Complexation between copper(II)-dissolved organic matter shows heavy metal pollution in large-scale estuaries in the north-west Pacific

Large-scale estuaries of Tumenjiang River, Liaohe River, Yellow River, Huaihe River, Changjiang River, and Zhujiang River in the north-west Pacific are confronted with latent heavy metal pollution. Here, we revealed copper pollution behavior and fate by copper(II)-binding with dissolved organic matter combined with fluorescence and 2-dimensional correlation spectra. Seven components were identified from titrants. Free amino acid-like, tryptophan-like, microbial-derived humic-like, polycyclic aromatic hydrocarbon-like, and fulvic-like occurred in all estuaries, whereas the latter two components were absent in the Tumenjiang River Estuary. Humic-like existed only in the Tumenjiang River Estuary, and D’tryptophan-like in the Yellow River Estuary. Polycyclic aromatic hydrocarbon-like exhibited a strong sensitivity of copper(II)-binding in Liaohe River, Changjiang River, and Zhujiang River estuaries, so did humic-like, microbial-derived humic-like, and free amino acid-like, respectively in Tumenjiang River, Yellow River, and Huaihe River estuaries. These findings would be conducive to a further comprehension of copper(II) environmental behaviors and preventing its ecological risks. Seven different components of complexes between copper(II) and dissolved organic matter were identified in six large estuaries in the northwest Pacific, suggesting latent heavy metal pollution, according to a spectroscopic analysis of fluorescence excitation-emission matrices.