Perchlorate salt in and round the Taklimakan Desert, China: its distribution and occurrence

Abstract

Perchlorate (ClO4-) is of growing concern due to its widespread occurrence on Earth and Mars, as well as potential adverse effect for human beings. In recent, the discovery of ClO4- on Mars has prompted a renewed interest in the formation and preservation of ClO4- in arid and semi-arid deserts on Earth, because the desert could serve as a viable analog for Martian landscape. In this study, we investigated the concentration of Cl-, ClO4-, and NO3- anions in sand, river sediment, moraine, and loess samples collected from the Taklimakan Desert, Xinjiang, NW China by ion chromatograph (IC). Furthermore, the speciation of Cl was determined for selected samples by the bulk XANES and μ-XRF-XRD-XANES techniques. The aims of this study are (i) to clarify the distribution of ClO4- in different types of samples and its possible formation mechanisms; (ii) to provide direct spectroscopic evidences for the presence of ClO4- in the sample; (iii) to provide insights into the prevalence of ClO4- on Mars. The moraine samples generally contain much higher concentrations of ClO4- in comparison with other samples investigated; which suggests that ClO4- could be readily preserved by the moraine resulting from its lack of liquid water. A weaker correlation between NO3- and ClO4- and the low ratios of NO3-/ClO4- were observed in the samples, possibly implying that atmospheric deposition of ClO4- produced by photochemical reaction in the atmosphere is not the only source for ClO4- in the samples from the Taklimakan Desert. These results were further confirmed by the Cl μ–XANES analyses showing different ratios of ClO4- in different interested points in the moraine sample.