GEOLOGICAL SURVEY CIRCULAR 692 

Selenium, Fluorine, and 

Arsenic in Surficial Materials 

of the Conterminous United 

States 

Selenium, Fluorine, and 

Arsenic in Surfic"ial Materials 

of the Conterminous United 

States 

By Hansford T. Shacklette, Josephine G. Boerngen, and 

John R. Keith 

GEOLOGICAL SURVEY CIRCULAR 692 

Washingto(l 1974 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, National Center, Reston, Va. 22092 
Abstract .......................................... . 

Introduction ...................................... . 

Selenium ......................................... . 

Analytical method ............................. . 

Results of analyses ............................ . 

Discussion .................................... . 

Fluorine .......................................... . 

Analytical method ............................. . 

CONTENTS 

1 

1 

2 

2 

2 

2 

3 

3 

Fluorine-Continued 

Results of analyses ............................ . 

Discussion .................................... . 

Arsenic ........................................... . 

Analytical method ............................. . 

Results of analyses ............................ . 

Discussion .................................... . 

References cited ................................... . 

ILLUSTRATIONS 

Page 

6 

6 

10 

10 

10 

10 

11 

Page 

FIGURE 1. Map showing selenium concentrations in surficial materials of the conterminous United States . . . . . . . . . . . 4 

2. Map showing physiographic regions of the conterminous United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3. Map showing fluorine concentrations in surficial materials of the conterminous United States . . . . . . . . . . . . 8 

4. Map showing arsenic concentrations in surficial materials of the conterminous United States ............. 12 

TABLES 

TABLE~ 1-3 · Concentrations of elements in samples of soils and other surficial materials from the conterminous 

United States: Page 

1. Selenium..................................................................................... 2 

2. Fluorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

3. Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

III 

Selenium, Fluorine, and Arsenic in 

Surficial Materials of the Conterminous 

United States 

By Hansford T. Shacklette, Josephine G. Boerngen, and John R. Keith 

ABSTRACT 

Concentrations of selenium, fluorine, and arsenic in 912, 911, 

and 910 samples, respectively, of soils and other regoliths from 

sites approximately 50 miles (80 km) apart throughout the 

United States are represented on maps by symbols showing five 

ranges of values. Histograms of the concentrations of these 

elements are also given. The geometric-mean concentrations 

(ppm) in the samples, grouped by area, are as follows: 

Selenium- Entire United States, 0.31; Western United States, 

0.25; and Eastern United States, 0.39. 

Fluorine- Entire United States, 180; Western United States, 

250; and Eastern United States, 115. 

Arsenic- Entire United States, 5.8; Western United States, 

6.1; and Eastern United States, 5.4. 

INTRODUCTION 

The concentrations of 38 elements in samples of 

soils and other regoliths from sites about 50 miles 

(80 km) apart on travel routes throughout the conterminous United States were given by Shacklette, 

Hamilton, Boerngen, and Bowles (1971), 

Shacklette, Boerngen, and Turner (1971), and 

Shacklette, Boerngen, Cahill, and Rahill (1973). 

After these reports were prepared, analytical 

methods became available for determining 

selenium, fluorine, and arsenic in surficial 

materials in concentrations as low as 0.1 ppm (part 

per million), 10 ppm, and 1 ppm, respectively. 

The samples were collected and prepared for 

analysis in the same manner as reported earlier 

(Shacklette, Hamilton, and others, 1971) and were 

analyzed in sequence that was completely random 

with respect to sampling locality. Selenium concentrations were determined by J. S. Wahlberg 

and M. W. Solt, and fluorine and arsenic concen1 

trations were determined by J. W. Budinsky, B. A. 

McCall, and Roosevelt Moore. 

We measured the precision of the analytical 

methods used for these elements by analyzing 48 

randomly selected samples in duplicate. The 48 

duplicates were randomly interspersed among the 

other 912 samples and were unknown to the 

analysts. The precision of each method was estimated by 48 

~(log x ·-logy ·) 2 

. 1 £ t sJ= z= 

96 0.00040, 

where s& is the precisiOn, and xi and Yi are, 

respectively, the determinations of each element 

for the ith sample and its corresponding duplicate. 

The analytical reproducibility, as well as the 

logarithmic variance, for each of the three 

elements is given later in this report. 

Analytical values for the three elements were 

transformed to a logarithmic form because the 

frequency distributions are more nearly symmetrical on a logarithmic scale than on an arithmetic scale. The best measure of central tendency 

in a lognormal distribution is the geometric mean, 

which is the antilogarithm of the mean logarithm. 

The most convenient measure of variation is the 

geometric deviation, which is the antilogarithm of 

the standard deviation of the logarithms. 

Estimates of the arithmetic mean (tables 1-3) were 

derived by the use of Sichel's (1952) technique. 

These methods of statistical evaluation are the 

same as those used for evaluating other elements 

in the samples, as reported by Shacklette, 

Hamilton, Boerngen, and Bowles (1971). 
Although most of the samples studied were 

collected along roads, the specific sampling sites 

were selected to obtain surficial materials that 

were as representative as possible of their natural 

condition. Some samples, of necessity, were 

collected in cultivated fields; the degree of contamination, if any, of these samples or of a few 

samples collected near road shoulders cannot be 

evaluated from the data at hand. Most surficial 

materials analyzed were sampled at a depth of 

about 8 inches (20 em). We believe that soils and 

other regoliths from this depth are influenced very 

little by the surficial contamination associated 

with roadways. 

Many geologists and other workers of the U.S. 

Geological Survey assisted in this study by collecting samples along travel routes to their own fieldstudy areas. This assistance, and that of computer 

specialists, was acknowledged in the earlier 

reports of this sampling program (Shacklette, 

Hamilton, and others, 1971; Shacklette, Boerngen, 

and Turner, 1971.) 

SELENIUM 

ANALYTICAL METHOD 

Selenium concentrations in the samples were determined by a chemical-X-ray fluorescence method. 

A 2-g (gram) soil sample is fused with 15-g sodium 

carbonate and 5-g sodium peroxide. The fusion 

cake is then dissolved in 200 ml (milliliters) of 

water, and the solution is filtered. The filtrate is 

acidified, a tellurium carrier added, and the 

selenium along with the carrier is precipitated by 

an iodide sulfite reduction reaction. The 

precipitate of selenium and tellurium is collected 

on a filter disk and dried, and the quantity of 

selenium is then determined by X-ray 

fluorescence. 

The logarithmic variance of the analytical 

method was measured as 0.042729. This means 

that the analyses are reproducible within a factor 

of 1.61, computed as the antilog of sa at the 68-

percent level of confidence, or within a factor of 

2.59, computed as the square of the antilog sa at 

the 95-percent level. The logarithmic variance of 

selenium measured in all 912 samples is 0.1476, indicating that the analytical-error variance contributed less than 29 percent to the total variance 

in the data. 

RESULTS OF ANALYSES 

Statistics for the selenium concentration of all 

samples, as well as of samples from both east and 

2 

west of the 97th meridian, are given in table 1. 

Figure 1 shows the distribution of the sample sites 

throughout the conterminous United States and 

the selenium concentrations of the samples, expressed in terms of five geometric ranges of concentration. 

TABLE !.-Concentrations of selenium, in pa-rts per million, in 

sa.mples of soils and other surficial materials from the conterminous United States 

[Number of samples is given in parentheses after area] 

... = ... ·;:::: ·E·~ ... - Area ~ ~ ~ 8 -~ e ; 

= g e 0 .., 

~ 

.s C,!) C,!) 

..,., ~8 

Entire conterminous 

United States (912) 0.1-4.32 0.31 2.42 0.45 

Western United States, 

west of the 97th 

meridian (492) ............. .1-4.32 .25 2.53 .38 Eastern United States, 

east of the 97th 

meridian (420) ............. .1-3.88 .39 2.17 .52 

'Estimated by method of Sichel (1952). 

DISCUSSION 

The concentrations of selenium in natural 

materials, including soils, have been extensively 

investigated because of the long-known toxicity of 

this element to domestic animals and man and, 

more recently, because the essentiality of selenium 

in animal metabolism has been established. The 

dual metabolic role of this element was discussed 

by Frost (1972). The relationships of selenium 

chemistry and agricultural practices were discussed in an agriculture handbook by Anderson, 

Lakin, Beeson, Smith, and Thacker (1961), and 

more than 200 literature references to the subject 

were given. More recently, reports were published 

of .selenium accumulation in soils, plants, and 

animals to levels that are toxic (Lakin, 1972) and cf 

effects of selenium deficiency in soils on animal 

health (Muth and Allaway, 1963; Allaway, 1969; 

and Oldfield, 1972). Selenium is generally considered to be nonessential in plant metabolism. 

Low concentrations of this element, however, have 

been shown to stimulate plant growth (Ganje, 

1966, p. 394). 

Lakin (1961, p. 27) outlined the sources of 

selenium in soils . as follows: "The selenium in soils 

may be derived (1) from parent material 

weathered from the underlying rock; (2) from 

wind- or water-deposited seleniferous materials; (3) 

from ground or surface water, by precipitation; ( 4) 

from volcanic emanations brought down by rain; 
and (5) from sediments derived from mining 

operations. All these types are known." 

In general, seleniferous soils of dry regions are 

alkaline, contain free calcium carbonate, and may 

support seleniferous plants that are toxic to 

livestock. In the United States most soils of this 

type are west of the 97th meridian. Soils of more 

humid regions are generally acidic and, even if 

seleniferous, are not known to support seleniferous 

plants. The differences in toxic properties of 

selenium in arid and humid regions were explained 

by Lakin (1961, p. 30): "Although many -factors 

govern the selenium uptake by plants, a partial 

measure of selenium's availability to plants is its 

solubility in water. Toxic soils contain watersoluble selenium; the others do not. From the 

physical chemistry of selenium one finds that it 

may be oxidized to selenates in a moist alkaline environment; the formation of selenates in an acid 

environment is not likely. One may conclude that 

in regions of low rainfall, the alkaline seleniferous 

soils will contain CaSe04, which is soluble in water 

and available to plants; in regions of high rainfall, 

the acid seleniferous soils will not contain selenic 

acid, which, if formed, would be leached out of the 

soil." In addition to water-soluble selenates, watersoluble organic selenium also occurs in some soils, 

and micro-organisms are thought to be important 

in its formation (Lakin, 1972, p. 183-184). 

Goldschmidt (1954, p. 532) stated that the abundance of selenium in magmatic rocks of the earth's 

crust is 0.09 ppm. This element is greatly enriched 

in certain geologic materials, such as phosphate 

rocks that may contain as much as 55 ppm and 

black shales that may contain up to 675 ppm 

(Lakin,1972,p.181). Vinogradov(1959,p.183)gave 

the selenium content of soils as 0.01 ppm, and 

Swaine (1955, p. 91) stated that most soils contain 

0.1-2 ppm selenium. In discussing geochemical 

prospecting by analyzing soils for selenium, 

Hawkes and Webb (1962, p. 372) stated that, 

because of the association of this element with 

epigenetic sulfides, the abundance of this element 

may be used as an indication of base-metal 

deposits. 

Studies of the distribution of selenium-indicator 

plants have led to the discovery of selenium-rich 

uranium deposits in the Western United States 

(Cannon, 1960). Some of the indicator plants concentrate selenium in their tissues by extracting it 

from selenium minerals that are relatively insoluble; when the plants die and decompose, the 

selenium is released in a chemical form that can be 

3 

absorbed by native nonseleniferous plants and by 

cultivated crop plants. These seleniumconcentrating plants were designated "seleniumconverter" plants by Beeson (1961, p. 37). 

The difference in geometric-mean concentrations of selenium in samples of surficial 

materials from the Eastern and Western United 

States, as given in table 1, is statistically significant at the 99-percent confidence level. Some 

patterns in the distribution of selenium concentrations are apparent at a smaller scale. The 

generally low concentrations in samples from the 

northern part of the Cordilleran Mountain region 

(fig. 2) and the high values in the northwestern 

part of the Great Plains region are thought to 

reflect concentrations in the bedrock that largely 

constituted the soil-parent material. The generally 

low concentrations in samples from the 

southeastern part of the Atlantic Coastal Plain 

region and the high values in samples from the 

deltas of major streams in the central part of the 

Gulf of Mexico coast probably reflect the chemical 

composition of the sediments from which the soils 

were formed. The absence of a clearly defined 

pattern of high values that correspond to the socalled seleniferous soils of the northern and 

western parts of the Great Plains region and the 

adjacent parts of the Rocky Mountains is probably 

a reflection of the fact that total, rather than 

available, concentrations of selenium were determined in this study; or, the absence may be due to 

insufficient sampling density, or it may reflect 

both factors. Nevertheless, the range in reported 

selenium values and the means that were computed are believed to be useful indicators of the 

concentrations of total selenium than can be expected to occur in surficial materials of the conterminous United States, although these values are 

higher than those given for soils by Hawkes and 

Webb (1962, p. 372) and Vinogradov (1959, p. 183). 

FLUORINE 

ANALYTICAL METHOD 

Fluorine was determined potentiometrically by 

using a fluoride specific-ion electrode, according to 

the procedure described by Ingram (1970). We 

found the logarithmic variance of the analytical 

method to be 0.11. This means that the analyses 

are reproducible within a factor of 2.17, computed 

as the antilog of sa at the 68-percent level of confidence, or within a factor of 4.72, computed as the 

square of the antilog of sn at the 95-percent level. 
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The logarithmic variance of fluorine concentrations in all 911 samples is 0.305, indicating that 

the analytical-error variance contributes less than 

37 percent to the total variance in the data. 

RESULTS OF ANALYSES 

Statistics for the fluorine concentration of all 

samples, as well as of samples from both east and 

west of the 97th meridian, are given in table 2. 

Figure 3 shows the distribution of the sample sites 

throughout the conterminous United States and 

TABLE 2.-Concentrations of fluor-ine, in parts per million, in 

samples of soils and other surficial materials from the conterminous United States 

[Number of samples is given in parentheses after area] 

Area 

Entire conterminous 

United States (911) ........ 10-3,680 180 3.57 400 

Western United States, 

west of the 97th 

meridian (491) ............. 10-1,900 250 2.66 410 

Eastern United States, 

east of the 97th 

meridian (420) ............. 10-3,680 115 4.38 340 

'Estimated by method of Sichel (1952). 

6 

the fluorine concentrations of the samples, expressed in terms of five geometric ranges of concentration. 

DISCUSSION 

Fluorine is widely distributed in nature, and is a 

common constituent of most soils and rocks. Most 

of the fluorine in soils is thought to be derived 

from the geologic parent materials. Hawkes and 

Webb (1962, p. 365) gave the average fluorine content (ppm) of rocks as follows: Ultramafic, 100; 

mafic, 370; felsic, 800; limestone, 51; sandstone, 

290; and shale, 590. Kokuba (1956) reported the 

following ranges in fluorine content (ppm): 100-800 

in 99 samples of volcanic rocks; 160-2,900 in 5 

volcanic ashes; and 120-2,400 in 28 samples of 

plutonic rocks. This element is added to soils in 

many regions by atmospheric fallout from industrial activity, by volcanic ejecta, or by the 

application of phosphate fertilizers and other fertilizers containing slag. 

The increasing importance of fluorine contamination of agricultural areas by industrial 

processes was emphasized in a report by the German Research Society (Deutsche Forschungsgemeinschaft, 1968, p. 1) as follows [translated]: 
Fluorine damage has been known and examined for almost 

100 years. While earlier it was mostly single occurrences, today, 

because of heavy industrialization of numerous districts, the 

areas have become very small where one can safely suspect no 

fluorine emissions. Meanwhile, we have learned that the source 

of these emissions is by no means limited to the use of fluorinecontaining raw materials (fluorspar) but also includes metalworking factories, hydrofluoric acid production, and 

enamelware factories, and that fluorine emissions also 

originate from electric power plants, brickworks, and so forth. 

One must further bear in mind that the emissions can be widely 

distributed by the wind and, also, that in nature soils with high 

fluorine contents occur, so that in a district with elevated 

fluorine levels in forage plants, for example, far-reaching 

sources must be considered if the emissions are not always 

present in an easily recognizable form. The fluorine problem in 

the German Republic is truly a general problem and not an occasional local condition. 

The high levels of fluorine in some soils may be 

attributed to volcanic activity. No soil sample 

reported in this study is thought to have been influenced by historic volcanism, although fluorine 

from ancient eruptions may remain in some of the 

soils that were sampled. The effects of a recent 

volcanic eruption on the fluorine content of surficial materials are illustrated by Thorarinsson's 

(1970) report of the Mount Hekla, Iceland, eruption 

of May 5-July 15, 1970, as follows: "The tephra 

production was considerable, totalling approximately 30 million m3

• * * * The area on land 

receiving more than 100 tons/km2 was about 9,500 

km2

, or nearly one-tenth of the country. * * * The 

tephra proved unusually rich in fluorine (up to at 

least 1,500 ppm) and caused lethal fluorine poisoning in the grazing livestock, especially sheep. The 

situation is really very serious, especially in some 

districts on the north coast where the tephra is 

very fine grained and washes out more slowly than 

expected. The new grass growing through this ash 

is also poisonous." 

Fluorine concentrations in some samples of the 

present study exceed that of the Iceland tephra, 

but for the most part, this fluorine is probably 

fixed in relatively insoluble compounds. Soluble 

fluorine compounds are almost completely fixed in 

a soil of pH 6.5 or greater in the presence of adequate amounts of calcium carbonate (CaC03) 

through the formation of relatively insoluble 

calcium fluoride (CaF2) (Brewer, 1966, p. 195). In 

the absence of adequate calcium, the formation of 

aluminum silicofluoride, (Al2SiF6h, accounts for 

the observed fixation of the fluoride (Brewer, 1966, 

p. 183). 

Although most of the samples of surficial 

materials collected for this study were from sites 

7 

where sources of possible contamination were not 

obvious, fluorine contamination may have occurred at some locations. For most elements considered in this study, particularly those that form 

compounds of low solubility, we believe that the 

depth at which the samples were collected 

precluded gross contamination. Robinson and 

Edgington (1946) reported that virgin soils contain 

more fluoride with depth, but that with regular 

fertilization soils had the greater fluoride concentrations near the surface. This observation agrees 

with the known low mobility of most fluorine compounds in soils. 

Fluorine, like selenium, plays a dual role in 

animal nutrition-small amounts are essential, 

but larger amounts may be deleterious 

(Underwood, 1971, p. 369-388). Animals may be 

adversely affected by eating forage plants that 

contain 50 ppm (dry-weight basis) or even less of 

fluoride, although the plants may exhibit normal 

growth (Brewer, 1966, p. 180). The importance of 

adequate fluorine in food or water for bone and 

tooth development in humans is well known, and 

problems of excessive fluorine in drinking water 

causing mottled teeth occur in local areas. 

Although low concentrations of fluorine have 

been reported by Nikolic (1956) and others to 

stimulate growth in plants, this element is not considered to be essential for plant growth (Brewer, 

1966, p. 180), and high concentrations in the air or 

soil are toxic to plants. Fluorine levels in soils that 

are injurious to plants are controlled more by soil 

type, calcium and phosphorus content, and soil pH 

than by total fluorine that is present because only 

the soluble fluorine is absorbed. Sandy acid soils 

low in phosphorus favor the development of soluble 

forms of fluorine. 

The differences in fluorine concentrations in 

samples of surficial materials from Western, compared with Eastern, United States (table 2) are 

significant at the 99-percent level of confidence. 

The high levels in samples from the central and 

north-central parts of the Cordilleran Mountain 

region (figs. 2, 3), probably reflect the higher 

fluorine concentrations in the rock types from 

which the soils were derived. Samples from the 

Appalachian Highland region and the Ozark region 

of Eastern United States (figs. 2, 3) tend to contain 

fluorine in concentrations that are greater than 

average, which probably also resulted from the 

higher fluorine content of the parent rocks. In con-· 

trast, the surficial materials from the Atlantic 
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old highly weathered marine deposits tend to contain fluorine in low concentrations. Individual 

sampling sites within this region where the soils 

contain exceptionally high fluorine concentrations 

may reflect industrial contamination. One site in 

central Florida that had high fluorine levels was 

associated with phosphate deposits, and the one 

site in western Kentucky having a high fluorine 

value was near a fluorspar mine. 

ARSENIC 

ANALYTICAL METHOD 

Arsenic concentrations in the samples were 

determined by an arsine evolutionspectrophotometric-isotope dilution method 

(Claude Huffman and J. I. Dinnin, U.S. Geological 

Survey, unpub. data, 1973). The logarithmic 

variance of this method was found to be 0.033. This 

means that the analyses are reproducible within a 

factor of 1.52, computed as the antilog of sa at the 

65-percent level of confidence, or within a factor of 

2.30, computed as the square of the antilog sa at 

the 95-percent level. The logarithmic variance of 

arsenic concentrations in all 910 samples is 0.093, 

indicating that the analytical-error variance contributes less than 36 percent to the total variance 

in the data. 

RESULTS OF ANALYSES 

Statistics for the arsenic concentration of all 

samples, as well as of samples from both east and 

west of the 97th meridian, are given in table 3. 

Shown in figure 4 are the distribution of the sample sites throughout the conterminous United 

States and the arsenic concentrations of the 

samples, expressed in terms of five geometric 

ranges of concentration. 

DISCUSSION 

Arsenic in measurable concentrations is a 

common constituent of rocks, soils, waters, and 

plants. This element is not considered to be essential for either plants or animals, and some arsenic 

compounds are extremely toxic to both. Relatively 

small amounts of arsenic are absorbed by most 

plants from soils that have natural arsenic concentrations. However, the arsenic levels in Douglas-fir 

stems have been used successfully in prospecting 

for ore deposits (Warren, Delavault, and Barakso, 

1968), and arsenic solubilization in the humus 

layer of some soils was attributed to plant action 

by Hawkes and Webb (1962, p. 360). Arsenic that 

10 

occurs as a soil contaminant resulting from 

agricultural practices may be absorbed by plants. 

Liebig (1966, p. 14) stated, "Crops grown on 

arsenic-contaminated soils contain more arsenic in 

the tops and roots than crops grown on unsprayed 

soils, but large amounts of these crops would have 

had to be consumed before toxicity to humans or 

animals resulted." 

Arsenic enrichment of the upper horizons of soil 

by means of plant transport and deposition of 

arsenic obtained from lower horizons probably is 

insignificant. Williams and Whetstone (1940, p. 12) 

reported that arsenic concentrations in native 

plants that grew on uncontaminated soils did not 

exceed 10 ppm in dry plant material and that most 

samples contained less than 1 to 2 ppm. Liebig 

(1966, p. 13) stated, "Apparently, the effect of 

arsenic toxicity is such that plant growth is limited 

before large amounts of arsenic are absorbed and 

translocated to the top." 

TABLE 3.-Concentrations of arsenic, in parts per million, in 

samples of soils and other surficial materialsfrorn the conter-

·minous United States 

[Number of samples is given in parentheses after area] 

Area 

Entire conterminous 

United States (910) 1-97 

Western United States, 

west of the 97th 

meridian ( 490) . . . . . . . . . . . . . 1.2-97 

Eastern United States, 

east of the 97th 

meridian (420)............. 1-73 

1

Estimated by method of Sichel (1952). 

5.8 2.02 

6.1 1.82 

5.4 2.24 

7.4 

7.2 

7.5 

Although the beneficial effects of certain organic 

arsenical compounds on the growth, health, and 

feed efficiency of poultry and pigs have been well 

established (Underwood, 1971, p. 427), most inorganic compounds are highly toxic to animals. 

Average arsenic concentrations (ppm) in rocks 

were given by Hawkes and Webb (1962, p. 360) as 

follows: Ultramafic, 2.8; mafic, 2; felsic, 1.5; shale, 

4; and black shale, 75-225. Arsenic concentrations 

in samples of soil from 12 great soil groups, as 

reported by Williams and Whetstone (1940, p. 6-

10), ranged from 0.2 to 41 ppm, with podzol soils 

having the lower range of values and the prairie 

and chestnut soils tending to fall in the upper 

range. Headden (1910, p. 349), in an early report on 

arsenic in · virgin prairie soils from Kansas and 

Colorado, stated, "I have examined virgin soils, all 
of them marly, from localities many miles apart, 

and have found them to contain arsenic, calculated 

as arsenic acid, as follows: 2.51, 2. 76, 2.8, 3.8, 3.99, 

4.2, 4.7, and 5.0 parts per million of soil [range, expressed as arsenic, 1.3-2.5 ppm]. These quantities 

cannot be considered as mere traces, but are quite 

small compared with the arsenic found to have accumulated in our orchard soils, which show an 

average of 47.7 parts arsenic acid per million." 

Arsenic contamination resulting from 

agricultural practices and industrial operations is 

widespread. Lead arsenate and paris green 

(arsenic trioxide and copper acetate) were widely 

used as insecticides on vegetables, fruits, and field 

crops from early in this century until they were 

almost completely replaced by chlorinated 

hydrocarbon insecticides around 1945-50. Apple 

orchards commonly received lead arsenate at the 

rate of 2 pounds per acre (2.2 kg/ ha) in each spraying, and the trees were sprayed 7-8 times per year 

(Dr. N. R. Benson, oral commun., May 12, 1971). 

Benson (1953, p. 215) wrote, "Almost all land that 

has been used for the commercial production of 

apples or pears in eastern Washington contains 

enough residual lead arsenate from insecticidal 

sprays to interfere with the growth of most plants. 

Keaton (1937) has shown that the unproductiveness of these soils is associated with arsenic 

residue and not with the lead residue." Arsenical 

compounds (principally sodium arsenite and 

arsenic trioxide) were widely used as herbicides 

until replaced by synthetic auxins at about the 

same time that the use of arsenical insecticides 

was discontinued. 

Hawkes and Webb (1962, p. 360) reported, "The 

As content of coal ash is extremely high. As a 

result, burning of coal releases As to the air and 

causes contamination of surficial material 

throughout the surrounding country." The concentrations of arsenic in soils that were attributed to 

smelter pollution in the Helena Valley, Mont., area 

where reported by Miesch and Huffman (1972, p. 

74) to decrease with distance of the sampling site 

from the smelter stack and with the depth at which 

the samples were collected. Expected concentrations of arsenic in the surface layer (0-1 inch; 0-

2.5 em) of soil ranged from 140 ppm at a distance of 

1 mile (1.6 km) to 4 ppm at a distance of 4 miles (6.4 

km). Soil from a depth of 6-10 inches (15-25 em) 

ranged from 13 ppm arsenic content 1 mile (1.6 km) 

from the stack to 5 ppm 4 miles (6.4 km) from the 

stack. 

11 

Mobility of arsenic in soils is generally low 

because of coprecipitation as As03;) with limonite 

and as FeAs04 (scorodite) (Hawkes and Webb, 

1962, p. 360); nevertheless, arsenic from surficial 

contamination has been reported to move down to 

depths of 2-3 feet (60-90 em) in irrigated orchards, 

although most of the arsenic remains in the upper 

12 inches (30 em) of soil (Dr. N. R. Benson, oral 

commun., May 12, 1971). The loss of arsenic from 

soils is thought to result from leaching and 

through conversion of arsenical compounds to· arsine (AsH3) by the action of soil fungi (Williams 

and Whetstone, 1940, p. 3-4). 

We do not know the extent of arsenic contamination of the soil samples used in this study. The 

selection of rural sites, the avoidance of cultivated 

soils where possible, and the depth at which the 

soils were sampled probably prevented a significant amount of contamination of the soil samples. 

The estimated arithmetic mean of these samples, 

7.4 ppm (table 3), is somewhat greater than the 

mean of 5 ppm given by Hawkes and Webb (1962, 

p. 360) and is more than twice the highest value 

found by Headden (1910, p. 349) in virgin prairie 

soils. The range in values in this report is considerably greater than is commonly reported for 

soils that are presumed to be uncontaminated; the 

highest values approach those of total arsenic at 

the lowest level classified as toxic by Benson (1953, 

p. 221). However, the toxicity of soils to plants 

depends on the available arsenic (commonly expressed as soluble or extractable arsenic), and we 

have no measure of the arsenic present in this 

form. 

The mean arsenic concentrations in soils from 

the Eastern and Western United States are similar 

(table 3). The most pronounced pattern in concentration (fig. 4) is that of low concentrations in 

many samples from the eastern and southern parts 

of the Atlantic Coastal Plain region (fig. 2). 

Clusters of high values appear in the central part 

of the Cordilleran Mountain region, the Ozark 

region, and parts of the Appalachian Highland 

region that may reflect the arsenic content of the 

parent geologic materials. 

REFERENCES CITED 

Allaway, W. H., 1969, Control of the environmental levels of 

selenium, in Hemphill, D. D., ed., Trace substances in environmental health-II: Missouri Univ. Proc. 2d Ann. Conf. 

on Trace Substances in Environmental Health, p. 181-206. 

Anderson, M.S., Lakin, H. W., Beeson, K. C., Smith, F. F., and 

Thacker, Edward, 1961, Selenium in agriculture: U.S. Dept. 

Agriculture, Agriculture Handb. no. 200, 65 p. 
61 

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o96 
Beeson, K. C., 1961, Occurrence and significance of selenium in 

plants, in Anderson, M. S., Lakin, H. W., Beeson, K. C., 

Smith, F. F., and Thacker, Edward, Selenium in 

agriculture: U.S. Dept. Agriculture, Agriculture Handb. 

no. 200, p. 34-40. 

Benson, N. R., 1953, Effects of season, phosphate, and acidity on 

plant growth in arsenic-toxic soils: Soil Sci., v. 76, no. 3, p. 

215-224. 

Brewer, R. F., 1966, Fluorine, chap. 12, in Chapman, H. D., ed., 

Diagnostic criteria for plants and soils: Riverside, California Univ., Div. Agric. Sci., p. 180-196. 

Cannon, H. L., 1960, The development of botanical methods of 

prospecting for uranium deposits on the Colorado Plateau: 

U.S. Geol. Survey Bull. 1030-M, p. 399-516. 

Deutsche Forschungsgemeinschaft, 1968, Fluor-Wirkungen: 

Forschungsergebnisse bei Pflanze und Tier [Effects of 

fluorine: Results of research with plants and animals]: 

Wiesbaden, Forschungsberichte 14, Franz Steiner Verlag, 

149 p. 

Frost, D. V., 1972, The two faces of selenium-Can selenophobia 

be cured?: Critical Reviews in Toxicology, v. 1, no. 4, p. 467-

514 (published by The Chemical Rubber Co.). 

Ganje, T. J., 1966, Selenium, chap. 25, in Chapman, H. D., ed., 

Diagnostic criteria for plants and soils: Riverside, California Univ., Div. Agric. Sci., p. 394-404. 

Goldschmidt, V. M., 1954, Geochemistry: Oxford, Clarendon 

Press, 730 p. 

Hawkes, H. E., and Webb, J. S., 1962, Geochemistry in mineral 

exploration: New York, N.Y., and Evanston, Ill., Harper & 

Row, Publishers, 415 p. 

Headden, W. P., 1910, The occurrence of arsenic in soils, plants, 

fruits and animals: Colorado Sci. Soc. Proc., v. 9, p. 345-360. 

Ingram, B. L., 1970, Determination of fluoride in silicate rocks 

without separation of aluminum, using a specific ion electrode: Anal. Chem., v. 42, no. 14, p. 1825-1827. 

Keaton, C. M.,1937, Influence of lead compounds on the growth 

of barley: Soil Sci., v. 43, p. 401-411. 

Kokuba, N., 1956, Fluorine in rocks: Faculty Sci. Kyushu Univ. 

Memoirs, ser. C, v. 2, p. 95-149. 

Lakin, H. W., 1961, Geochemstry of selenium in relation to 

agriculture, in Anderson, M. S., Lakin, H. W., Beeson, K. 

C., Smith, F. F., and Thacker, Edward, Selenium in 

agriculture: U.S. Dept. Agriculture, Agriculture Handb. 

No. 200, 65 p. 

___ 1972, Selenium accumulation in soils and its absorption 

by plants and animals: Geol. Soc. America Bull., v. 83, p. 

181-190. 

Liebig, G. F., Jr., 1966, Arsenic, chap. 2, in Chapman, H. D., ed., 

Diagnostic criteria for plants and soils: Riverside, California Univ., Div. Agric. Sci., p. 13-23. 

Miesch, A. T., and Huffman, Claude, Jr., 1972, Abundance and 

distribution of lead, zinc, cadmium, and arsenic in soils, in 

14 

Helena Valley, Montana, area environmental pollution 

study: U.S. Environmental Protection Agency, Office of 

Air Programs Pub. AP-91, p. 65-80. 

Muth, 0. H., and Allaway, W. H., 1963, The relationship of 

white muscle disease to the distribution of naturally occurring selenium: Jour. Veterinary Med. Assoc., v. 142, no. 

12, p. 1379-1384. 

Nikolic, S., 1956, Contribution a l'etude de l'action du nickel, du 

cobalt et du fluor dans Ia nutrition des plantes et dans la 

fertilisation [Contribution to the study of the action of 

nickel, cobalt, and fluorine in the nutrition and fertilization 

of plants], in Centre Internat. Engrais Chim., 5eme 

Assemblee Gen., 1956 (Beograd) Rappt.: v. 1, p. 195-218. 

Oldfield, J. E., 1972, Selenium deficiency in soils and its effect 

on animal health: Geol. Soc. America Bull., v. 83, p. 173-

180. 

Robinson, W. 0., and Edgington, G. 1946, Fluorine in soils: Soil 

Sci., v. 61, p. 341-353. 

Shacklette, H. T., Boerngen, J. G., Cahill, J. R., and Rahill, R. 

L., 1973, Lithium in surficial materials of the conterminous 

United States and partial data on cadmium: U.S. Geol. 

Survey Circular 673, 8 p. 

Shacklette, H. T., Boerngen, J. G., and Turner, R. L., 1971, Mercury in the environment-Surficial materials of the conterminous United States: U.S. Geol. Survey Circular 644, 5 p. 

Shacklette, H. T., Hamilton, J. C., Boerngen, J. G., and Bowles, 

J. M., 1971, Elemental composition of surficial materials in 

the conterminous United States: U.S. Geol. Survey Prof. 

Paper 574-D, 71 p. 

Sichel, H. S., 1952, New methods in the statistical evaluation of 

mine sampling data: London, Inst. Mining and Metallurgy 

Trans., v. 61, p. 261-288. 

Swaine, D. J., 1955, The trace-element content of soils: England, 

Commonwealth Agric. Bur., Commonwealth Bur. Soil Sci. 

Tech. Commun. 48, 157 p. 

Thorarinsson, Sigurdur, 1970, The "Hekla Fires''-A 

preliminary report of the 1970 Mt. Hekla volcanic eruption: 

Washington, Smithsonian Institution Center for Shortlived Phenomena, 2 p. 

Underwood, E. J., 1971, Trace elements in human and animal 

nutrition [3d ed.]: New York and London, Academic Press, 

543 p. 

Vinogradov, A. P.,1959, The geochemistry of rare and dispersed 

chemical elements in soils [2d ed.]: New York, Consultants 

Bur. Enterprises, 209 p. 

Warren, H. V., Delavault, R. E., and Barakso, J., 1968, The 

arsenic content of Douglas-fir as a guide to some gold, 

silver, and base metal deposits: Canadian Mining and 

Metallurgical Bull., July, 1968, p. 860-866. 

Williams, K. T., and Whetstone, R. R., 1940, Arsenic distribution in soils and its presence in certain plants: U.S. Dept. 

Agriculture Tech. Bull. 732, 20 p. 

:, u.s. GOVERNMENT PRINTING OFFICE: 1974-543-583/ 11'2