Elemental Analysis of Desert Varnish Samples in the Vicinity of Coal-Fired Power Plants and the Nevada Test Site Using Laser Ablation ICPMS

Abstract

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.

Rock varnish in New York: An accelerated snapshot of accretionary processes

“…New York varnishes display the same sub-micron cross-sectional texture of layering imposed by clay minerals, contain clay minerals as seen in HRTEM imagery, and host a variety of microbial forms that are enhanced in Mn in in situ EDS observations. There are dozens of elements enhanced in arid varnish over background values (Bard et al, 1978;Dorn et al, 1990;Lakin et al, 1963;Nowinski et al, 2010), including the zinc and barium observed here. However, rhenium enhancement has not been observed previously in arid varnishes.…”

“…Despite two centuries of research on riverine and other non-arid rock varnishes, the last few decades have seen researchers focus on Mn-rich coatings in deserts (Boizumault et al, 2010;Christensen and Harrison, 1993;Flood et al, 2003;Garvie et al, 2008;Hodge et al, 2005;Kuhlman and McKay, 2007;Kuhlman et al, 2006a;Lee and Bland, 2003;Liu and Broecker, 2007;Liu and Broecker, 2008b;Nowinski et al, 2010;Patyk-Kara et al, 1997;Perry et al, 2006;Schelble et al, 2005;Wang et al, 2011;Zerboni, 2008;Zhang et al, 1990;Zhou et al, 2000). The reasons for the apparent recent bias toward desert settings are unclear; it could have to do with the sociology of science where researchers focus on a perceived funding source, for example NASA-supported research regarding Martian analogs (DiGregorio, 2002;DiGregorio, 2010;Marlow et al, 2011).…”

Microanalytical methods for in-situ high-resolution analysis of rock varnish at the micrometer to nanometer scale

“…The source of these elements might be dust that was leached by rain or dew (Thiagarajan and Lee 2004). An atmospheric contribution to the varnish genesis was previously verified for Pb, Hg (Nowinski, Hodge et al 2010, Nowinski, Hodge et al 2013) and 210 Po (Hodge, Farmer et al 2005) enrichments in the outer varnish layers, elements that were emitted by nuclear testing sites, coalfired power plants and smelters. The enrichments in Ce, also observed in the REE patterns as positive Ce anomalies (Fig.…”

“…Nevertheless, all Californian samples have significantly higher Pb concentrations than the samples from Israel and South Africa (about 10 times more). The explanation therefore might be a larger Pb input by human activity in this area, for example from the previous use of leaded gasoline or from power plants (Nowinski, Hodge et al 2010, Dorn, Moore et al 2012.…”

Suitability of Mn‐ and Fe‐Rich Reference Materials for Microanalytical Research

“…The RMs were then used as microanalytical RMs for LA-ICP-MS investigations of Mn-rich materials (Garbe-Sch€ onberg and McMurtry 1994, Axelsson et al 2002, Hlawatsch et al 2002, assuming a sufficient homogeneity. Furthermore, the homogeneous NIST SRM 61X and USGS GSE-1G glasses were used for calibration of Mn-rich materials (Hlawatsch et al 2002, Huelin et al 2006, Wayne et al 2006, Xu et al 2007, Nowinski et al 2010, Macholdt et al 2015, although these samples have low Mn and/or Fe contents.…”