Contamination (noun)

1. The presence or addition of impurities or pollutants in something.
2. The process of making something impure by adding impurities or pollutants.

Origin:

Late middle english: from latin contaminatio(n-), from the verb contaminare 'pollute', from con- 'together' + taminare, frequentative of tangere 'to touch'.

Examples:

1. The contamination of the water supply caused health problems for the residents.
2. The contamination of the food by bacteria was a major concern.
3. The contamination of the soil by chemicals was a result of the spill.
4. The contamination of the sample made it impossible to get accurate results.
5. The contamination of the air by pollution was a major issue in the city.