不同温度和pH下氨氮对河蚬和霍甫水丝蚓的急性毒性

水环境中氨氮毒性与pH、温度等环境因子密切相关. 采用半静态方法研究不同pH和温度下氨氮对河蚬(Corbicula fluminea)和霍甫水丝蚓(Limnodrilus hoffmeisteri)的急性毒性效应. 结果表明:pH对氨氮毒性影响显著,其中NH₃₊NH₄+对河蚬和霍甫水丝蚓的LC₅₀(半致死浓度)随pH的增加而下降,其变化范围为11.78~83.82 mg/L,并且这2种水生生物对NH₃₊NH₄+毒性的敏感性差异不大；当温度分别为20、25和30 ℃时,NH₃₊NH₄+对河蚬的LC₅₀分别为70.86、37.85和19.14 mg/L,对霍甫水丝蚓的LC₅₀分别为65.88、42.73和21.21 mg/L,20 ℃时NH₃₊NH₄+对河蚬及霍甫水丝蚓的LC₅₀分别是30 ℃时的3.70和3.11倍. 表明水体pH和温度越高,氨氮的毒性作用越强. 通过比较氨氮水生生物基准中的FAV(最终急性值)和试验生物的LC₅₀发现,我国现有的氨氮基准能够很好地保护本土水生物种河蚬和霍甫水丝蚓. 

Influence of Environmental Factors on the Acute Toxicity of Ammonia to Corbicula fluminea and Limnodrilus hoffmeisteri

Aqueous ammonia exists in the form of both unionized ammonia (NH₃) and ionized ammonium (NH₄+). NH₃ is more toxic than NH₄+ to aquatic organisms, because NH₃ can readily diffuse through cell membranes and is highly soluble in lipids. The toxicity of ammonia can be affected by environmental parameters such as temperature, pH, alkalinity, salinity and oxygen concentration. The effects of water pH and temperature on toxicities of ammonia for two freshwater benthic invertebrate species (Corbicula fluminea and Limnodrilus hoffmeisteri) were investigated by the semi-static methods. The data gathered provide more information on the effects of ammonia toxicity to indigenous aquatic organisms. Temperature and pH had significant effects on the acute toxicity to C. fluminea and L. hoffmeisteri. The LC₅₀s of total ammonia decreased with increasing pH, ranging from 11.78 mg/L to 83.82 mg/L. Ammonia toxicities to the two aquatic species were similar. At temperatures 20,5 and 30 ℃, the LC₅₀s of C. fluminea and L. hoffmeisteri were 70.86,7.85,9.14 mg/L and 65.88,2.73,1.21 mg/L. The values at 20 ℃ were 3.70 and 3.11 times those at 30 ℃, respectively. The toxicity generally increased with increasing pH and temperature. Comparison of LC₅₀s and the final acute values 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 the long-term effects of toxic nitrogenous compounds.