Chemical mutagenesis

The interaction of certain environmental chemical compounds and cell metabolism may result in genetic changes in DNA structure, affecting one or more genes. These chemicalinduced mutations are known as chemical mutagenesis. Many cancers and other degenerative diseases result from acquired genetic mutations due to environmental exposure, and not as an outcome of inherited traits. Chemicals capable of inducing genetic mutation (i.e., chemical mutagenes or genotoxic compounds) are present in both natural and man-made environments and products.

Many plants, including edible ones, produce discreet amounts of some toxic compound that plays a role in plant protection against some natural predator. Some of these natural compounds may also be genotoxic for humans and animals, when that plant is consumed frequently and in great amounts. For instance, most edible mushrooms contain a family of chemical mutagenes known as hydrazines; but once mushrooms are cooked, most hydrazines evaporate or are degraded into less toxic compounds.

Among the most aggressive man-made chemical mutagenes are:

• • asbestos
• • DDT
• • insecticides and herbicides containing arsenic
• • industrial products containing benzene
• • formaldehyde
• • diesel and gasoline exhaust
• • polychlorinated biphenyl (PCB)

Exposure to some of these compounds may occur in the work place, others can be present in the polluted air of great cities and industrial districts. For instance, insecticide and herbicide sprayers on farms, tanners, and oil refinery workers are frequently exposed to arsenic and may suffer mutations that lead to lung or skin cancers. Insulation and demolition workers are prone to contamination with asbestos and may eventually develop lung cancer. Painters, dye users, furniture finishers, and rubber workers are often exposed to benzene, which can induce mutations in stem cells that generate white blood cells, thus causing myelogenous leukemia. People working in the manufacture of wood products, paper, textiles and metallurgy, as well as hospital and laboratory workers, are frequently in contact with formaldehyde and can thus suffer mutations leading to nose and nasopharynx tumors. Cigarette and cigar smoke contains a class of chemical mutagenes, known as PAH (polycyclic aromatic hydrocarbons), that leads to mutation in lung cells. PAH is also present in gas and diesel combustion fumes.

Except for the cases of accidental high exposure and contamination, most chemical mutagenes or their metabolites (i.e., cell-transformed by-products) have a progressive and gradual accumulation in DNA, throughout years of exposition. Some individuals are more susceptible to the effects of cumulative contamination than others. Such individual degrees of susceptibility are due to discreet genetic variations, known as polymorphism, meaning several forms or versions of a given group of genes. Depending on the polymorphic version of Cytochrome P450 genes, an individual may metabolize some mutagenes faster than others. Polymorphism in another group of genes, NAT (N-acetyltransferase), is also implied in different individual susceptibilities to chemical exposure and mutagenesis.

See also Immunogenetics; Mutants, enhanced tolerance or sensitivity to temperature and pH ranges; Mutations and mutagenesis