Collocations for contamination - noun

serious, widespread
possible, potential
environmental, food, soil, water
bacterial, chemical, radioactive

level
There is already a high level of environmental contamination.

cause
avoid, prevent
minimize (esp. AmE), reduce

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

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

contamination with
Wash everything thoroughly to avoid contamination with bacteria.

a risk of contamination
a source of contamination