The functional and structural observations of the neonatal reproductive system of alligators exposed in ovo to atrazine, 2,4-D, or estradiol

Abstract

Wild alligators exposed to persistent organochlorine contaminants, municipal waste compounds, and contemporary-use herbicides exhibit reproductive alterations that are thought to be caused by endocrine disruption. This study tests the hypothesis that these alterations, at least in part, result from exposure of alligator embryos to contemporary-use herbicides. Alligator eggs were collected early in development, exposed to estradiol-17β, atrazine, or 2,4-D (at dosages of 0.14, 1.4, and 14 ppm, plus a dosage of 0.014 ppm for estradiol-17β only) before the period of gonadal differentiation, and incubated at a temperature that would produce either 100% males or 100% females. Analysis of histology was performed on the gonads and reproductive tracts of hatchlings. In females, epithelial cell height of the Müllerian duct and medullary regression of the ovary were assessed, whereas in males, sex-cord diameter was measured. Eggs incubated at the female-determining temperature produced all female hatchlings, whereas the estradiol-17β treatments caused the production of females at the male-determining temperature. Neither atrazine nor 2,4-D had this effect. Both Müllerian duct epithelial cell height and medullary regression were increased in estradiol-treated animals, but no differences were noted between herbicide-treated alligators and controls. A previous study found that male alligators exposed to 14 ppm atrazine had elevated gonadal aromatase activity, but there was no difference in sex-cord diameter in this or any other treatment group. Additionally, we observed that hepatic aromatase activity was not altered by in ovo exposure to any of the treatments. These results indicate that these herbicides alone are not responsible for the gonadal abnormalities previously reported for juvenile alligators from Lake Apopka and emphasize the importance of anlyzing both the function ( i.e., steroidogenic enzyme activity) and the structure ( i.e., histological analysis) of the reproductive system. Structural assessment alone may be insufficient for detecting subtle endocrine alterations.

Topical dose delivery in the reptilian egg treatment model

“…Thus, the presence of exogenous hormone or hormone agonist/antagonist in the egg could alter normal endocrine function and, ultimately, influence gender determination. Indeed, exposure‐dependent increases in the proportion of females were observed when reptilian eggs were treated with 17β‐estradiol during incubation at male‐producing temperatures [8,11,13–30]. At incubation temperatures that typically produce a 1:1 sex ratio, treatment with nonaromatizable androgens increased the proportion of males [19,23,31,32].…”

Weight-of-the-evidence evaluation of 2,4-D potential for interactions with the estrogen, androgen and thyroid pathways and steroidogenesis

“…Crain et al 1997 andSpiteri et al 1999 reported results after dosing alligator's eggs with 2,4-D. Estradiol was used as a positive control. In the first study, on pipping, chorio-allantoic fluid was analyzed and blood from hatchlings (10-days post hatch) was analyzed for estradiol.…”

“…Crain et al (1997Crain et al ( , 1999 and Spiteri et al (1999) reported results after dosing alligator's eggs with 2,4-D. Estradiol was used as a positive control for estrogen pathway mediated effects; there was no positive control for androgen-mediated effects. In the first study, at pipping, chorio-allantoic fluid was analyzed and blood from hatchlings (10 days post hatch) was analyzed for testosterone.…”

“…The 1999 study included evaluation of testicular histopathology. Gonadal histopathology was evaluated in a study by Spiteri et al (1999) which followed a similar exposure regimen, but incubated eggs at two different temperatures. (Incubation temperature normally determines sex of alligator eggs.)…”

Metabolic ability and individual characteristics of an atrazine-degrading consortium DNC5

“…Due to its high mobility and long half life in soil, residues of atrazine and its metabolites have been detected in soil, surface water and groundwater years after their initial application [2]. In addition, there is some evidence which suggests that atrazine may be an endocrine-disrupting chemical, consequently, it might be harmful to human and animals [3,4]. With regard to these problems, the studies focus on efficient bioremediation strategies for atrazine polluted environments and reducing its contamination to safe level revealed their urgency.…”