Cd isotope fractionation during tobacco combustion produces isotopic variation outside the range measured in dietary sources

Abstract

Cadmium production has risen 1000-fold in the past 100 years, from under 20 to over 20,000 tons per year, causing anthropogenically-mobilized Cd to overwhelm natural sources in global cycling. Cadmium has no known biological function in humans, yet has biochemical behaviors similar to zinc and manganese, making exposure detrimental to human health. Identifying and quantifying the sources of Cd for human sub-populations is key to reducing exposures. Cadmium stable isotopes may provide a method for tracing Cd sources throughout the environment and the human body, but at present the limited database for high precision Cd isotopic compositions is inadequate to support such an analysis. Here, we provide new Cd isotope data on dietary sources, cigarette smoking components, and environmentally relevant standard reference materials. Results indicated that minor but significant variations are observed in food products (e.g., peanuts, sunflower seeds, spinach, kale, lettuce, cocoa powder; ~0.9‰ at 4 amu) that may be useful for tracing contamination in agricultural soils. In contrast, Cd isotope fractionation during smoking is larger (~6‰ at 4 amu) and has implications for tracing cadmium sources from tobacco combustion in the environment and throughout the human body. The primary inhaled component of cigarette smoke contains highest delta values (δ116/112Cd or δ114/110Cd ~5.2‰), while the second-hand smoke and cigarette ash have the lowest delta values (δ116/112Cd or δ114/110Cd ~−0.9‰). Used cigarette butts have δ114/110Cd ~2.4‰, in between the values measured in ash/s hand smoke and the inhaled smoke components. The high delta values of the inhaled smoke indicate that Cd isotopes may be used to determine the extent of Cd exposure due to smoking in human biological samples. This study provides new data for previously uncharacterized isotopic reservoirs that can be included in future studies of Cd source-exposure tracing.