Malignant transformation is a slow process. Children's ability to detoxify environmental chemicals is not fully developed. They lack certain mechanisms possessed by adults that enhance the removal of toxic chemicals from the body.
Thus children's exposures to environmental carcinogens must be minimised.
-- Pound for pound, children breathe more air, drink more water and consume more food than adults. This higher rate of intake means that children will receive higher doses of whatever contaminants are present in the air, water or food.
(In the US, it has been estimated that children aged 1-5 eat 3-4 times more per unit of body weight than the average adult. Infants and children drink more than 2 1/2 times as much water daily as adults do as a percentage of body weight. And the air intake of a resting infant is twice that of an adult under the same conditions.)
-- Children are also more susceptible to chemicals because of their smaller size. For example, a typical newborn weighs 1/20 of the weight of an adult male, but the infant's surface area is 1/8 as great. Therefore, the total area of skin that could be exposed to a chemical (by bathing in polluted water or rolling in dirt for instance) is 2 1/2 times as great per unit of body weight in the infant as in the adult.
-- Children absorb a greater proportion of many substances from the intestinal tract or lung. For example, children take up approximately half of the lead that they swallow while adults absorb only about one-tenth.
-- Children indulge in more hand-to-mouth activity than adults and transfer more foreign substances into their bodies through this route. Since children often play in the dirt, they are also closer to the source of many pollutants.
-- Children's biology is different. Their immune system is less developed, and may be less protective. For some toxicants, the body has developed biochemical detoxifying mechanisms; in some instances, these are less developed in children.
-- Cells that are developing (in children) are generally more vulnerable than cells that have completed development (in adults). This is particularly true for the central nervous system.