Spraying your lawn to get rid of pesky weeds may be killing off more than just the plants.

A new study found that the common herbicide atrazine disrupts organ development in tadpoles, resulting in deformed hearts as well as malfunctioning kidneys and intestinal tracts.

When tadpoles were exposed to high levels of atrazine, more than half developed smaller hearts. By contrast, only 2 percent to 3 percent of the tadpoles not exposed to the chemical had abnormal hearts.

The findings were detailed in the journal Environmental Health Perspectives in February. The study was funded by a Tufts University internal grant.

Atrazine works as an herbicide by blocking photosynthesis in plants, but scientists do not know why or how it harms organ development in tadpoles.

This is not the first time atrazine has been implicated as a toxin to amphibians. In 2003, research led by Tyrone Hayes at the University of California, Berkeley, found that atrazine affected sex development in frogs, essentially emasculating the males.

Unlike Hayes’s research, which focused on how atrazine affected adult amphibians, the new study, led by Kelly McLaughlin at Tufts University, focused on the middle stage—after very early development, but before the tadpoles became adults.

“For anything that’s going to be introduced into the environment, we have to make sure we look at the effects across all development stages,” McLaughlin said.

The next step, McLaughlin said, is to figure out exactly how atrazine disrupts organ development and to study the effects of lower doses over a longer period of time.