Deriving site-specific water quality criteria for ammonia from national versus international toxicity data

A key question to be asked when developing regional water quality criteria with scarce toxicity data is whether such data need to be locally derived. To address this, ammonia toxicity data from local aquatic species in the Liao River were compared against data from species native and non-native to China, based on comparisons of the overall trends of species sensitivity distributions and derived water quality criteria. Liao River data were acquired by acute and chronic tests using five local freshwater invertebrate species, and then compiled alongside published data from Chinese national guidelines and international literature. Models of best fit using three species sensitivity distribution approaches (log-logistic, log-normal, and Burr III) did not vary markedly (r² >0.9), and no specific model provided a best fit across all data sets. The comparisons of the overall trend of species sensitivity distribution curves showed no significant differences at either a national (Chinese native taxa tested in China versus non-native taxa) or regional level (Liao River taxa versus non-Liao River taxa). The comparisons also revealed that the inclusion or exclusions of different ecological groups had little influence on the overall trends of species sensitivity distributions. These findings suggested data on non-local and non-native species, and data from local species tested elsewhere, could be appropriate for guiding the derivation of ammonia water quality criteria for regions such as Liao River. However, caution is needed when using hazardous concentration 5% values in the development of site-specific water quality criteria for a river basin due to the considerable variation observed for ammonia (16.8-56.6 mg/L), although these differences were not statistically significant. Based on the toxicity test evaluation, a preliminary acute value of 10.0 mg/L and chronic value of 1.7 mg/L (at pH of 7.0 and 20 °C) are proposed as site-specific ammonia water quality criteria for the Liao River, China.