The Environment Ministry said Monday it has finished a preliminary assessment to determine if 39 chemicals pose a potential danger to humans and wildlife, and will perform in-depth tests on five chemicals that appear especially pernicious.

The research is part of a pilot program that will guide future efforts to gauge the harmfulness of some of the nearly 50,000 chemicals commercially circulating throughout Japan.

Of the 39 potentially harmful substances targeted by the ministry, 18 were found to pose a comparatively low risk to human health, while 15 were deemed to pose low risk to ecosystems. However, there was not enough information to evaluate the dangers posed by each chemical, and the ministry was unable to determine if nine could jeopardize human health and 15 could damage ecosystems.

Five chemicals -- acetaldehyde, p-dichlorobenzene, diethylhexyl phthalate, formaldehyde and dieldrin -- were deemed enough of a risk to merit further study.

All of the chemicals have received attention before, most notably diethylhexyl phthalate, a suspected endocrine disrupter used to soften plastics that came under scrutiny after it was found to be leaching from gloves used to handle boxed lunches.

The results of the tests on the five chemicals receiving further attention should be released during the summer. Steps will be considered to reduce levels of chemicals ultimately found to pose serious risks to people and ecosystems, the officials said.