Browsing by Author "Cox, Stephen B."
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Item A Comparative Study on the Relative Terrestrial Toxicity of Two Gas-To-Liquid (GTL) Base Oils to a Low Toxicity Mineral Oil (LTMO), a Diesel, and a Biodiesel(2012-08-10) Arneson, Lisa; Anderson, Todd A.; Cañas-Carrell, Jaclyn E.; Cox, Stephen B.Until now however, there has been little to no research on the relative terrestrial toxicity and of GTLs. The goal of this thesis was to bridge this gap in GTL knowledge. To achieve this goal, the relative terrestrial toxicities of four base oils (GTL-1, GTL-2, LTMO, Diesel) were compared. This research included freshly spiked soils and oil-spiked soils that had been previously weathered 90 days at climates (10oC and 30oC) similar to those of popular drilling locations. First the weathering of soils spiked with these four base oils was investigated. There were two different weathering studies and a soil microbial respiration assay that compared the four base oils. Additionally, the accuracy of the modified method (Total Petroleum Hydrocarbons) used to monitor the oil content was also confirmed. Follwing these studies, the four base oils and their relative toxicity were compared in freshly spiked soils and in weathered soils (previously weathered for 90 days at 10oC and 30oC) through a series of toxicity assays. An acute toxicity assay of earthworms (Eisenia fetida) was performed where the toxic endpoint was their mortality. Phytotoxicity assays which included alfalfa (Medicago stavia), thick spike wheatgrass (Elymus lanceolatus), and fourwing saltbrush (Atriplex canescens) were also performed. The toxic endpoints included lack of germination and affected biomass. Another acute toxicity assay of springtails (Folsomia candida) was performed where the toxic endpoint was their mortality. Additionally, the terrestrial toxicity of these two GTLs were were further investigated in a LC50 earthworm assay and an EC50 thickspike wheatgrass assay. In the LC50 and EC50 the GTLs were compared against LTMO, Diesel, and a biodiesel. Overall the GTLs illustrated less toxicity when compared to LTMO and Diesel. GLT-spiked soils performed better in the earthworm acute toxicity study, the alfalfa germination and biomass study, and the saltbrush germination study. Additionally, during observations of activity, springtails in GTL-spiked soils survived better than in other oil-spiked soils. In the LC50 and EC50 assays, GTL base oils performed better than Diesel and LTMO. In the earthworm LC50 study, GTLs showed similar toxicity to the biodiesel. In some cases the other oils performed better than the GTLs. In the EC50, the biodiesel had much less toxicity than the other oils. Freshly spiked Diesel was determined to be less toxic then freshly spiked GTL-2 in both the thickspike wheatgrass and saltbrush germination assays, and GTL-1 freshly spiked soils had a significant toxic response towards germination of thickspike wheatgrass. When comparing GTL-1 to GTL-2, GTL-1 was less toxic than GTL-2 in freshly spiked soil (earthworms, LC50, alfalfa biomass, and saltbrush germination). In other cases, GTL-2 was less toxic than GTL-1 in freshly spiked soil (alfalfa germination, wheatgrass germination, EC50, and possibly springtails). The relative GTL-1 and GTL-2 toxicities varied according to the temperature and weathering of soils.Item Acute and chronic toxicity of hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) in deer mice (Peromyscus maniculatus)(Texas Tech University, 2007-08) Smith, Jordan Ned; Cobb, George P.; Cox, Stephen B.; Smith, Ernest E.; Stormberg, Angelica I.; Theodorakis, Christopher W.Contamination of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been identified at areas of explosive manufacturing, processing, storage, and usage in a variety of environmental media. Conversion of RDX to anaerobic N-nitroso metabolites (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX)) has been demonstrated in the environment and in vivo, in the gastrointestinal tract of mammals. Thus, potential exists for human and wildlife exposure to these N-nitroso compounds. Few papers report acute or chronic toxicity of these N-nitroso metabolites, thus my research is to assess acute and chronic toxicity of these compounds. Acute toxicity was assessed using acute oral median lethal dose (LD50). This was determined in deer mice (Peromyscus maniculatus) of three age classifications (21 d, 50 d, and 200 d) for RDX, MNX, and TNX using the U.S. EPA Up-and-Down Procedure (UDP). Hexahydro-1,3,5-trinitro-1,3,5-triazine and N-nitroso metabolites caused similar overt signs of toxicity. Median lethal dose for 21 d deer mice were 136, 181, and 338 mg/kg for RDX, MNX, and TNX respectively. Median lethal dose for 50 d deer mice were 319, 575, and 999 mg/kg for RDX, MNX, and TNX respectively. Median lethal dose for 200 d deer mice were 158, 542, and 338 mg/kg for RDX, MNX, and TNX respectively. These data suggest that RDX is the most potent compound tested, and age dependent toxicity may exist for all compounds. Chronic toxicity was evaluated with a reproductive study and a multigenerational study. Following exposure, reproductive toxicity of TNX was evaluated in three consecutive cohorts (F1A-C) of deer mice. TNX was administered ad libitum via drinking water at four exposure levels-control (0 µg/L), 1µg/L, 10 µg/L, and 100 µg/L. Endpoints investigated include: reproductive success, offspring survival, offspring weight gain, offspring organ weights, and liver TNX residues. Data from this study indicate that TNX bioaccumulates in the liver and is associated with postpartum mortality, dose dependent decrease in body weight from birth to weaning, and decrease in kidney weight in deer mice offspring. While exposed to TNX via drinking water ad libitum, deer mice were bred in a multigenerational fashion (parents produced offspring, which bred to produce more offspring) to produce three generations F1A-D, F2A-B, and F3A. TNX was administered at four exposure levels-control (0 µg/L), 10 µg/L, 100 µg/L, and 1 mg/L. Endpoints investigated include: reproductive success, offspring survival, offspring weight gain, and offspring organ weights. Data from this study indicate that TNX is associated with decreased litter size and increased postpartum mortality of offspring. Brain weights demonstrated a generational increase in dosed mice euthanized near the time of puberty. No teratogenic effects were linked with exposure to TNX. With tissue samples from both the reproductive and multigenerational studies, 12 microsatellite DNA loci were amplified and analyzed using both change in original parent allele frequencies and the parent/offspring approach of direct mutation rate calculation to assess genotoxicty of TNX in vivo. Findings demonstrate no dose dependent differences in deviation from parent microsatellite DNA allele frequencies or direct microsatellite mutation rate using the parent/offspring approach.Item Antibiotics, bacteria, and antibiotic resistance genes: Aerial transport from cattle feed yards via particulate matter(2015) McEachran, Andrew D. (TTU); Blackwell, Brett R. (TTU); Hanson, J. Delton; Wooten, Kimberly J. (TTU); Mayer, Gregory D. (TTU); Cox, Stephen B.; Smith, Philip N. (TTU)Background: Emergence and spread of antibiotic resistance has become a global health threat and is often linked with overuse and misuse of clinical and veterinary chemotherapeutic agents. Modern industrial-scale animal feeding operations rely extensively on veterinary pharmaceuticals, including antibiotics, to augment animal growth. Following excretion, antibiotics are transported through the environment via runoff, leaching, and land application of manure; however, airborne transport from feed yards has not been characterized. oBjectives: The goal of this study was to determine the extent to which antibiotics, antibiotic resistance genes (ARG), and ruminant-associated microbes are aerially dispersed via particulate matter (PM) derived from large-scale beef cattle feed yards. Methods: PM was collected downwind and upwind of 10 beef cattle feed yards. After extraction from PM, five veterinary anti biotics were quantified via high-performance liquid chromatography with tandem mass spectrometry, ARG were quantified via targeted quantitative polymerase chain reaction, and microbial community diversity was analyzed via 16S rRNA amplification and sequencing. results: Airborne PM derived from feed yards facilitated dispersal of several veterinary antibiotics, as well as microbial communities containing ARG. Concentrations of several antibiotics in airborne PM immediately downwind of feed yards ranged from 0.5 to 4.6 μg/g of PM. Microbial communities of PM collected downwind of feed yards were enriched with ruminant-associated taxa and were distinct when compared to upwind PM assemblages. Furthermore, genes encoding resistance to tetracycline antibiotics were significantly more abundant in PM collected downwind of feed yards as compared to upwind. conclusions: Wind-dispersed PM from feed yards harbors antibiotics, bacteria, and ARGs.Item Antibiotics, Bacteria, and Antibiotic Resistance Genes: Aerial Transport from Cattle Feed Yards via Particulate Matter(2015) McEachran, Andrew D.; Blackwell, Brett R.; Hanson, J. Delton; Wooten, Kimberly J.; Mayer, Gregory D.; Cox, Stephen B.; Smith, Philip N.Background: Emergence and spread of antibiotic resistance has become a global health threat and is often linked with overuse and misuse of clinical and veterinary chemotherapeutic agents. Modern industrial-scale animal feeding operations rely extensively on veterinary pharmaceuticals, including antibiotics, to augment animal growth. Following excretion, antibiotics are transported through the environment via runoff, leaching, and land application of manure; however, airborne transport from feed yards has not been characterized. Objectives: The goal of this study was to determine the extent to which antibiotics, antibiotic resistance genes (ARG), and ruminant-associated microbes are aerially dispersed via particulate matter (PM) derived from large-scale beef cattle feed yards. Methods: PM was collected downwind and upwind of 10 beef cattle feed yards. After extraction from PM, five veterinary antibiotics were quantified via high-performance liquid chromatography with tandem mass spectrometry, ARG were quantified via targeted quantitative polymerase chain reaction, and microbial community diversity was analyzed via 16S rRNA amplification and sequencing. Results: Airborne PM derived from feed yards facilitated dispersal of several veterinary antibiotics, as well as microbial communities containing ARG. Concentrations of several antibiotics in airborne PM immediately downwind of feed yards ranged from 0.5 to 4.6 μg/g of PM. Microbial communities of PM collected downwind of feed yards were enriched with ruminant-associated taxa and were distinct when compared to upwind PM assemblages. Furthermore, genes encoding resistance to tetracycline antibiotics were significantly more abundant in PM collected downwind of feed yards as compared to upwind. Conclusions: Wind-dispersed PM from feed yards harbors antibiotics, bacteria, and ARGs.Item Bioaccumulation and effects of metal contaminated soil on Great Plains toads, Bufo cognatus.(Texas Tech University, 2008-08) Bryer, Pamela Jean; McMurry, Scott T.; Cox, Stephen B.; Hooper, Michael J.; Carr, James A.Smelting and mining sites create local contaminated areas due to atmospheric release and deposition of metals and by increasing metal-enriched soil runoff. One of the proposed mechanisms of amphibian declines is contamination of habitats by chemical pollutants. Due to the number of mining and smelting sites worldwide, there is a risk to numerous amphibian populations from metal contamination. Currently, little is known about the effects of metal contaminated soil on amphibians. While it is generally understood that certain metals are highly toxic at low concentrations to most any organism, the exposure potential between organisms varies greatly. Metal uptake from soil is difficult to predict due to a complex metal-soil-water-toad relationship. Because of this complex relationship the use of models and passive sampling devices are not possible. This study consists of a series of soil exposures to toads Great Plains toads, Bufo cognatus. Each study follows the same basic design to assess metal bioaccumulation in toads housed individually on contaminated soil. The soils used in this study all came from or were created to mimic the soil conditions at the Anaconda Smelter Superfund Site, Deer Lodge County, MT, USA. The site is characterized by elevated levels of arsenic, cadmium, copper, lead, and zinc. Following their exposure, toads were tested through a series of behavioral, physiologic, and biochemical assays to asses the effects of the exposure. Between the studies, soil origin, soil temperature, size/age of the toads, and exposure duration were varied. Over the course of the studies, all metals showed increased bioaccumulation as soil metal concentration or exposure duration increased. Arsenic was not detectable in small, young-of-the-year toads. Cadmium concentrations, numerically, increased the most across each of the studies. Lead concentrations increased in most cases of increased exposure, however, variation in lead uptake in the adult toads studied was large as exposure duration increased. Zinc and copper tissue concentrations, both regulated essential metals, each increased with increasing exposure, however, zinc showed only slight to moderate increases overall. Partitioning within the body was highly variable between metals and between the studies. Overall, for juvenile toads, skin accumulated the bulk of the metals while in adults most metals accumulated in liver and kidney. One study compared the uptake of metals from soil collected at the Anaconda Smelter site to a series of spiked soils meant to mimic the ratio of metals in the Anaconda Smelter soil. Interestingly, we found that bioavailability was different between these soils, but not in the expected pattern. Cadmium and lead were both more bioavailable in the Anaconda Smelter soil than the spiked soil. Metal contaminated soil exposure had clear effects on the health of the toads. Time taken to bury was measured as a potential indicator of detecting contaminated soil avoidance, however, no differences were seen between soils. Although not consistent between each study the following endpoints were found to change in response to increasing soil metal concentration: prey orientating reflex, hop length, righting reflex, body mass, delta-aminolevulinic acid dehydratase (ALAD) activity, urine specific gravity, and mortality. Consistently across studies, organ (liver, kidney, and spleen) morphometrics did not change. It is clear, from this study and the works of others, that metal contaminated soil poses potential harm to amphibian populations. The effect of metal contaminated soil on toads can have two important ecological affects: 1) toads suffer directly from the presence of metal contaminated habitats and die, and 2) toads can accumulate metal concentrations that are then passed on via predation to other organisms in the food web. Protecting toads from metal contaminated soil is a challenge given their ability to bury deeply in the soil and their free ranging nature.Item Conservation of vertebrate biodiversity in Texas: Setting priorities for reserve selection(2006-12) Law, Jeffrey J.; Willig, Michael R.; McIntyre, Nancy E.; Cox, Stephen B.Species extinction rates are increasing throughout the world. A way to combat the global loss of species is through the creation of well-placed wildlife reserves. The principle objective of this study was to determine which areas throughout Texas most efficiently and effectively preserve extant vertebrate biodiversity (amphibians, reptiles, and mammals) if protected in reserves. Secondarily, I quantified the effectiveness of using a particular vertebrate class as a surrogate for others. The Sites Simulated Annealing Algorithm was used to determine areas that effectively preserve biodiversity while minimizing cost. This was accomplished through the use of irreplaceability values. Irreplaceability is equal to the number of times each planning unit is selected in a final solution to the SSAA. The SSAA was run 200 times for each scenario to determine this value. Species distribution maps obtained from the Texas GAP project were the basis for biodiversity data, whereas economic value of land came from the National Agriculture Statistics Service. I identified the best sites to establish reserves with current protected areas forced into the solution and also ignoring current protection status. The areas of the highest conservation concern, based on irreplaceability, were the Edwards Plateau of Central Texas and the Trans Pecos Region of West Texas. Although the irreplaceability values of planning units for incorporation into the reserve systems are correlated for all possible pairs of vertebrate classes, the associations are quite weak.Item Determination of the effects of carbon nanotubes on plants, soil microorganisms and phytoremediation of arsenic and polycyclic aromatic hydrocarbons(2012-12) Shrestha, Babina; Anderson, Todd A.; Cox, Stephen B.; Payton, Paxton R.; Acosta-Martinez, VeronicaTremendous growth in nanotechnology research has been observed in recent years because of its potential application in diverse fields. Because of the unique physicochemical, mechanical, and electrical properties, carbon nanotubes (CNTs) are the most widely used nanomaterials. There are two main types of CNTs: single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Ecotoxicology studies on nanomaterials and CNTs have increased in recent years, however, there is still very limited literature available on the environmental impact of manufactured nanomaterials. Understanding the ecotoxicological effects of nanomaterials and CNTs is deemed necessary to prevent the possible risk to humans and organisms. The Environmental Protection Agency has been emphasizing the need for research leading to the application of nanomaterials for environmental protection as well as the assessment of risk associated with nanomaterial applications. The objective of this dissertation study was to determine the effects of MWNTs on plants, soil microorganisms, and phytoremediation of arsenic and polycyclic aromatic hydrocarbons (PAHs) in soil. It was observed during the study that MWNTs at concentrations up to 1000 mg/ kg have no effects on soil metabolic functioning and microbial community composition. However, pyrosequencing demonstrated a shift in soil microbial community structure to more tolerant genera like Rhodococcus, Cellulomonas and Nocardioides (Actinobacteria) and Pseudomonas (Gammaproteobacteria) in the presence of extremely high MWNT concentrations (10000 mg/kg). There were no negative effects of MWNTs on seedling growth and germination of corn, cotton, alfalfa and sorghum. Uptake of MWNTs in roots of 8 d old corn and cotton seedlings was low (< 20 mg MWNT/kg dry biomass) in most MWNT treatments except MWNT accumulation was high (between 20 - 40 mg/kg) at the highest treatment (10000 mg/kg) in both corn and cotton. Similarly, uptake in 40 d old corn was also low (< 20 mg MWNT/kg dry biomass) comparable to 8 d old seedlings. However, translocation to above ground parts was very limited for both 8 d old (corn and cotton) and 40 d old corn, and MWNTs were detected in only a few samples. There were no negative effects of MWNTs on plant photosynthetic response in corn, however maximum photosysnthesis rate and light saturated photosysnthesis were slightly stimulated in in the presence of the two highest concentrations of MWNTs. There were also no negative effects of MWNTs on photosysnthetic pigment content and total percent nitrogen in corn leaves. Similarly, MWNTs did not show oxidative stress on corn roots. The results from these studies suggest that there are no negative effects of MWNTs on soil microorganisms, germination and seedling growth and, physiological and biochemical responses in later stages of plant growth. However, plants can uptake CNTs. Hence, there is possibility of transfer of CNTs to higher organisms through food chain transfer. Also, the presence of extremely high concentration of MWNTs (10000 mg/kg) in a worst case scenario might cause changes in soil microbial community composition. A study conducted on the influence of MWNTs on PAH rhizodegration found pyrene mineralization in a sandy clay loam soil significantly increased by 21 % in the highest MWNT treatment group (100 mg/kg). Microbial community composition was not influenced by the MWNT treatments in this sandy clay loam soil (3.4 % organic carbon content). However, microbial community structure in both the control and MWNT treatments showed a dramatic shift in the presence of MWNTs in the sandy loam soil (0.5 % organic carbon content). Many microbial FAMEs (i15:0, 16:1ω5c, 10 Me 17:0, 10Me 16:0) were missing in the control soil and these FAMEs showed a lower abundance in the 25 mg/kg MWNT treatment (except 10Me 17:0) while the presence of these FAMEs was higher in the 50 mg/kg and 100 mg/kg MWNT treatments. This study was able to show that MWNTs can influence the different factors of PAH rhizodegradation which will depend on different soil types with different organic carbon content in soil. The results from the 28 d study on arsenic hyperaccumulation in Chinese brake fern (Pteris vittata) showed that arsenic hyperaccumulation decreased in the presence of MWNTs and functionalized MWNTs (FMWNTs) in soil after both 21 and 28 d of exposure. However, the decrease was only statistically significant in MWNT treated soil at 28 d. The study indicates that MWNTs and FMWNTs might sequester arsenic in soil making it less bioavailable for uptake and bioaccumulation in plants. These studies have provided useful data on the effects of MWNTs on contaminant bioavailability which will be useful in the evaluation of nanomaterials as well as possible applications in various remediation processes. Although nanomaterials are considered beneficial for use in various sectors, this study indicates the need for regulation of their application to minimize the future risk to humans and the ecosystemItem Effect of land use on the community composition of amphibians in playa wetlands(Texas Tech University, 2006-05) Venne, Louise S.; McMurry, Scott T.; Smith, Loren M.; Cox, Stephen B.Populations of amphibians are declining world-wide, likely as a consequence of anthropogenic (e.g., pollution, habitat alteration and loss, global climate change) and natural (e.g., global climate change, diseases, and invasive species) changes in the landscape. A number of natural and anthropogenic stressors may affect the distribution and abundance of amphibians on the Southern High Plains (SHP). Common stressors on the SHP include spatial and temporal variation in precipitation and temperature, the presence of pesticides, and deposition of sediment in playas. Sedimentation reduces hydroperiod of playas and is likely the most significant anthropogenic stressor on amphibians in playas, and a stressor that logically interacts with climatic variation. However, the interactions of these factors and their effects on amphibian communities are largely unexplored. In light of continued intensive agriculture and projected global climate change, there is a need to better understand the driving factors affecting amphibians in playa ecosystems. Objectives of this study were to: (1) determine the relationship between land use (cropland vs. native grassland), hydrologic factors, habitat characteristics, playa density, and the amphibian community (richness and composition). Two sets of 40 playas were studied in 2003 and 2004, evenly split between land uses (i.e., cropland and grassland). Playas were sampled every two weeks following initial inundation until dry or October 15 to determine presence/absence of amphibians. Vegetation was sampled during the month after initial inundation. Playa characteristics and sedimentation were measured once playas were dry. Amphibian species richness was different between years, but not land uses. Land use was not a good predictor of amphibian species richness (AICc relative importance < 0.395) and community composition (Mantel statistic r = -0.018, p = 0.725), however, hydroperiod was related to amphibian species richness and community composition. Hydroperiod was a strong predictor of amphibian species richness in 2004 (D=52%), however the relationship was weak in 2003 (D=3.4%). Precipitation likely affected the relationship difference between hydroperiod and amphibian species richness as 2003 was a drought year whereas 2004 was a deluge year. Habitat characteristics (vegetation cover, structure, and height, plus presence of modifications) influenced the relationship between hydrologic factors and amphibian community composition in 2003 (Mantel statistic r = 0.169, p = 0.055). Corrected AIC models of species richness which included habitat characteristics had some support (Äi = 4.18-7.33). Models of species richness which contained playa density consistently had some support in both years (AICc Äi > 0.63). Playas in the medium-textured soil zone had deeper sediment, and thus reduced volume. Also, most cropland playas have lost over 100% of their original playa volume due to sedimentation, facilitating a reduction in hydroperiod. Land use was not determined to be the main factor affecting amphibians, probably because it does not capture the variability inherent in playas with differing hydrologic regimes. Continued cultivation of the SHP and predicted climate changes likely will interact to influence amphibian communities in playa wetlands. Climate models predict increases in annual mean temperature, which coupled with sedimentation, will accelerate drying of cropland playas. Given the current gradient of hotter, dryer conditions in the southwestern reaches of the SHP compared to the northeastern portions, I predict that loss of species from playas will occur in a non-random pattern, beginning in the southwestern SHP with species which have long larval development periods. In order to maintain amphibian diversity in the SHP, a reduction in sediment deposition in playas must be attained and hydroperiod should be optimized by implementing buffers.Item Effects of long-term metal contamination on the structure and function of microbial communities in soils.(Texas Tech University, 2007-08) Humphries, Jennifer A.; Cox, Stephen B.; Zak, John; Hooper, Michael J.; Anderson, Todd A.Microbial communities are critical components of soils and are known to be important for a wide range of ecosystem-level processes. However, due in part to methodological limitations, much of the basic structure and activity of microbial communities in both pristine and anthropogenically disturbed soils remains unknown. One hundred years of mining and smelting activity at the Anaconda Smelter Site in Anaconda, Montana has caused high concentrations of metals to be deposited in surrounding areas, leading to significant degradation of the soils, loss of above-ground vegetation and toxicological effects on humans and wildlife. Different phytoremediation strategies were tested in situ within the 1.5 acre Dragstrip demonstration area, to assess the efficacy of different soil amendments (fertilizer formulations, organic matter, liming materials, and depth of soil plowing) for supporting plant growth. The success of plant-based remediation techniques is largely dependent on the health and stability of the soil, of which soil microbial communities play essential roles. While high concentrations of metals are known to negatively affect microbial activity, biomass, and enzyme function, amendment of soils during the remediation process may further modify microbial community structure and function in soils. Little is known about the effects of soil amendments on the structural and functional diversity of microbial communities in heavy metal contaminated soils. Additionally, a better understanding is needed of the effects of metals on microbial community structure and function following long-term in sutu exposure, and following contamination with increasing concentrations of metals. The following research attempts to characterize the effects of anthropogenic disturbance (i.e., soil metal contamination and/or different soil amendment strategies) on the structure and function of microbial communities in soils surrounding the Anaconda Smelter as follows: 1) Microbial communities within the six remediated Dragstrip demonstration plots and adjacent unremediated control plot were characterized using a combination of culture-based (Biolog) and non-culture based (DGGE) techniques to characterize the combined effects of soil metal contamination and amendment strategy on microbial community structural (community DGGE banding profiles) and functional diversity (community carbon substrate utilization profiles (SUPs)). 2) Microbial communities native to six smelter-impacted sites (representing a gradient of soil metal concentrations) and a non-impacted site (representing background levels of metals) were compared to determine the long-term effects of metal contamination on microbial community dynamics (microbial activity, biomass, structural diversity and functional diversity). 3) Soil native to two smelter-impacted sites and a non-impacted site (previously exposed to high, low or background concentrations of aerially-deposited metals, in situ, respectively) were artificially-amended with metal-salts in the laboratory to characterize the dose-response effects of increasing concentrations of metals on microbial community dynamics. Additionally, this research tested the hypothesis that soil metal contamination, acting as an extreme environmental stressor, will catalyze a shift in species diversity and abundance, causing initially unique communities to converge on a community with similar structure and function. Results from these studies show that several physiochemical soil characteristics (percent organic matter, soil pH, cation exchange capacity) significantly influence the bioavailability of metals in soils, and metal bioavailability in turn influenced the toxicity of metals to soil microbes. Not only did soil metals significantly decrease microbial activity and biomass, but they also caused significant shifts in community structure, indicating the potential for metal stress to shift species diversity and abundance. The effects of soil metal contamination on community SUPs was less pronounced, which may give evidence of functional redundancy within the enriched portion of the communities. Soil physiochemical profiles were influenced by soil remediation amendment strategies, and several physiochemical parameters (K, NH4organic matter, and cation exchange capacity) were correlated with shifts in microbial community structure, indicating that amendment strategy has the potential to modify microbial communities over time. Finally, while microbial communities were not observed to converge on a common community as a result metal stress, these studies have documented the potential for metal contamination to shape the structural and functional diversity of microbial communities in soils. Microbial community endpoints are increasingly being marketed as potentially good indicators of soil ecosystem health and stability. These studies have shown that microbial community activity, biomass, community structure, and community function are sensitive endpoints for monitoring microbial responses to metal stress. However, additional studies are necessary to truly understand the complexity of microbial community responses to long-term metal contamination.Item Effects of weather on mosquito biology, behavior, and potential for West Nile virus transmission on the Southern High Plains of Texas(Texas Tech University, 2005-08) Bradford, Carrie M.; Presley, Steven M.; Nisbett, Richard; McIntyre, Nancy E.; Cox, Stephen B.; Anderson, Todd A.The threat of emerging and resurgent vector-borne diseases associated with weather conditions, global climate change, and biologic attacks is of major concern. West Nile virus (WNV) first appeared in the United States in the summer of 1999. Since then it has spread rapidly across the nation and continues to be a threat to humans, domestic animals (particularly horses), and wildlife. The goal of this project was to model the factors involved in the WNV maintenance and transmission cycle. Mosquito surveillance to determine mosquito community dynamics and WNV infection in mosquito populations has been ongoing in Lubbock County, TX (33.65°N; 101.81°W; 975 m elevation), since the summer of 2002. West Nile virus was first detected in Lubbock County in late summer 2002 and has continued to appear each summer. The occurrence of WNV in mosquitoes collected over a three-year period was determined and related to very diverse annual weather conditions during those years in order to determine trends in WNV occurrence. Differences in weather conditions between study years was reflected in differences in mosquito collections and WNV maintenance and transmission. In the Lubbock area, 2003 was a drought year, and Culex tarsalis Coquillett dominated mosquito collections due to an abundance of stagnant pools that allowed for the proliferation of this species. Additionally, a large number of mosquito pools tested positive for WNV. The following year, however, was a wet year, and Aedes vexans Meigen, a floodwater species, dominated mosquito collections. During 2004, the number of WNV-positive mosquito pools was reduced by two-thirds, despite testing approximately the same number of pools. Modeling mosquito populations and WNV occurrence in relation to weather patterns revealed interesting trends. Both of these were predicted by weather conditions, typically rainfall and temperature, in the weeks prior to collection of WNV infected mosquitoes. By understanding the factors that drive mosquito populations and the occurrence of WNV, future patterns of disease occurrence can be predicted and efficient mosquito control operations can be initiated prior to a major disease outbreak. Models which explain when and why disease transmission occurred are important as related to effective surveillance and control activities as well as with respect to climate change and the potential for biologic attacks. Climate change is expected to increase the geographic distribution of many vector-borne diseases, and especially mosquito-borne diseases. Malaria, among other diseases, has already reappeared in regions in which it had previously been eradicated. Global warming that is projected to occur with climate change will allow for the geographic range of many mosquito species to be expanded, with the potential for these species to carry new diseases into naïve areas. Additionally, climate change is expected to increase the frequency of extreme events such as floods and droughts, which have previously been shown to facilitate the outbreak of various mosquito-borne diseases. Models of disease transmission will help public health officials initiate effective surveillance and proactive control strategies to prevent the further spread of disease. Acts of terrorism involving biologics is also of major concern. Models of disease transmission will aid in distinguishing between natural outbreaks of disease and a biologic attack. Understanding how a disease outbreak was initiated is also critical for effective surveillance and control operations, since biologic attacks could involve genetically altered pathogens, thus potentially requiring a different means of disease treatment or control.Item Genome sequencing of two chronic wound isolated pseudomonas aeruginosa strains to understand adaptation and antibiotic resistance(2015-05) Oates, Jessica L.; Maul, Jonathan D.; Cox, Stephen B.; Rees, Eric J.; Rumbaugh, Kendra P.; Mayer, Gregory D.Pseudomonas aeruginosa is capable of infecting numerous hosts, inhabiting various ecosystems, and tolerating a wide spectrum of environments. Numerous P. aeruginosa strains have been fully sequenced and annotated with comparative genomics providing the opportunity to address why this bacteria is so successful at colonizing different niches. Examining the genetic complexity of P.aeruginosa strains isolated from chronic wounds will further the understanding of how this bacteria adapts to the chronic wound environment and is able to withstand antibiotic treatment. Two P.aeruginosa strains (PA1922 and PA0312), isolated from patients receiving treatment for chronic wounds, were screened for antibiotic susceptibility and shotgun sequenced to characterize genetic content. The susceptibility profiles showed that both PA1922 and PA0312 were resistant to fluoroquinolones and beta-lactams antibiotics. Comparing these wound isolated strains to other Pseudomonas spp., unique genomic regions were identified. Metal resistance operons and antibiotic resistance determinants were found within these predicted genomic islands. A substitution identified in DNA gyrase specifically in subunit A Site 83 (Thr->Ile) was found which relates to fluoroquinolone resistance. PA1922 and PA0312 also have the exotoxin gene exoU which has been identified in highly virulent Pseudomonas strains. The combination of these antibiotic resistance and virulence factors along with the unique genomic regions enable PA1922 and PA0312 to adapt to the wound bed ecology. These multi-factorial determinants complicate treatment options as traditional antibiotic choices are no longer relevant. Understanding the complexity of the Pseudomonas aeruginosa genome and the mechanistic causes of antibiotic resistance and virulence within chronic wounds is critical.Item Impacts of climate change on the population dynamics of Aedes albopictus and disease dynamics of dengue(2009) Erickson, Richard A.; Cox, Stephen B.; Allen, Linda J. S.; Long, Kevin R.; Presely, Steven M.Item Influence of metal mixtures on co-occurring toxic metal bioavailability and effects in adult and developing deer mice(Texas Tech University, 2007-12) McBride, Tobias John; Hooper, Michael J.; McMurry, Scott T.; Cox, Stephen B.; Hoff, Dale J.The bioaccessibility, bioavailability, and bioaccumulation of inorganic metals are complex principles. Unlike organic xenobiotics, many metals are required for biological functions. Nonetheless, dramatically increased concentrations of any metal may interact adversely with biomolecules, initiating a toxicological response when above a certain concentration in the organism. The bioavailability of environmental metals depends not only on metal concentrations in relevant matrices (food, water, soil), but on the chemical/physical form in which metals occur, the concentrations of other metals which co-occur, and the physiological status of the individual. Studies of mixed metal and metalloid (As, Cd, Cu, Pb and Zn) exposure in deer mice (Peromyscus maniculatus) at the Anaconda Smelter Site demonstrated that accumulation and biomarkers did not respond to the extent anticipated based on individual metal levels alone. This dissertation focuses on factors influencing the uptake, accumulation and resultant health effects of inorganic metals in a ubiquitous wild rodent species, and attempts to explain results from an earlier wildlife assessment on an NPL Superfund site. We sought to explain the variability in the effects of Pb exposure seen with the extreme heterogeneity of co-occurring metal contaminants in site soils. Using soil feeding studies, we have dissected the roles of Cu and Zn in modulating Pb absorption and Zn's role in reactivating ALAD activity in mice receiving high Pb doses. Second, our focus involves a lifetime bioaccumulation study of mice that investigated lactational metal exposure through the first 21 days of life (from soil-dosed feed provided to dams), and follows accumulation through 100 days of life. Comparisons with studies where adult mice were fed soil metals in their diet demonstrated that the more realistic lifetime exposure approach changes the accumulation kinetics, leading to greater accumulation of Cd and As, while underestimating exposures to Pb in the younger individuals. Finally, we investigate the role of lactation in weanling metal bioaccumulation, demonstrating how lactation decreases the dam's metal accumulation, while significantly increasing As and Pb exposure risks to the developing young.Item Influence of wet distillers grains diets on beef cattle fecal bacterial community structure(2012) Rice, William C.; Galyean, Michael L. (TTU); Cox, Stephen B.; Dowd, Scot E.; Cole, N. AndyBackground: The high demand for ethanol in the U.S. has generated large stocks of wet distillers grains (DG), a byproduct from the manufacture of ethanol from corn and sorghum grains. Little is known, however, about the potential influence of dietary DG on fecal microbial community structure. A better understanding of the microbial population in beef cattle feces could be an important monitoring tool to facilitate goals of improving nutrient management, increasing animal growth performance and decreasing odors and/or shedding of pathogens. Five diets consisting of a traditional diet fed to finishing beef cattle in the Southern High Plains of Texas-CON (steam-flaked corn control with 0% DG), and four concentrations of DG in the dietary dry matter; 10 C (10% corn-based DG), 5S (5% sorghum-based DG), 10S (10% sorghum DG), and 15S (15% sorghum DG) were fed to steers at the Texas Tech University Burnett Animal Center. Diets were essentially isonitrogenous with a formulated crude protein value of 13.5%. Results: Fecal grab samples were obtained from 20 steers (n = 4 per diet) and the barcoded DNA pyrosequencing method was used to generate 127,530 16S operational taxonomic units (OTUs). A total of 24 phyla were observed, distributed amongst all beef cattle on all diets, revealing considerable animal to animal variation, however only six phyla (core set) were observed in all animals regardless of dietary treatment. The average abundance and range of abundance, respectively of the core phyla were as follows: Firmicutes (61%, 19 to 83%), Bacteroidetes (28%, 11 to 63%), Proteobacteria (3%, 0.34 to 17.5%), Tenericutes (0.15%, 0.0 to 0.35%), Nitrospirae (0.11%, 0.03 to 0.22%), and Fusobacteria (0.086%, 0.017 to 0.38%). Feeding DG-based diets resulted in significant shifts in the fecal microbial community structure compared with the traditional CON. Four low abundance phyla significantly responded to dietary treatments: Synergistetes (p = 0.01), WS3 (p = 0.054), Actinobacteria (p = 0.06), and Spirochaetes (p = 0.06). Conclusions: This is, to our knowledge, the first study using this method to survey the fecal microbiome of beef cattle fed various concentrations of wet DG. Comparison of our results with other cattle DNA sequencing studies of beef and dairy cattle feces from a variety of geographical locations and different management practices identifies a core set of three phyla shared across all cattle. These three phyla, in order of relative abundance are; Firmicutes, Bacteroidetes, and Proteobacteria. The presence of large animal-to-animal variation in cattle microbiome was noted in our study as well as by others. © 2012 Rice et al; BioMed Central Ltd.Item Quantifying the impacts of toxicants on ecological populations(2013-08) Erickson, Richard A.; Anderson, Todd A.; Cox, Stephen B.; Long, Kevin R.; Salice, Christopher J.; Maul, Jonathan D.The closely related field of ecotoxicology and environmental toxicology have traditionally taken a reductionist approach and studied the effects of individual stressors on individual organisms. This approach fails to consider how multiple chemicals will affect populations and ecological systems. As an alternative, my doctoral research has focused on developing a population model and an interspecific competition model to better understand how pesticides and a simple mixture of pesticides affect natural systems. Using this system, I found that pesticides affect populations at levels not necessarily expected using traditional approaches. Specifically, malathion, pendimethalin, and permethrin were used as pesticides for the study system because they are found in the playa wetlands of the Southern High Plains. I also found that the mixture of pesticides was more toxic than the toxicity of individual pesticides, but the increase in toxicity was still difficult to quantify.Item Soil properties and microbial functional diversity of surface soils in the Luquillo Experimental Forest of Puerto Rico(Texas Tech University, 1999-12) Cox, Stephen B.Microbial communities represent an important, yet poorly understood component of the biodiversity of tropical forest ecosystems. Nonetheless, methodological difficulties associated with sampling and identifying microbes prevents obtaining answers to many questions related to fundamental issues in microbial ecology. One such issue is whether or not patterns in soil microbial communities are discernible at broad spatial scales (e.g., hectares). I assessed microbial functional diversity (MFD) in the Luquillo Experimental Forest of Puerto Rico based on the differential catabolism of 95 carbon sources (Biolog method). Specifically, I: (1) examined the influence of extreme soil types associated with topography (ridges and riparian valleys) and soil nutrient characteristics in determining MFD, and (2) elucidated broad-scale patterns of MFD with respect to forest type (elevation) and landuse within a landscape modified by agricultural and forestry practices. I included abandoned pastures as a "forest type" in order to assess the impacts of clearcutting and cattle grazing on microbial diversity and nutrient status. Considerable spatial variation characterized soils of the LEF, and differences between sites within each combination of forest type and topographic position accounted for 11-60% of the total variation in soil properties. Considerable spatial variation also characterized indexes of MFD, and differences between sites within each combination of forest type and topographic position were significant in 22 of 28 analyses. Nevertheless, mean soil properties differed significantly among forest types, between topographic positions (ridge vs. valley), and between seasons (wet vs. dry). In contrast, indexes of MFD were not different among forest types and between topographic positions. Of the 14 soil characteristics examined, P, Ca, and pH accounted for unique variation in MFD, and when variation in MFD due to these dominant soil parameters was removed, the interaction between forest type and topography was significant for diversity, evenness, and richness, and approached significance for total activity. Mantel analyses and Metric Multi-Dimensional Scaling revealed that microbial communities of different forest types and topographic positions exhibited distinct profiles of substrate utilization; however, differences among forest types depended on topographic position. Functional diversity of bacterial communities does exhibit distinctive patterns at the scale of the entire LEF, with the soil environment mediating the mechanisms related to forest type, topography, and season.Item The effect of arsenic trioxide on the grey flesh fly Sarcophaga bullata (Diptera: Sarcophagidae)(2011-05) Dacko, Nina M.; Presley, Steven M.; Cox, Stephen B.; Cobb, George P.Larvae of Sarcophaga bullata (Diptera: Sarcophagidae), a necrophagous insect commonly utilized in the field of entomotoxicology, were reared on rabbit tissues of rabbits that were previously exposed to arsenic trioxide (As2O3) by different methods. We observed the effects of arsenic (As) and As metabolites in acute versus chronic exposure in rabbit tissues on growth rate (mean larval length), metamorphosis, mortality and reproductive output of S. bullata. The New Zealand white rabbit was utilized as a vehicle to create natural concentrations of As and As metabolites in liver tissue and to serve as food media for S. bullata. Acutely exposed rabbits (2 per group) received three different doses of As2O3 corresponding to the dosages of half the median lethal dose or 0.5 MLD (10.1 mg/kg body weight (BW)), median lethal dose or MLD (20.2 mg/kg BW) and twice the median lethal dose or 2 MLD (40.4 mg/kg BW) and one control rabbit received dosing vehicle only. Chronically exposed rabbits received a dosage of 1.5 mg/kg BW daily for 35 days and one rabbit received dosing vehicle only. Rabbits were subsequently euthanized either eight hours post-exposure (acute) or on day 36 (chronic). The liver of these rabbits were removed and half was used as food media for 100 S. bullata larvae per experimental rabbit liver. The remaining half of the rabbit liver was used as a food media for 100 offspring of the prior experimental fly generation. Ten of these larvae were sampled and measured every eight hours until the onset of larval migration, for both generations of flies. Larval and pupal mortality was recorded, as well as the number of offspring, per dose group. ANOVA revealed a significant increase in mean larval body length in MLD as compared to the chronic dose group. Metamorphic time of S. bullata was positively correlated to the concentration of total As in exposed rabbit liver and mortality was negatively correlated to the concentration of total As in exposed rabbit liver. The reproductive output of S. bullata was not correlated to the concentration of total As in rabbit liver tissue.Item The effect of daily temperature variability on microbial and plant processes in a Chihuahuan Desert ecosystem(2012-05) van Gestel, Natasja; Zak, John; Tissue, David T.; Strauss, Richard E.; Scwhilk, Dylan W.; Cox, Stephen B.Worldwide, the daily temperature range of air (DTRair = Tmax – Tmin) has decreased by 0.07 °C per decade, with a 43% stronger decline for arid and semiarid regions. Although the daily temperature range of soil (DTRsoil) has not been widely measured, it is reasonable to assume that it has decreased at a similar rate and magnitude as DTRair. The role of temperature on plant and soil processes has been extensively studied, but the role of temperature variability on these processes has been largely ignored. In arid systems where DTRsoil is characteristically high, projected additional reductions in DTRsoil may have significant impacts on ecosystem functioning. My dissertation focuses on elucidating the role of high temperature variability on microbial and plant processes in an arid ecosystem, both intra- (i.e. seasonal) and inter-annually. Using a passive temperature manipulation experiment that successfully reduced DTRsoil in a Chihuahuan Desert soil at Big Bend National Park, my field study evaluated the biomass and activity responses of microorganisms in response to year-round reductions in DTRsoil, and subsequent changes to soil nutrient levels. In addition, changes to leaf-level physiology, leaf N content and leaf xylem water status of the dominant and representative plant species of arid landscapes, Larrea tridentata (creosotebush), were measured in response to reduced DTRsoil. To better link below-ground processes to plant responses, I conducted all measurements on the same day. High temperature variability was an important stressor to microbial growth as soil microbial biomass C and N increased in response to reductions in DTRsoil. Reduced DTRsoil benefited both dormant and active microbial populations through increased biomass C and N relative to control plots in both dry (spring) and wet (summer) seasons. In contrast, microbial activity, measured as CO2 evolution from soil in inter-shrub spaces, was more sensitive to soil water content and less sensitive to temperature variability than microbial biomass. Therefore, reductions in DTRsoil generated the largest effects on CO2 evolution in summer, which is the wettest season in Big Bend National Park. Increased microbial biomass reduced soil exchangeable N, most likely because extra N was required for biomass construction. However, soil exchangeable N levels did not always decrease in response to increased microbial biomass, suggesting that mineralization of N from a more stable pool of soil organic matter functioned to replenish depleting levels of soil exchangeable N. Although, I observed changes to belowground dynamics, including soil nutrient status and soil CO2 efflux rates, reductions in leaf [N] in Larrea tridentata did not alter photosynthetic rates in response to reductions in DTRsoil. Lastly, I compared different multiple regression models that utilized daily insolation and air temperature data to predict daily maximum and minimum soil temperatures at two soil depths (0 and 15 cm). Using a weighted average of current and past insolation (to incorporate a “heat” storage effect) in combination with air temperature provided the best fit for observed daily maximum and minimum soil temperature near the soil surface. An analytical solution can then be applied to use the predicted soil surface temperature data to estimate daily maximum and minimum soil temperatures deeper into the soil profile. In summary, my research generated three major findings. First, deserts dominated by Larrea may function temporarily as a source of C, resulting in a positive feedback to rising global temperatures. This imbalance will be sustained as long as the C and energy source (i.e. soil organic matter) continue to fuel higher levels of microbial activity. Second, if additional N incorporated into microbial biomass (labile pool) was derived from a more stable pool, this could increase volatile losses of N and further limit N in this N-limited system, and in turn, affect future primary productivity. Third, my dissertation produced promising results for predicting the soil thermal environment from above-surface conditions in a desert system. Using the same variables, this approach could be used in other arid systems with limited soil temperature data. Predicting future soil thermal regime is necessary to anticipate impacts on ecosystem function.Item The impacts of simulated nitrogen deposition on soil microbial communities along the Pine Canyon Watershed at Big Bend National Park, TX(2011-08) Grizzle, Heath W; Zak, John; Acosta-Martinez, Veronica; Cox, Stephen B.; McIntyre, Nancy E.; Strauss, Richard E.Anthropogenic nitrogen deposition in arid ecosystems is relatively low when compared to mesic systems. However, because arid ecosystems are characterized by low precipitation and high potential evapotranspiration rates in addition to nutrient limitations additional anthropogenic N deposition will likely have major effects on community structure and function of soil microorganisms relative to the effects found in mesic systems. Determining the impacts of N deposition in arid systems is critical as they cover more than 40% of the global land surface, contain a large portion of agricultural lands and are inhabited by more than 1 billion humans. This study evaluated how a simulated increase in annual N deposition and variable precipitation affected soil microbial functional diversity in a mid-elevation Sotol grassland and high-elevation Oak-Pine forest in the Chihuahuan Desert in Big Bend National Park, TX. Microbial functional diversity functional diversity parameters and monthly precipitation were measured and evaluated at both sites biannually from August 2003 to August 2006 and seasonally in the Sotol grassland in 2007. Differences in bacterial and fungal functional diversity on carbon substrates and fungal functional diversity on nitrogen substrates were estimated via Biolog microtiter plates from 2003 to 2007. Additionally, FAME analysis was used to evaluate relative proportions of soil bacteria and fungal groups during 2007. Finally, extracellular enzymes were evaluated during 2007 to evaluate the contribution of microbial enzyme activity on carbon, nitrogen and phosphorus cycling. Fungal functional diversity on carbon substrates was increased by low level nitrogen treatments in the Oak-Pine forest. However, increased nitrogen deposition did not effect carbon utilization in the Sotol grasslands. Fungal utilization of amino acids was significantly altered by increased nitrogen deposition in the Sotol grasslands. Additionally, Gram-negative bacterial community abundance and nitrogen cycling enzymes showed a seasonal response to additional nitrogen deposition in the Sotol grasslands. Seasonal influences and variable precipitation had a strong effect on most of the measured microbial community structural and functional parameters in the Sotol grasslands throughout the project. The difference in responses between the sites is largely due to differences in soil temperature, precipitation patterns and the different plant communities associated with each site.Item Toxicity and bioavailability of explosive metabolites to invertebrates(Texas Tech University, 2006-12) Zhang, Baohong; Anderson, Todd A.; Cobb, George P.; McMurry, Scott T.; Cox, Stephen B.; Jackson, W. AndrewRDX and its N-nitroso metabolites were rapidly absorbed into earthworms. The BCFs were 1.86, 0.39, and 0.05 for RDX, MNX and TNX, respectively. It is unlikely that earthworms reduce RDX to MNX and MNX to TNX. Other biotransformation pathways may be involved in earthworm biodegradation of RDX. MNX and TNX were also absorbed by PSDs. Organic matter content is one soil factor that affected the ratio of MNX or TNX uptake into earthworms vs. uptake into PSDs. A linear relationship between PSD uptake and earthworm uptake was observed. These data indicate that C18 PSDs may be used as a surrogate for soil organisms such as earthworms and provide a simple and easy chemical test for assessing the bioavailability of contaminants in soils. MNX and TNX inhibited earthworm growth, caused death, and inhibited reproduction. Earthworms were more sensitive to TNX in sandy loam soil than other conditions. The LOLC for MNX and TNX was 100 mg/kg in sandy loam soil, and 200 mg/kg in silt loam soil. At 7 days of exposure, the LOEC for earthworm growth was 50 mg/kg for TNX and 100 mg/kg for MNX. After 35 days of exposure, earthworm growth was reduced 8-39% by TNX in sandy loam soil, whereas TNX only inhibited earthworm growth 5-18% in silt loam soil. MNX affected glutathione synthesis and the activity of GPX and ChE although no significant effects were observed on protein content, CAT, and GCS activity. Surprisingly, MNX enhanced ChE activity, especially the activity of AChE. AChE activity was enhanced more than 3-fold in earthworms exposed to 50 mg/kg MNX for 30 days. RDX N-nitroso metabolites, especially MNX, may cause oxidation stress in earthworms. MNX and TNX affected cricket egg hatching. TNX was more toxic to eggs than MNX. After 30 days exposure, the EC20, EC50, and EC95 were 47, 128, and 247 ìg/g for TNX, and 65, 140, and 253 ìg/g for MNX in topical tests and 21, 52, and 99 ìg/g for MNX, and 12, 48, and 97 ìg/g for TNX in sand. These data can be used for defining criteria for environmental management of RDX and performing specific risk assessment of RDX and its N-nitroso metabolites.