Effects of Sterilization and Temperature on the Decrease Kinetic of Lead Bioavailability in Two Different Soil Groups

Sorption of metal ions by soil and clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The impacts of sterilization and incubation temperature on the decrease kinetic of Pb bioavailability in two different groups of soils were studied. Surface soils were sampled from Guilan and Hamadan provinces in the north and northwest of Iran with temperate and semiarid climates. The decrease kinetic of Pb bioavailability in the Pb(NO₃)₂ treated (400 μg Pb g^?1) soils has been studied in solid state incubation in sterile and unsterile conditions at 15, 27 and 37°C. The decrease of DTPA-extractable Pb in both groups of soils is often characterized by an initial rapid step followed by a slow step. The temperate soil with high affinity surface sites for Pb sorption compared to semiarid soils had a lower DTPA-extractable Pb in each time of extraction. Sterilization and soil incubation at lower temperature decreased the rate of Pb sorption/precipitation processes. Among the kinetic models the second order model and Elovich kinetic equation were the better choice to express the decrease kinetic of Pb bioavailability according to higher determined coefficient and the small standard error of the estimate. The determination coefficients of the mass transfer equation were increased and the standard errors of the estimates were decreased in sterile and unsterile conditions by increasing incubation temperature from 15 to 37°C.