Garald L. Horst

Remediating TNT-contaminated soil by soil washing and Fenton oxidation

Abstract Past disposal practices at munitions production facilities have generated numerous hectares of TNT-contaminated soil. We previously showed that Fenton oxidation could destroy TNT in soil and water. Our objective was to determine the potential of combining Fenton oxidation with soil washing to remediate TNT-contaminated soil and to test whether plants could be established on washed soil. Aqueous soil washing effectively reduced CH3CN-extractable TNT concentrations but large volumes of water were required to meet remediation goals. This volume was reduced when the wash water temperature was increased to 45°C. Complete destruction of TNT in wash solutions was achieved by Fenton oxidation with greater than 40% mineralized. Combining soil washing with phytoremediation will require plant establishment on the washed soil. We observed no significant reduction in tall fescue (Festuca arundinacea Schreb.) germination or early seedling development in contaminated soil following two wash cycles (soil:H2O, 1:5). This corresponded to reducing CH3CN-extractable soil concentrations from 499 mg TNT kg−1 to approximately 72 mg TNT kg−1. Our results indicate Fenton oxidation can be combined with soil washing for effective abiotic remediation of TNT-contaminated soils. Washed soils may be planted to tall fescue, demonstrating the potential of combining soil washing, Fenton oxidation and phytoremediation into an integrated treatment train for TNT-contaminated sites.

Germination and seedling development of switchgrass and smooth bromegrass exposed to 2,4,6-trinitrotoluene

It is estimated that explosives contaminate approximately 0.82 million cubic metres of soil at former military installations throughout the US; major contaminants often include 2,4,6-trinitrotoluene (TNT) and its degradation products. At some sites, phytoremediation may be a viable option to incineration or other costly remediation treatments. Grasses may be particularly suited for remediation because of their growth habit and adaptability to a wide range of soil and climate conditions. We characterized the effects of TNT on germination and early seedling development of switchgrass and smooth bromegrass to evaluate their potential use on contaminated sites. Switchgrass and smooth bromegrass seeds were germinated in nutrient-free agar containing 0 to 60 mg TNT litre(-1). Smooth bromegrass germination decreased as TNT concentration increased, while switchgrass germination was unaffected by TNT. Concentrations up to 15 mg TNT litre(-1) did not affect switchgrass root growth rate, but bromegrass root growth was reduced at TNT concentrations above 7.5 mg litre(-1). At 7.5 mg TNT litre(-1), however, shoot growth rate was reduced in both species. Examination at 20-fold magnification revealed switchgrass radicles were unaffected by TNT, while smooth bromegrass radicles appeared slightly swollen. Results indicate switchgrass is more tolerant of TNT than smooth bromegrass, but the establishment of both species may be limited to soil containing less than 50 mg kg(-1) of extractable TNT.

TNT and 4-amino-2,6-dinitrotoluene influence on germination and early seedling development of tall fescue

Cost-effective and environmentally acceptable methods are needed to remediate munitions-contaminated soil. Some perennial grass species are tolerant of soil contaminants and may promote remediation because of their high water use and extensive fibrous root systems. The effects of 2,4,6-trinitrotoluene (TNT) and its reduction product, 4-amino-2,6-dinitrotoluene (4ADNT), on germination and early seedling development of tall fescue (Festuca arundinacea Schreb.) were determined. Tall fescue seeds were germinated in nutrient-free agar containing 0-60 mg TNT litre(-1) or 0-15 mg 4ADNT litre(-1). Germination decreased linearly as TNT concentration increased but was not significantly affected by 4ADNT at these concentrations. Concentrations less than 30 mg TNT litre(-1) or 7.5 mg 4ADNT litre(-1) had little effect on seedling growth and development. Higher TNT or 4ADNT concentrations substantially delayed seedling development, caused abnormal radicle tissue development, and reduced secondary root and shoot growth. Seedling respiration rates decreased linearly with increasing TNT concentration. Experiments indicate that tall fescue may be grown in soils that maintain soil solution concentrations of 30 mg TNT litre(-1) or less.

The microclimate in tall fescue turf as affected by canopy density and its influence on brown patch disease

Microenvironment was monitored within tall fescue (Festuca arundinacea) experiment plots in which the severity of brown patch disease, caused by Rhizoctonia solani AG-1-IA, was found to correlate with canopy density. Canopy density was varied either by planting cultivars that produced different densities, or by planting a single cultivar at three seeding rates. Air and foliage temperatures within the canopy differed by only approximately 1°C between low- and high-density canopies during 1993 and 1994 in both studies. In a wet year, 1993, leaf wetness and relative humidity did not differ significantly between low- and high-density canopies. In 1994, which was more typical in regards to weather, a denser canopy promoted leaf wetness and high relative humidity in both studies. Leaf wetness duration averaged over 10 days was 0.8 h longer in the high-density cultivar Arriba than in the low-density cultivar Fawn. In addition, the period of relative humidity above 90% was 2.3 h longer in Arriba than in Fawn. Canopies of tall fescue with different plant densities were inoculated in the laboratory with R. solani and placed under uniformly high humidity and temperature. Hyphae grew between leaf blades separated by up to 8 mm. Interblade hyphal growth occurred more frequently in high-density canopies because of the closer proximity of leaf blades, and as a result, mycelia and necrosis spread more rapidly from inoculation sites in high-density canopies. It was concluded that microenvironmental conditions and the physical proximity of leaf blades in high-density turfs can be more favorable for brown patch disease.

A crop water stress index for tall fescue (Festuca arundinacea Schreb.) irrigation decision-making — a traditional method

Abstract A high irradiance plant growth chamber was used to study crop water stress indices (CWSI) and baselines with increasing soil water deficit for Tall Fescue (Festuca arundinacea Schreb.). Canopy temperatures for turf plugs were continuously measured with infrared thermometers, along with plant water use, measured with electronic mini-lysimeters. Net radiation, canopy and air temperatures, and vapor pressure deficit (VPD) levels were recorded and analyzed statistically. The canopy–air temperature differential (Tc−Ta) increased with a decrease in soil moisture content. Tc−Ta increased as net radiation became greater, independent of soil water deficit. Canopy temperature of well-watered plants decreased at rate of 2.4°C for each 1 kPa reduction in air vapor pressure deficit for all net radiation levels. For each 100 Wm−2 increase in net radiation, canopy temperature of well-watered plants increased at a rate of 0.6°C and was well correlated (well-watered baseline) with VPD. Increases in canopy temperature coupled with a decrease in transpiration rate were hallmark signs of water stress progression. However, (Tc−Ta) and VPD baseline relationships correlated poorly for moderate-stress and severe stress conditions regardless of net radiation levels. Thus, even with the increased precision and replications of a controlled environment study, lower limit crop water stress baselines were quite variable.

Growth and development of smooth bromegrass and tall fescue in TNT-contaminated soil.

Plants can be used for effective and economical remediation of soil provided they are tolerant or resistant to contaminants. This study was conducted to determine effects of 2,4,6-trinitrotoluene (TNT) on growth and development of smooth bromegrass and tall fescue. Seeds of both species were grown in contaminated and non-contaminated soil mixed at ratios to obtain a range of concentrations and also in non-contaminated soil underlain by contaminated and non-contaminated soil mix. Germination, shoot and root dry weight, root length and area were measured. Germination and height of both species decreased with increasing TNT concentration. Shoot dry weight from tall fescue was 50% greater than smooth bromegrass at a given TNT concentration. Root length, area and dry weight of both species decreased with increasing TNT concentration. Root area and dry weight were greater for smooth bromegrass compared to tall fescue. This research indicates tall fescue and smooth bromegrass can germinate and grow in soils with concentrations less than 31 and 24 mg TNT l(-1), respectively.

A site-specific sensor for measuring leaf wetness duration within turfgrass canopies

Leaf wetness is a key factor in the initiation and development of many plant diseases. Measurement of leaf wetness duration in turfgrass requires sensors that do not disrupt the canopy environment and are representative of leaf surfaces. Therefore, a small (5 mm head width) sensor was developed that can be inserted into grass blades with only minor modification of the canopy and can capture the spatial variability of leaf wetness. The sensor detected wetness onset and depletion in a tall fescue turf canopy in the field with an average error of less than 20 min when compared with a tactile method. The sensor indicated leaf wetness over 1 h before moisture was visible and detected wetness depletion 1 h after moisture was no longer visible, suggesting that the sensor is sensitive to microscopic water films. When the sensor was compared with a leaf latent heat flux. model in tall fescue canopies, no significant differences between the two methods were found in detecting wetting and drying episodes and in measuring leaf wetness durations. However, the sensor was sufficiently sensitive to record 1 h later wetness depletion (P < 0.01) and 1 h longer periods of leaf wetness (P < 0.01) in a high plant density canopy as compared with a low-density canopy, whereas no significant differences in moisture conditions between the two canopies was found using the leaf latent heat flux model.

Trinexapac-ethyl influence on cell membrane thermostability of Kentucky bluegrass leaf tissue

Abstract Trinexapac-ethyl [(4-cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid methyl ester] is a turfgrass growth regulator used to reduce clipping yields and mowing frequency. Kentucky bluegrass ( Poa pratensis L.) plants treated with trinexapac-ethyl are less heat tolerant than untreated plants. Electrolyte leakage tests can determine cell membrane thermostability (CMT) of several species and is related to relative heat tolerance, but has not been used to determine differences in CMT in plants caused by the influence of the growth regulator trinexapac-ethyl. We conducted one experiment, repeated twice with an electrolyte leakage test to determine the influence of trinexapac-ethyl on CMT of Kentucky bluegrass. Kentucky bluegrass plants treated with trinexapac-ethyl had less CMT than untreated plants. This shows that an electrolyte leakage test for CMT can determine growth regulator influences on the heat tolerance of a C 3 turfgrass.

Tall fescue canopy density effects on brown patch disease

Canopy density was investigated as a factor determining the severity of brown patch disease, caused by Rhizoctonia solani, in the field. In two separate experiments, tall fescue (Festuca arundinacea) cv. Fawn was seeded at 10 to 50 g/m 2 to create canopies with different levels of blade density (i.e., numbers of leaf blades per unit area) and verdure. Brown patch lesion development was more severe at the 50-g/m 2 seeding rate than at 10 g/m 2 in both experiments. Six cultivars of tall fescue, representing combinations of susceptibility (as determined in a growth chamber) and stature (tall, medium, or dwarf), were evaluated in the field for brown patch disease severity and canopy density. Disease severity measured over 2 years was highly correlated with blade density and verdure, but was not related to cultivar susceptibility. The tall cultivars produced the least dense canopies and sustained the least amount of disease. The medium and dwarf groups, however, could not be distinguished on the basis of canopy density or response to brown patch disease. These results show that canopy density directly affects brown patch disease severity under field conditions and is, in part, related to a cultivars stature.

Differential Tolerance of Cool- and W arm-Season Grasses to TNT -Contaminated Soil

ABSTRACT Plants can be used for effective and economical remediation of soil provided they are tolerant or resistant to the contaminants. Greenhouse experiments were conducted to determine the tolerance of the cool-season grasses: smooth bromegrass (Bromus inermus Leyss.) and tall fescue (Festuca arundinaceae Schreb), and the warm-season grasses: big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) to TNT (2,4,6-trinitrotoluene) in soil. TNT-contaminated soil was mixed with uncontaminated soil to obtain water-extractable TNT concentrations ranging from 71 to 435 mg kg-1, corresponding to acetonitrile-extractable concentrations of 278 to 3115 mg kg-1. Germination, shoot and root dry weight, and root area were measured in response to TNT concentrations in the soil mixtures. Germination and height of the warm-season grass species were more sensitive than the cool-season grass species to increasing TNT concentrations in soil. Significant reductions in shoot and root growth were observed in cool-season grasses at lower TNT concentrations in soil compared with warm-season grasses in the soil mixtures. Results indicated that the warm-season grasses can be established in soil containing less than 86 mg of water-extractable TNT kg-1, based on 80% of measured growth in uncontaminated control soil.