Toxicology of Industrial Compounds

160 BIOMARKERS AND RISK ASSESSMENT
increased risk of lung cancer. As, however, epidemiological studies relate to
exposure a few decades earlier the risks of present exposures can only be
predicted. The levels of aromatic adducts are elevated in white blood cells
or lymphocytes in many of these groups. The reported total aromatic
adduct levels usually range between 1 and 10 adducts per 10 8 nucleotides.
Long-lived lymphocytes tend to have higher levels of adducts than shortlived
granulocytes (Savela and Hemminki, 1991; Grzybowska et al., 1993).
As a rule of thumb, it can be assumed that in a steady-state (i.e. long term
exposure) lymphocytes contribute to the level of adducts overwhelmingly.
Because they represent about 25 percent of the DNA in blood, the
relationship between total white blood cell (WBC) and lymphocyte DNA
adducts should be about 1:4, granulocytes only contributing to the amount
of DNA denominator. Yet one has to be cautious in the comparison of
results between various assays even within a laboratory as the results may
‘drift’ with time.
The levels of white blood cell/lymphocyte aromatic adducts from
workers in several industries, as measured by postlabelling, and as
compared to ambient air concentrations of benzo (a) pyrene (BP) and 1hydroxypyrene
levels are presented in Table 12.1. A boxplot presentation
of the adduct levels of bus maintenance and truck terminal workers is
shown in Figure 12.1 (Hemminki et al., 1994). The differences that were
statistically significant from the controls were, in addition to the groups of
maintenance and terminal workers, garage workers and diesel forklift
drivers.
There does not seem to be a direct relationship between exposure and
adduct levels. Electrode, coke and aluminium workers, exposed up to
several 100 ng m −3 concentrations of BP, do not differ from the control
more than foundry workers, exposed to less than 1/10 of the cited levels.
The apparently higher level of adducts in the aluminium and electrode
former workers (and controls) as compared to the other measurements, is
due a method applied earlier with higher amounts of radioactive ATP. The
later assays were carried out in small volumes but high concentrations of
ATP (Hemminki et al., 1993b; Szyfter et al., 1994). An increased level of
lymphocyte adducts has also been found in garage and truck terminal
workers, with estimated exposures of about 10 ng m −3 (Hemminki et al.,
1994). This would imply that the detection limit of the postlabelling
method in humans exposed to PAHs lies somewhere between 1 and 10 ng
m −3 BP. Whether diesel exhaust is a particularly potent inducer of adducts
remains to be demonstrated. The differences between the exposed and the
controls are statistically significant among foundry workers, all bus
maintenance personnel and garage workers as a subgroup, all truck
terminal workers and the diesel forklift drivers in particular. Coke
workers differed significantly from the local controls in summer when