Astrid R. Jacobson

Aging and temperature effects on DOC and elemental release from a metal contaminated soil

The combined effect of time and temperature on elemental release and speciation from a metal contaminated soil (Master Old Site, MOS) was investigated. The soil was equilibrated at 10, 28, 45, 70 and 90 degrees C for 2 days, 2 weeks, and 2 months in the laboratory. Dissolved organic carbon (DOC), total soluble elements (by ICP), and labile metals (by DPASV) were determined in the filtered (0.22 microm) supernatants. For the samples equilibrated at 90 degrees C, DOC fractions were size fractionated by filtration and centrifugation; a subsample was only centrifuged while another was also filtered through a 0.45 microm filter. Analyses of the supernatants (ICP, DPASV, DOC) were performed on all size fraction subsamples. Dissolved organic carbon (DOC) increased both with temperature and incubation time; however, metal behavior was not as uniform. In general, total soluble metal release (ICP) paralleled the behavior of DOC, increasing with both time and temperature, and confirming the importance of soil organic matter (SOM) in metal retention. Voltammetric analysis (dpasv) of Cu and Zn showed that very little of these metals remains labile in solution due, presumably, to complexation with dissolved organic matter. Labile concentrations of Cd, on the other hand, constituted a significant portion (50%) of total soluble Cd. Copper and Al increased in solution with time (up to 2 months) and temperature up to 70 degrees C; however, at 90 degrees C the soluble concentration declined sharply. The same behavior was observed after equilibration for longer periods of time (550 days) at lower temperatures (23 and 70 degrees C). While concentrations of labile Cu and total soluble Cu and Al increased in the unfiltered samples, the trend remained the same. DPASV analysis showing shifts in labile Cu complexes with temperature and time, together with the results from the unfiltered samples, lead to the hypothesis that Cu was complexing with large polymers that could form at the elevated temperature, and thus be removed from the analyzed solution. It is possible that Cu and Al released by SOM oxidation has re-sorbed or complexed to more recalcitrant organic matter or to mineral phases. Variations in the relative molecular size fractions present within the DOC pool produced by increased time and temperature may influence the element-DOC complexes present in solution and their behavior in soil environments.

Measurement of fluid contents by light transmission in transient three-phase oil-water-air systems in sand

Most three-phase flow models lack rigorous validation because very few methods exist that can measure transient fluid contents of the order of seconds of whole flow fields. The objective of this study was to develop a method by which fluid content can be measured rapidly in three-phase systems. The method uses the hue and intensity of light transmitted through a slab chamber to measure fluid contents. The water is colored blue with CuSO4. The light transmitted by high-frequency light bulbs is recorded with a color video camera in red, green, and blue and then converted to hue, saturation, and intensity. Calibration of hue and intensity with water, oil, and air is made using cells filled with different combinations of the three fluids. The results show that hue and water content are uniquely related over a large range of fluid contents. Total liquid content is a function of both hue and light intensity. The air content is obtained by subtracting the liquid content from the porosity. The method was tested with static and transient experiments. Measurements made with the light transmission method (LTM) and synchrotron X rays of the static experiment agreed well. In the transient experiments, fingers were formed by dripping water on the surface in a two-dimensional slab chamber with partially oil-saturated sand. The LTM is able to capture the spatial resolution of the fluid contents and can provide new insights in rapidly changing, three-phase flow systems.

The phytotoxicity of ZnO nanoparticles on wheat varies with soil properties.

Zn is an essential element for plants yet some soils are Zn-deficient and/or have low Zn-bioavailability. This paper addresses the feasibility of using ZnO nanoparticles (NPs) as soil amendments to improve Zn levels in the plant. The effects of soil properties on phytotoxicity and Zn bioavailability from the NPs were studied by using an acidic and a calcareous alkaline soil. In the acid soil, the ZnO NPs caused dose-dependent phytotoxicity, observed as inhibition of elongation of roots of wheat, Triticum aestivum. Phytotoxicity was mitigated in the calcareous alkaline soil although uptake of Zn from the ZnO NPs occurred doubling the Zn level compared to control plants. This increase occurred with a low level of Zn in the soil solution as expected from the interactions of Zn with the soil components at the alkaline pH. Soluble Zn in the acid soil was 200-fold higher and shoot levels were tenfold higher than from the alkaline soil correlating with phytotoxicity. Mitigation of toxicity was not observed in plants grown in sand amended with a commercial preparation of humic acid: growth, shoot uptake and solubility of Zn from the NPs was not altered by the humic acid. Thus, variation in humic acid between soils may not be a major factor influencing plant responses to the NPs. These findings illustrate that formulations of ZnO NPs to be used as a soil amendment would need to be tuned to soil properties to avoid phytotoxicity yet provide increased Zn accumulations in the plant.

Whither goes soil science in the United States and Canada

Institutional and student surveys carried out in 1992 and 2004 suggest that soil science education is experiencing a significant decline in the United States and Canada. The present article reports on the data obtained in these surveys, particularly the fact that the enrollment in MSc and PhD programs in soil science in US and Canadian universities in 2004 was approximately 40% less than that in 1992. Some of the possible causes of this drop are analyzed in detail, such as the tendency of soil science education programs to keep emphasizing the agricultural side of soil science (i.e., its connection to crop production), despite the open intention of most students to pursue careers dealing predominantly, or at least in part, with environmental issues. It is argued that measures could still be taken by soil science educators and soil scientists to revert the downward trend in enrollments. Among these are licensing soil scientists, being vigilant about oversimplifications and misrepresentations of soil processes by researchers in other disciplines, expanding the scope of soil science and actively promoting its achievements, and making sure that the public at large is aware of the intrinsic, challenging complexity of soils and that it mandates a unique pluridisciplinary approach. We believe that if some of these measures were adopted, soil science could relatively and rapidly regain its place in the pantheon of science.

Coupled effects of solution chemistry and hydrodynamics on the mobility and transport of quantum dot nanomaterials in the vadose zone

To investigate the coupled effects of solution chemistry and hydrodynamics on the mobility of quantum dot (QD) nanoparticles in the vadose zone, laboratory scale transport experiments involving single and/or sequential infiltrations of QDs in unsaturated and saturated porous media, and computations of total interaction and capillary potential energies were performed. As ionic strength increased, QD retention in the unsaturated porous media increased; however, this retention was significantly suppressed in the presence of a non-ionic surfactant in the infiltration suspensions as indicated by surfactant enhanced transport of QDs. In the vadose zone, the non-ionic surfactant limited the formation of QD aggregates, enhanced QD mobility and transport, and lowered the solution surface tension, which resulted in a decrease in capillary forces that not only led to a reduction in the removal of QDs, but also impacted the vadose zone flow processes. When chemical transport conditions were favorable (ionic strength of 5 × 10(-4)M and 5 × 10(-3)M, or ionic strengths of 5 × 10(-2)M and 0.5M with surfactant), the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were meso-scale processes, where infiltration by preferential flow results in the rapid transport of QDs. When chemical transport conditions were unfavorable (ionic strength of 5 × 10(-2)M and 0.5M) the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were pore-scale processes governed by gas-water interfaces (GWI) that impact the mobility of QDs. The addition of surfactant enhanced the transport of QDs both in favorable and unfavorable chemical transport conditions. The mobility and retention of QDs was controlled by interaction and capillary forces, with the latter being the most influential. GWI were found to be the dominant mechanism and site for QD removal compared with solid-water interfaces (SWI) and pore straining. Additionally, ripening phenomena were demonstrated to enhance QDs removal or retention in porous media and to be attenuated by the presence of surfactant.

Alleviating Moisture Content Effects on the Visible Near-Infrared Diffuse-Reflectance Sensing of Soils

With rising ambient temperature and atmospheric carbon dioxide levels, there is an urgent need to monitor soil carbon stocks over large regions of the earth. Near-infrared diffuse reflectance sensing (NIRS) of soils, using satellite- or airplane-based instruments, is increasingly regarded as a potential method of choice for this purpose. Considerable research has been devoted to NIRS in the last few years, but this research has been generally restricted to sieved air-dried soils analyzed under laboratory conditions. For NIRS to be useful for the estimation of soil carbon stocks in the field, a technique must be developed to account, among other things, for the presence of moisture in the surface layer of soils. In this context, a first objective of the research described in this article was to determine whether, for three soils with contrasting characteristics, a simple constant proportionality factor relates NIR spectra obtained at different moisture contents, and whether there is relative constancy of this proportionality factor among soils, suggesting the possibility of a practical strategy to correct NIR spectra for soil moisture. A second objective of the research was to use ratio and derivative analysis to identify portions of NIR spectra that appear least affected by moisture content and on which a determination of other parameters such as organic matter content could be based. Because constant proportionality of the spectra at different moisture contents seems elusive, at best, the most significant result obtained is the identification of specific wavelength ranges in the NIR spectra, at 800 to 1400 nm, 1600 to 1700 nm, 2100 to 2200 nm, and 2300 to 2500 nm, where the first derivative of the spectra seems independent of the moisture content of the soil samples. This observation suggests that an operational method could be developed, focused on these wavelength intervals, to obtain moisture-independent estimates of a range of soil parameters under field conditions.

A Root-Colonizing Pseudomonad Lessens Stress Responses in Wheat Imposed by CuO Nanoparticles

Nanoparticle (NPs) containing essential metals are being considered in formulations of fertilizers to boost plant nutrition in soils with low metal bioavailability. This paper addresses whether colonization of wheat roots by the bacterium, Pseudomonas chlororaphis O6 (PcO6), protected roots from the reduced elongation caused by CuO NPs. There was a trend for slightly elongated roots when seedlings with roots colonized by PcO6 were grown with CuO NPs; the density of bacterial cells on the root surface was not altered by the NPs. Accumulations of reactive oxygen species in the plant root cells caused by CuO NPs were little affected by root colonization. However, bacterial colonization did reduce the extent of expression of an array of genes associated with plant responses to stress induced by root exposure to CuO NPs. PcO6 colonization also reduced the levels of two important chelators of Cu ions, citric and malic acids, in the rhizosphere solution; presumably because these acids were used as nutrients for bacterial growth. There was a trend for lower levels of soluble Cu in the rhizosphere solution and reduced Cu loads in the true leaves with PcO6 colonization. These studies indicate that root colonization by bacterial cells modulates plant responses to contact with CuO NPs.

Quantification of Cryptosporidium parvum in natural soil matrices and soil solutions using qPCR

Traditional microscopy methods for the detection and quantification of Cryptosporidium parvum in soil matrices are time-consuming, labor-intensive, and lack sensitivity and specificity. This research focused on developing a qPCR protocol for the sensitive and specific detection and quantification of C. parvum in natural soil matrices and soil-water extracts. The physico-chemical parameters - lysis media, number of thermal shocks and thawing temperatures - controlling DNA extraction efficiency were investigated. Experimental results identified oocyst age as a critical parameter affecting oocyst disruption and quantification. The most efficient oocyst disruption method for C. parvum oocysts regardless of their age was established as 5 thermal shocks with thawing at 65°C in Tris-EDTA (TE) buffer. In addition to the purification columns used to remove PCR inhibitors present in environmental matrices, a combination of 3mM MgCl(2) and 600ng/μl BSA yielded the highest amplicon yield for both young and aged oocysts. Sucrose flotation was determined to be a better oocyst isolation method than two-phase flotation. The optimized parameters for DNA extraction and the qPCR assay resulted in very specific and sensitive detection of C. parvum. Minimum detection limits were 0.667 for young C. parvum oocysts and 6.67 for aged C. parvum oocysts per PCR reaction. The accuracy of the detections and quantifications was 0.999. Protocol performance was tested in contrasting soil samples and soil-water extract samples on the basis of percentage of recovery (PR) values. Depending on the number of oocysts used to inoculate the samples, the average PR values ranged from 7.2 to 43.5%, 29.3-52.5%, and 11.5-60.8% for Trenton, Greenson, and Sparta soil-water extracts, respectively, and 12.1-77% for DI water. PR values ranged from 4.3% to 107.8% for Trenton, Greenson and Sparta soil samples.

Electron paramagnetic resonance analysis of the distribution of a hydrophobic spin probe in suspensions of humic acids, hectorite, and aluminum hydroxide-humate-hectorite complexes.

Until recently, there were no techniques capable of direct observation of the microscale locations where nonpolar organic compounds accumulate when associated with natural geosorbents. The ability of electron paramagnetic resonance (EPR) spectroscopy to monitor and elucidate directly the different molecular-scale environments of paramagnetic spin probes has been demonstrated lately in model soils, yet it remains untested in complex systems. In this general context, the present investigation was aimed at assessing the extent to which EPR could be used to monitor the sorption of 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy benzoate (TEMPO benzoate), a hydrophobic spin probe, on a smectite (hectorite), two humic acids, and their complexes in the presence or absence of aluminum hydroxide. Results demonstrate that EPR is able to monitor easily adsorption on these sorbents in batch-style experiments. Distribution coefficient (Kd) values of 455.4 and 483.1 ml/g were found for the adsorption of TEMPO benzoate on hectorite-humic acids complexes, compared to respective Kd values of 46 and 147 ml/g predicted solely on the basis of the mass of humic acids present in the complexes. These observations confirm the significant role of hectorite for the sorption of hydrophobic compounds, together with humic acids, contrary to common belief that emphasizes the almost exclusive sorptive role of organic matter. In addition, for the first time, EPR is able to provide evidence that hydrophobic molecules in the presence of geosorbents can segregate in multimolecular clusters that are in equilibrium with aqueous probe concentrations below the probes solubility threshold. Possible consequences of this clustering process in terms of the fate and transport of hydrophobic compounds in subsurface environments are discussed.

Ceramic Aggregate Sorption and Desorption Chemistry: Implications for Use as a Component of Soilless Media

Ceramic aggregates (Turface® and Profile®) are common soilless media components, but their sorption/desorption chemistry is poorly understood. We investigated: labile (readily desorb-able or readily plant-available) ion concentrations; the effect of rinsing and soaking pretreatments on labile ions; sorption of applied nutrients; and nutrient uptake from the aggregates by plants. Variability in labile ions was extremely high among bags of aggregates. Manganese, boron, magnesium, calcium, sulfur and potassium were most likely to desorb in excess for plants. Phosphorus, iron, copper and zinc were sorbed by the aggregates; only copper was found nearly deficient in plant tissue. Rinsing and soaking pretreatments adjusted labile ions to more suitable concentrations for plants. However, growth data suggested a worst-case scenario of high levels of labile ions may not be mitigated by these pretreatments. With frequent leaching after planting or where the aggregates are a minor component of media, excessive nutrient uptake would likely be limited.