Collocations for contamination - noun

massive, serious, widespread | cross-
Chopping boards can be a source of cross-contamination.

environmental, food | bacterial, radioactive

level
There is already a high level of environmental contamination.

avoid, prevent | reduce

~ by
Always keep food covered to prevent contamination by flies.

~ from
There is a danger of serious contamination from radioactive waste.

~ with
Wash everything thoroughly to avoid contamination with bacteria.

a source of contamination