In this process a piece of tissue is cut from a healthy plant and grown in a sterile environment into several plantlets that root in pasteurized soil before being transferred to the field.

FORBES: Millions Served

Soldiers may be getting it from soil or from field hospitals in Iraq or even the big U.S. base in Landstuhl, Germany.

FORBES: War Wounds

However in the case of Neal Soil Suppliers - where dairy and food effluent was spread over a field - there had been "substantial and serious pollution".

BBC: Gwent Levels waste dumping: David John Neal pleads guilty