Sep. 29, 2009 (United Press International) -- Two University of South Florida biologists say the popular weed killer atrazine interferes with the growth of fish and amphibians.

Jason Rohr and Krista McCoy, in an article published in Environmental Health Perspectives, reported on their examination of more than 100 studies of the environmental effects of atrazine, The St. Petersburg Times reported. The studies showed that the weed killer does not kill fish or amphibians but can cause changes in their reproductive, immune and other systems.

Atrazine's manufacturer, the Swiss-based chemical giant, Syngenta (NYSE:SYT) , says the weed killer is safe and calls it a "mainstay of American agriculture." Europe banned atrazine in 2004, but it remains legal in the United States.

The chemical kills weeds by inhibiting photosynthesis. Rohr and McCloy also found evidence it makes amphibians and fish more vulnerable to infection by damaging their immune systems, creates reproductive changes in male frogs and made fish less likely to avoid predators.

The biologists did not recommend a ban but said the Environmental Protection Agency should weigh atrazine's good effects against the potential damage.