Synthetic Kryptonite Gas (UE-43)

Synthetic Kryptonite Gas is an experimental chemical weapon created by the DOD.

History
After John Henry Irons attacked the DOD, Sam Lane took his Pre-Crisis doppelgänger's keychain and adopted the latter's concept to weaken Kryptonians. The gas was then developed among multiple type of weapons, with it being utilized by a eradicated Reno Rosetti against Superman.

The gas later infected Jordan Kent and caused water in his lungs to freeze up. Eventually, Clark was forced to send him to the Fortress of Solitude and use a thermal technology in order to burn the Kryptonite out of his system. While the Kent family dealt with the infection, Lane arrived in Smallville with a canister of the gas and used it against the Subjekts.

Overview
The Synthetic Kryptonite Gas is able to invade Kryptonian (and hybrids) respiratory system, weakening them from inside their body and allow them to be vulnerable to traditional combat and military tactics. The gas is also infectious, causing respiratory diseases similar to a flu and also causing water to freeze its victims' lungs due to their power of superhuman breath.