Imidacloprid sorption and transport in cropland, grass buffer, and riparian buffer soils

Authors: SATKOWSKI, L - University Of Missouri; GOYNE, K - University Of Missouri; ANDERSON, S - University Of Missouri; Lerch, Robert; WEBB, E - Us Geological Survey (USGS); SNOW, D - University Of Nebraska

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2018
Publication Date: 4/12/2018
Citation: Satkowski, L.E., Goyne, K.W., Anderson, S.H., Lerch, R.N., Webb, E.B., Snow, D.D. 2018. Imidacloprid sorption and transport in cropland, grass buffer, and riparian buffer soils. Vadose Zone Journal. doi:10.2136/vzj2017.07.0139.
DOI: https://doi.org/10.2136/vzj2017.07.0139

Interpretive Summary: Neonicotinoid insecticides are commonly used for pest control in corn and soybean production throughout the US Corn Belt. Recent studies indicate that neonicotinoids are harmful to pollinating insects and insect-eating birds, but little is known about the fate of these insecticides in the soil environment. The objective of this study was to evaluate the binding and leaching of the neonicotinoid imidacloprid (ICD) in soils collected from cropland (crop), grass vegetative buffer strips (VBS), and riparian VBS. Soils were collected at six randomly chosen sites that encompassed all three land uses. Results showed that binding of ICD was greater in riparian VBS than grass VBS and cropland soils. Binding of ICD was strongly related to the soil organic matter content which was greatest in the riparian VBS soils. Leaching studies showed that ICD also leached to a greater extent through cropland than grassland or riparian VBS soils. Results of model simulations of the leaching studies highlighted the multiple ways in which ICD can bind to soil. Greater binding and less leaching in the grass and riparian VBS soil compared to the crop soil showed that VBS may be a viable means to mitigate ICD loss from cropland. Land managers and producers will benefit from this research as it clearly demonstrated that grass VBS and multi-species riparian areas can reduce the movement and ecological impacts of ICD.

Technical Abstract: An understanding of neonicotinoid sorption and transport in soil is critical for determining and mitigating environmental risk associated with the most widely used class of insecticides. The objective of this study was to evaluate mobility and transport of the neonicotinoid imidacloprid (ICD) in soils collected from cropland (crop), grass vegetative buffer strips (VBS), and riparian VBS. Soils were collected at six randomly chosen sites within grids that encompassed all three land uses. Single-point, batch sorption experiments were conducted using radio-labeled 14C-ICD to determine solid-to-solution partition coefficients (Kd). Column experiments were conducted using soils collected from the three vegetation treatments at one site by packing soil into glass columns. Water flow was characterized by applying bromide as a nonreactive tracer. A single pulse of 14C-ICD was then applied, and ICD leaching was monitored for up to 45 days. Bromide and ICD breakthrough curves for each column were simulated using CXTFIT and HYDRUS-1D models. Sorption results indicated that ICD sorbs more strongly to soil from riparian VBS (Kd= 22.6 L/kg) than crop (Kd= 11.3 L/kg; p = 0.04) and soil organic carbon was the strongest predictor of ICD sorption (p < 0.0001). The column transport study found mean peak concentrations of ICD at 5.83, 10.84 and 23.8 pore volumes for crop, grass VBS, and riparian VBS, respectively. HYDRUS-1D results indicated that the two-site, one-rate linear reversible model best described results of the breakthrough curves, indicating the complexity of ICD sorption and demonstrating its mobility in soil. Greater sorption and longer retention by the grass and riparian VBS soil compared to the crop soil suggests that VBS may be a viable means to mitigate ICD loss from agroecosystems.