Papers by David A Cassada
![Research paper thumbnail of Chromatographic and spectral investigations on the in vivo metabolites of 6-nitrobenzo[a]pyrene](https://a.academia-assets.com/images/blank-paper.jpg)
Journal of Chromatography A, 1988
6-Nitrobenzo[a]pyrene (6-NBaP) occurs in the environment, is mutagenic in the Ames assay in the p... more 6-Nitrobenzo[a]pyrene (6-NBaP) occurs in the environment, is mutagenic in the Ames assay in the presence of added S9 and is carcinogenic to male but not female mouse liver when injected intraperitoneally (i.p.) into mice. In order to understand what kinds of active metabolites could have been produced in vivo, both male and female mice were injected i.p. with 6-NBaP in dimethyl sulfoxide. Twenty-four hours after injection, urine, feces, blood, liver and spleen (non-target tissue) were examined for metabolites by chromatographic and high-resolution mass spectral means. On the basis of the mass spectral fragmentation patterns of synthetic and metabolic standards, it was observed that both male and female animals excreted ring-hydroxylated metabolites of 6-NBaP in the urine to differing extents. Male animals additionally excreted 6-aminobenzo[a]pyrene and the significance of this observation is discussed.
Journal of the American Chemical Society, 1986
A complete heavy-atom microwave structure and fully geometry-optimized structures at the a b init... more A complete heavy-atom microwave structure and fully geometry-optimized structures at the a b initio 6-3 IC* and MP2/6-31G* levels are presented for cyclopropylamine. The experimental C2C3 bond length (1.5 12 A) is essentially unchanged relative to cyclopropane whereas there is a small but distinct shortening of C I C z . The latter effect is attributed primarily to hybridization changes at C I . Amino group parameters are discussed in terms of four-electron repulsive interactions between filled amino and cyclopropyl orbitals, and previous analyses of the cyclopropylamine structure are evaluated.
Toxins, 2014
Several groups of microorganisms are capable of producing toxins in aquatic environments. Cyanoba... more Several groups of microorganisms are capable of producing toxins in aquatic environments. Cyanobacteria are prevalent blue green algae in freshwater systems, and many species produce cyanotoxins which include a variety of chemical irritants, hepatotoxins and neurotoxins. Production and occurrence of potent neurotoxic cyanotoxins β-N-methylamino-L-alanine (BMAA), 2,4-diaminobutyric acid dihydrochloride (DABA), and anatoxin-a are especially critical with environmental implications to public and animal health. Biomagnification, though not well understood in aquatic systems, is potentially relevant to both human and animal health effects. Because little is known regarding their presence in fresh water, we investigated the occurrence and potential for bioaccumulation of cyanotoxins in several Nebraska reservoirs. Collection and analysis of 387 environmental and biological samples (water, fish, and aquatic plant) provided a snapshot of their occurrence. A sensitive detection method was developed using solid phase extraction (SPE) in combination with high pressure liquid chromatography-fluorescence detection (HPLC/FD) with confirmation by liquid chromatography-tandem mass spectrometry (LC/MS/MS). HPLC/FD detection limits ranged from 5 to 7 µg/L and LC/MS/MS detection limits were <0.5 µg/L, while detection limits for biological samples were in the range of 0.8-3.2 ng/g depending on the matrix. Based on these methods, measurable levels
Water Environment Research, 2010
Thirty-six papers were published in 2009 describing new methods for analysis of veterinary pharma... more Thirty-six papers were published in 2009 describing new methods for analysis of veterinary pharmaceuticals, natural and synthetic steroid hormones, and their occurrence in agricultural settings. New methods continue to be developed and applied toward understanding the sources and environmental significance of these chemicals. Advances in sample preparation methods and instrumentation provide detection limits into parts per trillion ranges. Analysis of water samples indicates that many of these compounds do occur in the environment.
Water Environment Research, 2009
Toxicon, 2013
Blue-green algae, also known as cyanobacteria, can produce several different groups of toxins in ... more Blue-green algae, also known as cyanobacteria, can produce several different groups of toxins in the environment including hepatotoxins (microcystins), neurotoxic non-protein amino acids β-methylamino-l-alanine (BMAA), and 2,4-diaminobutyric (DABA), as well as the bicyclic amine alkaloid anatoxin-a. Few studies have addressed the methods necessary for an accurate determination of cyanotoxins in environmental samples, and none have been published that can detect these cyanotoxins together in a single sample. Cyanotoxins occur in a wide range of environmental samples including water, fish, and aquatic plant samples. Using polymeric cation exchange solid phase extraction (SPE) coupled with liquid chromatography and fluorescence detection (HPLC/FD), and liquid chromatography ion trap tandem mass spectrometry (LC/MS/MS), these compounds can for the first time be simultaneously quantified in a variety of environmental sample types. The extraction method for biological samples can distinguish bound and free cyanotoxins. Detection limits for water ranged from 5 to 7 μg/L using HPLC/FD, while detection limits for and LC/MS were in the range of 0.8-3.2 μg/L.
Journal of Hazardous Materials, 2009
Dinoseb, a dinitroherbicide, was once commonly used in aerial crop dusting of agronomic crops in ... more Dinoseb, a dinitroherbicide, was once commonly used in aerial crop dusting of agronomic crops in the western United States. Widespread use combined with improper disposal practices at rural air strips has contaminated numerous sites. Our objective was to determine if zerovalent iron (Fe 0 ) could remediate dinoseb-contaminated soil. This was accomplished by conducting a series of batch experiments where we first determined if Fe 0 could remove dinoseb in aqueous solutions, then in contaminated soil slurries, and finally, in unsaturated soil microcosms (25 • C, Â g = 0.30 kg H 2 O kg −1 ). Results showed quantitative dinoseb removal in the presence of Fe 0 in all three media (aqueous solutions, soil slurries, moist soils) and that removal increased by including either ferrous or aluminum sulfate with the iron treatment. Incubating contaminated soils with Fe 0 or Fe 0 plus salts (FeSO 4 or Al 2 (SO 4 ) 3 ) resulted in 100% removal of dinoseb within 7 d. Liquid chromatography/mass spectrometry (LC/MS) analysis of degradation products showed the transformations imposed by the iron treatments were reduction of one or both nitro groups to amino groups. These amino degradation products were further transformed to quinonimine and benzoquinone and did not persist. These results support the use of zerovalent iron for on-site treatment of dinosebcontaminated soil.
Journal of Food Science, 2010
This study was conducted to evaluate the effect of pulsed electric field (PEF) treatment on antho... more This study was conducted to evaluate the effect of pulsed electric field (PEF) treatment on anthocyanin extraction from red cabbage using water as a solvent. Mashed cabbage was placed in a batch treatment chamber and subjected to PEF (2.5 kV/cm electric field strength; 15 micros pulse width and 50 pulses, specific energy 15.63 J/g). Extracted anthocyanin concentrations (16 to 889 microg/mL) were determined using HPLC. Heat and light stabilities of the control and PEF-treated samples, having approximately the same initial concentrations, were studied. PEF treatments enhanced total anthocyanin extraction in water from red cabbage by 2.15 times with a higher proportion of nonacylated forms than the control (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.05). The heat and light stabilities of the PEF-treated samples and control samples were not significantly different (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 0.05). Practical Application: An innovative pretreatment technology, pulsed electric field processing, enhanced total anthocyanin extraction in water from red cabbage by 2.15 times. Manufacturers of natural colors can use this technology to extract anthocyanins from red cabbage efficiently.
Journal of Environment Quality, 2003
physical-chemical characteristics that allow for mobility and moderate persistence. Atrazine, the... more physical-chemical characteristics that allow for mobility and moderate persistence. Atrazine, the most wide-Profiles of ground water pesticide concentrations beneath the Nespread pesticide in the nation's ground water, and its braska Management Systems Evaluation Area (MSEA) describe the effect of 20 yr of pesticide usage on ground water in the central Platte transformation products together with cyanazine, sima-Valley of Nebraska. During the 6-yr (1991-1996) study, 14 pesticides zine, and alachlor and metolachlor and their transformaand their transformation products were detected in 7848 ground water tion products are the most commonly detected herbisamples from the unconfined water table aquifer. Triazine and acetcides in row-cropped regions (Barbash et al., 1999) (see amide herbicides applied on the site and their transformation products for chemical names of pesticides detected in had the highest frequencies of detection. Atrazine [6-chloro-N-ethylthis study).
Journal of Environment Quality, 2003
Atrazine is the most widely detected pesticide in the nation's ground water and the USEPA has set... more Atrazine is the most widely detected pesticide in the nation's ground water and the USEPA has set 3 g L Ϫ1 Better management practices can counter deterioration of ground as the maximum contaminant level (MCL) in drinkwater quality. From 1991 through 1996 the influence of improved irrigation practices on ground water pesticide contamination was assessed ing water. at the Nebraska Management Systems Evaluation Area. Three 13.4-ha Generally, nonpoint-source loading of pesticides in corn (Zea mays L.) fields were studied: a conventional furrow-irrigated shallow ground water beneath agricultural fields is visufield, a surge-irrigated field and a center pivot-irrigated field, and a alized as a complex, nonuniform network of macropores center pivot-irrigated alfalfa (Medicago sativa L.) field. The corn fields conveying contaminants through the vadose zone to the received one identical banded application of Bicep (atrazine [6-chlorowater table where high input concentrations are par- -diamine] ϩ metolachlor tially masked by vertical and radial dilution. The major- ity of loading has been attributed to the transfer, mixing, acetamide]) annually; the alfalfa field was untreated. Ground water application, and disposal or "routine use" of pesticides samples were collected three times annually from 16 depths of 31 multiin agriculture. Hallberg (1989), however, points out that level samplers. Six years of sample data indicated that a greater than 50% reduction in irrigation water on the corn management fields low-
Journal of Environment Quality, 1994
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Journal of Environmental Engineering, 2006
Years of wastewater discharge at the Department of Energy&amp;amp;amp;#x27;s Pantex Plant hav... more Years of wastewater discharge at the Department of Energy&amp;amp;amp;#x27;s Pantex Plant have contaminated the vadose zone and underlying perched aquifer with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Because the vadose zone is acting as a continual source of groundwater ...
Journal of Chromatography A, 2001
A method using liquid chromatography-tandem mass spectrometry has been developed for determinatio... more A method using liquid chromatography-tandem mass spectrometry has been developed for determination of trace levels of tetracycline antibiotics in ground water and confined animal feeding operation waste water. Oxytetracycline (OTC), tetracycline (TC), and chlortetracycline (CTC) were extracted from water samples using both polymeric and C extraction 18 cartridges. The addition of a buffer containing potassium phosphate and citric acid improved tetracycline recoveries in 21 lagoon water. Method detection limits determined in reagent water fortified with 1 mg l OTC, TC, and CTC were 0.21,
Journal of Chromatography A, 1999
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The Journal of Chemical Physics, 1984
ABSTRACT
IUBMB Life, 2012
Depurinating DNA adducts formed by aromatic hydrocarbons and catechol estrogen quinones play a ma... more Depurinating DNA adducts formed by aromatic hydrocarbons and catechol estrogen quinones play a major role in cancer initiation. Most of these adducts depurinate instantaneously, but some guanine adducts depurinate from DNA with half-lives of hours. We report here, that after 10 h at 37 8C, reaction of estradiol-3,4-quinone (E 2 -3,4-Q) with ds-DNA to yield N7Gua and N3Ade adducts was complete and more efficient than with ss-DNA. When E 2 -3,4-Q reacted with t-RNA, no adducts were detected after 10 h, and the level of N3Ade and N7Gua adducts after 10 days was less than half that with ss-DNA after 10 h. Reaction of E 2 -3,4-Q and dG yielded 4-OHE 2 -1-N7dG, which spontaneously depurinated to yield 4-OHE 2 -1-N7Gua. To investigate the mechanism of depurination, E 2 -3,4-Q was reacted with carbocyclicdeoxyguanosine, in which the ring oxygen of the deoxyribose moiety is substituted with CH 2 , and depurination was observed. The results from this experiment demonstrate that the oxocarbenium ion mechanism plays the major role in depurination and provides the first experimental evidence for this mechanism. A newly discovered b-elimination mechanism also plays a minor role in depurination. Understanding why the depurinating estrogen-DNA adducts come from DNA, and not from RNA, underscores the critical role that these adducts play in initiating cancer. 2011 IUBMB IUBMB Life, 64(2): 169-179, 2012
Food Microbiology, 2013
The effect of nitrite and erythorbate on Clostridium perfringens spore germination and outgrowth ... more The effect of nitrite and erythorbate on Clostridium perfringens spore germination and outgrowth in ham during abusive cooling (15 h) was evaluated. Ham was formulated with ground pork, NaNO2 (0, 50, 100, 150 or 200 ppm) and sodium erythorbate (0 or 547 ppm). Ten grams of meat (stored at 5 °C for 3 or 24 h after preparation) were transferred to a vacuum bag and inoculated with a three-strain C. perfringens spore cocktail to obtain an inoculum of ca. 2.5 log spores/g. The bags were vacuum-sealed, and the meat was heat treated (75 °C, 20 min) and cooled within 15 h from 54.4 to 7.2 °C. Residual nitrite was determined before and after heat treatment using ion chromatography with colorimetric detection. Cooling of ham (control) stored for 3 and 24 h, resulted in C. perfringens population increases of 1.46 and 4.20 log CFU/g, respectively. For samples that contained low NaNO2 concentrations and were stored for 3 h, C. perfringens populations of 5.22 and 2.83 log CFU/g were observed with or without sodium erythorbate, respectively. Residual nitrite was stable (p &amp;amp;amp;amp;amp;amp;gt; 0.05) for both storage times. Meat processing ingredients (sodium nitrite and sodium erythorbate) and their concentrations, and storage time subsequent to preparation of meat (oxygen content) affect C. perfringens spore germination and outgrowth during abusive cooling of ham.
Food and Chemical Toxicology, 2011
Blue-green algae (BGA) have been consumed as food and herbal medicine for centuries. However, saf... more Blue-green algae (BGA) have been consumed as food and herbal medicine for centuries. However, safety for their consumption has not been well investigated. This study was undertaken to evaluate in vitro and in vivo toxicity of cultivated Nostoc commune var. sphaeroides Kützing (NO) and Spirulina platensis (SP). Neither NO nor SP contained detectable levels of microcystin (MC)-LA, MC-RR, MC-LW and MC-LR by LC/MS/MS. Cell viability remained ∼70-80% when HepG2 cells were incubated with 0-500 μg/ml of hexane, chloroform, methanol and water-extractable fractions of NO and SP. Four-week-old male and female C57BL/6J mice were fed an AIN-93G/M diet supplemented with 0%, 2.5% or 5% of NO and SP (wt/wt) for 6 months. For both genders, BGA-rich diets did not induce noticeable abnormality in weight gain and plasma alanine aminotransferase (ALT) and aspartate aminotransferase concentrations except a significant increase in plasma ALT levels by 2.5% NO supplementation in male mice at 6 month. Histopathological analysis of livers, however, indicated that BGA did not cause significant liver damage compared with controls. In conclusion, our results suggest that NO and SP are free of MC and the long-term dietary supplementation of up to 5% of the BGA may be consumed without evident toxic side-effects.
Environmental Science & Technology, 2011
Analytical Chemistry, 2000
Solid-phase microextraction (SPME) and gas chromatography/mass spectrometry have been combined fo... more Solid-phase microextraction (SPME) and gas chromatography/mass spectrometry have been combined for tracelevel determination of very polar compounds in water, including the widely used gasoline oxygenates ethanol and methyl tert-butyl ether (MTBE). A relatively simple extraction method using a divinylbenzene/Carboxen/poly-(dimethylsiloxane) SPME fiber was optimized for the routine analysis of ethanol and MTBE in groundwater and reagent water. A sodium chloride concentration of 25% (w/w) combined with an extraction time of 25 min provided the greatest sensitivity while maintaining analytical efficiency. Replicate analyses in fortified reagent and groundwater spiked with microgram per liter concentrations of ethanol and MTBE indicate quantitative and reproducible recovery of these and related oxygenate compounds. Method detection limits were 15 µg L -1 for ethanol, 1.8 µg L -1 for tert-butyl alcohol, 0.038 µg L -1 for tert-amyl methyl ether, 0.025 µg L -1 for ethyl-tertbutyl ether, and 0.008 µg L -1 for MTBE.
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Papers by David A Cassada