Washington :  Wastewater from large dairy farms contains significant concentrations of estrogens, also known as feminizing hormones, that can persist for months or even years, says a study.

In the absence of oxygen, estrogens rapidly convert from one form to another; this stalls their biodegradation and complicates efforts to detect them, the researchers found.

The study, led by Wei Zhen from the University of Illinois (Urbana-Champaign) Sustainable Technology Center (ISTC), is the first to document the unusual behaviour of estrogens in wastewater lagoons, the journal Environmental Science & Technology reported.

Hormones that end up in surface or groundwater could contaminate sources of drinking water for humans, Zheng said. "The estrogens may also be taken up by plants - a potential new route into the food chain," he added, according to a university statement.

Even low levels of estrogens can "feminize" animals that spend their lives in the water, causing male fish, for example, to have low sperm counts or to develop female characteristics (such as producing eggs), undermining their ability to reproduce. Just as new mothers undergo hormonal changes that enable them to breastfeed, lactating cows generate estrogenic hormones that are excreted in urine and faeces, said Zheng.

Recent studies have detected estrogenic hormones in soil and surrounding watersheds after dairy wastewater was sprayed on the land as fertilizer. "These estrogens are present at levels that can affect the (reproductive functions of) aquatic animals," Zheng said.