Fractional-Isotopic Composition of Lead Compounds in Soils of the Kologrivskii Forest Reserve

Resumo

Isotopic composition of lead is a very sensitive indicator allowing us to determine even very low contamination of soils by this element, which is not noticeable from the change in its concentration against the background of the natural variability. Isotopic composition of loosely bound lead fractions (exchangeable and specifically sorbed) changes in soils of the Kologrivskii Forest State Natural Reserve under the impact of global or regional atmospheric transport and deposition of contaminants, though these soils are not subjected to the local technogenic pollution. The maximum portion of lead bound with the soil organic matter in the upper organic horizons reaches 75% of the total lead content. The portion of lead bound with iron and manganese (hydr)oxides increases down the soil profile. The portion of the residual fraction of lead also increases significantly down the soil profile. The most pronounced changes are observed for the ²⁰⁶Pb/²⁰⁷Pb ratio, which decreases from 1.20–1.24 to 1.15–1.18 under the impact of global pollution. The technogenic compounds of lead migrate down the soil profile. In the gray-humus gley alluvial soil (Fluvic Gleysol), low values of the ²⁰⁶Pb/²⁰⁷Pb ratio are observed for the exchangeable and specifically sorbed lead fractions in the entire soil profile, which is explained by the worse conditions for lead fixation in the profile of this soil in comparison with those in the podzolic soils.