Change of the cadmium, lead and uranium species after addition of biochar into the soils
Using the method of chemical fractionation the change in the reserve of Cd, Pb and U in exchangeable forms (Me<sub>ex</sub>) in sod podzolic sandy and medium loamy and peaty soils after adding 5 wt. % biochar has been investigated. It was found that in the presence of biochar in sandy soil, the content of Cd<sub>ex</sub>, Pb<sub>ex</sub>, and U<sub>ex</sub> decreased by 20, 50 and 46 %, respectively. In medium loamy soil, the content of Cd<sub>ex</sub> and Pb<sub>ex</sub> is reduced by 26 and 63 %, and in peat soil, the content of Pb<sub>ex</sub> and U<sub>ex </sub>is decreased by 8.5 and 46 %, respectively. However, in the peat soil, the addition of biochar had practically no effect on the content of Cd<sub>ex</sub>, and in medium loamy soil, it led to an increase in the content of U<sub>ex</sub>. The results of the study show that biochar at a dose of 5 wt. % can improve the quality of soils (decrease acidity, increase the content of exchangeable K and Ca) and reduce the mobility and biological availability of Cd and Pb in sandy and medium loamy soils, and U in sandy and peaty soils in regions with an increased content of them.