Effects of toxin from Bacillus thuringiensis (Bt) on sorption of Pb (II) in red and black soils: equilibrium and kinetics aspects

Bt crops have been widely commercialized for cultivation in the world, but as yet, the effects of Bt toxin on sorption of heavy metals in soils has not been reported. In this study, the effects of toxin from Bacillus thuringiensis on Pb (II) sorption by red (Ultisol) and black soil (Vertisol) were studied using the batch method. The results showed that Pb(II) sorption by both soil types decreased in the presence of Bt toxin from 0 to 10 mg/L, which was probably due to the sorptive sites competition and Pb-toxin complex formation. The Langmuir and Freundlich isotherm models were fitted well to the sorption data at different Bt toxin additions. The sorption capacity of black soil for Pb (II) was higher than that of red soil, however, the influential trends of Bt toxin to the maximum capacity of Pb (II) in both soils was reversed. Sorption of Pb (II) in both soils was rapid and reached equilibrium within 80 min, following the pseudo-second-order kinetic model. Decreasing sorption of Pb (II) by red and black soils was observed in the presence of Bt toxin, suggesting that the environmental risk of Pb(II) may increase if Bt toxin is released by Bt crops.