Page 194 - Materials Chemistry, Second Edition

L1644_C04.fm Page 166 Tuesday, October 21, 2003 3:13 PM

4. Calculate an acceptable concentration (8-h time-weighted average) to
prevent cancer effects in workers where there is working lifetime exposure
to an airborne threshold toxicant. The pollutant has a potency factor of
–1
0.002 (mg/kg/day) , the absorption factor is estimated at 80%, and the
exposure time is 5 days per week, 50 weeks per year over a 30-year period.
The worker is assumed to breathe for 3.5 h per workday at the rate of 1.5
3
3
m /h and 3.5 h per workday at a moderate breathing rate of 1 m /h.
–4
5. The reference dose (RfD) for arsenic is set at 3.0 × 10 mg/kg/day and
–1
the carcinogenic oral scope is 1.75 (mg/kg/day) . Discuss which would
be more stringent: oral concentration standard based on a carcinogenic
risk or on RfD.
3
6. A 70-kg person is exposed to 1.33 ng/m of cadmium in the air and also
consumes an average of 53 g fish per day twice a week taken from a
contaminated river with a cadmium concentration of 0.2 µg/g. The refer-
3
–2
ence concentration is 2.0 × 10 µg/m , reference dose is 1.0 × 10 –3
3 –1
mg/kg/day and the inhalation unit factor (mg/m ) . Calculate his or her
lifetime cancer and noncancer risks.
7. Suppose a 70-kg person consumes an average of 5.6 g fish per day with
–1
a concentration of DDT (oral potency factor = 0.34 (mg/kg-day) ) equal
to 50 ppb (0.05 mg/L). Calculate the maximum lifetime cancer risk from
this source.
8. Suppose that a 70-kg individual eats 7 g fish per day taken from a river
contaminated by methylene chloride and that the bioconcentration factor
(BCF) is 2 L of water per kilogram of fish. What concentration of meth-
ylene chloride (mg/L) in the river water would produce a lifetime risk of
–7
6 × 10 to this individual? (Bioconcentration factor is a measure for the
characterization of the accumulation of a chemical in an organism. It is
defined as the concentration of a chemical in an organism — plants,
microorganisms, animals — divided by the concentration in a reference
compartment, e.g., food, surrounding water.)
9. The reference dose (RfD) for 1,1-dichloroethylene is set at 0.009
–1
mg/kg/day and its oral potency factor is 0.58 (mg/kg-day) . Discuss
which would be more stringent: a dichloroethylene oral concentration
–6
standard based on a carcinogenic risk of 1 × 10 or a standard based on
RfD.
10. Consider the issue of indoor air pollution caused by sidestream smoke
emitting roughly 0.4 mg/cigarette of 1,3-butadiene. Calculate the average
–6
concentration of 1,3-butadiene producing a 1 × 10 lifetime cancer risk
using standard values of inhalation. The inhalation potency factor of 1,3-
–1
–1
butadiene is 6.1 × 10 (mg/kg-day) .
11. Estimate and discuss what would be better regarding the cancer risk:
drinking unchlorinated groundwater with 25 ppb of benzene, which has
–2
–1
an oral potency factor of 2 × 10 (mg/kg-day) , or switching to a surface
water supply that, as a result of chlorination, has a chloroform concen-
–1
–3
tration of 50 ppb (which has a potency factor of 6.1 × 10 (mg(kg-day) ).
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