Toxicity of ammonia, nitrite and nitrate to Litopenaeus vannamei juveniles in low-salinity water in single and ternary exposure experiments and their environmental implications.

Information on toxicity of nitrogen compounds for Litopenaeus vannamei in coastal ecosystems and culture under low salinity is scarce. Acute toxicity trials were conducted in L. vannamei to determine the single and combined effects of ammonia, nitrite and nitrate at a salinity of 3 g/L. The 96 h-LC50 was 29.0 mg/L for total ammonia nitrogen (TAN); 10.6 mg/L for nitrogen as nitrite (NO2--N); and 900 mg/L for nitrogen as nitrate (NO3--N). The joint effects of ammonia, nitrite and nitrate exposure were antagonistic at 24-72 h; and additive from 72 to 96 h. The proposed safety levels of single exposure to TAN, NO2--N and NO3--N for L. vannamei are 1.45, 0.53 and 45.0 mg/L, respectively. When in mixture, the proposed level of TAN/NO2--N/NO3--N is 0.05 TU (Toxicity Unit) corresponding to 0.48, 0.08 and 14.6 mg/L of TAN, NO2--N and NO3--N, respectively.