Spencer S. Walse

Quaternary amines as nitrosamine precursors: a role for consumer products?

Nitrosamine formation has been associated with wastewater-impacted waters, but specific precursors within wastewater effluents have not been identified. Experiments indicated that nitrosamines form in low yields from quaternary amines, and that the nitrosamines form from the quaternary amines themselves, not just lower order amine impurities. Polymeric and benzylated quaternary amines were more potent precursors than monomeric quaternary alkylamines. Pretreatment of quaternary amines with ozone or free chlorine, which deactivate lower order amine impurities, did not significantly reduce nitrosamine formation. The nitrosamine formation pathway is unclear but experiments indicated that transformation of quaternary amines to lower order amine precursors via Hofmann elimination was not involved. Experiments suggest that the pathway may involve quaternary amine degradation by amidogen or chloramino radicals formed from chloramines. Quaternary amines are significant constituents of consumer products, including shampoos, detergents, and fabric softeners. Although quaternary amines may be removed by sedimentation during wastewater treatment, their importance should be evaluated on a case-by-case basis. The high loadings from consumer products may enable the portion not removed to serve as precursors.

Fipronil effects on estuarine copepod (Amphiascus tenuiremis) development, fertility, and reproduction: a rapid life-cycle assay in 96-well microplate format.

Fipronil is a novel gamma-aminobutyric acid receptor-specific phenylpyrazole insecticide commonly used near estuarine environments for rice production, turf-grass management, and residential insect control. In this study, we evaluated the acute, developmental, and reproductive toxicity of fipronil to the estuarine harpacticoid copepod Amphiascus tenuiremis. Fipronil was highly toxic to A. tenuiremis (adult 96-h median lethal concentration [LC50] = 6.8 microg/L) and was more toxic to male copepods (96-h LC50 = 3.5 microg/L) than to nongravid female copepods (96-h LC50 = 13.0 microg/L). By using a newly developed 96-well microplate-based life-cycle toxicity test, we successfully reared single individuals of A. tenuiremis to adulthood in 200-microl microwells and concurrently assessed developmental and reproductive effects (after paired virginal matings) of environmentally relevant aqueous fipronil concentrations (0.16, 0.22, and 0.42 microg/L measured). Throughout the entire life cycle, copepod survival in all treatments was >90%. However, fipronil at 0.22 microg/L and higher significantly delayed male and female development from stage 1 copepodite to adult by approximately 2 d. More importantly, fipronil significantly halted female egg extrusion by 71% in the 0.22-microg/L fipronil treatment, and nearly eliminated reproduction (94% failure) in the 0.42-microg/L fipronil treatment. A three-generation Leslie matrix-based population growth model of fipronil reproductive and life-cycle impacts predicted a 62% decline in population size of A. tenuiremis relative to controls at only 0.16 microg/L.

Quantifying host potentials: indexing postharvest fresh fruits for spotted wing drosophila, Drosophila suzukii.

Novel methodology is presented for indexing the relative potential of hosts to function as resources. A Host Potential Index (HPI) was developed as a practical framework to express relative host potential based on combining results from one or more independent studies, such as those examining host selection, utilization, and physiological development of the organism resourcing the host. Several aspects of the HPI are addressed including: 1) model derivation; 2) influence of experimental design on establishing host rankings for a study type (no choice, two-choice, and multiple-choice); and, 3) variable selection and weighting associated with combining multiple studies. To demonstrate application of the HPI, results from the interactions of spotted wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae), with seven “reported” hosts (blackberries, blueberries, sweet cherries, table grapes, peaches, raspberries, and strawberries) in a postharvest scenario were analyzed. Four aspects of SWD-host interaction were examined: attraction to host volatiles; population-level oviposition performance; individual-level oviposition performance; and key developmental factors. Application of HPI methodology indicated that raspberries (meanHPIvaried = 301.9±8.39; rank 1 of 7) have the greatest potential to serve as a postharvest host for SWD relative to the other fruit hosts, with grapes (meanHPIvaried = 232.4±3.21; rank 7 of 7) having the least potential.

Selenium Accumulation, Distribution, and Speciation in Spineless Prickly Pear Cactus: A Drought- and Salt-Tolerant, Selenium-Enriched Nutraceutical Fruit Crop for Biofortified Foods

The organ-specific accumulation, spatial distribution, and chemical speciation of selenium (Se) were previously unknown for any species of cactus. We investigated Se in Opuntia ficus-indica using inductively coupled plasma mass spectrometry, microfocused x-ray fluorescence elemental and chemical mapping (μXRF), Se K-edge x-ray absorption near-edge structure (XANES) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). μXRF showed Se concentrated inside small conic, vestigial leaves (cladode tips), the cladode vasculature, and the seed embryos. Se K-edge XANES demonstrated that approximately 96% of total Se in cladode, fruit juice, fruit pulp, and seed is carbon-Se-carbon (C-Se-C). Micro and bulk XANES analysis showed that cladode tips contained both selenate and C-Se-C forms. Inductively coupled plasma mass spectrometry quantification of Se in high-performance liquid chromatography fractions followed by LC-MS structural identification showed selenocystathionine-to-selenomethionine (SeMet) ratios of 75:25, 71:29, and 32:68, respectively in cladode, fruit, and seed. Enzymatic digestions and subsequent analysis confirmed that Se was mainly present in a “free” nonproteinaceous form inside cladode and fruit, while in the seed, Se was incorporated into proteins associated with lipids. μXRF chemical mapping illuminated the specific location of Se reduction and assimilation from selenate accumulated in the cladode tips into the two LC-MS-identified C-Se-C forms before they were transported into the cladode mesophyll. We conclude that Opuntia is a secondary Se-accumulating plant whose fruit and cladode contain mostly free selenocystathionine and SeMet, while seeds contain mainly SeMet in protein. When eaten, the organic Se forms in Opuntia fruit, cladode, and seed may improve health, increase Se mineral nutrition, and help prevent multiple human cancers.

Stereoselective degradation of aqueous endosulfan in modular estuarine mesocosms: formation of endosulfan γ-hydroxycarboxylate

Solutions of alpha-endosulfan, beta-endosulfan, and technical grade endosulfan (70alpha:30beta) were added to modular estuarine mesocosms; the kinetics and degradation products from each mesocosm are reported. The persistent product endosulfan sulfate was generated in all cases; however, its yield was approximately a factor of three higher from alpha-endosulfan relative to beta-endosulfan. Beta-endosulfan hydrolyzed faster than alpha-endosulfan to endosulfan diol, which then rapidly degraded to endosulfan ether, endosulfan alpha-hydroxyether (major product), and endosulfan lactone. The ring-opened form of the lactone, endosulfan gamma-hydroxycarboxylate, is reported for the first time; it appears to be a terminal product, at least over the timescale of the experiment. The equilibrium between endosulfan gamma-hydroxycarboxylate and endosulfan lactone is dependent on pH, as only the protonated form of the gamma-hydroxy acid undergoes ring-closure. The pKa of the gamma-hydroxy acid was determined to be 5.7, implying that the lactone will quickly open and deprontonate under environmentally relevant conditions.

The fate of fipronil in modular estuarine mesocosms

The degradation and corresponding product manifold for the pesticide fipronil was determined in three replicate estuarine mesocosms. Aqueous fipronil concentrations rapidly decreased over the 672 h timescale of the experiment (95% removal). Loss was apparently first-order in fipronil, although there appeared to be a change in the removal mechanism after 96 h that corresponded to a dramatic slowdown in its disappearance. The reduction product of fipronil, fipronil sulfide, was not detected in the water column; however, it formed rapidly in sediments and was identified as the major product of fipronil degradation in the system (20% yield at 672 h, with respect to initial fipronil concentration). Fipronil sulfone is thought to form primarily via biological oxidation; and, although it was generated rapidly in the water column (10% yield), only trace amounts were detected in the sediment (1% yield). The direct photolysis product of fipronil, fipronil desulfinyl, was present in all samples; it formed rapidly in the water column (4% yield) and partitioned into the sediment phase (7% yield) over the course of the experiment. The mass balance on fipronil and associated products was 42% at 672 h.

Developmental and Geographical Variation in the Chemical Defense of the Walkingstick Insect Anisomorpha buprestoides

Anisomorpha buprestoides, a walkingstick common in the southeastern United States, sprays chemicals that irritate and repel threatening insects, birds, or mammals. The active chemical in this substance was initially identified as a monoterpene dialdehyde. This compound can be present in several stereoisomeric forms, and subsequent studies have revealed that A. buprestoides produces at least three diastereomers: anisomorphal, dolichodial, and peruphasmal. However, no inquiry has been made to date into the geographical or developmental dependence of this variation. We report here that different populations of adult A. buprestoides spray either anisomorphal, or peruphasmal, or a mixture of the two stereoisomers. Additionally, offspring of a peruphasmal-producing population produced a variable mixture of anisomorphal and dolichodial but switched to peruphasmal upon reaching sexual maturity. This appears to be the first report of a developmentally regulated change in walkingstick insect chemical defense. Our results suggest a more complex role of these substances in the overall chemical ecology of walkingstick insects.

Relative Configuration of Natural Products Using NMR Chemical Shifts

We have measured and quantum chemically computed NMR chemical shifts for three monoterpene diastereomers produced by the walkingstick, Anisomorpha buprestoides. By taking into account the Boltzmann distribution of conformers, the combined RMSDs between experimental and calculated (1)H and (13)C NMR shifts were able to determine the correct isomer, especially when only aliphatic nuclei were used. The calculated relative energies and interproton distances were also consistent with chemical isomerization experiments and NOE-based interproton distance calculations. Complementary to the NOE-based method, a comparison between experimental and calculated NMR chemical shifts can provide an efficient method to assign the relative configuration of natural products.

Quantification, localization, and speciation of selenium in seeds of canola and two mustard species compared to seed-meals produced by hydraulic press.

Brassica plants accumulate selenium (Se) especially in seeds when grown in soils laden with Se. We report a chemical analysis of Se in Brassica seeds (canola, Indian mustard, and white mustard) and in their hydraulically pressed seed meals, which are used as a Se supplement in livestock animal feeds. Complementary techniques were used to measure total Se concentrations, to map the localization of Se, and to quantify different Se forms. Seeds and hydraulically pressed seed meals contained an average of 1.8 and 2.0 μg Se g(-1) DW, respectively. Selenium was primarily located in cotyledons and roots of seed embryos. Microfocused Se K-edge XANES and bulk XANES showed that seeds contained 90% of Se as C-Se-C forms. Hydraulically pressing seeds for oil caused changes in the forms of Se as follows: 40-55% C-Se-C forms, 33-42% selenocystine, 5-12% selenocysteine, and 11-14% trimethylselenonium ion. Aqueous extracts of seed and seed meals were also analyzed by SAX-HPLC/ICPMS and found to contain mainly the C-Se-C form SeMet, but also another C-Se-C form MeSeCys, which is of dietary pharmacological interest for cancer inhibition. In addition, SAX-HPLC/ICPMS also detected selenocystine and selenocysteine, further confirming the results obtained by XANES analyses.

Remediation of fungicide residues on fresh produce by use of gaseous ozone.

Ozone fumigation was explored as a means for degrading organic fungicide residues on fresh produce. Fungicides sorbed onto model abiotic glass surfaces or onto grape berries were fumigated separately in a flow-through chamber. Gaseous ozone at a constant concentration of 150 ± 10 ppmv (μL·L(-1)) selectively oxidized fungicides sorbed to model surfaces. Over 140 min, boscalid and iprodione levels did not change significantly based on a single-factor analysis of variance (ANOVA) at the 95% level of confidence (p = 0.05); however, pseudo-first-order losses resulted in observable rate constants of ozonolysis, k(ozonolysis) (min(-1)), of 0.0233 ± 0.0029 (t(1/2) ≈ 29.7 min), 0.0168 ± 0.0028 (t(1/2) ≈ 41.3 min), and 0.0127 ± 0.0010 (t(1/2) ≈ 54.6 min) for fenhexamid, cyprodinil, and pyrimethanil, respectively. The relative degradation of fungicides on berries at gaseous ozone concentrations of 900 ± 12 ppmv (μL·L(-1)) over 2 h was similar to that on glass; decreases in residue concentration were observed for only fenhexamid (∼ 64%), cyprodinil (∼ 38%), and pyrimethanil (∼ 35%) with corresponding k(ozonolysis) (min(-1)) of 0.0085 ± 0.0021 (t(1/2) ≈ 81.5 min), 0.0039 ± 0.0008 (t(1/2) ≈ 177.7 min), and 0.0036 ± 0.0007 (t(1/2) ≈ 192.5 min). Heterogeneous rate constants of gaseous ozone reacting with a sorbed fungicide, k(O(3)) (M(-1)·min(-1)), were calculated for both surfaces and indicate losses proceed ∼ 15-fold slower on grapes. The kinetics and mechanism of fungicide removal, supported by gas chromatography- and liquid chromatography-mass spectrometry product analyses, is discussed in the context of facilitating compliance with maximum residue level (MRL) tolerances for fresh produce.