Are Environmental Factors contributing to the growing Incidence of Cancer?

Across the EU, cancer is responsible for one death in four. Geneticsusceptibility contributes to cancer, as do certain lifestyle-relatedfactors, but this is not all. It was previously suggested thatlifestyle-related factors, improvements in screening and long lifeexpectancy alone could not account for the recently observed growingincidences of cancer in high income countries. Indeed, certainenvironmental factors might play a more important role in carcinogenesisthan previously expected.A team of European and American researchers recently analysed thecarcinogenic effect of certain environmental factors rated as certainly orpotentially carcinogenic by the International Agency for Cancer Research(IACR). To this end, the authors have overviewed the existing scientificliterature in order to explain the current increase in cancer incidence andto justify the hypothesis according to which this could mainly be relatedto environmental factors. In particular, they analysed the examinedmicroorganisms (including viruses), radiation (including radioactivity,ultraviolet (UV) rays, and pulsed electromagnetic fields) andxenochemicals.The main results are as follows:In addition to ionizing irradiation (such as the exposure to radon or nuclear activities) non-ionizing irradiation including UV and pulsed electromagnetic fields (EMF) can cause cancer, in particular, skin cancer (UV), some acute leukaemia and brain tumours in children (EMF). Regarding outdoor air pollution, long-term exposure in adults to particles and to polycyclic aromatic hydrocarbons (PAH), for example in the air of polluted cities, can increase the risk of death due to lung cancer by 8% (without considering the effect of tobacco smoking). The risk is higher for the more polluted cities and smoking can add to this risk. A recent European study estimated that the proportion of lung cancer attributable to traffic-related air pollution and environmental tobacco smoke (ETS) in never- and ex-smokers was 5%-7% and 16%-24% respectively. In addition to PAH and fine particles, NO2 might also be involved. The relevance of pesticides in carcinogenesis is steadily increasing. In children, several epidemiological studies revealed an increased relative risk of cancer associated with parental exposure to occupational or non-occupational pesticides. Moreover, a positive association has been found by several studies testing the direct exposure of children to pesticides. On the other hand, epidemiological studies in adults have provided conflicting results. For dioxins, although their carcinogenic mechanisms are not clear, a strong association between chronic exposure and an increased incidence of all cancer types has been put forward. Chlorine is not itself carcinogenic but combined with organic matter in drinking water, it forms chlorination disinfection by-products (e.g. trihalomethanes and haloacetic acids) that have been demonstrated to be mutagenic both in vitro and in vivo. Certain metals and metalloids have been rated as certain or probable carcinogens by the IARC. For example, lung cancer has been reported to be associated with exposure to heavy metals, including lead, hexavalent chromium and nickel. Nevertheless, their mechanism of action is not yet well understood. Overall, this study provides evidence that supports the fact that, due totheir mutagenic and/or promoting properties, many environmental factors,including viruses, radiation and xenochemicals can contribute to causing avariety of cancers. The need remains to estimate the overall risk fractionattributable to these environmental factors.Source: Belpomme D. et al. (2007) « The multitude and diversity ofenvironmental carcinogens »,

Environmental Research, In Press.
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