( CNN ) The Pueblo Chemical Depot will begin destroying the United States ' largest remaining stockpile of chemical weapons Tuesday in southern Colorado . There are 2,611 tons of World War II-era mustard agent at the Pueblo depot . Here are nine things to know about these chemical weapons and how we got here : . 1 . First use : April 22 marks the 100th anniversary of the first use of chemical weapons in modern warfare at Ypres in Belgium . 2 . Huge production : From World War I to 1968 , the United States produced nearly 40,000 tons of chemical weapons . These weapons were either nerve agents or blister agents . 3 . Scary stuff : Mustard agent is a blister agent , which can cause skin redness and itching , eye irritation , scarring , and an increased risk for lung and respiratory cancer . 4 . Into the sea : From 1967 to 1970 , the U.S. Army disposed of thousands of chemical warfare agents and ammunition into the sea as part of Operation Cut Holes and Sink 'Em ( CHASE ) . 5 . No more : Congress passed a law in 1972 known as the Marine Protection , Research and Sanctuaries Act prohibiting this kind of dumping . 6 . Date of destruction : In 1997 , the United States ratified the Chemical Weapons Convention Treaty and agreed to destroy all of its chemical weapons by April 29 , 2012 . 7 . Work not done : 90 % of the U.S. stockpile -- 30,500 tons -- was destroyed by the treaty date in 2012 at depots in Alabama , Arkansas , Indiana , Maryland , Oregon , Utah and Johnson Atoll in the Pacific . The remaining 10 % -- close to 3,100 tons -- is at two sites in Colorado and Kentucky . 9 . Do n't burn it : Residents in Colorado and Kentucky protested the use of incineration to get rid of the chemical weapons stockpile . The process of neutralization was adopted . 8 . Pueblo 's stockpile : The Pueblo Chemical Depot has about 780,000 shells containing mustard agent . 9 . The last one : The Blue Grass Army Depot in Richmond , Kentucky , will have the remaining chemical agent stockpile , which is a fifth of the size of the one at Pueblo Chemical Depot . But the Kentucky site has a larger variety of chemical weapons , including nerve agent .
On Tuesday , the Pueblo Chemical Depot will begin to destroy the largest stockpile of chemical weapons in the U.S . The U.S. government has spent more than a decade trying to get rid of its most dangerous chemicals and is now finally ready to do so.