United States Nuclear Regulatory Commission

Office of Public Affairs

Washington, DC 20555

Phone 301-415-8200 Fax 301-415-2234

Internet:opa@nrc.gov

No. 96-100 FOR IMMEDIATE RELEASE

(Thursday, July 11, 1996)

NOTE TO EDITORS:

The Nuclear Regulatory Commission has received the attached

report from its Advisory Committee on Nuclear Waste. The report,

in the form of a letter, provides comments on the health effects

of low levels of ionizing radiation.

#

Attachment:

As stated
July 10, 1996

The Honorable Shirley Ann Jackson

Chairman

U.S. Nuclear Regulatory Commission

Washington DC 20555-0001

Dear Chairman Jackson:

SUBJECT: HEALTH EFFECTS OF LOW LEVELS OF IONIZING RADIATION

The health effects of ionizing radiation are central to many of

the regulations that are promulgated by the Nuclear Regulatory

Commission (NRC). The validity of the linear- no threshold (LNT)

dose-response relationships in the area of low doses and low dose

rates has been questioned. This letter supports the Commission's

present course of action of a review and analysis by the National

Council on Radiation Protection and Measurements (NCRP) leading

to an evaluation of this important issue.

Our discussion and recommendations concerning this subject derive

from the first meeting of the Joint Subcommittee of the Advisory

Committee on Reactor Safeguards (ACRS) and the Advisory Committee

on Nuclear Waste (ACNW) held on March 26, 1996. Presentations

were made by members of the NRC staff, including the visiting

medical fellow, and representatives from institutions and agencies such as the NCRP, the Health Physics Society, and the Massachusetts Emergency Management Agency. Written comments were also

received from the public.

Most national and international scientific committees dealing

with the subject take the view that the safest approach to

regulation is one that relies on the LNT model of response to

doses of ionizing radiation. This model holds that the ill

health effects observed at high doses and high dose rates (mainly

among atomic bomb survivors) can be extrapolated linearly to low

doses and low dose rates, down to the smallest doses. The NRC

staff prepares regulations on the basis of this model. One of

the basic questions in this field is whether the LNT model

is valid at the low doses and rates normally encountered in many

of the regulatory domains. The increasing emphasis placed by the

Commission on risk-informed regulation makes it imperative that

the actual health risk of low levels of ionizing radiation be

assessed accurately.

The NRC is currently funding a contract with the NCRP to make a

critical evaluation of the LNT assumption. The ACNW has not

reached conclusions on the validity of the LNT model, and will

continue to study the matter. We see the NCRP study as an
opportunity to obtain an independent review of the data and their

quality.

The presence of unavoidable background radiation and the need for

very large samples have made it difficult in the past to obtain

definitive data on the validity of the LNT model. As with all

small-effects phenomena, the quality of the data and the statistical interpretation of the results govern the ability of any

study to contribute to the testing of the model. However,

investigators in the field have recently been able to account for

the effect of such confounding factors such as variation in background radiation. Some studies in the United States, as well as

in China, Sweden, Poland, and Canada, have arrived at conclusions

that do not support the LNT model. Other research concludes that

it is likely that at least a threshold or perhaps a corresponding

zero equivalent point with beneficial risk decrements (hormesis)

exists at lower doses.

A notable example of the latter is a ten-year study by Johns

Hopkins University of U.S. nuclear shipyard workers which, we

were told, showed lower mortality, no increase in malignancies

among workers exposed to radiation when compared to those who

were not exposed, and no "healthy worker effect." This study may

be particularly significant since the investigators were looking

for evidence to support the LNT model. Another study, of Canadian women patients in tuberculosis sanitariums who underwent repeated fluoroscopy to monitor response to therapy, is used frequently to show the validity of the LNT model, but examination of

data at lower doses shows significant beneficial effects. The

1994 report of the United Nations Scientific Committee on the

Effects of Atomic Radiation (UNSCEAR) contains an extensive

appendix detailing cellular repair mechanisms (called "adaptive

response mechanisms") that could contribute to an explanation of

a threshold, or, if such cellular responses were stimulated by

low doses of radiation, to an explanation of beneficial effects.

In contrast, some of the public comments received by the Subcommittee suggested that the LNT model underestimates the harmful

effects of low doses of radiation. Also NCRP Report No. 121,

"Principles and Application of Collective Dose in Radiation

Protection," issued November 1995 and discussed with the Joint

Subcommittee at its March 26, 1996 meeting, finds that "from the

point of view of the scientific bases of collective doses for

radiation protection purposes, it is prudent to assume the effect

per unit dose in the low-dose region following single acute

exposures or low-dose fractions is a linear response."

In the face of conflicting views, the general belief of the

national and international committees dealing with the matter has

been that using the LNT model for regulatory purposes is a safe

and conservative approach and, if there is error, it is on the

side of enhanced protection. However, if there is a health

benefit at low doses, this logic is incorrect. Even if there is

no evident health benefit, there are significant societal costs
associated with this conservatism that could be avoided or

reduced if a threshold level could be established below which no

harm occurs. A basic principle of risk-informed regulation is to

prevent a situation in which scarce resources are misspent

to avoid negligible risks, while significant risks remain

unattended for want of resources to deal with them. Owing to the

potentially significant costs of the present conservatism, we

conclude that a reexamination of the regulatory model is

appropriate.

It is obvious that agreement on an appropriate dose-response

model is made more difficult by the differing voices on this

subject within the scientific community and those outside of this

community, including regulators, policy makers, and members of

the public. The first task required to reach such an agreement

is an impartial review of the data and their quality in the face

of the extensive application of the LNT model in regulations and

scientific opinion.

We recommend that the need for special attention be conveyed to

the NCRP regarding its study. Such attention should include:

(1) assurance that the study includes scientists other than those

who are "recognized experts" with a reputation built on the LNT

model, (2) an evaluation of the data by an entity with expertise

in statistics or information science, but no prior position on

LNT - such as the National Institute of Standards and Technology

(NIST) as well as the NCRP study committee, and (3) consideration

of essentially all studies that could relate to the LNT.

The Committee strongly believes in the NCRP goal of critically

evaluating data related to low dose health effects. We will

follow the program through interaction with NRC's Office of

Research and will report to the Commission on the study and its

implications.

Sincerely,

/S/

Paul W. Pomeroy

Chairman, ACNW