toxicity vs perniciousness

toxicity and perniciousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
toxicity	Yes	No	No	No
perniciousness	Yes	No	No	No

As nouns, toxicity and perniciousness are synonyms defined as:

toxicity (noun)	perniciousness (noun)
grave harmfulness or deadliness	grave harmfulness or deadliness
the degree to which something is poisonous