Studies On Acute Toxicity Of Three Heavy Metal Ions To The Nemertean Cephalothrix Simula (Iwata, 1952)

The nemertean Cephalothrix simula (Iwata,1952) , which is one of the most common intertidal nemerteans in Qingdao and vicinity, was selected as experimental animal to study the acute toxicity of three heavy metal ions (Cu²⁺, Zn²⁺ and Cd²⁺) to it at three temperature levels (12°C, 20°C, 28°C).1. The acute toxicity of Cu²⁺ to the nemertean Cephalothrix simula was experimentally studied. In 24h, 48h, 72h and 96h, the LC50s of Cu²⁺ were 13.764, 3.717, 2.311 and 1.109 mg/L respectively at 12°C and 6.015, 1.299, 0.477, 0.339 mg/L respectively at 20°C. At 28°C only the LC50s in 24h and 48h were got, which were 1.144 and 0.261 mg/L, respectively. The tolerance to Cu²⁺ declined with the duration of exposure. The two-way analysis of variance performed on mortality value showed that there was significantly positive correlation between the temperature levels and the mortality of the nemertean, and between Cu²⁺ concentration and nemertean mortality. The interaction of temperature and Cu²⁺ on the lethal effects on the nemertean is significant (P<0.01).2. The acute toxicity of Zn²⁺ to the nemertean Cephalothrix simula was experimentally studied. In 24h, 48h, 72h and 96h, the LC50s of Zn²⁺ were 137.436, 76.570, 52.470 and 36.804 mg/L respectively at 12°C , 105.467, 47.027, 29.342 and 18.560 mg/L respectively at 20°C, 68.001, 39.345, 23.551 and 15.194 mg/L at 28°C. The tolerance to Zn²⁺ declined with the time of exposure. The two-way analysis of variance performed on mortality value showed that there was significantly positive correlation between the temperature levels and the mortality of the nemertean. The concentration of Zn²⁺ was also same as the temperature levels. The interaction of temperature and Zn²⁺ on the lethal effects on the nemertean is significant (P<0.01). The toxicity of Cu2 + to Cephalothrix simula was stronger than Zn²⁺.3. The acute toxicity of Cd²⁺ to the nemertean Cephalothrix simula was experimentally studied. In 24h, 48h, 72h and 96h, the LC50s of Cd²⁺ were 294.153, 138.326, 85.846 and 50.615 mg/L respectively at 12°C and 183.742, 66.345, 36.588, 26.235 mg/L respectively at 20°C. At 28°C only the LC50s of Cd²⁺ in 24h , 72h and 96h were gotten, which were 71.642, 24.105 and 20.715 mg/L. The tolerance to Cd²⁺ declined with the time of exposure. The two-way analysis of variance performed on mortality value showed that there was significantly positive correlation between the temperature levels and the mortality of the nemertean. The concentration of Cd²⁺ was also same as the temperature levels. The interaction of temperature and Cd²⁺ on the lethal effects on the nemertean is significant (P<0.01). The toxicity of the three heavy metal ions to the nemertean Cephalothrix simula was , Cu²⁺>Zn²⁺>Cd²⁺.