Wetland Atrazine Concentrations and Occurrence of Testicular Oocytes in Rana pipiens from Randomly-Selected Sites in the Prairie Pothole Region

Abstract

The Prairie Pothole Region (PPR) of the United States supports a high density of wetlands interspersed in an agricultural matrix. Row-crops, primarily corn and soybeans, dominate the southern PPR, while small grains and grasslands typify the north. Recent laboratory and field studies report that the corn herbicide atrazine disrupts normal sexual development in amphibians. In 2005, we measured atrazine concentrations during three surveys in 10 wetlands distributed from the southern (intensive corn production) to the northern (sparse or no corn production) PPR and collected Rana pipiens (northern leopard frog) metamorphs. Atrazine was detected in at least one water sample from every wetland, with concentrations ranging from < 0.011 (i.e. < method nominal detection limit) to 0.805 μg/L. The overall sex ratio did not diverge from 1:1; however there was a strong negative correlation between average atrazine concentrations at each site where more than 25 total specimens were collected and the female to male sex ratio. Gross gonadal abnormalities were noted in 3% of all metamorphic R. pipiens. The gonads of 55 % of all fully metamorphosed (Gosner stage 46) males contained testicular oocytes (TO’s). Atrazine concentrations were not significantly correlated with gross gonadal anomalies or TO’s. The lack of consistent, significant correlations between atrazine concentrations and gonadal anomalies in R. pipiens does not support the hypothesis linking atrazine with endocrine disruption in developing amphibians.