Del Norte County officials say a suspicious substance detected last week in the mailroom at Pelican Bay State Prison was identified in preliminary testing as ricin, a potentially lethal poison derived from the waste product of castor beans.No injuries have been reported and the investigation is ongoing.A joint statement from the county Sheriff’s Office, Office of Emergency Services and Public Health said the suspicious envelopes were received July 23 at the prison. The envelopes reportedly contained a then-unknown substance found during the prison’s mail-screening process.#placement_573654_0_i{width:100%;max-width:550px;margin:0 auto;}var rnd = window.rnd || Math.floor(Math.random()*10e6);var pid573654 = window.pid573654 || rnd;var plc573654 = window.plc573654 || 0;var abkw = window.abkw || '';var absrc = 'https://ads.empowerlocal.co/adserve/;ID=181918;size=0x0;setID=573654;type=js;sw='+screen.width+';sh='+screen.height+';spr='+window.devicePixelRatio+';kw='+abkw+';pid='+pid573654+';place='+(plc573654++)+';rnd='+rnd+';click=CLICK_MACRO_PLACEHOLDER';var _absrc = absrc.split("type=js"); absrc = _absrc[0] + 'type=js;referrer=' + encodeURIComponent(document.location.href) + _absrc[1];document.write('');The location where the suspicious envelopes was opened was immediately quarantined, according to the statement.Three people were taken from the prison to a hospital for medical evaluations and later were released.Public health officials notified those who might have been directly exposed and said they were working to ensure there was no further risk to the public.A collaborative investigation was launched by local, state and federal law enforcement and public health officials. A Humboldt County-based hazardous material team was called to the prison to conduct the initial testing.The material found in the envelope was sent to an accredited laboratory for further analysis. Subsequent tests reportedly were underway.The press statement said correctional operations and security at the prison were not affected by the investigation.Meantime, the Del Norte County Office of Emergency Services was activated to support medical health efforts in the area.The California Department of Corrections and Rehabilitation (CDCR) said in a statement that a letter claiming to contain a suspicious substance was received in the administration building at the prison. Investigators sealed the letter in a bag to contain the threat of exposure and the building was evacuated.Terry Thornton, the CDRC deputy press secretary, gave a statement to news station KRCR in which he said 116 employees who work in the administration building, mailroom and warehouse were put on a precautionary quarantine.Thornton said the employees were released the following morning, July 24, with no signs of illness or injury.Operations at Pelican Bay State Prison were otherwise normal and the inmate population was unaffected, according to Thornton.Centinela State Prison in Imperial, California reportedly had received a similar letter and subsequently evacuated staff from its mailroom. There were no injuries reported in that incident.CDCR assistant secretary Jeffrey Callison declined to comment on July 29 regarding details of the investigation beyond the official statement from his agency. googletag.cmd.push(function() { googletag.display('ad-1515727'); });