Distribution and possible immobilization of lead in a forest soil (Luvisol) profile*

Abstract

Geochemical analyses using a sequential extraction method and lead adsorption studies were carried out in order to characterize the distribution and adsorption of lead on each genetic horizon of a Luvisol profile developed on a pelagic clayey aleurolite. Clay illuviation is the most important pedogenic process in the profile studied. Its clay mineralogy is characterized by chlorite/vermiculite species with increasing chlorite component downward. The amount of carbonate minerals strongly increases in the lower part of the profile resulting in an abrupt rise in soil pH within a small distance. The Pb content of the soil profile exceeds the natural geochemical background only in the Ao horizon, and its amount decreases with depth in the profile without correcting for differences in bulk density, suggesting the binding of Pb to soil organic matter. According to the sequential extraction analysis the organic matter and carbonate content of the soil have the most significant effect on lead distribution. This effect varies in the different soil horizons. Lead adsorption experiments were carried out on whole soil samples, soil clay fractions, as well as on their carbonate and organic matter free variant. The different soil horizons adsorb lead to different extents depending on their organic matter, clay mineral and carbonate content; and the mineralogical features of soil clays significantly affect their lead adsorption capacity. The clay fraction adsorbs 25% more lead than the whole soil, while in the calcareous subsoil a significant proportion of lead is precipitated due to the alkaline conditions. 10 and 5% of adsorbed Pb can be leached with distilled water in the organic matter and clay mineral dominated soil horizons, respectively. These results suggest that soil organic matter plays a decisive role in the adsorption of Pb, but the fixation by clay minerals is stronger.

Effect of soil composition on adsorption of lead as reflected by a study on a natural forest soil profile

“…Their amount decreases with depth (from 90% to 60%), while the carbonate content (almost solely represented by calcite) of this soil strongly increases in the lower part of the profile resulting abrupt increase in soil pH within a small distance (from 6.85 to 8.41 at a few cm thick transition of B and BC horizons). The clay mineralogy of the studied profile is characterized by vermiculite and chlorite/vermiculite intergrade mineral species with increasing chlorite component downwards, as indicated by its stability to heat treatments (Sipos et al, 2002).…”

Lead in Agricultural Soils and Cultivated Pastures Irrigated with River Water Contaminated by Mining Activity

“…Most contaminated soils contain various pollutants due to the anthropogenic activities, such as the discharge of foundry waste and lead classifies as the second most polluting substance [Liu et al 2015]. The soil adsorbs lead in different degrees, depending on the content of organic matter, carbonate, clay minerals, oxides of Mn, hydroxides of Fe and Al and mineralogical characteristics [Kabata-Pendias 2011, Sipos et al 2005]. The mobilization of lead is generally slow, but the increase in acidity, the formation of lead-organic matter complexes can increase its solubility [Kabata-Pendias 2011].…”

The Ecotoxicology of Heavy Metals from Various Anthropogenic Sources and Pathways for their Bioremediation

“…As the binding of heavy metal is stronger to the organic matter of the soil, the more immobile in the soil it will become but with the possibility of being picked up easier by the plants. This is a reported behavior for Cd [50], Cu [51], Pb [52], and Zn [53]. Generally, the presence of heavy metals in soil affects the plants growing and the content of plants dry matter, decreasing it [54,55].…”