Police were called at 13:38hrs on Thursday, 10 August to reports of an unidentified substance being delivered in an envelope to a business in Stoney Street, SE1.
Officers, London Ambulance Service and London Fire Brigade attended.
The property was evacuated as a precaution.
The substance has now been identified as a naturally occurring substance.
Three people were treated at the scene for minor injuries as the result of an irritant and did not require hospital treatment.
The premises will be handed by officers back over to the owners soon.
No arrests have been made.
This is not being treated as a terror related incident.