New research from Spain indicates a potential link between certain agricultural fungicides and earlier onset of menstruation in girls. The study, published in Environmental Research, monitored 506 girls as part of the Spanish INMA (Environment and Childhood) project. It found that higher levels of the pesticide-related chemical ethylene thiourea (ETU) could be associated with increased likelihood of earlier menarche.

Researchers analyzed urine samples from girls aged 7 to 10 to measure pesticide metabolites, continuing to follow their development into adolescence. They focused on exposure markers for modern pesticides, including insecticides and fungicides that may disrupt hormones. The data suggested that earlier puberty, now a growing public health issue, could correlate with these chemicals. Typically, menarche occurs between ages 12 and 13, but the age has decreased over the past century. Early puberty can increase risks for various health issues, such as metabolic and cardiovascular problems, as well as certain cancers.

The strongest evidence involved ETU, a breakdown product of ethylene-bis-dithiocarbamate fungicides like mancozeb. Girls with higher ETU levels were 32 to 39 percent more likely to experience menarche during the study than those with undetectable levels. Diet, particularly the consumption of conventionally grown fruits and vegetables, appeared to be the main exposure pathway for ETU. While modern pesticides are also present in non-agricultural settings, food is the primary source for most people.

The study found the average age of menarche was just over 12 years, with a range from 9 to 15 years. Conversely, another pesticide marker, TCPy, associated with the insecticide chlorpyrifos, showed a trend towards later menarche. The reasons for this contrasting finding remain unclear.

While the findings suggest a connection, they do not prove pesticides cause earlier puberty. Biological mechanisms can potentially explain the association, such as effects on thyroid hormones and reproductive pathways, but the study was observational, limiting causal conclusions. Researchers noted limitations due to estimating exposure from a single childhood urine sample. Given that these chemicals exit the body relatively quickly, a single measurement may not accurately portray long-term exposure.

Despite these limitations, the study provides initial evidence connecting non-persistent pesticide exposure with puberty timing in girls. Researchers advocate for larger studies to verify the results and enhance understanding of how pesticide mixtures affect child development.