svEPA
United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21401
Research and Development
EPA-600/S3-82-085 Oct. 1982
Project Summary
The Characterization of the
Chesapeake Bay: A Systematic
Analysis of Toxic Trace
Elements
Howard M. Kingston, Robert R. Greenberg, Ellyn S. Beary, Billy R. Hardas,
John R. Moody, Theodore C. Rains, and Walter S. Liggett
As part of a multidisciplinary study
of Chesapeake Bay, the National
Bureau of Standards (NBS) was asked
to develop the techniques and proce-
dures necessary to measure trace and
toxic element concentrations within
the water column throughout the
length of Chesapeake Bay. The Inor-
ganic Analytical Research Division of
the Center for Analytical Chemistry at
NBS has completed the analysis for
selected elements (Cd, Ce, Co, Cr, Cu,
Fe, Mn, Mo, Ni, Pb. Sc, Sn, Th, U, and
Zn), including some elements at
concentrations consistently below
one picogram per milliliter (part per
trillion). The characterization of Ches-
apeake Bay can be divided into five
major phases. The first included the
development and construction of a
sampling system for the trace metallic
elements dissolved in water and a
filtration system for collecting the
particulate elemental component.
The second phase consisted of
sampling chemical stabilization by
acidification and storage of the sam-
ples in the field. The total complement
of 102 samples was obtained, filtered,
acidified and stabilized. There were
also 51 replicate bottom samples
obtained and frozen for archival use. A
series of over 30 blanks was also
prepared and integrated with the 102
water samples to be analyzed.
The third major phase of activity
consisted of the chemical separation
and preparation of samples for the
analytical instrumental methods. The
chemical separation/sample prepara-
tion stage of this work has been
described in the literature for both
instrumental techniques.
The fourth major phase consisted of
the instrumental analysis of the
samples for the trace elements. The
total number of elemental concentra-
tions resulting from the analyses of
the contracted elements exceeded
3000 and involved several thousand
more unreported analyses totaling
over 5000 separate determinations.
The fifth major phase involved data
reduction and evaluation of the statis-
tical significance of the blank. The
blanks were statistically modeled for
each element, and the blank and
uncertainty of the blanks were applied
to the data. The concentrations were
adjusted uniformly to at least the 95
percent confidence limit.
This Project Summary was devel-
oped by EPA's Chesapeake Bay
Program, Annapolis, MD, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
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Introduction
This report describes the National
Bureau of Standards' (NBS) efforts in a
multidisciplinary study of Chesapeake
Bay coordinated by the U.S. EPA's
Chesapeake Bay Program. The NBS
used the best available technology to
determine the trace and toxic element
concentrations in the water column. As
part of this program, the NBS has
collected and analyzed both the dis-
solved and suspended participate
fractions of 102 water samples covering
the entire length of Chesapeake Bay.
The elements of interest include Cd, Ce,
Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sc, Sn,
Th, U, and Zn. These analyses were
accomplished using specific chemical
preconcentration, separations and
manipulations to prepare the samples
for analysis by Neutron Activation
Analysis (NAA) and Graphite Furnace
Atomic Absorption Spectrometry
(GFAAS).
Except for neutron activation analysis
and anodic stripping voltammetry, no
analytical techniques are currently
available for the untreated sample
determination of trace elements in
seawater at concentrations below five
fjg L~\ Usually it is necessary to pre-
concentrate the trace elements from a
large volume and separate the transition
elements from the alkali and alkaline
earth elements. In such sample prepa-
rations, the efficiency of concentration,
completeness of separation, and total
analytical blank become critical to the
final instrumental method.
A more recent separation procedure
utilizing Chelex resin produced a
sample devoid of alkali, alkaline earth,
and halogen elements, and left a dilute
nitric acid/ammonium nitrate matrix
containing only the trace elements of
the seawater sample. This procedure
was used in conjunction with GFAAS to
analyze Chesapeake Bay estuarine
samples.
Procedure/Methodology
The method of preparation described
for solid samples from 100 mL of
estuarine or seawater uses Chelex 100
resin, followed by the determination of
12 trace elements by NAA. This proce-
dure has been used to analyze NBS
SRM 1643a, as well as high salinity
water samples collected near the mouth
of Chesapeake Bay.
The extremely low trace concentra-
tions in these estuarine waters caused
the procedural blank to be of paramount
importance. The integrity of the sample
can be compromised by just a brief
exposure to normal laboratory air or less
than exhaustively cleaned container
materials, etc In addition, the extremely
high concentrations of alkali, alkaline
earth, and halogen elements in the
marine water .matrix make direct
analysis difficult or impossible for most
analytical techniques.
To circumvent these problems, spe-
cial chemical and instrumental proce-
dures were developed and chemical
separation/preconcentration proce-
dures based on the chelating resin
Chelex-100 were applied prior to NAA
and GFAAS analysis. The elimination of
the matrix elements allowed the deter-
mination of many elements that could
not otherwise be analyzed and en-
hanced the sensitivity of other elements
of interest. The control of the blank in
this procedure has enabled its contri-
bution to be low enough not to limit the
measurement of most elements in
pristine samples.
To ensure sample integrity and
accurate analytical blank determina-
tions, 30 dissolved and particulate
blanks were prepared during the sample
collection. The blanks were then carried
through all manipulations and analyses
as additional samples interspersed
throughout the analyses, with a mini-
mum of three per set.
Evaluations were made using com-
puter-assisted statistical comparisons
with data of known statistical reliability
The analysis, blank contribution, correc-
tions, and mathematical manipulation
of the data in this report have resulted in
58 data sets which are of known
statistical reliability. These data sets
contain the sample numbers arranged
in a numerical sequence approximating
the geological arrangement of Chesa-
peake Bay, from Susquehanna River to,
and including, the Atlantic Ocean. The
concentrations are given as a best
value, and a maximum and minimum
value which represent at least the 95
percent confidence limit of the concen-
tration. The significant figures of each
concentration are determined by the
range of the maximum and minimum
value.
The potential information m the
particulate elemental concentration
data is even more difficult to under-
stand. Although it may appear initially to
be uncertain in interpretive value, a
technique long used in the study of
atmospheric particulate material is
applicable. The comparison of elemen-
tal ratios for different samples instead of
the absolute concentration is informa-
tive. By normalizing the concentration
of each element to a crustal element,
such as Sc, problems caused by differ-
ing amounts of bottom sediment sus-
pended in water (loading effects) are
eliminated.
Scandium was chosen for this pur-
pose because it has relatively few
anthropogenic uses. Since it is not used
in a refined form in industry and is
refractory in nature, it is not expected to
be introduced into the environment in
an enriched state or in significant
quantities. When these ratios are
divided by ratios of average crustal
material, a crustal enrichment factor
(EF) results. This is done for conven-
ience and to allow a crude comparison
with naturally occurring material.
I n these data the concentrations from
Wedepohls'1 compilation for crustal
elements has been used. Similar
though not identical results could be
obtained using other compilations.
Additionally, the computation of EFs
relative to average soils and average
sedimentary rocks would be of value to
see how the suspended sediments of
Chesapeake Bay differ from those
natural materials.
Ideally, the EFs for each element will
remain constant if the sources contribu-
ting to the suspended sediment remain
the same. Although the concentration
of the various elements may fluctuate
several orders of magnitude from
sampling to sampling, the EFs should be
constant if the sources are constant as
they are not effected by mass loading.
Conclusions
Uses of these EFs to produce an
interpretive model for evaluating and
concluding elemental relationship and
origins can be postulated. However,
actual conclusions cannot be drawn
until a rigorous scrutiny of the statistical
significance of the individual sets of
enrichment factors has been com-
pleted. Because this technique has not
been used for water particulates previ-
ously, many cross references between
elements and geological positioning, as
well as within set limits, must be
evaluated.
In this report, the enrichment factors
normalized to the Wedepohl crustal
numbers have been given without
interpretation to at least the 90 percent
confidence limit.
These data are of sufficiently well
known reliability that statistical com-
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parison can be performed resulting in
significant trends of known reliability.
This work has not been included in this
report and is of a sufficiently complex
nature to comprise a separate effort,
which has been recently initiated.
References
1. Wedepohl, K.H. 1966, "Origin and
Distribution of the Elements." L.H.
Aherns, ed. Pergamon Press, London.
pp 999-1016.
Howard M. Kingston, Robert R. Green berg, EllynS. Beary, BillyR. Hardas. John
R. Moody, Theodore C. Rains, and Walter S. Liggett are with the National
Bureau of Standards, Washington, DC 20234.
Duane Wilding was the EPA Project Officer (for information, see below).
The complete report, entitled "The Characterization of the Chesapeake Bay: A
Systematic Analysis of Toxic Trace Elements," (Order No. PB 82-265 265;
Cost: $18.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For information contact David Flemer at:
Chesapeake Bay Program
U.S. Environmental Protection Agency
2083 West Street. Suite 5G
Annapolis, MD 21403
» US GOVERNMENT PRINTING OFFICE 1SM-559-017/0851
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