The Environment Ministry on Wednesday added four more substances to a priority list of agents that are being studied to determine the risks they pose as endocrine disrupters, ministry officials said.

A ministry investigative panel on endocrine disrupters decided during a meeting Wednesday to include butyl benzyl phthalate, diethyl phthalate, diethylhexyl adipate and triphenyl tin on the list, the officials said.

The first three are substances used in the making of plastics while the latter is used in paints for the hulls of ships, they said.

This brings the number of substances on the priority list to 12, they said.

The substances will be assessed for their effects on human reproductive functions, according to the officials.

The ministry has been conducting a risk-assessment program on the endocrine-disrupting properties of more than 40 chemical substances since the beginning of fiscal 2000. The program is scheduled to run for three years.

Medical equipment

The Health Ministry will check plastic medical equipment for the presence of endocrine disrupters, ministry sources said Wednesday.

The Health, Labor and Welfare Ministry will check whether endocrine disrupters -- which may affect sperm production -- are present in equipment such as plastic bags and plastic tubes used for drips or dialysis and whether they are absorbed by humans, the sources said.

It will be the first time for the government to check medical equipment for the presence of endocrine disrupters, the sources said. Previous safety checks have focused on dioxin generated when the equipment is burned.

Plastic equipment is widely used in medical institutions because it is relatively inexpensive and durable.

But experiments on animals indicate a substance called DEHP, which is used as an additive to process one kind of plastic, affects sperm production.