Marsh frog response to urea fertilizer during the embryonic, larval, and metamorphosis stages: a new perspective into urea toxicity on amphibians.

Amphibian populations are declining worldwide. These declines are caused by a variety of factors, one of which is the use of fertilizers in agriculture. This is especially true for tadpoles, which may develop in fertilizer-polluted agricultural water bodies. Nevertheless, there is little data on the toxicological consequences of fertilizers on amphibians. The goal of this study was to determine the acute and chronic toxicity of urea fertilizer on marsh frogs' (Pelophylax sp.) embryonic, larval, and metamorphic stages. For this purpose, in a static-renewal test, individuals were exposed to twelve nominal concentrations (0 to 15000 mg/L) of urea for 122 days to determine hatching success, survival, growth, development, and metamorphic traits, as well as histological consequences. Based on the results, at concentrations greater than 500 mg/L, no hatching occurred. Survivorship was unaffected for the first 72 hours, but it reached 0% on day 26 at concentrations greater than 150 mg/L. Survival and development rates decreased significantly in 100 and 150 mg/L treatments after a longer duration (day 86). Growth was reduced as well, but it was only significant at 150 mg/L. Metamorphosis time and percentage were significantly impacted, but not metamorphosis size. Increased urea fertilizer concentrations had significant histopathological consequences for the skin, gills, liver, kidneys, and striated muscles. Our results suggest that urea fertilizer, at concentrations commonly found in agroecosystems, may pose a serious threat to temperate anuran species inhabiting these conditions.