The U.S Postal Service has shut down the service that processes government mail, pending test results of mail delivered to Senate Majority Leader Bill Frist’s (R-Tenn.) office Monday afternoon that appears to contain the toxin ricin.

“We’ve closed our V Street facility — and government mail is being held until we’re given the OK,” said Postal Service spokesman Bob Anderson. The Northeast D.C. facility distributes mail to the House and Senate as well as a number of other government agencies.

The Postal Service is also testing a powdery substance found at its Wallingford, Conn., branch. Anthrax spores were found at that facility in 2001, after anthrax-laced letters were sent to lawmakers on Capitol Hill.

“We’re still waiting for the test results to find out what it is,” Anderson said. An Associated Press report states the envelope containing the suspect powder is addressed to the Republican National Committee.

“[The letters] don’t seem to be connected, just on their face. But we’re not ruling anything out,” said Kevin McDonough, assistant postal inspector for the Boston division.

Unlike the envelope sent to Frist’s office, which was addressed by hand, the envelope containing the suspect powder was pre-addressed to the Republican National Committee and did not include a return address, McDonough said.

“This envelope that was addressed to the RNC was a pre-addressed enveloped,” he said, adding that it was the “type of envelope the RNC would have solicited donations from the public [with].”

In the meantime, the Senate’s three office buildings remain closed following the discovery of ricin powder in Frist’s office late Monday afternoon. Initial testing has shown it may be the toxin ricin.

The Capitol as well as House office buildings remained open early Tuesday morning; however, all mail delivery has been suspended. Unopened mail in the Senate office buildings is being collected and removed.

In remarks on the Senate floor this morning, Frist announced that debate would continue on the transportation reauthorization bill; however, some committee meetings may be canceled due to the building closures. The Senators will hold weekly policy lunches as scheduled. Vice President Cheney arrived at the Capitol this morning for a pre-scheduled meeting with the Republican Conference.

“There is no cause for alarm,” Frist urged at a Monday-night press conference prior to the announcement that the buildings would be closed. Staff working in a fourth-floor corridor facing Constitution Avenue were evacuated from the building Monday night.

“We’ve undertaken the procedures of decontaminating some 16 people who were on the floor,” Capitol Police Chief Terrance Gainer said. Ventilation systems were also shut down to prevent the possible spread of the material.

Capitol Police conducted at least eight tests of a white powder, first reported by a postal worker in Room 454 of the Dirksen Senate Office Building around 3 p.m. Monday. Six of the tests registered positive for ricin — a toxin derived from castor beans — prompting police to send samples to Fort Detrick in Frederick, Md., for additional testing. Results are expected Tuesday afternoon.

“This substance is being subjected to scientific testing but has preliminarily been identified as a form of ricin,” a notice on Frist’s Web site states. Frist described the powder as a “bioterrorist agent” at the press conference.

According to the Centers for Disease Control and Prevention, ricin is a “biologic toxin” that can be fatal if it is ingested or injected, although exposure can also occur through inhalation.

“Ricin is considered to be a much more potent toxin when inhaled or injected compared with other routes of exposure,” a CDC Web site states. Although a 500-microgram dose of ricin, equivalent in size to the head of pin, would be lethal if injected, the CDC notes, a “greater amount” would need to be inhaled or swallowed to be toxic.

Symptoms of ricin poisoning, which the CDC states develop within a few hours of inhaling “significant amounts of ricin,” may include difficulty breathing, fever, cough, nausea and tightness in the chest. The poison can prevent cells from producing necessary proteins, and can lead to kidney failure, respiratory failure, circulatory collapse and fluid loss.

“Nobody is sick. We don’t expect anybody to get sick,” Frist said Monday. According to the CDC there is no reliable test available to confirm ricin exposure. The Attending Physician’s Office referred inquires about the ricin incident to the Capitol Police.

An e-mail issued by the House Emergency Communications Center at 3 a.m. Tuesday morning states that no ricin contamination has been identified on the House side, but the Capitol Police have directed staff not to move, open or otherwise handle mail.

“Capitol Police are developing a protocol for the retrieval of mail previously delivered,” the e-mail states. Staff are advised to contact the police at (202) 225-5151 if they have suspicions about any mail items.

The FBI is assisting Capitol Police with the investigation, an FBI spokeswoman said Tuesday morning. Mailing a “threatening letter” is a federal offense, the spokeswoman explained.

Safety procedures for opening mail, including the use of irradiation to neutralize any potentially harmful substances, were implemented on Capitol Hill following the October 2001 incident in which anthrax-laced letters were sent to several offices, including that of Senate Minority Leader Tom Daschle (D-S.D.).

The 2001 incident shut down the Hart Senate Office Building for more than three months, until January 2002. The decontamination process, which required the use of chlorine dioxide gas, cost about $27 million.

The irradiation process would likely not affect ricin, which is classified as biotoxin, and according to the CDC is not affected by “extreme conditions such as very hot or very cold temperatures.” Irradiation can kill bacteria, such as anthrax, and other disease-causing germs.

The Postal Service is also in the process of installing new Biohazard Detection Systems in each of its major mail processing and distribution facilities, such as the Brentwood Mail Processing and Distribution Center in Northeast Washington. BDS can be programmed to detect a variety of “bioagents.”

“BDS is being installed to detect anthrax only, but the system is expandable and can test for other bioagents,” Anderson said, although he could not confirm if the system can detect ricin.

Anderson could not confirm whether a BDS unit will be installed at the V Street facility, but noted that all mail moved through the branch is irradiated. “The mail is sanitized no matter what it is,” he said.

In October 2003, an envelope containing a threatening note and a sealed vile containing ricin were processed at a Greenville, S.C., mail distribution facility. No apparent cases of ricin-related illness resulted from the incident. In January, the FBI, in conjunction with the United States Postal Inspection Service and the United States Department of Transportation, offered a reward of up to $100,000 for information leading to the arrest and conviction of the letter’s author.

The Senate is scheduled to convene at 9:45 a.m. Tuesday and the House will be in session as scheduled. The Senate restaurants are closed and Capitol tours are suspended. According to the Senate Web site, an announcement about the status of the Senate office buildings is expected at 5 p.m. Tuesday.