Controls on the valence species of arsenic in tobacco smoke: XANES investigation with implications for health and regulation.

Arsenic (As) is one of four metals/metalloids in tobacco being considered for regulation. In vitro toxicological response to As varies substantially, determined primarily by valence and compound speciation, and inorganic arsenite (As(III)) compounds are the most toxic to humans. This study uses X-ray absorption near edge structure (XANES) to determine valence states of As from the tobacco plant to the crucial combustion stage that creates respirable smoke. Samples studied include cultivated plants (some burdened with additional As), reference standards, and commercial products, along with smoke condensate and ash from these samples. The relative contributions of As(III) and As(V) to the XANES spectra are analyzed, and a consistent pattern of redox changes emerges. Tobacco leaf and manufactured products tend to be dominated by As(V) whereas combustion produces respirable smoke invariably in As(III) form and ash invariably as As(V). The valence state of precursor tobacco is not a controlling factor because all the As mobilized in smoke is reduced during combustion. This study concludes that tobacco combustion exposes smokers to potentially the most toxic forms of arsenic, and this exposure is magnified in regions where arsenic is present in tobacco crops at relatively high concentrations.

Inorganic arsenic levels in rice milk exceed EU and US drinking water standards.

Under EU legislation, total arsenic levels in drinking water should not exceed 10 microg l(-1), while in the US this figure is set at 10 microg l(-1) inorganic arsenic. All rice milk samples analysed in a supermarket survey (n = 19) would fail the EU limit with up to 3 times this concentration recorded, while out of the subset that had arsenic species determined (n = 15), 80% had inorganic arsenic levels above 10 microg l(-1), with the remaining 3 samples approaching this value. It is a point for discussion whether rice milk is seen as a water substitute or as a food, there are no EU or US food standards highlighting the disparity between water and food regulations in this respect.