Hydrogen-deficient molecules in natural riverine water samples—evidence for the existence of black carbon in DOM

Understanding the role of black carbon (BC) in the natural environment is very important because of the potential impacts of black carbon on human health, global carbon cycling, and pollutant transport. There has been circumstantial evidence for the existence of black carbon molecules in dissolved organic matter (DOM); however, direct evidence has been lacking. In this paper, the presence of black carbon-like material in DOM is demonstrated for the first time. Electrospray ionization (ESI) with ultra-high resolution mass spectrometric analyses of DOM samples reveals the existence of hydrogen-deficient molecules. The van Krevelen analysis of the ultra-high resolution mass spectra clearly differentiates black carbon-like material from the complex assemblage of other, relatively hydrogen-rich natural molecules and indicates that the hydrogen-deficient molecules in the DOM are from black carbon-like material. The observation of black carbon molecules in DOM suggests that BC may be degraded and included in the active carbon pools of the earth.