The more recent toxicity data contain chronic toxicity responses to ammonia for a number of sensitive species. This has the effect of significantly lowering the 95% species protection (PC95) value to 460 lg total NH3–N/L (Table 2), compared to the current ANZECC/ARMCANZ (2000) guideline value of 910 lg total NH3/L. The corresponding PC90 value for chronic effects in a disturbed environment was 750 lg total NH3–N/L. For acute effects, as might occur over a short time frame, a PC95 value of 1.55 mg total NH3–N/L was calculated (based on acute NOECs calculated by dividing the acute LC50 data by 5). The corresponding acute PC90 value
was 2.26 mg total NH3–N/L.