Desert varnish is a thin manganese-iron rich dark coating that forms on rocks most often in arid climates. This coating may be up to a few hundred microns in thickness and is thought to grow by approximately one micron per thousand years. Recent research has shown that many elements are incorporated into this coating, and, in spite of its slow growth, it may serve as a passive environmental monitor for recent and historical air pollution. To test this hypothesis, small pieces of varnished rock were probed directly by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Results were obtained for 11 elements (13 The LA-ICPMS data indicate that many of the elements commonly found in fly ash from coal-fired power plants (e.g., Cr, Co, Ni, Cu, Zn, Cd, Sn, Sb, Tl and Pb) were highly enriched in the rock coatings in relation to the upper continental crust (UCC). For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the rock varnish coincide with the peak tracer concentration locations. Thus, these elements in rock varnish hold promise for identifying those geographical regions impacted by nearby power plants. Overall, the results indicate that rock varnish can be used as a passive environmental monitor of relatively recent events, and that the trace element fingerprints held in rock varnish may also hold much potential in forensic air pollution studies.

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A rapid method is presented for measuring V(IV) and V(V) in groundwater, without preconcentration or complexing agents, using direct injection of the water samples (which were collected under an argon atmosphere) into an ion chromatograph-inductively coupled plasma mass spectrometer (ICPMS). The mobile phase is 1.5% v/v nitric acid, which minimizes the buildup of solids in the ultrasonic nebulizer, the torch, and on the entrance cones of the ICPMS -a problem with methods using organic complexing agents and inorganic salts. The result is much less instrument downtime for cleaning the affected parts. Limits of detection are 0.02 g L -1 for V(IV) and 0.06 g L -1 for V(V). The pentavalent form of vanadium represents 98% to 99% of the vanadium in these Southern Nevada groundwater samples and ranges from 3.7±0.1 g L -1 to 82.1±0.5 g L -1 . The remaining few percent is V(IV). Total vanadium was determined by ICPMS for a mass-balance comparison.

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