The state is testing soil in neighborhoods near the Gowanus Canal in Brooklyn for potentially toxic vapors as part of a "soil vapor intrusion investigation,” officials said.

The New York State Department of Environmental Conservation is focusing on a 100-block radius near the polluted waterway, where around 100 property owners have already given permission for indoor air testing.

"This expanded soil vapor study has been communicated to the landlords and homeowners in the area we're targeting, and our doors are always open if residents have questions about what's going on," Sean Mahar, interim commissioner of the state’s DEC, said Sunday.

The Gowanus Canal has long been known as a heavily polluted waterway. Earlier this year,  DEC data revealed dangerous levels of cancer-causing chemicals inside some buildings, prompting further investigation, according to Mahar.

"Anytime we find elevated readings, that is a cause for concern with us. That's why we mobilized effectively right away to get in to do the sampling that we need to do and then take any mitigation efforts that we need," Mahar said.

Mahar said the DEC has been hosting availability sessions and putting out community newsletters to the thousands who live in Gowanus.

The DEC said the best time for testing is during the heating season — fall and winter months — when buildings are enclosed and more susceptible to soil vapor intrusion.