We banned use of Carbon tetrachloride back in 1987. It was a great chemical for cleaning clothes and electronics - it evaporated completely, dissolved most organic dirt but didn't touch fabric or components and was non-conductive. It was also a great conductor of heat and used for cooling in some electronics designs. It was also highly effective for fighting fires. A stream of CCl4 would evaporate into a large cool cloud displacing all the Oxygen the fire needed to sustain itself.
It was also a great destroyer of Ozone and considering that our Ozone layer is what keeps us from getting terminal sunburn every time we step outside, the ban was a good thing.
The funny thing is, it is not going away. From the American Geophysical Union:
Ozone-depleting compound persists, new research shows
New research shows Earth’s atmosphere contains an unexpectedly large amount of an ozone-depleting compound from an unknown source decades after the compound was banned worldwide.
Carbon tetrachloride (CCl4), which was once used in applications such as dry cleaning and as a fire-extinguishing agent, was regulated in 1987 under the Montreal Protocol along with other chlorofluorocarbons that destroy ozone and contribute to the ozone hole over Antarctica. Parties to the Montreal Protocol reported zero new CCl4 emissions between 2007-2012.
However, the new research shows worldwide emissions of CCl4 average 39 kilotons (about 43,000 U.S. tons) per year, approximately 30 percent of peak emissions prior to the international treaty going into effect.
“We are not supposed to be seeing this at all,” said Qing Liang, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study published online in the Aug. 18 issue of Geophysical Research Letters, a journal of the American Geophysical Union. “It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources.”
My bet is marine algae - there is so much that we do not know about the Ocean that covers 70% of our Planet.