Metals are acquired by the growing tobacco plant from soil, fertilisers, and industrial pollution. Smoking liberates some of these metals from tobacco into smoke to be inhaled by the smoker and bystanders. Arsenic, cadmium, nickel and lead are the main contributors to the health risks of metals in smoke. The health risk depends on the 'form' of the metal. The burning process may completely transform the metal from a low toxicity form to high toxicity, and vice versa. In research commissioned by the RIVM, chromium in tobacco smoke was found in its least toxic form. Arsenic, by contrast, is present in its most toxic form. The research was conducted by the University of St Andrews in Scotland.

This report describes the chemical form, or speciation, of several metals known to be present in tobacco and tobacco smoke. To this purpose, we used one of the world's most powerful synchrotrons, the Diamond Light Source, in the UK. This was necessary, as it is difficult to determine the speciation of arsenic and chromium in tobacco and tobacco smoke. The results of the experiments were in good agreement with predictions based on theoretical models. Therefore, these models were also used to predict the chemical composition of other metals present in tobacco smoke.

During our study, TobReg, the WHO expert panel set up to advise on the scientific basis of tobacco product regulation, has recommended that manufacturers test the levels of arsenic, cadmium, lead and nickel in tobacco. The results of the present study support the prioritisation of metals in their list.