The others arrested include a man in charge of pollution control and a labour welfare officer, police said, adding all were held late last night.
They said bodies of five workers were handed over to the next of kin yesterday, while two others, hailing from Nepal, were cremated here.
Meanwhile pollution control board officials said power connection to the factory had been cut and the unit would be sealed, pending further investigations.
Initially, two workers accidentally fell into the tank. Several other colleagues jumped into the tank to rescue them.
However, many of them fainted after inhaling the toxic gas. Seven of them, in the age group of 21-35, died on the spot while nine others were rescued by fellow workers and fire and rescue service personnel.