The University of Tokyo’s medical school discharged at least 5 tons of formalin solution, a preservative, into sewers over five years and has been engaging in the practice for 30 years, it was learned Tuesday.

University authorities said water quality tests on the chemical cleared the Tokyo Metropolitan Government’s waste standards.

The facility has been dumping the solution for the past 30 years, sources at the university, also known as Todai, said.

The university will recycle formalin solution in tanks as a temporary measure, officials at the institution said.

Although the practice may not violate the Poison Law and the Waste Disposal Law, the metro government will investigate and issue directives to the institution, the officials said.

According to the university, its forensic laboratory usually uses about 50 liters of 15 percent formalin solution to preserve a human body.

It has dumped the solution for about 100 bodies every year into the public sewage system, it said, noting that some blood from the bodies was also discharged after sterilization.

The university’s pathology laboratory also dumped a small amount of formalin solution, it added.

The metro government officials said formalin is considered a medicine and a toxin by law, but there are no clear guidelines directing how to properly disposed of it.