c/EPA
United States
Environmental Protection
Agency
Environmental Monitoring
and Support Laboratory
PO Box 15027
Las Vegas NV 89114
EPA-600 3-79-030
March 1979
Research and Development
Ecological
Research Series
Development of
a Strategy for
Sampling Tree Rings
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to foster
technology transfer and a maximim interface in related fields. The nine sereies are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6 Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy—Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans,plant and animal species, and
materials. Problems are assessed for their long-and short-term influences Investiga-
tions include formations, transport, and pathway studies to determine the fate of
pollutants and their effects. This work provided the technical basis for setting standards
to minimize undesirable changes in living organisms in the aquatic, terrestrial, and
atmospheric environments.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161
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EPA-600/3-79-030
March 1979
DEVELOPMENT OF A STRATEGY
FOR SAMPLING TREE RINGS
by
Jerry A. Riehl
Northwest Environmental Technology Laboratories, Inc
Mercer Island, Washington 98040
Contract No. CB-7-0771-A
Project Officer
Gilbert D. Potter
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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FOREWORD
Protection of the environment requires effective regulatory actions which
are based on-sound technical and scientific information, This information
must include the quantitative description and linking of pollutant sources,
transport mechanisms, interactions, and resulting effects on man and his
environment. Because of the complexities involved, assessment of specific
pollutants in the environment requires a total systems approach which tran-
scends the media of air, water, and land. The Environmental Monitoring and
Support Laboratory-Las Vegas contributes to the formation aid enhancement of
a sound monitoring data base for exposure assessment through programs
designed to:
develop and optimize systems and strategies for monitoring
pollutants and their impact on the environment
demonstrate new monitoring systems and technologies by
applying them to fulfill special monitoring needs of the
Agency's operating programs
This report documents the development of a strategy to retrospectively
monitor pollutant levels in air by measuring arsenic concentrations in samples
of wood obtained from annual growth rings of trees in the vicinity of a
smelter. Such information can provide a basis to assess the relative
risks to the health and well -being of a local population exposed to environ-
mental hazards and to aid in the improvement of our environmental quality.
The advantage of such a program will permit us to assess the effectiveness
of past environmental control technologies with those of the future and
establish an environmental baseline with which to compare future control
technologies.
Federal and local agencies interested in assessing past exposures of
local populations to hazardous or carcinogenic materials released to the
environment will find this study useful. In addition, the information it
provides may be used to determine the effectiveness of newer control method-
ologies. Additional information about the study may be obtained by contact-
ing the Monitoring Systems Research and Development Division, Environmental
Monitoring and Support Laboratory, Las Vegas, Nevada.
'
George B. Morgan
Director
Environmental Monitoring and Support Laboratory
Las Vegas
ill
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ABSTRACT
A method for determining retrospective pollution levels has been
investigated. This method relates arsenic concentration in tree rings to
arsenic-in-air concentrations based qualitatively on arsenic emissions from a
nearby smelter, corrected for climatological and meteorological effects. To
evaluate the validity of the method, a unique pollution study area was
identified and characterized in detail. Several select trees were sampled
and the arsenic concentration determined by neutron activation analysis.
These concentrations were compared to certain known phases in the production
history of the smelter, coupled with the expected climatology and meteorology
of the area. Positive correlations were found thus satisfying the goals of
the preliminary project. Major problems encountered were low arsenic
concentrations and an inadequate number of samples. Recommendations for
future studies are given.
iv
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CONTENTS
Foreword i i i
Abstract i v
Figures vi
Tables yii
Acknowledgment viii
Section
1. Introducti on 1
2. Summary 2
3. Recommendations 3
4. Background Information 4
Tree ring analysis 4
Probl em i denti fi cati on 5
5. The ASARCO Tacoma Smelter Study Area 7
Uniqueness of the study area 7
Uniqueness of the sampling sites 7
Other important considerations 9
6. The Hi story of the Tacoma Smel ter 10
Production and emissions 10
Control efforts 12
7. The Sampling Site 13
Location 13
Subject trees 13
Soil 16
8. Experimental Systems and Techniques, 17
Neutron activation analysis , 17
Elements analyzed , 17
Tree sample collection , 18
Soi 1 sample col 1 ection 20
9. Meteorological Information 22
Climatological data 22
10. Experimental Results and Conclusions,.. 26
Introduction , 26
Experimental results 27
Discussion 33
Concl us i ons 37
References 38
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FIGURES
Number Page
1 The ASARCO Tacoma smelter study area 6
2 Air pollution monitoring network surrounding
ASARCO smel ter i n Tacoma 8
3 Topographic map of southern portion of Maury
Island with site of study trees identified 14
4 Photographs of the study area 15
5 Annual precipitation (A) and 10-year running
mean (M), 1893-1970 25
6 Comparison of upper and lower tree rings - tree #5 28
7 Yearly variation of arsenic concentration - tree #5 34
8 Yearly variation of arsenic concentration - tree #1 35
VI
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TABLES
Number Page
1 Total Production for the Tacoma ASARCO Smelter/
Refinery, 1971-1975 11
2 Description of Trees Used in the Analysis 16
3 Description of Tree Ring Samples 19
4 Description of the Soil Samples 20
5 Temperature Statistics (C) for Tacoma, Washington,
for the Period 1930-1960 23
6 Precipitation Statistics (cm) for Tacoma, Washington
for the Period 1930-1960 24
7 Arsenic Content, in Study Trees 30
8 Arsenic Content in Tree #1, Sample 1-L ;* ,.,..,.. 31
9 Arsenic Content in Trees #1 and #5 During
Strike Years 31
10 Arsenic Content in Needles, Soil and Cones 32
VI1
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ACKNOWLEDGMENT
This report is the result of the cooperation, assistance, and
participation of many individuals.
Personnel of the U.S. Environmental Protection Agency's Region X Office
provided considerable guidance and information during the course of this
study. These include Dr. Robert Courson, Dr. James Everets, and Mr. Robert
Coughlin. Their efforts were needed and appreciated.
I am also greatly indebted to many staff members of the Puget Sound Air
Pollution Control Agency for their valuable input, especially in historical
documentation.
For allowing me to freely choose trees for sampling on their property, I
am equally indebted to Mr. and Mrs. Alan Houston and Mr. Lewis Duncan. Their
interest in this project and enthusiasm to cooperate were heart-warming.
Finally, I wish to acknowledge the input of Dr. William Kreiss, a
meteorologist with Physical Dynamics, Inc., of Seattle. His general guidance
and encouragement were appreciated and his meteorological expertise made
Section 9 possible.
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SECTION 1
INTRODUCTION
The primary difficulty in relating the incidence and causation of human
disease to environmental factors in epidemiological studies results from the
lack of good retrospective data. Because many diseases develop over a period
of years, it is of major importance to determine an accurate chronology of
those items that lead directly to the initiation of the disease. Few
accurate methods exist, especially in the area of pollution-caused diseases.
This project is a first step in the development of such a method.
The technique of dendrochronology is most often used to estimate the age
of a tree. By carefully evaluating the successive layers of xylem growth, or
"tree rings" as they are commonly called, from the pith to the cambium, the
age of a tree can be accurately determined. This technique is widely known
and used. Also, local climatic history can be reconstructed from a detailed
analysis of tree rings. In general, the width of the ring is related to the
precipitation and temperature exposure. In addition, patterns of varying
ring widths are established over a period of years due to exposure to various
weather conditions, and these can be traced from tree to tree in a given
climatic area. These patterns have been used to date items ranging from the
age of windfalls to the age of objects constructed from wood.
Directly related to this, but even less well known, is the fact that
other information is also stored in the rings of xylem growth. As will be
discussed in this report, some trace chemical elements known to be
nonessential for tree growth are found in the xylem. Furthermore, the
concentration of these nonessential elements in tree rings can vary from year
to year, and it has been demonstrated that they can be related to a pollution
source many kilometers away. Such elements possibly enter the tree via the
soil by rainout or fallout.
The development of this method for retrospective determination of
pollutant levels is based on the above facts. The subject of this study is
the demonstration that the concentration of some pollutants in the rings is
proportional to the pollution to which the trees are exposed.
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SECTION 2
SUMMARY
The concentration of arsenic in tree rings was found to be proportional
to the annual emission of arsenic from a copper smelter 8 kilometers away
from the trees. The study site is on an island, and so transport from the
stack by air has been validated. Although positive correlations were made,
several anomalies exist that need to be answered. An apparent lag of one to
two growing seasons in the uptake of arsenic from the soil was identified in
tree rings taken from lower portions of the tree. On the other hand, no lag
was noted between production output from the smelter and tree rings taken
from higher elevations in the tree, suggesting a direct uptake from the air
through the needles. Although the evidence is not conclusive, some species
of trees appear to behave differently from others, but all species evaluated
showed the lag effect in samples collected nearest the root system.
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SECTION 3
RECOMMENDATIONS
The data contained in this report suggest that tree ring analyses are
valid indicators of past pollution levels. This presents the possibility of
retrospective evaluation of pollution. Several important steps must be
taken, however, before the method can be demonstrated to be quantitative.
First, pollutants other than arsenic need to be evaluated for this study
area. Second, a larger number of sample trees needs to be evaluated. Third,
other species of trees need to be evaluated in greater detail than was
possible in this study. Fourth, duplicate increment samples should be taken
during the sampling stage, and one of these should be mounted, polished and
varnished in order to eliminate or at least minimize ring-counting errors.
Fifth, definite climatological-growth relationships need to be developed, a
major factor in this type of study. Finally, higher neutron flux should be
used for the analysis to maximize the pollutant activity in the rings.
Whereas this study was conducted in a short time and on a limited budget,
future studies should be extended in time and budget in order to accurately
assess all of the possible variables and draw conclusive results.
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SECTION 4
BACKGROUND INFORMATION
TREE RING ANALYSIS
The trace element concentrations in the xylem ring of trees are known to
be proportional to the elemental concentration in the soil (Lepp, 1975).
Early studies (Sheppard and Funk, 1975) have shown that the rings of trees
whose roots were exposed to contaminated water in an Idaho river downstream
from a mine contained trace-metal concentrations that were directly
proportional to the yearly pollution levels of the river and the yearly
output of the mine. Tree rings examined in certain Pennsylvania trees
(Pillay, 1975) contained concentrations of trace metals known to be present
in the local atmosphere, and the observed variations in the rings suggested a
relationship proportional to the pollution in the environment. Heavy metal
studies by Ault et al. (1970) and Ward et al. (1973) have shown that lead
levels in tree rings could be correlated with local traffic density. On the
other hand, a detailed study by Szopa et al. (1973) showed that lead levels
in oak trees near an abandoned highway continued to register high lead levels
after the abandonment, suggesting that direct yearly correlations may be in
error. (This study, however, did not consider the possibility of root uptake
of lead from the soil.) Finally, unpublished tree-ring data taken by the
author on trees located in polluted and unpolluted environments have clearly
indicated that certain environmental contaminants present in air pollution
are concentrated in tree rings, that the concentrations of these elements
appear to be a function of the type of soil in which the tree is located, and
that the concentration varies annually.
While all of these results indicate that a relationship may exist between
the concentration in the rings and the local environment, a detailed analysis
of all relevant variables was needed in order to evaluate the validity of
this method as a tool for retrospectively determining pollution levels. This
report describes the progress to date concerning the first step in this
verification process—a simple demonstration of the correlation between
tree-ring concentration and the polluted environment of the tree.
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PROBLEM IDENTIFICATION
Several parameters needed to be determined in order to develop this
method for use as a technique for retrospective determination of pollution.
These included tree-related parameters. Processes related to the uptake,
transport, and deposition of trace elements in the tree needed to be
understood. Items such as diffusion of trace elements to adjacent rings, the
preferential uptake of certain species from the soil, the effects of soil
diffusion and leaching, the uptake of the elements directly from the air
through broad leaves and needles, all needed to be understood. Equally
important were the pollution source-related parameters. An accurate
chronology of the source emissions was needed, as well as the various
transport processes and mechanisms. In addition, a well-defined
meteorological history was mandatory. No one parameter stood out as most
important. All were related in one way or another and had a direct effect on
the accuracy of the method—hence on the demonstration of the method
validity.
A most important first step in the demonstration of the validity of this
method was the identification and characterization of an ideal study area.
This unique site was found to be located in a second growth area in the Puget
Sound of northwestern Washington. The area contained a single major source
of pollution, and the only direct means of pollutant transport was by air
(Fig. 1). Equally important was the tree-ring concentration/pollution
environment correlation mentioned above. This has been verified, at least
qualitatively, and the remainder of this report discusses the results.
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GREATER PUGET
SOUND
Figure 1. The ASARCO Tacoma smelter study area
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SECTION 5
THE ASARCO TACOMA SMELTER STUDY AREA
Several important parameters qualified the selected study area as ideal
for this demonstration project. These were related to four distinct factors
that substantially reduced the level of error: a well-defined and
characterized study system; ideal sampling sites; ideal chemical tracer
elements and techniques for the analysis; and an established meteorological
history of the area.
UNIQUENESS OF THE STUDY AREA
Much scientific work related to this project, and especially to the
overall study area, had been done in the recent past. Tree-ring analyses
previously performed by the author had formed the basis for this
demonstration project. Detailed studies on the particulate (Nelson and
Roberts, 1975) and gaseous (Washington State, 1976) emissions had been
conducted; dispersion modeling of the gaseous emission had been accomplished
(Cramer et al., 1976); an extensive air pollution monitoring system was in
use (Fig. 2); the surrounding water and sediments between the source and the
sampling sites on Maury Island (Fig. 2) had been characterized in detail
(Crecelius et al., 1975); and many other pollutant-related studies, ranging
from arsenic levels in hair and urine (Johnson and Lippman, 1973) to cadmium
levels in vegetable gardens (Heilman and Ekuan, 1977), had been conducted.
In general, considerable information was available on the selected study
area.
UNIQUENESS OF THE SAMPLING SITES
Two distinct sampling sites were identified near the City of Dockton on
Maury Island (see Fig. 2). Maury Island and Vashon Island are bridged with
fill area and lie west of Seattle and north of Tacoma, the two major urban
areas in Puget Sound. Although close to these cities, they are virtually
isolated (ferry connections only). Both islands consist mainly of small
farms and second growth timber, have little or no industrial sources, and
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Figure 2. Air pollution monitoring network surrounding
ASARCO smelter in Tacoma
8
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for the most part have no local anthropogenic stationary pollution sources.
The prevailing winds are northerly and southwesterly, depending on the
season, and both sampling sites lie within the southwesterly plume envelope
of the smelter. Since Tacoma is bordered on the north by Puget Sound, the
only possible path from the smelter to the sampling sites is by air
transport. The sites lie about 8 kilometers (km) from the smelter, within
known plume touchdown areas. In Section 7, these sites are described in
detail and the trees that will be studied are illustrated.
OTHER IMPORTANT CONSIDERATIONS
The experimental techniques and the meterological considerations employed
in the study are described in Sections 8 and 9. They illustate the overall
importance of these parameters in the demonstration project. In Section 10,
the experimental results are discussed.
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SECTION 6
THE HISTORY OF THE TACOMA SMELTER
PRODUCTION AND EMISSIONS
Detailed chronologies of the arsenic production levels and the
corresponding stack emission levels from the American Smelting and Refining
Company (ASARCO) smelter in Tacoma were either non-existent or unavailable
to the public. However, certain specific facts related to"the stack
emissions were known and hence enabled an evaluation to be made concerning
the validity of tree-ring analysis as a method for retrospective
determination of pollution levels.
The Tacoma smelter began operation in 1890 as a lead smelter. In 1902
copper smelting capabilities were added (Cramer et al., 1976; ASARCO, 1976).
ASARCO bought the smelter in 1905 and used it for both lead and copper
smelting until 1911 when it was converted to a copper-only facility. The
smelter was used to process both copper ore and copper concentrates into
blister copper. In 1915, a refinery was added to treat the blister copper
produced at the smelter.
Since both lead and copper ores contain arsenic in varying amounts, it
follows that arsenic could have been produced at the smelter as early as
1890. Consequently, a detailed analysis of the tree rings between 1885 and
1915 for arsenic provided valuable information about the validity of
tree-ring analyses, especially concerning diffusion between the rings. An
evaluation of Section 10 shows this to be true for certain species of trees.
Theoretically, arsenic emissions from the stack should have been
proportional to the yearly production of arsenic, as is implied above,
corrected of course for the addition of pollution abatement equipment on the
stack. But ASARCO considered its production information proprietary.
However, certain known facts enabled an evaluation of the validity of the
method. First, some production data had been released to the U.S.
Environmental Protection Agency (EPA)* This is shown in Table 1. Second,
*Coughlin, R. L., private communication, May, 1977
10
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although more indirect in nature, it was known that the production levels
were especially low in 1967 and 1968 due to a 9-month strike from July 1967
to April 1968. Because the arsenic in question in this project was suspected
of being incorporated into the tree structure during the spring growth
portion of the yearly cycle, the 1968 (or 1969, depending on the lag between
stack emissions and appearance in the tree) tree rings should have been low
in arsenic. A similar situation should have existed in the 1959-60 period
where again a strike of many months duration lowered production and emissions
levels considerably. Again, the evidence presented in an evaluation of
Section 10 indicates this is indeed true.
TABLE 1.
TOTAL PRODUCTION FOR THE TACOMA ASARCO
SMELTER REFINERY, 1971-75 (SHORT TONS)
Year
1971
1972
1973
1974
1975
Material
processed
380 x 103
406 x 103
384 x 1()3
350 x 103
333 x 103
Smelter Cu
output
88.2 x 103
99.8 x 103
95.5 x 103
86.6 x 103
72.3 x 103
Refined Cu
output
NA
NA
120.1 x 103
117.4 x 103
119.7 x 103
As203
output
9.8 x 103
13.3 x 103
13.1 x 103
9.7 x 103
NA
Finally, the United States Bureau of Mines Annual Minerals Yearbook reported
information in 1961, 1962, and 1963 (USBM, 1961; 1962; 1963) that was hoped
could yield a valuable fourth set of data points that could have been
utilized in the evaluation. The 1961 book reported a 17% decrease in white
arsenic production (As203—nearly 100% of the arsenic produced in the
United States is this species) from the 1960 level; the 1962 book reported an
increase of 7 percent over 1961; and the 1963 book reports a 4-percent
decrease from the 1962 production level. Unfortunately, these small changes
could not be accounted for because of the variability found in the data. A
detailed explanation of this can be found in Section 8. A continuing effort
is underway to obtain as much white arsenic production data as possible for
incorporation into future phases of the project.
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CONTROL EFFORTS
The control of arsenic emissions from the smelter has been both direct
and indirect. An indirect control resulted from a "shutdown" policy that
ASARCO followed in the past few years. When meteorological conditions forced
gaseous S02 concentrations around the smelter to exceed certain values, the
smelter was automatically shut down. A detailed search for information on
the "down time" of the smelter was not fruitful, as no records were
available.* As a direct control, ASARCO started a pilot baghouse in early
1974 in order to determine the best available technology for reducing stack
particulate emissions. This baghouse was completed near the end of 1976,
according to ASARCO, (ASARCO, 1976) and is still in operation. No effect on
1977 emissions could be determined. To date, these two control efforts
represent the total control operations that affected arsenic output from the
smelter.
*This control methodology is explained in detail by Cramer et al. (1976) but
no record was available concerning the frequency of these shutdowns..
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SECTION 7
THE SAMPLING SITE
LOCATION
As mentioned earlier, the two sampling sites used in this project are
located on Maury Island near the town of Dockton, Washington (see Fig. 2),
are in a known smelter plume touchdown area, and lie about 8 km downwind from
the stack. Site No. 1 (the major site) lies to the southwest of Dockton,
while Site No. 2 (a backup site) lies northwest of the town in the Dockton
King County Park. Both sites are shown in Figure 3. Site No. 1 was used for
the initial phase of the project for several reasons: the trees were of the
desired age; several species of trees were available for incremental coring;
and the trees were clustered together in a small area, with each tree having
a similar environmental exposure. The trees at Site No. 2 were marginal in
age, of a single species, and more widely scattered—thus, less desirable for
this study. Permission was granted to the author by both landowners to
collect all of the samples needed.
Site No. 1 (see Fig. 3) is described legally as: King County Property,
30-22-03, tax lot 9035, that portion of the north one-half of GL 4 measured
on east line ELY of Manzanita Road, less the county road. The total size of
the site is 13.27 acres (53,702 square meters (m2)), and the five subject
trees are located on the site within 100 m of each other. Figure 4d shows a
southerly view of the smelter as viewed from the reference point on Figure 3.
SUBJECT TREES
Previous studies by the author indicated that Pseudotsuga taxi folia
(Douglas Fir) trees provided adequate yearly sample sizes and reasonable
pollutant sensitivities for an arsenic analysis in individual tree rings.
Unfortunatley, finding these trees of the proper age (older than 1890) and in
sufficient quantity in close proximity to each other was not possible in the
vicinity of the smelter. Consequently, Abies grandis (Grand Fir) and Thuja
plicata (Western Red Cedar) were also sampled. Table 2 describes the trees
selected from study Site No. 1. This mix was considered acceptable in that a
comparison between various types of trees was desired. Since the increment
borer that was used for tree ring extraction was of limited length and did
13
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• v-Yxiij:^.
v^v^M' \'1'
Manzanfta.
N
t
0.5 km 1.0 km
Figure 3, Topographic map of southern portion of Maury
Island with site of study trees identified
14
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(a) Trunk view of tree #1
(b) Trunk view of tree #5
(.c) Trunk view of tree #3
Figure 4. Photographs of the study area
(d) ASARCO smelter as viewed from
reference point on Figure 3
15
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not penetrate to the core, the age of the larger trees was estimated. This
and other sampling information will be discussed in detail in Section 8.
Figures 4a, 4b and 4c show pictures of trees 1, 3 and 5.
TABLE 2. DESCRIPTION OF TREES USED IN THE ANALYSIS
Age Diameter
Tree # Name Type (years) (meters)
1 Abies grandis Grand Fir est 130 1.3
2 Pseudotsuga taxi folia Douglas Fir est 100 1.0
3 Abies grandis Grand Fir 85 - 0.9
4 Thuja plicata Western Red 93 0.9
Cedar
5 Abies grandis Grand Fir est 110 1.0
SOIL
The soil at the sampling site is called Everett-Alderwood (EwC), which is
a gravelly sandy loam, usually characterized by a 6 to 15 percent slope
(USDA, 1973). Both Everett and Alderwood soils are somewhat/similar in that
they are well-drained, dark to grey in color, and situated on a moderately
strong substratum. The soil depth is typically 75 centimeters (cm) and, in
the undeveloped states, covered with timber. The soil samples that were
collected closely resembled this description. As will be discussed in
Section 8, a 20-cm layer of litter, composed primarily of decaying leaves and
needles, covered the soil.
16
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SECTION 8
EXPERIMENTAL SYSTEMS AND TECHNIQUES
NEUTRON ACTIVATION ANALYSIS
The arsenic determinations in the tree rings were made with neutron
activation analysis (NAA) at the University of Washington Nuclear Reactor
Laboratory in Seattle and the Washington State University Nuclear Reactor in
Pullman. The University of Washington facility has a graphite-moderated
reactor with a thermal neutron flux of about 10*2 neutrons per centimeter
squared per second. Washington State University has a swimming pool reactor
with a thermal neutron flux of about 1Q13 neutrons per centimeter squared
per second. The U of W reactor flux proved to be marginal for the analysis
of the trace amounts of arsenic found in the small tree-ring samples;
however, the larger WSU reactor was adequate. The WSU reactor was to be used
if arsenic sensitivity proved to be a problem, but was shut down during the
early stages of the project for reactor control system modifications. The
use of the smaller flux reactor placed constraints on the earlier analyses
and necessitated the use of two yearly rings per sample in most cases instead
of one. While this limited the anticipated quantitative accuracy and
affected the proposed yearly tree pollutant-smelter production correlations,
good qualitative and semiquantitative conclusions could be drawn.
High resolution germanium-lithium (Ge-Li) detectors with state-of-the-
art, computer-supported gamma-ray analyzer systems were used to analyze the
gamma-ray spectra. All quantitative determinations for 7fy\s were performed
internally by computer employing the photopeak analysis method developed by
Korthoven (1970).
ELEMENTS ANALYZED
Arsenic was the only element analyzed in this study. While previous
unpublished work by the author has shown that other pollutant species were
also present in the tree rings taken from Pseudotsuga taxifolia (Douglas Fir)
in the same general vicinity, arsenic was selected for a variety of reasons.
First, it is not native to the trees in the study area. Also, it is emitted
in large amounts from the ASARCO smelter (Crecelius et a!., 1975), probably
of the order of 2 x 10^ kilograms AS203 per year. Third, and
17
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equally important, natural arsenic consists of 100 percent 75/\s which, as
the target material, has a good-sized thermal neutron capture cross section
of 4.5 barns; the resultant radioactive species, 76As, has an ideal
half-life of 26.4 hours for the analysis (Lederer et al . , 1967). Typically,
arsenic can be detected in concentrations as small as 1 microgram per gram
(ug/g) of material with NAA. The nuclear reactions that characterize this
analytical determination are,
75As + n— *76As + capture 7 -ray
+ 0-ray + 7 -ray (559 keV)
Other higher energy gamma rays are also emitted in the 7^As decays, but
their intensities are less than the 559-keV photopeak.
TREE SAMPLE COLLECTION
Several tree-ring core samples were collected from each of the subject
trees (Table 3). Two complete sets of cores were taken from each tree and
one set was retained as a U.S. Environmental Protection Agency archive. In
addition, several of the cores collected were either retained as samples or
used as "practice cores" to develop ring-counting, ring-separation, drying,
and weighing techniques in the laboratory.
Pruning spray was employed to keep tree infection to a minimum, and a
5-millimeter (mm) diameter by 38-centimeter (cm) long stainless steel
increment corer was used to extract the cores. The instrument was kept in an
organic oil when not in use to eliminate metal oxidation and subsequent
sample contamination. A silicone lubricant was sprayed on the corer during
operation to reduce friction. Later examination showed that neither of these
materials introduced contamination in the ring samples and no evidence of any
elements characteristic of stainless steel was noted in the gamma-ray
spectra.
All sample cores were placed in new glass tubes in the field and sealed
to reduce subsequent contamination. The tubes, designed by the author, were
washed in concentrated hydrochloric acid and rinsed with distilled water
prior to use in the field. The cores were typically 30 cm long, since that
was the maximum obtainable with the instrument. This allowed an 85- to
125-year-old sample to be taken, a range which proved satisfactory for the
study.
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TABLE 3. DESCRIPTION OF TREE RING SAMPLES
Sample
Type
Height above
ground (m)
Location on tree
(north 0°)
1-L-A Abies grandis
1-L-B
1-L-C
1-M-A
1-M-B
1-U-A
1-U-B
2-L-A Pseudotsuga
2-L-B taxi folia
2-U-A
2-U-B
3-L-A Abies grandis
3-L-B
3-M-A
3-M-B
3-U-A
3-U-B
4-L-A Thuja plicata
4-L-B
4-L-C
4-M-A
4-M-B
4-U-A
4-U-B
5-L-A Abies grandis
5-L-B
5-M-A
5-M-B
5-U-A
5-U-B
1.4
1.4
1.4
4.8
4.8
5.4
5.4
1.4
1.4
3.8
3.8
1.4
1.4
3.7
3.7
4.3
4.3
1.4
1.4
1.1
4.3
4.3
5.6
5.6
1.4
1.4
4.0
4.0
4.9
4.9
90°
85°
95°
90°
85°
90°
85°
180°
355°
180°
355°
270°
275°
270°
275°
270°
265°
100°
90°
270°
90°
85°
85°
90°
270°
275°
270°
265°
270°
265°
L, M, U = lower, middle, upper sections of tree
19
-------
Since most of the trees were located on a hillside with a western
exposure, the majority of samples was taken from either the east or the west
side of the tree so that the ladder used could be placed on reasonably level
ground. The one exception was the Douglas Fir which was located on an
incline with a northern exposure.
SOIL SAMPLE COLLECTION
Soil samples were collected with a 2.5-cm diameter soil corer. The
length of the corer was about 15 cm, but the instrument was designed with
extension arms which allowed sample cores to be taken up to 60-cm depth. In
general, about 20 cm of litter overburden was present and most soil samples
were collected between 20-cm and 35-cm depth. Table 4 describes the soil
samples in detail. All soil samples were placed in clean, scalable
polyethylene vials in the field to keep contamination to a minimum. The
typical size of each sample was 2.0-cm diameter by 2.5-cm length . A
stainless steel spatula was used to cut the samples to length, while in the
corer and to transfer them to the vials in the field. Due to the dampness of
the soil, most samples remained intact until removed for drying and weighing
in the laboratory.
TABLE 4. DESCRIPTION OF THE SOIL SAMPLES
Sample
Tree
Material
Depth from
surface (cm)
Location from tree
(m) (north = 0°)
1-S-l
l-S-2
l-S-3
l-S-4
l-S-5
l-S-6
5-S-l
5-S-2
5-S-3
5-S-4
5-S-5
5-S-6
5-S-7
1
1
1
1
1
1
5*
5
5
5
5
5
5
Litter
Soil
Soil
Soil
Soil
Soil
Litter
Litter**
Soil
Soil
Soil
Soil
Soil
10 - 12.5 1.0 60°
20 - 22.5
22.5 - 25
25 - 27.5
27.5 - 30
30 - 32.5
10 - 12.5 0.8 270°
20 - 22.5
22.5 - 25
25 - 27.5
27.5 - 30
30 - 32.5
32.5 - 35
* This core was taken midway between trees 4 and 5
** Approximately 2.5 cm of decaying bark was encountered between
the litter and soil.
20
-------
Needle samples were extremely difficult to obtain in that the lowest
branches on most trees were over 15 meters (m) above the ground. Tree #1
did, however, have a small branch at about 7 m and a limited number of Grand
Fir needles were otained. In order to have a comparison with other needles,
both live needle and cone samples were collected from a small 4-year-old
Grand Fir that lies about 10 m southwest of tree #2 (Douglas Fir) and about
60 m due east of tree #1. In addition, dead needles were collected from the
base of tree #1 and tree #5 while collecting the soil samples. All samples
were placed in clean polyethylene vials to prevent contamination.
21
-------
SECTION 9
METEOROLOGICAL INFORMATION
Crucial to accurate chronological dating of past air pollutant emissions
from the ASARCO smelter was a complete record of local meteorology for the
period of concern. These data were needed to accurately define dispersion
from the stack to the site, and to establish a normal climatological-growth
relationship for trees at the site. This relationship was needed for two
reasons: to ensure that trees at the site, which is an area of wet climate
and lack of temperature extremes, do reflect past climatic changes, and to
ensure that the samples taken from the trees reflect normal growth patterns
unaffected by local anthropogenic effects.
Since complete records of temperature, precipitation, and wind existed
for Tacoma, Seattle, and Vashon Island from 1890 to the present, the author
believed that qualitative relationships could be established for related
tree-ring concentrations and stack emissions. However, many of the
meterological parameters needed to accurately define stack plume dispersion
were not available. Furthermore, the vast amount of data needed to verify
the climatological-growth relationship for the Puget Sound area did not exist
at the start of the project, thus creating a problem from the outset.
The analytical sensitivity for arsenic became a problem early in the
analysis; therefore, full-scale dispersion modeling was not required to
interpret the data and a simpler evaluation was made. The relative freedom
of the study area from localized weather events made it possible to
extrapolate with good reliability the available Tacoma, Seattle, and Vashon
Island climatological data, thus providing the necessary weather/climate
descriptors for the study area. From this, qualitative estimates of the
yearly tree growth and yearly deposition of arsenic were made. A comparison
of the growth estimates with the weights of the specific rings was made in
order to evaluate the accuracy of and verify qualitatively the
climatological-growth relationship.
CLIMATOLOGICAL DATA
Temperature and precipitation data for Tacoma for the period 1930-1960
were taken from Phillips' climatological summary (Phillips, 1960). Table
22
-------
5 lists the maximum, minimum, and average temperature by months as well as
the record maximum and minimum temperatures for each month of the period
denoting the year in which they occurred. An evaluation of the annual
results at the bottom of the table shows 1955 to be a year of extremes in
temperature, an important fact that will be discussed later.
Table 6 lists the mean monthly precipitation for the 1930-1960 period
along with the maximum and minimum monthly averages for the period, and the
monthly 24-hour maximum. The significant anomaly is the 47.9 cm of
precipitation which occurred in December 1933. This is also important and
will be discussed later on. The tabulation of 24-hour maximum precipitation
reinforces the previous statement that 5 cm of rain in 24 hours is a heavy
rainfall for the area. Figure 5 shows the annual precipitation for the study
area, along with the 10-year running mean for the years 1893-1970.
TABLE 5. TEMPERATURE STATISTICS (°C) FOR TACOMA, WASHINGTON
FOR THE PERIOD 1930-1960
Month
Daily
maximum
Daily
minimum
Monthly
average
Record
high
Record
low
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Ann.
7.2
9.4
11.3
15.0
18
20
23.4
23.0
20.1
15.5
10.6
8.6
15.2
.3
.5
1.2
2.6
3.7
5.8
8.5
10.9
12.6
12.7
10.8
7.8
4.3
3.1
7.1
4.4
5.9
7.5
10.4
13.4
15.7
18.0
17.8
15.4
11.7
7.5
5.8
11.2
19.4 (1935)
22.8 (1938)
22.8 (1934)
30.0 (1934)
32.8 (1936)
36.1 (1955)
35.6 (1958)
35.0 (1936)
31.1 (1944)
27.8 (1931)
20.6 (1949)
18.3 (1934)
36.1 (1955)
-12.2 (1950)
-11.7 (1950)
-7.8 (1955)
-4.4 (1955)
-1.1 (1955)
2.8 (1955)
5.6 (1957)
7.8 (1935)
2.8 (1948)
-1.1 (1935)
-13.3 (1955)
-10.0 (1932)
-13.3 (1955)
23
-------
TABLE 6. PRECIPITATION STATISTICS (cm) FOR TACOMA,
WASHINGTON, FOR THE PERIOD 1930-1960
Month
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Annual
Mean
total
13.6
10.6
9.7
6.0
4.1
3.7
1.9
2.1
4.5
9.7
12.6
15.6
94.1
Monthly
maximum
24.3 (1953)
18.6 (1932)
18.1 (1950)
13.4 (1938)
11.2 (1948)
14.2 (1946)
7.6 (1948)
5.7 (1948)
10.0 (1933)
22.4 (1947)
24.8 (1937)
47.9 (1933)
47.9 (1933)
Monthly
minimum
1.7 (1949)
3.9 (1934)
4.6 (1944)
0.6 (1955)
0.4 (1947)
0.2 (1951)
0.0 (1958)
0.2 (1955)
0.5 (1942)
1.3 (1936)
2.0 (1952)
5.0 (1930)
0.0 (1958)
24- hour
maximum
6.9 (1935)
7.9 (1951)
5.5 (1948)
3.5 (1937)
2.9 (1948)
5.0 (1936)
2.7 (1948)
5.0 (1936)
- 5.4 (1945)
6.1 (1934)
7.0 (1937)
6.3 (1933)
7.9 (1951)
24
-------
1143
1016
c
o
•r-
-P
O
d)
0.
1900 1910
1920
I960 1970
YEAR
Figure 5, Annual precipitation (A) and 10-year
running mean (M), 1893-1970
25
-------
SECTION 10
EXPERIMENTAL RESULTS AND CONCLUSIONS
INTRODUCTION
As indicated in Section 4, a relationship evidently exists between
pollutant concentrations in tree rings and the pollutants present in the
atmospheric environment of the tree. Section 5 describes the uniqueness of
the study area used in this demonstration project: the area surrounding the
Tacoma ASARCO Smelter. The history of this smelter is given in Section 6.
While a detailed chronology of pollutant emissions could not be compiled for
the smelter, several specific phases in its history were identified. These
could possibly indicate the pollution present in the atmospheric environment
of the trees used in this study. They were:
- 1890 -- began operation as a smelter,
- 1911 -- switched to copper smelting,
- 1930's — depression years,
- 1959-1960 — shut down during strike,
- 1965 -- became the only commercial source of arsenic
production in the United States,
- 1967-1968 -- shut down during strike,
- 1971-1974 -- definite records of arsenic production available.
These indicators were used to develop a tree-ring analysis scheme which could
demonstrate that the arsenic concentration in the rings was proportional to
the ejection of arsenic into the environment. By evaluating tree rings
before 1890, after 1890, around 1911, during the depression years, during the
strike years, and between 1971 and 1974, evidence could be gathered to
correlate with the above indicators.
In addition to this, Section 4 also identified several factors that could
adversely affect the interpretation of the experimental results. These were:
- diffusion between rings,
- soil leaching and uptake effects,
26
-------
- direct uptake from the air by needles, and
- meteorological variation.
Other possible adverse effects could be that:
- different tree species exhibit differing effects, and
- different trees of the same species have different
uptake patterns.
The tree rings contained the needed information. If diffusion between rings
was taking place, arsenic should be found in rings formed before 1890. If
soil leaching and uptake were problems or if direct uptake from the air was
occurring, one might note differences in arsenic concentrations in the rings
as a function of height in the tree. Finally, if species effects were
important, or if different trees of the same species presented a problem, the
chosen tree mix (three Grand Firs, one Cedar, and one Douglas Fir) should
answer these questions. In order to accomplish this and check for method
validity, the six specific regions of interest based on the history of the
smelter were evaluated.
EXPERIMENTAL RESULTS
A detailed evaluation of the increment cores indicated that the preferred
cores were from tree #2, the Douglas Fir. They were by far the largest
individual rings, typically about double the weight of the Grand Fir and
Western Red Cedar. Here, individual rings could be analyzed at the
University of Washington, whereas in all other trees, 2 years of growth per
sample were required to have sufficient arsenic activity for counting.
Unfortunately, the center of the tree was decomposed and only samples dating
back to 1937 could be obtained. The best tree was #5, a Grand Fir. It had
the most clearly defined rings; its A and B cores and its lower, middle and
upper cores matched reasonably well (see Fig. 6). Consequently, it was
selected as first choice. Tree #1, a Grand Fir and the largest tree in the
group, had extremely narrow rings and had little similarity in adjacent rings
as a function of height in the tree. Since arsenic sensitivity was a major
problem and ring counting was almost impossible in the earlier years, most of
the tree#l samples were saved as archives for future evaluation. One set of
rings was analyzed at Washington State University,with the higher-neutron-
flux reactor, evaluating individual rings between 1954 and 1977. This
allowed a detailed evaluation of both of the strikes. Similar ring-counting
problems were encountered with tree #4, the Western Red Cedar, and tree #3, a
smaller Grand Fir, especially in the earlier years. Patterns of similarity
could be noted in certain years however, and usually the years following 1940
could be counted with confidence.
27
-------
1976 = = 1976
1972 ;=«---:= 1972
1967 1—-•---••••= 1967
i960 !-::::::! 196°
1Q._ = .,c,r= 1955
1952
£ ^-;S 1941
1941 ^:- ;;,-== 1937
1937 i::;^;!E 1933
1933 —;:--' =
— .--:= 1926
1926 — ^'-' =
1919 —-:::•= 1919
-v^ 1912
1898 =---_-_-_-.= 1898
1890 ^: --_-_-_-.= 1890
1884
LOWER UPPER
Figure 6. Comparison of upper and lower
tree rings - tree #5
28
-------
It is important to note here that the cores could not be mounted and
polished to aid ring counting in the traditional manner because this would
have introduced contamination in the rings. In the future, duplicate cores
(approximately 1 cm apart) will be taken and one sample will be used for ring
counting in the traditional manner and the other will be used for chemical
analysis.
For this study the cores were placed on clean white paper and patterns or
ring maps (Fig. 6) were constructed for each core. A sharp-pointed knife was
used to roll the cores back and forth as an aid in ring identification. As
was noted above, great difficulty was encountered and undoubtedly led to
ring-counting errors, except for tree #5 which was far easier.
The cores were placed on clean paper and covered with Handi-WrapR so
that they could be cut with the sharp-pointed knife without direct handling.
The Handi-WrapR also kept the small individual samples from moving once
they had been cut. The cuts were made along the lines separating yearly
growth. The individual samples were then placed on laboratory spot-test
trays that were properly labeled, transferred to the drying ovens, and
weighed to constant weight. As indicated earlier, several test cores were
employed in developing the technique. After weighing, the ring samples were
transferred to clean polyethylene vials and irradiated in the reactor. After
irradiation the samples were transferred to clean unirradiated vials and
counted.
The experimental results of the study are shown in Tables 7 through 10.
The concentrations were determined by comparing the sample activities to the
activity of arsenic standards that were irradiated simultaneously. The
standards used at the University of Washington (Table 7 data) were A.$203
standards prepared by the author. The standards used at Washington State
University (Table 8 data) were National Bureau of Standards Orchard Leaves
(SRM-1571) containing 14±2 yg/g arsenic. Special sample holders were used to
ensure reproducible geometries during both irradiation and counting at both
laboratories. Traditional gamma-ray standards, e.g., 137cs, 60co,
65zn, 57co, and ^Ha, were used to calibrate the gamma spectrometers
each day. In order to ensure that each sample was exposed to a similar
neutron flux, a cluster of 11 samples was the maximum possible at the
University of Washington. At Washington State University, three levels were
used and iron-flux monitors were employed to account for flux differences.
This allowed 24 samples to be irradiated at once. Since the University of
Washington reactor building was open only 8 hours per day and all 11 samples
had to be counted, counting times were limited to a maximum of 40 minutes.
No time restraint was necessary at Washington State University and all 24
samples were counted consecutively for 1-hour per sample. The first
irradiations on tree #5 were of 1-hour duration and 1-day cooling to
Registered trade name
29
-------
TABLE 7.
ARSENIC CONTENT IN STUDY TREES (MICROGRAMS As/g Wood)
Year
Samples
5-L
5-M 5-U 4-L 4-M
Year
Sample Sample
3-L Year 2-1
Smelting
begins
Depres-
sion
years
Strike
Stri ke
1886-87
88-89
90-91
90-93
94-95
1910-11
12-13
14-15
16-17
1920-21
22-23
24-25
26-27
28-29
30-31
1932
1933
34-35
1957-58
59-60
61-62
63-64
1965
66-67
68-69
70-71
72-73
74-75
76-77
—
—
Trace
5.10
24.5
22.2
8.88
14.0
12.6
12.0
16.2
8.18
10.2
10.7
6.53
4.62
2.18
18.0
28.7
20.3
11.7
46.9
194
47.2
113
27.7
28.4
—
8.05
7.16
8.75
1.32
3.04
6.77
2.94
13.14
18.5
11.9
57.1
14.3
69.3
36.7
— - 20.9 3.30
7.0 4.82
8.84
6.04 11.6 3.66
4.52 14.8 5.05
6.14
2.87
0.3 5.51 3.27
0.8 6.83 2.57
8.12 0.59
3.13 5.78
8.58
9.67
5.74 22.3 5.13
6.07 43.8 6.44
6.96
15.1
12.5
1886-87
88-89
92-93
94-95
1914-15
16-17
1956-57
58-59
60-61
62-63
64-65
66-67
68-69
70-71
72-73
74-75
76-77
30.7
13.0
12.5
11.0
22.0
10.2
16.9
10.7
10.3
12.4
9.41
12.5
9.83
9.01
5.05
11.9
17.6
1958 9.32
1959 10.6
1960 5.71
1961 3.43
1968 3.73
1969 6.01
1972 4.19
1973 5.48
L, M, U = lower, middle, upper sections of tree.
to reduce 24Na interference); 20-, 30- and sometimes 40-minute counts were
made, depending on the arsenic activity. The remainder of the University of
Washington irradiations were of 2-hour duration and 2-day cooling. This
resulted in similar arsenic activity, but decreased the 24Na from about
1-1/2 lifetime decay to 3 lifetimes and hence increased the arsenic
sensitivity with respect to the sodium. In all cases, sodium was the main
interference. A similar irradiation-cooling cycle was used at Washington
30
-------
State for tree #1 samples. In all, 108 samples were analyzed at the
University of Washington and 31 samples at Washington State. Six of the 108
samples were irradiated twice at the University of Washington to
experimentally check the difference between 1-hour and 2-hour irradiations.
Seven of the 108 samples were irradiated at Washington State to
experimentally check the difference between the reactors. These results are
shown in Table 9.
TABLE 8. ARSENIC CONTENT IN TREE #1,
SAMPLE 1-L (ug As/g wood)
Year
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
As
0.393
0.402
0.488
0.541
0.313
0.344
0.441
0.277
0.249
0.499
0.338
Year
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
As
0.432
0.319
0.267
0.335
0.382
0.327
0.430
0.355
0.391
0.571
0.668
TABLE 9. ARSENIC CONTENT IN TREES #1 and #5
DURING STRIKE YEARS (yg As/g wood)
Year
1965
1966-67
1968-69
1970-71
1972-73
1974-75
1976-77
5-L W.S.U.
0.33
0.44
1.39
1.00
0.65
0.48
0.37
1-L W.S.U.
0.39
0.38
0.30 Strike
0.35
0.39
0.48
1.08
31
-------
Several additional irradiations were initially conducted on the extra
increment cores to determine if acceptable arsenic sensitivity could be
obtained from single rings. These studies indicated that at the University
of Washington single rings could be evaluated only for Douglas Firs. Single
rings could be evaluated for the other species only at Washington State.
Six different needle samples, one small Grand Fir cone, three soil
samples and three standards, were also irradiated at the University of
Washington reactor. These results are shown in Table 10. Two-hour
irradiations and 2-day cooling periods were employed, but counting periods
varied, depending on the activity. An evaluation of these data shows that
arsenic concentrations are far greater in all of these than in the rings.
TABLE 10. ARSENIC CONTENT IN NEEDLES, SOILS
AND CONES (yg As/g wood)
Sample
1-N-l
l-N-2
l-N-3
l-N-4
Young Grand Fir
Young Grand Fir
1-N-D
5-S-l
5-S-2
5-S-4
Description
New needle
1-year old
2-year old
2-3 years old
New needle
Cone
Dead needle
Litter
Top 2.5 cm
7.5 cm deep
Weight
(ing)
4.6
5.1
12.2
15.2
8.2
105.9
3.5
19.0
18.1
18.3
Arsenic
content
39,957
7,588
23,820
27,368
10,634
46,260
92,857
27,437
21,833
19,781
All samples were oven-dried to constant weight. Since meteorological
conditions were important to the transport and rainout-fallout of the
pollutants, a comparison between the rainfall in the study area and the
growth (weight) of the rings was used as a first approximation to establish a
simple growth-climatology correlation. This in turn was used to give an
estimate of the expected atmospheric arsenic concentrations. The ring
weights and the expected growth showed a good correlation.
32
-------
DISCUSSION
An evaluation of the data in Table 7 indicates that in the case of tree
#5 the method appears to be valid. For instance, no evidence of arsenic can
be found prior to 1890 in either upper, middle, or lower section ring
samples. Also, the arsenic concentration drops off during the depression
years and there are corresponding decreases following the strike years (see
Fig. 7). Of special interest is the fact that in the upper and middle
samples, the arsenic concentration changes show a direct relation to stack
changes in the same year (see strike year data in Table 7), while in the
lower samples the tree change apparently lags behind the stack change by at
least 1 year. This is seen to some extent in the Table 7 data for the other
trees as well. The single-ring data from tree #1 given in Table 8 also show
a drop in arsenic concentration for the 2 years following the 1959-1960
strike, but the decrease in arsenic for the 1967-1968 strike actually occurs
during the same years (see Fig. 8). This will be discussed later.
On the other hand, an evaluation of the data from trees #3 and #4 shows
that arsenic can be found in the rings before 1890. In both cases the center
of the tree was penetrated during sample extractions. The importance of this
is uncertain. In addition, the fact that the cores of these trees are so
close to 1890 in age may also affect the results. The most probable answer
is ring-counting errors. As stated earlier, a definite pattern correlation
could be seen in the tree #5 samples and counting was easily accomplished.
However, these patterns were difficult to establish and compare in the
majority of the other trees; so counting back to 1890 could be in great
error.
The decrease in arsenic concentration in tree #5 between 1910 and 1915
suggests the smelter change could have had an effect on the atmospheric
concentration of arsenic. This can be interpreted to mean that either less
arsenic was present in the atmosphere, or the arsenic was gradually
eliminated from the soil, indicating the soil could have been saturated.
However, the data of both tree #3 and tree #4, if they are accurate, show
similar concentrations in the 1890's which leads one to believe saturation
effects are small. On the other hand, the arsenic concentration in tree #5
is greater in 1910-1915 than in 1890-1895 which indicates a buildup. Since
no arsenic production records are available from ASARCO and since no records
are available that would indicate how the smelter output should have varied
as it changed from lead to copper smelting, it is unclear what should have
occurred. It is known that lead arsenate is a common ore of lead, but it is
also known that many copper ores are also high in arsenic. One thing is
clear: the expected growth during that time period is high for all of the
years. Thus, decreasing arsenic in tree #5 between 1910-1915 is probably not
a function of adverse growth, or meteorology.
33
-------
-o
o
o
en
30
20
GO
LU
O
O
o
a 10
CO
O LOWER SAMPLES
V MIDDLE SAMPLES
D UPPER SAMPLES
1885 | 1895
SMELTING BEGINS
O
0--O
a
\
/ \
/ \
I O
1910
1920
1930
i
V
57.9
n
11
( I
\ I
\!
I b
I
I
b
4-1955 \ 1965 /
DEPRESSION YEARS STRIKE YEARS
1975
Figure 7. Yearly variation of arsenic concentration - tree #5
-------
1.50
1.25
o
o
CO
«=c
cr.
=3
1.00
0.75
o
o
o
oo
0.50
0.25
OA
o /
o
' \ I
b'
o
/
/
o
50 1955
1960
J
1965
1
1970
1975
STRIKE 1
STRIKE 2
Figure 8, Yearly variation of arsenic concentration - tree #1
*U. S. GOVERNMENT PRINTING OFFICE: 1979-684-481
35
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The strike data (1959-1960 and 1967-1968) for trees #2, #3, #4, and #5
all indicate the method is apparently valid. Consistency is noted
throughout. Again the lower samples in trees #4 and #5 appear to lag behind
the upper samples by 1 to 2 years. The more easily interpreted yearly ring
data in tree #2 confirms that it is at least 1 year. The more complete data
for tree #1 (Fig. 8) show low arsenic concentration for 2 years following the
early strike, but also show low concentrations during the strike period for
the later strike. The explanation for this is not clear.
The apparent exceedingly high values of arsenic found in tree #5 in the
periods of 1968-69 and 1972-73 (Table 7) cannot be accounted for in counting
statistics. These samples were reirradiated in the Washington State
University reactor to resolve this anomally and to compare with tree #1, and
the comparative results are shown in Table 9. The WSU data appear more
normal for tree #5 and suggest the U of W data may be incorrect.
The comparative 2-year data for tree #1 in Table 9 were obtained by adding
the single-year data reported in Table 8. An evaluation of-the data in Table
9 shows that little correlation exists between trees #1 and #5. The large
increase in arsenic concentration in tree #1 (Tables 8 and 9) and also in
tree #3 (Table 7) can be explained as an excess of unbound arsenic that was
present in the sap and may have been deposited during the extensive
oven-drying process. One would expect the outer sap wood to carry the
majority of the nutrients (and foreign material). The lack of correlation
between the U of W and WSU data for tree #5 cannot be explained.
It can be seen in Figure 7 that during the depression years (1932-1935)
the arsenic levels were exceedingly low. A cutback in production in the
early stages of the depression would explain the data if one assumes the
2-year lag. Since 1930-1932 were exceedingly good growing years in the Puget
Sound area (sample weights were above normal which confirms this), climate
could not account for any variations this large.
The scatter in the data is too high to enable comparisons between the
measured values of arsenic in the rings and direct production data available
from ASARCO in 1971 and 1974. This variability is one of the limiting
factors in the analysis. In general, a plus or minus value of 10 to 15
percent can be placed on most of the data presented in Table 7. Typical
40-minute counts yielded an integrated photopeak area of 100 to 500 counts,
which statistially indicates about a 10-percent accuracy. While the
integrated photopeaks for tree #1 in the WSU data were typically 10 times as
large, the excess arsenic found in these years made it impossible to compare
with the ASARCO data.
Many limiting factors have been identified that need to be resolved prior
to validating this method. The limited number of trees evaluated is far from
the number that should be checked. At least 10 to 20 cores should be
36
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evaluated in order to increase accuracy, and dendrochronologists generally
select no less than 20 cores in a particular area. On the other hand, other
equally important, unscientific factors were identified that made the method
validation equally difficult. Since sensitivity is a problem, the extraction
of larger bore samples would aid in decreasing this limitation.
Unfortunately, larger samples are harder if not impossible to obtain. Since
most trees that could be used in analyses of this type lie on private
property, permission must be obtained in order to sample them. The author
found this permission hard to obtain. After considerable time, some
individuals could be interested in becoming part of the study—as long as
small bore samples were to be taken. No one wants 1.5 to 2-cm cores taken
from his trees, especially when it is known that the larger holes need to be
plugged to prevent serious infection.
CONCLUSIONS
Despite the noted problems, the available evidence favors this method.
Although the results indicate that arsenic sensitivity is far less than that
required to develop a quantitative theory, the experiments did show that
changes in smelter production can be related to changes in tree pollutant
concentrations. Further phases of the project should eliminate many problems
and lead to an analytical validation.
37
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REFERENCES
1. ASARCO, Inc. Annual Report, 1976
2. Ault, W.U., R.G. Senechal , and W.E. Erlebach. Environmental
Science and Technology, Vol. 4, 1970. p. 305.
3. Cramer, H.E. , J.F. Bowers, and H.V. Geary. Assessment of the
Air Quality Impact of $$2 Emissions from the ASARCO Tacoma Smelter,
EPA 910/9-76-028, Environmental Protection Agency. July, 1976.
4. Crecelius, E.A., M.H. Bothner, and R. Carpenter. Environmental
Science and Technology, Vol. 2, 1975. p. 325.
5. Heilman, P.E. and G.T. Ekuan. Heavy Metals in Gardens Near the
ASARCO Smelter, Tacoma, Washington. EPA-68-01-2989, Environmental
Protection Agency, April, 1977.
6. Johnson, D.J. and L. Lippman. Environmental Contamination With Lead
and Arsenic From a Copper Smelter. Paper 73-AP-37 presented at Pacific
Northwest International Section, Air Pollution Control Association
meeting, Seattle, Washington, November 29, 1973.
7. Lederer, C.M., J.M. Hollander, and I. Perlman. Table of Isotopes, John
Wiley and Sons, Inc., 6th Ed., 1967.
8. Lepp, N.W. Environmental Pollution. Vol. 2, 1975. p. 49.
9. Phillips, E.B. Climatology Summary: Tacoma, Washington, Office
of the State Climatologist, U.S. Weather Bureau, Seattle, Washington,
1960.
10. Nelson, P.A. and J.W. Roberts. A Comparison of the Efficiency of the
#1 ESP and the Pilot Baghouse in Controlling Particulate Emissions at the
ASARCO Tacoma Smelter. Paper presented at Pacific Northwest Internatinal
Section, Air Pollution Control Association meeting, Vancouver, B.C.,
November 19, 1975.
11. Pillay, K.K.S. Activation Analysis and Dendrochronology for Estimating
Pollution Histories, Transactions of American Nuclear Society, Vol. 21,
Supplement 3, 1975. p. 22.
38
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REFERENCES (Continued)
12. Sheppard, J.C. and W.H. Funk. Environmental Science and Technology,
Vol. 2, 1975. p. 638.
13. Szopa, P.S., E.A. McGuiness and J.D. Pierce. Wood Science and
Technology. Vol. 6, 1973. p. 72.
14. United States Bureau of Mines - Minerals Yearbook, Vol. I,
U.S. Department of Interior, 1961.
15. United States Bureau of Mines - Minerals Yearbook, Vol. I,
U.S. Department of Interior, 1962.
16. United States Bureau of Mines - Minerals Yearbook, Vol. I,
U.S. Department of Interior, 1963.
17. Ward, N.I., R.R. Brooks and R.D. Reeves. Environmental Pollution,
Vol. 6, 1974. p. 149.
18. Washington State Air Monitoring Data, annual publication of Department
of Ecology, Air Programs Division, Olympia, Washington 98504, 1976.
39
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/3-79-030
2.
3. RECIPIENT'S ACCESSION NO.
flTLE AND SUBTITLE
DEVELOPMENT OF A STRATEGY FOR SAMPLING TREE RINGS
5. REPORT DATE
. March 1979
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
Jerry A. Riehl
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
Northwest Environmental Technology Laboratories, Inc.
5709 - 80th S.E,
Mercer Island, Washington 98040
10. PROGRAM ELEMENT NO.
1AA601
11. CONTRACT/GRANT NO.
CB-7-0771-A
2. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency-Las Vegas, NV
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, NV 89114
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/07
5. SUPPLEMENTARY NOTES
Dr. Gilbert D. Potter, Project Officer
16. ABSTRACT
A method for determining retrospective pollution levels has been investigated.
This method relates arsenic concentration in tree rings to arsenic-in-air con-
centrations based qualitatively on arsenic emissions from a nearby smelter,
corrected for climatological and meteorological effects. To evaluate the validity
of the method, a unique pollution study area was identified and characterized in
detail. Several select trees were sampled and the arsenic concentration determined
by neutron activation analysis. These concentrations were compared to certain
known phases in the production history of the smelter, coupled with the expected
climatology and meteorology of the area. Positive correlations were found thus
satisfying the goals of the preliminary project. Major problems encountered were
low arsenic concentrations and an inadequate number of samples. Recommendations
for future studies are given.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I F;ield/Group
Dendro chronolo gy
Arsenic
Air Pollution
Retrospective Monitoring
06C
07B,E
18B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report/
Unclassified
21. NO. OF PAGES
48
20. SECURITY CLASS (TMipage)
Unclassified
22. PRICE
A03
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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