Changes in Sorption of Imidacloprid with Incubation Time

Abstract

Changes in sorption of the insecticide imidacloprid (1‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐N‐nitro‐2‐imidazolidinimine) with aging in three soils have been determined. Soil moisture was adjusted to −33 kPa and 14C‐ and analytical‐grade imidacloprid added to the soil at a rate of 1.0 mg kg−1. Imidacloprid‐spiked soils were incubated at 25°C for 16 wk. Replicate soil samples were periodically extracted successively with 0.01 M CaCl2, acetonitrile, and 1 M HCI. Sorption, as indicated by the sorption coefficient (Kd) values, was highest in the soil with highest organic C content, and increased by an average factor of 2.8 in the three soils during the incubation period. This increase was the result of a decrease in the imidacloprid extractable with CaCl2 (solution phase) and the increase in the amount of imidacloprid extractable with acetonitrile and HCI (sorbed phase) with incubation time. It is not known whether the increase in sorption was the result of imidacloprid diffusion to less accessible or stronger binding sites with time, a rate of degradation in solution and on labile sites that is faster than the rate of desorption, or a combination of the two processes. These results are, however, further evidence that increases in sorption during pesticide aging should be taken into account during characterization of the sorption process for mathematical models of pesticide leaching.

Behavior and Fate of Imidacloprid in Croatian Olive Orchard Soils Under Laboratory Conditions

“…However, variability in K OC sor values for the soils of different type and characteristics, and even for the soils with the same content of organic matter, indicated that not only organic matter content, but also its structure, aromaticity and polarity, affected the distribution of pesticide molecules in the soil/water system (Schwarzenbach et al, 2002). The values of K OC sor coefficient for IMI in the tested soils varied from 172 to 305 L/kg (Table 3), and they are consistent with reported K OC sor values (Cox et al, 1998b;Krohn & Hellpointner, 2002), especially for soils with similar textural characteristics. Estimated values of our study prove that, according to the McCall classification for the mobility of pesticides (McCall et al, 1980), IMI can be categorized as having a medium mobility (K OC sor 150 -500 L/kg) (Comfort et al, 1994), showing less tendency to be sorbed by the examined soils.…”

“…Among the processes that determine the behavior and fate of pesticides in the soil/water environment, sorption-desorption and degradation processes are the key processes affecting pesticide persistence, transport and bioavailability determining the amount of pesticide that can reach the target organism and that can be volatilized, or leached. Information regarding the sorption and desorption characteristics of IMI are essential for predicting its fate within the soil environment (Cox et al, 1998a;Cox et al, 1998b;Cox et al, 2001;Fernandez-Bayo et al, 2007;Liu et al, 2006;Ping et al, 2010). Capri et al (2001) and Cox et al (1998c) investigated the effect of selected soil properties on the sorption of IMI using the batch equilibrium technique.…”

“…Field and laboratory studies have determined that IMI sorption to soil particles increases as the concentration of the insecticide decreases (Cox et al, 1998a;Kamble & Saran, 2005;Oi, 1999). Cox et al (1997;1998b;1998c) have found that the potential for IMI to leach would decrease, as the OC levels and laminar silicate clay content in the soil increase. In contrast, IMI sorption in a calcerous soil was found to decrease with the addition of OC (obtained from peat and tannic acid) , which increased the mobility and leaching potential of IMI.…”

“…less desorption than predicted by sorption isotherms (Cox et al, 1997;Fernandez-Bayo et al, 2007;Papiernik et al, 2006). This behavior can be attributed to a portion of the sorbed compound that is bound irreversibly to soil surfaces (Celis & Koskinen, 1999;Cox et al, 1997;Cox et al, 1998b). Numerous studies indicated that values for IMI half-lives (DT 50 ) are highly dependent on experimental conditions; namely field or laboratory, (Krohn & Hellpointner, 2002).…”

Relationship between plant uptake of pesticides and water-extractable residue in Japanese soils

“…Therefore, the reduction of C water in soils caused by soil aging was larger than that of C total . Several studies reported that soil sorption of pesticides such as imidacloprid, 26,27) nicosulfuron, 28) and simazine 29) increased during the aging period; thus, it is implied that the dissipation of C water is affected not only by general dissipation factors such as biodegradation, hydrolysis, and volatilization, but also by increasing soil sorption with increased aging time.…”