Acute toxicity of copper oxide nanoparticles to <i>Daphnia magna</i> under different test conditions

The acute toxicity of monodispersed 6 nm and <100 nm poly-dispersed copper oxide nanoparticles toward Daphnia magna was assessed using 48 h immobilization tests. CuSO4 was used as a reference. Four different exposure conditions were tested, to study whether the toxicity of the nanoparticle suspensions changed in a way similar to what is known for dissolved Cu: first in ISO standard test conditions (pH 7.8), second with slight acidity (pH 6.5), third in the presence of citric acid, and fourth in the presence of humic acid. For all four exposure conditions, the toxicity of Cu employed in the three forms followed the same sequence, i.e., CuSO4 > monodispersed 6 nm CuO ≫ poly-dispersed CuO. The toxicity of all Cu forms decreased from pH 6.5, ≫ pH 7.8, > pH 7.8 + citric acid, to ≫ pH 7.8 + humic acid. This pattern is in agreement with concentrations of Cu2+ calculated using the equilibrium model MINTEQ. These findings show that the acute toxicity of copper oxide nanoparticles is governed by test water composition and the chemical species Cu2+.本研究采用48小时不动试验，评估了单分散6纳米氧化铜纳米颗粒及粒径<100纳米的多分散氧化铜纳米颗粒对大型溞（Daphnia magna）的急性毒性，并以硫酸铜（CuSO4）作为参比试剂。为探究纳米颗粒悬浮液的毒性变化规律是否与溶解性铜的已知规律一致，本研究设置了四种不同暴露条件：其一为ISO标准试验条件（pH 7.8），其二为弱酸性环境（pH 6.5），其三添加柠檬酸，其四添加腐殖酸。在四种暴露条件下，三种形态铜的毒性均遵循相同排序：硫酸铜（CuSO4）> 单分散6纳米氧化铜纳米颗粒 ≫ 多分散氧化铜纳米颗粒。所有形态铜的毒性随环境变化呈递减趋势：pH 6.5 ≫ pH 7.8 > pH 7.8 + 柠檬酸 ≫ pH 7.8 + 腐殖酸。该变化规律与采用平衡模型MINTEQ计算得到的铜离子（Cu²+）浓度变化趋势一致。本研究结果表明，氧化铜纳米颗粒的急性毒性由试验水体的化学组成及铜离子（Cu²+）的化学形态共同决定。