Effect of Time-Dependent Sorption on the Dissipation of Water-Extractable Pesticides in Soils

Abstract

The dissipation behavior of water-extractable pesticides in soils is important when assessing the phytoavailability of pesticides in soils. This process is less understood than pesticide extraction with organic solvents. To elucidate the dissipation behavior of water-extractable pesticides in soils, we conducted an incubation study using 27 pesticides and five Japanese soils. The rate of decrease of the level of pesticides in water extracts was faster in soils than that of total extracts (water extracts and acetone extracts). This suggests that time-dependent sorption contributed to the difference in the dissipation between the pesticides in water and total extracts from soils. Increased apparent sorption coefficients (Kd,app) with time were positively and significantly correlated with Kd,app values of a 0 day incubation [Kd,app(t0)]. This empirical relationship suggests that Kd,app(t0) values can predict the time-dependent increase in Kd,app and the dissipation of water-extractable pesticides in soils.

Effects of temperature on the dissipation of total- and water-extractable pesticides in Japanese soils

“…The test conditions-chemicals, soils, laboratory incubation except for incubation temperature, sequential extraction of soils and pesticide analysis-are described in our previous report, 4) in which soil samples were incubated at 25±2°C.…”

“…The concentration of water-extractable pesticides in soil, the C WE (µg g −1 DW), and the concentration of total-extractable (water-and acetone-extractable) pesticides in soil, the C TE (µg g −1 DW), were calculated as described in the previous study. 4) 2. Data analysis Two kinetic models, SFO (Eq.…”

“…All data at 25°C used for data analysis were reported in our previous study. 4) To ensure the quality of the E a calculation, the following conditions for data selection had to be satisfied:…”

“…To verify the method for correcting the dissipation rate constants (k, k 1 and k 2 ) at different temperatures by using E a values measured in laboratory experiments, field experiments were conducted in a field located in Tsukuba City, Japan, during spring-summer and autumn-winter periods. Details of the spring-summer experiment were described in a previous report, 4) and the autumn-winter experiment was conducted in the same way as the spring-summer test except for crop cultivation. The pesticides (dinotefuran, imidacloprid, clothianidin, thiacloprid, fosthiazate, metalaxyl, fenobucarb, flutolanil, procymidone and tolclofos-methyl) and the characteristics of the field soil (FS) are shown in Tables 1 and 2, respectively.…”

“…In addition, we indicated that the dissipation behavior of water-extractable pesticides was quite different from that of total-extractable pesticides in soils with organic carbon (OC) content of 1% or more. 4) In other words, the dissipation time for 50% (DT 50 ) of water-extractable pesticides in soil was clearly shorter than that of total-extractable pesticides, and the dissipation of water-extractable pesticides was better fitted by biphasic models, i.e., a double firstorder in parallel (DFOP) model as compared with a single firstorder (SFO) model applied to the dissipation of total-extractable pesticides in soil.…”