Acute Exposure Studies Research Articles

LC50 values for rats acutely exposed to vapors of acrylic and methacrylic acid esters.

Acute exposure studies were conducted using adult male Sprague-Dawley rats to obtain LC50/24 concentrations for the common esters of acrylic and methacrylic acids. The order of acute toxicity was determined to be methyl acrylate greater than ethyl acrylate greater than butyl acrylate greater than butyl methacrylate greater than methyl methacrylate greater than ethyl methacrylate. Four-hour daily exposures (excluding weekends) of young adult male rats to 110 ppm methyl acrylate in air over a period of 32 d failed to produce significant differences in body or tissue weights, blood chemistries, gross metabolic performance, and spontaneous small-intestinal motor activities when compared with a sham-exposed group.

Toxicity of ammonia to early life stages of the green sunfish Lepomis cyanellus

Toxicity of ammonia to early life stages of green sunfish Lepomis cyanellus was studied. One chronic and four acute exposure studies were conducted. During the chronic study green sunfish were exposed to a series of ammonia concentrations from the blastula stage through 40 days post-hatching. During the acute studies, juvenile green sunfish were exposed at four pH levels, 6·6, 7·2, 7·7 and 8·7, to derive 3-, 6-, 12-, 24-, 48-, 72- and 96-h LC 50 and EC 50 concentrations of un-ionised (NH 3) and total ammonia (NH 3N). Pre-hatching embryological stages were found to be the most resistant stages studied. Hatching success was unaffected when incubation was at ammonia concentrations ranging from undetectable through 0·91 mg litre −1 NH 3, the highest concentration tested. Growth was inhibited at 0·49 mg litre −1 NH 3 but not at 0·22 mg litre −1 NH 3. All larvae died within 10 days of hatching at 1·02 mg litre −1 NH 3. The 96-h LC 50 concentrations at pH values of 6·6, 7·2, 7·7 and 8·7 were 0·50, 1·06, 1·34 and 1·73 mg litre −1 NH 3, or 272, 139, 57 and 9 mg litre −1 NH 3N, respectively.

An Air Quality Data Analysis System for Interrelating Effects, Standards, and Needed Source Reductions: Part 7. An O3-SO2Leaf Injury Mathematical Model

Leaf injury data from acute and chronic exposure studies of Dare soybean were regressed against the logarithms of exposure time and O3 and SO2 concentrations to develop a new two-pollutant leaf injury model (which explains 88% of the variance) and to calculate the parameters of best fit for this new model and a previously developed one-pollutant model. Using the calculated parameters, the percentage of leaf surface Injured over a growing season by O3, SO2, or both simultaneously was estimated for an ambient air sampling site located 2 miles from a coal burning power plant. For this site, the one- and two-pollutant models predicted that SO2 effects would be negligible If SO2 concentrations never exceeded the National Ambient Air Quality Standard (NAAQS) of 0.50 ppm, averaged over 3 h. However, calculations suggest that O3 may injure up to 24% of Dare soybean leaf surface over a growing season even though the O3 NAAQS of 0.12 ppm, averaged over 1 h, is never exceeded. Because the 3 h SO2 standard is exceeded at very few places, the O3 model is usually sufficient to estimate Dare soybean leaf Injury. Leaf injury is estimated by taking the logarithm of the summation of each daytime hour’s exponentiated O3 concentration (c) measured at an ambient air sampling site over a growing season. This is expressed as: z = -0.0828 + 0.4876 in (Σco3 2.618), where z is the Gaussian transform of percent leaf injury. The methods developed in this paper, using Dare soybean data as an example, may apply to other plants.

Thymic atrophy induced by acute exposure of 3,3′,4,4′-tetrachloroazobenzene and 3,3′4,4′-tetrachloroazoxy-benzene in rats

The effects of 3,3′4,4′-tetrachloroazobenzene (TCAB) and 3,3′4,4′-tetrachloroazoxybenzene (TCAOB) on lymphoid organs in male Sprague-Dawley rats were investigated in various acute exposure studies. Significant thymic atrophy was observed in rats 10 days after the i.p. administration of either compound (on days 1 and 5) at a dose of 25 mg/kg. When 8-week-old animals were studied, the relative thymus weight was reduced to 69% and 49% of the control value of by the respective treatment of TCAB and TCAOB. In 2 groups of weanling rats the same dosage of TCAOB was able to reduce the relative thymus weight to 31% and 38% of the comparable control animals. In addition, TCAOB causes a decrease in the body weight gain and a decrease in the weights of major organs in the weanling animals. This toxic response cannot be explained solely on the basis of decreased food intake since qualitatively the same results were observed in a pair-feeding experiment. The involvement of glucocorticoid hormones was rejected as the underlying mechanism since adrenalectomy was found to provide no protection towards the degenerative effect seen upon the lymphoid tissues. This investigation constitutes the first study concerning the effects of these 2 environmental and occupational toxicants on lymphoid organs.

Glucocorticoid regulation of plasma ketone body concentration in insulin devicient man.

This study was designed to assess the hyperketonemic activity of glucocorticoids in insulin deficient diabetic man. Both the duration of exposure and the site of action of glucocorticoids were examined relative to a significant increase in plasma ketone body concentration. Six stable insulin dependent diabetic subjects participated in a control, an acute glucocorticoid exposure, and a prolonged glucocorticoid exposure study. For the control study, no glucocorticoids were administered before or during the study. During the acute glucocorticoid exposure study, acute hypercortisolemia was induced for 80 min by the bolus iv administration of 50 mg of cortisol. In the prolonged glucocorticoid exposure study, 24 h of prolonged glucocorticoid stimulation was produced by the oral administration of 1.0 mg of dexamethasone, at 24 and 12 h prior to study. During these studies, a hepatic stimulating effect of glucocorticoids independent of the free fatty acid mobilization activity of glucocorticoids was assessed by a...

A Freeze-Fracture Study of Ozone-Induced Morphological Changes in Primate Lung

Previous studies of acute exposures of rats and other mammals to ozone demonstrated severe pulmonary parenchymal lesions in the central region of the pulmonary acinus and extensive edema. In this study, an adult Rhesus monkey was exposed to 4 ppm ozone for 4 hours and euthanized immediately after the exposure. A control Rhesus monkey was also euthanized. The lungs were fixed via the trachea at 30 cm of water pressure with Karnovsky's fixative. Tissue was selected from acini of the right diaphragmatic lobes. Much of the selected tissue in the exposed primate was edematou.s. Tissue blocks (1mm2 × 2mm) were immersed in a cryoprotective agent (25% glycerol/0.2 M cacodylate buffer) for 2 hours, mounted in apposed specimen holders, and rapidly frozen in Freon 22 (cooled in liquid nitrogen).

Two studies of acute internal exposure to man involving cerium and tantalum radioisotopes.

Abstract Actual exposures of humans to internal radioactive contamination provide our most valuable data in determining the behavior of these substances in man. Two recent exposures at the National Reactor Testing Station demonstrate the markedly different behavior that can result from inhalation of insoluble particulates. In one incident, an individual received a body burden of 36 μCi of 141Ce, 27 μCi of 144Ce and 13.5 μCi of 95Zr-95Nb. Over 99.7% of his total body burden was eliminated in only 4 days, all of which was through the gastrointestinal tract with a total dose of about 10.3 rems to the lower large intestine. In the other incident, an individual received a body burden of 30 μCi of 182Ta and 150 μCi of 183Ta. Approximately 93% of the activity was eliminated in 7 days, the elimination being entirely in the feces. The remaining activity decreased at a rate not statistically different than the 115-day radiological half life of 182Ta, resulting in a dose of 13 rems to the lungs. The actual biological elimination could be detected only on large samples of feces and amounted to less than 0.05%/day. The major contaminants were not detected in 24-hr urines in either incident.