Toxicology of Industrial Compounds

urinary concentration at certain time points the net total cumulative
excretion of day 2 can be calculated.
Monitoring in occupational toxicology
N.P.E.VERMEULEN ET AL. 19
In occupational toxicology generally four monitoring approaches are
distinguished, namely: environmental monitoring (EM), biological
monitoring (BM), biological effect monitoring (BEM) and health
surveillance (HS) (Figure 2.5). EM and BM are concerned with the
measurement and assessment of ambient exposure and health risk
compared to appropriate references. EM determines xenobiotics at the
workplace, BM determines xenobiotics or their metabolites in tissues or
secreta. BEM is concerned with the measurement and assessment of early,
non-adverse, biological alterations in exposed workers to evaluate
exposure and/or health risk compared to appropriate references. HS is
concerned with periodic medico-physiological examination of exposed
workers with the objective of protecting and preventing occupationally
related diseases (Zielhuis and Henderson, 1986).
EM was shown to be of limited value for assessing the internal dose of a
chemical by not taking into account for example toxicokinetic and
toxicodynamic processes determining the ultimate fate of xenobiotics in the
body. To a certain extent, BM appeared to overcome the problems
inherently related to EM. BM assesses the overall exposure to xenobiotics
that are present at the workplace through measurement of the appropriate
determinant(s) in biological specimens collected from the worker at specific
timepoints (ACGIH, 1990).
Ideally, not only the relation between exposure and effect is known, but
also the toxicokinetic and toxicodynamic interactions linking these two. If
these processes are elucidated, quantitative knowledge of a determinant of
one of the different monitoring methods allows an assessment either of the
level of exposure or of the level of effect (Figure 2.5). For example, the
level of urinary mercapturic acid excretion could assess the potential health
hazard of an occupational exposure situation (Henderson et al., 1989).
In practice, a complete view on the relation between toxicokinetics and
toxicodynamics has not been elucidated for a single chemical up to now.
Occupational monitoring methods all have their specific values based on
their selectivity, sensitivity, validity and logistics and should therefore be
used complementary to each other. All methods operate on the continuum
from exposure to effect, the limits between which occupational toxicology
studies operate.