Benzo(a)pyrene and polycyclic aromatic hydrocarbons

Food Toxicology 2(2+0)
Lesson 24 : Polycyclic Aromatic Hydrocarbons and Other Processing Products

Benzo(a)pyrene and polycyclic aromatic hydrocarbons

A large number of PAHs have been identified as pyrolysis products of foods. PAHs most likely to pose human health problems are benzo(a)pyrene (3,4-benzpyrene, BP) and 7,12-dimethylbenzanthrene (DMBA). Although most PAHs, particularly the low-molecular-weight compounds, are noncarcinogenic, both PAHs and many other similar compounds are potent carcinogens that are active after metabolic conversion to electrophilic epoxide derivatives. Benzo(a )pyrene has been identified in the charred crusts of biscuits and bread, broiled and barbecued meats (up to 200 ppb in charcoal-broiled meats), broiled fish, and roasted coffee. Broiled high-fat hamburger contains about 43 ppb of PAHs, whereas lean beef may have only 3 ppb of PAHs. Steaks cooked close to the charcoal to be well done can produce.The amount of contamination by PAHs falls off rapidly as the distance of the meat from the charcoal increases. On heating starch to temperatures promoting pyrolysis (390?C), detectable benzo(a)pyrene (<1 ppb) can be formed, usually at the surface, e.g., bread crust.

The major site for PAH-induced carcinogenesis is the skin. Tumors can be produced at other sites following ingestion, but the concentrations required are quite high. Synthetic DMBA is an exception, which serves as a model PAH and is a potent inducer of mammary tumors. Inhaled PAHs (tobacco smoke) have been implicated in cancer of the respiratory system, and the magnitude of this disease is likely to be more than that by the dietary route. PAHs can induce cytochrome P450, an enzyme responsible for their bioactivation. Thus, dietary exposure may substantially increase the sensitivity to subsequent PAH exposures.

The toxic effects of PAHs in tissues other than germ cells have been demonstrated to be due to its metabolite, an epoxide, which interacts with DNA, RNA, and other macromolecules. Thus, the rates of epoxide forming and -detoxifying enzyme activities in various tissues can be important determinants of tissue-specific toxicity.

Long-term health effects of exposure to PAHs may include cataracts, kidney and liver damage, and jaundice. Repeated skin contact to the PAH naphthalene can result in redness and inflammation of the skin. Breathing or swallowing large amounts of naphthalene can cause the breakdown of red blood cells. Studies of workers exposed to mixtures of PAHs and other compounds have noted an increased risk of skin, lung, bladder, and gastrointestinal (GI) cancers. One of the greatest sources of exposure to PAHs is breathing these compounds in tobacco smoke.

Last modified: Friday, 24 February 2012, 10:33 AM