 There is evidence of chemical pollutants causing frog developmental deformities ( extra limbs , or malformed eyes ) . Pollutants have varying effects on frogs . Some alter the central nervous system ; others like <unk> cause a disruption in the production and secretion of hormones . Experimental studies have also shown that exposure to commonly used herbicides such as glyphosate ( <unk> Roundup ) or insecticides such as malathion or <unk> greatly increase mortality of tadpoles . Additional studies have indicated that terrestrial adult stages of amphibians are also susceptible to non @-@ active ingredients in Roundup , particularly <unk> , which is a surfactant . <unk> has been shown to cause male tadpoles of African clawed frogs to become hermaphroditic with development of both male and female organs . Such feminization has been reported in many parts of the world . In a study conducted in a laboratory at Uppsala University in Sweden , more than 50 % of frogs exposed to levels of estrogen @-@ like pollutants existing in natural bodies of water in Europe and the United States became females . Tadpoles exposed even to the weakest concentration of estrogen were twice as likely to become females while almost all of the control group given the heaviest dose became female . 
