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Plutonium Discharge into Sink Below Federal and State Limits

BOULDER, Colo. – Using detailed measurements made with the assistance of a National Nuclear Security Administration (NNSA) team, the National Institute of Standards and Technology (NIST) has determined that a discharge of plutonium powder into the sanitary sewer system from a laboratory room sink at NIST on June 9 was below federal and state limits.

Boulder wastewater officials have said in a statement that the wastewater treatment process has shown no indication of contamination. NIST has been consulting closely with the City of Boulder wastewater officials and city management since the incident. In the same statement, wastewater and city officials did not express health concern for the local population due to the discharge.

"The health and safety of our personnel and local communities is our top priority," James M. Turner, NIST deputy director, said. "The fact that this incident occurred is not acceptable. We are actively investigating what happened and have enlisted the help of top radiation safety experts to review our procedures. We are committed to strengthening our safety program and its implementation to help prevent safety incidents in the future."

An NNSA Radiological Assistance Program (RAP) team entered the contaminated laboratory room on Thursday evening, June 19, with NIST health physicists and made extensive radiation measurements. These measurements were shared with Department of Energy (DoE) analysts across the country, who calculated how much plutonium can be accounted for in the lab, thus helping to set an upper limit on the amount possibly discharged into the sanitary sewer.

A report from DoE with the calculations using the new data was received by NIST on Monday, June 23.

An inspector from the Nuclear Regulatory Commission (NRC) observed the process Thursday.

The original entire powdered plutonium sample was a well-characterized reference sample containing about ¼ gram of plutonium (about 1/100th ounce). The NNSA radiation measurements, combined with measurements made by NIST, showed that between 76 and 87 percent of the original sample remains in the laboratory room, primarily at the spill site and with the original glass vial container. The maximum amount that likely could have been lost when a researcher washed his hands in the laboratory sink immediately after discovering the cracked vial is about 0.06 gram.

Federal and state regulations permit the discharge of 0.0000002 microCuries per milliliter of plutonium into sanitary sewer systems. The DoE and NIST calculations indicate that at most 0.06 grams of the entire plutonium sample could had been lost down the sink drain, which corresponds to a discharge of about 0.00000014 microCuries per milliliter, given the average discharge of wastewater from NIST. This means that any plutonium washed down the drain would have been below the legal limits.

According to NIST radiation safety experts, prior to entering the contaminated laboratory, air sampling had not shown airborne contamination. In the course of repeated entries to the contaminated lab room, air sampling equipment placed by the team detected airborne contamination, likely as a result of the team's activities. The team ceased operations and subsequent air sampling showed that radiation readings had returned to normal background levels in the spill room laboratory. Since responding to the incident, NIST radiation safety experts have monitored and found no evidence of any releases of contaminated air to the atmosphere.

NIST is contracting with radiation clean-up experts for further operations in the contaminated laboratory room and will ensure that all operations are rigorously conducted to ensure the safety of clean-up crews, NIST building occupants, the public and the environment.

Radiation health effects from plutonium primarily come from alpha particles, which do not penetrate the skin. Adverse health effects from plutonium exposure occur primarily with ingestion or inhalation of the particles.

In consultation with medical experts, NIST continues to monitor the health of the laboratory personnel who were confirmed to have had trace levels of external contamination, as well as others who could potentially have been exposed. Initial testing for possible exposure to large doses of internal contamination have been clear for all personnel tested, and a small sample of results from more sensitive tests are promising. However, it will not be known if internal exposure to plutonium occurred until final results from the more sensitive tests are received.

Measuring internal exposure to plutonium is complex, requiring multiple tests and specialized personnel, sampling kits and equipment. Some tests require repeated bioassay sampling and a week or more to analyze results. In addition to relying on the advice from its own occupational safety and health professionals and health physics staff, NIST has sought the advice of radiation health experts from DoE and the Colorado Department of Public Health and Environment, as well as physicians who specialize in responding to potential internal exposure to plutonium. Several different types of tests have been conducted, are under way, or may be conducted in the future based on the advice provided by these professionals. The privacy of these medical test results is protected under the Health Insurance Portability and Accountability Act and the Privacy Act.

Once testing is completed and full results received, NIST will provide aggregate information (that protects individual privacy rights) about whether any internal exposure has been detected.

In addition, NIST is investigating the incident with the assistance of additional radiation safety and occupational safety and health experts, who are expected to arrive at the site by Tuesday, June 24. NIST is cooperating with the NRC and has notified appropriate city, county and state officials.

"We are grateful to the City of Boulder, NNSA, DoE, Colorado state public health officials, and others for their assistance as we continue to respond to this incident," Turner said.

Released June 24, 2008, Updated February 2, 2023