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Press Release

Table of Contents

Acknowledgements

Main findings

Recommendations

I. Introduction

II. National Primary Drinking Water Regulations – Radionuclides
A. Bone dose estimation in ICRP 2
B. Bone dose estimation, present-day dose conversion factors
1. Bone doses according to FGR 11
2. Bone doses according to FGR 13

III. Conclusions

IV. Costs

V. Estimating the impact of residual radioactivity

VI. Other risks and radionuclides

References

I. Introduction

The National Primary Drinking Water Regulations specify rules that will protect drinking water and will maintain it in a state that is safe to drink. In these regulations, 40 CFR 141.66 sets safe drinking water standards for radionuclides in public water supplies under the Safe Drinking Water Act.¹ These standards are set in two ways: by specifying maximum contaminant levels of drinking water or by specifying maximum allowable dose to the whole body or any organ as a result of ingestion of drinking water. However, as demonstrated below, the concentration limits currently in effect for alpha-emitting transuranic radionuclides in drinking water are grossly inadequate to protect public health. Achievement of reductions in concentration is necessary to protect public health.

The current maximum contaminant level (MCL) as set forth in 40 CFR 141.66(c) for gross alpha particle activity, including radium-226, but excluding uranium and radon, is 15 picocuries per liter. There is a sub-limit for radium-226 and radium-228, combined, of 5 picocuries per liter (including any naturally present radium-226 and radium-228). For instance, if water is contaminated with plutonium-239 alone, the level of contamination could reach as high as 15 picocuries per liter if no other qualifying alpha-emitting radionuclides were present. If radium-226 is present to the maximum allowable limit of 5 picocuries per liter,² then the rule allows a maximum contaminant level for gross alpha of 10 picocuries per liter. For instance, if plutonium-239 were the only alpha-emitting, long-lived transuranic radionuclide present, the MCL for plutonium-239 in this case would be 10 to 15 picocuries per liter, depending on the concentration of radium-226.

This standard was set in 1976, based on scientific assessments done in the late 1950s by the International Commission on Radiological Protection (ICRP) and the National Committee on Radiation Protection and Measurements (NCRP), a United States agency, and published as ICRP Publication 2 and in abbreviated form in the U.S. by the National Bureau of Standards as NBS Handbook 69.³

But the science has changed since then. As a result of these changes, as well as changes in the dose conversion factors adopted by the EPA since that time, dose estimates to the most exposed organ, while complex to assess, are far greater than those implied by the limit of 10 to 15 picocuries per liter when evaluated according to the methods specified in NBS 69.

It is therefore necessary that the MCLs of transuranics in drinking water be changed in order that the MCL remain within the spirit and framework of the standards as promulgated in 1976. This can be done based on the dose conversion factors that the EPA has since adopted and published in Federal Guidance Report 11,⁴ which are the basis for present EPA regulation and risk estimation. They were published in 1988. The EPA has since published Federal Guidance Report 13. This is the most recent EPA scientific publication relevant to safe drinking water standards. The scientific basis of this guidance (ICRP 72)⁵ has been adopted for some federal dose calculation purposes, but not yet sanctioned for use in regard to assessing doses from drinking water. In this report, we will consider the changes in the drinking water standards for alpha-emitting, long-lived transuranic radionuclides.

The basis for the needed MCL change is the potential danger that residual radioactive pollutants remaining after cleanup of the Cold War nuclear weapons production sites will pose to individuals in this generation and future generations. Of particular concern are the long-lived transuranic radionuclides neptunium-237, plutonium-238, plutonium-239, plutonium-240, plutonium-242, americium-241, and americium-243. All of these are man-made radionuclides.

Footnotes

² This assumes that no radium-228 is present. The radium MCL in the rule is set for the combined concentration of Ra-226 and Ra-228. The former is an alpha-emitter and the latter is a beta-emitter. Hence the latter is omitted from the gross alpha part of the rule.

³ ICRP-2, 1959 & NBS 69. NBS 69, which also bears the series title NCRP Report No. 22, is a recommendation of the National Committee on Radiation Protection and Measurements, which is now known as the National Council on Radiation Protection and Measurements (NCRP). Tables and scientific discussion are drawn from ICRP-2, 1959. NBS Handbook 69 was published in 1959 and then again, with an added table and errata, in 1963. We cite NBS 69 throughout this report. The dose conversion factors, the scientific content, and other details in NBS 69 are the same as those in ICRP 2. ICRP 2 was published by the International Commission on Radiological Protection in 1959. The NCRP was (and is) a participating organization in ICRP.

⁴ FGR 11, 1988.

⁵ ICRP-72, 1996.