Their derivatives are used in plastics and as flame retardants in many different products. They're super common. Sorry no citation. I'm an organic chemist that have worked with those chemicals
"If your hand causes you to sin, cut it off. It is better for you to enter into life maimed, rather than having two hands, to go to hell, into the fire that shall never be quenched— where 'THEIR WORM DOES NOT DIE AND THE FIRE IS NOT QUENCHED.' And if your foot causes you to sin, cut it off. It is better for you to enter life lame, rather than having two feet, to be cast into hell, into the fire that shall never be quenched— where 'THEIR WORM DOES NOT DIE AND THE FIRE IS NOT QUENCHED.' And if your eye causes you to sin, pluck it out. It is better for you to enter the kingdom of God with one eye, rather than having two eyes, to be cast into hell fire— where 'THEIR WORM DOES NOT DIE AND THE FIRE IS NOT QUENCHED.'"
(Mark 9:43-48 NKJV)
His emphasis: the condemned people's worm will not die (there is no more death! per Revelation 20) and their fire will not be quenched. ie they will suffer for eternity.
Jesus' teaching on hell:
"Then his master, after he had called him, said to him, 'You wicked servant! I forgave you all that debt because you begged me. Should you not also have had compassion on your fellow servant, just as I had pity on you?' And his master was angry, and delivered him to the torturers until he should pay all that was due to him."
(Matthew 18:32-34 NKJV)
This is a parable that teaches about heaven and hell. His point is that when God is offering such generous forgiveness to you and you refuse to forgive, you won't be forgiven and you will pay for all that you owe. In my case, the debt of punishment for my sins was paid for by Christ on the cross through His death, but in this person in the parable's case, he will have to pay for all of his sins on his own by being tortured until it's all paid. When will that be accomplished? It'll take eternity.
Furthermore, in Malachi 4:1, etc the context will tell you that God's point there is that there will not be any residual influence (root) or legacy (branch) from sinners in heaven.