Andre Peters

The fate of silver nanoparticles in soil solution--Sorption of solutes and aggregation.

Nanoparticles enter soils through various pathways. In the soil, they undergo various interactions with the solution and the solid phase. We tested the following hypotheses using batch experiments: i) the colloidal stability of Ag NP increases through sorption of soil-borne dissolved organic matter (DOM) and thus inhibits aggregation; ii) the presence of DOM suppresses Ag oxidation; iii) the surface charge of Ag NP governs sorption onto soil particles. Citrate-stabilized and bare Ag NPs were equilibrated with (colloid-free) soil solution extracted from a floodplain soil for 24h. Nanoparticles were removed through centrifugation. Concentrations of free Ag ions and DOC, the specific UV absorbance at a wavelength of 254 nm, and the absorption ratio α254/α410 were determined in the supernatant. Nanoparticle aggregation was studied using time-resolved dynamic light scattering (DLS) measurement following the addition of soil solution and 1.5mM Ca(2+) solution. To study the effect of surface charge on the adsorption of Ag NP onto soil particles, bare and citrate-stabilized Ag NP, differing in the zeta potential, were equilibrated with silt at a solid-to-solution ratio of 1:10 and an initial Ag concentration range of 30 to 320 μg/L. Results showed that bare Ag NPs sorb organic matter, with short-chained organic matter being preferentially adsorbed over long-chained, aromatic organic matter. Stabilizing effects of organic matter only come into play at higher Ag NP concentrations. Soil solution inhibits the release of Ag(+) ions, presumably due to organic matter coatings. Sorption to silt particles was very similar for the two particle types, suggesting that the surface charge does not control Ag NP sorption. Besides, sorption was much lower than in comparable studies with sand and glass surfaces.

Biochar Reduces Zinc and Cadmium but not Copper and Lead Leaching on a Former Sewage Field

The leaching of trace metals from anthropogenically contaminated sites poses the risk of groundwater pollution. Biochar has recently been proposed as a soil additive to reduce trace-metal concentrations in the soil solution and to increase water retention, thus reducing drainage. However, field studies on the effects of biochar addition on trace-metal leaching are scarce. Therefore, we added 0, 1, 2.5, and 5 g 100 g of biochar derived from giant miscanthus ( × J.M. Greef & Deuter ex Hodk. & Renvoize) to soil contaminated by former wastewater irrigation and examined water retention and cumulative leaching of Zn, Cd, Cu, and Pb in a 2-yr field study. Cumulative trace-metal leaching was determined by self-integrating accumulators (SIAs) based on ion-exchange resins and compared with data calculated from mean concentrations in the soil solution collected with tension lysimeter plates and groundwater recharge rate. The highest rate of biochar addition increased water retention and thus reduced the amount of drainage water. Mean cumulative Zn and Cd fluxes decreased due to both reduced concentrations in the soil solution and reduced drainage. Although Cu and Pb concentrations in the soil solution increased with biochar addition, the reduced drainage resulted in similar fluxes in the biochar and the control treatment. The cumulative Zn, Cd, and Cu fluxes determined with SIAs were in the same range as the calculated values, while SIA-based Pb fluxes were much higher than those calculated. Since the suction plates excluded colloids, the high SIA-based Pb fluxes indicate colloidal transport and reveal the importance to elucidate the colloidal pathway for risk assessment.

Effect of Soil Water Repellency on Energy Partitioning Between Soil and Atmosphere: A Conceptual Approach

Water repellency (WR) is a phenomenon known from many soils around the world and can occur in arid as well as in humid climates; few studies, however, have examined the effect of soil WR on the soil-plant-atmosphere energy balance. The aim of our study was to estimate the effects of soil WR on the calculated soil-atmosphere energy balance, using a solely model-based approach. We made out evapotranspiration to have the largest influence on the energy balance; therefore the effect of WR on actual evapotranspiration was assessed. To achieve this we used climate data and measured soil hydraulic properties of a potentially water-repellent sandy soil from a site near Berlin, Germany. A numerical 1D soil water balance model in which WR was incorporated in a straightforward way was applied, using the effective cross section concept. Simulations were carried out with vegetated soil and bare soil. The simulation results showed a reduction in evapotranspiration of 30–300 mm year−1 (9%–76%) at different degrees of WR compared to completely wettable soil, depending on the severity degree of soil WR. The energy that is not being transported away by water vapor (i.e., due to reduced evapotranspiration) had to be transformed into other parts of the energy balance and thus would influence the local climate.

Long-term Release of Sulfate From Building Rubble–Composed Soil: Lysimeter Study and Numerical Modeling

Abstract High sulfate concentrations in the groundwater occur in several cities and particularly in Berlin, Germany. Building rubble–composed soils and landfills are a major source of dissolved sulfates. This study assesses the sulfate release dynamics of such rubble-composed substrates. The substrate was taken from a building rubble landfill in Berlin, which was created after World War II. It was poured into two lysimeters, which were irrigated repeatedly for 2 years to simulate several years of groundwater recharge. Sulfate concentration in the leachate was measured monthly. Sulfate release dynamics were effectively described with PHREEQC, assuming either one or two sulfate pools with kinetically limited dissolution. The volume that percolated the lysimeter column was 2,440 L, corresponding to 17 years of local groundwater recharge. At the beginning, sulfate concentrations increased from approximately 10·10−3 mol ·L−1 to 13·10−3 mol · L−1, which is close to gypsum solubility concentration. After 1.8 pore volumes, a decrease was observed, and after 8 pore volumes, concentrations were relatively constant at levels less than 3·10−3 mol · L−1. The data were best described by a model that included a kinetically limited dissolution of gypsum from two sulfate pools different in their effective surface areas. One pool can be ascribed to fine-grained gypsum particles, whereas the other can be ascribed to coarse-grained ones. Overall, rubble-composed substrates can be a severe long-term source of sulfates.