I have heard that 'wormwood' means Chernobyl in Ukrainian, so I looked into it, and apparently it is another word for it.
But still, Chernobyl didn't kill 1/3 of life on earth or poison 1/3 of the waters or whatever.
Lets take a look at the scripture to see whats to come:
Quote
"And the third angel sounded, and there fell a great star from heaven, burning as it were a lamp, and it fell upon a third of the rivers, and upon the springs of water; And the name of the star is called Wormwood: and a third of the waters became Bitter; and many people had died of the waters, because they were made bitter." (Revelation 8:10, 11 - KJB)
So, from what we know, it is literally "like a star" burning as it comes down. I suppose it could be a large asteroid or comet.
It causes 1/3 of the rivers & freshwater on earth to become poisoned.