PROBLEM 7-4: BIOACCUMULATION OF HEPTACHLOR IN BEEF
Heptochlor
- Insecticide
- Use currently limited to control of fire ant in power transformers
- Neurotoxin and possible carcinogen.
- Previously used in agriculture
- Plants treated with heptachlor were sometimes used as animal fodder, legally after a prescribed interval to allow the heptachlor to break down.
- In several cases, dairy products from cows fed such fodder were found to be contaminated by heptachlor, indicating that either the waiting period was not long enough or ignored. This problem is based on a hypothetical such scenario.
Perform a Monte Carlo analysis of human adult exposure to heptachlor through beef consumption in this scenario.
Assumptions:
- For four years, clippings from plants treated with heptachlor were used as cattle feed before adequate time delay
- Samples of clippings showed between 20 and 100 ppm (95% interval, normally distributed) heptachlor, dry weight.
- The contaminated clippings had been mixed with regular feed at rate of 0 to 20% (uniformly distributed)
- Cattle ate 10 - 12 kg of feed per day (95% interval, normally distributed)
- The steady-state bioaccumulation of heptachlor is
daily intake X fat content X biostransfer factor
- The biotransfer factor (BTF) for heptachlor to beef is 0.00655 (mg/kg fat)/(mg/day)
- Fat content of beef is 21.5% on average, with 95th percentile at 25%
- Adults eat 250-350 mg of beef per day (mean 270 and s.d. 12, lognormally distributed)
MONTE CARLO SIMULATION (PROB 7-4)
Median Mean 95th perc. 99th perc. Max
1.9X10-6
4.2X10-6 1.66X10-5 3.17X10-5 9.54 X10-5
With 46 values > 4 X10-5 deleted:
SENSITIVITY ANALYSIS
Correlations
fatprop feedcons clipprop heptrat beefcons
feedcons -0.001
clipprop 0.026 0.007
heptrat 0.001 0.000 -0.000
beefcons 0.009 0.002 0.002 -0.009
LADD 0.073 0.037 0.389 0.225 0.715
Subsimulation LADD vs proportion of fat in beef:
Vs. consumption of feed by cattle:
vs. proportion of clippings in feed:
vs. concentration of heptachlor in clippings:
vs. beef consumption:
Subsimulation ln(LADD) vs ln(fat proportion in beef):
vs. ln(feed consumption):
vs. ln(proportion of clippings in feed)
vs. ln(proportion of heptachlor in clippings)
vs ln(beef consumption)
Correlations for logs of subsimulation:
ln(fatprop) ln(fc) ln(cr) ln(hr) ln(bc)
ln(feedcons) 0.044
ln(cliprat) 0.040 0.009
ln(heptrat) 0.047 0.011 0.013
ln(beefcons) 0.005 -0.019 0.015 -0.055
ln(LADD) 0.083 0.021 0.610 0.176 0.771