Risk
Assessment Calculations
Exposure Reconstruction Case Study
Birth Defects (Styrene, MEK)
By: Henry P. Shotwell, Ph.D., CIH
Senior Vice-President
Atlantic Environmental, Inc.
Facts: A female lead
packer in a plant that manufactures polystyrene
plastic containers for food “to go” gave birth
to a female with cleft palate and hare lip. The
woman was Hispanic and in her late 30’s when she
became pregnant. Her duties were essentially
to assign crew members to various tasks and to
fill in where additional help was needed.
On occasion, the Plaintiff used a stencil
and ink roller or a can of spray paint to label
shipping cartons of product. The paint and ink
were in common use, available as consumer products
and contained volatile organic chemicals (VOCs).
Labeling was done for about 1 hour per day in
a plant bay having an area of 37,500 square feet
and an unobstructed height of 36 feet to the roof,
for a volume of 1.35 million cubic feet.
Air sampling showed no detectable VOC after
a seven-hour sampling program which collected
air at a rate of 28 mL/min. (11.76 L collected)
activated charcoal, during stenciling activities.
Approach: A search of
the National Library of Medicine’s Toxline databases
showed no reported association between cleft palate/harelip
and inhalation exposure to either styrene or to
MEK. A search for cleft palate/harelip alone
showed an incidence among Latinos that was 3 times
higher than among non-Latinos.
Assuming a lower limit of detection for
styrene and MEK of 5 micrograms, and given the
volume of the workplace at 1.35 million cubic
feet, the potential exposure concentration to
styrene and MEK would be less than 5 mcg per 3.8
x 104 M3 or less than 0.1
mg per million cubic Meters of air (less than
1 ten millionth of a milligram per cubic Meter
of air). The OSHA PEL for styrene is 426 mg/M3
air (TWA-8) and for MEK, the PEL is 590 mg/M3
(TWA-8). The exposure potential to either of
these is extraordinarily small compared to the
allowable limits.
Commentary: This type of case
is not amenable to quantitative argument. Rather,
the medical literature is used to support the
hypothesis that exposure to styrene or to MEK
does not result in cleft palate/harelip and that
these conditions occur naturally in the Latino
population 3 times more frequently than in non-Latinos.
Actual measurements can be used in further support
of the hypothesis that very low-level exposure
to styrene and MEK did not produce cleft palate/harelip
in a woman who was nearing the end of her child-bearing
capability and who comes from an ethnic group
which is prone to this condition.
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