Five men in their 40s and 50s who worked for a chemical company handling dyes and pigments have developed bladder cancer, the health ministry said Friday.

The ailment is uncommon and attention has focused on the possible absorption of carcinogens at the factory.

The health ministry asked two chemical industry bodies — the Japanese Chemistry Industry Association and the Japan Dyestuff and Industrial Chemicals Association — to safeguard workers from exposure to certain chemicals by making sure they wear gas masks and get proper ventilation.

The ministry will also inspect 41 companies nationwide that deal with o-Toluidine, a particularly toxic chemical.

The ministry has declined to disclose the name or the location of the firm, which has a workforce of 40, citing ongoing investigations.

The workers, including one who has already left the company, each worked there for a period of 18 to 24 years. They were involved in the manufacturing of dyes and pigments that contain chemicals called aromatic amines. Some of the aromatic amines, such as o-Toluidine and o-Anisidine, are considered carcinogenic.

New regulations take effect in Japan in April on the handling of 24 aromatic amines.

“Japan is significantly behind other countries in measures against aromatic amines,” said Momo Takise, a spokeswoman for the Tokyo-based Nissenken Quality Evaluation Center. “It has been relatively strict on formaldehyde, but has left other toxic chemicals pretty much unregulated.”

The center offers testing for textiles under the international certification mechanism called Oeko Tex. Firms often need this certification to sell textile products overseas.

According to Takise, aromatic amines are among Azo dye compounds, which are used in a wide range of textile products, including clothes, bedsheets and towels. Azo compounds occupy nearly 70 percent of the 6,000 coloring agents, of which around 5 percent are known to generate carcinogenic aromatic amines.

The revisions to the Control of Household Products Containing Harmful Substances Law, which will come into force on April 1, will ban all products containing the 24 substances in concentrations of 30 milligrams or more per kilogram. Violators will be punished by up to a year in prison or a ¥300,000 fine.

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