1) Assume that in the past ten years an anomalously large fraction of the population of Bugtown has died from a rare liver disease (Buggtown has about 100,000 residents, and an average of 3 per year have died over the last five years). Many in the town suspect that the culprit is an understudied chemical, EZ-kil, found in water leaching from old storage tanks at what used to be a pesticide production facility. The concentration of the chemical found in drinking water in the town is 7 micrograms per liter. People generally drink about 1 liter of tap water per day, and there are no other known risk pathways for the chemical.
There is only one study that has been done on the risk of liver disease from EZ-kil. Researchers took four groups of rats (50 per group, for 200 total) and fed them various amounts of the chemical, and then looked for signs of the disease. In the group that got no EZ-kil, there was no disease observed. In the group of rats fed 1000 micrograms per day, two died from the disease. In the group fed 2000 microrgrams per day, fifteen died from it, and twenty-two died in the group fed 4000 micrograms per day (assume that any rats which got the disease died from it).
Using the results of this study, what is the risk of this disease for a tap-water drinking citizen of Miningtown? (To convert from rat dose to human dose, use the equation: (Human body weight / rat body weight)^ 0.75. Rats weigh about half a kilogram each).
a) (2 pts) Construct a dose-response graph for the rat study. Clearly indicate units on the axes.
b) (1 pts) Fitting a line to the data, what is the equation for the relationship between the dose and the response?
c) (2 pts) What is the dose-response equation for humans?
d) (2 pts) Does this chemical seem to be a likely culprit?
2) (2 pts) Explain why a linear fit to experimental data may overestimate the actual risk of a certain chemical which is present in the environment only in very low doses.
3) (2 pt) Can you think of reasons why it might underestimate the actual risk? (You will not get credit for "No", even if it is a verifiably correct response).
4) (2 pts) List some reasons why we use animal models in risk assessment, and why they might not be good estimators of human risk in some cases.
5) (7 pts) In her first major decision as director of the EPA, Christine Todd Whitman overturned the new national standard on arsenic in drinking water (it had recently been approved by the previous director, Carol Brower, after much study). Whitman claimed that the new standard of 10 ppm was too expensive and that we needed to do more research to determine what an appropriate standard would be. Other options were 50 ppm and 5 ppm. Eventually, the EPA decided that changing to the 10 ppm standard was the best course. Assume you are a congressional aid, and your boss wants to know: did Whitman do the right thing?
You should be able to find the information you need to answer this quesiton on the web. A good place to start would be the EPA's website (www.epa.gov), in particular on EPA's tecnhical fact sheet on the arsenic issue, but you probably won't be able to find all of the information you need there. If you can't get all of the information, do the best that you can, and explain where you had to make assumptions.