Use of P-XRF Spectrometers for Pesticide Detection:
a Case Study of Navajo Textiles Treated with Arsenic
Martina Dawley1*, Jae Anderson2 and Nancy Odegaard3
1Arizona State Museum, University of Arizona, USA
2Department of Agriculture Biosystems Engineering, University of Arizona, USA
3Department of Materials Science & Engineering, University of Arizona, USA
Submission: March 26, 2018; Published: June 20, 2018
*Corresponding author: Martina Dawley, Assistant Curator of American Indian Relations, Arizona State Museum, University of Arizona, 1013 E. University Blvd. Tucson, AZ 85721,Email: firstname.lastname@example.org
How to cite this article: Martina D, Jae A, Nancy O. Use of P-XRF Spectrometers for Pesticide Detection: a Case Study of Navajo Textiles Treated
002 with Arsenic. Glob J Arch & Anthropol. 2018; 4(5): 555647. DOI: 10.19080/GJAA.2018.04.55D5647
The development of a protocol to test for significant presence of arsenic-based pesticide residues was undertaken using an Olympus Innov-X Delta Professional Portable X-ray fluorescence (pXRF) spectrometer on a significant textile collection at Arizona State Museum (ASM). The non-destructive / non-invasive technique was utilized due to its handheld movability, fast detection and differentiation for a broad range of elements, and internationally adopted by the field of museum conservation as a viable scientific tool in testing cultural materials. Preparing a range of known contaminated arsenic-based wool samples resulted in instrumentation calibration for confident levels of arsenic-based residues. Assuring confident levels of arsenic detection with a pXRF spectrometer initiated a protocol to safely and efficiently test the textiles.
After a history of use in environmental conservation on the analysis of soils and sediments, the p-XRF spectrometer or analyzer has become a powerful instrument in museum conservation. One important use is in the detection of toxic metals found in pesticide residues such as arsenic (As), lead (Pb), mercury (Hg), and zinc (Zn).In the past, pesticides, herbicides, and fungicides were commonly used to prevent, destroy, repel or mitigate pests to preserve museum collections. Thus, museum professionals are interested in the chemical analysis of potentially treated material cultural items, because they want to know what a substance is composed of (qualitative) and how much is present (quantitative) . Its use for detection of toxic metal pesticide residues has evolved from sealed radioactive sources, which depend on the half-life of the source, to the use of x-ray tube sources. The newer instruments can detect and differentiate a broader range of elements, including lighter elements, with improved analytical software that allows for batch processing of data. The pXRF instrument is capable of being calibrated using given elemental concentrations vs. calculated elemental concentrations, termed empirical calibration . An award from the National Center for Preservation Training and Technology (NCPTT) funded the purchase of an up-to-date x-ray tube source pXRF analyzer, to develop calibration standards, and to test a collection of 430 Dine’ (Navajo) textiles.
A handheld p-XRF instrument’s “detection limits are a function of testing time, sample matrix, and the presence of an interfering element” . The Olympus Innov-X Delta pXRF is equipped with a silicon drift detector (SDD) that converts X-rays emitted from atoms into electric signals producing a limit of detection of <5ppm for low-density arsenic samples (i.e. soils, powders, and liquids). Thus, a one-to-two-minute test results in a detection confidence of 99.7% .
Given no available industry reference standards for arsenic in wool, the need to develop empirical calibration standards for a p-XRF spectrometer was essential for assured wool textile arsenic analysis. On startup, an initial calibration check procedure was conducted against an alloy 316 stainless steel coupon to determine a variety of parameters are within factory pre-set tolerances. Following p-XRF startup procedures, additional measurements were conducted on an uncontaminated wool control sample and other potential interfering elements, such as underlying testing surfaces, to verify negative presence of arsenic.
The p-XRF calibration method was a sequential series of steps starting with an investigation into the properties related to Navajo textiles. This led to preparing 15 Chimayo wool test
samples to be homogeneous contaminated with five known
arsenic concentrations (5000ppm, 2500ppm, 1000ppm,
500ppm, and 100ppm) and tested with the p-XRF instrument.
Each concentration set consisted of three samples dipped into
one arsenic solution, air-dried, and p-XRF tested in five different
areas to ensure uniformity and quality of concentration. Each
p-XRF reading was conducted in the manufacturer’s “soil” mode
for a period of 90 seconds with beam settings at 40kV for 60
seconds and 15kV for 30 seconds. A p-XRF arsenite (As III)
calibration curve for dry wool p-XRF readings resulted in a linear
regression of 99% as shown in (Figure 1) .
As pesticide residues of toxic metals (As, Hg, Pb, and Zn)
on wool textiles are generally not visible and do not have an
odor, the potential health hazard of poisoning was generally not
evident to collectors, curators, researchers, or students handling
and examining them up close. Thus, to determine the potential
human health risk, the handheld p-XRF instrument proved to be
the fastest, least invasive, and most efficient method for analysis.
All the Navajo textiles in the collection were tested, the readings
were recorded, compiled, and organized into a schematic of
very high to very low arsenic levels . In addition, the highest
occurrences of arsenic could be organized by collectors/donors,
regional location, and historical era.
50 textiles were initially tested. They were systematically
removed from storage cabinets, unrolled, and examined. After
following the p-XRF calibration protocol, a four-quadrant system
was used to determine the approximate location where the
textile readings were taken. The quadrants were identified as
Q1, Q2, Q3, Q4 based on available photographs or sketches of
each textile. The location of the textile catalog number label was
used to orient the position of the textile in a photograph. The
convention for catalog number label placement was the back
side of the textile so that side was recorded as recto label and the
reverse side was recorded as verso label. A distinction for testing
sites above the catalog number or below the catalog number was
based on the way the catalog number tag was positioned to be
read right-side up. Initial readings for the textiles were made
directly above or below the catalog number label and included
5 to 10 readings taken from the recto and verso for each textile.
Preliminary data showed that textiles with less than 100ppm
of arsenic from the first reading were most likely to have
subsequent readings below 100ppm. Likewise, if the first p-XRF
reading was higher than 100ppm then subsequent readings
were most likely to have subsequent readings above 100ppm.
The testing protocol was modified after the textiles were tested.
For the remaining textiles initial readings were made above or
below the catalog number label while the textile remained rolled
in storage if the catalog number label was easily seen (Figure
2). If the label was not easily accessible, the textile had to be
removed and unrolled. Furthermore, if the p-XRF readings tested
above 100ppm, then the textile was removed from the cabinet,
unrolled, and tested in two or more random areas recto and
verso to the label, and plotted using the four-quadrant system.
The p-XRF analyzer was a useful tool for completing an
important survey for the presence of arsenic on a large and
significant Arizona State Museum textile collection. Calibration
standards based on known chemical concentrations of arsenic
on wool textile samples were critical. For example, within the
group of tested textiles having more than 100ppm of arsenic,
69% were made and collected in the 1800s, 26% were made
and collected in the 1900s, and 5% had an unknown time-period
Navajo textiles proved to be an excellent object-form for this
type of investigation because they have a uniform format, density,
and consistent use of wool. They are secular objects woven for
several types of use and were often treated with pesticides to
prevent or arrest insect damage. The pXRF survey provided
important knowledge of arsenic-based pesticide residues in
Arizona State Museum’s textile collection, identified trends
relating to time-period and collector, and created a foundation
for further research. The pXRF continues to be an important
tool for pesticide residue detection in museum collections but
external calibration samples provide important user confidence
in the instrumentation and data results generated during