Sorption characteristics and persistence of herbicide bispyribac sodium in different global soils.

The dissipation kinetics and the adsorption characteristics of bispyribac sodium, a pyrimidinyloxybenzoic herbicide, in 21 types of soil collected from different locations in the U.S., Italy, Spain, Greece, France, U.K., the Netherlands, Germany, and India were evaluated under laboratory conditions. The soil sorption study was conducted using the batch equilibrium process. The paper also investigated the adsorption efficiency of bispyribac sodium in the presence of different kinds of background electrolytes, surfactants, and different temperatures in two different soils. The results showed that the Freundlich equation fits its adsorption well, and the Freundlich adsorption constant values (Kf) ranged from 0.3 to 5.6 mL g(-1). Adsorption isotherms were nonlinear, with 1/nf values <1. Bispyribac sodium adsorption by two soils increased with increasing electrolytes concentration using CaCl2, KCl, NH4Cl, KH2PO4 and MgCl2 as a background electrolytes. The adsorption coefficient value decreased when anionic and nonionic surfactants were used at the three surfactant concentrations in two types of soil but increased with cationic surfactant, and temperature. Sorption was positively correlated with OM and negatively correlated with a soil pH of 5.0 to 8.1. The free energy (ΔG) values of bispyribac sodium in the soils were less than 40 kJ mol(-1) and negative values were obtained. This indicates that the adsorption of bispyribac sodium is mainly a physical and spontaneous process. The GUS values were less than 2.9 in all the soil types studied, and the residues of bispyribac sodium were low to moderate to leacher (mobile) in the soil.