The poison that sickened 10 Japanese company employees after they drank tea brewed from the same water pot was a toxic sodium compound that affects the central nervous system, police said Tuesday.
Police still had no clues to who might have put the chemical in the pot, which had been filled with water between Friday night and Monday, they added.
The 10 workers at Xyence Co., a wood preservative company in Niigata, 256 kilometers (159 miles) northwest of Tokyo, were hospitalized Monday after suffering nausea and numbness during their morning tea break.
The case gave Japan another shock two weeks after curry laced with cyanide and arsenic killed four people at a festival in southwestern Japan. It also raised fears of copycat attacks.
Lab tests on the tea revealed traces of sodium azide, a chemical used in many industrial products, including air-bag mechanisms, said police spokesman Masashi Toma.
The victims of the poisoning were in stable condition, but three suffered mild liver disorders Tuesday, said Yasuo Hirose, an official at the Niigata City Hospital.
The March 1995 nerve gas attack on Tokyo subways carried out by the Aum Shinri Kyo religious cult has made Japan particularly wary of poisoning incidents. The subway gassing killed 12 people. (js)