many environmental contaminants alter the reproduction of animals by altering the development and function of the endocrine system . 
 the ability of environmental contaminants to alter the endocrine system of alligators was studied both in a descriptive study in which juvenile alligators from a historically contaminated lake were compared to animals from a control lake and in an experimental study in which hatchling control alligators were exposed in ovo to several endocrine - disrupting standards and two modern - use herbicides . 
 endocrine status was assessed by examining plasma hormone concentrations , gonadal - adrenal mesonephros ( gam ) aromatase activity , and gonadal histopathology . in the descriptive study , juvenile alligators from the contaminated lake 
 had significantly lower plasma testosterone concentrations ( 29.2 pg / ml compared to 51.3 pg / ml ) , whereas plasma 17 beta - estradiol concentrations did not vary when compared to controls . 
 gam aromatase activity was significantly decreased n the alligators from the contaminated lake ( 7.6 pmol / g / hr compared to 11.4 pmol / g / hr ) . in the experimental study , 
 the endocrine - disrupting standards had the expected effects . 
 17 beta - estradiol and tamoxifen caused sex reversal from male to female , with a corresponding increase in aromatase activity . 
 vinclozolin had no apparent effect on male or female alligators . among the herbicides tested , 
 atrazine induced gam aromatase activity in male hatchling alligators that was neither characteristic of males nor females , although testicular differentiation was not altered . 
 exposure to 2,4-dichlorophenoxyacetic acid had no effect on the endocrine parameters that were measured . 
 together , these studies show that exposure to some environmental chemicals ( such as atrazine ) can alter steroidogenesis in alligators , but the endocrine alterations previously noted for lake apopka , florida , alligators can not be fully explained by this mechanism.imagesfigure 1 .