干旱区生态环境知识资源中心

Desert varnish samples were collected near two coal-fired power plants to determine if the varnish contained a record of recent air pollution. Samples were collected: (1) in the fallout patterns of the shuttered Mohave Power Plant (MPP), located in Laughlin, NV; and (2) near the operating Reid-Gardner Power Plant (RGPP), just east of Las Vegas, NV. Small pieces of varnished rocks were analysed by field portable X-ray fluorescence spectroscopy (FPXRF). Results were obtained for 15 elements: Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Zr, Mo, Hg and Pb. The FPXRF data indicate that the elements commonly found in fly ash from coal-fired power plants (e.g. Cr, Zn, As and Pb) had significantly higher concentrations in the rock coatings in relation to the unvarnished substrate rock. For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the desert varnish coincided with the peak tracer concentration locations. Thus, these elements in desert varnish hold promise for identifying those geographical regions affected by nearby power plants. However, additional samples are required to demonstrate unequivocally that the power plants are indeed the sources of these elements. Overall, it is apparent that desert varnish can be utilised as a passive environmental monitor to investigate recent air pollution (past 20-30 years) and that FPXRF can be used as a surveying tool to obtain multi-element data from a large number of samples.