Determination of Sorption Coefficient of Phosphorus Applied for Sugarcane Production in Southwestern Florida.

Phosphorus is among the essential nutrients applied to sugarcane ( L.) fields in the form of a fertilizer mixture (N, P, and K) in southwestern Florida. Sorption coefficient is used for modeling P movement, and in this study, we hypothesized that the sorption coefficient determined using fertilizer mixture (N, P, and K) will be significantly different from values determined using KCl and CaCl, the electrolytes most commonly used for conducting sorption experiments. Supporting electrolytes, 0.01 mol L KCl, 0.005 mol L CaCl, deionized (DI) water, simulated Florida rain, and fertilizer mixture prepared in Florida rain were used to characterize P sorption. Immokalee (Sandy, siliceous, hyperthermic Arenic Alaquods) and Margate (Sandy, siliceous hyperthermic Mollic Psammaquents) are the dominant mineral soils used for sugarcane production in southwestern Florida; we used the A and B horizons of Margate soil and the A and B horizons of the Immokalee soil for sorption experiments in this study. Freundlich sorption isotherms described P sorption data. The Freundlich sorption isotherm coefficients followed the trend 0.005 mol L CaCl > 0.01 mol L KCl ≈ fertilizer mixture > simulated Florida rain ≈ DI water. Sorption coefficients were used for modeling P movement with HYDRUS 1D; similar P results were obtained with the 0.01 mol L KCl and fertilizer mixture electrolyte treatments. The sorption coefficient for DI water and simulated Florida rain overpredicted P movement. The P sorption data showed the importance of choosing the appropriate electrolyte for conducting experiments based on the composition of fertilizer.

Soil temperature, nitrogen concentration, and residence time affect nitrogen uptake efficiency in citrus.

We try to elucidate which environmental and soil factors control nitrogen uptake efficiency in citrus. Effects of residence time and nitrogen (N) concentration (three 500-mL applications of 7 mg N L(-1), representative of reclaimed water used for citrus irrigation in central Florida, or one 150-mL application of 70 mg N L(-1)) on nitrogen uptake efficiency (NUE) of young citrus seedlings were studied. Increasing residence times from 2 to 8 h increased NUE from 36 to 82% and from 17 to 34% for high and low application frequencies, respectively. We developed a model to predict N uptake based on root density, N concentration, and soil temperature (Ts). Assuming a base temperature (Tb) of 10 degrees C, N uptake temperature sum (UTS) = sigma(Ts - Tb)/24 (degrees CdN, degree day units of N uptake). To eliminate the risk of N leaching for young seedlings, minimum uptake periods of 5 and 16 degrees CdN were required at initial soil N concentrations of 0.9 and 2.5 mg N L(-1), respectively. After correcting for differences in root length, this information was then used to predict the effect of irrigation practices on N uptake from reclaimed water for mature trees. Applying 2500 mm yr(-1) vs. 400 mm yr(-1) reclaimed water reduced the NUE of N in this water from 100 to 63% during the summer and from 100 to 28% during the winter. Reductions in NUE at higher irrigation rates appeared to be related to N displacement below the root zone prior to complete N uptake.

Dosimetry modeling of inhaled formaldehyde: comparisons of local flux predictions in the rat, monkey, and human nasal passages.

Formaldehyde-induced nasal squamous cell carcinomas in rats and squamous metaplasia in rats and rhesus monkeys occur in specific regions of the nose with species-specific distribution patterns. Experimental approaches addressing local differences in formaldehyde uptake patterns and dose are limited by the resolution of dissection techniques used to obtain tissue samples and the rapid metabolism of absorbed formaldehyde in the nasal mucosa. Anatomically accurate, 3-dimensional computational fluid dynamics models of F344 rat, rhesus monkey, and human nasal passages were used to estimate and compare regional inhaled formaldehyde uptake patterns predicted among these species. Maximum flux values, averaged over a breath, in nonsquamous epithelium were estimated to be 2620, 4492, and 2082 pmol/(mm(2)-h-ppm) in the rat, monkey, and human respectively. Flux values predicted in sites where cell proliferation rates were measured as similar in rats and monkeys were also similar, as were fluxes predicted in a region of high tumor incidence in the rat nose and the anterior portion of the human nose. Regional formaldehyde flux estimates are directly applicable to clonal growth modeling of formaldehyde carcinogenesis to help reduce uncertainty in human cancer risk estimates.

Dosimetry modeling of inhaled formaldehyde: binning nasal flux predictions for quantitative risk assessment.

Interspecies extrapolations of tissue dose and tumor response have been a significant source of uncertainty in formaldehyde cancer risk assessment. The ability to account for species-specific variation of dose within the nasal passages would reduce this uncertainty. Three-dimensional, anatomically realistic, computational fluid dynamics (CFD) models of nasal airflow and formaldehyde gas transport in the F344 rat, rhesus monkey, and human were used to predict local patterns of wall mass flux (pmol/[mm(2)-h-ppm]). The nasal surface of each species was partitioned by flux into smaller regions (flux bins), each characterized by surface area and an average flux value. Rat and monkey flux bins were predicted for steady-state inspiratory airflow rates corresponding to the estimated minute volume for each species. Human flux bins were predicted for steady-state inspiratory airflow at 7.4, 15, 18, 25.8, 31.8, and 37 l/min and were extrapolated to 46 and 50 l/min. Flux values higher than half the maximum flux value (flux median) were predicted for nearly 20% of human nasal surfaces at 15 l/min, whereas only 5% of rat and less than 1% of monkey nasal surfaces were associated with fluxes higher than flux medians at 0.576 l/min and 4.8 l/min, respectively. Human nasal flux patterns shifted distally and uptake percentage decreased as inspiratory flow rate increased. Flux binning captures anatomical effects on flux and is thereby a basis for describing the effects of anatomy and airflow on local tissue disposition and distributions of tissue response. Formaldehyde risk models that incorporate flux binning derived from anatomically realistic CFD models will have significantly reduced uncertainty compared with risk estimates based on default methods.

Respiratory tract toxicity in rats exposed to Mexico City air.

The rat has been used extensively as a health sentinel, indicator, or monitor of environmental health hazards, but this model has not been directly validated against human exposures. Humans in Mexico City show upper respiratory tract lesions and evidence of pulmonary damage related to their environmental inhalation exposure. In this study, male and female F344 rats were exposed (23 hr/day) in Mexico City to local Mexico City air (MCA)* for up to seven weeks. Controls were maintained at the same location under filtered air. Prior to these exposures, several steps were taken. First, the nasal passages of normal male rats shipped from the United States and housed in Mexico City were examined for mycoplasma infection; no evidence of infection was found. In addition, a mobile exposure and monitoring system was assembled and, with an ozone (O3) exposure atmosphere, was tested along with supporting histopathology techniques and analysis of rat nasal and lung tissues. Last, the entire exposure model (equipment and animals) was transported to Mexico City and validated for a three-week period. During the seven-week study there were 18 one-hour intervals during which the average O3 concentration of MCA in the exposure chamber exceeded the US National Ambient Air Quality Standard (NAAQS) of 0.120 ppm 03 (hourly average, not to be exceeded more than once per year). This prolonged exposure of healthy F344 rats to MCA containing episodically low to moderate concentrations of 03 (as well as other urban air pollutants) did not induce inflammatory or epithelial lesions in the nasal airways or lung as measured by qualitative histologic techniques or quantitative morphometric techniques. These findings agree with those of previous controlled O3 inhalation studies, but they are in contrast to reports indicating that O3-polluted MCA causes significant nasal mucosal injury in adults and children living in southwestern Mexico City. Taken together, these findings may suggest that human airways are markedly more susceptible to the toxic effects of MCA than are the airways of the F344 rat.

A hybrid computational fluid dynamics and physiologically based pharmacokinetic model for comparison of predicted tissue concentrations of acrylic acid and other vapors in the rat and human nasal cavities following inhalation exposure.

To assist in interspecies dosimetry comparisons for risk assessment of the nasal effects of organic acids, a hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of inhaled vapors in the rat and human nasal cavity. Application to a specific vapor would involve the incorporation of the chemical-specific reactivity, metabolism, partition coefficients, and diffusivity (in both air and tissue phases) of the vapor. This report describes the structure of the CFD-PBPK model and its application to a representative acidic vapor, acrylic acid, for interspecies tissue concentration comparisons to assist in risk assessment. By using the results from a series of short-term in vivo studies combined with computer modeling, regional nasal tissue dose estimates were developed and comparisons of tissue doses between species were conducted. To make these comparisons, the assumption was made that the susceptibilities of human and rat olfactory epithelium to the cytotoxic effects of organic acids were similar, based on similar histological structure and common mode of action considerations. Interspecies differences in response were therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity. The results of simulations with the seven-compartment CFD-PBPK model suggested that the olfactory epithelium of the human nasal cavity would be exposed to tissue concentrations of acrylic acid similar to that of the rat nasal cavity when the exposure conditions are the same. Similar analysis of CFD data and CFD-PBPK model simulations with a simpler one-compartment model of the whole nasal cavities of rats and humans provides comparable results to averaging over the compartments of the seven-compartment model. These results indicate that the general structure of the hybrid CFD-PBPK model applied in this assessment would be useful for target tissue dosimetry and interspecies dose comparisons for a wide variety of vapors. Because of its flexibility, this CFD-PBPK model is envisioned to be a platform for the construction of case-specific inhalation dosimetry models to simulate in vivo exposures that do not involve significant histopathological damage to the nasal cavity.

Origin and distribution of potassium bromate-induced testicular and peritoneal mesotheliomas in rats.

Tissue sections were examined from a 2-year bioassay of male Fischer 344 rats treated with potassium bromate administered in drinking water. All animals exhibiting peritoneal mesotheliomas also had mesotheliomas of the tunica vaginalis testis mesorchium (the reverse was not true), and the correlation of these 2 types of mesotheliomas was highly significant (r2 = 0.98). Mapping of the tunica vaginalis tumors at all time points and at all bromate concentrations revealed a pattern of increasing incidence of tumor formation on the mesothelium of the tunica vaginalis testis as a function of proximity to the mesorchial ligament. Thus, the mesorchium appears to be the major mesothelial target site for potassium bromate-mediated carcinogenesis. The frequency of occurrence of mesotheliomas by location was tunica vaginalis testis (25%), mesosplenium (20%), mesentery (10%), mesojejunum/mesocolon (8%), bladder (6.5%), mesogastrium (13%), liver serosa (5%), and kidney, small intestine, and rectum (1% each). A complete cross-section of the rat testis was prepared and used to construct a complete map of the mesothelium. Any attempt to determine the role of local dose and tissue susceptibility for the purpose of interspecies risk extrapolation must take into account the complex anatomy and physiology of this region of the visceral and testicular suspensory apparatus. Improved histologic approaches are needed for adequate assessment of this delicate suspensory system.

Morphologic analysis correlates with gene expression changes in cultured F344 rat mesothelial cells.

The gene expression pattern of mesothelial cells in vitro was determined after 4 or 12 h exposure to the rat mesothelial, kidney, and thyroid carcinogen and oxidative stressor potassium bromate (KBrO(3)). Gene expression changes observed using cDNA arrays indicated oxidative stress, mitotic arrest, and apoptosis in treated immortalized rat peritoneal mesothelial cells. Increases occurred in oxidative stress responsive genes HO-1, QR, HSP70, GADD45, GADD153, p21(WAF1/CIP16), GST's, GAPDH, TPX, and GPX-1(0); transcriptional regulators c-jun, c-fos, jun B, c-myc, and IkappaB; protein repair components Rdelta, RC10-II, C3, RC-7, HR6B ubiquitin-conjugating enzyme and ubiquitin; DNA repair components PCNA, msh2, and O-6 methylguanine DNA methyltransferase; lipid peroxide excision enzyme PLA2; and apoptogenic components TNFalpha, iNOS1 and FasL. Decreases occurred in bcl-2 (antiapoptotic), bax alpha, bad, and bok (proapoptotic) and cell cycle control elements (cyclins). Cyclin G and p14ink4b (which inhibit entry into cell cycle) were increased. Numerous signal transduction, cell membrane transport, membrane-associated receptor, and fatty acid biosynthesis and repair components were altered. Morphologic endpoints examined were number of mitotic figures, number of apoptotic cells, and antibody-specific localization of HO-1 (which demonstrated increased HO-1 protein expression). PCR analysis confirmed HO-1, p21(waf1/cip1), HSP70, GPX1, GADD45, QR, mdr1, PGHS, and cyclin D1 changes. A model for KBrO(3)-induced carcinogenicity in the F344 rat mesothelium is proposed, whereby KBrO(3) generates a redox signal that activates p53 and results in transcriptional activation of oxidative stress and repair genes, dysregulation of growth control, and imperfect DNA repair leading to carcinogenesis.

Histopathology of nasal olfactory mucosa from selected inhalation toxicity studies conducted with volatile chemicals.

In recent years, histopathologic changes have been reported in the olfactory mucosa of rodents exposed, by inhalation, to a variety of volatile chemicals. In order to better characterize these lesions, a panel of experienced pathologists reviewed microscopic lesions of the olfactory epithelium of rats reported in 10 inhalation studies conducted with 8 different chemicals. The objectives were to determine if the olfactory epithelial lesions are morphologically similar or different for the chemicals of interest, to develop and recommend appropriate diagnostic criteria and nomenclature to characterize the morphology of these olfactory lesions, and to provide specific criteria for judging the degree of severity of the olfactory changes in these studies. The results indicated that the distribution and nature of the lesions were similar in all the examined studies in which olfactory changes were observed. Recommended standardized nomenclature and diagnostic criteria and a uniform method for scoring lesion severity based on the extent of distribution and severity of tissue damage are presented.

Application of a hybrid computational fluid dynamics and physiologically based inhalation model for interspecies dosimetry extrapolation of acidic vapors in the upper airways.

This study provides a scientific basis for interspecies extrapolation of nasal olfactory irritants from rodents to humans. By using a series of short-term in vivo studies, in vitro studies with nasal explants, and computer modeling, regional nasal tissue dose estimates were made and comparisons of tissue doses between species were conducted. To make these comparisons, this study assumes that human and rodent olfactory epithelium have similar susceptibility to the cytotoxic effects of organic acids based on similar histological structure and common mode of action considerations. Interspecies differences in susceptibility to the toxic effects of acidic vapors are therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity. The acute, subchronic, and in vitro studies have demonstrated that the nasal olfactory epithelium is the most sensitive tissue to the effects of inhalation exposure to organic acids and that the sustentacular cells are the most sensitive cell type of this epithelium. A hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of organic acids in the rodent and human nasal cavity. The CFD-PBPK model simulations indicate that the olfactory epithelium of the human nasal cavity is exposed to two- to threefold lower tissue concentrations of a representative inhaled organic acid vapor, acrylic acid, than the olfactory epithelium of the rodent nasal cavity when the exposure conditions are the same. The magnitude of this difference varies somewhat with the specific exposure scenario that is simulated. The increased olfactory tissue dose in rats relative to humans may be attributed to the large rodent olfactory surface area (greater than 50% of the nasal cavity) and its highly susceptible location (particularly, a projection of olfactory epithelium extending anteriorly in the dorsal meatus region). In contrast, human olfactory epithelium occupies a much smaller surface area (less than 5% of the nasal cavity), and it is in a much less accessible dorsal posterior location. In addition, CFD simulations indicate that human olfactory epithelium is poorly ventilated relative to rodent olfactory epithelium. These studies suggest that the human olfactory epithelium is protected from irritating acidic vapors significantly better than rat olfactory epithelium due to substantive differences in nasal anatomy and nasal air flow. Furthermore, the general structure of the hybrid CFD-PBPK model used for this study appears to be useful for target tissue dosimetry and interspecies dose comparisons for a wide range of inhaled vapors.

Computer simulation of inspiratory nasal airflow and inhaled gas uptake in a rhesus monkey.

There is increasing evidence that inspiratory airflow patterns play a major role in determining the location of nasal lesions induced in rats by reactive, water-soluble gases such as formaldehyde and chlorine. Characteristic lesion patterns have also been seen in inhalation toxicity studies conducted in rhesus monkeys, the nasal anatomy of which resembles that of humans. To examine the hypothesis that regions of high airflow-dependent uptake and lesions occur in similar nasal locations in the primate, airflow and gas uptake patterns were simulated in an anatomically accurate computer model of the right nasal airway of a rhesus monkey. The results of finite-element simulations of steady-state inspiratory nasal airflow for the full range of resting physiological flow rates are reported. Simulated airflow patterns agreed well with experimental observations, exhibiting secondary flows in the anterior nose and streamlined flow posteriorly. Simulated airflow results were used to predict gas transport to the nasal passage walls using formaldehyde as an example compound. Results from the uptake simulations were compared with published observations of formaldehyde-induced nasal lesions in rhesus monkeys and indicated a strong correspondence between airflow-dependent transport patterns and local lesion sites. This rhesus computer model will provide a means for confirming the extrapolation of toxicity data between species by extrapolating rat simulation results to monkeys and comparing these predictions with primate lesion data.

Nasal epithelium as a sentinel for airborne environmental pollution.

A wide range of chemicals, particulate matter, and gaseous air pollutants are present in urban atmospheres and may pose a significant health risk for human populations. Nasal passages are the first site of contact of the respiratory tract with the environment and offer significant protection to the lower respiratory tract by conditioning the inspired air. This activity, which includes removal of certain pollutants, places the nose at risk of pathological changes, including cancer. Mexico City residents are exposed to a complex mixture of air pollutants. Based on predicted nasal air flow characteristics, four nasal biopsy sites were selected for study in adult male volunteers from a control low polluted town (n = 12) and southwest metropolitan Mexico City permanent residents (n = 54). Clinical data with emphasis on nasal symptoms and histopathological changes including basal and goblet cell hyperplasia, squamous metaplasia, epithelial dysplasia, and neovascularization were evaluated. Immunohistochemical staining was used to assess accumulation of p53 protein. Control individuals had no respiratory symptoms and their biopsies were unremarkable. Mexico City residents complained of epistaxis, rhinorrea, nasal crusting, dryness, and nasal obstruction. Their biopsies showed patchy shortening of cilia, deciliated areas, basal cell hyperplasia, and squamous metaplasia. Dysplastic lesions were predominantly located on antral squamous epithelium and in squamous metaplastic epithelium of the posterior inferior turbinates and they exhibited p53 nuclear accumulation. Individuals with > 10 h of daily outdoor exposure for 5 years or more had the highest rate of dysplasia. Subjects with epistaxis were more likely to have dysplasias and neovascularization. Results of this study suggest: (a) Nasal lesions in Mexico City residents are likely the result of many potentially toxic and/or carcinogenic pollutants, including ozone, aldehydes, particulate matter, and unmeasured pollutants; (b) the alteration of the nasal mucociliary defense mechanisms and the effects of reactive and/or water-soluble materials and particulates could be playing a major role in the nasal pathology; (c) the accumulation of p53 protein in dysplastic nasal lesions in the context of prolonged exposure to air pollutants raises the possibility that p53 mutations are already present and are providing the squamous cells with a selective advantage for clonal expansion; and (d) the nasal passages provide a valuable sentinel tissue for the detection of toxic air pollutants.

Chemically-induced nasal carcinogenesis and epithelial cell proliferation: a brief review.

An increased rate of cell proliferation has long been recognized as an important factor in both human and experimental carcinogenesis, and may be a major risk factor for cancer development in a number of tissues. Limited information exists, however, regarding the relevance of increased cell proliferation and nasal cancer. Examples of toxicological studies utilizing nasal cell proliferation data as an important endpoint are briefly reviewed. Data for one of the most extensively studied chemicals, the weakly genotoxic carcinogen formaldehyde, support the contention that the concentration-response relationship for tumor incidence is a function of formaldehyde-induced target cell proliferation, in addition to other factors including target cell population size. The increasing importance of utilizing cell proliferation data in determining dose-response relationships and in biologically-based risk assessment models is discussed.

Correlation of regional formaldehyde flux predictions with the distribution of formaldehyde-induced squamous metaplasia in F344 rat nasal passages.

Squamous epithelium lines the nasal vestibule of the rat, rhesus monkey, and human. Respiratory, transitional, and olfactory epithelia line most areas posterior to the nasal vestibule. Inhaled formaldehyde gas induces squamous metaplasia posterior to the nasal vestibule and does not induce lesions in the nasal vestibule in rats and rhesus monkeys, indicating that squamous epithelium is resistant to irritant effects of formaldehyde and that squamous metaplasia may be an adaptive response. If squamous metaplasia is determined by formaldehyde dosimetry rather than by tissue-specific factors, squamous epithelium may be protective by absorbing less formaldehyde than other epithelial types. In a previous study, a three-dimensional, anatomically accurate computational fluid dynamics (CFD) model of the anterior F344 rat nasal passages was used to simulate inspiratory airflow and inhaled formaldehyde transport. The present study consisted of two related parts. First, the rat CFD model was used to test the hypothesis that the distribution of formaldehyde-induced squamous metaplasia is related to the location of high-flux regions posterior to squamous epithelium. Regional formaldehyde flux into nonsquamous epithelium predicted by the CFD model correlated with regional incidence of formaldehyde-induced squamous metaplasia on the airway perimeter of one cross-sectional level of the noses of F344 rats exposed to 10 and 15 ppm formaldehyde gas for 6 months. Formaldehyde flux into nonsquamous epithelium was estimated to vary by an order of magnitude depending on the degree of formaldehyde absorption by squamous epithelium. These results indicate that the degree to which squamous epithelium absorbs formaldehyde strongly affects the rate and extent of the progression of squamous metaplasia with continued exposure to formaldehyde. In the second part of this study, the CFD model was used to predict squamous metaplasia progression. Data needs for verification of this model prediction are considered. These results indicate that information on the permeability of squamous epithelium in rats, monkeys, and humans is important for accurate prediction of uptake in regions posterior to the nasal vestibule.

Chloroform-induced olfactory mucosal degeneration and osseous ethmoid hyperplasia are not associated with olfactory deficits in Fischer 344 rats.

Adult female F-344 rats were trained (avoidance rate > 70%) over four days with a coupled tone- (n = 10 rats/dose) or 2 ppm acetaldehyde-cued (n = 6 rats/dose) foot shock paradigm. Rats were gavaged with chloroform dissolved in corn oil for 5 days/week for 3 week at 0 or 400 (tone-cued) or 0, 34, 100, or 400 (odor-cued) mg/kg body weight/day. Tone-cued response was reevaluated 6, 16, and 38 days after the first chloroform dose (day 1). Olfaction was assessed on days 6-7, 20-21, and 41-42 using 2 or 0.0002 ppm acetaldehyde. Nasal histopathology (n = 4-5 rats/dose) was assessed on days 6, 20, and 42. Significantly decreased body weights were observed following a single 100 or 400 mg/kg chloroform dose. Body weights in the 400 mg/kg/day chloroform group remained depressed for 17 days. Histopathology revealed degenerative changes in olfactory mucosa and underlying ethmoid turbinate bones that were essentially identical in nature and severity, including dose-response and progression, to those reported previously for chloroform gavage (Larson et al., Food Chem. Toxicol., 1995;33:443 456). At all dose level and sacrifice timepoints, however, regions of morphologically normal olfactory mucosa were present, especially in dorsal medial and ventral lateral regions of the nose. Neither odor- nor tone-cued avoidance behaviors were affected, indicating that even fairly severe and extensive chloroform-induced olfactory mucosal degeneration is not associated with a detectable olfactory deficit in rats.

Computer simulation of inspiratory airflow in all regions of the F344 rat nasal passages.

Data from laboratory animal experiments are often used in setting guidelines for safe levels of human exposure to inhaled materials. The F344 rat has been used extensively in laboratory experiments to determine effects of exposure to inhaled materials in the nasal passages. Many inhaled materials induce toxic responses in the olfactory (posterior) region of the rat nasal passages. The location of major airflow routes has been proposed as playing a dominant role in determining some olfactory lesion location patterns. Since nasal airflow patterns differ significantly among species, methods are needed to assess conditions under which these differences may significantly affect extrapolation of the effects of local dose in animals to potential disease outcome in humans. A computational fluid dynamics model of airflow and inhaled gas uptake has been used to predict dose to airway walls in the anterior F344 rat nasal passages (Kimbell et al., Toxicol. Appl. Pharmacol., 1993; 121, 253-263). To determine the role of nasal airflow patterns in affecting olfactory lesion distribution, this model was extended to include the olfactory region. Serial-step histological sections of the nasal passages of a F344 rat were used to construct the computer model. Simulations of inspiratory airflow throughout the rat nasal passages were consistent with previously reported experimental data. Four of the five major simulated flow streams present in the anterior nose (dorsal lateral, middle, ventral lateral, and ventral medial streams) flowed together to exit ventrally at the nasopharyngeal duct, bypassing the ethmoid recesses. The remaining dorsal medial stream split to flow both medially and laterally through the olfactory-epithelium-lined ethmoid recesses in a Z-shaped pattern when viewed sagitally. Simulated flow in the ethmoid recesses was more than an order of magnitude slower than flow in the anterior and ventral parts of the nasal passages. Somewhat higher volumes of flow were predicted in the dorsal medial stream when the nasal vestibule was reshaped to be upturned, and more flow was allocated to the dorsal medial stream with increased inspiratory airflow rate, suggesting that rats may be able to allocate more airflow to this stream by both modifying the shape of the nasal vestibule and increasing inhaled air velocity during sniffing. The present study provides the first description of flow in the complex olfactory region of the nose of the F344 rat. This model will be used to evaluate the role of airflow patterns in determining the distribution of xenobiotically induced olfactory mucosal lesions. This information, combined with models of disposition in the airway lining, will provide comprehensive dosimetry models for extrapolating animal response data to humans.

Neurotoxicological evaluation of ethyl tertiary-butyl ether following subchronic (90-day) inhalation in the Fischer 344 rat.

The purpose of this study was to evaluate whether repeated 6-h exposure (65 exposures over a 14- week period) of male and female Fischer-344 rats (n = 12 rats/sex/concentration) to ethyl tertiary-butyl ether (ETBE) atmospheres at 500, 1750, or 5000 ppm would result in neurotoxicity. Neurotoxicity was assessed by a blinded functional observational battery (FOB), motor activity, and terminal neuropathology. Motor activity was assessed 4 days prior to ETBE exposure and following 20, 42, and 65 days of exposure. The FOB was assessed 4 days prior to ETBE exposure and following 1, 6, 10, 20, 42, and 65 days of exposure. Transient ataxia, a sign of narcosis, was noted in male rats immediately following the 6-h exposure to 5000 ppm ETBE. Statistically significant treatment effects on motor activity were not observed. Minor changes in grip strength and hindlimb splay were observed; however, none demonstrated a dose-response relationship or a consistent pattern of neurological dysfunction. No gross or microscopic abnormalities were observed in the central, peripheral, or autonomic nervous systems of rats exposed to 5000 ppm ETBE. No statistically significant differences in brain weight or size were observed in ETBE-exposed rats. A statistically significant increase in body weight was observed in female rats exposed to 5000 ppm following 42 and 65 exposure days. Although ataxia was a common feature of acute ETBE neurotoxicity in rats following high-level exposure, adverse neurological effects are not expected in the general public at the anticipated exposure levels associated with automotive refueling.

A brief review of formaldehyde carcinogenesis in relation to rat nasal pathology and human health risk assessment.

The 1980 report that inhaled formaldehyde induced nasal squamous cell carcinomas in rats had a significant societal impact and resulted in extensive research in the fields of rodent nasal pathology and human cancer risk assessment. This article presents an overview of the evolution of these events. It is concluded that the nasal passages of humans and rats are fundamentally identical biological target organs. Nevertheless, in the case of human health risk assessment, minor differences between these species may be critically important. Special attention should be paid to interspecies differences in nasal dosimetry and local metabolism; thus, chemical toxicity data derived from rats require careful interpretation when used for human risk assessments. In the case of formaldehyde, it is recommended that low-concentration (< or = 2 ppm airborne exposure) extrapolation, where no tissue damage is observed, be uncoupled from the responses at high concentrations (> or = 6 ppm), where epithelial degeneration, regenerative cell replication, and inflammation appear to be essential driving forces in formaldehyde carcinogenesis. The presence of treatment-related nasal lesions in rats following exposure to chemicals should always be treated as an indication of a potential human health risk, whether exposure is by the inhalation, oral, or dermal route.

Design and evaluation of an olfactometer for the assessment of 3-methylindole-induced hyposmia.

Few studies objectively evaluate olfactory function in animals following exposure to chemicals that induce nasal toxicity. An olfactometer capable of generating a reproducible olfactory stimulus and measuring an odorant-cued behavioral response was developed for rats from a commercially available two-way shuttle box. The box was modified to deliver the test odorant, acetaldehyde, to either of two chambers separated by a physical barrier consisting of a downward-directed airwall sandwiched between two exhaust panels. Male Fisher 344 rats were trained with either a coupled odorant- or tone-cued active avoidance paradigm in order to compare auditory-cued versus olfactory-cued learning and memory. Odorant-cued animals had faster acquisition and longer retention of the avoidance behavior than tone-cued animals. Animals given the model olfactory toxicant 3-methylindole (3-MI, 400 mg/kg, ip) had reduced odorant-cued avoidance, while no effect on tone-cued behavior was observed. In a follow-up study, additional odorant-trained rats were dosed with 0, 100, 200, or 300 mg/kg of 3-MI ip and olfactory function reassessed 6 days later. Histopathologic evidence of moderate to severe olfactory epithelial damage was observed in all rats 7 days after 3-MI administration. Only the highest 3-MI dose (300 mg/kg) was associated with a significant reduction in odor-cued avoidance behavior as compared to that seen in control. These results indicate that use of this olfactometer can provide a functional assessment of chemically induced olfactory toxicity and complements more routine nasal pathology.

Histopathological changes in the upper respiratory tract of F344 rats following infection with a rat-adapted influenza virus.

The present study determined the morphogenesis of upper respiratory tract disease in rats following infection with a rat-adapted influenza virus. Sixty-eight 60-day-old, male F344 rats were infected by intranasal inoculation and necropsied at days 1, 2, 4, 7, 14, and 28 post-inoculation (PI). Responses to infection were studied by routine light microscopy for histopathologic changes and immunocytochemistry for localization of viral antigen. Severe infection-induced changes involved the respiratory epithelium and underlying lamina propria, and the nasal-associated lymphoid tissue, with minimal involvement of the transitional epithelium. The lesions were most severe on the septum and the medial aspect of the nasoturbinates. Viral antigen, located in the respiratory epithelium of affected regions at days 1 and 2 PI, was associated with neutrophilic infiltration and epithelial necrosis and erosion. At day 4 PI, an infiltrate of lymphocytes, macrophages, and fewer neutrophils was present, often accompanied by epithelial regeneration. Changes in the nasal-associated lymphoid tissue were evaluated using morphometric analysis and consisted of hyperplasia (days 4 to 7 PI) followed by progressive involution (days 14 to 28 PI). Mild lesions associated with foci of viral antigen were also observed in the nasal olfactory epithelium on days 1, 2, and 4 PI. The changes observed in the present study indicate the potential value of rat-adapted influenza virus infection as a model of human influenza.