NEWBURGH, N.Y. — In this chronically struggling city along the Hudson River, residents beset by poverty, high crime, and boarded-up homes now have an entirely new worry: that their tap water may have exposed them to a chemical linked to cancer.

State officials recently launched an ambitious effort to offer blood tests to Newburgh’s 28,000 residents after the chemical PFOS — used for years in firefighting foam at the nearby military air base — was found in the city’s drinking-water reservoir at levels exceeding federal guidelines.

‘‘The fact that I’ve been drinking that water for years, and my daughter’s been drinking and bathing in it, that’s shocking to me,’’ said Stuart Sachs, who moved to Newburgh from Brooklyn 14 years ago. ‘‘My daughter is 11. What diseases is she going to have to look forward to? It’s scary.’’

PFOS, or perfluorooctane sulfonate, has been linked to cancer, thyroid problems, and other serious health issues.

Results of the blood testing won’t tell people whether they are actually at increased risk for any specific health problem, but will show how their exposure compares to others.

Associated Press