In the present study, the effects of water hardness (as CaCO3) on the acute toxicity to Chinese rare min￣now (Gobiocypris rarus) were investigated. For cadmium (Cd), the 96￣h median lethal concentration (96h￣LC50 ) was 4.30, 12.06, 19.99 mg•L￣1, under 50, 250 and 450 mg•L￣1 concentrations of CaCO3, respectively, and the cor￣responding safety concentration (SC) was 0.430, 1.206 and 1.999 mg•L￣1. For copper (Cu), the 96 h￣LC50 was 0.046, 0.148, 0.228 mg•L￣1, respectively, and the corresponding SC was 0.0046, 0.0148, 0.0228 mg•L￣1, respective￣ly. The relationship between acute toxicity of Cd to rare minnow and water hardness is:ln 96 h￣LC50= 0.687 ln H￣1.243 (r= 0.998), while for Cu, the relationship is:ln 96 h￣LC50= 0.727 ln H￣5.923 (r= 0.999). The hardness slope of toxicity of Cd2+and Cu2+was 0.687 and 0.727, respectively. The results showed that the water hardness effective￣ly reduced the acute toxicity of Cd2+ and Cu2+to G.rarus, and the hardness slope of heavy metals in G.rarus was quite different from that in other species. The present study also imply that the toxicity and ecological risk evalua￣tion of Cd2+ and Cu2+ under different water hardness conditions should depend on the specific hardness slopes of different species.%为研究水体硬度对稀有鮈鲫Cd2+和Cu2+毒性效应的影响,开展了96 h急性毒性试验。试验结果发现,当水体硬度(以CaCO3计,下同)为50 mg•L￣1、250 mg•L￣1、450 mg•L￣1时,Cd2+对稀有鮈鲫的96 h半数致死浓度(96 h￣LC50)分别为4.30 mg•L￣1、12.06 mg•L￣1、19.99 mg•L￣1,对应的安全浓度(SC)依次为0.430 mg•L￣1、1.206 mg•L￣1、1.999 mg•L￣1；Cu2+对稀有鮈鲫的96 h￣LC50分别为0.046 mg•L￣1、0.148 mg•L￣1、0.228 mg•L￣1,对应的SC依次为0.0046 mg•L￣1、0.0148 mg•L￣1、0.0228 mg•L￣1。计算得到Cd2+对稀有鮈鲫急性毒性与水体硬度的拟合方程为ln 96 h￣LC50=0.687 ln H￣1.243(r=0.998)；Cu2+对稀有鮈鲫急性毒性与水体硬度的拟合方程为ln 96 h￣LC50=0.727 ln H￣5.923(r=0.999),Cd2+和Cu2+对稀有鮈鲫的硬度斜率分别为0.687和0.727。这些结果表明,水体硬度可有效降低Cd2+和Cu2+对稀有鮈鲫的急性毒性,且稀有鮈鲫的硬度斜率与其他物种差异较大。在评估不同硬度水体下Cd2+和Cu2+的生物毒性及其生态风险时,应根据测试物种特异的硬度斜率而定。
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