Toxicity of lipid-soluble copper(II) complexes to the marine diatom Nitzschia closterium: Amelioration by humic substances

Abstract

Algal assays, using the marine diatom Nitzschia closterium, have established that humic acid (5 mg kg −1) can ameliorate the toxicity of the lipophilic complex Cu(oxine) 2 (3 × 10 −8 mol l −1 in unsupplemented seawater). The toxicity of Cu(PAN) 2 is not ameliorated [PAN = 1-(2-pyridylazo)-2-napthol]. In conjunction with previous visible absorption spectrophotometry and polarographic measurements it was established that humic acid sequesters copper(II) from the hydrophobic complexes, releasing a ligand molecule. The copper(II) toxicity may be ameliorated provided the ligand itself is not toxic. Fulvic acid was significantly less effective in ameliorating toxicity. Because of the significant competition from Ca(II) and Mg(II) in seawater, it is inferred that humic substances may be more effective in ameliorating toxicity of hydrophobic copper complexes in fresh water.