Amino acids-mediated transport of nitenpyram through saturated soil porous media: Combined roles of amino acid types and soil properties

Research on the transport characteristics of neonicotinoid pesticides through soil, particularly in the presence of common amino acids, is lacking in the current scientific literature. This study investigated the effects of three amino acids, such as glycine, aspartic acid, and histidine, on the mobility features of nitenpyram (NTP, a typical neonicotinoid pesticide). Two soil samples with diverse physico-chemical properties were used in the experiments. In general, increased levels of clay and soil organic matter were shown to be advantageous in limiting the movement of NTP in the soil columns. Interestingly, the three amino acids inhibited NTP mobility through the soil with higher iron-aluminum oxides over a broad pH range of 5.0-9.0. This can be attributed to the presence of additional sites for NTP deposition, created by the adsorbed amino acids, as well as the enhanced electrostatic attraction force between NTP and the soil. In contrast, these amino acids enhanced NTP transport through soil with higher organic matter. This is because the amino acid coating on soil surfaces hinders the contact between soil organic matter and NTP (e.g., through hydrophobic and pi-pi interactions). Additionally, the degree of the inhibitory or promoting effects of amino acids was in the order of histidine > aspartic acid > glycine, strongly dependent on their chemical structures (e.g., molecular size and functional group types). Moreover, a numerical model (i.e., the two-site nonequilibrium model) was employed to reveal the mechanisms of the impacts of amino acids on NTP transport through different soils. The results are helpful for understanding the fate of neonicotinoid pesticides in soil and aquatic environments containing various amino acids.