De-contaminating is the process of removing or neutralizing harmful substances from an object or environment. Its antonyms refer to the opposite of this process, meaning either leaving harmful agents as they are or introducing them. The antonym for de-contaminating would be "contaminating," which means introducing harmful agents such as toxins or pollutants into an object or environment. Another antonym for de-contaminating is "polluting," which means making an area or substance dirty, impure, or unhealthy. Lastly, "poisoning" is also an antonym, indicating the intentional or accidental introduction of harmful substances into an object or the environment.