Which preposition to use with adulteration

of Occurrences 20%

Is not the adulteration of food just now as scandalous as it is unchecked?

by Occurrences 1%

Adulteration by means of these leaves is by no means a new species of fraud; and several acts of parliament, from the time of George II., have been passed, specifying severe penalties against those guilty of the offence, which, notwithstanding numerous convictions, continues to the present time. 1798.

Which preposition to use with  adulteration