Police have held four people in China after a piece of radioactive Iridium-192 was reported missing on Friday at 2:00 am. The material was later retrieved in Nanjing, Jiangsu on Saturday.

The four detained workers admitted losing the Iridium-192 on Saturday afternoon. After undergoing health examinations, all of the 93 employees of a construction site in Nanjing showed normal results, according to China Daily.

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Nanjing environmental bureau's nuclear and radiation management department director Zhang Shida said they first received a report about the incident on Friday at 2:00 am. They teamed up with the police to form a response team.

When the Tianjin Hongdi Engineering Inspection Development Co Ltd conducted a monitoring operation at the construction site near Puliu on Wednesday morning, they discovered that the Iridium-192 was missing.

On Saturday morning, the response team narrowed down the search area to a two-meter-squared-area 1 kilometer from the said site. The radioactive material was found at 5:00 pm.

To ensure safety, the 10 people deployed in the area used protective clothing and only conducted a search for a maximum of two minutes. The soybean-sized Iridium-192 was then placed inside a lead container by the team.

Zhang said the Iridium-192's radioactive effect will not stay in the environment after it was removed, and it cannot be passed from one person to another.

The environmental bureau said the material was covered by a plastic bag. So, this could mean that someone might have touched the material before throwing it away.

According to Tang Shuangling, director of Nanjing University of Science and Technology's radiation prevention department, the Iridium-192's harmful effect depends on the length and strength of the radiation.

Tang also cautioned people not to pick up metals and instructed them to avoid touching objects with illuminant surfaces. He said these objects must first be tested by professionals.

The news about the missing radioactive material had been circulated online on Friday evening and was shared over 10,000 times, but the official information was not released until Saturday noon.