Effect of combined pollution of heavy metals on river ecosystem and its evaluation

通过批量实验研究了Ca、Mg、Zn和Al复合金属污染对日本河流中典型硅藻Nitzschia palea（NIES-487）存活的影响。实验条件为pH 6、25℃、4000 lx连续光照、一天多次搅拌。结果表明，添加Ca或Mg可减轻聚合铝对内眦菱形藻存活的抑制作用。然而，它们在日本河流中的浓度低于实验中的浓度。结果表明，Ca、Mg对内稃菱形藻的存活影响不显著，Zn浓度低于100μg/L时，内稃菱形藻的存活没有受到影响。当Zn浓度为30μg/L时（即Zn不影响内眦菱形藻存活的浓度），共存的聚合铝在低浓度下抑制内眦菱形藻的存活。结果表明，Zn和聚合Al复合污染对藻类的生长有抑制作用，即使在中性pH条件下，Zn浓度为30μg/L（日本水质标准上限）时，Zn和聚合Al复合污染也能抑制藻类的生长。值得注意的是，从土壤中溶出的铝或从矿山和工业工厂排放的铝有可能对河流生态系统产生不利影响。

The effect of combined metals pollution such as Ca, Mg, Zn and Al on survival of Nitzschia palea (NIES-487), typical diatom found in Japanese rivers, was studied in batch experiments to assess river ecosystem. The experiments were conducted under the condition of pH 6, 25℃, continuous irradiation of 4000 lx and several times of stirring in a day. The concentrations of chlorophyll a were monitored during the experiments.It was shown that the addition of Ca or Mg mitigated the inhibition of polymerized Al to the survival of Nitzschia palea. However, their concentrations in Japanese rivers were lower than those in the experiments. Then, it was concluded that mitigation of Ca or Mg was not significant.Zn less than 100μg/L did not affect the survival of Nitzschia palea. At 30μg/L of Zn, which is the concentration of not affecting its survival, coexistent polymerized Al inhibited the survival of Nitzschia palea under low concentrations. However, combined effect of Zn and polymerized Al did not show the inhibition under high polymerized Al concentrations because of its high inhibition effect.From these results, it was concluded that combined metals pollution of Zn and polymerized Al inhibited the algal survival even under neutral pH condition and 30μg/L of Zn, which is the upper limit of Japan water quality standard. It should be noted that Al eluted from soils or discharged from mines and industrial works has the possibility of affecting adverse effect on river ecosystem.