The U.S. Department of Health and Human Services (HHS) have added four more substances to the human carcinogen list.

On Thursday, Oct. 2, the agency released its 13th Report on Carcinogens, which is a document identifying physical, biological and chemical agents that are potential cancer hazards for all people residing in the United States. The latest report lists 243 carcinogens

The HHS report highlights that ortho-toluidine, a substance that is used in the manufacturing process of pesticides, dyes and rubber chemicals, has been re-evaluated and is now listed as "known to be human carcinogen." It was previously listed as "reasonably anticipated to be a human carcinogen." Some previous studies have associated the substance to bladder cancer.

Three other substances have been listed as "reasonably anticipated to be a human carcinogen." The first of these three substances is 1-bromopropane, a colorless liquid used in spray adhesives. The substance is used for dry cleaning and also to get rid of residues from electronics and metals. When the substance is inhaled it may cause tumors to develop in the lungs, digestive tract and skin.

The second of the "reasonably anticipated" substance is cumene, a colorless and flammable liquid that is found in refined fuels and crude oil. When cumene fumes are inhaled it may result in the development of lung and liver tumors.

The last substance added in the new list of carcinogens is pentachlorophenol (PCP), which is a mixture of chemicals generally used as a pesticide, wood preservative and disinfectant. Even though the substance is very dangerous, it is also very effective and increases the life span of wood. People who work in the production and treatment of wood are normally exposed to the substance as well as its by-products that are also included in the new list. Exposure to PCP is believed to cause tumors in several organs. It also increases the risk of blood cancer.

"Identifying substances in our environment that can make people vulnerable to cancer will help in prevention efforts," says Linda Birnbaum, director of the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program (NTP).

Birnbaum suggests that the release of the report is important as it provides research agencies and health regulatory agencies with valuable details about the listed carcinogens. The report is also important to general public so that they can be aware of the harmful effects of the substances and reduce their exposure to these carcinogens.