The Environment Ministry plans to launch a survey this year on the dumping of medical substances by hospitals, ministry officials said Saturday.

The ministry will begin examining samples taken from rivers near some hospitals amid concern the chemical substances may pose a hazard to humans and the ecosystem, they said.

With the absence of a ban, some hospitals are believed to be dumping surplus medicine into rivers even though some drugs contain toxic substances or components suspected of inducing genetic mutations.

"We have so far been unable to take measures despite being aware of the dangers to some extent. We hope to use the survey as a tool to determine the effect of medicines on the environment and the necessity of restrictions," an official in the ministry's Environmental Safety Division said.

The survey will be conducted as part of the ministry's annual investigations of various chemical substances in the environment, carried out since 1974 when the ministry was still the Environment Agency.

The ministry will examine the environment for contamination of four drugs this fiscal year -- antiepileptic phenobarbital and phenytoin, antipyretic-analgesic phenacetin and dermatologic agent methoxsalen.

It plans to expand its inspections gradually to include such medicines as antibiotics and anticancer drugs.