This is about the mandatory controls on toxic substances that presents risk of causing cancer.
Error 1: Substances should be plural.
Error 2: "a risk of" is the correct idiom which was just clouded or put in blur by one in a million chances... risk
as little as one in a million chances of
C and E uses "it" to refer to substances. This is wrong.
"A risk to cause" and "A risk for" are incorrect usage.
Impossible is nothing to God.