Dr. Margaret Kripke Statement/Answers to I-Team



Posted on September 3, 2011 at 5:12 PM

Updated Saturday, Sep 3 at 5:17 PM

Note: The following is a letter KHOU sent to Dr. Margaret Kripke.  We have inserted her specific answers to each question we asked.   In addition, we have posted both our letter and her answers in their entirety below.

Dr. Kripke,

Per our conversation earlier today, KHOU is preparing a one-hour news special on issues related to radionuclides in some parts of Texas and Houston drinking water.  Our upcoming program will deal with many statewide and federal issues. It will also address both past and/or present issues related to the city of Houston’s water supply including the alpha radiation detected in Houston’s water emitted from uranium, radium, and radon.  

In particular, our planned broadcast will also address various statements you made, primarily in an on-camera interview produced by the City of Houston that is posted on the city’s website, and also at a town hall forum directed specifically to a group of residents in the Chasewood neighborhood of Houston.  For your convenience, here is a link to the Houston site:


Some of these statements have come under criticism by various scientists who have expertise in nuclear physics, radiation, and the public health. 

We would appreciate you answering these questions separately, as we have numbered them below,

1) On the city’s website you say in part:  “The reports that I’ve read from the National Academy of Sciences and other places, the experts agree that at these low levels of alpha radiation, there is not a risk of developing cancer from that radiation by itself.”

Dr. Arjun Makhijani, a former member of the radiation advisory committee to the EPA, and a scientist whose work you reference in your report on environmental cancer risks , has responded to your statements in an on-camera interview. Specifically, he says:

“(Kripke) referred to the National Academies Study, and I have read those studies and I know what they say. And you should ask Dr. Kripke whether she remembered what’s in those studies when she made that statement, because her representation of those studies is wrong.” 

In addition, in writing he also cites the following quotations of these studies from the National Academies-

From the BEIR VII report: “The BEIR VII committee concludes that current scientific evidence is consistent with the hypothesis that there is a linear dose-response relationship between exposure to ionizing radiation and the development of radiation-induced solid cancers in humans.”

And from BEIR VI: “Furthermore, the existing biologic evidence suggests that any exposure, even very low, to radon might pose some risk.” 

How would you respond to Makhijani, who says how you have characterized the conclusions of the National Academies is “wrong” ?

He also says that the widespread scientific viewpoint is that any radiation at any amount, especially when internalized, is a risk,  given the monoclonal nature of cancer.  Therefore he believes it is at least inaccurate, if not wrong, to tell the public  “that at these low levels of alpha radiation, there is not a risk of developing cancer from that radiation by itself.”  Again, we ask your response.

DR. KRIPKE ANSWER 1: Dr. Makhijani is an acknowledged expert, and I do not disagree with his statements.  What I was trying to convey is that the risk of developing cancer solely from the low doses of alpha radiation in the drinking water in question is extremely small.  Dr. Makhijani is correct that the risk is not zero, but it is unlikely that anyone would develop cancer from the doses of alpha radiation present in the drinking water over the time period in question.

2) The EPA, in its December 7, 2000 notice in the federal register on drinking water regulatiosn, also says the National Academies believe in a  “linear no threshold” of radiation approach, or one that believes NO amount of alpha radiation is safe to ingest, even at low levels,  also citing the BEIR reports of the National Academies: 

EPA’s application of the LNT model to estimate and regulate cancer risks from environmental exposures to radionuclides is entirely consistent with all past and current observations and recommendations of the International Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), the National Academy of Sciences Committee on the Biological Effects of Ionizing Radiation (BEIR), and the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR), and the National Radiation Protection Board (NRBP). Citing the recommendations of these national and international advisory bodies, the U.S. Department of Energy, the U.S. Nuclear Regulatory Commission, and other Federal and State agencies with regulatory authority over radioactive materials also apply the LNT model as the basis for setting regulations and guidelines for radiation protection.

Do you agree or disagree with the EPA’s interpretation of what the National Academies believe? If you agree with the EPA, do you still believe your characterization of what the National Academies said was appropriate, as it is portrayed on the city’s website?   

DR. KRIPKE ANSWER 2:  I agree that it is most likely that there is a linear dose-response for the biological effects of alpha radiation and that any exposure to alpha radiation could increase a person’s lifetime risk of developing cancer.   However, it is unlikely that the low dose of alpha radiation found in Houston’s drinking water would cause cancer by itself.

3) Another point of concern for a number of scientists is also where you say on the website:  

“In extremely high doses radium is known to cause cancer: cancer of the bones or cancer of the blood cells or leukemia. But this is in doses that are much much higher, hundreds of thousands of times higher than what’s in the drinking water of a place like the city of Houston.”

Makhijani and others believe the above statement (and the segment of your interview that it is a part of) is misleading, especially for the public, as in the context delivered it could give the impression that there is no risk of a negative health outcome from drinking radium in water UNLESS it is at the levels you cite.  Do you disagree? Can you understand their viewpoint? Did you mean to give that impression to the public with that part of the interview, that there is a threshold for cancer risk from radium exposure and that it is at the levels you mention?

DR. KRIPKE ANSWER 3: My statement is factually correct.  I certainly did not imply that there is no risk of a negative outcome, nor that there is a threshold for cancer development.

4) Again regarding your web video interview segment about radium: Makhijani used federal guidance report 13 and a  recent city of Houston annual water quality report to check your statement.   His findings are attached in a spreadsheet.   He concluded that at “hundreds of thousands of times” the average radium levels in houston’s water, every person in the city of Houston would have a 100% chance of coming down with one or more types of cancer, and would in fact likely come down with multiple forms of cancer.   (Note: he performed this calculation using the most conservative possible numbers- throwing out the “higher” readings from Chasewood and using the average score of radium in Houston’s water instead.  He also used “200,000” to represent “hundreds of thousands.”)


We have had Dr. Makhijani’s work and conclusions and calculations checked by a number of scientists and they agree with him.   Dr. Joshua Hamilton of Brown University says if he were to encounter “hundreds of thousands of times” the radiation in Houston’s water- he would deal with that only behind thick protective glass and lead shields. We also consulted the NRDC’s senior nuclear scientist Tom Cochran, among others. All agree that the public should be concerned about radium in their water at “much, much” lower levels than are mentioned in your statement and that there are possible health consequences at these lower levels.

What is your response to Makhijani, Cochran, and Hamilton on this?

DR. KRIPKE ANSWER 4: My statement is consistent with Dr. Makhijani’s calculations and Dr. Hamilton’s opinion, since I stated that at these doses, alpha radiation clearly causes cancer.  As to Dr. Cochran’s statement, I agree that we should make every attempt to reduce exposure to known carcinogens, but this does not mean that every exposure will cause cancer.  It would be helpful if someone would put the Houston experience in the context of the amount of alpha radiation received from cosmic rays when flying in an airplane or living at high altitude.  How much exposure to alpha radiation is received from these sources compared to what was present in the drinking water in Houston?  This would help put things in perspective for the public.

5) You have publicly stated several times that you are not a “radiation expert.”  What is your expertise?

DR. KRIPKE ANSWER 5: My expertise is in the biology of cancer induced by ultraviolet radiation.  The molecular mechanism of cancer induction by UVR differs from that of alpha radiation, but many of the issues are the same, including the issue of dose-response and cumulative lifetime risk of cancer development from UV exposure.  However, my studies have focused mainly on the interactions between UV radiation and the immune system and between the immune system and cancer.

6) Are you satisfied with your video statements at the Houston website, their presentation in terms of context, and that they give the public an accurate representation of what your views are?

DR. KRIPKE ANSWER 6: In retrospect, I would have preferred to state that the risk of developing cancer from alpha radiation in the drinking water is very small, which would be more scientifically accurate than stating that there is no risk. 

7) Are you satisfied with the City continuing to post your interview with them, in its current form, online?

DR. KRIPKE ANSWER 7: Yes, I am, because the public health message should be that it is unlikely that cancer would develop as a result of drinking water under the conditions in question. Moreover, I do not think it appropriate to scare people into thinking that they will get cancer when the risk is so low.

We would appreciate hearing from you on these seven questions by the end of the day tomorrow, Thursday August 25.


Mark Greenblatt
Investigative Reporter

David Raziq
Exec. Producer for Investigative