Results of NTP-sponsored mouse cytogenetic studies on 1,3-butadiene, isoprene, and chloroprene.

Studies were conducted to determine the cytotoxic and cytogenetic effects of 1,3-butadiene and two structural analogs, chloroprene and isoprene, in the bone marrow cells of B6C3F1 mice exposed to the chemicals by inhalation. In one study, animals were exposed to 1,3-butadiene concentrations of 6.25, 62.5, or 625 ppm 6 hr/day on 10 exposure days and in the second study, to the same concentrations on weekdays for 13 weeks. Chloroprene and isoprene treatments involved 6 hr/day exposures on 12 exposure days at concentrations of 0, 12, 32, 80, and 200 ppm for chloroprene and 0, 438, 1750, and 7000 ppm for isoprene. In the 10-day study, 1,3-butadiene induced significant increases in sister chromatid exchange (SCE) at 6.25 ppm, micronuclei at 62.5 ppm, and chromosomal aberrations at 625 ppm. In the 13-week study, the frequency of micronucleated normochromatic erythrocytes in the peripheral blood was significantly elevated in all exposure groups including the 6.25-ppm group. Isoprene induced both SCE and micronuclei, whereas chloroprene gave negative results for all cytogenetic end points assessed in bone marrow cells.