DENVER -- Tests have revealed that some employees at the National Institute of Standards and Technology were contaminated by plutonium after a spill earlier this month.

Contamination was initially found on a desk, a notebook and a chair used by a researcher.

The institute said the researcher who had been working with the plutonium had washed his hands during the incident.

NIST officials announced late Friday that a "small number of personnel" were shown to have internal plutonium exposure but they didn't say how many. Officials said internal plutonium exposure can lead to cancer and that the individuals affected were undergoing treatment to remove the plutonium from their bodies.

"We are concerned for the health and safety of our personnel and deeply regret these results showing internal plutonium exposure," said James Turner, NIST deputy director.

Sen. Ken Salazar (D-Colo.) released a statement Saturday saying: "This terrible news realizes our fears. We must work to see that those who were exposed and have been contaminated get the absolute best medical care available. Meanwhile, tests on others who may have been exposed and on water supplies must proceed with the utmost urgency to ensure that anyone else who may be contaminated gets immediate treatment."

Radiation from plutonium is weak but hazardous if ingested or inhaled.

The spill happened June 9 at NIST's Boulder campus when a vial with about a quarter gram of plutonium-containing powder cracked and spilled some particles.

After the spill, radiation was found in various parts of NIST's Building 1 and two sinks. NIST officials also said trace amounts of the plutonium may have been washed into Boulder's sanitary-sewer system because researchers washed their hands after the spill. No adverse effects from the potential plutonium release into the wastewater system were found, according to acting interim City Manager Maureen Rait.

Officials also said Friday that three additional small spots of trace-level contamination were found Thursday in a different NIST building from where the spill happened, and that the traces were found on items that belonged to someone who was at the lab after the accident before it was reported.

Colorado Democratic congressman Mark Udall said a review of NIST's safety practices is needed.

"As far as I know, there was no protocol in place to deal with the spill," he said.

Tara Trujillo, a Udall spokeswoman, said a congressional hearing is scheduled July 15.

Turner has said NIST will cooperate with Udall, and has called the spill "not acceptable."

Gail Porter, a NIST spokeswoman, said the lab does have a radiation safety program in place, and that they're investigating how the spill occurred. Porter also said NIST is asking radiation experts to help them review their safety procedures.

"We are committed to strengthening our programs and their implementation to prevent such incidents in the future," Porter said.

She said 29 people have undergone testing for plutonium exposure so far. She said NIST officials did not release how many people have internal plutonium exposure because all lab personnel will undergo additional, more sensitive tests, which detect lower levels of contamination.

The results of those tests are expected within four weeks.

Udall said he hopes the congressional hearing will bring answers about how the spill happened, how it was handled, and what NIST plans to do to prevent an accident from happening again. He said he also wants to know what they would do if a spill happened again.

NIST is an agency within the U.S. Department of Commerce best known for running the atomic clock that is used to maintain the official U.S. time.