A village of about 4,000 has become
established on a site where once there was a chemical plant producing
pesticides. These families are from a secluded religious sect who
support themselves through subsistence farming operations, growing their own
crops and raising their own chickens for meat and eggs. They have
drilled shallow wells, from which they obtain their own water.
This year it was found that much of the
food and water being consumed by these families are contaminated by the
residual chemicals left by the former plant. Eight chemicals in
particular have been identified and the concentrations in soil and water
have been shown in table 1. You are assisting with a risk assessment
for the families for the exposure up to this point. They have
been moved to a safe piece of land, but the concern is for the exposure up
to this point. Assume a median life exposure in this case to be 30
years. Also assume ALL food and water has up to this time originated
from this site, and that all vegetables, grains, and crops grown in the soil
are subject to an uptake of twice the concentration that is in the soil (bioconcentration
factor of 2), and this has already been included in the calculation of the
intake (column 6). The chronic daily intake calculations are shown as
tables 4 & 5.
Complete table 3B (non-carcinogens in
foods grown in the soil), and complete BOTH summary tables (2C and 3C).
Then characterize the risk and hazard index by answering the following
1. What would be the expected number of additional
cancer deaths from this community due to these food and water exposures
2. LIST the chemicals that SEPARATELY exceed the E-01
de minimis level for carcinogens EITHER IN FOOD OR WATER. IF these
listed chemicals were all hypothetically removed, recalculate the total
carcinogenic risk from the remaining exposures (food and water combined);
does it still exceed de minimis?
3. This is not practical, so the following options are
considered. Calculate risk and H.I. for each option, and indicate the
safest (lowest risk) option
A: Replace the soil used to grow food but water continues to be
B: Cut off the shallow wells and supply water from a (safe) deep
C: Remove the DDT group (DDT, DDE, & dieldrin) from food and
water, using a readily available
4. What is the total Hazard Index
from the original eight chemicals?
5 Does it exceed the
"Action level"? If so, by how many times?
6. Now assume that because of the
proposed remedial option you have chosen in #3, re-calculate the HI. In
other words, if you have chosen to remove certain chemicals to reduce the
carcinogenic risk, these will be removed from the non-carcinogenic list
as well. [Note: the first version of this question
erroneously had the word "not" before "...be removed". It was an
7. Considering for this question ONLY Thallium Sulphate,
what would the concentration of this substance in water need to be such that
the H.I. from thallium sulphate does not exceed 1.00?
[#8 and 9 are NOT RELATED TO THE ABOVE CALCULATIONS]
8. Propylene oxide has been found in air
at a concentration of 60 micrograms per cubic metre of air.
Carry out a "lifetime" (70 yr) assessment of this exposure considering both
carcinogenic and non-carcinogenic effects. Calculate the risk and
hazard index, and characterize both in terms of appropriate actions.
Assume the receptors (exposed people) to be full-time residents of community
just downwind from the source. Assume a sedentary lifestyle (assume
respiration of 0.85 cu m air/hr) and that they seldom leave the premises.
What are your recommendations if the residents are to remain at the
premises? Note: your single solution would need to address both
carcinogenic and non-carcinogenic exposure.
9. You are advising a northern First
Nations community about consuming fish that contains organic mercury at a
concentration of 100 micrograms mercury per kg. Currently each
person consumes a mean of 420 g fish a day. What are your
recommendations? [Use 'methyl mercury' data from the IRIS database]