Clothianidin decomposition in Missouri wetland soils

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Neonicotinoids are a class of pesticides that have been prevalently used in agriculture since the 1990s. Globally, most neonicotinoid application ([about]60%) is delivered via seed or soil treatment. Studies have shown that [about]5% of the neonicotinoid coating is taken up by the plant while the remaining [about]95% is left behind in soil, soil water, or becomes drift (<1%). Neonicotinoids can persist in agricultural soils for extended periods of time; however, they also have a high leaching potential into ground and surface waters. Many studies have found negative effects associated with neonicotinoids and non-target taxa, including aquatic invertebrate, pollinating species, and insectivorous birds. Clothianidin (CTN) degradation and sorption were evaluated to assess the potential for wetland soils to mitigate potential environmental risks associated with neonicotinoids. Solid-to-solution partition coefficients (K[d]values) were determined via a single-point sorption experiment, and sorption isotherm experiments were conducted using the two most contrasting soils. Clothianidin degradation was determined under oxic and anoxic conditions over the course of 60 days. Clothianidin degradation data were fit to zero-order and first-order kinetic decay models to determine CTN half-life ([t0.5])values. Sorption results indicated that CTN sorption to wetland soil is relatively weak (average K[d] = 3.58 L kg-]); thus, CTN has potential to be mobile within wetland soils. However, anoxic and oxic incubation results showed that anoxic conditions significantly increased CTN degradation in wetland soils (anoxic average [t0.5]=27.2 days; oxic average [t0.5]= 149.1 days). A significant negative correlation existed between anoxic half-life values and organic carbon content (r[2]=0.782; p=0.046). Greater CTN degradation rates in wetland soils under anoxic conditions suggests that managing wetlands to facilitate anoxic conditions could help mitigate CTN presence in the environment and reduce exposure to non-target organisms.