The use of ozone in the remediation of polycyclic aromatic hydrocarbon contaminated soil

The potential of using ozone for the removal of phenanthrene from several different soils, both alone and in combination with biodegradation using a microbial inoculant (Pseudomonas alcaligenes PA-10), was examined. The greater the water content of the soil the less effective the ozone treatment, with air-dried soils showing the greatest removal of phenanthrene; while soils with higher levels of clay also reduced the effectiveness of the ozone treatments. However, at least a 50% reduction in phenanthrene levels was achieved in air-dried soil after an ozone treatment of 6 h at 20 ppm, with up to 85% removal of phenanthrene achieved in sandy soils. The biodegradation results indicate that P. alcaligenes PA-10 may be useful as an inoculant for the removal of PAHs from contaminated soils. Under the conditions used in our experiments, however, pre-ozonation did not enhance subsequent biodegradation of phenanthrene in the soils. Similar levels of phenanthrene removal occurred in both non-ozonated and ozonated Cruden Bay soil inoculated with P. alcaligenes PA-10. However, the biodegradation of phenanthrene in ozonated Boyndie soil was much slower. This may be due to the release of toxic products in this soil during ozonation.     

Remediation efficiency of vapour extraction of sandy soils contaminated with cyclohexane: Influence of air flow rate, water and natural organic matter content

This work reports the analysis of the efficiency and time of soil remediation using vapour extraction as well as provides comparison of results using both, prepared and real soils. The main objectives were: (i) to analyse the efficiency and time of remediation according to the water and natural organic matter content of the soil; and (ii) to assess if a previous study, performed using prepared soils, could help to preview the process viability in real conditions. For sandy soils with negligible clay content, artificially contaminated with cyclohexane before vapour extraction, it was concluded that (i) the increase of soil water content and mainly of natural organic matter content influenced negatively the remediation process, making it less efficient, more time consuming, and consequently more expensive; and (ii) a previous study using prepared soils of similar characteristics has proven helpful for previewing the process viability in real conditions.     

Cry1Ab protein from Bt transgenic rice does not residue in rhizosphere soil

Expression of Cry1Ab protein in Bt transgenic rice (KMD) and its residue in the rhizosphere soil during the whole growth in field, as well as degradation of the protein from KMD straw in five soils under laboratory incubation were studied. The residue of Cry1Ab protein in KMD rhizosphere soil was undetectable (below the limit of 0.5 ng/g air-dried soil). The Cry1Ab protein contents in the shoot and root of KMD were 3.23-8.22 and 0.68-0.89 microg/g (fresh weight), respectively. The half-lives of the Cry1Ab protein in the soils amended with KMD straw (4%, w/w) ranged from 11.5 to 34.3d. The residence time of the protein varied significantly in a Fluvio-marine yellow loamy soil amended with KMD straw at the rate of 3, 4 and 7%, with half-lives of 9.9, 13.8 and 18d, respectively. In addition, an extraction method for Cry1Ab protein in soil was developed, with extraction efficiencies of 46.4-82.3%.     

Soil remediation time to achieve clean-up goals II: Influence of natural organic matter and water contents

This work reports a relatively rapid procedure for the forecasting of the remediation time (RT) of sandy soils contaminated with cyclohexane using vapour extraction. The RT estimated through the mathematical fitting of experimental results was compared with that of real soils. The main objectives were: (i) to predict the RT of soils with natural organic matter (NOM) and water contents different from those used in experiments; and (ii) to analyse the time and efficiency of remediation, and the distribution of contaminants into the soil matrix after the remediation process, according to the soil contents of: (ii1) NOM; and (ii2) water. For sandy soils with negligible clay contents, artificially contaminated with cyclohexane before vapour extraction, it was concluded that: (i) if the NOM and water contents belonged to the range of the prepared soils, the RT of real soils could be predicted with relative differences not higher than 12%; (ii1) the increase of NOM content from 0% to 7.5% increased the RT (1.8-13 h) and decreased the remediation efficiency (RE) (99-90%) and (ii2) the increase of soil water content from 0% to 6% increased the RT (1.8-4.9 h) and decreased the RE (99-97%). NOM increases the monolayer capacity leading to a higher sorption into the solid phase. Increasing of soil water content reduces the mass transfer coefficient between phases. Concluding, NOM and water contents influence negatively the remediation process, turning it less efficient and more time consuming, and consequently more expensive.     

Fluorescent Tracer Studies of Pollutant Transport in the San Francisco Bay Area

To simulate the transport and diffusion of airborne contaminants across a metropolitan region, point-source releases of fluorescent tracer material were made near various urban centers and some 50 samplers were arrayed in expected downwind directions. The effects of land-water, hill-valley, and urban-rural differences on airflow and diffusion were observed in their existing interrelationships during these experiments. Since the tracer could be assessed with high sensitivity over great distances, tracer results provided a quantitative indicator of pollutant dispersion across an extensive metropolitan complex.

From July 1967 through June 1968, the test series included typical seasonal weather patterns, with emphasis on those conducive to the travel and accumulation of pollutants. In each test about 15 kilograms of tracer material were released during two-hour periods, and significant dosages were found at downwind distances up to 80 kilometers. All tests were conducted during daylight hours, to coincide better with the oxidant-type pollution important in this region.

Dispersion characteristics showed much greater complexity than predictable from classical models, thus limiting the applicability of such models in this region. Built-up urban areas increased the initial dispersion rates of tracer clouds, and travel over water tended to decrease them. Hilly terrain resulted in increased dispersion, but channeling associated with such terrain caused locally higher concentrations. The complex horizontal dosage patterns obtained did confirm previously observed airflow patterns as aids in predicting pollutant distributions.     

Soil remediation time to achieve clean-up goals I: Influence of soil water content

The current models are not simple enough to allow a quick estimation of the remediation time. This work reports the development of an easy and relatively rapid procedure for the forecasting of the remediation time using vapour extraction. Sandy soils contaminated with cyclohexane and prepared with different water contents were studied. The remediation times estimated through the mathematical fitting of experimental results were compared with those of real soils. The main objectives were: (i) to predict, through a simple mathematical fitting, the remediation time of soils with water contents different from those used in the experiments; (ii) to analyse the influence of soil water content on the: (ii(1)) remediation time; (ii(2)) remediation efficiency; and (ii(3)) distribution of contaminants in the different phases present into the soil matrix after the remediation process. For sandy soils with negligible contents of clay and natural organic matter, artificially contaminated with cyclohexane before vapour extraction, it was concluded that (i) if the soil water content belonged to the range considered in the experiments with the prepared soils, then the remediation time of real soils of similar characteristics could be successfully predicted, with relative differences not higher than 10%, through a simple mathematical fitting of experimental results; (ii) increasing soil water content from 0% to 6% had the following consequences: (ii(1)) increased remediation time (1.8-4.9h, respectively); (ii(2)) decreased remediation efficiency (99-97%, respectively); and (ii(3)) decreased the amount of contaminant adsorbed onto the soil and in the non-aqueous liquid phase, thus increasing the amount of contaminant in the aqueous and gaseous phases.     

Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils

Rhizosphere is a microbiosphere and has quite different chemical, physical and biological properties from bulk soils. A greenhouse experiment was performed to compare the difference of fractionation and bioavailability of trace elements Cr, Ni, Zn, Cu, Pb and Cd between rhizosphere soil and bulk soil. In the meantime, the influence of air-drying on the fractionation and bioavailability was also investigated by using wet soil sample as a control. Soils in a homemade rhizobox were divided into four zones: rhizosphere, near rhizosphere, near bulk soil and bulk soil zones, which was designated as S1, S2, S3 and S4. Elemental speciations were fractionated to water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3) by a sequential extraction procedure. Speciation differences were observed for elements Cr, Ni, Zn, Cu, Pb and Cd between the rhizosphere and bulk soils, and between the air-dried and wet soils as well. The concentrations of all six heavy metals in fraction B1 followed the order of S2 > S3 > S1 > S4 and for B2, the order was S2 > S3 S4 > S1. For B3, the order was S1 > S3 S4 > S2, while for Cd the order was S2 > S3 approximately/= S4 > S1. The air-drying increased elemental concentration in fractions B1 and B2 by 20-50% and decreased in fraction B3 by about 20-100%. Correlation analysis also indicated that the bioavailability correlation coefficient of fraction B1 in rhizosphere wet soil to plants was better than that between either air-dried or nonrhizosphere soils. Therefore, application of rhizosphere wet soils should be recommended in the future study on the speciation analysis of trace elements in soils and bioavailability.     

Quantity and spectroscopic properties of soil dissolved organic matter (DOM) as a function of soil sample treatments: air-drying and pre-incubation

The dissolved organic matter (DOM) in soils is essentially defined by the way in which it is obtained. Therefore, we need to understand as to how pre-treatment of a soil will affect the characteristics of DOM, since this fraction may be strongly influenced by a soil's water content. The effect of two different pre-treatments on DOM from the A-horizons of a large variety of ecosystems and regions were compared. In both cases the soils were allowed to air-dry. In one case the air-dried soil was directly extracted (AD), while in the other case it was preincubated for 1 week at 50% of its water holding capacity (INCU). AD is simpler, but INCU brings the soil, and especially its microbial population, back to a standardised state, which is more representative of the usual state in the field. Both methods are used whenever an adjustment of the soil water content is essential to compare different regions or to eliminate short term weather effects. A significant regression indicated that the dissolved organic carbon (DOC) extracted from INCU samples was only 20% of AD DOC. Both the absorptivity (UV absorption divided by DOC) of 86% of the samples, and a fluorescence emission spectrum based Humification Index in all cases increased as a result of preincubation. This would indicate that labile compounds released during drying were metabolised during the incubation. However, the magnitude of this increase varied, and no correlation with soil organic and microbial carbon, pH, or texture could be detected. The results show that DOM extracted from AD and INCU soils is not comparable and that the differences are mainly due to the impact of air-drying on the microbial activity.     

Soil vapor extraction in sandy soils: influence of airflow rate

Airflow rate is one of the most important parameters for the soil vapor extraction of contaminated sites, due to its direct influence on the mass transfer occurring during the remediation process. This work reports the study of airflow rate influence on soil vapor extractions, performed in sandy soils contaminated with benzene, toluene, ethylbenzene, xylene, trichloroethylene and perchloroethylene. The objectives were: (i) to analyze the influence of airflow rate on the process; (ii) to develop a methodology to predict the remediation time and the remediation efficiency; and (iii) to select the most efficient airflow rate. For dry sandy soils with negligible contents of clay and natural organic matter, containing the contaminants previously cited, it was concluded that: (i) if equilibrium between the pollutants and the different phases present in the soil matrix was reached and if slow diffusion effects did not occur, higher airflow rates exhibited the fastest remediations, (ii) it was possible to predict the remediation time and the efficiency of remediation with errors below 14%; and (iii) the most efficient remediation were reached with airflow rates below 1.2 cm(3)s(-1) standard temperature and pressure conditions.     

Forms of cadmium in sandy soils after amendment with soils of higher fixing capacity

Most of the Cd applied through phosphatic fertilizers in sandy soils tends to stay in mobile forms (soluble or exchangeable) and hence the risk of it leaching to underground water or its uptake by plants is higher. A sequential extraction procedure was used to assess the efficacy of amending materials (soils containing inorganic or organic adsorption components) on the re-distribution of forms of Cd in a sandy soil. Amendment of the sandy soil with each of the three soils (yellow earth, lateritic podzolic and peaty sand) was generally effective in altering the more mobile or available forms of Cd to immobile or unavailable forms. The extent of alteration varied with the type of component present in the amendment soil, pH and the rate of Cd addition. The yellow earth was more effective at pH 7, whereas the peaty sand was equally effective at both pH 4 and 7 in altering the mobile to immobile forms. The lateritic podzolic soil was the least effective of the soils used at any of the pH values.     

Metal accumulation in wild plants surrounding mining wastes

Four sites were selected for collection of plants growing on polluted soil developed on tailings from Ag, Au, and Zn mines at the Zacatecas state in Mexico. Trace element concentrations varied between sites, the most polluted area was at El Bote mine near to Zacatecas city. The ranges of total concentration in soil were as follows: Cd 11-47, Ni 19-26, Pb 232-695, Mn 1132-2400, Cu 134-186 and Zn 116-827 mg kg(-1) air-dried soil weight. All soil samples had concentrations above typical values for non-polluted soils from the same soil types (Cd 0.6+/-0.3, Ni 52+/-4, Pb 41+/-3mg kg(-1)). However, for the majority of samples the DTPA-extractable element concentrations were less than 10% of the total. Some of the wild plants are potentially metal tolerant, because they were able to grow in highly polluted substrates. Plant metal analysis revealed that most species did not translocate metals to their aerial parts, therefore they behave as excluder plants. Polygonum aviculare accumulated Zn (9236 mg kg(-1)) at concentrations near to the criteria for hyperaccumulator plants. Jatropha dioica also accumulated high Zn (6249 mg kg(-1)) concentrations.     

A lysimeter experiment to investigate temporal changes in the availability of pesticide residues for leaching

Leaching of three pesticides (isoproturon, chlorotoluron and triasulfuron) and a tracer (bromide) were determined in four contrasting soils ranging in texture from sandy loam to clay. The compounds were applied to undisturbed columns of soil and four columns for each soil were randomly selected and leached with 24-mm equivalent of water at prescribed time intervals (3, 9, 24, 37 and 57 d after application). A rapid decline in leached loads of isoproturon and chlorotoluron as time from application to irrigation increased was observed in all soils. In contrast, triasulfuron and bromide loads only decreased rapidly in the clay soil. Bromide losses decreased with decreasing clay contents of the soil and therefore with a decrease in structural development. Magnitudes of pesticide losses varied from soil to soil, depending on structural development and the organic carbon content. Pesticide degradation experiments on disturbed and undisturbed soil samples showed that the rapid decline of leached loads with time was faster than could be explained by degradation alone. Five physico-chemical processes are put forward to explain the different patterns of pesticide leached loads observed in the soils: (1) relative extent of preferential flow, (2) sorption capacity of the compounds to the different soils, (3) extent of degradation of the compounds in the soil, (4) variation in sorption kinetics between compounds associated with pesticide diffusion into soil aggregates, and (5) protection of the compounds by a combination of intra-aggregate diffusion and the presence of preferential flow pathways.     

Residual gasoline saturation in unsaturated soil with and without organic matter

The goal of this study was to investigate the influence of one variable, natural organic matter, on residual gasoline saturation in sandy soils. Capillary pressure-saturation (P_c−S) relationships (air-gasoline) were determined for three physically-similar sandy soils, with different organic carbon contents (0.086%, 0.89% and 1.65%) and residual gasoline saturations were compared. Two initial moisture conditions, residual water saturation and air-dry, were evaluated. One soil type was packed to two different bulk densities. Visualization of the soils using cryo-scanning electron microscopy was performed to aid in better understanding the role of the organic matter in the soil. The results showed that soils with higher organic contents had higher residual gasoline saturations when starting with an initially air-dry soil. Increasing the bulk density of the same air-dried soil resulted in an increase in residual gasoline saturation. In the presence of a residual water saturation, however, residual gasoline saturations were virtually identical for the three soils and independent of bulk density; approximately 5–10 times lower than in soil that was initially air-dry. The presence of the residual water effectively coated the surface of the soil thereby reducing or eliminating gasoline/soil interactions. Some residual water may also be occupying very small pore spaces, making these locations inaccessible to the gasoline.     

Evaluation of air permeability in layered unsaturated materials

Field estimation of air permeability is important in the design and operation of soil-vapor extraction systems. Previous models have examined airflow in homogenous soils, incorporating leakage through a low-permeability cap either as a correction to the airflow equation or as a boundary condition. The dual leakage model solution developed here improves upon the previous efforts by adding a leaky lower boundary condition, allowing for the examination of airflow in heterogeneous layered soils. The dual leakage model is applied to the evaluation of pump tests at a pilot soil-vapor extraction system at the Savannah River Site in South Carolina. A thick, low-permeability, stiff clay layer divides the stratigraphy at the site into two units for evaluation. A modified version of the previous model, using the water table as the impermeable lower boundary, is used to evaluate the permeability of the low-permeability stiff clay layer (3.2 x 10(-10) cm(2)) and permeable sand (7.2 x 10(-7) cm(2)) beneath it. The stiff clay permeability estimate is used in the evaluation of the shallow unit. Permeability estimates of the shallow sand (3.8 x 10(-7) cm(2)) and kaolin cap (1.5 x 10(-9)cm(2)) were obtained with the dual leakage model. The shallow unit was evaluated using the previous model for comparison. The effects of anisotropy were investigated with a series of model simulations based on the shallow unit solution. The anisotropy sensitivity analysis suggests that increased anisotropy ratio or decreased axial permeability has a significant impact on the velocity profile at the lower boundary, especially at high values of the anisotropy ratio. This result may increase estimates of SVE removal rates for contaminants located at the interface of the lower boundary, typical of chlorinated solvent contamination.     

Pressurized liquid extraction of six tetracyclines from agricultural soils

Veterinary antibiotics used in agriculture can be introduced into the environment through land application of animal manure, accumulating in soils and groundwaters and posing a significant risk to human health and animal well-being. As the analysis of tetracyclines in soil is challenging due to their strong interaction with soil minerals and organic carbon, the objective of this study was to develop a reliable and reproducible method for quantitative analysis of chlortetracycline and oxytetracycline, and their respective metabolites in soils. A method based on pressurized liquid extraction (PLE) with in-cell clean-up was developed for the extraction of chlortetracycline and oxytetracycline and four likely metabolites from a set of four soils. Optimized conditions included a cell size of 22?mL, soil loading of 5?g, pH of 8.0, methanol:water ratio of 3:1, 50?°C, and two cycles. Soil extracts were analysed by high-performance liquid chromatography (HPLC) coupled with ion trap mass spectrometry (MS). Recoveries of seven tetracyclines from soil ranged from 41% to 110%. The limits of detection for tetracyclines were 0.08–0.3 µg g^?1 soil, and intra- and inter-day variation ranged from 0.12–0.34%. The proposed PLE method is suitable for quantification of tetracyclines in agricultural soils at typical concentrations expected in contaminated environments.     

Distribution and partitioning of depleted uranium (DU) in soils at weapons test ranges - investigations combining the BCR extraction scheme and isotopic analysis

Depleted uranium (DU) has become a soil contaminant of considerable concern in many combat zones and weapons-testing sites around the world, including locations in Europe, the Middle East and the USA, arising from its dispersion via the application of DU-bearing munitions. Once DU is released into the environment its mobility and bioavailability will, like that of other contaminants, largely depend on the type of associations it forms in soil and on the nature of the soil components to which it binds. In this study we used the BCR sequential extraction scheme to determine the partitioning of DU amongst soil fractions of texturally varying soils from locations affected by weapons-testing activities. Isotopic analyses (MC-ICP-MS and alpha-spectrometry) were performed to verify the presence of DU in whole soils and soil fractions and to determine any preferential partitioning of the contaminant. Results identified soil organic matter as being consistently the most important component in terms of DU retention, accounting for 30-100% of DU observed in the soils examined. However, at greater distances from known contamination points, DU was also found to be largely associated with the exchangeable fraction, suggesting that DU can be mobilised and transported by surface and near-surface water and does remain in an exchangeable (and thus potentially bioavailable) form in soils.     

Effect of phosphate addition on the sorption-desorption reaction of selenium in Japanese agricultural soils

Desorption levels of soil-sorbed selenium (Se) were studied by adding phosphate to 22 typical Japanese agricultural soils. Soil-soil solution distribution coefficients of Se (Kd-Se) were measured using a batch process as an index of Se sorption level, adding 75Se as a tracer. After the Kd measurement, extraction of soil-sorbed 75Se with a 0.1 M or 1 M Na2HPO4 solution followed to determine the amount of 75Se desorbed by the phosphate. When the 0.1 M Na2HPO4 solution was used, 18-70% of soil-sorbed Se was extracted (average: 47%). However, when the 1 M Na2HPO4 solution was used, 27-83% of soil-sorbed Se was extracted (average: 57%). The observed 75Se desorption percentage indicated the maximum Se removability by phosphate addition. The desorption percentage of Se with 1 M Na2HPO4 correlated with Kd-Se values, suggesting that the soil sample with higher Kd-Se contained more reactive components for phosphate-sorption than the soil sample with lower Kd-Se. To evaluate the effect of phosphate concentration on the Se sorption, the Kd-Se was measured for two typical soils under different levels of phosphate (0.1-10 mM PO4). The Kd values were decreased by phosphate addition for both soils. The Kd decrease was observed even for just 1 mM PO4. The phosphate addition with 1 mM PO4 is the same level as in P fertilizer applied to paddy fields in Japan. Therefore, it was suggested that Se desorption should occur in Japanese soils due to the phosphate input.     

Distribution coefficient of selenium in Japanese agricultural soils

In order to evaluate the selenium (Se) sorption level in Japanese soils, soil/soil solution distribution coefficients (K(d)s) were obtained for 58 agricultural soil samples (seven soil classification groups) using 75Se as a tracer. Although several chemical forms of Se are present in agricultural fields, selenite was used, because it is the major inorganic Se form in acid soils such as found in Japan. The Kd values obtained covered a wide range, from 12 to 1060l/kg, and their arithmetic mean was 315l/kg. Among the soil groups, Andosols had higher Kd values. The Kd values for all samples were highly correlated with soil active-aluminum (Al) and active-iron (Fe) contents. Thus, active-Al and active-Fe were considered to be the major adsorbents of Se. Then, a new sequential extraction procedure was applied to 12 soil samples in order to quantify the effect of soil components on Se adsorption. The sequential extraction results showed that 80-100% of the adsorbed Se was recovered as Al-bound Se and Fe-bound Se. The amount of Al-bound Se was the highest in the soils that showed high Kd values, though the relative contribution of Fe-bound Se tended to increase with decreasing Kd values. The high values of Kd seemed to be caused mainly by the adsorption of Se onto active-Al in Japanese soils.     

Fate of 3,3′,4,4′-tetrachloroazobenzene in soybean plants grown in treated soils

Three soils of varying organic matter (OM) concentrations (0, 1.7 and 57%) were treated with 3,3′4,4′-tetrachlorazobenzene (TCAB) at the 25 ppm level. Germinated soybeans$\text{(Glycine}$$\text{max}$ (L.) Merr.) were planted in the treated soils, along with controls, and grown for 12 days. The shoots, roots and soil were air-dried and analyzed for TCAB and 3,3′,4,4′-tetrachloroazoxybenzene (TCAOB). TCAB appears to translocate from the treated soil into the plant shoots and roots. Residue levels varied with the percentage organic matter of each soil; levels as high as 58.4 ppm were identified in roots of soybeans grown in 1.7% OM soil and 0.620 ppm in the shoots from 0% OM soil. TCAOB was identified in soil and root extracts with the highest levels in soybean roots grown in 0% OM soil, 0.317 ppm. Residues of TCAB and TCAOB decreased in soil and root and shoot tissues as percentage OM increased. Bound residues of TCAB were released from roots grown in 0% OM soil by refluxing with boron trifluoride methanol (BF₃CH₃OH).     

Simultaneous analysis of triasulfuron, metsulfuron-methyl and chlorsulfuron in water and alkaline soils by high-performance liquid chromatography

A method capable of simultaneously detecting residues of three sulfonylurea herbicides at microgram/l and microgram/kg level in water and alkaline soils has been described. The method is based on solid phase extraction and HPLC with UV detection. In alkaline soils especially those containing low organic carbon it was possible to extract the herbicides with de-ionised water and no clean up step was needed. Soil samples spiked with technical grade triasulfuron, metsulfuron-methyl and chlorsulfuron were extracted twice by shaking with de-ionised water for one hour and centrifuging at 10,000 rpm for 15 minutes. Supernatants filtered through glass micro-fibre filters were passed through C18 cartridges previously pre-conditioned with methanol and de-ionised water at a flow rate of < 20 ml/min. Residues of the herbicides retained on the cartridge were eluted with acidified methanol. The eluate was analysed by HPLC. A C18 column was used with a mobile phase of methanol/water (40 + 60, V/V for for the herbicide residues were 1.0 microgram/l and 3 micrograms/kg in water and soil, respectively. The average recoveries for water samples ranged from 73-94%, while for soil samples recoveries were 77-97% for the three compounds studied.