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Prepositions after verbs

Contaminate with or contaminate by?

With usually names the contaminating substance. By often names the source, process, or agent causing contamination.

Quick answer

Choosing with or by

Use contaminated with for the harmful material itself and contaminated by for the cause or source. The active verb contaminate also commonly takes a direct object.

The water was contaminated with lead.
The river was contaminated by factory waste.
Chemicals can contaminate soil quickly.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
contaminated with + substance

Naming the pollutant

With introduces the harmful material found in something.

The food was contaminated with bacteria.
2
contaminated by + source

Naming the cause

By introduces the agent or source responsible.

The beach was contaminated by an oil spill.
3
contaminate + object

Active verb use

The verb often takes a direct object without a preposition.

Smoke can contaminate indoor air.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
contaminate with
The milk was contaminated with chemicals.
focus on the substance present
contaminate by
The site was contaminated by industrial waste.
focus on the source or cause
contaminate + object
Pesticides contaminated the river.
active transitive use

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Using by for the substance itself

With is more natural when naming the material found in something.

✕ The water was contaminated by lead. ✓ The water was contaminated with lead.

Adding unnecessary prepositions in active clauses

Contaminate can directly take an object.

✕ The chemicals contaminated with the soil. ✓ The chemicals contaminated the soil.

Quick practice

Choose the expression that matches the intended meaning.

1. The vegetables were contaminated ___ pesticides.
2. The lake was contaminated ___ nearby factories.
3. Toxic smoke can contaminate ___ air inside homes.

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Frequently asked questions

Can both with and by be correct in one sentence?

Yes. For example: The river was contaminated with mercury by mining operations.

Is contaminate formal?

Yes. Pollute is often broader and more common in everyday contexts.

Can contaminate describe ideas or data?

Yes. It can be used figuratively, as in contaminated data.

calculate, by, calculate, in, calculate, from "call for" or "call on"? "campaign for" or "campaign against"? cancel by, due, at, in or for? capitulate to, in, like, by or after? captivate by, for, with, from or in? "capture by" or "capture in"? "care about" or "care for"? carry with, by, in, to or into? carve into, out, in, on or with? cast in, into, for, by or on? "catch in", "catch by" or "catch on"?

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