Exposure groups

The critical group for a particular set of circumstances should be selected carefully. Adequate attention should be paid to the habits of ethnic and cultural minorities as well as those of indigenous people where apphcable. Their hving patterns and habits of consumption of food and water could give rise to pathways and elevated exposure levels that are unanticipated by conventional analysis. 

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In an animal study of rats exposed by inhalation to ethylene oxide at 10, 33, or 100 ppm for approximately two years (245), and in a separate chronic rat study in which rats were exposed to 50 or 100 ppm of ethylene oxide (240), increased incidences of mononuclear cell leukemia, peritoneal mesothelioma, and various brain tumors have been reported. In an NTP (246) two-year inhalation study of mice at 50 and 100 ppm, alveolar/bronchiolar carcinomas and adenomas, papillary cystadenomas of the harderian gland, and malignant lymphomas, uterine adenocarcinomas, and mammary gland tumors were increased in one or both exposure groups. 

Homogeneous exposure group A population or group of workers with similar exposure. 

In a cross-sectional study of sewer and water treatment workers, Richardson (1995) evaluated the association of hydrogen sulfide exposures to reduced lung function using spirometric testing. Job titles were used to categorize sewer workers into high, medium, and low exposure groups however, there was... 

Exposure Group Adenomas Adenocarcinomas + Squamous Cell Carcinomas Squamous Cysts Only All Tumors... 

Further details of the above study were discussed in U.S. EPA (1994). After the last exposure, methemoglobin levels were elevated in a dose-dependent manner 17 ppm, 0% to 2.9% (no different from controls) 45 ppm, 2.2% to 5.4% and 87 ppm, 4.2% to 23%. The animals exposed at 45 and 87 ppm were anemic with decreases in RBC counts, hemoglobin content, MCHb concentration, and hematocrit, and accompanying increases in erythropoietin foci, reticuloendothelial cell hypertrophy, and hemosiderin deposition in the spleen. The animals in the 87-ppm exposure group were judged cyanotic. In the 17-ppm exposure group, effects were limited to mild splenic congestion. 

Test Species/Strain/Number Adult male Sprague-Dawley rats, 5/exposure group Exposure Route/Concentrations/Durations Inhalation 0-150 ppm for 8 h... 

In a study by Haun et al. (1970), male and female rhesus monkeys (three to five per group, sex ratio per exposure varied) and male squirrel monkeys (two to four per exposure group) were exposed to monomethylhydrazine for 60 min (rhesus monkeys) and 15, 30, or 60 min (squirrel monkeys) (Table 3-3). For the rhesus monkeys (three males and two females), there were no deaths following a 60-min exposure to a mean concentration of 160 ppm (range, 145-170 ppm),... 

The acute toxicity of monomethylhydrazine in dogs was also studied by Haun et al. (1970). Three groups of male and female beagle dogs (two to five per exposure group) were exposed to monomethylhydrazine for 15 min (380- 400 ppm), 30 min (180-200 ppm), or 60 min (92-104 ppm) (Table 3-3). Deaths occurred within 2 h following termination of the exposure. The study authors calculated 15-min, 30-min, and 1-h LC50 values of 390, 195, and 96 ppm, respectively. 

Jacobson et al. (1955) assessed the lethality of monomethylhydrazine in rats (10 per exposure group strain not specified) following a single 4-h exposure to various unspecified concentrations. An LC50 of 74 ppm (139 mg/m3) was reported. Based upon the exposure-response data, an LC20 of =70 ppm (=132... 

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