Toxic effects of NH4+-N on embryonic development of Bufo gargarizans and Rana chensinensis

Abstract

Although nitrogen fertilizer is commonly used worldwide, little information is currently available about NH₄⁺-N toxicity on amphibians. This study determined the acute and chronic toxic effects of NH₄⁺-N on two native Chinese amphibian species (Bufo gargarizans and Rana chensinensis), and compared the negative sensitivity of different embryos to NH₄⁺-N. Static renewal aqueous exposures were performed using B. gargarizans and R. chensinensis embryos at Gosner stage 2 over 96 h. In terms of 96 h-LC₅₀, B. gargarizans and R. chensinensis embryos had significantly different responses to NH₄⁺-N, and the latter was more sensitive to NH₄⁺-N than the former. In the chronic toxicity test, exposure to 10 mg L^-1NH₄⁺-N or higher significantly decreased the hatching rate of embryos in both species. Significant increases in the abnormality rate of embryos at 50 mg L^-1NH₄⁺-N or higher were observed and morphological abnormalities were characterized by axial flexures, yolk sac edema, and hyperplasia in both species. Additionally, the total length of embryos decreased in a dose-dependent manner after exposure to NH₄⁺-N. The results indicate that NH₄⁺-N exposure can increase abnormality and inhibit the hatching and development of embryos in B. gargarizans and R. chensinensis.

Keywords: Bufo gargarizans; Embryo; LC(50); NH(4)(+)-N; Rana chensinensis.