Chlorine and childhood cancer

Maria do Carmo Freitas of the Technological and Nuclear Institute in Sacavém, Portugal, and statistician Maria Martinho of the Department of Economic and Social Affairs at the United Nations Headquarters in New York, USA, emphasise that potential emissions from paper-related industry, forest fires, pesticides manufacturing, heavy chemical industry and fossil fuel power stations may lead to higher levels of chlorine-containing carcinogens in the air.

Freitas and colleague have investigated the correlation between atmospheric pollution levels of 22 chemical elements, including arsenic, nickel, lead and mercury, as gleaned from an analysis of lichens used as biomarkers of these pollutants and looked at the leukemia deaths in 275 counties across Portugal.

They explain how lichens have been used as accurate biomarkers of pollution levels since the 1970s. Lichens are excellent biomonitors because they depend largely on atmospheric depositions for their nutrient supply, thus showing elemental compositions which reflect the gaseous, dissolved and/or particulate elements in the atmosphere, the team explains. Collecting and analysing lichens across a large geographical area thus reveals the elements present in the air across that area and so gives researchers a map of pollutants which can be overlaid with epidemiological data, on leukemia incidence, for example.

The team further explains that leukemia typically results from malignant transformation of white blood cells and accounts for almost a third of all cancers in children under the age of fifteen years. In Portugal, during the period 1970 to 1999 there were 30 cases per million children each year on average. However, while some evidence has linked the disease to exposure to ionising radiation or to the known carcinogen benzene the cause of most cases remains unknown. Previous work has also found no correlation between atmospheric levels of arsenic, mercury nickel and lead as revealed by lichen surveys. However, chlorine-content has been associated with the incidence of diabetes and there are significant associations with malignant growths and bromine, iodine, nickel, lead, sulfur, antimony and vanadium contents of lichens.

"The significant association found of course does not imply causality," explains Freitas. "More research will be needed to confirm causality and if so the underlying mechanisms."