Assessment of common scab-inducing pathogen effects on potato underground organs via computed tomography scanning.

Common scab caused by Streptomyces scabies is a major bacterial disease of potato (Solanum tuberosum). Its best known symptom is superficial lesions on the surface of progeny potato tubers, observed at harvesting. In this study, effects of S. scabies on space occupancy by underground organs and on structural complexity of root systems are investigated during growth via computed tomography (CT) scanning. Two groups of potato plants were grown in a greenhouse in middle-sized plastic pots. Using a high-resolution X-ray CT scanner formerly used for medical applications, their underground organs and surrounding medium (sieved and autoclaved homogeneous sand) were submitted to CT scanning 4, 6, and 8 weeks after planting. For one group, sand was inoculated with the common scab-inducing pathogen (S. scabies EF-35) at potting. Space occupancy by underground organs was estimated via curve fitting applied to histograms of CT scan data, while three-dimensional skeletal images were used for fractal analysis. Root systems of diseased plants were found to be less complex than those of healthy plants 4 weeks after planting, and the relative growth rates derived from space occupancy measures were of different sign between the two groups from week 4 to week 8.

Optimizing the molarity of a EDTA washing solution for saturated-soil remediation of trace metal contaminated soils.

Three experiments were conducted to optimize the use of ethylenediaminetetraacetic acid (EDTA) for reclaiming urban soils contaminated with trace metals. As compared to Na(2)EDTA, (NH(4))(2)EDTA extracted 60% more Zn and equivalent amounts of Cd, Cu and Pb from a sandy loam. When successively saturating and draining loamy sand columns during a washing cycle, which submerged it once with a (NH(4))(2)EDTA wash and four times with deionised water, the post-wash rinses largely contributed to the total cumulative extraction of Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn. Both the washing solution and the deionised water rinses were added in a 2:5 liquid to soil (L:S) weight ratio. For equal amounts of EDTA, concentrating the washing solution and applying it and the ensuing rinses in a smaller 1:5 L:S weight ratio, instead of a 2:5 L:S weight ratio, increased the extraction of targeted Cr, Cu, Ni, Pb and Zn.

Prediction of drip-loss, pH, and color for pork using a hyperspectral imaging technique.

Many subjective grading methods with poor repeatability and tedious procedures are still widely used in meat industry. In this study, a hyperspectral-imaging-based technique was investigated to evaluate its potentials for objective determination of pork quality attributes. The system extracted spectral and spatial characteristics simultaneously to determinate the quality attributes, drip loss, pH, and color, of pork meat. Six feature band images were selected for predicting the drip loss (459, 618, 655, 685, 755 and 953nm), pH (494, 571,637, 669, 703 and 978nm) and color (434, 494, 561, 637, 669 and 703nm), respectively. Two intensity indices of the band images were used as inputs to establish neural network models to predict the quality attributes. The results showed that with the hyperspectral-imaging system, the drip loss, pH, and color of pork meat could be predicted with correlation coefficients of 0.77, 0.55 and 0.86, respectively. Pork meat could be classified based on their exudative characteristics and color successfully.

Biosorption of heavy metals by red algae (Palmaria palmata).

The biosorption of heavy metals from aqueous solutions was investigated, using a cheap and abundant dry biomass of red algae P. palmata. The Freundlich, Langmuir and Brunauer Emmer and Teller (BET) models were used to describe the uptake of lead (pb2+), copper (Cu2+), nickel (Ni2+), cadmium (Cd 2+) and zinc (Zn2+) on P. palmata. The good fits of the Langmuir and BET models to the experimental data reflected that the sorption on P. palmata was a multi-layer sorption, in which a Langmuir equation could be applied to each layer. The highest maximum sorption capacity q(max), derived from the Langmuir model was 15.17 mg g(-1) for lead and 6.65 mg g(-1) for copper (dry weight metal/dry weight biosorbent) at a pH of 5.5-6. The affinity of metals for P. palmata was found to decrease in the order: Pb2+ > Cd2+ > Cu2+ > Ni2+. The factors influencing copper and lead uptake were found to be contact time, pH, initial concentration and temperature. Biosorption of copper and lead was a rapid process, with 70% and 100% of the respective uptakes occurring within the first 10 minutes.

Estimates of total polychlorinated biphenyl (PCB) compounds in soils/sediments by hydrogenolysis to dicyclohexyl.

A method to determine the total PCB content by hydrogenolysis (hydrodechlorination and hydrogenation) of chlorinated biphenyl compounds was extended to natural particulate matrices (soil and sediment). The contaminated soil was suspended in hexane in the presence of Pd/gamma-Al2O3 in a hydrogen atmosphere then permitted to react for one hour at 65 degrees C. Dicyclohexyl, recovered in the hexane, was quantified by gas chromatography mass spectrometry. The reaction was very efficient for soil/sediment in hexane suspension and virtually complete provided that excess catalyst was added to samples that were burdened with higher PCB loadings prior to reaction otherwise some partial hydrogenation of biphenyl was also observed. The proposed method was validated with the analysis of five certified reference materials.

Subsurface irrigation as a microbial delivery tool for bioaugmentation: transport, distribution and survival in large packed soil columns.

Traditionally, soil surface inoculation and surface irrigation are used for delivery, transport and distribution of bacteria for agricultural and in-situ environmental decontamination applications. The objective of this study was to test whether subsurface irrigation with a water table management (WTM) system, successfully used previously for nutrient delivery, could also be used to deliver bacteria to soil depths. Twelve stainless steel columns, 1000 mm in length and 200 mm in diameter, were packed with a sandy loam soil. Four experimental treatments, two subsurface irrigation and two surface irrigation, were randomly allocated, in triplicate, to the twelve columns. The transport, implantation and survival of Sinorhizobium (Rhizobium) meliloti, strain A-025, in these columns were monitored at different depths and times after surface and subsurface irrigation. Even though the transport of bacterial cells was slower with the subsurface irrigation regime than with surface irrigation, more bacteria were implanted at different depths with subsurface irrigation. The numbers of bacterial cells distributed with subsurface irrigation were 1.6x10(5), 1.3x10(5), 2.6x10(5) and 2.9x10(5) cfu (colony forming units) x g(-1) of soil at 60, 300, 500 and 700 mm depths, respectively, whereas with surface irrigation the numbers were 2.0x10(4), 3.0x10(4), 1.9x10(5), 9.0x10(2) cfu x g(-1) of soil. These results dearly indicate that subirrigation can be used effectively to bioaugment a sandy loam soil matrix.

Biofiltration of residual fertilizer nitrate and atrazine by Rhizobium meliloti in saturated and unsaturated sterile soil columns.

This study was undertaken to investigate whether microbial bioaugmentation of subsurface soil with subsurface irrigation could be used as a biofiltration/biocontrol technology for agricultural pollutants. Nine Plexiglas columns, 458 mm long x 139 mm in diameter, were packed with a sterilized sandy loam soil. Subsurface irrigation, through a controlled water table management system, was used to deliver bacteria, Rhizobium meliloti A-025, to the soil and to maintain aerobic (unsaturated) or anaerobic (saturated) conditions in the columns. Nitrate and atrazine, a fertilizer and a corn herbicide, were applied to the soil surface, and leaching was affected by simulated rainfall events. The soil and drainage waters were analyzed for nitrate and atrazine residues after each rainfall simulation throughout the experimental period during which the soil was kept saturated for a total of 80 days and unsaturated for a total of 70 days. The monitoring of transport and survival of the implanted bacterial strain (A-025) showed that subsurface irrigation was successful in introducing and transporting the bacteria throughout the soil columns. During the saturated period, significantly more (95% probability) nitrate-N leached into the drainage waters from the control columns than from the bioaugmented columns; the increase being 450% or more for the abiotic control columns. The amount of atrazine that leached into the drainage waters during the unsaturated period was also significantly more from control columns as opposed to bioaugmented columns, with the increase being 262%.

Effect of bioaugmentation on microbial transport, water infiltration, moisture loss, and surface hardness in pristine and contaminated soils.

Three different soils, a clay, a pristine sandy loam and a PCB-contaminated sandy loam, were bioaugmented to determine the influence of clay content and contaminants on the transport of bacteria in unsaturated soils, using surface irrigation water as a transport medium. The results indicate that the transport of the implanted bacteria was influenced negatively more by the presence of PCBs than by the clay content of the soil. Transport was directly related to the frequency of irrigation and length of the intervals between irrigation periods, making these variables important factors to consider when applying bioaugmentation via downward percolating water. Other parameters measured after bacterial bioaugmentation were water infiltration, moisture loss, and surface hardness of these soils. Surface water infiltration was affected more by the soil clay content than by the hydrophobic contaminant. Infiltration was significantly but differently influenced by bioaugmentation, positively in clay, negatively in sandy loam, and negatively (to a lesser extent) in the PCB-contaminated sandy loam soils. Moisture loss was slower in the bioaugmented soil than in the control soils, with this difference being most pronounced in the PCB soil. High moisture loss in the bioaugmented clay soil rendered it the hardest soil for surface penetration.

Bioremediation of residual fertilizer nitrate: I. Laboratory demonstration of an on-farm in situ pollution control system.

This exploratory laboratory study was undertaken to develop and test an in situ bioremediation system intended to point the way toward a possible field application. The proposed method uses a water table management (WTM) system to deliver nutrients or other amendments to subsoil microorganisms for biostimulation and subsequent biodegradation of pollutants in the saturated and unsaturated zones of the soil. The study was carried out on packed soil columns and bioremediation of residual fertilizer nitrate was attempted. Different levels of organic carbon supplement (glucose C) were introduced into these columns via subirrigation in order to supplement the readily available organic carbon levels in the soil. The study was carried out in two experimental setups. The first setup investigated (i) the effect of addition of a high (970 mg L(-1)) and a low (120 mg L(-1)) glucose C level and (ii) the efficacy of using the subirrigation system as a method for nutrient delivery in bioremediation of leached nitrate. This setup was monitored with time, depth, and with reference to the nitrate residue in the soil solution. Leached nitrate was denitrified to less than 10 mg L(-1) nitrate N at both glucose levels. The second setup investigated the effect of a range of low levels of glucose C on nitrate decontamination, soil pH, and total microbial count in order to find out an optimal glucose C level that reduced the most nitrate and maintained the pH homeostasis of soil.

Bioremediation of residual fertilizer nitrate: II. Soil redox potential and soluble iron as indicators of soil health during treatment.

The prospect of using wastewater containing high loads of soluble organic matter (OM) for removing residual agricultural chemicals (fertilizer, pesticide, or herbicide) in farm soil, although promising, could have adverse effects on soil agricultural quality as a result of development of redoximorphic features in the soil profile. In this study, the effect of organic carbon supplement for bioremediation of residual fertilizer nitrate on soil properties, redox potential (Eh), pH, and metal ion mobilization was studied using sandy soils packed in columns. The study was included in a general project, described elsewhere (Ugwuegbu et al., 2000), undertaken to evaluate use of controlled water table management (WTM) systems to supply organic carbon for creating a reduced environment conducive to denitrification of residual fertilizer nitrate leaching from the farm to subsurface water. The columns were subjected to subirrigation with water containing soluble organic carbon in the form of glucose. The work was carried out in two experimental setups and the long-term effect of a range of glucose concentrations on the Eh, pH, and soluble levels of Fe and Mn was investigated. From the results obtained, it could be concluded that excessive organic carbon supplement to soil can have adverse effects on soil quality and that Eh and soluble Fe are the two most practical parameters for monitoring soil health during treatment of farm chemicals.

Fate of metolachlor under subirrigation in a sandy soil: a lysimeter study.

A three-year field lysimeter study was conducted to investigate the role of subirrigation systems in reducing the risk of water pollution from metolachlor (2-chloro-N-(2-ethyl-6-methlphenyl)-N-(2-methoxy-1-methylethyl)ace tamide). Nine large PVC lysimeters, 1 m long x 0.45 m diameter, were packed with a sandy soil. Three water table management treatments, i.e. two subirrigation treatments with constant water table depths of 0.4 and 0.8 m, respectively, and a free drainage treatment in a completely randomized design with three replicates were used. Corn (Zea mays L.) was grown in each lysimeter, and at the beginning of summer of each year metolachlor was applied, at the locally recommended rate of 2.75 kg a.i./ha. Soil and water samples were collected at different time intervals after each natural or simulated rainfall event. Metolachlor was extracted from these samples and analyzed using Gas Chromatography. Results obtained in this three year study, (1993-1995), lead to the conclusion that metolachlor is quite mobile since it leached to a depth of 0.85 m below the soil surface quite early in the growing season. Metolachlor concentrations decreased with depth as well as with time. The shallower water table in the 0.4 m subirrigation treatment showed less residues in the soil solution than that of other treatments. However, a mass balance study, supported by an independent laboratory investigation, shows that water table management, statistically, has no significant effect on the reduction of metolachlor residues in sandy soils.