Viruses, X-rays and compounds found in grilled meats joined the official list of known or suspected cancer-causing agents.

The list, issued every two years by the National Institute of Environmental Health Sciences and the National Toxicology Program, also adds chemicals used in textile dyes, paints and inks.

"For the first time ever, viruses are listed in the report: hepatitis B virus, hepatitis C virus, and some human papillomaviruses that cause common sexually transmitted diseases," the NIEHS said in a statement.

They include the hepatitis B and hepatitis C viruses, which can cause liver cancer, and human papillomaviruses, also known as human wart viruses, which are sexually transmitted and can cause cervical cancer.

About 1 million U.S. residents are chronically infected with hepatitis B and 3 million with hepatitis C virus, both of which can be transmitted by injected drug use, sexual contact and blood transfusions.

An estimated 20 million people in the United States are infected with genital wart viruses, which often produce no symptoms, and 5.5 million new people are infected each year.

"Other new listings include lead and lead compounds, X-rays, compounds found in grilled meats, and a host of substances used in textile dyes, paints and inks," the NIEHS said.

"X-radiation and gamma-radiation are listed in the report as 'known human carcinogens' because human studies show that exposure to these kinds of radiation causes many types of cancer including leukemia and cancers of the thyroid, breast and lung," the agency added.

"The risk of developing cancers due to these forms of ionizing radiation depends to some extent on age at the time of exposure."

Children exposed to high levels of X-rays have a higher risk of leukemia and thyroid cancer, while men and women exposed to chest area X-rays at certain times can have higher risks of breast and lung cancer.

"Exposure to X-radiation and gamma radiation has also been shown to cause cancer of the salivary glands, stomach, colon, bladder, ovaries, central nervous system and skin," the NIEHS said.

Sources include medical scans, scientific research, military testing and nuclear accidents.

Industrial chemicals added to the suspected carcinogen list include naphthalene, an ingredient in mothballs and toilet bowl deodorants, and lead used to make lead-acid storage batteries, ammunition, and cable coverings.

Also included are heterocyclic amine compounds, which are formed when meats and eggs are cooked or grilled at high temperatures and also found in cigarette smoke.