New insights into the interactions between humic acid and three neonicotinoid pesticides, with multiple spectroscopy technologies, two-dimensional correlation spectroscopy analysis and density functional theory.

The widespread use of neonicotinoid pesticides in agricultural production has caused pressure on the environment. In the present work, the interactions between humic acid (HA) and three neonicotinoid insecticides, dinotefuran, clothianidin and nitenpyram, were investigated by using multiple spectroscopy techniques combined with two-dimensional correlation spectroscopy analysis and density functional theory (DFT). Dinotefuran, clothianidin and nitenpyram could quench the endogenous fluorescence of HA through a static quenching process dominated by hydrogen bonds and van der Waals forces. According to the revised Stern-Volmer equation and DFT calculation, the binding abilities of the three pesticides with HA were ranked as dinotefuran < clothianidin < nitenpyram. The results of dynamic light scattering showed that neutral conditions were more conducive to the combination of HA and dinotefuran, clothianidin and nitenpyram. Through Fourier transform infrared spectroscopy (FTIR) combined with two-dimensional correlation analysis (2D-COS), the functional group with the strongest binding ability in the HA-dinotefuran, HA-clothianidin and HA-nitenpyram system was CH, CO and CO, respectively. The work will help to further understand the behavior of neonicotinoid pesticides in the environment.