The authors regret to inform that the following sentence has been misworded in the abstract. “Toxicity of Ni at pH 4 was negatively related to DOC concentration and amount of humic-like and fulvic-like DOC and positively related to fluorescence index.” should read “Toxicity of Ni at pH 4 was POSITIVELY related to DOC concentration and amount of humic-like and fulvic-like DOC and NEGATIVELY related to fluorescen...