RISK ASSESSMENT Tests/exams
Download the Excel spreadsheet here (NOW with completed cells)
The assessment has been carried out on a self-sufficient population
of subsistence farmers who have been exposed to contaminated food
and water for 30 years.
(The BCF (Bioconcentration factor : 2x) has been factored in at column 6)
1. Complete the chart by filling in the missing blank (white) values (Note: the
dark shaded cells have no data)
2. What is the total combined carcinogenic risk (water + food) for this exposure? ... 3.72E-05
3. What is the LEAST number of chemicals to be targeted and removed for the
combined exposure to not exceed de minimis levels? .........FOUR
4. Now assume that a new deep artesian well can supply clean water, leaving only
the contaminated soil for growing food. Will the de minimis level still be exceeded
if residents use uncontaminated water, but continue to use the same contaminated
soil for their food supply? YES, the risk is 2.21E-05
5. If de minimis is STILL exceeded by the food, advise the residents how they should
alter their food intake from this home grown supply so as to be acceptably safe.
This is >22 times too high. They should reduce their intake of THESE FOODS to no more
than 45 g per day and find another source of food
6. What was the combined non-carcinogenic hazard index for these people BEFORE
the water was replaced? .... 1.8
7. After the water is replaced, does the food exposure represent a level above what
is acceptable, or is the level approximately satisfactory?
It is now 1.006, approximately at the acceptable HI of 1.00
Please note that the answers to Q3B and 3C (marked * and **) were originally transposed
when I first prepared the above page. The correct values were used in marking the papers
so no adjustment is necessary. The values shown are now correctly placed.
END OF TEST PAPER: =================================================================