Nadya Teutsch

Distribution of natural and anthropogenic lead in Mediterranean soils

Abstract The concentrations and isotopic composition of Pb have been combined with a selective sequential dissolution procedure to track the distribution of anthropogenic and natural Pb in the soil of semiarid climate and the penetration pathway of petrol-Pb within the soil profile. Soil samples were collected from soil profiles adjacent to a major highway (8–23 m) and from soil profiles 500 m away from the same highway. The selective sequential dissolution procedure was used to determine the distribution of Pb between the different soil components: soil carbonate, organic matter, Fe-oxides and hydrous oxides, and aluminosilicates. Natural Pb is associated mainly with aluminosilicates (∼60%) and Fe-oxides (∼30%), and only a small fraction with the soil carbonate and organic matter (∼10%). In contrast to the distribution of natural Pb, the distribution of anthropogenic Pb, which accumulates mainly in the upper part of the soil profile, is ∼40% with the soil carbonate, ∼10% with organic matter, ∼35% with Fe-oxides, and only ∼15% with aluminosilicates. On the basis of concentration and isotopic composition of total Pb, the deeper horizon of the roadside soil (10–30 cm) and the soil sampled 500 m from the highway seem uncontaminated. However, the isotopic composition of the labile components in the soil (Pbcarb, Pborg, and PbFe-ox) indicates that these soils are actually contaminated. This contamination implies that over the period of vehicle pollution (∼40 yr), petrol-Pb has penetrated through the entire roadside soil profile (25–30 cm). Furthermore, Pb isotopes in aluminosilicates of the upper part of the roadside soil indicate that this Pb too is anthropogenic. Measurements of Pb concentration and isotopic composition in roadside soil profiles sampled in 1997 and archived samples collected at the same location in 1982 provided a unique opportunity to trace petrol-Pb penetration into the soil.

The influence of rainfall on metal concentration and behavior in the soil

The effect of rainfall on the behavior of Fe, Mn, Cu, Zn, Pb, and Ti in mature soils developed on same-age volcanic bedrock in Hawaii was studied. Concentrations of the mentioned metals in total digested and weak acid-leached soil and bedrock samples were analyzed. Mass transport calculations yielded the quantity of metal enrichment or depletion in the soils relative to the bedrock. In addition, elemental mobility and the distribution between the labile and the residual fraction were examined. Based on mass transport calculations there is no significant effect of rainfall amount on the enrichment or depletion of any elements (except Cu) within soils receiving less than 570 mm/yr (4 sites). In the intermediate sites (4 sites, 930–1380 mm/yr) there is a variable effect of rainfall on all elements in the soil, but the extent of variation differs from one metal to the other. In the rainy site (2500 mm/yr) there is a large degree of enrichment or depletion of certain metals. Manganese and Zn are highly depleted and Pb is strongly enriched, whereas Fe and Cu do not show a significant mass change. Among all elements, Pb is the only one that has a continuous effect of rainfall throughout the transect. Lead is enriched in all the sites and this enrichment is well correlated with increasing rainfall. Iron is immobile in the soil, reflecting the relative stability of the Fe-rich phases and its high correlation with Ti. The mass change of Mn throughout the transect is remarkably correlated with Al (R2 = 0.87). The behavior of the trace metals Pb, Zn, and Cu in the Kohala soils is different because of the phases with which these metals are likely to be associated. Lead is probably adsorbed and coprecipitated mostly with Fe oxides and hydrous oxides. Zinc is presumably associated with Mn and Al oxides and hydrous oxides and with organic matter, whereas Cu is most likely complexed by organic matter.

Influence of Intrinsic Colloid Formation on Migration of Cerium through Fractured Carbonate Rock.

Migration of colloids may facilitate the transport of radionuclides leaked from near surface waste sites and geological repositories. Intrinsic colloids are favorably formed by precipitation with carbonates in bicarbonate-rich environments, and their migration may be enhanced through fractured bedrock. The mobility of Ce(III) as an intrinsic colloid was studied in an artificial rainwater solution through a natural discrete chalk fracture. The results indicate that at variable injection concentrations (between 1 and 30 mg/L), nearly all of the recovered Ce takes the form of an intrinsic colloid of >0.45 μm diameter, including in those experiments in which the inlet solution was first filtered via 0.45 μm. In all experiments, these intrinsic colloids reached their maximum relative concentrations prior to that of the Br conservative tracer. Total Ce recovery from experiments using 0.45 μm filtered inlet solutions was only about 0.1%, and colloids of >0.45 μm constituted the majority of recovered Ce. About 1% of Ce was recovered when colloids of >0.45 μm were injected, indicating the enhanced mobility and recovery of Ce in the presence of bicarbonate.

Uranium and Cesium sorption to bentonite colloids under carbonate-rich environments: Implications for radionuclide transport

In the context of geological disposal of radioactive waste, one of the controlling mechanisms for radionuclide migration through subsurface strata is sorption to mobile colloidal bentonite particles. Such particles may erode from the repository backfill or bentonite buffer and yield measurable (0.01-0.1 g/L) concentrations in natural groundwater. The extent of sorption is influenced by colloid concentration, ionic strength, radionuclide concentration, and the presence of competing metals. Uranium (VI) and cesium sorption to bentonite colloids was investigated both separately and together in low ionic strength (2.20 mM) artificial rainwater (ARW) and high ionic strength (169 mM) artificial groundwater (AGW; representative of a fractured carbonate rock aquitard). Sorption experiments were conducted as a factor of colloid concentration, initial metal concentration and opposing metal presence. It was shown that both U(VI) and Cs sorption were significantly reduced in AGW in comparison to ARW. Additionally, the sorption coefficient Kd of both metals was found to decrease with increasing colloid concentration. Competitive sorption experiments indicated that at high colloid concentration (1-2 g/L), Cs sorption was reduced in the presence of U(VI), and at low colloid concentration (0.01-0.5 g/L), both Cs and U(VI) Kds were reduced when they were present together due to competition for similar sorption sites. The results from this study imply that in brackish carbonate rock aquifers, typical of the Israeli northern Negev Desert, both U(VI) and Cs are more likely to be mobile as dissolved species rather than as colloid-associated solids.