Exposure to pesticides during childhood may quietly alter one of the most important milestones of adulthood.
Researchers in Spain found that exposure to two common compounds associated with pesticides was linked to changes in the timing of the menstrual cycle. One was associated with an earlier first period, while the other was associated with a later period. The findings suggest that chemicals capable of disturbing hormonal activity may affect puberty in different and sometimes conflicting ways.
The study published in Environmental researchin which 506 girls participated in the INMA (Childhood and Environment) Collaborative Birth Cohort Study. Researchers from the University of Granada and the ibs.granada Institute for Biomedical Research followed participants from Asturias, Guipuzcoa, Sabadell and Valencia.
Urine samples were collected between 2013 and 2016, when the girls were 7 to 10 years old. The researchers used those samples to look for compounds that are produced during the body’s processing of many pesticides. They then followed the girls until they were 14-16 years old and recorded when each participant had her first menstrual period.
Two chemicals, opposing effects
The most notable finding concerns ethylene thiourea (ETU), a residue associated with dithiocarbamate fungicides. Girls with higher ETU concentrations tend to experience menarche (first menstruation) at a younger age.
ETU can interfere with thyroid function. Because thyroid hormones help coordinate growth, metabolism and development, researchers suspect that this imbalance could affect the biological signals that control the onset of puberty.
A different pattern emerged for TCPy, a substance formed when the body breaks down the insecticide chlorpyrifos. Girls in whom TCPy is detected usually start menstruating later. This association was particularly notable among participants who were overweight or obese, suggesting that body composition may influence how exposure to chemicals affects growth.
How endocrine disorders affect development
Puberty depends on a carefully coordinated exchange of signals between the brain, ovaries, thyroid, and other parts of the endocrine system. Endocrine disruptors can interfere with this communication by mimicking hormones, blocking them, or changing how they are produced and processed. Exposure may be especially important during childhood, when the reproductive system is still developing.
The timing of first period is more than just a developmental milestone. Early menarche has been associated with emotional and psychological difficulties during adolescence, as well as a higher risk of hormone-dependent cancer, including breast cancer, later in life. Delayed puberty may also indicate developmental disorders, although its causes and consequences can vary greatly.
Chlorpyrifos and several dithiocarbamate fungicides, including mancozeb and manib, are no longer approved in the European Union due to concerns regarding neurodevelopment, fertility, and environmental damage. Chlorpyrifos has also been targeted internationally as a persistent organic pollutant. However, exposure can continue through residues, environmental contamination, imported products, or other pesticides still in use.
Under the Green Deal’s “farm to fork” strategy, the European Union has set non-binding targets to reduce the use and risks of chemical pesticides and the use of the most dangerous pesticides by 50% by 2030. Such studies may help identify exposures that deserve the most attention as regulatory bodies work to achieve these targets.
Reference: “Age at menarche and exposure to non-persistent pesticides in Spanish girls from the INMA (Environment and Childhood) Project” by Carmen Freire, Alicia Olivas Martínez, Francesca Castillo, Alba Jimeno Romero, Sara López de Cali, Beatriz Suarez, Adonina Tardón, Marta M. Rodriguez Suarez, Mónica Joxens, Martín Freiheid, Andrea Benito and María José López Espinosa, April 6 2026, Environmental research.
doi: 10.1016/j.envres.2026.124450
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