Towards a more accurate quantitative assessment of seasonal Cryptosporidium infection risks in surface waters using species and genotype information.

Many Cryptosporidium species/genotypes are not considered infectious to humans, and more realistic estimations of seasonal infection risks could be made using human infectious species/genotype information to inform quantitative microbial risk assessments (QMRA). Cryptosporidium oocyst concentration and species/genotype data were collected from three surface water surveillance programs in two river basins [South Nation River, SN (2004-09) and Grand River, GR (2005-13)] in Ontario, Canada to evaluate seasonal infection risks. Main river stems, tributaries, agricultural drainage streams, water treatment plant intakes, and waste water treatment plant effluent impacted sites were sampled. The QMRA employed two sets of exposure data to compute risk: one assuming all observed oocysts were infectious to humans, and the other based on the fraction of oocysts that were C. hominis and/or C. parvum (dominant human infectious forms of the parasite). Viability was not considered and relative infection risk was evaluated using a single hypothetical recreational exposure. Many sample site groupings for both river systems, had significant seasonality in Cryptosporidium occurrence and concentrations (p ≤ 0.05); occurrence and concentrations were generally highest in autumn for SN, and autumn and summer for GR. Mean risk values (probability of infection per exposure) for all sites combined, for each river system, were roughly an order of magnitude lower (avg. of SN and GR 5.3 × 10-5) when considering just C. parvum and C. hominis oocysts, in relation to mean infection risk (per exposure) assuming all oocysts were infectious to humans (5.5 × 10-4). Seasonality in mean risk (targeted human infectious oocysts only) was most strongly evident in SN (e.g., 7.9 × 10-6 in spring and 8.1 × 10-5 in summer). Such differences are important if QMRA is used to quantify effects of water safety/quality management practices where inputs from a vast array of fecal pollution sources can readily occur. Cryptosporidium seasonality in water appears to match the seasonality of human infections from Cryptosporidium in the study regions. This study highlights the importance of Cryptosporidium species/genotype data to help determine surface water pollution sources and seasonality, as well as to help more accurately quantify human infection risks by the parasite.

Fate of Clostridium difficile during wastewater treatment and incidence in Southern Ontario watersheds.

AIMS: To investigate the prevalence of Clostridium difficile encountered during sewage treatment and in water sources into which treated effluent was directly or indirectly discharged. METHODS AND RESULTS: Samples from wastewater treatment plants (WWTPs) and rivers were collected and then enriched for Cl. difficile. Each of the isolates was subjected to toxinotyping and DNA typing using ribotyping, in addition to pulse-field gel electrophoresis. Cl. difficile was isolated from 92% (108/117) of the raw sludge and 96% (106/110) of the anaerobic digested sludge samples from two Ontario WWTPs. The pathogen was recovered from 73% (43/59) of dewatered biosolids and effluent discharge, in addition to river sediments 39% (25/64). Ribotype 078 (commonly associated with Community Acquired infections) was recovered from raw sewage (19%; 21/108), digested sludge (8%; 8/106), biosolids (35%; 15/43) and river sediments (60%; 15/25). CONCLUSIONS: Clostridium difficile is commonly encountered in raw sewage and survives the wastewater treatment process. The pathogen can then be disseminated into the wider environment via effluent and land application of biosolids. SIGNIFICANCE AND IMPACT OF THE STUDY: The study has illustrated the wide distribution of toxigenic Cl. difficile in WWTPs and river sediments although the clinical significance still requires to be elucidated.

Using Campylobacter spp. and Escherichia coli data and Bayesian microbial risk assessment to examine public health risks in agricultural watersheds under tile drainage management.

Human campylobacteriosis is the leading bacterial gastrointestinal illness in Canada; environmental transmission has been implicated in addition to transmission via consumption of contaminated food. Information about Campylobacter spp. occurrence at the watershed scale will enhance our understanding of the associated public health risks and the efficacy of source water protection strategies. The overriding purpose of this study is to provide a quantitative framework to assess and compare the relative public health significance of watershed microbial water quality associated with agricultural BMPs. A microbial monitoring program was expanded from fecal indicator analyses and Campylobacter spp. presence/absence tests to the development of a novel, 11-tube most probable number (MPN) method that targeted Campylobacter jejuni, Campylobacter coli, and Campylobacter lari. These three types of data were used to make inferences about theoretical risks in a watershed in which controlled tile drainage is widely practiced, an adjacent watershed with conventional (uncontrolled) tile drainage, and reference sites elsewhere in the same river basin. E. coli concentrations (MPN and plate count) in the controlled tile drainage watershed were statistically higher (2008-11), relative to the uncontrolled tile drainage watershed, but yearly variation was high as well. Escherichia coli loading for years 2008-11 combined were statistically higher in the controlled watershed, relative to the uncontrolled tile drainage watershed, but Campylobacter spp. loads for 2010-11 were generally higher for the uncontrolled tile drainage watershed (but not statistically significant). Using MPN data and a Bayesian modelling approach, higher mean Campylobacter spp. concentrations were found in the controlled tile drainage watershed relative to the uncontrolled tile drainage watershed (2010, 2011). A second-order quantitative microbial risk assessment (QMRA) was used, in a relative way, to identify differences in mean Campylobacter spp. infection risks among monitoring sites for a hypothetical exposure scenario. Greater relative mean risks were obtained for sites in the controlled tile drainage watershed than in the uncontrolled tile drainage watershed in each year of monitoring with pair-wise posterior probabilities exceeding 0.699, and the lowest relative mean risks were found at a downstream drinking water intake reference site. The second-order modelling approach was used to partition sources of uncertainty, which revealed that an adequate representation of the temporal variation in Campylobacter spp. concentrations for risk assessment was achieved with as few as 10 MPN data per site. This study demonstrates for the first time how QMRA can be implemented to evaluate, in a relative sense, the public health implications of controlled tile drainage on watershed-scale water quality.

Increased risk for Campylobacter jejuni and C. coli infection of pet origin in dog owners and evidence for genetic association between strains causing infection in humans and their pets.

We compared Campylobacter jejuni/coli multilocus sequence types (STs) from pets (dogs/cats) and their owners and investigated risk factors for pet-associated human campylobacteriosis using a combined source-attribution and case-control analysis. In total, 132/687 pet stools were Campylobacter-positive, resulting in 499 strains isolated (320 C. upsaliensis/helveticus, 100 C. jejuni, 33 C. hyointestinalis/fetus, 10 C. lari, 4 C. coli, 32 unidentified). There were 737 human and 104 pet C. jejuni/coli strains assigned to 154 and 49 STs, respectively. Dog, particularly puppy, owners were at increased risk of infection with pet-associated STs. In 2/68 cases vs. 0.134/68 expected by chance, a pet and its owner were infected with an identical ST (ST45, ST658). Although common sources of infection and directionality of transmission between pets and humans were unknown, dog ownership significantly increased the risk for pet-associated human C. jejuni/coli infection and isolation of identical strains in humans and their pets occurred significantly more often than expected.

Differentiation of Candida strains by lectin-mediated agglutination kinetics.

The lectin-mediated agglutination kinetics of Candida albicans, Candida tropicalis, Candida glabrata, Candida krusei, Candida kefyr, and Candida parapsilosis strains isolated from immunocompromised patients was investigated. The rate of the lectin-induced cell agglutination depends on the physiological state of the yeast cell population. Therefore, the Candida strains have to be cultivated and investigated under identical conditions. Lentil lectin (prepared from Lens culinaris), castor lectin, and concanavalin A were used. Different yeast species showed different agglutination behaviour. Furthermore, the lectin-mediated rate of agglutination is a strain-specific property which makes it possible to distinguish between different yeast strains of the same species. It is concluded that the lectin-mediated agglutination kinetics allows reproducible differentiation of yeast strains of the same species.

Characterization of metal-resistant soil eubacteria by polymerase chain reaction--denaturing gradient gel electrophoresis with isolation of resistant strains.

Contamination of soils with heavy metal ions is a major problem on industrial and defense-related sites worldwide. The bioavailability and mobility of these contaminants is partially determined by the microbial biomass present at these sites. In this study, we have assessed the effect of the addition of a mixture of toxic metal salts on the prokaryotic community of microcosms consisting of sandy-loam soil using direct molecular analysis of the recoverable eubacterial 16S rDNA molecules by polymerase chain reaction--denaturing gradient gel electrophoresis (PCR-DGGE) and limited phospholipid fatty acid analysis (PLFA). Addition of toxic metals (nonradioactive surrogates of Sr, Co, Cs, Cd) resulted in rapid (ca. 1 week) changes in the DGGE profile of the indigenous eubacterial community when compared with pristine controls. These changes were stable over the course of the experiment (8 weeks). No changes in the eubacterial population of control microcosms were detected. The major changes in community structure in metal-contaminated microcosms consisted of the appearance of four novel bands not detected in controls. Sequence analysis of these bands suggested that two organisms related to the genus Acinetobacter and two related to the genus Burkholderia carried a selective advantage over other indigenous eubacteria under heavy metal induced stress. The Burkholderia spp. were then cultured and further characterized using lipid analysis.

Comparative study of the in vitro behavior of cord blood subpopulations after short-term cytokine exposure.

We investigated the effect of short-term cytokine exposure on defined cord blood subpopulations. CD34+Thy1+, CD34+Thy1-, CD34+38-, CD34+38+, CD34+DR+, CD34+DR-, CD34+Rhodamine123 (Rh123)- and CD34+Rh123+ cells were incubated for 7 days in IMDM + 10% FCS + IL3 + IL6 + G-CSF + SCF (36GS) + flt3L. We evaluated LTHC-IC, immunophenotype and nucleated cell count for each cell population before and after cytokine exposure. Short-term exposure of CD34+38+, CD34+Thy1-, CD34+DR+, CD34+DR- and CD34+Rh123+ cells to 36GS causes a significant increase in cell number, whereas CD34+38-, CD34+Thy1+, and CD34+Rh123- cells show only a limited increase. CD34 status post cytokine incubation shows that CD34+38+, CD34+Thy1-, CD34+DR+, and CD34+Rh123+ fractions have a lower proportion of cells remaining CD34+ than CD34+38- CD34+Thy1+, CD34+DR- and CD34+Rh123- fractions. LTHC-IC analyses among input subpopulations show a higher frequency among CD34+38+, CD34+Thy1-, CD34+DR+, CD34+DR- and CD34+Rh123+ cells as compared with CD34+38-, CD34+Thy1+ and CD34+Rh123- cells. However, when LTHC-IC were evaluated after cytokine exposure, CD34+38-, CD34+Thy1+, and CD34+Rh123- cells showed a higher frequency of LTHC-IC as compared with other subpopulations. Addition of flt3L to 36GS doubled the numbers in all subpopulations without altering the proportion of CD34+ cells. Results suggest that CD34+38-, CD34+Thy1+ and CD34+Rh123- cells have a limited proliferative response to cytokines, the stem cell component of these populations is largely maintained and that expansion is derived from mature cell populations.

Effect of toxic metals on indigenous soil beta-subgroup proteobacterium ammonia oxidizer community structure and protection against toxicity by inoculated metal-resistant bacteria.

Contamination of soils with toxic metals is a major problem on military, industrial, and mining sites worldwide. Of particular interest to the field of bioremediation is the selection of biological markers for the end point of remediation. In this microcosm study, we focus on the effect of addition of a mixture of toxic metals (cadmium, cobalt, cesium, and strontium as chlorides) to soil on the population structure and size of the ammonia oxidizers that are members of the beta subgroup of the Proteobacteria (beta-subgroup ammonia oxidizers). In a parallel experiment, the soils were also treated by the addition of five strains of metal-resistant heterotrophic bacteria. Effects on nitrogen cycling were measured by monitoring the NH3 and NH4+ levels in soil samples. The gene encoding the alpha-subunit of ammonia monooxygenase (amoA) was selected as a functional molecular marker for the beta-subgroup ammonia oxidizing bacteria. Community structure comparisons were performed with clone libraries of PCR-amplified fragments of amoA recovered from contaminated and control microcosms for 8 weeks. Analysis was performed by restriction digestion and sequence comparison. The abundance of ammonia oxidizers in these microcosms was also monitored by competitive PCR. All amoA gene fragments recovered grouped with sequences derived from cultured Nitrosospira. These comprised four novel sequence clusters and a single unique clone. Specific changes in the community structure of beta-subgroup ammonia oxidizers were associated with the addition of metals. These changes were not seen in the presence of the inoculated metal-resistant bacteria. Neither treatment significantly altered the total number of beta-subgroup ammonia-oxidizing cells per gram of soil compared to untreated controls. Following an initial decrease in concentration, ammonia began to accumulate in metal-treated soils toward the end of the experiment.

Detection of Sphingomonas spp in soil by PCR and sphingolipid biomarker analysis.

Sphingomonas spp possess unique abilities to degrade refractory contaminants and are found ubiquitously in the environment. We developed Sphingomonas genus-specific PCR primers (SPf-190 and SPr1-852) which showed specific amplification of a 627-bp 16S rDNA fragment from Sphingomonas spp. A PCR assay using these Sphingomonas specific primers was developed to detect Sphingomonas aromaticivorans B0695R in three texturally distinct soil types, showing detection limits between 1.3-2.2 x 10(3) CFU g(-1) dry soil. A sphingolipid extraction protocol was also developed to monitor Sphingomonas populations in soil quantitatively. The detection limit of the assay was 20 pmol g(-1) dry soil, equivalent to about 3 x 10(5) cells g(-1) dry soil. Survival of S. aromaticivorans B0695R was monitored in the three different soils by antibiotic selective plate counting, PCR and sphingolipid analysis. All three approaches showed that the B0695R cells persisted in the low biomass Sequatchie sub-soil at about 3-5 x 10(7)cells g(-1) dry soil. In comparison to the plate counting assay, both the PCR and sphingolipid analysis detected a significantly higher level of B0695R cells in the clay soil and Sequatchie top-soil, indicating the possibility of the presence of viable but non-culturable B0695R cells in the soils. The combination of PCR and sphingolipid analysis may provide a more realistic estimation of Sphingomonas population in the environment.

Energy transfer and charge separation in photosystem I: P700 oxidation upon selective excitation of the long-wavelength antenna chlorophylls of Synechococcus elongatus.

Photosystem I of the cyanobacterium Synechococcus elongatus contains two spectral pools of chlorophylls called C-708 and C-719 that absorb at longer wavelengths than the primary electron donor P700. We investigated the relative quantum yields of photochemical charge separation and fluorescence as a function of excitation wavelength and temperature in trimeric and monomeric photosystem I complexes of this cyanobacterium. The monomeric complexes are characterized by a reduced content of the C-719 spectral form. At room temperature, an analysis of the wavelength dependence of P700 oxidation indicated that all absorbed light, even of wavelengths of up to 750 nm, has the same probability of resulting in a stable P700 photooxidation. Upon cooling from 295 K to 5 K, the nonselectively excited steady-state emission increased by 11- and 16-fold in the trimeric and monomeric complexes, respectively, whereas the quantum yield of P700 oxidation decreased 2.2- and 1.7-fold. Fluorescence excitation spectra at 5 K indicate that the fluorescence quantum yield further increases upon scanning of the excitation wavelength from 690 nm to 710 nm, whereas the quantum yield of P700 oxidation decreases significantly upon excitation at wavelengths longer than 700 nm. Based on these findings, we conclude that at 5 K the excited state is not equilibrated over the antenna before charge separation occurs, and that approximately 50% of the excitations reach P700 before they become irreversibly trapped on one of the long-wavelength antenna pigments. Possible spatial organizations of the long-wavelength antenna pigments in the three-dimensional structure of photosystem I are discussed.

Effects of ammonium dinitramide on preimplantation embryos in Sprague-Dawley rats.

Ammonium dinitramide (ADN) is a class 1.1 oxidizer that may be used in rocket propellants and explosives. Previous studies have shown that ADN is a female reproductive toxicant, causing implantation failure in Sprague-Dawley rats when it is administered during the preimplantation period of gestation. The purpose of this follow-up study was to identify the mechanism(s) associated with implantation failure following exposure to ADN. Mated female rats were treated with 2.0 grams per liter (g l-1) ADN in their drinking water for 24, 48, 72, or 96 h before preimplantation embryos were harvested from the oviducts or uterine horns. On gestation day 1 (GD-1), comparable numbers of morphologically normal two-cell embryos were harvested from the oviducts of the treatment and control groups. On GD-2, the development of the embryos harvested from the treated animals was either slowed or halted when compared to the control embryos. By GD-4, 98% of the embryos harvested from the control group had developed to the morula or blastocyst stage; these were collected from the uterine horns. On GD-4 in the treated group, 41% of the harvested embryos remained at the two- to six-cell stage and 59% were degenerate; 82% of these embryos were collected from the oviducts. These data suggest that the implantation failure seen in animals treated with ADN is due to embryolethality.

Sequential biological immunosuppression. Induction therapy with rabbit antithymocyte globulin.

This paper describes 108 consecutively treated patients receiving 109 cadaveric (CD) and living donor (LD) renal allografts using a protocol of quadruple sequential immunosuppression with a rabbit anti-human thymocyte IgG (Thymoglobuline), azathioprine, tapering corticosteroids, and delayed introduction of cyclosporine A. The average length of induction was 6.1 d with an average Thymoglobuline dose of 2.0 mg/kg/d. The mean serum creatinine pre-transplant of the cohort was 877 +/- 263 (sd) mumol/L, 146 +/- 44 mumol/L by 3 months post-transplant, and 136 +/- 40 mumol/L at 1 yr. The overall 4-yr actuarial patient survival was 96.6%, and allograft survival was 88.6% at 2 yr and 83.6% at 4 yr. The incidence of acute rejection episodes defined by intention to treat was 32%. Additionally, eight patients in this series received retreatment with Thymoglobuline for a first acute rejection, and only one of these had a second rejection. This was in contrast to 5/11 recurrent rejections following steroid treatment only, and 5/13 recurrences following OKT3 treatment for the first rejection episode. The side-effect profile of Thymoglobuline was largely benign, and the biological agent was well tolerated with initial fever in 75%, chills in 27%, and leucopenia in 22% of the patients. All other drug-related adverse events had a prevalence of less than 3%, and clinical signs of meningismus were seen in only one patient. There were five associated episodes of CMV. We conclude that Thymoglobuline as part of a quadruple sequential immunosuppressive regimen for renal transplantation is well tolerated and can be associated with a good short- and long-term outcome of renal transplantation.

Sarcoma cells engineered to secrete IFN-gamma or IL-2 acquire sensitization to immune cell killing via different mechanisms.

The murine fibrosarcoma FS29 can be more efficiently killed by syngeneic lymphocytes when it has been engineered to secrete either interferon gamma (IFN-gamma), or interleukin 2 (IL-2). The mechanisms by which the two cytokines enhance target sensitivity differ. Supernatant from IFN-gamma-secreting cells can enhance the sensitivity of unmodified cells. The enhanced sensitivity correlates with MHC upregulation observed on both the IFN-gamma-secreting and supernatant-treated cells. In contrast, supernatant from IL-2-secreting cells does not affect the sensitivity of unmodified cells. IL-2 can be detected, by a bioassay, bound to the extracellular matrix of the secreting tumour cells.

In vivo/in vitro comparison of the pharmacokinetics and pharmacodynamics of 3,3',4,4'-tetrachlorobiphenyl (PCB77).

The rat hepatoma cell line, H4IIE, serves as a useful tool to assess potential biological effects such as induction of cytochrome P4501A1 expression. The objectives of this study were twofold: to investigate the kinetic time course and dosimetry of PCB77 in rat hepatoma cells dosed with PCB77 and in liver of rats given i.p. doses of PCB77, and to compare in vitro and in vivo P4501A1 enzyme induction responses. For the 4-day time-course study, H4IIE cells were exposed with two doses of [14C]PCB77 (0.9 and 3 microg/plate) and harvested at 15 and 30 min, 1, 2, 4, 8, and 12 hr, and 1, 2, 3, and 4 days. PCB77-derived radioactivity was detected in the cells as early as 15 min postdosing. For the dose-response study, the cells were dosed with various concentrations of PCB77 (0.00316-5.37 microg/plate) and harvested on Day 3 since ethoxyresorufin O-deethylase (EROD) activity in vitro reached its maximum on the third day postdosing. Time-course and dose-response studies revealed that only 1-3% of the total delivered dose was found in the cells, with the remainder in the media and adhering to the culture plates. For the dose-response study in vivo, male Fischer rats were dosed with a single i.p. injection of various concentrations of PCB77 (0.1-50 mg/kg body wt) and euthanized on Day 3. PCB77-derived radioactivity and EROD induction in vivo were measured. When EROD activity and PCB77-derived radioactivity in the rat hepatoma cells and in the rat liver were compared on an equivalent weight basis, there was a significant correlation (r2 = 0.985) between them. Prior to this study, no information on quantitative dosimetry and EROD activities of PCB77 has been reported to validate the in vitro assay with in vivo data.

IL-12 stimulation but not B7 expression increases melanoma killing by patient cytotoxic T lymphocytes (CTL).

Recent studies have demonstrated that rodent tumour cells engineered to secrete a variety of cytokines, or to express foreign antigens, MHC molecules or co-stimulatory molecules, are rejected by syngeneic animals. These observations have led to the initiation of a number of clinical trials using genetically modified tumour cells, to attempt to stimulate a patient anti-tumour immune response. In this study, a protocol has been developed to test in vitro the specific cytotoxic anti-tumour response generated from melanoma patient lymphocytes. The results showed that IL-12 in combination with IL-2 enhanced the autologous anti-melanoma CTL response, whereas B7.1 antigen expression on tumour cells did not increase anti-melanoma CTL generation. This method could be used to design more appropriate genetically modified tumour vaccines.

Evaluating human variability in chemical risk assessment: hazard identification and dose-response assessment for noncancer oral toxicity of trichloroethylene.

Human variability can be addressed during each stage in the risk assessment of chemicals causing noncancer toxicities. Noncancer toxicities arising from oral exposure to trichloroethylene (TCE) are used in this paper as a case study for exploring strategies for identifying and incorporating information about human variability in the chemical specific hazard identification and dose-response assessment steps. Toxicity testing in laboratory rodents is the most commonly used method for hazard identification. By using animal models for sensitive populations, such as developing fetuses, testing can identify some potentially sensitive populations. A large variety of reproductive and developmental studies with TCE were reviewed. The results were mostly negative and the limited positive findings generally occurred at doses similar to those causing liver and kidney toxicity. Physiologically based pharmacokinetic modeling using Monte Carlo simulation is one method for evaluating human variability in the dose-response assessment. Three strategies for obtaining data describing this variability for TCE are discussed: (1) using in vivo human pharmacokinetic data for TCE and its metabolites, (2) studying metabolism in vitro, and (3) identifying the responsible enzymes and their variability. A review of important steps in the metabolic pathways for TCE describes known metabolic variabilities including genetic polymorphisms, enzyme induction, and disease states. A significant problem for incorporating data on pharmacokinetic variability is a lack of information on how it relates to alterations in toxicity. Response modeling is still largely limited to empirical methods due to the lack of knowledge about toxicodynamic processes. Empirical methods, such as reduction of the No-Observed-Adverse-Effect-Level or a Benchmark Dose by uncertainty factors, incorporate human variability only qualitatively by use of an uncertainty factor. As improved data and methods for biologically based dose-response assessment become available, use of quantitative information about variability will increase in the risk assessment of chemicals.

A trichloroethylene risk assessment using a Monte Carlo analysis of parameter uncertainty in conjunction with physiologically-based pharmacokinetic modeling.

A Monte Carlo simulation is incorporated into a risk assessment for trichloroethylene (TCE) using physiologically-based pharmacokinetic (PBPK) modeling coupled with the linearized multistage model to derive human carcinogenic risk extrapolations. The Monte Carlo technique incorporates physiological parameter variability to produce a statistically derived range of risk estimates which quantifies specific uncertainties associated with PBPK risk assessment approaches. Both inhalation and ingestion exposure routes are addressed. Simulated exposure scenarios were consistent with those used by the Environmental Protection Agency (EPA) in their TCE risk assessment. Mean values of physiological parameters were gathered from the literature for both mice (carcinogenic bioassay subjects) and for humans. Realistic physiological value distributions were assumed using existing data on variability. Mouse cancer bioassay data were correlated to total TCE metabolized and area-under-the-curve (blood concentration) trichloroacetic acid (TCA) as determined by a mouse PBPK model. These internal dose metrics were used in a linearized multistage model analysis to determine dose metric values corresponding to 10(-6) lifetime excess cancer risk. Using a human PBPK model, these metabolized doses were then extrapolated to equivalent human exposures (inhalation and ingestion). The Monte Carlo iterations with varying mouse and human physiological parameters produced a range of human exposure concentrations producing a 10(-6) risk.

Oncogenic potential of inhaled hydrazine in the nose of rats and hamsters after 1 or 10 1-hr exposures.

Hydrazine (N2H4) is used as a fuel for missiles and standby power systems of operational military aircraft. Maintenance of missiles and aircraft may result in accidental human exposure to high concentrations for brief periods of time. The purposes of this study were to assess the oncogenic potential of N2H4 in rats and male hamsters exposed to a high concentration of N2H4 for repeated short exposures and to investigate the relationships of acute and subchronic effects of N2H4 to nasal tumorigenesis. In phase 1 (acute and subchronic) and Phase 2 (lifetime experiments, groups of male and female Fischer 344 rats and male Syrian golden hamsters were exposed by inhalation to 0, 75 (Phase 2 only), or 750 ppm N2H4 for 1 (acute) or 10 (subchronic) 1-hr weekly exposures. Rodents were euthanized 24 hr after exposures 1 and 10 and 24 to 30 months poststudy initiation. Significant reductions in body weight were observed in N2H4-treated rodents compared to controls during the exposure interval. No hydrazine-induced mortality was detected. Histopathologic examination after the acute and subchronic exposures revealed degeneration and necrosis of transitional, respiratory, and olfactory epithelia in the anterior nose and, in rats exposed subchronically, squamous metaplasia of the transitional epithelium. Minimal to mild rhinitis resulted from N2H4 exposures. Apoptosis was observed in olfactory and squamous metaplastic transitional epithelium. Lesions occurred at sites reportedly having high air-flow and generally appeared to be more severe in the anterior portion of the nose. By 24 months, the squamous metaplastic transitional epithelium reverted back to normal-appearing transitional epithelium. By 24+ months, low incidences (sexes combined) of hyperplasia (5/194, 2.6%) and neoplasia (11/194, 5.7%) were detected, principally in the transitional epithelium of the 750 ppm N2H4-treated rats. A similar incidence of hyperplasia (2/94, 2%) and neoplasia (5/94, 5.3%) was detected in the high-exposure group of hamsters. The location and type of N2H4-induced proliferative lesions were similar to those reported in a chronic N2H4-exposure study (5.0 ppm x 6 hr/day x 5 days/week for 1 year) conducted in our laboratory, but the chronic study had much higher incidences (rats, sexes combined: hyperplasia 15.5% vs 2.6% and polypoid adenoma 44.6% vs 5.2%). The product (CD) of concentration + time was the same (750 ppm hours) for the high-dose groups for both studies, but the duration of exposure was 150 x longer and the concentration was 150 x lower in the chronic study.(ABSTRACT TRUNCATED AT 400 WORDS)