Environmental Issues

Problem 1
Estimate the incremental cancer risk for a 60-kg worker exposed to a particular carcinogen under the following circumstances. Exposure time is 5 days per week, 50 days per year, over a 25-year period of time. The worker is assumed to breathe 20 m3 of air per day. The carcinogen has a potency factor of 0.2 (mgkg-day)-1 and its average concentration is 0.05 mgm3.

Given
BW  60kg Frequency  5 dayswk, 50 wksyr Duration  25yrs
Inhalation rate 20m3day PF  0.2 kg-daymg Ave. Concentration  0.05 mgm3
Estimated Lifespan  70yrs

Incremental Cancer Risk (CR)  Chronic Intake (CI) x Potency Factor (PF)

Chronic Intake (CI) Cave x Irate x Frequency x DurationBW x Est. Lifespan x 365daysyr
CI (0.05 mgm3)(20 m3day)(5 dayswk)(50wksyr)(25 yrs)(60kg) (70yrs) (365daysyr)
CI (0.05)(20)(5)(50)(25)mg(60)(90)(365)kg-dayCI  4.077 x 10-3 mgkg-day

Incremental Cancer Risk (CR)  (4.077 x 10-3 mgkg-day) x (0.2 kg-daymg)
Incremental Cancer Risk  8.154 x 10-3

Problem 2
Suppose drinking water contains 1.0 mgL of toluene and 0.01 mgL of tetrachloroethylene(C2Cl4). A 70kg adult drinks 2L per day of this water for 10years. What the hazard index suggest that this was a safe level of exposure

Given
RfD for toluene 0.200 mgkg-day
RfD for tetrachloroethylene(C2Cl4) 0.010 mgkg-day
BW  70 kg Intake  2 Lday Ctoluene  1.0 mgL CC2Cl4  0.01 mgL

Hazard Index (HI)  Chronic Daily Intake (CDI)  Reference Dose (RfD)

CDI  (Concentration x Intake)  Body Weight (BW)

CDItoluene  (1.0 mgL) (2Lday)  (70kg)
CDItoluene  2.86 x 10-2 mgkg-day

CDIC2Cl4  (0.01 mgL) (2Lday)  (70kg)
CDIC2Cl4  2.86 x 10-4 mgkg-day

HItoluene  2.86 x 10-2 mgkg-day  0.200 mgkg-day
HItoluene  0.143

HIC2Cl4  2.86 x 10-4 mgkg-day  0.01 mgkg-day
HIC2Cl4  0.0286

Hazard index values for toluene and tetrachloroethylene are less than 1.0, and as such suggest that no adverse health effects to the subject can occur. Thus, the exposure levels are safe.

Problem 3
Suppose 30 out of 500 rats exposed to potential carcinogen develop tumors. A control group of 300 rats not exposed to carcinogen develops only 10 tumors.
Based on these data, compute

a) The relative risk
Relative Risk  (XC x NN)  (XN x NC)
Where
XC   of tumors in rats exposed to carcinogen (30)
NN   of rats not exposed to carcinogen (300)
XN   of tumors in rats not exposed to carcinogen (10)
NC   of rats exposed to carcinogen (500)

Relative Risk  (30)(300)  (10)(500)
Relative Risk  1.8

b) The attributable risk
Attributable Risk  XC(XCXN)YC(YCYN)

Where
XC and XN are the same as above
YC   of rats exposed to carcinogen without tumors  NC - XC
YN   of rats exposed not exposed to carcinogen without tumors  NN   XN

Attributable Risk  (30)(30  10)  (470)(470  290)  0.75  0.62
Attributable Risk  1.37

c) The odds ratio
Odds Ratio  XC x YNXN x YC
Where
XC,YN, XN, and YC are the same as above.

Odds Ratio  (30) (290)8700(10) (470)4700Odds Ratio  1.85

Do these indicators suggest that there might be a relationship between exposure and tumor risk
All three values of the indicators are greater than one, thus these suggest that a relationship exists between tumor risk and exposure.