(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

eakage and loss was comparable whether mice were treated with 440 mg/kg of benzene or a
60/160 mg/kg mixture of hydroquinone/phenol.
6.2.2.2 In Vivo
Consistently positive findings for chromosome aberrations in bone marrow and lymphocytes of
benzene-treated animals support human case reports and epidemiology studies. Analyses of
chromosomal aberrations, sister chromatid exchange, and micronuclei in bone marrow and
lymphocytes of both mice and rats exposed orally or by inhalation, give positive results.
Inhalation: Bone marrow preparations from male rats exposed to 750 and 7500 ppm benzene
for single and multiple exposure periods showed significantly increased frequencies of
chromosomal aberrations (Anderson and Richardson, 1981). Male Wistar rats exposed to
100 and 1000 ppm benzene for 6 hours also had elevated frequencies of chromosomal
aberrations in bone marrow cells (Styles and Richardson, 1984). Tice et al. (1980, 1982)
reported that male and female DBA/2 mice acutely exposed to 3100 ppm showed significant
increases in SCE in bone marrow cells, but chromosome aberrations were not significantly
increased. Significant linear increases in SCE were also observed when DBA/2 and C56Bl/6
mice were exposed to benzene at concentrations of 28—5000 ppm; the response leveled at
3000 ppm for DBA/2 mice and at 2000 ppm for C57Bl/6 mice.
Evaluation of micronucleus frequencies in peripheral blood polychromatic erythrocytes (PCE)
and normochromatic erythrocytes (NCE) permits assessment of both recently induced (PCE,
24-hour lifespan) and chronically accumulated bone marrow damage (NCE, 30-day lifespan)
(ATSDR, 1993, 1997). Erexson et al. (1986) reported significant dose-dependent increases in
lymphocyte SCE and in micronuclei of bone marrow PCEs in DBA/2 mice exposed to 10, 100,
and 1000 ppm benzene for 6 hours. Increases in micronuclei were clear and dose-dependent
for all doses, while doubling of SCE was seen only at 1000 ppm benzene. Dose-dependent
increases in peripheral blood lymphocyte SCE at exposures of 3, 10, and 30 ppm, and in
micronucleated-PCE of bone marrow at 1, 3, 10, and 30 ppm were reported in Sprague Dawley
rats. Again, induction of increased micronuclei was significant, but SCE induction at 30 ppm
was marginal (11.1 SCE/metaphase vs 8.6 SCE in controls). Effects of benzene exposure
duration and dose regimen were examined by Luke et al. (1988a,b) by exposing male and
female DBA/2 mice to 300 ppm benzene, 5 days/week or 3 days/week for 1–13 weeks.
Micronucleated-PCEs were affected by benzene inhalation independent of exposure and
regimen; micronucleated-NCE were affected only with 5-day/week exposure. Males were more
sensitive than females. In a similar study, using male mice of DBA/2, C57Bl/6, and B6C3F1
strains, exposed to 300 ppm benzene, 6 hours/day, 5 days/week or 3 days/week for 13 weeks,
micronuclei increases in PCE were strain specific (DBA/2 >C57Bl/6 = B6C3F1), while
micronucleated-NCE were again regimen specific and strain specific in the reverse order from
micronucleated-PCEs (C57Bl/6 = B6C3F1 >DBA/2). Farris et al. (1997) studied induction of
micronucleated-PCE in bone marrow and blood, and micronucleated-NCE in blood of male mice
at low inhalation concentrations of 1, 10, 100, and 200 ppm benzene for 1, 2, 4, and 8 weeks,
but effects were seen only at 100—200 ppm. Hematological effects also were not observed
until exposure reached 100 ppm and are discussed later in this document. Micronuclei/PCE
frequency plateaued at week 2 (4.2% at 100 ppm, 8.6% at 200 ppm vs. 1.0% in control;
micronuclei/NCE 1.34% at 100 ppm, 3.25% at 200 ppm vs. 0.18% in control). Using a benzene
dose of 200 ppm for 5 days, Valentine et al. (1996) investigated reduction in benzene toxicity in
transgenic knock-out mice lacking CYP2E1 compared to wild-type mice and B6C3F1 mice.
CYP2E1 competent mice demonstrated decreased bone marrow cellularity and increased
Benzene VCCEP Submission
March 2006
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