[M-ZZ45] 地球化学の最前線：その魅力や将来の展望を語り合う

[MZZ45-P14] 日本沿岸域における植物プランクトンに対する銅の毒性

*小畑 元¹、Wiwit -¹、黄 国宏²、Lu Chia-Jung¹、福田 秀樹³、小川 浩史¹、高橋 一生⁴、眞塩 麻彩実²、武田 重信⁵ (1.東京大学大気海洋研究所海洋化学部門、2.金沢大学理工研究域、3.東京大学大気海洋研究所国際・地域連携研究センター、4.東京大学農学生命科学研究科、5.長崎大学大学院水産・環境科学総合研究科)

キーワード：海洋、銅、有機配位子、配位子滴定法

Copper in seawater is essential for phytoplankton growth, but it is toxic at high concentrations. The bioavailability and toxicity of Cu depend on its chemical species. It is well known that free cupric ion is the most toxic for phytoplankton. In this study, we estimated the free cupric ion concentrations in Japanese coastal waters to evaluate the effect of Cu toxicity on phytoplankton growth. Incubation experiments were carried out using natural phytoplankton assemblages in seawaters collected at Otsuchi Bay on the Pacific Ocean side of the northern Japan and around Goto Nada in the East China Sea. They were incubated for 14 days with the addition of up to 100 nM Cu. Copper speciation parameters were obtained by using reverse titration methods with competitive ligand exchange adsorptive cathodic stripping voltammetry. During the incubation experiments, chlorophyll-a contents increased with the addition of less than 10 nM Cu but decreased with the addition of 100 nM Cu due to Cu toxicity. During the experiments, we did not detect increases of Cu-binding organic ligand accompanying with phytoplankton growth. We simulated the free cupric ion concentrations using initial Cu speciation parameters obtained using competitive ligand exchange adsorptive cathodic stripping voltammetry with varying Cu concentrations. Assuming one class of organic ligand in the sample, estimated free cupric ion concentrations were inconsistent with our incubation results. In contrast, by assuming two classes of ligands, we obtained reasonable free cupric ion concentrations in seawater which agreed well with our incubation results. This simulation results suggested that the accurate detection of weaker class of organic ligand is crucial for evaluating Cu toxicity in seawater.