Study of different fractions of Zn, Cu, Pb and Cd during vermicomposting of cattle manure

In order to study the changes in different fractions of Zn, Cu, Cd and Pb during the vermicomposting process of cattle manure, an experiment was conducted based on completely randomized design with factorial arrangement replicated three times. The first experimental factor was presence and absence of earthworm, and period of vermicomposting (0, 30, 60 and 90 days) was taken into account as the second factor. A five-step sequential extraction procedure recommended by Tessier was used for fractionation of Zn, Cu, Cd and Pb during the process of vermicomposting of caw manure. The exchangeable, carbonate-bound, Fe-Mn oxides-bound, organic matter-bound and residual fractions of metals were determined using atomic absorption apparatus (FAAS, Thermo element MK-M6). The results showed that pH of vermicompost decreased 0.4 of unit and dissolved organic carbon (DOC) increased 0.15 percent in treatments of with worm. The bioavailability of Zn, Cu and Cd, not Pb increased significantly in the compost samples. Following earthworm activity, the highest content of Zn, Cu and Cd were observed as bounded by carbonate, organic matter and exchangeable fractions, respectively, while the most amount of Pb was found in organic band fraction. Zn and Cd concentrations in carbonate and exchangeable fractions significantly increased in earthworm treatments, Zn 16.4 and 18.21 percent and Cd 10 percent increased in this fractions, however the concentration of those in residual fraction decreased by the end of incubation period. It is concluded that earthworm activity increases the bioavailability of some of metals (Cd, Zn, and Cu) during the vermicomposting process.