Pharmacology, Toxicology and Environmental Health Commons^™

Immunosuppression By Aflatoxin B1 In C57bl/6 Mice And Its Relationship With Neuroendocrine Mechanisms, Yasuhiko Hatori

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Aflatoxin B₁ (AFB₁), a secondary metabolite of Aspergillus flavus and Aspergillus parasiticus, is known for its potent carcinogenicity and immunosuppressive effects. It is also known that AFB₁ toxicity appears in different degrees in different animal species and strains.

The present study was performed to reveal the involvement of the hypothalamus-pituitary-adrenal gland (HPA) axis in the immunosuppressive effects of AFB₁ on C57BL/6 mice. Splenic lymphocytes were assayed to investigate their phenotyping using flow cytometry, proliferative response against mitogen and allogenic lymphocytes, cytolytic cell activity, and IL-2 production. In addition, antibody-mediated immunocompetence was checked using sheep …

Selenium And Iron In The Rat Intestine: Effects On Lipid Peroxidation, Sileny Vega

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Effects of Fe and Se status on GSHPx activity and lipid peroxidation in liver and intestinal mucosa were studied. Rats were Se and Fe supplemented (+Se+Fe), Se-deficient and Fe-supplemented (-Se+Fe), Se supplemented and Fe overloaded (+Se++Fe) by intramuscular injection, or Se deficient and Fe overloaded (-Se++Fe) for 20d. Fe overloaded tissues had more Fe, but hemoglobin was unaffected. Liver and mucosal GSHPx activity was low in Se-deficient rats. Thiobarbituric acid reactive substances (TBARS) were higher in Fe overloaded and -Se++Fe vs +Se++Fe tissues. Mucosal TBARS was higher in -Se++Fe rats gavaged with CBrCl₃. In experiment 2, Fe overload …

A Quantitative Assessment Of Minerals Of Toxicological Importance In Utah Fast Foods, Lisa R. Williams

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

X-ray flourescence (XRF) and atomic absorption spectrophotometry (AAS) measurements for manganese, iron, copper, and zinc were compared for 96 samples of 21 foods from different sources. Correlation coefficients were 0.94 for manganese, 0.99 for iron, 0.93 for copper, and 0.91 for zinc for XRF vs. AAS determinations.

Similiar comparisons were performed on 228 samples of fast foods purchased in Utah retail outlets. Correlation coefficients ranged from 0.91 for copper to 0.97 for iron and zinc. Comparisons of values generated by XRF for manganese, iron, copper, zinc, selenium, arsenic, and aluminum to values certified by the National Bureau of Standards indicated …

Immunologic, Hematologic, And Endocrine Responses To Subacute And Subchronic Exposures To Graded, Subanesthetic Levels Of Nitrous Oxide In Cd-1 Mice, Charles E. Healy

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Nitrous oxide (N₂O) oxidizes vitamin B12. disrupting deoxyribonucleic acid (DNA) synthesis. Occupational exposures to subanesthetic levels of the gas have been documented that may result in suppressed proliferative cell activities. Male CD-I mice were exposed to 0, 50, 500, and 5000 parts of N₂O per million parts of air (ppm) for 6 hr/day, 5 days/week for 2 and 13 weeks. Splenic lymphocytes were assayed for responsiveness to mitogens and for the ability to produce interleukin-2 (lL-2) . Tritiated-thymidine ([³H]-TdR) uptake was measured in CD-I splenic lymphocytes cultured in a mixed-lymphocyte culture (MLC). Cytolytic cell …

The Immunological And Neurochemical Toxicity Of Benzene And Its Interaction With Toluene In Mice, Gin-Chang Hsieh

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Benzene and toluene are known groundwater contaminants . Male CD-I mice were continuously exposed to 0, 31, 166, and 790 mg/ L benzene and 0, 17, 80, and 405 mg/L toluene, respectively, in drinking water for four weeks. Benzene caused a reduction of leukocytes, lymphocytes and erythrocytes, and resulted in a macrocytic anemia. Lymphocyte response to both B- and T-cell mitogens, mixed lymphocyte response to alloantigens, and the ability of cytotoxic lymphocytes to lyse tumor cells were enhanced at the lowest dose of benzene and depressed in the higher dosage animals. Benzene at doses of 166 and 790 mg/L decreased …

Effects Of Antiepileptic Drugs On Immune Function In Human Subjects And Mice, Nadine C. Margaretten

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A number of immune abnormalities have been found in epileptic patients treated with antiepileptic drugs (AED). The alterations seen range from mild suppression of immunoglobulins to severly impaired humoral and cellular immunities. There is evidence for both drug effects and genetic or acquired factors as contributors to these abnormalities. In order to examine the basis for immune abnormalities in patients with epilepsy, a number of experimental designs were employed: clinical studies, in vitro studies, and use of an animal model.

Peripheral blood mononuclear cells (PBMC) isolated from epileptic patients currently receiving AED were found to have a reduced OKT4+/0KT8+ ratio. …

Sunlight And Plants, Some Pursuits In Physiological Ecology, Martyn M. Caldwell

Faculty Honor Lectures

A physiological ecologist, as the name suggests, focuses on the interface between plant physiology and the ecology of individual organisms. Yet, one in this field should know something about disciplines ranging from physiology, or in the case of the subject of this lecture, even photochemistry, to the study of entire ecosystems.

Synthesis Of 6-Aminopenicillanic Acid-Protein Conjugates For Development Of Enzyme Immunoassay For B-Lactam Antibiotics, Alice Ann Heth

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

An enzyme immunoassay specific for several β-lactam antibiotics rather than individual antibiotics was investigated. The goal to develop an enzyme immunoassay for analysis of a whole class of compounds at one time is different than the goal of most enzyme immunoassays which desire specificity for drugs or hormone levels. Detection of the presence of all β-lactam antibiotics is wanted and identification of specific antibiotics is not needed.

6-Aminopenicillanic acid, the common structural moiety of β-lactam antibiotics was used tin this investigation. Methods of preparation of 6-aminopencillanic acid conjugates and antibodies needed for enzyme immunoassays have been developed. 6-Aminopenicillanic acid was …

Effects Of 3, 5, 6-Trichloro-2-Pyridinol On Thyroid Function, Charles Franklin Luke

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

3,5,6-trichloro-2-pyridinol, when administered in the diet, increases the feed efficiency (the ratio of weight gain to feed consumed) in various species of domestic animals and also appears to be retained in the liver at low concentrations, possibly by binding to a specific macromolecule. Because of its structural similarities to the outer ring of the thyroid hormones, trichloropyridinol and three structural analogs (2,4,5-trichlorophenol, 4-bromo-2,5-dichlorophenol, or 4-iodo-2,5-dichlorophenol) were tested for ability to compete in vitro with 3,5,3'-triiodothyronine (T₃) for nuclear receptors specific for the thyroid hormones. All four of the halogenated compounds were found to be weakly competitive for the …

Natural Killer Cell Activity And Beta-Endorphin In The Mink (Mustela Vison) And The In Vitro Effect Of Beta-Endorphin In Immunologic Assays, Nancy Cathleen Pace

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The purpose of this study was to investigate natural killer cell activity and the possible role of beta- endorphin in a natural model of autoimmune orchitis, the dark mink.

An assay was developed to study natural killer cell activity in the mink and base-line levels of activity in this specie were determined. Natural killer cell activity was assessed in fertile mutation mink, primary infertile dark mink and secondary infertile Utah dark mink with autoimmune orchitis. The study included three sampling times: November, March and April. Natural killer cell activity was significantly lower in mink studied in April than it was …

Residents' Annoyance Responses To Aircraft Noise Events, United States, National Aeronautics And Space Administration

Transportation

In a study conducted in the vicinity of Salt Lake City International Airport, community residents reported their annoyance with individual aircraft flyovers during rating sessions conducted in their homes. Annoyance ratings were obtained at different times of the day. Aircraft noise levels were measured, and other characteristics of the aircraft were noted by trained observers. Metrics commonly used for assessing aircraft noise were compared, but none performed significantly better than A-weighted sound pressure level. A significant difference was found between the ratings of commercial jet aircraft and general aviation propeller aircraft, with the latter being judged less annoying. After the …

Evaluation Of Allergic Hypersensitivity To 2,4-D, Malathion, And Captafol In Mice, Janette R. Cushman

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

2,4-D-specific IgE antibodies were detected in serum of BALB/c mice using the rat passive cutaneous anaphylaxis (PCA) test following the second intraperitoneal immunization with 1, 10, or 100 ug of 2,4-D0keyhole limpet hemocyanin (KLH) conjugate administered with aluminum hydroxide adjuvant. The groups that received 1 ug of 2,4-D conjugate had the highest antibody titers (geometric mean of 60). A paper radioallergosorbent test (PRAST) was developed for determination of 2,4-D-specific IgE. The PRAST was equally as sensitive as and showed a positive correlation with the PCA assay.

The anhydride of the diacid metabolite of malathion (MMA) coupled to KLH elicited MMA-specific …

Pharmacokinetic Assessment Of The Influence Of Dietary Fiber On The Absorption And Disposition Of Selected Model Xenobiotics As It Relates To Colon Cancer, Joseph Donald Debethizy

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Selected drugs are being utilized as models of putative colon carcinogens in a study of the influence of major types of dietary fiber upon drug pharmacokinetics. Adult, male Wistar rats were pretreated with standardized, isocaloric hydrated gelatin diets containing no fiber or 15% (w/w) cellulose, lignin, hemicellulose (metamucil), or pectin for 30 days. An additional group was fed lab chow ad libitum as a reference control.

The pharmacokinetics of acetaminophen, FD & C Red No. 2 and mirex were examined following oral administration in three separate experiments. Among fiber types, pectin and hemicellulose (Metamucil) caused higher peak plasma concentrations of …

Influence Of Lipophilicity On The Accumulation And Distribution Of Halogenated Phenols And A Pyridinol As Metabolites Of Pesticides In The Rat, Assed A. Attumi

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Exposure to halogenated phenols and pyridinols is of increasing concern because of their wide use and distribution. This research was initiated to determine the distribution, accumulation, and depletion of a group of halogenated phenols and a pyridinol in selected tissues of male weanling rats at different time intervals following a single oral dose of 0.33 or 1.66 m moles per kg body weight. The halogenated phenols and pyridinol were distributed differently in every tissue sampled following their administration, even though the amount administered was the same in each case. The concentrations in tissue were found in the order: 2,4,5-trichlorophenol > 4-bromo-2,5-dichlorophenol …

Alterations In Rat Brain Norepinephrine And Dopamine Levels And Synthesis Rates In Response To Five Neurotoxic Chemicals: Acrylamide, 2,5-Hexanedione, Tri-O-Tolyl Phosphate, Leptophos, And Methyl Mercuric Chloride, Charles N. Aldous

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Acrylamide, 2,5-hexanedione, Tri-o-tolyl phosphate and leptophos belong to three fundamentally different chemical classes but all four chemicals cause central-peripheral distal axonopathy. Some of these compounds have been shown to alter brain steady state levels of neurotransmitters or to inhibit the activities of adenosine triphosphatases which are involved in the uptake and storage of biogenic amines. Tests were performed to determine alterations in steady state levels of rat brain norepinephrine and dopamine in response to doses of the above chemicals and of the central nervous system toxin, methyl mercuric chloride sufficient to cause ataxia. Catecholamine synthesis rate constant estimations were performed. …

Accumulation Of Formaldehyde And Its Relation To Postmortem Aging Of Non-Gadoid Fish Species, Mohamad A. Al-Kanhal

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Three non-gadoid fish species, trout (Cynoscion regalis), English sole (Paraophyrys vetulus) and Pacific red snapper (Scomber japonicus) have been tested for the recovery of trimethylamine oxide (TMAO), trimethylamine (TMA), dimethylamine (DMA), and formaldehyde (FA) during postmortem storage at 4°C and -5°C. TMAO, TMA, and DMA content was determined by measuring them as the salt derivative of picric acid. FA was determined by using the 3-Methyl-2-Benzothiazolinone hydrazone test.

In muscle tissue of red snapper and English sole, it was clear that initially TMAO decreased during storage at 4°C, while the amounts of TMA, DMA, and …

Inhibition Of Synaptosomal Biogenic Amine Transport By A Diverse Group Of Neurotoxic Chemicals, William M. Bracken

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Synaptosomal membrane functions were monitored, after in vitro exposure to select environmental pollutants, in synaptosomal preparations originating from rat cerebral cortices. The uptake of NE and 5HT into the synaptosomes was monitored as was the K⁺-dependent phosphate activity of the membrane. CH₃HgCl, Hg(NO₃)₂, CdCl₂, diisopropylfluorophosphate (DFP), paraoxon, acrylamide and Kepone were the test chemicals whose effects were studied.

CH₃HgCl, Hg(NO₃)₂ and Kepone had the greatest inhibitory effects on NE and 5HT uptake. The concentrations producing 50 percent inhibition (IC₅₀) were 1.4 x 10 …

Pesticide Exposure Studies: Direct And Indirect Detection Of Absorption Of 2,4-D And Pronamide Herbicides In The Guinea Pig And Occupationally Exposed Workers, Ibrahim A.R. Al-Jabery

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A simple high pressure liquid chromatography procedure was used to determine 2,4-D and pronamide exposure in spraymen and their dermal absorption and excretion in guinea pigs.

Results of dermal application of these herbicides to guinea pigs demonstrated a strong correlation between the applied dermal dose and the urinary residue excretion over the dosage range tested. As the dosage was increased, the urinary excretion of residues was also increased. However, the excretion of 2,4-D amine mixture following dermal treatment of guinea pigs was prolonged as compared to that of pronamide.

Residue levels of these compounds were also determined to estimate skin …

A Computer Simulation Study Of Blood Cholinesterase Inhibition In Parathion Treated Rats, Scott Christopher Hennes

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A computer simulation model of blood cholinesterase inhibition in rats resulting from a single oral or dermal dose of parathion was developed and tested. The model consists of a set of non-linear differential equations describing the absorption, distribution and metabolism of parathion and the kinetics of inhibition and reactivation of erythrocyte and plasma cholinesterase. The equations are numerically integrated to produce the time-course of each of the cholinesterase activities of the blood. The model was tested for validity by a comparison of the activities predicted by the model to values determined experimentally in male rats. The model successfully simulated plasma …

Leptophos Metabolism In The Rat: An In Vivo Study Of Oxidative Versus Conjugative Modes Of Metabolism, David Richard Hampson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The objectives of this research were to examine the metabolism in vivo of the pesticide leptophos in the rat under normal conditions and during inhibition of the mixed-function oxidases and during depletion of glutathione. Glutathione is a cofactor in the conjugation reactions of the glutathione-S-transferases. Both the mixed-function oxidase system and the glutathione-S-transferases have been shown to be important in the biotransformation of other organophosphate pesticides.

Urinary metabolites of leptophos were extracted, derivatized and subsequently analyzed by gas-liquid chromatography. The methods used to analyze for alkyl phosphonates were subject to several shortcomings and modifications of the original procedure were necessary. …

The Effects Of Tri-O-Tolyl Phosphate (Totp) On The Immune System Of Mice, Craig R. Brinkerhoff

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

TOTP is a prevalent industrial and environmental contaminant which has been shown to be a neurotoxic agent. This study was undertaken to investigate the effects of this compound on the immune system. Several techniques were employed to test the humoral as well as cellular effects. Male Swiss Webster mice were administered by gastric gavage with three doses of TOTP (5, 50, and 500 mg/kg) and one dose TMTP (50 mg/kg) in corn oil once a week for 13 weeks. Control animals were given corn oil alone.

Lymphocyte transformation was determined on cultures of splenic cells obtained from animals sacrificed at …

Geophysical Surveys For Buried Waste Detection At The Idaho National Engineering Laboratory, U.S. Department Of Energy

All U.S. Government Documents (Utah Regional Depository)

This report describes a series of geophysical surveys performed at the Idaho National Engineering Laboratory (INEL). The main purpose of the surveys was to evaluate techniques, principally ground-penetrating radar, for detecting and mapping radioactive wastes buried in shallow trenches and pits.

Central Nervous System Toxicity Of Alpha-Chaconine In Rats, Charles Newell Aldous Iii

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Effects of alpha-chaconine were examined in the central nervous system on the basis of electrophysiological tests and by assaying for changes in the levels of several known neurotransmitters of the brain. The possibility that brain acetylcholine levels might increase corresponding to acetylcholinesterase inhibition in treated rats was investigated where an increase would suggest that the anti-acetylcholinesterase activity of alpha-chaconine was physiologically significant.

Various doses of alpha-chaconine were given to rats prepared for physiological tests. Some symptoms were observed at relatively low doses (8 to 10 milligrams per kilogram). These included constriction of abdominal muscles, respiratory impairment, and sedation. At the …

The Covalent Interaction Of Hepatic Metabolites Of The Insecticide Chlordane With Cellular Macromolecules In The Rat And Mouse In Vitro, Alan A. Brimfield

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This investigation addressed several aspects of the covalent interaction of metabolites of the insecticide chlordane with cellular macromolecules in vitro. Microsomal preparations from the liver of mice and rats were used and covalent binding to microsomal protein and RNA or to added calf thymus DNA was studied. Pure ¹⁴C-labelled cis- and trans-chlordane isomers as well as an isomeric mixture (¹⁴C-cis-chlordane plus ¹⁴C-trans-chlordane 3:1, w:w) were used as substrates for the in vitro system. Biochemical parameters investigated included inhibition of microsomal mixed-function oxidase and epoxide hydratase plus the induction of these enzymes by pretreatment with chlordane …

A Rapid And Specific Gas Chromatographic Analysis For Cysteine-S-Sulfonate To Determine The Distribution Of Sulfite In Mammalian Plasma, Joseph Don Debethizy

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

It has been shown in previous studies that when sulfite is absorbed by rabbits via either inhalation of SO₂ or oral exposure to sulfite, the hydrated form, bisulfite, interacts with plasma disulfides where it is suspected to be in the form, cysteine-S-sulfonate. A rapid and specific gas chromatographic analysis procedure for cysteine-S-sulfonate has been developed to better study the distribution of sulfite in biological systems. Sulfonated proteins are enzymatically hydrolyzed to ensure stability of the acid labile S-sulfonate disulfide. The hydrolysate is then applied to a 6 cm cation-exchange column and eluted with 0.1 N HCl which elutes the …

The Toxicity, Metabolism And Distribution Of Carbaryl In Three Species Of Labops With And Without Piperonyl Butoxide Treatment (Hemiptera:Miridae), Deifalla H. Osman

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Carbaryl toxicity, metabolism, and distribution in adults of three species of grass bugs from the genus Labops were studied in relation to species, sex, and treatment with piperonyl butoxide. LC₅₀ values for 8 hour exposure periods ranged from 0.02-0.14, 0.03-0.3, and 0.2-0.7 μg carbaryl/vial for L. utahensis, L. hirtus, and L. hesperius respectively. The males were more susceptible to carbaryl than females. Males of L. utahensis were more susceptible than L. hirtus and L. hesperius respectively.

The synergist difference values (LC₅₀ of carbaryl alone - LC₅₀ values of carbaryl after piperonyl butoxide treatment) were measured. …

Toxicological And Biochemical Investigations Of Alpha-Chaconine In Potato (Solanum Tuberosum L. ) Tubers: Physiologic Disposition And Tissue Binding, And Inhibition Of Tissue Cholinesterases And Isoenzymes, Sydney Obodoechina Alozie

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The distribution, absorption, metabolism and tissue binding of radioactivity were studied in hamsters after oral and intraperitoneal administration of alpha-chaconine- (³H). The material was well absorbed from the gastrointestinal tract and nearly 22 percent of the label was excreted via urine and feces in 7 days. The excretion was higher in urine (21 percent) than in feces ( < 1 percent). Tissue concentrations of radioactivity peaked at 12 hours following oral administration, with the highest concentrations found in lungs, liver, spleen, skeletal muscle, kidney and pancreas, with heart and brain containing moderate amounts. Concentrations of radioactivity in tissues following intraperitoneal administration were significantly higher than those observed after oral treatment. Excretion of chloroform-soluble products in the feces was 10 times higher than that of the chloroform-insoluble metabolites after both oral and intraperitoneal administration. In the urine, the activity was predominantly in the chloroform-insoluble form and the chloroform-soluble metabolites were relatively minor in amounts (0.27, 0.85, and 2.45 percent versus 0.005, 0.14 and 0.19 percent of dose for 12, 24 and 72 hours, respectively). After 7 days, the chloroform-soluble metabolites in urine increased to 20 percent of the excreted radioactivity, while the amount of chloroform-insoluble metabolites was less than 1 percent. Subcellular distribution of the labeled compound indicated the highest concentration of radioactivity in the nuclear and microsomal fractions of brain, liver and heart tissues. A small amount of radioactivity, shown by a minor peak, was also observed in the fractions between the mitochondrial and microsomal fractions on a sucrose gradient. Binding of radioactivity was observed in brain, testes, kidney, lung, liver and heart. All of the label in the brain appeared to be in the bound form. The results indicated that alpha-chaconine is slowly absorbed from the gastrointestinal tract after oral administration, and persists in various tissues, much of it in bound (non-extractable) form (in nuclear and microsomal fractions).

Excretion of alpha-chaconine- (3H) and its metabolites was investigated after oral and intraperitoneal administration in hamsters. The separation of the glycoalkaloid and its metabolites in feces and urine was accomplished by thin-layer chromatography. An increase in the concentration of excreted …

Subtle Teratogenic Effects Of Locoweed In Rats, Benjamin K. Nelson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Locoweed, a well-known teratogenic plant affecting livestock, is prevalent in mountain regions of the Western United States. Two common species (Astragalus lentiginosus and A. wootoni), administered to pregnant rats, induced behavioral deviations in their offspring. Treated mothers consumed less feed and gained less wieght during gestation than controls when gavaged locoweed at the rate of 1 gram whole plant per day on days 7 through 17 of gestation. A. lentiginosus reduced pup weight at birth (13% less than controls) and this weight reduction (as much as 29% less than controls) continued at least four weeks. A. lentiginosus also …

Carbon, Nitrogen And Algal Biomass In Cold Desert Soil Crusts, Mary Cleave Vogelsberg

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The algal biomass, total organic carbon, total nitrogen and percent soil moisture of soil crusts for a ten month period are presented for the Curlew Valley region of northern Utah. The estimates establish a significant relationship among these parameters.

A method involving chlorophyll extraction to determine the biomass of soil algae has been developed, and from this method the following conclusions are suggested: the revegetation of soil surfaces by algal crusts after lethal treatment, without physical disruption, appears to be rapid; there is no apparent relationship between the amount of algal biomass and the type of vascular vegetation present.

Nitrogen Fixation In Arid Western Soils, Robert Charles Rychert

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Nitrogen fixation by blue-green algae-lichen crusts from South Curlew Valley, Utah, in the Great Basin Desert, was studied using the acetylene reduction technique. A molar ratio of 3 moles C₂H₄ produced/mole of N₂ fixed was used to estimate nitrogen (N₂) fixation by acetylene reduction. Nostoc was found to be present in many of the lichen thalli examined microscopically. Crust nitrogen fixation decreased rapidly below -1/3 bar pressure (water potential) which indicated that nitrogen fixation occurs only when the crust is wet. This would suggest that most of the crust nitrogen fixation in the Great …