Exposure to 50 and 100 mg/L NO3–N caused significant mortalities
in B. gargarizans larvae. Our results showed that NO3–N can be
seriously hazardous for amphibian survival, as has been suggested
previously (Geoffrey et al., 2006; Garcia-Munoz et al., 2011).
Though there is no report regarding nitrate converts to nitrite in
the gut of tadpoles, some mechanisms for nitrate toxicity in fish
and prawns have been proposed. The main toxic effect of nitrate
on aquatic animals is due to the blockade of the oxygen-carrying
capacity of hemoglobin, which may induce methaemoglobinaemia.
In the gut, bacteria convert nitrate to nitrite, which competes with
oxygen and binds to hemoglobin (Cheng and Chen, 2002; Jensen,
2003). Thereby, the oxygen-carrying capacity of the hemoglobin