"it was concluded that concentrates were being stolen from shipments in transit and replaced with inert material."

Sneaky buggers!! I wonder if they got the idea from watching Breaking Bad!

... they steal methylamine from a train that runs through New Mexico but Walt calls the task impossible. Jesse comes up with a plan involving siphoning off 1,000 gallons and replacing it with water.

http://www.youtube.com/watch?v=dQ4xMGmH9ho