Russ Research Group: Chemical / Biological Studies of Ancient Paints and Hazardous Explosive Detection

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My research is focused on two projects: (1) Chemical analysis of prehistoric rock paints; and (2) Methods to detect explosives at a distance. At first these might seem diametrically opposed, but in fact both require the use of sophisticated, state-of-the-art chemical instruments.

Chemical/Biological Studies of Ancient Paints in the Lower Pecos Region of Texas

For more than 7000 years humans inhabited the region around the confluences of the Pecos and Devils Rivers with the Rio Grande (see map).  Thousands of years before the Anasazi began leaving traces in the Four Corners Region, the earliest Texans began producing an incredible abundance of art—spectacular paintings that in some cases completely cover the back walls of large, dry rock shelters.  Based on radiocarbon analysis and stylistic interpretations, the vast majority of the rock art was produced between 3000 – 4000 years ago.  This coincides with a period of elevated human population, thus the production of the rock art might be connected to a distinct cultural phenomenon.  In other words, the creation of the paintings might very well be a response to natural stresses that are uniquely human. [Illustration: Map indicating the research area]

Our research uses state-of-the-art analytical methods to probe the mysteries of the art by understanding the chemistry of the ancient paints.  Specifically, we want to know what substances were used to prepare the paints, how various paintings or motifs are related based on chemical similarities, and how the ancient paints remain intact on the  rock substrate.  The most compelling question in the study of prehistoric rock paints is the nature of the vehicle/binder, i.e., fats or oils added to inorganic pigments to create a fluid paint that adheres to the rock surface.  Our most recent study used gas chromatography-mass spectrometry (GC-MS), which led us to conclude that the only fats or oils that remain in the paints today are not from the original paint recipe, but instead from microbes that are growing on the rock surface (Spades & Russ, 2005). [Photo: The "Ghost Shaman" in Fate Bell Shelter]

Another study was aimed at identifying the organisms that occur naturally the rock surfaces, and how these microbes impact the preservation of the rock art.  Although most of the paintings appear clear to the naked eye, in actuality the paint layers are encased within a natural rock coating composed almost entirely of calcium oxalate.  This is easily observed in the photograph here, a side-view of a thin-sectioned sample of paint.  Our results demonstrate the there are numerous strains of bacteria growing on the rock surfaces, mostly the species Bacillus.  Moreover, these microbes produce calcium oxalate, at least in culture media.  Thus, that these artifacts remain intact for thousands of years is not due to characteristics of the paints, per se, but from natural bacterial producing a mineral accretion that keeps the paints attached to the rock substrate (Hess, Coker, Loutsch & Russ, 2007). [Photo: Side view of typical paint sample]

Standoff Hazardous Explosive Detection System (SHADES)

Improvised Explosive Devices (IEDs) are the n umber one cause of casualties in Iraq.  Our research, funded by the U.S. Department of Defense, is aimed at developing a new system for detecting explosives rapidly and at a distance in environments such as the streets of Iraq.  This Standoff Hazardous Explosive Detection System (SHADES) is being developed by a team of scientists and engineers at Arkansas State University, Radiance Technologies, and here at Rhodes.  Our group is focused on three interconnected studies:  (1) Sample collection, (2) concentrating explosive compounds , and (3) detection of target compounds. [Photo: Prof. Russ (left) with student researchers]

Sample Collection

One of our primary objectives is to develop an air collector that eliminates dust, dirt and sand prior to injection into the extremely sensitive SHADES detector.  We are testing various virtual impactors to isolate the target compounds we detect from airborne particulate matter, the latter is discharged from the device while the former is injected into the detector system.

Concentrating Explosive Compounds

Once the air sample is “cleaned” via the virtual impactor, the next step is to extract and detect the explosives.  We are employing Solid Phase Micro-Extractors (SPMEs) to simultaneously collect and concentrate explosive molecules for final analysis.  The SPME is a small polymer fiber that has an affinity to various classes of compounds, in our case we are using 2,4-dinitrotoluene (DNT) as our primary target analyte since this is the primary degradation product of TNT (2,4,6-trinitrotoluene).

Detection of Target Compounds

Our group is using gas chromatography with an electron capture detector (GC-ECD) to detect explosive compounds.  We are experimenting with various instrument parameters, SPMEs and valve systems that allow us to minimize the amount of sample that we can detect.  On the left is a typical result (chromatogram) of a single experiment, where the presence of the target compound (2,4-DNT) is observed via the peak  on the right side of the chromatogram.  This peak was the result of analyzing a particular SPME exposed to the target compound for five seconds.