Interaction and coexistence characteristics of dissolved organic matter with toxic metals and pesticides in shallow groundwater

The long-term and large-scale utilization of fertilizers and pesticides in facility agriculture leads to groundwater pollution. However, the coexistence and interactions between organic fertilizers (i.e., organic matter), toxic metals, and pesticides in shallow groundwater have seldom been studied. Thus, the study sought to characterize said interactions via fluorescence, ultraviolet-visible spectroscopy (UV-Vis), and Fourier-transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy and chemometric techniques. The results indicated that groundwater DOM was comprised of protein-, polysaccharide-, and lignin-like substances derived from organic fertilizers. Protein-like substances accounted for the binding of Co, Ni, and Fe, while polysaccharide- and lignin-like substances were mainly responsible for Cr and Mo complexation. Moreover, lignin- and polysaccharide-like substances played a key role in the binding of pesticides (i.e., dichlorodiphenyltrichloroethane endosulfan, gamma-hexachlorocyclohexane [gamma-HCH], monocrotophos, chlorpyrifos, and chlorfenvinphos), rendering the conversion of gamma-HCH to beta-hexachlorocyclohexane (beta-HCH) and the degradation of DDT to dichlorobenzene dichloroethylene (DDE) ineffective. However, the presence of protein-like substances in groundwater benefited the degradation and conversion of gamma-HCH and alpha-endosulfan. Redundancy analyses showed that lignin- and polysaccharide-like matter had the most impacts on the coexistence of DOM with toxic metals and pesticides. (C) 2019 Elsevier Ltd. All rights reserved.