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Experiment BT1<br />

Most previous risk assessments have been based on the data from experiment BT1 (Maltoni et al.,<br />

1984). In this study, 30 Sprague Dawley rats of each sex were exposed to concentrations of vinyl<br />

chloride ranging from 50 to 10,000 ppm for four hours daily, five days per week for 52<br />

weeks, beginning at 13 weeks of age. A positive control group received 2,500 ppm of vinyl acetate.<br />

After treatment the animals were observed for their lifespans up to 135 weeks. Survival of both males<br />

and females decreased in a dose-related manner, especially at concentrations above 500 ppm. Vinyl<br />

chloride was more toxic to females than to males in this experiment. Vinyl chloride was associated with<br />

an increased incidence of liver angiosarcomas in a dose-related fashion. These results are presented in<br />

Table 9 (Maltoni et al., 1984). In addition to liver angiosarcomas, vinyl chloride (at concentrations<br />

above 2500 ppm) caused an increased incidence of zymbal gland carcinomas, nephroblastomas,<br />

hepatomas, and neuroblastomas. The incidence of liver angiosarcomas was probably underestimated at<br />

the higher exposure levels due to mortality resulting from tumors at other sites.<br />

Table 9:<br />

Study<br />

Incidence of liver angiosarcomas (LAS) in male and female Sprague-Dawley rats<br />

exposed to 52 weeks to vinyl chloride (Maltoni et al., 1984)<br />

Exposure level LAS incidence 1 corrected LAS incidence 2<br />

(ppm)<br />

male female male female<br />

BT1 0 0/30 0/30 0/22 0/29<br />

50 0/30 1/30 0/26 1/29<br />

250 1/30 2/30 1/28 2/26<br />

500 0/30 6/30 0/22 6/28<br />

2,500 6/30 7/30 6/26 7/24<br />

6,000 3/30 10/30 3/17 10/25<br />

10,000 3/30 4/30 3/21 4/25<br />

BT2 0* 0/85 0/100 0/61 0/68<br />

100 0/60 1/60 0/37 1/43<br />

150 1/60 5/60 1/36 5/46<br />

200 7/60 5/60 7/42 5/44<br />

BT6 30,000 5/30 13/30 5/22 13/24<br />

BT9 0 0/50 0/50 0/29 0/38<br />

50 1/150 12/150 2/70 12/110<br />

BT15 0 0/60 0/60 0/25 0/44<br />

1 0/60 0/60 0/48 0/55<br />

5 0/60 0/60 0/43 0/47<br />

10 0/60 1/60 0/42 1/46<br />

25 1/60 4/60 1/41 4/40<br />

LAS incidence in historical 1/1179 2/1202 1/364 2/541<br />

controls<br />

1 Number in denominator - number of animals necropsied.<br />

2 Number in denominator - number of animals alive when first liver angiosarcoma was observed.<br />

558

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