazine developed gonadal abnormalities, including hermaphroditism, and smaller larynxes.

  3. Exhibit C

    Full sex reversal

    A 2010 study by the same group found that male frogs exposed to 2.5 ppb were demasculinized, and about 10% developed into functional females that mated and laid eggs.

  4. Exhibit D

    A contested result

    The EPA's 2007 review of 36 studies concluded atrazine does not cause consistent, reproducible effects on amphibian gonads. A 2010 review by Rohr and McCoy found fairly consistent effects on other endpoints, such as metamorphosis and immune measures.

  5. Exhibit E

    Rules today

    The EU hasn't approved atrazine since 2004. In the US it's still registered, and in 2024 the EPA revised its aquatic level of concern to 9.7 µg/L (60-day average), based on aquatic plant communities.

Questions people ask about Feminizing Frogs

What kind of chemical is atrazine?

It's a widely used weedkiller.

Source: Write-up · Exhibit A (The herbicide) · US EPA (Jul 8, 2024): EPA announces update on atrazine; Rohr & McCoy (2010), A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians, Environmental Health Perspectives

Which frog species was used in Hayes's lab studies?

Xenopus laevis, the African clawed frog.

Source: Write-up · Exhibit B (The 2002 study) · Hayes et al. (2002), Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses, PNAS

What share of exposed males became functional females in the 2010 study?

About 10%.

Source: Write-up · Exhibit C (Full sex reversal) · Hayes et al. (2010), Atrazine induces complete feminization and chemical castration in male African clawed frogs, PNAS

What did the EPA's 2007 review conclude?

It found no consistent, reproducible effects on gonads.

Source: Write-up · Exhibit D (A contested result) · US EPA (2007): White paper on the potential for atrazine to affect amphibian gonadal development; Rohr & McCoy (2010), A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians, Environmental Health Perspectives

Since what year has the EU not approved atrazine?

2004.

Source: Write-up · Exhibit E (Rules today) · US EPA (Jul 8, 2024): EPA announces update on atrazine

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. What kind of chemical is atrazine?

    1. A herbicide
    2. An antibiotic
    3. A fertilizer
    4. A food dye
    Show the answer

    Answer: A. A herbicide It's a widely used weedkiller. Source: Write-up · Exhibit A (The herbicide) · US EPA (Jul 8, 2024): EPA announces update on atrazine; Rohr & McCoy (2010), A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians, Environmental Health Perspectives

  2. Which frog species was used in Hayes's lab studies?

    1. African clawed frog
    2. Poison dart frog
    3. Bullfrog
    4. Glass frog
    Show the answer

    Answer: A. African clawed frog Xenopus laevis, the African clawed frog. Source: Write-up · Exhibit B (The 2002 study) · Hayes et al. (2002), Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses, PNAS

  3. What share of exposed males became functional females in the 2010 study?

    1. About 10%
    2. About 50%
    3. About 90%
    4. None
    Show the answer

    Answer: A. About 10% About 10%. Source: Write-up · Exhibit C (Full sex reversal) · Hayes et al. (2010), Atrazine induces complete feminization and chemical castration in male African clawed frogs, PNAS

  4. What did the EPA's 2007 review conclude?

    1. No consistent, reproducible gonadal effects
    2. Atrazine should be banned
    3. Atrazine kills frogs outright
    4. Only fish are affected
    Show the answer

    Answer: A. No consistent, reproducible gonadal effects It found no consistent, reproducible effects on gonads. Source: Write-up · Exhibit D (A contested result) · US EPA (2007): White paper on the potential for atrazine to affect amphibian gonadal development; Rohr & McCoy (2010), A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians, Environmental Health Perspectives

  5. Since what year has the EU not approved atrazine?

    1. 2004
    2. 1984
    3. 2014
    4. 2024
    Show the answer

    Answer: A. 2004 2004. Source: Write-up · Exhibit E (Rules today) · US EPA (Jul 8, 2024): EPA announces update on atrazine

Cite this case file

Easterling, Marcus. "Feminizing Frogs." The Detail Department (DetailEnjoyer), case file DD-679, last updated Dec 14, 2025. https://detailenjoyer.com/case/feminizing-frogs/

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