"The substance had arrived by mail and it was addressed to Donald Trump Jr.," said New York Police Department spokesman Carlos Nieves.
Vanessa Trump was hospitalized after she complained of nausea following her exposure, New York officials said.
Three patients from the household were transported to the NewYork-Presbyterian/Weill Cornell Medical Center for further evaluation, said Fire Department spokeswoman Sophia Kim.
The three included Vanessa Trump's mother, though she had not complained of symptoms, the police spokesman said.
Donald Trump Jr, the eldest son of U.S. President Donald Trump, has been in the public eye for his role in 2016 meetings with a Russian attorney and others where the Trump campaign was offered potentially damaging information about Democratic rival Hillary Clinton.
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