Exposure chamber

The exposure chamber is a flat-bottomed shell vial, 2.0 cm. in diameter by 4.0 cm. long. The open end is heated in the flame and lightly pressed upon a flat surface to give a rolled edge projecting both outward and inward. On the outside this holds in place a metal cover (Figure 1), and on the inside it prevents spilling of the insecticidal solution... 

Figure 1. Small Vial Exposure Chamber with Screen Top in Place...

This exposure chamber is not restricted to any species of test insect and the extract of tissue suspected of containing a given insecticide may, of course, be prepared in any desired manner. The use of the common housefly, Musca domestica, as test insect and... 

The conditions under which the material is tested are crucial. The top of the exposure chamber must be sealed and the tank should contain no free air space. A stirring mechanism in the tank keeps the leachate mixture homogeneous and a heater block keeps it at an elevated temperature as required for the test. Stress conditions of the material in the field should also be simulated as closely as possible. The original U.S. EPA Method 9090 test included a rack to hold specimens under stress conditions but was revised when some materials shrank in the leachate. Due to the hazardous nature of the material, testing should be performed in a contained environment and safety procedures should be rigorously followed. 

These considerations are included here because in the discussion that follows HC1 decay will be ignored, to facilitate the calculations. HC1 decay is also important when measuring PVC toxic potency, because the walls of exposure chambers are made of non-sorptive materials, where such decay is minimised. In this connection it is worth pointing out that the highest concentration of HCl found when fire fighters entered buildings actually on fire was ca. 280 ppm [25, 26]. 

Rats were exposed to vapor concentrations of either 260 or 5,900 ppm hexachloroethane for 8 hours (Weeks et al. 1979). The 5,900 ppm vapor concentration was generated at 50 C and crystallized as it entered the exposure chamber. At the higher concentration the exposed animals showed signs of distress (staggering gait) during exposure, and 2 of 6 were dead at the end of 8 hours. No animals died at the lower exposure concentration. 

Zwart et al. (1990) exposed groups of five male and five female Wistar rats to phosgene at varying concentrations for 5, 10, 30, or 60 min. The test atmosphere was monitored at both the inlet and outlet of the glass exposure chambers by gas chromatography and infrared analysis. The 10-min LC50 value was 80 ppm, and the 30-and 60-min LC50 values were 20 and 12 ppm, respectively. 

In another study, Hartley guinea pigs (five per group) were exposed to phosgene at 0, 0.25, or 0.5 ppm for 4 h (Slade et al. 1989). The exposure chamber and atmosphere generation and measurement systems were similar to those used by Hatch et al. (1986). The LFP concentrations were measured 16 to 18 h after exposure. These investigators found that the LFP concentrations were elevated by 90% in animals exposed to phosgene at 0.25 ppm and 250% in animals exposed at 0.5 ppm, when compared with controls. 

The vapor pressures of the three components of Otto Fuel II differ considerably. During vapor generation studies with Otto Fuel II, PGDN was the only component vaporized into inhalation exposure chambers in sufficient quantity to allow direct analysis (Stewart et al. 1974 MacEwen and Vemot 1982). In light of the low toxicity of dibutyl sebacate and 2-nitrodiphenylamine and the fact that they do not vaporize to a detectable extent at test compound generation temperatures up to 45°C, the toxicity of Otto Fuel II has been evaluated in terms of PGDN. Chemical and physical data for PGDN are listed in Table 2-2. 

Three male squirrel monkeys previously trained to perform visual discrimination or visual acuity threshold tests were exposed continuously for 90 d to PGDN at a concentration of 262 mg/m3 (approximately 37 ppm) (Jones et al. 1972). The animals were removed from the exposure chambers for a 2-h period once a week for the respective behavior tests. A fourth trained monkey exposed to filtered room air under the same conditions served as the control. The only sign during exposure was mydriasis (excessive dilatation of the pupil of the eye), which increased from slight to moderate. There were no changes in avoidance behavior in the monkeys as determined by the visual tests. 

Barcroft (1931) described the controlled exposure of a 45-year-old, 70-kg man and a 12-kg dog to a concentration of HCN at 500-625 ppm in an airtight chamber. The human volunteer attempted to maintain the same level of activity as the dog. The dog became unsteady at 50 seconds (s), unconscious at 75 s, and convulsive at 90 s. One second later, the man walked out of the exposure chamber with no apparent effect. At 5 min after initiation of exposure, the man experienced a momentary feeling of nausea, and at 10 min from the... 

Groups of ten male Crl CD rats were exposed to HCN in polymethymethacrylate exposure chambers under flow-through conditions (E.I. du Pont de Nemours 1981). The chamber atmosphere was measured continuously by infrared spectrophotometry measurements were validated by gas chromatography. The experiment was performed in duplicate with one set of animals exposed head-only to the test gas while the other set was allowed free movement inside the exposure chamber. Free-moving rats inhaled concentrations of 273 to 508 ppm for 5 min, 110 to 403 ppm for 15 min, 128 to 306 ppm for 30 min, or 76 to 222 ppm for 60 min. The postexposure observation period was 14 d, during which body weights were monitored. 

The extent of bleeding in a plastic is evaluated with a test known as the sandwich method. The test sample is placed between a white, smooth surface of plasticized PVC on the top and a standardized sheet of filter paper underneath. The resulting sandwich is then placed between layers of foam material, which in turn are covered by glass plates. The resulting sandwich is allowed to remain in an exposure chamber at 50°C for 72 hours [48]. 

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