Physical and chemical formations of lead contaminants in clay and sediment

The impact of tree barriers on the dispersal of lead in the soil at highway roadsides

Tree windbreaks are common features in high-traffic roadsides that mitigate air pollution, winds, and noise. The impact of tree barriers on the dispersal of lead in the soil was studied at highway roadsides located near Holon city, Israel. A discontinuous line of trees parallel to the highway separated the highway from agricultural fields. The line includes alternating trees and openings; thus, it was divided into two groups: one consists of the areas hidden by trees (windbreaks) and the other includes the open areas exposed to the road (gaps). At each of the windbreaks and gaps, soil samples were collected from the upper 0-5 cm depth at various distances from the road: 6, 11, 27, 40, 60 m. Lead concentration and soil properties associated with lead adsorption (organic matter, texture, calcium carbonate) were determined for all soil samples. At both the windbreak and gap areas, the averages and the medians of lead content declined nonlinearly with increasing distance from the highway. At 6 m distance, the average lead content in the windbreak areas was higher than that in the gaps (176 and 157 mg kg^-1, respectively). At the area between 17 and 40 m distance, an opposite trend was seen. High significant positive correlations were found between lead and calcium carbonate and organic matter contents at both the windbreaks and the gaps. Yet, organic matter content less than 2% did not correlate with lead.

Evolution of tubular copper sulfide nanostructures from copper(i)–metal organic precursor: a superior platform for the removal of Hg(ii) and Pb(ii) ions

Room temperature synthesized porous mixed phase copper sulfide acts as an effective adsorbent for the removal of heavy metal ions from water.

ZnS nanoparticle gels for remediation of Pb2+ and Hg2+ polluted water

ZnS nanoparticle (NP) gel networks were used as cation exchange materials for the removal of Pb(2+) and Hg(2+) from aqueous solutions. First, the suitability of the gel as a remediation material was studied by analyzing the mechanism of the cation exchange reaction. ZnS NP gels can exchange with other divalent cations (Pb(2+), Hg(2+)) under mild reaction conditions. The speed of the reaction is influenced by the reduction potential of the incoming cation. The ZnS aerogels can remove Pb(2+) and Hg(2+) from aqueous solutions with a wide range of initial concentrations. For initial Pb(2+) concentrations of 100 ppb, the Pb(2+) concentration can be reduced below the action limit established by the EPA (15 ppb). Under thermodynamically forcing conditions, the water remediation capacity of the ZnS NP aerogels was determined to be 14.2 mmol Pb(2+)/ g ZnS aerogel, which is the highest value reported to date.

Engineered nanomaterials in soils and water: how do they behave and could they pose a risk to human health?

It is inevitable that, during their use, engineered nanoparticles will be released into soils and waters. There is therefore increasing concern over the potential impacts of engineered nanoparticles in the environment on aquatic and terrestrial organisms and on human health. Once released into the environment, engineered nanoparticles will aggregate to some degree; they might also associate with suspended solids, sediment, be accumulated by organisms and enter drinking water sources and food materials. These fate processes are dependent on the characteristics of the particle and the characteristics of the environmental system. A range of ecotoxicological effects have also been reported, including effects on microbes, plants, invertebrates and fish. Although available data indicate that current risks of engineered nanoparticles in the environment to environmental and human health are probably low, our knowledge of the potential impacts of engineered nanoparticles in the environment on human health is still limited. There is therefore a need for continued work to develop an understanding of the exposure levels for engineered nanoparticles in environmental systems and to begin to explore the implications of these levels in terms of the ecosystem and human health. This will require research in a range of areas, including detection and characterization, environmental fate and transport, ecotoxicology and toxicology.

Reduction of Pb and Zn bioavailable forms in metal polluted soils due to paper mill sludge addition. Effects on Pb and Zn transferability to barley

In the last few years solidification/stabilisation of acidic soils polluted by heavy metals with low-cost sorbents has been investigated. Paper mill sludges are produced in large amounts and their disposal is a serious environmental problem. The possibility was therefore studied of using paper mill sludge as a stabilizer to reduce the bioavailable metal forms in polluted soils and thus the transferability of metals to plants (barley). We first investigated the sorbing properties of paper mill sludge for Zn(II) and Pb(II) and then their fractionation both in a polluted soil and in the same soil amended with paper mill sludge in order to check the decrease in mobile forms. Finally in both soils we tested the uptake of two metals by common barley in order to assess the performance of soil remediation from an ecological point of view. The addition of paper mill sludge to a soil contaminated by lead and zinc induces a decrease in the mobile forms of both metals, probably due to the presence in sludge of organic matter and kaolinite, which are able to bind the metals very strongly. The decrease in the mobile forms, which are the most readily available for uptake by plants, corresponds to a decrease in plant uptake.

Study of pH-dependent charges of soils by surface acid–base properties

The pH-dependent charges of Hungarian soils have been studied via surface acid-base properties. The intrinsic stability constants of protonation and deprotonation processes, as well as the concentration of surface sites, have been determined by surface complexation modeling. The protonation and deprotonation constants have been nearly the same for most soils. There is a relation between the concentration of surface sites and composition, expect for the freshly deposited soils with high primary silicate content. The results show that the concentrations of silanol and aluminol sites are different for each soil, the intrinsic stability constants of protonation and deprotonation processes, however, are nearly the same within experimental error. This can only be explained if these stability constants are real thermodynamic equilibrium constants. The fact that these constants are nearly the same supports the conclusion that we succeeded in excluding all processes that would disturb the measurements. The parameters characteristic of the edge sites of the soils are of two types: (a) the parameters depending on the quality and composition of the soils, (i.e.), the concentration of surface sites; (b) the parameters depending on the thermodynamically well-defined acid-base processes, independent of soil composition.

The effect of mineral composition on the sorption of cesium ions on geological formations

The sorption of cesium-137 on rock samples, mainly on clay rocks, is determined as a function of the mineral composition of the rocks. A relation between the mineral groups (tectosilicates, phyllosilicates, clay minerals, carbonates) and their cesium sorption properties is shown. A linear model is constructed by which the distribution coefficients of the different minerals can be calculated from the mineral composition and the net distribution coefficient of the rock. On the basis of the distribution coefficients of the minerals the cesium sorption properties of other rocks can be predicted.

Study of the change in the properties of Mn–bentonite by aging

In this paper the structure and properties of fresh manganese(II)-bentonite was compared with that of an old substance. It was concluded that the oxidation state of Mn changed. This did not cause many changes in the scanning electron microscope (SEM) and in the X-ray diffraction (XRD) studies; caused minor changes in the Mn concentration (determined by XRF) and thermoanalytical and electron spectroscopy analysis (ESCA). The change in the oxidation state of manganese was indicated by the colors of the samples, the difference in the surface sites, titration curves, redox potentials, adsorption, and catalytic activity of the fresh and the old Mn-bentonite. Potentiometric titration data were evaluated by a surface complexation model using the FITEQL3.2 computer program. Stability constants of edge charge reactions and the number of aluminol, silanol, and edge sites were calculated. Potentiometric titration data of commercial and freshly made MnO2 were also evaluated; the calculated constants and site numbers were compared with that of found in literature. Catalytic and adsorption activity of the samples were also investigated. It was found that fresh Mn-bentonite does not adsorb valine, while the old one and MnO2 does. Fresh Mn-bentonite does not catalyze the decomposition of H2O2, while the old one, as well as MnO2 does.