Handbook of Solvents - George Wypych - ChemTech - Ventech!

1092 Myrto Petreas
even after log-log transformations. The decay of styrene concentrations in alveolar air and
in venous and arterial blood was slower in the first 30 to 50 minutes than later on. The authors
concluded that post-exposure alveolar air measurements were poor predictors of exposures
to styrene, whereas arterial blood would be the best index of exposure. For practical
reasons, they recommended capillary blood samples from fingertips as a surrogate for arterial
blood.
In a follow-up study 62 using the same experimental set up as above, seven male subjects
were exposed to 50 ppm (210 mg/m 3 ) of styrene in inspired air for 30 minutes at rest,
followed by 30 minute exposure periods under exertion at intensities of 50, 100 and 150 W.
The mean alveolar air concentration at the end of the first 30-minute period was 16% of the
concentration in the inspired air and 23% at the end of the final period. Both the arterial and
venous blood concentrations of styrene rose with increasing workload during exposure with
no equilibrium achieved between alveolar air and arterial blood during 2 hours of total exposure.
Weak correlations were found for the amount of styrene taken up per kg of body
weight and the concentrations of styrene in alveolar air 0.5 and 2 hours after exposure. The
elimination was faster during periods of exercise than during rest periods, leading to the authors’
recommendation for leisure time physical activity for people exposed to solvents as a
means to enhance elimination.
In another study, 63 four male volunteers were exposed to 80 ppm of styrene in a chamber
for 6 hours. Venous blood samples were collected during exposure and a nearly simultaneous
set of 10 blood and mixed exhaled air samples were collected following exposure for
up to 40 hours. Blood levels during exposure rose rapidly and reached an almost constant
level by the end of the 6 hours. Following exposure, the results showed that styrene was
cleared from the blood according to a linear two-compartment pharmacokinetic model,
with half-life values of 0.58 and 13 hours, for the rapid and slow elimination phases, respectively.
Retention of styrene was studied in a chamber setting where healthy males were exposed
to either constant or fluctuating air concentrations of styrene. 26 A computer-controlled
system was used to generate time-varying air concentrations over 4-5 hrs with a
mean air concentration of 50 ppm. End-exhaled air measurements taken throughout the exposure
period showed styrene retention of 93.5% during constant exposures, but higher retention
(96-97%) during fluctuating exposures. The authors speculated that the difference
in retention was related to non-steady-state behavior of styrene in the richly perfused tissues.
In summary, pulmonary retention during exposure is about 60-70% 62,64 with exhaled
concentrations accounting for 25-35%. 60 Higher retention (96-97%) was observed when
volunteers were exposed to fluctuating, rather than constant, air concentrations. 26 Following
exposure, the desaturation curve shows two exponential decays with half-lives of 13
minutes 60 to 52 minutes 63 for the rapid elimination phase and 4 hours 60 to 20 hours 63 for the
slower elimination phase. A third compartment can be defined to represent elimination
from the adipose tissue with a half-life of 3 days. 62
Measurements of styrene in venous blood at the end of the workshift and/or prior to
the next shift have been recommended by the ACGIH. 2 Monitoring of urinary metabolites
of styrene has also been recommended by the ACGIH 2 at the end of the week, even though
they are not specific to styrene exposure. Styrene in exhaled air after the end of exposure
was not recommended as a BEI because the levels would be too low to detect, leading to uncertainties.
Terminology
ACGIH American Conference of Governmental Industrial Hygienists
Alveolar air Gas in the alveoli