Influence Of Environmental Factors On The Acute Toxicity Of Ammonia To Corbicula Fluminea And Limnodrilus Hoffmeisteri And Validation Of Aquatic Criteria For Ammonia In China

Ammonia is among the common contaminants in aquatic environments. In aqueous solution, ammonia exists in two forms, un-ionized ammonia (NH3) and ionized ammonium (NH4+), and NH3is much more toxic to aquatic organisms than NKt+as NH3is a neutral molecule and thus is able to diffuse across the epithelial membranes readily than the charged ammonium ion. Toxicity of ammonia is affected by environmental parameters, such as temperature, pH, alkalinity, salinity and oxygen concentration. The objective of the present study was to evaluate the influence of water pH and temperature on toxicities of ammonia to freshwater benthic invertebrates (Corbicula fluminea and Limnodrilus hoffmeisteri) by the semi-static method. The data gathered in this study were able to provide more information on the effects of ammonia toxicity to indigenous aquatic organisms. Acute96-h ammonia toxicity tests indicated that temperature and pH had significantly effects on the acute toxicity to C. fluminea and L. hoffmeisteri. The96-h LC50values of total ammonia decreased with increasing pH and ranged from10mg N/L to85mg N/L, and ammonia toxicities to the two aquatic organisms were similar. At temperature20,25and30℃, the96-h LC50values of C. fluminea and L. hoffmeisteri were70.9,37.8,19.1mg N/L and65.9,42.7,21.2mg N/L, and the values at30℃was3.7and3.1 times of those at20℃, respectively. The toxicity generally increased with increasing pH and temperature. Comparison of LC50values and the final acute values (FAV) used to derive the acute water quality criterion (WQC) indicates that acute WQC may adequately protect C. fluminea and L. hoffmeisteri. In addition to our acute toxicity results, it is recommended that chronic ammonia toxicity should also be studied in order to better understand long-term effects of toxic nitrogenous compounds.This study modified the national and Tai Lake basin criteria for ammonia which were derived in the paper "Development of Aquatic Water Quality Criteria for Ammonia in Freshwater Ecosystem of China Based on Lake Tai Basin". According to the characteristics of aquatic biota composition in China, a total of45toxicity data of aquatic organism were screened including vertebrates, arthropoda, mollusca and annelida. The approach of species sensitivity distribution was.used to discuss the sensitivity of various organisms and to derive the aquatic water quality criteria in China and Tai Lake basin of ammonia. Acute48-h toxicity tests of ammonia on Daphnia magna were conducted using the water from Tai Lake basin, the aquatic region criteria for ammonia was developed by "water-effect ratio procedure". The results showed that the Log-Slogistic3model provided the best fit for various sets of data, the modified national acute and chronic criteria were4.686mg N/L and0.614mg N/L, respectively. And invertebrates were more sensitive for ammonia than vertebrates; The acute criteria for ammonia for Tai Lake basin was3.888mg N/L, while the chronic criteria was0.510mg N/L, criteria of Tai Lake basin were more stringent than the national criteria, all the criteria can adequately protect indigenous aquatic organisms; The48-h EC50values measured by D. magna acute toxicity experiments with Tai Lake water and laboratory water were63.182,57.389mg N/L and53.612mg N/L, according to the experimental results, water effect ratios (WERs) were1.179and1.070, which were greater than1.0, suggesting that the matched laboratory water were "over protective" of ammonia toxicity for site-specific aquatic organisms. The research provides important information for the study of water quality criteria and standards for ammonia in China.