Investigation of associations between chemical element contents in native lichens and childhood leukaemia

After a study in which the harmful atmospheric chemical elements (As, Hg, Ni, Pb) were investigated as leukaemia inducers, we have extended this work to 22 chemical elements using data from a lichen survey held in 1993 in Continental Portugal and childhood leukaemia death counts in 275 counties for the period 1991?1998. Kriging models were used to estimate lichen biomonitoring measurements at the county level. Bayesian spatial hierarchical models were used to explore the association between these and childhood leukaemia death counts. A significant positive association between the risk of childhood leukaemia and the levels of chlorine was found. Industries related to the emission of carcinogenic chlorine compounds and/or carcinogenic compounds, which easily react with atmospheric chlorine, were pointed out as potentially inducing this association.