Cambria County Coroner Jeff Lees told WJAC that authorities believe Plummer absorbed a substance through her skin or had a reaction after handling drug paraphernalia while cleaning her son's home.
She began having shortness of breath and was taken to the hospital, where she died Nov. 6, WJAC reported. Her son died the next day, according to the news station.
"This is a caution for safety, for anyone coming into contact with any type of powder substance," Lees told WJAC. "You should use extreme caution and notify the proper authorities."
Authorities couldn’t immediately identify the drugs involved in the case. Toxicology results for the Plummers won't be back for another six to eight weeks.
The Cox Media Group National Content Desk contributed to this report.