The agricultural use of pesticides to control undesirable species, coupled with fertilizers to promote yield, has gained momentum in recent years despite a growing body of research highlighting the potential adverse ecological effects of these chemicals. However, co-applications of these agrochemicals leave non-target organisms at risk of exposure. While individual pesticide and fertilizer compounds are known to have adverse effects on amphibians, research on agrochemical co-exposures in terrestrial phase amphibians is limited. This study aimed to evaluate changes in hepatic biomarkers, specifically liver glutathione (GSH) and metabolites identified by metabolomic profiling, as well as pesticide bioaccumulation following amphibian agrochemical exposure. Southern leopard frogs (Lithobates sphenocephala) were reared from eggs through 30-90 days post-metamorphosis. For terrestrial exposures, 48 frogs were placed individually in microcosms sprayed with an individual chemical or tank mixture for 8-hours. Frogs were divided randomly across 8 chemical treatments: control (C), atrazine (Z), alachlor (L), urea (N), atrazine + alachlor (ZL), atrazine + urea (ZN), alachlor + urea (LN), or atrazine + alachlor + urea (ZLN). Following exposure, amphibians were immediately euthanized and the liver dissected. Hepatic GSH was determined colorimetrically, while concentration and metabolomic profiles were determined via GC-MS.
Results/Conclusions
The urea treatment had a significant effect by increasing liver GSH levels (nM/mL) (ANOVA p = 0.011), while none of the other chemicals resulted in significant effects on this biomarker. When urea was combined with atrazine in the ZN treated frogs, the ZN treatment resulted in a significantly higher GSH levels relative to the urea (34% higher; ANOVA p = 0.003) and ZL (91% higher; ANOVA p = 0.007) treated frogs. Frogs in the ZLN treatment had bioconcentration factors that were 4-6 times greater than frogs in the ZN and LN treatments, which was also supported by perturbations in the hepatic metabolome. Co-exposure to agrochemicals in amphibians may enhance bioaccumulation and impair normal metabolic function, thereby limiting the overall health and stability of amphibian populations in agricultural areas.