Ok well one way to look at it is we should have some interesting meteor showers in the future..two of the comets being new ones..Lemmon and Ison..that means two more debris clouds Earth gets to eventually go through... or is Pannstarrs new also? If so, that makes three. Quoting: PolarPrecursor
I think we go through the tail of Lemmon around August.
It is very unlikely that it is toxic in anyway.
However, the world is getting Very Weird and anything could happen?
So I will speculate a little more, here it is......
The tail of Lemmon sweeps across the Earth and is far richer in deadly Cyanide than the Science community predicted.
As the Earth meets the Tail of the Comet a Green grey cloud falls to the East of Baghdad and extends northwards,East of Moscow and South, covering India and Pakistan and many places to the East, Quickly dissipating, the toxic cloud poisons one fourth of the Planet in a North to South strip,engaging the sufferance of a multitude.Rolling quietly towards the East as the plane turns through that day.
Drought and famine take more than poison.
A Strictly speculative scenario, do with it what you will.
Laugh if you like.