This document summarizes a study that used portable X-ray fluorescence spectrometry (XRF) to rapidly detect toxic metals like lead in non-crushed oyster shells. The researchers developed a methodology to use a portable XRF to simultaneously detect multiple elements in oyster shells without crushing them. Lead contamination was confirmed in contaminated oyster shells using both XRF and scanning electron microscopy with energy dispersive spectroscopy (SEMeEDS). The portable XRF provided a quick, non-destructive, and cost-effective way to assess lead contamination in oyster shells.

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Rapid detection of toxic metals in non-crushed oyster shells by portable X-ray
fluorescence spectrometry
Ju Chou a,*, Garret Clement a
, Bradley Bursavich a
, Don Elbers a
, Baobao Cao b
, Weilie Zhou b
a
Department of Chemistry and Physics, Southeastern Louisiana University, Hammond, LA 70402, USA
b
Advanced Material Research Institute, University of New Orleans, New Orleans, LA 70148, USA
A rapid, simultaneous multi-element analytical methodology for non-crushed oyster shells has been developed using XRF and contamination
of lead on oyster shells was confirmed by XRF and SEMeEDS.
a r t i c l e i n f o
Article history:
Received 30 August 2009
Received in revised form
10 February 2010
Accepted 15 February 2010
Keywords:
Portable XRF
Lead (Pb)
Contamination
Oyster shells
SEM
EDX
a b s t r a c t
The aim of this study was the multi-elemental detection of toxic metals such as lead (Pb) in non-crushed
oyster shells by using a portable X-ray fluorescence (XRF) spectrometer. A rapid, simultaneous multi-
element analytical methodology for non-crushed oyster shells has been developed using a portable
XRF which provides a quick, quantitative, non-destructive, and cost-effective mean for assessment of
oyster shell contamination from Pb. Pb contamination in oyster shells was further confirmed by scanning
electron microscopy with energy dispersive spectroscopy (SEMeEDS). The results indicated that Pb is
distributed in-homogeneously in contaminated shells. Oyster shells have a lamellar structure that could
contribute to the high accumulation of Pb on oyster shells.
Published by Elsevier Ltd.
1. Introduction
Environmental pollution by toxic metals such as lead and
arsenic is a global environmental issue. It received special atten-
tions in New Orleans, Louisiana after Hurricane Katrina (Cobb et al.,
2006; Abel et al., 2007; Mielke et al., 2006). Louisiana is the nation's
largest oyster producer in the United States, and simultaneously,
hundreds of million pounds of oyster shells are disposed of annu-
ally as wastes. Enormous amounts of oyster shells have been
disposed into public areas and lands. If they were left in toxic metal
contaminated areas, the toxic metals could accumulate on oyster
shells (Huanxin et al., 2000; Gifford et al., 2006). Very recently our
research group used a portable X-ray fluorescence (XRF) for field
screening for soils in New Orleans to identify lead contaminant
sites. Surprisingly oyster shells were found to be contaminated by
lead in a residential area in New Orleans. Being that New Orleans is
famous for seafood where oyster shells are everywhere, this has
become a major environmental concern.
Oysters could be contaminated with a variety of toxins from their
surroundings (Gold-Bouchot et al., 1995; Hayes et al., 1998). Lead
contamination in oysters and their shells were found in different
countries (Gold-Bouchot et al., 1995; de Astudillo et al., 2005; Jeng
et al., 2000) in the world. Oyster shells are normally analyzed by
different techniques such as atomic absorption spectroscopy
(Huanxin et al., 2000; Tudor et al., 2006), inductivelycoupled plasma-
atomic emission spectroscopy (ICP-AES) (Protasowicki et al., 2008;
Chang et al., 2007; Kilbride et al., 2006), X-ray diffraction analysis
(XRD) (Medakovic et al., 2006), scanning electron microscopy-energy
dispersive spectroscopy (SEMeEDS) (Medakovic et al., 2006; Yoon
et al., 2003) and other techniques. (Almeida et al., 1998; MacFarlane
et al., 2006). Most of analyses were done on crushed shell samples
and required a sample treatment/digestion process.
A portable XRF is a surface analytical technique and has been
widely used for screening heavy metals including toxic metals. It
provides rapid and non-destructive analysis which is an ultimate
goal of the field analysis. It can also spontaneously analyze multi-
elements, mainly heavy metals (Hou et al., 2004; Radu and
Diamond, 2009). So far, its primary use is analyzing multi-
elements in soils and air filters (Mark et al., 1995; Hürkamp et al.,
2009; Melamed, 2005). A recent application for determination of
metal residues in active pharmaceutical ingredients by XRF was
reported (Margui et al., 2009). We are developing an analytical
method for rapid detection of toxic metals, especially Pb on
contaminated oyster shells by a portable XRF. Since the method-
ology is applied to non-destructive shells, it provides toxic metal
* Corresponding author.
E-mail address: Ju.Chou@selu.edu (J. Chou).
Contents lists available at ScienceDirect
Environmental Pollution
journal homepage: www.elsevier.com/locate/envpol
0269-7491/$ e see front matter Published by Elsevier Ltd.
doi:10.1016/j.envpol.2010.02.015
Environmental Pollution 158 (2010) 2230e2234

3. Author's personal copy
contamination on both inner shells and outer shells. It would also
eliminate procedures associated with sample treatment/digestion,
thus this technique can minimize volume of hazardous waste. The
method reported here could be used across the United States and
elsewhere in the world.
2. Material and methods
2.1. Sampling and XRF analysis
Three oyster shells were collected from a residential area in New Orleans and the
Seafood Market located in downtown Hammond, Louisiana. Each oyster shell was
sealed in a reclosable zip-bag bag and was brought back to the research lab for
analysis. All of oyster shells were then carefully washed with distilled water to
remove all dirt on shell surfaces. After each shell was dried completely, it was then
directly analyzed by a portable XRF.
In this study, non-crushed oyster shells were analyzed by a handheld Alpha XRF
analyzer provided by Innov-X Systems, Woburn, MA. The Innov-X Alpha XRF consists
of an X-ray tube and has a solid state silicon PiN diode detector. The XRF analyzer was
configured for Soil Mode and the energy was set at 40 keV and the current was set at
35 mA by the manufacturer. The X-ray beam is 6 mm in diameter. The soil mode is
employed in this analysis. The analyzer was standardized first by a standardization
cap for Soil Mode analysis and this was done each time when it was turned on. A
standard check with a Pb standard solution on a clean oyster shell was measured after
standardization. Various elements (most of metals) were then detected simulta-
neously by the XRF. By determining intensities of X-rays at a particular frequency
during a given amount of time, the concentration of that particular element in the
sample can be determined as ppm (one part per million). In this study, the
measurement time was 30 s for all measurement. The measurement time was
determined bya pre-test on an oyster shell. The time required was less than 30 s when
the relative standard deviation of Pb was set at 10% in the XRF analyzer. After each
measurement, metal concentrations were generated immediately in ppm and
experimental results were exported into a computer for analysis. The ppm unit was
converted to mg/Kg.
The quantitative analysis of Pb is based on emission line of 12.61 eV (Lb1) since this
line does not overlap with any emission lines of As. Typically, the emission line of As
Ka1 (10.54 eV) interferes with the Pb La1 (10.55 eV). The Inno-X XRF analyzer uses the
As Ka1 and Pb La1 lines to quantify As by simple subtraction when they are both
present. This correction usually leads to fairly accurate results for As measurement.
The quantitative analysis of Sr is determined by Sr Ka1 line at 11.47 keV. The detection
limit for Pb and As is 10 ppm claimed by the manufacture. If the concentration of Pb
and As was lower than 10 ppm, <LOD (limit of detection) is reported.
The program employed in this study is supplied by the manufacturer and it is
proprietary. Data can be displayed as concentrations of elements in ppm for each
element measured or be graphed as an X-ray fluorescence spectrum for an indi-
vidual test as desired. The spectrum is displayed as the intensity on the y-axis versus
the energy of the fluorescence X-rays on the x-axis. The program also allows one to
export data into an Excel file for further data analysis.
This standardization does not considered the roughness of oyster shells which
could affect the quality of the measurement. However, sample analysis was performed
by measuring several different areas and averaging out the data in an attempt to
average the surface roughness.
2.2. Verification of XRF with standard lead solution
After the portable XRF was standardized by a standardization cap, it was further
verified by a standard lead nitrite solution. A clean oyster shell was chosen to verify
the lead concentration on the oyster shell. A standard lead nitrite solution with
a concentration of 200 mM was used to spike (contaminate for the purpose of
verification) the clean outer shell. A spot of the oyster shell was marked and chosen
to spike aliquots of the standard solution with varying levels of lead. Then the same
spot was analyzed by the portable XRF after each application.
2.3. SEMeEDS measurement
Scanning electron microscope (SEM, JEOL Model 5410) with energy dispersive
X-ray spectrometer (EDS) was used to image oyster shell surfaces. As a regular
procedure, the oyster shells were deposited with 10 nm Au to improve sample
conductivity, and then subjected to SEMeEDS examinations.
3. Results and discussion
3.1. XRF analysis on oyster shells
Pb is the focus of this paper, but other elements were simulta-
neously detected. An example of heavy metal contaminated oyster
shells and analysis of non-crushed oyster shell by a portable XRF are
shown in Fig. 1. The numbers on the oyster shells were spots
examined by the portable XRF. Both outer and inner shells were
analyzed in this study, but experiment results reported here were
mainly on outer shells.
A clean oyster shell collected from the Seafood Market in
downtown Hammond was chosen to verify the Pb concentration on
the oyster shell. A spot was selected to spike the Pb standard
solution and then examined by the portable XRF. A known quantity
of Pb standard solution was added to the chosen spot on the clean
oyster shell to test whether the portable XRF response of the
sample is the same as that added. The same spot was repeated with
the different concentrations of the standard Pb solution and then
analyzed by the portable XRF after each application. Fig. 2 shows
the plot of the Pb concentration detected by the portable XRF
versus the concentration of the Pb standard solution added. The
detected Pb concentration increased with increasing the concen-
tration of the standard Pb solution added on the oyster shell. A
calibration curve is determined, and the correlation coefficient (R2
)
of the straight line is 0.987 as shown in Fig. 2. Percent recovery of
the spike was calculated for each spike based on the below
equation. The calculated spike recovery on the oyster shell ranged
from 84% to 120%.
%recovery ¼
cðspike sampleÞ
cðaddedÞ
 100%
For comparison, three types of oyster shells (no Pb, medium Pb
and high Pb) were selected for analyses using the portable XRF. A
clean oyster shell (from the Seafood Market in Hammond) was
characterized by the XRF and was compared with two contaminant
Fig. 1. Images of an example of contaminated oyster shells (top) and analysis of non-
crushed oyster shell by a portable XRF (bottom).
J. Chou et al. / Environmental Pollution 158 (2010) 2230e2234 2231

4. Author's personal copy
oyster shells collected from a residential area in New Orleans.
Different areas of oyster shells were analyzed by the portable XRF.
Typical XRF spectra of three oyster shells were shown in Fig. 3.
On the clean oyster, only peaks of Ca (3.7 keV and 4.0 keV) and Sr
(14.2 keV, 15.8 keV) were observed. The chemical composition of
oyster shells is predominantly Ca as calcium carbonate (CaCO3)
with impurities. Besides carbonates, other minor elements such as
Sr were also observed. No Pb peak was observed indicating that the
oyster shell was not contaminated by lead as shown no Pb in Fig. 3.
On the oyster shell with medium Pb level, the XRF spectrum is
shown in Fig. 3 (med Pb). Not only peaks from Ca and Sr were
observed, but peaks from Fe (6.4, 7.1 keV), Zn (8.6, 9.6 keV) and Pb
(10.6, 12.6 kev) were also observed. All peaks were assigned based
on photon energies and emission lines of elements (http://
xdb.lbl.gov/xdb.pdf). The assigned peaks for each element are
shown in Fig. 3. The concentration of Pb in this spectrum (med Pb)
was 970 Æ 40 mg * kgÀ1
. Small amount of other elements such as Fe,
Zn were also detected. On the oyster shell with high Pb level (high
Pb in Fig. 3), strong peaks from Pb were observed. The Pb concen-
tration was detected as 8300 Æ 200 mg * kgÀ1
in the high Pb shell. A
small extra peak from As at 11.7 kev was observed as shown in Fig. 3
(high Pb). As has another emission line at 11.7 kev (Ka2) which
normally is not sensitive enough to quantify As at environmental
legislation levels. However, it does not overlap with any Pb emis-
sion lines, thus it can be used as an indicator of the presence of As
and also can be used for As quantification when As has a high
concentration in samples. The presence of emission line at 11.7 kev
on the oyster shell simply indicated that the shell collected from
New Orleans was contaminated by As. These results indicate that
heavy metals such as Pb, As, Fe, Zn are able to accumulate on oyster
shells (Huanxin et al., 2000).
Different spots of each outer shell were tested by the portable
XRF. The Pb concentration on high Pb oyster shell is listed in Table 1.
The numbers in the Table 2 represent measured spots as shown in
Fig. 1. Pb concentration on different spots on the shell varied and
the distribution of Pb on the shell were found not homogenous.
Without sample treatment, rough surfaces were examined by the
portable XRF and analysis on a single spot could not provide an
accurate result. However, more precise results can be achieved if an
entire shell surface is examined and analysis results are averaged
out. When a shell surface was analyzed by the portable XRF,
different spots, where surface roughness could vary, were selected.
The average of element concentration was calculated to report the
element concentration on the oyster shell measured. The reported
average of concentration of different elements is based on multi-
measurements on the entire surface. By this method, the rough-
ness of shell surface should be taken into account. The mean of Pb,
As and Sr concentrations in three oyster shells was listed in Table 2.
The mean values were obtained based on nine measurements on
different spots on each outer shell. For the clean oyster shell, the
concentration of Pb and As is lower than the limit of detection. For
medium Pb oyster shell, the mean of the Pb concentration was
1380 Æ 533 mg * kgÀ1
(n ¼ 9). The average of Pb concentration in
the oyster shell with high Pb level was determined to be
6474 Æ 1963 mg * kgÀ1
.
For the two contaminated shells, the inner shells were also
examined by the portable XRF. Different spots of inner shells were
marked and tested. The average of lead concentration in the inner
shells with high and medium Pb level was 1310 Æ 420 mg * kgÀ1
and 320 Æ 130 mg * kgÀ1
respectively. The XRF results indicated
that the inner shells contained less Pb and As than their outer shell
surfaces. These results further suggest that oyster outer shells may
accumulate more Pb than inner shells. The lower concentration
observed in the inner shell also suggested that the outer shells have
more porous structure than inner shells and thus has higher surface
area than inner shells.
y = 0.7843x + 12.905
R2
= 0.987
0
20
40
60
80
100
120
140
160
180
0 50 100 150 200 250
Pb added (mg*kg-1
)
gk*gm(detaluclaCFRXbP1-
)
Fig. 2. A plot of Pb concentration in mg * kgÀ1
from XRF results versus concentration of
standard lead solution spiked on the clean oyster shell.
Fig. 3. XRF spectra of three different oyster shells.
Table 1
Average concentration of Pb, As and Sr on outer oyster shells (values in mg * kgÀ1
).
Oyster shells Mean of concentration (mg * kgÀ1
)
Pb As Sr
No lead (n ¼ 9) <LOD <LOD 1097 Æ 308
Medium lead (n ¼ 9) 1380 Æ 533 178 Æ 59 711 Æ 111
High lead (n ¼ 9) 6474 Æ 1963 662 Æ 165 904 Æ 90
J. Chou et al. / Environmental Pollution 158 (2010) 2230e22342232

5. Author's personal copy
On the clean oyster shell, the content of Sr is 1097 mg * kgÀ1
and
is calculated as 0.13% of SrO (weight percent). The SrO percentage
does not have significant difference with reported value of 0.33%
(Yoon et al., 2003). Almost all environmental samples containing Ca
also contain Sr in the ratio of the geological abundances. The data
presented here seems indicating that the Sr content found in
different regions' oyster shells could vary only slightly with the
geological variance.
3.2. Characterization of oyster shells by SEMeEDS
In order to confirm the results obtained by the XRF, SEMeEDS
was used to characterize oyster shells. Both cleaned and high Pb
contaminated oyster shells were characterized by SEMeEDS. ED
spectra were taken during imaging process on each oyster shell.
Shell samples were coated with 10 nm Au before they were
examined by SEM-EDS.
A typical morphology of the oyster shell with high Pb contam-
ination as well as its ED spectrum is shown in Fig. 4. A large peak
from Ca is observed and it is in good agreement with XRF results. C,
O and Si were also observed by the EDS, but they were not detected
by the portable XRF. These peaks were also observed on the cleaned
oyster shell. The Au peak was observed in the ED spectrum, but it
was attributed to Au sputtering treatment, not from the oyster shell
itself. A small peak at 2.4 kev was detected and it is attributed to Pb.
At 2.3e2.4 keV there is also a K line of S which is an element that
could be present in oyster shells. If this peak was contributed from
the presence of the S, we should have observed it from both clean
and contaminated shells. However, this peak was not observed on
the clean shell by the ED spectrums, indicating that the peak was
not due to the S, but from the Pb.
Peaks from Fe, Zn and As were also detected in other parts of the
oyster shell and were shown in other ED spectra (data not shown
here). Results from the ED spectrum further confirmed semi-
quantitatively existence of Pb, As, Cu Fe and Zn on the contami-
nated shell. However, Sr was not detected by the EDS because their
concentrations maybe too low to be detected by the EDS.
A SEM image of the Pb contaminated oyster shell and a high
resolution SEM (inset) are shown in Fig. 4. The high resolution SEM
image indicates that the oyster shell has a lamellar structure. It was
estimated that oyster shell had 10e20 layers per micrometer on the
shell surface. The accumulation of heavy metals may occur on the
surfaces or between the thin layers, which explains the origin of its
outstanding Pb accumulation ability. This kind of lamellar structure
may provide high surface areas and could contribute to high
accumulation ability to Pb.
3.3. Comparison of crushed and non-crushed oyster shell's analysis
A disadvantage of the XRF method on non-crushed oyster shells
is lack of homogeneity of the matrix and roughness of oyster shells.
However this can be achieved by analyzing more sample spots over
the entire surface obtaining an average of results. When oyster
shells grow in Pb contaminated water, the Pb can bioaccumulate
inside the oyster shells over time. Oyster shells need to be crushed
in order to analyze Pb contamination throughout the oyster shells.
This analysis would give a more accurate result compared to the
XRF analysis on non-crushed samples. However, the analysis on
crushed samples cannot reflect where the contamination was on
the shells, and could not indicate if Pb contaminant is throughout
the shell, or on the inner/outer surface of the shell. When shells
were left in Pb contaminated soils, Pb accumulated on the shell,
most specifically, on the shell surface not the inner layers of shells.
This accumulation is different from live oyster shells that grow in
Pb contaminated water. Pb analysis based on crushed samples will
not be suitable for this purpose. The analysis of oyster shells
reported in this paper for surface analysis of Pb contamination is
preferable to the traditional crushed shell method in determining
the past environment of shells buried in soil.
When oyster shells are left in different environments, different
metals, especially Pb can accumulate on oyster shell surfaces and
this accumulation will result in oyster shell with surface Pb. In New
Orleans, soils are highly contaminated by Pb in some areas. Oyster
shells collected in New Orleans were left in these contaminated
soils and Pb accumulated on the shell surfaces. This is why Pb is
observed on the oyster shells collected in New Orleans. From this
point of view, buried oyster shells can be served as an environ-
mental indicator for Pb contamination.
4. Conclusions
The portable XRF can be used to analyze multi-elements spon-
taneously on a non-crushed oyster shell or a similar species known
to concentrate a variety of heavy metals from its surroundings. The
XRF analysis on non-crushed sample is used to quantitatively
analyze Pb concentrations that Pb accumulates to a surface. In
addition, the portable XRF instrument does not require sample
digestion, thus it is especially suitable for fast screenings, field
testing and rapid identification of oyster shell metal (Pb and As)
contamination.
Table 2
Pb concentration on different spot points of the high Pb oyster shell (in mg * kgÀ1
).
Spot on the shell 1 2 3 4 5 6 7 8 9
Pb (mg * kgÀ1
) 7413 7834 6922 8139 6690 5824 2114 8331 4997
Fig. 4. SEM image (top) of the oyster shell with high lead level and its ED spectrum
(bottom). Inset: high resolution of SEM image of lamellar structure of the oyster shell.
J. Chou et al. / Environmental Pollution 158 (2010) 2230e2234 2233

6. Author's personal copy
Acknowledgements
The authors would like to acknowledge Lead Grant and the
Faculty Development Grant (Southeastern Louisiana University) for
financial support and Innov-X Systems (Woburn, MA) for generous
loan of a portable XRF for this work. L. Zhou acknowledges partial
support from Louisiana Board of Regents Contract No. LEQSF(2007-
12)-ENH-PKSFI-PRS-04.
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