# Feminizing Frogs (DD-679)

> 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.

- Department: Nature (also Science)
- First published: 2025-12-14
- Last updated: 2025-12-14
- Permalink: https://detailenjoyer.com/case/feminizing-frogs/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## On the timeline

- **2004**: The EU stops allowing atrazine, largely because of groundwater limits
- **2024**: The EPA sets atrazine's aquatic level of concern at 9.7 µg/L

Full timeline: https://detailenjoyer.com/timeline/?case=feminizing-frogs

## Quick facts

- **DD-679-F01**: Hayes's 2002 study reported effects in frogs at 0.1 parts per billion of atrazine. _(Write-up · Exhibit B (The 2002 study))_
- **DD-679-F02**: The EPA's 2007 review found no consistent, reproducible gonadal effects. _(Write-up · Exhibit D (A contested result))_

## Write-up

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

1. **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. **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. **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. **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. **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.

## Related case files

- [Water Table Troubles (DD-071)](https://detailenjoyer.com/case/water-table-troubles/): Another case where groundwater is at stake
- [Turtle Torpor (DD-683)](https://detailenjoyer.com/case/turtle-torpor/): Another case about animals that live in water

## Reel vs. record

- **Note**: Presented as settled, but it's contested: the EPA's 2007 review of 36 studies found no consistent, reproducible effects on amphibian gonadal development. Hayes's lab studies (2002, 2010) did find them.
- **Missing specifics**: the key results come from lab-raised African clawed frogs (Xenopus laevis). Effects were reported at 0.1 ppb (2002), and at 2.5 ppb about 10% of genetic males became functional females (2010).
- **Missing context**: a 2010 review (Rohr & McCoy) found fairly consistent sublethal effects on fish and amphibians, such as on metamorphosis and immune measures, but not consistent mortality at environmental concentrations.
- **Missing regulation**: the EU hasn't approved atrazine since 2004. The US still registers it, and the EPA's 2024 aquatic level of concern is 9.7 µg/L, based on effects on aquatic plants.
- **Wording**: 'feminizing' fits the 2010 sex-reversal result, but the research is about hormones and gonads, not frog behavior or 'orientation', as some online claims put it.

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

- Duration: 20.6 s · Published: 2025-12-14
- File: https://detailenjoyer.com/assets/videos/DSP2s26EZoh.mp4

### Transcript

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!

## Questions & answers

**Q: What kind of chemical is atrazine?**  
A: 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)_

**Q: Which frog species was used in Hayes's lab studies?**  
A: 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)_

**Q: What share of exposed males became functional females in the 2010 study?**  
A: 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)_

**Q: What did the EPA's 2007 review conclude?**  
A: 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)_

**Q: Since what year has the EU not approved atrazine?**  
A: 2004. _(Source: Write-up · Exhibit E (Rules today) · US EPA (Jul 8, 2024): EPA announces update on atrazine)_

## Sources

- [Hayes et al. (2002), Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses, PNAS](https://doi.org/10.1073/pnas.082121499)
- [Hayes et al. (2010), Atrazine induces complete feminization and chemical castration in male African clawed frogs, PNAS](https://doi.org/10.1073/pnas.0909519107)
- [US EPA (2007): White paper on the potential for atrazine to affect amphibian gonadal development](https://archive.epa.gov/scipoly/sap/meetings/web/pdf/2007_amphibian_white_paper.pdf)
- [Rohr & McCoy (2010), A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians, Environmental Health Perspectives](https://doi.org/10.1289/ehp.0901164)
- [US EPA (Jul 8, 2024): EPA announces update on atrazine](https://www.epa.gov/pesticides/epa-announces-update-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/