Tolerance of ciliated protozoanParamecium bursaria (Protozoa, Ciliophora) to ammonia and nitrites

Abstract

The tolerance to ammonia and nitrites in freshwater ciliateParamecium bursaria was measured in a conventional open system. The ciliate was exposed to different concentrations of ammonia and nitrites for 2h and 12h in order to determine the lethal concentrations. Linear regression analysis revealed that the 2h-LC₅₀ value for ammonia was 95.94 mg/L and for nitrite 27.35 mg/L using probit scale method (with 95% confidence intervals). There was a linear correlation between the mortality probit scale and logarithmic concentration of ammonia which fit by a regression equationy=7.32x–9.51 (R ²=0.98;y, mortality probit scale;x, logarithmic concentration of ammonia), by which 2 h-LC₅₀ value for ammonia was found to be 95.50 mg/L. A linear correlation between mortality probit scales and logarithmic concentration of nitrite is also followed the regression equationy=2.86x+0.89 (R ²=0.95;y, mortality probit scale;x, logarithmic concentration of nitrite). The regression analysis of toxicity curves showed that the linear correlation between exposed time of ammonia-N LC₅₀ value and ammonia-N LC₅₀ value followed the regression equationy=2 862.85e ^−0.08x (R ²=0.95;y, duration of exposure to LC₅₀ value;x, LC₅₀ value), and that between exposed time of nitrite-N LC₅₀ value and nitrite-N LC₅₀ value followed the regression equationy=127.15e ^−0.13x (R ²=0.91;y, exposed time of LC₅₀ value;x, LC₅₀ value). The results demonstrate that the tolerance to ammonia inP. bursaria is considerably higher than that of the larvae or juveniles of some metozoa, e.g. cultured prawns and oysters. In addition, ciliates, as bacterial predators, are likely to play a positive role in maintaining and improving water quality in aquatic environments with high-level ammonium, such as sewage treatment systems.