While smoking among 15 to 19 year olds did show a substantial dip from 1981 to 1986, the proportions of young smokers rose again over the 1990s.

Exposure to POPs during development and in utero is currently considered an important, plausible mechanism for the etiology of certain cancers of reproductive tissues.

Long-Latency Carcinogens

Because of the long-latency of most carcinogens, childhood exposures presumably also have implications for most adult-onset malignancies. For instance, it is now well established that childhood exposure to ultraviolet radiation that leads to severe sunburn is a strong risk factor for adult development of melanoma (see below). Only a few other types of adult-onset cancers, however, are as well linked to specific causal exposures during childhood.

Tobacco

Despite ongoing debate concerning the role of exposure to ETS in inducing cancer during childhood, there is agreement that lifetime exposure to ETS considerably increases the odds of developing several types of cancer in adulthood. A child's exposure to tobacco carcinogens can be both passive and active. The latter is of particular concern as Health Canada statistics indicate that while smoking among 15 to 19 year olds did show a substantial dip from 1981 to 1986, the proportions of young smokers rose again over the 1990s.

Asbestos

Chronic exposure to asbestos has been associated with significantly greater risk of lung cancer and malignant mesothelioma in adults. Both these associations came to light from studies of those occupationally exposed, such as workers in asbestos mines, shipyards and production of insulation materials. These cancers do not appear to develop until many years or decades after such long-term exposure. However, because there appears to be no threshold below which exposure to asbestos is safe, it is appropriate to minimize exposure as early in life as possible.

Asbestos fibres are extremely durable and are heat-, fire- and acid-resistant. As a result, substantial amounts of asbestos were used in a variety of products in homes, schools and public buildings constructed prior to the 1980s. Risk of exposure and subsequent health effects occurs when the asbestos fibres are airborne, such as when the asbestos-containing material deteriorates. Inhaled asbestos fibres can become lodged in the lungs. Children can be exposed where there is deteriorating asbestos in schools or homes built before the 1980s. They can also be exposed to fibres brought home on the clothing, shoes or bodies of parents whose work involves asbestos.

The British Columbia Ministry of Health document, "Asbestos: When Should I Worry?" elaborates on the health effects from asbestos and provides some suggestions for determining if there is risk of exposure to asbestos in the home.

Ultraviolet Radiation

Ultraviolet radiation in the 290 to 320 nm wavelengths of the light spectrum, the so-called UV-B rays of sunlight, is highly penetrating and is associated with the most significant damage to skin. Cumulative, lifetime damage to skin cells, especially in individuals who always burn easily can result in several types of skin cancer. Of these, malignant melanoma is the greatest public health concern since it has demonstrated rapidly rising incidence rates and can be associated with significant mortality.

It appears that episodic, acute exposure to sunlight (i.e., seasonal exposure) that is sufficient to cause blistering sunburn during childhood and adolescence substantially increases the risk of melanoma in adulthood.70 For this reason, public health campaigns have strongly emphasized the importance of protecting infants, children and youths from excessive sun exposure as a preventive measure. (The environmental etiology of skin cancers is considered in detail in the unit on dermatological effects.)

POPs

The recent National Research Council Review of Literature concerning health effects from hormonally active agents (i.e., endocrine disruptors) included consideration of their potential role in human carcinogenesis. While they conclude that there is only limited evidence of a link between adult exposure to persistent organic pollutants and various cancers, the NRC highlights that there is essentially no research on the carcinogenic effects of exposure to such environmental agents during development and in utero.71 This is currently considered an important, plausible mechanism for the etiology of certain cancers of reproductive tissues.

The increase in testicular cancer incidence in Ontario between 1964 and 1996 has been greatest among adolescent and young men aged 15 to 29 years.72 These trends agree with reports of increased incidence in testicular cancer worldwide.73 It is speculated that this trend may reflect greater prenatal exposure to hormonally active toxins.74