Carcinogenic Nitrosamines: Remediation by Zeolites

Abstract

Cancer is a terrible killer that destroys the health and career of humans. Among various factors that induce cancer and tumor, environment pollution is the chief criminal because it affects the human life timelessly and universally. Human cancer is influenced by life style, smoking and taking processed meats as well as overdrinking beer are harmful for health because of the existence of N-nitrosamines. N-Nitrosamines are compounds with an N-nitroso group N-NO. They have been recognized as strong carcinogens or potent carcinogens, and the nitrosamines in environment such as tobacco smoke cause serious health hazard to people. Tobacco smoking is associated with the cancers of lungs, larynx, oral cavity and pharynx, pancreas, kidney, and bladder. Consequently, the health consequences of exposure to environmental tobacco smoke has been a cause of scientific and public health concern because of increasing evidence showing that acute respiratory illness, chronic respiratory symptoms are associated with exposure to tobacco smoke. Nevertheless, no matter how often antismoking campaigns are shown, some people will never give up cigarette so that smoking is still a serious environmental problem in many countries. Tobacco-specific N-nitrosamines (TSNA) are the most abundant carcinogens identified in tobacco and tobacco smoke, and the health hazard caused by the TSNA in cigarette smoke has been well established. Besides, N-nitrosamines were known many years ago to be present in food treated with sodium nitrite, which made fish meal hepatotoxic to animals through formation of N-nitrosodimethylamine (NDMA). It is necessary to remove N-nitrosamines in environment in order to protect the health of people. However, it is difficult to selectively capture carcinogens in the environment where numerous constituents are mixed. For instance capturing and degrading N-nitrosamines in complex media such as tobacco smoke is a challenge for chemists. Here zeolite is a solution because it is a molecular sieve that can selectively eliminate carcinogens. Zeolite is a class of alumino-silicates, characterized by ordered micro-porous structures with acidic-basic sites on the surface and energetic field inside the pores. Zeolites have many applications, mostly as adsorbents and catalysts because of their unique shape-selectivity. This review includes some latest research progresses in adsorption and catalytic degradation of N-nitrosamines by zeolite materials, either fundamental or pilot researches, emphatically the special selectivity of zeolite toward N-nitrosamines along with the specific degradation manners of the carcinogens. Many efforts on elevating the efficiency of zeolite with metal oxides modifiers are described and the research progress on the removal of N-nitrosamines in smoke is summarized. Finally the development of new functional materials to control the pollution of N-nitrosamines is prospected.