2) Reference doses (RfDs) derived from epidemiologic data generally would involve fewer uncertainty factors than those derived solely from animal data. True or False 3) In estimating actual human exposures to an environmental hazard, risk assessors often employ conservative, \"health-protective\" assumptions that presume people are exposed to the highest level of hazard that can be considered credible. True or False 4) New animal toxicity data has recently become available that strongly indicates the Reference Dose (RfD) for a regulated chemical found in drinking water should be decreased by two-fold in order to be protective of public health. One option regulators would have to maintain the prevailing level of population health protection for this chemical would be reduce it\'s legally allowable limit in drinking water by two-fold. True or False Solution 2) Answer: TRUE In epidemiologic data, the Reference doses (RfDs) derived by experimenting with human population, but in animal data , the experiments are done on those animals which genetically mimic the human, genarally on mice, rat, monkey etc. So the Reference doses (RfDs) derived from epidemiologic data generally have fewer uncertainty factors than those derived solely from animal data. 3) Answer: False Risk assessment combines what is currently known about chemical toxicity and exposure to characterize potential health problems, but there are significant uncertainties in each step of the process. Some uncertainties are addressed by regulatory agencies through the use of health- protective assumptions that may result in overestimates of risk. These include assuming that animal toxicity test results are predictive of human responses, and that there is some risk of a carcinogenic response at even extremely low doses. These health-protective assumptions are often criticized by chemical defenders as leading to biased risk assessments. However, there are other uncertainties that are currently ignored in conventional risk assessment, which may result in underestimating health risks. Important factors that could affect health outcomes are often ignored because critical data are lacking. For example, risk assessment values are derived based on the assumption that people are exposed to a single chemical at a time, and that there is no significant interaction between chemicals that heightens the probability of adverse outcomes. Variations in susceptibility to a toxic chemical between people are often ignored, even though it is known that factors such as health status or genetic characteristics can greatly affect how someone responds to chemical exposure. 4) Answer: TRUE.

1. 2) Reference doses (RfDs) derived from epidemiologic data generally would involve fewer
uncertainty factors than those derived solely from animal data.
True or False
3) In estimating actual human exposures to an environmental hazard, risk assessors often employ
conservative, "health-protective" assumptions that presume people are exposed to the highest
level of hazard that can be considered credible.
True or False
4) New animal toxicity data has recently become available that strongly indicates the Reference
Dose (RfD) for a regulated chemical found in drinking water should be decreased by two-fold in
order to be protective of public health. One option regulators would have to maintain the
prevailing level of population health protection for this chemical would be reduce it's legally
allowable limit in drinking water by two-fold.
True or False
Solution
2) Answer: TRUE
In epidemiologic data, the Reference doses (RfDs) derived by experimenting with human
population, but in animal data , the experiments are done on those animals which genetically
mimic the human, genarally on mice, rat, monkey etc. So the Reference doses (RfDs) derived
from epidemiologic data generally have fewer uncertainty factors than those derived solely from
animal data.
3) Answer: False
Risk assessment combines what is currently known about chemical toxicity and exposure to
characterize potential health problems, but there are significant uncertainties in each step of the
process. Some uncertainties are addressed by regulatory agencies through the use of health-
protective assumptions that may result in overestimates of risk. These include assuming that
animal toxicity test results are predictive of human responses, and that there is some risk of a
carcinogenic response at even extremely low doses. These health-protective assumptions are
often criticized by chemical defenders as leading to biased risk assessments. However, there are
other uncertainties that are currently ignored in conventional risk assessment, which may result
in underestimating health risks. Important factors that could affect health outcomes are often
ignored because critical data are lacking. For example, risk assessment values are derived based
on the assumption that people are exposed to a single chemical at a time, and that there is no
significant interaction between chemicals that heightens the probability of adverse outcomes.

2. Variations in susceptibility to a toxic chemical between people are often ignored, even though it
is known that factors such as health status or genetic characteristics can greatly affect how
someone responds to chemical exposure.
4) Answer: TRUE