Amphibians and agrochemicals: Dermal contact and pesticide uptake from irrigated croplands in SW Georgia

Background/Question/Methods

Although isolated wetlands comprise a significant portion of amphibian breeding habitats throughout the United States, they are not protected under the Clean Water Act.  In SW Georgia where agriculture is dominant within the landscape, many isolated wetlands are now surrounded by irrigated croplands as a result of conversion from longleaf pine (Pinus palustris) forests.  Beyond altering historic landscape features, these irrigated croplands also introduce a large number of agrochemicals into wetland habitats.  Because juvenile and adult amphibians move to and from these isolated wetlands during breeding season, they may come into direct dermal contact with residual and recently applied pesticides.  To determine if amphibians moving through irrigated croplands have quantifiable pesticide body burdens, we collected tadpoles and adult leopard frogs (Rana sphenocephala), Southern toads (Anaxyrus terrestris), gray treefrogs (Hyla versicolor) and soil from terrestrial habitats surrounding 3 forested wetlands and 3 agricultural (cotton or peanut crops) wetlands on or near the Joseph Jones Ecological Research Center in Newton, GA.  Our extractions were performed on whole body frog tissues or soil and we analyzed samples using a LC/MS for pesticide quantification.

Results/Conclusions

Glyphosate, pendimethalin, metolachlor, and chlorothalonil are among the most commonly applied pesticide active ingredients in SW Georgia for cotton and peanut crops.  Reference wetland soils were devoid of pesticides across all sampling dates.  Although soil samples collected before spring spraying on agricultural fields had no residual pesticides from the previous year’s applications, soil samples collected after spring applications had measurable pesticide loads.  Preliminary results indicate that amphibians moving throughout irrigated cropland sites after spray events had measurable pesticide body burdens (>20 ppb), while those collected from reference wetlands had body burdens below the detection limits of our LC/MS.  Our results suggest that amphibians moving throughout agricultural landscapes during breeding season do come into contact with recently sprayed pesticides and that dermal routes of exposure may be contributing to global declines.  While our data cannot rule out inhalation and dietary routes of exposure, dermal exposure and accumulation of pesticides in amphibians has been recently demonstrated and should be included in modeling efforts that are designed to protect amphibians in agricultural landscapes.