The US city of Philadelphia issued a formal apology for experiments conducted on African-American inmates at a prison decades ago.

From the 1950s to the 1970s, inmates of Holmesburg Prison were intentionally exposed to pharmaceuticals, viruses, fungus, asbestos, and even dioxin, a component of Agent Orange.

The vast majority of those subjected to this wide range of experimentation were African-American men, many of them illiterate, awaiting prosecution, and attempting to save enough money to make bail, Xinhua news agency reported.

“This is yet another tragic example of disgraceful and unethical practices of medical experimentation on people of colour throughout our country’s history,” the city said on Thursday.

Philadelphia Mayor Jim Kenney also issued a statement, saying that “the historical impact and trauma of this practice of medical racism has extended for generations”.

“Without excuse, we formally and officially extend a sincere apology to those who were subjected to this inhumane and horrific abuse,” Kenney added.

“We are also sorry it took far too long to hear these words.”

The experiments were conducted by University of Pennsylvania researcher Albert Kligman, a long-standing faculty member in the Department of Dermatology before his death in 2010.

The university’s school of medicine in 2021 apologised “for the pain Kligman’s work caused to incarcerated individuals, their families, and our broader community”.