Unmanifested dangerous good loaded onto helicopter

During routine helicopter operations a helideck assistant (HDA) picked up a case containing a water testing kit whilst back loading cargo onto the Helicopter. This cargo was not destined for the Helicopter and as such was not on the manifest. The heliport was advised of the error after the helicopter had left. It was later discovered that a small vial of liquid containing ethanol (15ml) was inside the case.