Mainz, Germany  - The clean-up of a former plant which made horrific German poison-gas shells used in the First World War is complete after 20 years of work, an official told legislators Thursday.

The Espagit factory in Hallschlag, Rhineland Palatinate state accidentally exploded in 1920 when an estimated 20,000 poison-gas shells were on the premises. The debris meant the site was an ecological disaster area for decades.

Attacks with gas clouds on enemy lines during the First World War left huge numbers of men maimed or blinded. The Allies also resorted to the tactic. The Chemical Weapons Convention (CWC) now outlaws stockpiling and use of chemical weapons.

Espagit made chemical weapons from chlorine, arsenic and phosgene gas and had no waste-treatment ponds, simply spraying its effluent onto nearby barren hillsides so that it seeped into the ground.

The state government has paid engineers to recover the chemicals and old ammunition and to seal the ground with extra topsoil and wire-netting to prevent anyone digging up stray shells that may have been missed.

The state interior minister, Karl Peter Bruch, said in the state assembly in Mainz the project had cost 55 million euros (84 million dollars), 10 times as much as budgeted 20 years ago, but the site was no longer a danger to the environment. (dpa)