Handbook of Solvents - George Wypych - ChemTech - Ventech!

20.6 Chromosomal aberrations 1377
pared to a control group. These same investigators looked at workers exposed to benzene
levels from 25 to 120 ppm, and found that they had significant chromosomal aberrations as
compared to the normal population (which has a general background exposure to benzene
levels). The study of Forni et al. 14 showed significant chromosomal aberrations in those patients
who were exposed mainly to benzene, and not to those who were exposed to toluene
only. Hartwich et al. 30 looked at 9 healthy refinery workers who were exposed to low levels
of benzene, and also found significantly increased chromosomal changes compared to the
control group. The National Research Council Advisory Center and Toxicology Study 31
concluded that close correlation between occupational exposure to benzene and persistence
of chromosomal aberrations can be discussed only when there is an association between
benzene induced hematopoietic disease and chromosomal aberrations, however, the absence
of chromosomal changes, cannot be a determinant in the temporal relationship between
exposure to benzene and hematopoietic diseases. 31 While some studies suggested that
the chromosomal changes require heavy exposure to benzene, the study by Picciano,
1979, 32 looked at chromosomal changes in 52 workers exposed to a mean benzene concentration
of less than 10 ppm compared to non-exposed controls. There was a statistical significant
increase in chromosomal aberrations in exposure as low as less than 10 ppm.
Furthermore, these same investigators 33 reported a dose response increase in the aberrations
when the exposed workers were divided into smaller groups by the exposure levels (less
than 1 ppm, 1-2.5 ppm, and 2.5-10 ppm). Drivers of petrol tankers and crew members of
gasoline tankers, ships and petrol station attendants were studied for chromosomal
changes. 15 The degree of exposure to benzene of the three groups was estimated to be at a
mean of 0.4 ppm, and the crew members were estimated to be at 6.56 ppm while engaging in
handling of gasoline. The frequency of chromosomal and chromatoid aberrations in the
petrol tanker drivers was significantly greater than in those of petrol attendants and the crew
members. The effects of long-term benzene exposure from the incidents of chromosomal
changes were studied in 16 female workers who were exposed to a maximum of 40 ppm
benzene between 1-20 years. 34 The cytogenetic study was conducted 6 months after benzene
was eliminated from the work environment, and they have found no significant increase
in chromosomal changes. Clare et al. 35 looked at chromosomal changes in the
peripheral lymphocytes of workers after a single, one exposure to benzene. Exposure levels
were described as high after a spillage of a large amount of benzene during the loading of a
ship. Three months after the incident, chromosomal analysis showed no significant abnormalities.
The authors concluded that there was no evidence of lasting chromosomal damage
in the peripheral blood lymphocytes of these exposed workers. Golomb et al. 18 reviewed the
literature and reported the results in regards to exposure to benzene and chromosomal
changes. They have stated that they studied exposure data on 74 patients with acute leukemia.
They describe that 75% of the exposed patients had an abnormal karyotype, whereas
only 43% of the patients characterized as non-exposed had an abnormal karyotype. While it
is true that these findings are in agreement with previous studies 18 they still could not explain
the 43% of the patients who were not exposed, and still had abnormal chromosomal
changes. This is a very important observation, since some investigators in the field claimed
that the “absence of chromosomal changes” in benzene exposed individuals negates the
clinical causative diagnosis of benzene induced hematopoietic disease. Essentially, all of
the studies show that benzene can cause chromosomal changes, but does not cause it in all
the patients, and the absence of chromosomal changes cannot and does not rule out the ex-