A mutagen is anything that can cause permanent changes in an organism's genetic material, usually DNA, thus resulting in mutations. Mutations are changes in DNA sequences that can affect gene functioning and that can be inherited. While many mutagens can be carcinogenic (i.e., cancer-causing), not all mutagens necessarily cause cancer, and not all carcinogens are mutagens.
Mutagens can be classified into chemical, physical and biological. Among the former are some widely used petrochemicals (such as benzene, vinyl chloride and ethylene oxide), tobacco products, and some compounds of various metals (including of aluminum, arsenic, cadmium, chromium, lead, manganese, mercury, molybdenum, nickel, selenium and tellurium). Physical mutagens include ionizing radiation (such as X-rays, gamma rays, and cosmic rays), ultraviolet radiation and extreme heat. Biological mutagens include some viruses, some bacteria and some transposons.
The most common mechanism by which mutagens cause mutations is by directly reacting with DNA and altering its chemical structure, which leads to errors during DNA replication. Another type of direct damage to DNA is the breaking apart of its strands by ionizing radiation. Others include blocking DNA replication and insertions into the DNA thereby distorting the helix.
Some substances, called protomutagens, are not mutagenic in themselves but become mutagenic after they are metabolized in the body, typically by enzymes in the liver. Examples include aflatoxin, which is produced by certain molds on grains and peanuts, benzopyrene, which is found in tobacco smoke and charred foods, and nitrosamines, which are found in some preserved foods and formed in the stomach from nitrites and amines.
The deterioration of the earth's environment, including the ever-growing pollution of the air, water, soil and foodstuffs, is contributing to an increase in exposure by humans and other organisms to mutagens. The consequences can include an increased cancer risk, a rise in inherited diseases, an acceleration of aging and age-related diseases, damage to reproductive health and fertility, and an increased incidence of chronic and metabolic diseases. They also include an increased risk of extinctions, particularly for species with small population sizes or that are already under stress from other factors (such as habitat loss and climate change), thus reducing biodiversity and disrupting ecosystems.