Richard E. Zartman

Cadmium application and pH effects on growth and cadmium accumulation in switchgrass

Recent efforts have been initiated to develop switchgrass (Panicum virgatum L.), which requires nitrogen (N) for productivity, as a bioenergy crop. Alternatives to inorganic fertilizers are needed to reduce input costs and maintain a positive energy balance. Municipal sludge may be an economical source of N and other nutrients for biomass production but switchgrasss response to heavy metals in the sludge is unknown. A study was conducted to determine the interaction of soil pH and Cd application on biomass accumulation and Cd allocation of switchgrass. ‘Alamo’ switchgrass was grown in pots at five soil pH levels (4.0, 5.1, 5.8, 6.6, and 7.3) and four soil Cd levels (0, 50, 100, and 200 mg Cd kg−1). Two hundred milligrams Cd kg−1 decreased biomass accumulation of all plant components by 95%. Cadmium concentrations of 900 mg kg−1 were found in root tissue of plants grown in soil with 200 mg Cd kg−1 and a pH of 4.0. Soil pH should be maintained near neutral to minimize Cd accumulation by switchgrass. †Research conducted while employed by Texas A&M University Agricultural Research and Extenstion Center, Route 2, Box 10888, Stephenville, TX 76401.

Aflatoxin Toxicity Reduction in Feed by Enhanced Binding to Surface-Modified Clay Additives

Animal feeding studies have demonstrated that clay additives, such as bentonites, can bind aflatoxins in ingested feed and reduce or eliminate the toxicity. Bentonite deposits are found throughout the world and mostly consist of expandable smectite minerals, such as montmorillonite. The surfaces of smectite minerals can be treated with organic compounds to create surface-modified clays that more readily bind some contaminants than the untreated clay. Montmorillonites treated with organic cations, such as hexadecyltrimethylammonium (HDTMA) and phenyltrimethylammonium (PTMA), more effectively remove organic contaminants, such as benzene and toluene, from water than untreated clay. Similarly, montmorillonite treated with PTMA (Kd = 24,100) retained more aflatoxin B1 (AfB1) from aqueous corn flour than untreated montmorillonite (Kd = 944). Feed additives that reduced aflatoxin toxicity in animal feeding studies adsorbed more AfB1 from aqueous corn flour than feed additives that were less effective. The organic cations HDTMA and PTMA are considered toxic and would not be suitable for clay additives used in feed or food, but other non-toxic or nutrient compounds can be used to prepare surface-modified clays. Montmorillonite (SWy) treated with choline (Kd = 13,800) and carnitine (Kd = 3960) adsorbed much more AfB1 from aqueous corn flour than the untreated clay (Kd = 944). A choline-treated clay prepared from a reduced-charge, high-charge montmorillonite (Kd = 20,100) adsorbed more AfB1 than the choline-treated high-charge montmorillonite (Kd = 1340) or the untreated montmorillonite (Kd = 293). Surface-modified clay additives prepared using low-charge smectites and nutrient or non-toxic organic compounds might be used to more effectively bind aflatoxins in contaminated feed or food and prevent toxicity.

Value-added processing of peanut meal: aflatoxin sequestration during protein extraction.

The efficacy of a bentonite clay, Astra-Ben 20A (AB20A), to sequester aflatoxin from contaminated (approximately 110 ppb) peanut meal during protein extraction was studied. Aqueous peanut meal dispersions (10% w/w) were prepared by varying the pH, temperature, enzymatic hydrolysis conditions, and concentrations of AB20A. After extraction, dispersions were centrifuged and filtered to separate both the water-soluble and the water-insoluble fractions for subsequent testing. Inclusion of AB20A at 0.2 and 2% reduced (p < 0.05) aflatoxin concentrations below 20 ppb in both fractions; however, the higher concentration of AB20A also reduced (p < 0.05) the water-soluble protein content. Inclusion of 0.2% AB20A did not affect protein solubility, total soluble solids, or degree of hydrolysis. Peanut meal adsorption isotherms measured the AB20A capacity to sequester aflatoxin. These results are discussed in the context of a process designed to sequester aflatoxin from contaminated peanut meal, which could enable derivatives of this high protein material to be utilized in enhanced feed and/or food applications.

CASTOR TOXIN ADSORPTION TO CLAY MINERALS

The extremely toxic protein, ricin, is derived from castor beans and is a potential terrorist weapon. Adsorption to clays might minimize the environmental persistence and toxic effects of this toxin. Ricin adsorption to clay minerals was measured using batch adsorption isotherms. Enzyme-linked immunoassay methods were used to quantify aqueous ricin concentrations. Montmorillonite, sepiolite and palygorskite effectively adsorbed ricin from aqueous solutions and yielded mostly Langmuir-type isotherms. The monolayer adsorption capacity from a Langmuir equation fit at pH 7 was 444 g ricin/kg for montmorillonite (SWy-2), but was only 5.6 g ricin/kg for kaolinite (KGa-1b). Monolayer capacities for sepiolite (SepSp-1) and palygorskite (PFl-1) at pH 7 were 59.2 and 58.1 g ricin/kg. The high-charge montmorillonite (SAz-1) effectively adsorbed ricin at pH 7, but yielded a linear isotherm with K = 5530 L/kg. At pH 5, both montmorillonites (SWy-2 and SAz-1) yielded Langmuir-type isotherms with monolayer capacities of 694 and 641 g ricin/kg. Clay samples with higher cation exchange capacities generally adsorbed more ricin, but adsorption also followed specific surface area. X-ray diffraction of <2 μm SWy-2 treated with 470 g ricin/kg indicated expansion up to 34.6 Å at buffered pHs of 4 and 7, but not at pH 10. Furthermore, ricin adsorption was greatest at pH 4 and 7, but minimal at pH 10. Treatment with 1.41 kg of purified ricin/kg clay at pH 5 yielded a 35.3 Å peak and adsorption of ~1.2 kg ricin/kg. Similar treatment with lower-purity ricin yielded less expansion and lower adsorption. The 35.3 Å peak interpreted either as a d002 or d001 reflection indicates a 70.6 Å or a 35.3 Å ricin/SWy-2 complex. This implies that adsorption and air drying have compressed interlayer ricin molecules by 18 to 65%. Effective ricin adsorption by montmorillonite suggests that it could be used to minimize the toxic effects of dispersed ricin.

EFFECTS OF STORAGE METHODS ON CHEMICAL VALUES OF WATERLOGGED SOILS

Nutrient properties of wetlands are primary evaluated by soil chemical analysis. Therefore, appropriately collecting and storing waterlogged soil samples is crucial to accurately representing in situ soil-nutrient conditions. A west Texas playa wetland and surrounding outerbasin soils were sampled to compare the effects of three soil storage techniques on various chemical constituents. Techniques evaluated were the following: (1) drying at room temperature, (2) freezing, and (3) purging with nitrogen gas. Drying and freezing are typical methods used in storing terrestrial soils. We hypothesized that the purging technique would facilitate an anaerobic environment and inhibit aerobic chemical transformations. Soils were analyzed for total Kjeldahl nitrogen (TKN), NO3+NO2−N, NH4−N, extractable P, Cu, Fe, Mn, Zn, and pH. Values for NO3+NO2−N and Cu were significantly greater in dried samples than both frozen and purged samples, and generally were significantly lower in pH. Based on this study, we recommend that wetland soils not be dried before analysis.

Genetic variability and molecular responses of root penetration in cotton

Compacted soils restrict root penetration hindering productivity. In this paper, genetic variability of cotton (Gossipium spp.) root capacity to penetrate hard soil layers and the patterns of gene expression during penetration event were investigated. To mimic hard soil layers, wax-petrolatum mixtures were used. Genetic variability among 27 cotton genotypes for the root capacity to penetrate wax-petrolatum disks of 500-700 g wax/kg of mixture was high indicating that breeding efforts targeted to improve this trait can be successful. In the root tips of a cotton strain with high root penetrating ability (G. hirsutum HS 200) which penetrated through wax-petrolatum disks (P), quantity of four polypeptides with molecular weights 35-66 kDa increased compared to those root tips which grew in the absence of mechanical impedance (NP). Differential display showed significant differences in the sets of mRNA expressed in P and NP roots. Out of a total of 917 cDNAs scored in the differential display experiment, 118 cDNAs, or 13%, were specific to P roots and hence could be associated with the root penetration event. Further detailed study of gene expression in penetrated roots will pinpoint molecular factors involved in root penetration ability in cotton.

Mowing rights-of-way affects carbohydrate reserves and tiller development

Intensive mowing has contributed to the loss of some climax grasses in Texas highway rights-of-way. The overall objective of this study was to evaluate the effect of different mowing heights and frequencies on total non-structural carbohydrate (TNC) concentration and tiller density in short and mid-grasses grown along highway rights-of-way. Shortgrasses were represented by blue grama [Bouteloua gracilis (H.B.K) Lag ex Steud.], and mid-grasses were represented by silver bluestem [Bothriochloa saccharoides (Sw.) Rydb], both of which are indigenous species. During 1999 and 2000, grasses were either non-mowed (control) or subjected to mowing heights of 5 and 10 cm, and 5 mowing frequencies (monthly, bi-monthly, tri-monthly, 1-time-only at the beginning or end of the growing season). Plants of both species mowed less frequently at either stubble height had higher TNC concentrations than plants subjected to more frequent mowing. Mowing produced fewer (P < 0.05) tillers after 2 consecutive mowing seasons than after 1 mowing season in silver bluestem. Silver bluestem tiller growth was more susceptible to frequent mowing than blue grama. Mowing during periods of rapid inflorescence development reduced tiller density in both species after 2 mowing seasons. Mowing height and frequency guidelines are proposed to maintain roadside grasses in their most productive state through planning mowing practices around the target plants natural growth habit and its ability to respond to defoliation.

Biosolids Effects in Chihuahuan Desert Rangelands: A Ten-Year Study

Arid and semiarid rangelands are suitable for responsible biosolids application. Topical application is critical to avoid soil and vegetation disturbance. Surface-applied biosolids have long-lasting effects in these ecosystems. We conducted a 10-year research program investigating effects of biosolids applied at rates from 0 to 90 dry Mg ha−1 on soil water infiltration; runoff and leachate water quality; soil erosion; forage production and quality; seedling establishment; plant physiological responses; nitrogen dynamics; biosolids decomposition; and grazing animal behavior and management. Biosolids increased soil water infiltration and reduced erosion. Effects on soil water quality were observed only at the highest application rates. Biosolids increased soil nitrate-nitrogen. Biosolids increased forage production and improved forage quality. Biosolids increased leaf area of grasses; photosynthetic rates were not necessarily increased by biosolids. Biosolids effects on plant establishment are expected only under moderately favorable conditions. Over an 82-mo exposure period, total organic carbon, nitrogen, and total and available phosphorus decreased and inorganic matter increased. Grazing animals spent more time grazing, ruminating, and resting in biosolids-treated areas; positive effects on average daily gain were observed during periods of higher rainfall. Our results suggest that annual biosolids application rates of up to 18 Mg ha−1 are appropriate for desert rangelands.

Enzyme-Linked Immunosorbent Assay Measurement of Castor Toxin in Soils

Abstract Published Enzyme-Linked ImmunoSorbent Assay (ELISA) techniques to determine ricin, a castor (Ricinus communis) toxin, were developed for human sera, biological fluids, and tissue samples. This study was conducted to adapt existing ELISA procedures to soil extracts and demonstrate its use. These modifications of published generic ELISA methods include elimination of phosphate buffers in the soil extraction procedure and addition of bovine Fraction V albumin to block nonspecific sites on the microtiter plates. Using this method with commercially available biochemicals and equipment, it was possible to detect the presence of ricin in a soil after harvest and two years post-harvest.

Influence of Soluble Feed Proteins and Clay Additive Charge Density on Aflatoxin Binding in Ingested Feeds

Hartley et al. (1963) isolated and identified toxic metabolites of Aspergillus flavus as aflatoxins B1, B2, G1, and G2; named from the blue and green fluorescence of the compounds under ultraviolet light. The aflatoxins are a group of mycotoxins produced by Aspergillus fungi that are both toxic and carcinogenic to animals and humans (Murphy et al., 2006). Aflatoxin B1 (AfB1) and mixtures of B1, G1, and M1 are proven human carcinogens (IARC, 1993). Aflatoxin B1 is the most toxic (Figure 1), most abundant, and the most potent natural carcinogen known (Squire, 1981). An estimated 4.5 billion people living in developing countries are chronically exposed to uncontrolled amounts of aflatoxins (Williams et al., 2004). Iraq produced aflatoxins for use in biological warfare between 1985 and 1991, but the weapons had little military value (Zilinskas, 1997). After ingestion, aflatoxins are converted to the reactive 8,9-epoxide form that can bind to DNA and proteins. Aflatoxin consumption results in diseases that are loosely called aflatoxicoses. Chemically, aflatoxins are derivatives of difuranocoumarin (Bennett & Klich, 2003). Various methods have been used to reduce the toxicity of aflatoxin-contaminated grains. Cleaning to remove damaged corn kernels is sometimes effective in reducing aflatoxin concentrations, but undamaged kernels can also contain high aflatoxin concentrations (Vincelli et al., 1995). Treatment with anhydrous ammonia can be used to detoxify grain that is to be used on the farm (Vincelli et al., 1995). Brekke et al. (1977) ammoniated trout feed contaminated with 180 μg/kg aflatoxins, which inactivated the aflatoxins and reduced the carcinogenicity to a level not significantly different than the control. Grove et al. (1981) examined the ammoniation products of aflatoxin model coumarins and determined that the keto group in the cyclopentene ring is required for ammonia-induced decomposition. Nixtamalization is an Aztec word that means lime-cooked corn (Herrera et al., 1986) and is an ancient method used to soften grain before it is used in foods. Nixtamalization also increases protein quality and niacin bioavailability (Sefa-Dedah et al., 2004). The strong alkalinity imparted by lime (CaO, Ca(OH)2 ) might have a similar effect on aflatoxins as ammonia. Arrriola et al., (1988) examined the effect of nixtamalization on aflatoxin fate during tortilla preparation using 2-10% CaO. Nixtamalization decreased aflatoxin concentrations at even the lowest CaO concentrations. However, nixtamalization did not