^t^¡\h

SELENIUM

IN

AGRICULTURE

Agricaltare Handbook No. 200

Agricaltaral Research Service

U.S. DEPARTMENT OF AGRICULTURE

In Cooperation With the

Geological Survey

U.S. DEPARTMENT OF THE INTERIOR
SELENIUM

IN

AGRICULTU^IE

, U 1/ -i Éy M. S. Anderson, H, W. Lakin, K. C. Beeson,

Floyd F. Smith, and Edivard Thacker ,^ , ^i,- ' 1^' rr^t_ -

7-

Agriculture Handbook No. 20Ö /

Agricultural Research Service )

ILS. DEPARTMENT OF AGRICULTURE

In Cooperation With the

Geological Survey

U.S. DEPARTMENT OF THE INTERIOR
Foreword

About 1930 the subject of selenium in agriculture came up for consideration by scientists of the United States Department of Agriculture and Ijy various experiment stations of "Western States. Numerous IjuUetins and otlier

publications have been issued on this subject. The publications of the Department on various phases of the selenium problem are, for the most part, out

of print or in very short supply. Each of the Department pulilications presented some segment of the work, but not one dealt with the subject as a whole.

It seems timely that a ¡oublication on selenium should be prepared while

the services of several people are aA^ailable who had some part in the initiation

and conduct of the research two to three decades ago. In order to develop the

contemplated writing project, it was necessary to call upon members of different groups within the Department of Agriculture and to enlist cooperation of

the U.S. Department of the Interior.

This Handbook summarizes research that covers especially problems of

selenium in soils, its absorption by plants, and the toxic effects of these plants

upon animals eating the vegetation.

The authors preparing the manuscript for this handliook are:

M. S. Anderson, soil scientist (coordinator). Soil and Water Conservation

Eesearch Division, Agricultural Eesearch Service, U.S. Department of Agriculture, presently retired ;

H. W. Lakin, chemist, Geological Survey, U.S. Department of the Interior,

Denver, Colo., and formerly with the U.S. Department of Agriculture;

K. C. Beeson, chemist, Soil and "Water Conservation Research Division,

presently on foreign assignment ;

Floyd Smith, entomologist. Entomology Research Division, Agricultural

Research Service; and

EdivajicL J. Thacker, biochemist. Soil and "\"\''ater Conservation Research

Division, presently with the Agricultural Research Service Internal Audit

Staff.

CECIL H. "WADLEioir,

Director^ Soil and Water Conservation Research Division.

January 1961

m
Contents

Page

History of selenium toxicity 2

Organization of governmental research 2

Geochemistry of selenium in relation to agriculture, 3

Abundance of selenium in the earth's crust 3

Sources of selenium in selenium-rich sedimentary

rocks 5

Selenium in native sulfur 6

Selenitim in sulfides 6

Transport of selenium in natural waters 9

Behavior of selenium in the zone of "weathering. _ 11

Vertical and lateral distribution of selenium in sedimentary rocks of western United States 12

Selenium anomalies in western united States 13

Sedimentary rocks of Cretaceous age 13

Rocks and sediments of various ages 23

Discussion 23

Chemical determinations of selenium 24

Old methods 24

Current methods 24

Selenium content of soils 27

Toxic seleniferous soils—Pedocals 27

Nontoxic seleniferous soils—Pcdalfers 28

Properties of toxic seleniferous soils 30

Reduction of toxicity by soil amendments 33

Occurrence and significance of selenium in plants-_ 34

Species differences in the absorption and accumulation of selenium 34

Selenium indicator plants 35

Selenium converter plants 37

Distribution of selenium in the plant 37

Occurence and significance of selenium in plants—

Continued

Effect of stage of growth on selenium content

Effect of selenium on growth of plants

Miscellaneous factors affecting the absorption of

selenium by plants

Use and limitations of selenium as an insecticide. _

Tolerance of insects to selenium

Compatibility with other insecticides

Kinds of plants treated

Forms of selenium insecticides

Methods of application

Quantity marketed

Dangers of treated plants and soils to animals..

Health hazards from selenium residues

Effect of selenium on animals

Experimental work with laboratory animals

Experimental work with large animals

Protective measures against selenium

Favorable effects of selenium in the diet

Selenium and human nutrition

Conclusions

Management of seleniferous lands

Acquisition of lands

Land management practices

Grazing lease practices

The example and the future

Summary

Literature cited

Appendix

V

Page

39

39

40

41

42

42

43

43

43

44

44

45

46

50

51

51

52

52

53

53

53

55

55

55

55

55

63

Washington, D.C. Issued August 1961^

For sale by the Superintendent ol Documents, U.S. Government Printing Office, Washington 25, D.C. Price 50 cents (paper)
SELENIUM IN AGRICULTURE

By M. S. ANDERSON, H. "W. L,AKIN, K. C. BEESON, FLOYD F. SMITH, and EDWARD THACKER

Economic losses from poisonous plants have

been reported in the agricultural literature for

many centuries. The overall magnitude of such

losses will never be known, but to individual

herdsmen they often meant financial ruin. Too

often, however, losses of this kind have been accepted as one of the hazards of livestock farming.

Traditionally, these livestock losses have been

ascribed to toxic compounds or poisonous constituents characteristic of specific plant species.

The alkaloids, oxalates, hydrocyanic acid, and

nitrates are some of the components of plants

long known to be toxic to animals and humans.

Generally, the livestock loss was not associated

with location as much as with the species of poisonous plants, except inasmuch as there is a location factor associated with the occurrence of

specific species.

Beath and associates, in publications of the

Wyoming Agricultural Experiment Station (4, <?,

H),^ describe a numl)er of plants of the State that

are a hazard to many livestock owners. Some

species of wide distribution that contain toxic

organic constituents include death camas, larkspurs, arrowgrass, white loco, lichens, water hemlock, and ceitain lupines. The reports mentioned

above describe each species and tell of its places

of growth and when the plant appears. Clinical

symptoms of animals poisoned by the ditferent

plant species are given and are often followed

by descriptions of treatments that should be

applied.

It is important to know something about the

range plants that are poisonous because of organic

chemical groups present, in order properly to distinguisli between range poisoning caused by such

vegetation and possible poisoning due to inorganic

constituents such as selenium compounds as the

dominant poisons.

Nutritional problems in animals grazed in specific locations have been recognized; some of

these were assumed to be caused by deficiencies of

certain essential nutrients in the forage. For example, deficiencies of phosphorus in the soil and

forage have long been recognized as a cause of

osteomalacia in animals. Prior to 1930, the presence of toxic quantities of a mineral element in

^ Italic numbers in parentheses refer to Literature

Cited, p. 56.

certain plants that grew in soils containing excessive quantities of an element was not accepted

as an important factor in animal poisoning.

Hence, the discovery that selenium is the toxic

factor in "alkali disease" not only supplied the

answer to a nutritional problem of long standing

but also opened up a whole new concept of soilplant-animal interrelationships.

For more than a decade, mostly during the

1930's, an intensive investigation was cxjnducted

on selenium in rocks, soils, plants, and animal

tissues. From the work of the U.S. Department

of Agriculture and the activities in certain Western States, particularly by the South Dakota and

Wyoming Agricultural Experiment Stations, the

agricultural significance of selenium was fairly

well established. A large number of Federal and

State publications, in addition to articles in scientific journals were published.

This liandbook summarizes earlier selenium investigations, and réévaluâtes the earlier work in

the liglit of later experience.

Many persons took a prominent part in the

selenium studies. A few of those in the Department of Agriculture who made important contributions include the following: Horace G. Byei-s,

Henry G. Knight, Thomas D.Rice, W. O. Robinson, H. W. Schoening, W. T. Miller, Anna HurdKarrar, A. G. Johnson, John T. Miller, Hazel

Munsell, K. T. Williams, R. A. Osborne, and P. L.

Gile.

In the State experiment stations the following

investigators deserve inclusion in a list of those

making notable contributions: Kurt Franke and

A. L. Moxon, of South Dakota ; and O. A. Beath,

of Wyoming.

The names of two scientists outside the T'nited

States should also be included. These are George

Ancizar Sordo of Colombia, South America (7),

and Dr. Figuera of ^Mexico {208).

Is alkali disease caused by any of the constituents often found to be toxic in plants? In

some initial experiments with rats, animals fed

fluorine and certain other toxic constituents developed symptoms difi'erent from those of alkali

disease {23, 133). Kniglit tlien suggested that

tests l)e made of the vegetation for selenium. It

soon l)ecame known that this element was associated in some way with the problem under consideration, for very small quantities were often
f- '

AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

present in materials tested. Kiiio'ht's siio-a-eslioii,

made at an inter-Bureau meetiiio' and followed by

the disfovery of the elements in the A-eg-etation,

touched otf a series of investigations that broug-ht

selenium into the limelight as a toxic factor to be

reckoned Avith in certain areas of Western States.

It was at once apparent that knowledge of the

presence of selenium in soils of a State might

be I'esponsible for unwarranted prejudice against

agricultural products of that State. Grain and

other feeds shipped out of tlie State jnight be

imder sus]:)icion, even though only a small area

of land were seleniferous. There might l)e a decrease also in the selling price of land in areas

where selenium had been found, and county taxes

might be ad\'ersely afi'ected. As a result the U.S.

Dei^artment of xYgriculture adopted a cautious

policy in ])ublishing results and their interpretations, until such time as atïected areas could be

well delineated and the real hazards of the presence

of selenium known.

A Departmental staff was at work promptly

after Knight suggested the analysis studies of

vegetation and soils for selenium. Time of publication may have little meaning as to priorities

of specific disco\eries as the research proceeded.

Little attem])t will be made here to observe such

ajjpai'ent priorities.

History of Selenium Toxicity

By M. S. AxDERsox

A disease of domestic animals pecvüiar to certain soils of the Great Plains has been known

since early settlement of the Nebraska Territory.

Apparently, the first written mention of the disease in this country is found in a statistical report on sickness and mortality in the Army

of the United States (llß), dated 1857, and

published in 1860. Dr. Madison calls attention

to a "very fatal disease"' among cavalry horses

in August 1856 at Fort Eandall on the west side

of the Missouri River near what is now central

South Dakota. He recognized the disease as new,

fviicl gave a very satisfactory description of the

symptoms. He also correctly ascribed the origin

of Vhe trouble to the pasturage. Later the disease was called ''alkali disease." This name resulted from the false assmnption that saline

waters and salt crusts, largely sulfates, were the

cause of the trouble. A similar animal disease

was known in Mexico more than 200 years earlier.

The trouble seemed to be associated with vegetation grown on outwash from certain mines in the

vicinity of Irapuato. These mines utilized the

Patio process, which involves recovery of silver

with mercury. This gave rise to the false assumption that mercury in the local vegetation

was the source of trouble. The disease was known

locally as Soliman disease, later shown to be identical with the alkali disease of the United States.

Vegetation from a market in Irapuato and from

nearby areas showed that plants of the Crucifer

family frequently contained enough selenium to

constitute a health hazard. Local information

indicated that certain people who lived essentially on food ¡produce in the area sometimes had

health problems.

Evidence of seleniferous vegetation in other

parts of the world far antedates the observations

in the Western Hemisphere. There is little doubt

that similar troubles were observed by Marco Polo

in western China and eastern Turkestan at least

as early as 1275 A.D. The following, from a

translation by Komroff (98) is of interest:

"It is a fact that when they take that road

they cannot venture among tlie mountains with

any beast of burden excepting those accustomed to

the country, on account of a poisonous plant growing there, which if eaten by them has the effect

of causing the hoofs of the.animals to drop off.

Those of the country, however, being aware of

its dangerous quality, take care to avoid it."

Organization of Governmental Research

By ]\I. S. ANDERSON

As a result of conferences with mauA' ranchers

Kurt W. Franke (58) of the South Dakota

Agricultural Experiment Station started work in

1028 on the so-called alkali disease of livestock.

Great credit is due him for the approach he macle

to a study of the problem in South Dakota. His

work in that State was later carried on by A. L.

Moxon, who published an excellent paper entitled

"Selenium Poisoning" (131). In this report he

gave a historical resume, listing some of the

earlier work in which selenium presumably played

a part. The earlier work included a report by

the Kansas station in 1891 and the Wyommg

station in 1893. Peters (Ui), oí the Nebraska
SELENIUM IN AGRICULTURE

Station, mentions related -n-ork in 1904; in 191U

the South Dakota station mentions tlie advisability of conducting cooperative investigations

by that State on the so-called alkali disease.

These are only a few of the reports in which

animal diseases on western ranges are described.

The data, accumulated over a period of years

on the poorly understood animal sicknesses on

ranges, provided a good background for su):)sequent studies. The important impact from sucli

recoi'ds dates from 1931, when the U.S. Dejiartment of Agriculture called a conference in "Washington, D.C., to discuss the problem, its ramifications, and possible cooperative investigations that

might l>e undertaken.

In 1933 a Presidential order authorized tlie

Secretary of Agriculture to set aside $35,000 for

work on the alkali disease, designated in the Department as the osteoedemic project. Appro{n'iations for this work were later included in the

regular budget of the U.S. Department of Agriculture. Such appropriations were continued

until the beginning of "World War TI. Appropriate bureaus and laboratories of the Department

took part in the work that involved soils, plants,

and animals.

The work on alkali disease was begun during

the period of severe economic depression. Under

the circumstances the services of several chemists

and otlier scientists were readily obtained. Considerable persuasion was exercised on the former

Bureau of Cliemistry and Soils to initiate mass

collection of soils to be analyzed in great numbers in a relati^'ely short time. It was not known

at that time what place a soil analysis might have

in relation to plant composition.

Since various factors influence the availabilitj'

to plants of other elements in soils, it was assumed

that a similar condition exists for selenium. Later,

it developed that the selenium I'ontents of certain

kinds of i^lants were of particular importance,

whereas other plant species resisted absolution of

selenium.

The organization of Federal experimental work

establislied a progressive policy involving collection of samples of soils, vegetation, and other

materials; chemical analyses of these materials;

and interpretation of the data with respect to a

soil-plant-animal relationship. Additional areas

were examined each summer, and generalizations

regarding tlie selenium problem were continuously

broadened.

When the investigation of alkali disease was

begun, no one anticipated that its ramifications

might extend far beyond the borders of the United

States. However, not only did the trouljle extend

northward into Canada and southward into

Mexico, but soils in other countries and in other

entirely dití'erent circumstances produce some seleniferous vegetation. xA-inone' these are Ararentina and Spain {'200).

Geochemistry of Selenium in Relation to Agriculture

Bv H. ^Y. LAKIN

ABUNDANCE OF SELENIUM

THE EARTH'S CRUST

IN

Selenium is one of the dispersed elements, occurring in minute amounts in all materials of the

earth's crust and rarely concentrated in any material in amounts above 100 p.p.m. (parts per million). From nine papers published between 1924

and 1952, Fleischer {53) compiled estimates of the

abmidances of the elements in the earth's crust.

The abundance of selenium in igneous rocks was

given in three of these papers as 0.09, 0.09, and

0.1 p.p.m. ; the estimates for selenium in the earth's

crust ranged from 0.03 to 0.8 p.p.m.

Estimates made by geochemists of the average

selenium content for the most common rock types

are included in table 1. The estimates are

probably of ' the correct order of magnitude—

although based on vei-y meager data—because the

data available in the literature are much less

^ Pnlilication authorized by the Director, U.S. Geological Survey.

numerous for selenium than for those elements

readily determined by emission spectrograpliy.

Goldschmidfs value {72^ 73) for selenium in

igneous rocks—0.09 p.p.m.—is based on considerations of the sulfur-selenium ratio in sulfides of

various geologic origin,- in which the selenium

content is sufficiently high to be measurecl. He

concluded that the average ratio is 6,000 to 1. As

his estimate for sulfur in igneous rocks is 52(J

p.p.m., his average value for selenium is one sixthousandth of this figure, or approximately 0.09

p.p.m. Sindeeva and Kurbanova {IGG) found 0.1

to 0.37 p.p.m. in 16 of IS composite samples of various types of igneous rocks from various regions of

the Soviet Union. Leutwein and Starke (UO) reported from 0.15 to 0.46 p.p.m. of selenium in 5

samples of diabase collected from below the selenium-rich Kupferscliiefer in a mine near W^ettin

aljout 30 miles northwest of Leipzig in central

Germany. Davidson and Powers {1^2) present

81 analyses of volcanic rocks from Western ITnited

States and report that only 1 of 42 samples of
AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

TABIJO L—P^stimates of average selenium content

of earth materials

Material Authority Selenium

content

Igneous rocks

Igneous rocks of

U.S.S.R.

Limestones

Limestones and

dolomites.

Shales

Goldschmidt (72)

Sindeeva and

Kurbanova {166).

Rank ama and

Sahama {1^8).

Krauskopf {99)

Minami {121)

Krauskopf {99)

Vinogradov (198)

Krauskopf (99)

Vinogradov (198)

Swaine (176)

P.p.m.

0. 09

. 14

< 1

. 1-1. (?)

. 6

Shales _ . 5-1. 0(?)

Shales and clays

Sandstones

.6

1. (?)

Soils. __ .01

Soils. . 1-2. 0

crystalline volcanic rocks contained more than 2

p.p.m. selenium; it contained 5 p.p.m.

Beath and others {16) describe a tuff of Eocene

age in Wyoming that contained from 12.5 to 187

p.p.m. of selenium. Later work by Everett and

Bauerle {61) revealed that the selenium content

of the tuff is extremely variable; 198 samples assayed during the course of a drilling program contained less than 50 p.p.m., 6 samples contained

between 50 and 120, and 2 contained 120. One

surface sample contained 890 p.p.m. Davidson

and Powers {IfH) report analyses of 32 samples of

tuffs and vitrophyres from the Western United

States; of these, only 3 contained from 0.5 to 3

p.p.m. selenium and the rest contained less than

2 p.p.m.

The selenium content of sea water is extremely

low. Byers and others {27) found no selenium in

samples of sea water from the Atlantic Ocean off

the coast of Ocean City or from the Pacific Ocean

at lat. 4:6°39' and long. 147°4:7; but about 0.25

p.p.b. (parts per billion) was found in a sample

from Puget Sound off' Point No Point. These

workers concluded that selenium is not present in

sea water in amounts in excess of 0.25 p.p.b., the

lower limit of their analytical method , except

near the mouths of streams carrying selenium.

Although Goldschmidt and Strock (7^) found 4

p.p.b. of selenium in a sample of sea water from

the North Sea, Byers and others attributed this

selenium to the Elbe Kiver, which carries minute

amounts of selenium. Lakin and Byers {101)

found 3 p.p.b. of selenium in 4 samples of water

from the Gulf of California 30 and 70 miles southeast of the mouth of the Colorado Eiver. The

selenium content of Japanese coastal waters ranges

from 4 to 6 p.p.m. (Ishibashi and others, 92). The

relative absence of selenium in sea water and its

presence in most sea-floor samples examined are

l^resumably the result of the precipitation of

selenium as a basic ferric selenite.

The selenium content of limestones is variable,

but usually low. Goldschmidt and Strock {7.If)

reported less than 0.1 p.p.m. in a composite of 32

Devonian limestones from Germany. Byers {23)

found from 0.3 to 6 p.p.m. in 3 samples of Fort

Hays limestone in Kansas; Moxon and others

{130) found a maximum of 3 p.p.m. in 5 composite

samples of the same formation in South Dakota.

The Smoky Hill member of the Niobrara formation, described as a calcareous marl, in many

places contains as much as 20 p.p.m. selenimn.

Moxon and others {128) found 0.25 and 0.8 p.p.in.

selenium in limestones of Mississippian and Ordovician age. Knight and Beath (.97), on examination of limestones in Wyoming, found 14.3

p.p.m. in limestone beds of the Phosphoria formation, 6.68 in a limestone member of the Frontier

formation, and 1.54 of selenium in a limestone

member of the Thaynes formation. Fleming and

Walsh {55) reported a limestone containing 2

p.p.m. of selenium in Ireland.

Shales commonly contain more selenium than

other sedimentary rocks. For example, Älinami

{121) reported a composite of 36 European Paleozoic shales as containing 1.2 p.p.m. selenium,

a composite of 14 Japanese Paleozoic shales as

containing 0.24 p.p.m., and a composite of 10

Japanese Mesozoic shales as containing 0.38 p.p.m.

Byers (25), whose method of analysis permitted

the detection of 0.1 p.p.m. of selenium, reported

that selenium was detected in all 500 samples of

Pierre shale. Ancizar-Sordo {1) reported a seleniferous area in Stttamarchan, State of Boyaca,

Colombia, in which the soils were developed from

a gray shale. The 2 samples of shale examined

contanied 1 and 14 p.p.m. selenium, respectively.

Fleming and Walsh {55) assumed the source of

selenium in Irish lacustrine soils containing 30

to 1,200 p.p.m. selenium to be a pyritic shale of

early Carboniferotis age containing as much as

28.5 p.p.m. The Kupferschiefer in central Germany is a copper-rich black shale of Permian

age that has been reported by Leutwein and

Starke {110) to contain as much as 15 p.p.m.

selenium. Sindeeva and Kurbanova {166) give

0.3, 0.74, and 9.0 p.p.m. for the selenium content

of 3 samples of shale of Silurian age from the

Baltic region. Beath and others {16) report as

much as 680 p.p.m. in a sample of vanadiferous

shale zone of the Phosphoria formation in w^tern Wyoming; Davidson and Gulbrandsen {I^l)

report samples of mudstone from the Phosphoria

formation containing more than 1,500 p.p.m.

selenium.

Sandstones are usually more permeable than

limestones and shales, and their gross composition

is more variable. These properties are reflected

in the selenium content of sandstones. Moxon

{123) failed to find any selenium in 10 samples

of sandstones in South Dakota, rang-ing- from

Cretaceous to Tertiary in age. Knight and Beatli
SELENIUM IN AGRICULTURE

{97) examined sandstones containing carbonaceous shale bands in the Medicine Bow formation

in AYyoming and found that the carbonaceous

shale band contained 14.39; sandstone adjacent

to the shale, 112.8; and the sandstone 10 inches

from the shale-sanclstone contact, only 2.86 p.p.m.

of selenium. Beath and others (16) describe a

sandstone, presumably of Tertiary age, from Carbon Coimty, Wyo., that contains 112 p.p.m. of

selenium, 91.4 p.p.m. being water soluble. One

may conclude that the selenium content of sandstones is locally variable; local enrichment may

occur because of precipitation of selenium from

ground waters mo\-ing through the beds long

after their deposition. Krauskopf {99) discussed

briefly the processes of enrichment of selenium

and other metals in red beds. The same processes

probably are operative in sandstones containing

selenium associated with uranium on the Colorado Plateau (Coleman and Delevaux, 37).

The selenium content of phosphate rocks is

variable, ranging from less than 0.1 to 55 p.p.m.

in 96 representative samples reported by Eader

and Hill {H7). Davidson and Gulbrandsen

(4-?) report up to 300 p.p.m. selenium in phosphate rock from the Phosphoria formation.

There is no consistent correlation between selenium and the joyrite or organic matter content of

these rocks; although the dark-colored pyritiferous phosphate rock of the Phosphoria formation in Idaho is highest in selenium content, the

dark-colored pj-rite-free rock is medium, ancl the

light-colored rock is lowest, the range given by

Eader and Hill m7) is from less than 0.9 to 30

p.p.m. of selenium. These authors reported that

0.6 percent of the total selenium was watersoluble in one sample of an Idaho phosphate rock.

They also found that primary phosphate deposits

are generally higher in selenium (average of 41

samples, selenium less than 10.9 p.p.m.) than

secondary deposits (average of 34 samples, selenium less than 2 p.p.m.), and suggest it has Ijeen

leached from the secondary deposits. According

to these authors only a small portion of the selenium in the raw materials from which superphosphate and phosphoric acid are made is found

in the finished products.

SOURCES OF SELENIUM IN SELENIUM - RICH SEDIMENTARY

ROCKS

Various processes ha\e be«n suggested for the

anomalous concentrations of selenium in sedimentary rocks. Some suggested processes of concentration are (1) precipitation of selenium from

volcanic emanations by rain; (2) deposition of

erosional products from volcanic sulfur, seleniferous tuffs, and sulfide deposits; and (3) precipitation of selenium from streams or ground water

carrying unusual quantities of selenium from

older seleniferous sediments.

Selenium is one of the volatiles in magmas, and

much of it escapes into the air during volcanic

activity. Although much of the selenium in the

earth's crust is contained in disseminated pyrite

and in sulfide ores, the anomalous seleniferous content of the sedimentary rocks of Western United

States may be accounted for by introduction of

the selenium into the sediments from the volatile

products during a long period of volcanism.

I)uring the period from Devonian time, 260 million years ago, through Miocene time, approximately 10 million yeai-s ago (f/J), that part of

this continent west of the present Mississippi

River was at many times below sea level, closed

on the northeast by the Canadian shield, and closed

on the east by the Appalachian uplift. An uplift

at the approximate location of the present western

coast or perhaps farther west was in a state of

intermittent volcanic activity {Jf6). The normal

eastward sweep of the winds must have carried

the ash and gases from this volcanism across the

region occupied by our continent. The selenium

in these gases was probably oxidized to selenium

dioxide, carried down by rain and eventually precipitated as a basic ferric selenite or reduced to

Se= and precipitated with pyrite. The semiclosed nature of the sea prevented oceanic currents

from conveying fine sediments away. As a consequence, one may assume that selenium accmnulated

in these sediments that would eventually become

sedimentary rocks. Activity of selenium-oxidizing and -reducing bacteria (Zo Bell, 212, p. 100)

on the floor of such inland seas could locally render

selenimn soluble by oxidative action or insoluble

by reductive action, and thus cause further localization of the selenium in the sediments.

Vinogradov (197) compares the soils of the

Russian plains with those of Xorth America, but

states : ''However, on the Russian plains, we do

not find those local concentrations of products of

volcanic origin such as boron, arsenic, selenium,

and some other chemical elements. What happens in soils in the United States of America could

be attril^uted to the different histories of these

two platforms." Goldschmidt (73) presents a

slightly different picture as follows: "It appears

that the great igneous activity that has occurred

in the Cordilleran region of North America has

been instrumental in producing nmnerous vein deposits of selenides, and also, perhaps through

volcanic emanations, adding considerably to the

small amounts of selenium normally present in

sediments." Ifthe abnormal amounts of selenium

found in our soils today have their principal origin in volcanic emanations or in an abundance of

sulfide deposits rich in selenium that is subsequently distributed during wentlioring, magmatic

activity in one form or another is assumed by

many geologists to be the primary source of the

selenium of our western Plains.
6 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

SELENIUM IN NATIVE SULFUR

In an oxygen-deficient envirovnnent, selenium is

associated with sulfur; it is found in or associated

with Sulfides and volcanic sulfur. The selenium

contents of some samples of volcanic sulfur are

listed in table 2. The 2 samples from Kilauea

containing 1,400 and 2,200 p.p.m. selenium, reported by Byers and others i'28), represent recent

deep-seated activity. The -Í samples of sulfur collected by T. S. Lovering (table 2 footnote) in 1957

give some insight into tlae variation of the selenium content of the Plawaiian sulfurs: The sulfur from the "Blowhole" cinder cone (Se l,ßOO

p.p.m.) and the Kew Pit crater (Se 1,600 p.p.m.)

are thought to represent magmatic sulfur from

depth; the sulfur from the Spatter cone (Se 900

p.p.m.) may be reAvorked near-surface sulfur, as

the eruption was feeble and of short duration;

the sulfur from the sulfur bank (Se 4 p.p.m.) at

Kilauea has probably been moved many times.

This suggests a partial separation of selenium

from sulfur during sublimation. The low selenium content of the sulfurs from JNIexico, West

Indies, and Iceland may represent residual selenium-])oor fractions or may be indicative of

selenium-poor provinces.

Some old analyses of selenosulfur reported

from the literature by Palache and others (/, p.

143,' HI) show: Kilauea, Hawaii, 5.18 percent;

]N"ew Zealand, 0.30 and 0.19 percent; Lipari Islands, 0.28 and 0.27 percent; and Vulcano, Lipari

Islands, 1.0.3 and 0.88 percent selenium. Some

new determinations of five samples of selenosulfur

from Vulcano range from 0.07 to 0.18 pei'cent

.selenium, with an average of 0.13 percent (Garavelli, 67).

The selenium in Hawaiian soils is proljably

derived from volcanic enumations (Byers and

others, 28). Postulation of this source is supported by the demonstrated presence of selenium

in the gases given off by Kilauea (0.005 mg. in

GOO ml. of gas) and its i-elati\'e absence in Hawaiian lava (less than 0.1 p.p.m.).

Data on selenium in sulfur from sedimentary

rocks are strangely lacking. Although Byers

and others {27, p. 66) state that the absence of

selenium in secondary sulfur has been repeatedly

demonstrated, they neither give any data nor state

the source, of the .sulfur examined. Strode (J75)

reports the presence of selenium in sulfur of volcanic origin and then states: "On the other hand,

the large occurrences of sulphur in sedimentary

rocks are either free from selenium (Louisiana)

or contain only traces of the element (Sicily)."'

These observed cliiïerences in the selenium eontent of sulfur of volcanic origin and sulfur of

sedimentary origin fit the chemical behavior of

the two elements: in the Aveathering zone sulfur

is readily oxidized to sulfate and is mobile; only

under special circumstances is selenium oxidized

to the soluble mobile selenate.

SELENIUM IN SULFIDES

Because of the similar ionic radii of sulfide ion

(S^) and selenide ion (Se=), selenium readily replaces sulfur in sulfide minerals. Although some

selenium is found in naturally occurring selenides

of silver, copper, lead, mercury, and nickel in

many parts of the world (Earley, 4-7), the bulk

of the selenium in tlie earth's crust occurs in sulfide minerals. The annotated bililiography on the

TABLE 2.—SeJenimn in mlfm

Location

Colorado

Kilauea, HawaiiHawaii

Mexico.

West IndiesAlaska

Iceland _

Description

Crude sulfur, ^'\^lcau Mine, Gunnison County

Lava of 1919 acted upon by solfatara sases, 1920

Sulfur from the Southwest Crack at the great Solfatara collected

in 1921 before the great overflow of March 7, 1921.

(Sulfur from "Blowhole" cinder cone, 1955 lava

Sulfur from New Pit crater 1955, Kalapana Ed

Sulfur from Spatter cone on road cut NE of Kala))ana—1955

erudition.

Sulfur bank, Kilauea volcano

(Sulfur from Popocatepetl collected on the border of the States of

Mexico and Puebla.

Sulfur from Popocatepetl Industrial Museum, Mexico City

Sulfur from Citlaltepetl, State of Puebla

Sulfur from El Chickosa, State of Chiapas

Sulfur from Montserrat

Sulfur and arsenic sulfide incrustation, Fumarole No. 135, Valley

of 10,000 Smokes.

Sulfur from hot springs deposits at Krisuvik

Reference

(23)

(S8)

{S8)

(')

(')

(')

0)

(808)

(308)

(SOS)

(S08)

(37)

(211)

(63)

Selenium

p.p.m.

8, .350

1,400

2,200

1,600

1,600

900

10

0

5

1,200

18.9

1 Sulfur collected by T. S. Lovering in January 1957, and analyzed by W. A. Bowles, Jr.; the sulfur from the "Blowhole" cinder cone and New Pit crater is thought to be from a deeper source than that from the fapatter cone.
SELENIUM IN AGRICULTURE

geology of selenium by Luttrell {lU)^ offers

a covei'age of the literature on selenium minerals.

The distribution of selenium in varioussulficles

througliout the world, shown in table 3, is taken

from the comprehensive compilation by ^Michael

Fleischer (5^). Data recently published by Takimoto and others {180) on Japanese sulfides do

not alter the general distribution for the sulfides

listed in table 3. Some galenas are high in

selenium, however, and Davidson (4Ö) has reported more than 1 percent selenium in some

stibnite (SbsSa) samples and more than 0.1 percent in many others. Edwards and Carlos {If8)

found 7 to 9 p.p.m. selenium in four samples of

stibnite from Australia. These values are higher

than the majority of their values for sphalerite

and galena. Davidson (1^0) suggests that the selenium content of stibnite may normally be relatively high.

The data in table o show a concentration of

selenium in all the types of sulfide minerals examined; only 4 of 233 samples show no selenium

in measurable amounts. Selenium is markedly

higher in the sulfide minerals from sedimentary

rocks of AYestern United States (table 4), as reported by Coleman and Delevaux (37). To illustrate, the highest value for selenium in pyrite in

table 3 is 300 p.p.m. ; \\\ contrast, the pyrite from

the sandstone-type uranium deposits in the Colorado Plateau carries as much as 3 percent. Correspondingly, only 13 ( 12 percent ) of the 115 samples of pyrite in table 3 contained more than 100

p.p.m. Se, whereas 29 of the 92 samples (31 percent) from the Colorado Plateau contained more

than 100 p.p.m. This may be a further indication

tliat the Avestem part of the United States is

anomalously high in selenium.

Selenium is localized in some sulfide deposits.

Coleman and Delevaux {37) describe a "persistent

^galena' band developed in the vanadium deposits

witliin the lintrada sandstone [Rifle District, Garfield County, Colo.] composed of galenaclausthalite (PbS and PbSe) in solid solution

* * * the average selenium content of nine samples is 12.2 i^ercent with a high of 18 percent."

Bergenfelt {18) found 1.5 percent selenium in

galena from northern Sweden. Although other

examples can be cited, the role of selenium-rich

sulfides in the fonnation of seleniferous soils is

difficult to evaluate.

In the milling of sulfide-ore deposits, slime

dumps rich in sulfides accumulate. These sulfiderich slime dumps are commonly near stream beds,

and the slimes may be carried by floods to be deposited on alluvial plains below the mill. Three

examples are known of the deposition on flood

plains of selenium-bearing slimes from mining

operations.

One sample, described by Byers {25), is located

in the valley of the Guanajuato River, State of

Guanajuato, Mexico, where chronic poisoning of

domestic animals has resulted. During the 200

years that a silver mine near the river has been

in operation, the slime dumps have been periodically eroded away by the Guanajuato River and

deposited on the flood plain downstream from tlie

mine. Byers reported that a sample of water

collected 0.25 mile below the slime dump contained

0.2 p.p.m. soluble selenium and that this water

was used for irrigation. The surface soils of the

alluvial plain contained 1 to 6 p.p.m. selenium:

adjacent soils not subject to flooding and samples

below 12-inch depth in the flood plain contained

0.1 to 0.4 p.p.m. selenium. This report is of interest because the selenium content of the sulfides

is not high. Three samples of the ore—wastes

high in marcasite and other sulfides and of the

slime—contained, respectively, 16, 7, and 4.6 p.p.m.

of selenium.

Another area of flood plain contamination 1)y

selenium-rich sulfide slimes has Ijeen observed

near Park City, Utah (Lakin and Byers, 102).

Ore from nearljy mines is milled in Park City:

the silver-, gold-, lead-, and zinc-rich concentrates

are shipped to Salt Lake City, and the rejected

slimes are collected in settling basins along Silver

Creek. Samples of the ores contained as much as

.540 p.p.m. of selenium, and samples of the slimes

ranged in selenium content from 25 to 125 p.p.m.

The selenimn content of silt samples from the

stream bed ranged from 70 p.p.m. for those below

the settling basin on Silver Creek to 20 p.p.m. in

silt, 14 miles below the basins at the confluence of

Silver Creek with the "Weber River. Although the

Weber carries 3 to 5 times as much water as Silver

Creek, a sample of sediment along the Weber 1

mile below the mouth of Silver Creek contained

5 p.p.m. of selenium. A sample of water from Silver Creek contained only 0.001 p.p.m. of selenium,

and the vegetation collected in the flood plain was

of relatively low selenium content (0.5 to 70

p.p.m. ). These mines had been open about 70 years

when the streams were sampled. Perhaps, pollution by wastes from these mines will also cause an

agricultural problem in the years ahead.

The third example of flood plain contamination

with seleniferous material is cited by Trelease

and Beath {18.5) from unpublished work of Beath.

The Jordan River in Owyhee Comity, Idaho,

drains a mining district that has produced large

quantities of silver and gold ore. The authors

state : "One of the most abundant of the silver ores

in the district was naumamiite (AgjSe) containing 23 percent selenium." Selenium poisoning

has occurred on the gi-asslands of the flood plains

below the mines. The silt deposited on these

plains contained from traces to 25 p.p.m. Se, and

grass growing in it contained up to 116 p.p.m.

These examples of the erosion of seleniumbearing waste from mining operations show the

rapid consentrations of sclenium in the sediments below mine workings and grossly exaggerate the selective solution'and precipitationThat

might occur in the normal weathermg of sulfide
00

TABLE 3 —.Selenium in some Sulfide minerals ^

Maximum

concentration

Samples in each selenium concentration of—

Minerals

5,000

p.p.m.

or more

1,000-

4,999

p.p.m.

500-999

p.p.m.

200-499

p.p.m.

100-199

p.p.m.

50-99

p.p.m.

10-49

p.p.m.

<io

p.p.m.

Not

fovnid

Total

samples

Sphalerite - .- -_

P.p.m.

900

2, 100

300

11

63

132

57

Nu mber A'H mber Number

1

2

Number

3

7

3

Nmnber

__

10

Number

1

4

16

Number

9

22

43

1

11

Number

27

1

40

7

6

Number Number

41

Chalcopyrite 43 2

Pyrite- 3

1

115

9

20

9

Marcasite

Pyrrhotite 3

1

1

Troilite: 1

Arsenopyrite 2 3

' Data from Fleischer (04)-

>

O

M

a

d

f

c!

S3

>

a

Cd

o

o

o

o

ci

TABLE 4.—Selenium in snlßde minernls from some 7'ochs of the Western United. States ^

Maximum

concentration

Samples in each selenium concentration range of—

Minerals and source

1 percent

or more

5,000-

9,999

p.p.m.

1,000-

4,999

p.p.m.

500-999

p.p.m.

200-499

p.p.m.

100-199

p.p.m.

50-99

p.p.m.

10-49

p.p.m.

3-9

p.p.m.

<3

p.p.m.

Total

samples

Sedimentary rocks:

Pyrite

Pyrite marcasite

Marcasite

Percent

3

5

.65

Number

2

2

Number

3

4

1

Number

7

9

Number

2

Number

5

4

1

Number

9

4

1

2

Number

9

7

Number

19

8

1

3

Number

21

S

2

1

Number

33

12

Number

no

60

6

Hydrothermal vein deposits and intrusive

rocks:

Pyrite 3 9

Ö

>

i

H

O

>

O

a

o

d

d

w

Data from Coleman and Delevaux (37).
SELENIUM IN AGRICULTURE

bodies, but represent only acceleration of the same

processes.

Native selenium has resulted from the oxidation

of selenides and seleniferous sulfides in the Colorado Plateau. Thompson and others {182) report

t-n'o occurrences of native selenium associated with

uranium and vanadium ores of the sandstone-type

on the Colorado Plateau. Davidson {JfO) reported elemental selenium associated with uranium

ores of the Powder River Basin, "Wyoming, and

Thompson and others (182) have reported elemental selenium in the Black Hills. Trites and

Lakin {191), in a study of the zone of oxidation

in seleniferous pyritic sandstone-type uranium

deposits in the Gas Hills area in the central part

of Wyoming and the Baggs area on the WyomingColorado border, found the rock highest in selenium content was sandstone containing red elemental selenium with varying amounts of hydrous

iron oxide that may contain some basic ferric seleTiite. These pink sandstones contained as much

as 2.7 percent selenium. Coleman and Delevaux

{37) have reported the presence of soluble selenium in mine and ground waters.

TRANSPORT OF SELENIUM IN

NATURAL WATERS

In the western United States both solution and

redeposition of selenium are now taking place.

The meager data available on the Colorado Eiver

Basin are sufficient to illustrate these phenomena.

An outline of the Colorado River Basin with the

location of sampling points is given in figure 1.

The selenium contents of samples of the Colorado

River and some of its tributaries are given in table

5. The upper reaches of the Colorado and its

tributaries are usually selenium-free. The selenium content rises in irrigated areas and may be

derived from the leaching of irrigated seleniferous

lands. The high selenium content of water from

drainage ditches of irrigated areas along the Gunnison and Colorado Rivers (table 6) as compared

to the relatively low selenium content of these

rivers shows that the water draining irrigated

mildly seleniferous lands is much enriched in selenium. Salt crusts on walls of drainage ditches in

the same areas contain 16 to 260 p.p.m. (See

table 7.)

Much selenium is moved annually by these

streams. From 2.4 to 5.9 tons of selenium per

month passed a water gage station on the Gunnison River just above its confluence with the Colorado River during a 6-month period, April 1 to

September 30, 1936 (table 8). The total for the

6 months Avas 23.5 tons. The variation with time

suggests an increasing return of seleniferous irrigation-drainage waters to the river in July,

August, and September. The high spring value

probably represents a flushing-out of salts deposited in the fall on the walls and floor of drainage ditches.

Figure 1.—The Colorado River Basin showing location of

sampling points in tables 5 and 6.

The selenium content of a sample of Colorado

River water collected at Yuma, Ariz., was -i p.p.b.

(parts per billion) (table 5). Lakin and Byers

{101) reported 3 p.p.b. Se in waters from the Gulf

of California 30 and 70 miles southeast of the

mouth of the Colorado River. The selenium content of composite sea-floor samples ranged from

none detected to 0.4 p.p.m. ; the highest value was

in a composite core 120 miles southeast of the

mouth of the Colorado River.

From these data it is evident that selenium is

being carried seaward by the Colorado River and

is eventually deposited in the muds of the sea floor.

It is also evident that irrigation practices hasten

the movement of selenium. The use of these

seleniferous waters downstream by other irrigation projects may create additional seleniferous

agricultural areas, but the data available in the

literature are inadequate to evaluate the hazards

involved.

Few data are available on the Missouri-Mississippi River basin. Byers {23) reported as much

as 1,200 p.p.b. in drainage water from the Belle

Fourche irrigation project in Butte CouTity,

S. Dak. Sea-floor samples from the Gulf of

Mexico range in seleniuin content from 0.6 to 1.0

p.p.m. (Lakin and Byers, 101). Apparently

selenium is moving downstream in this river sys-
10 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

TAIîLE f).—Selenium content of water from the Colorado River and üome of itf: trihtitaries

Lal)orMtorv

No.

Stream and location Reference Se

B-14417_.

B-14423_.

B-15197_.

B-15196_

B-14422_.

B-15201_.

B-14427_

B-14420_-

B-14420A

B-18090__

B-18ü89_.

Î3-Ï800.3^

B-20536_.

B-20.537__

B-20535_.

Colorado River, near Cameo, Colo

Gunnisou River, near Cimarrón, Colo

Uncompahgre River, 5 miles south of Onray, Colo

Uucompahgre River, 13 miles south of Montrose, Colo-_-

Uucompahgre River at Colona, Colo. (Dec. 1934)

Uuoompahtire River at Colona, Colo. (May 193.5)

Gunnisou River, Vi mile north of Delta, Colo

Gunnisou River, near Redlands (near Grand Junction),

Colo.

Colorado River, near Grand .Junction, Colo

Paria Ri^ er, Lees Ferrv, Ariz

Little Colorado River, Grand Fails, Ariz

Colorado River, Topock, Ariz

Williams River, Planet, Ariz

Gila River, Coolidge Dam, Ariz

Gila River, Gillespie Dam, Ariz

Colorado River, Yuma, Ariz

Williams and Byers

do

do

do

do

, table 1).

.do_

dodo.

_do.

Byers and others (27, table 13).

.l.do

Williams and Byers (306, table 1).

Byers and others (27, table 13)

J_-do

_do-

_doP.p.b.

0

0

0

0

3

2

7

80

30

1

1

0

0

1

2

4

TABLE 6.—Selenium content of abater from drainage ditches of irrigated areas cdong the Gunnisou and

Colorado Rivers ^

Laboratorv

No.

Field

No.

Location Se

B-14421

B-14424

B-14426

B-14419

B-15203

B-15204

B-14418

0

9

11

3

9

11

2

8

Drainage ditch in Montrose, Montrose County, Colo

Main lateral, 1 mile south of Chipeta, Montrose County, Colo

Rehef drainage ditch, 2 miles east of Montrose, Montrose County, Colo

Main drain, 1.6 miles east of Jjoma, Mesa County, Colo

Surface drainage, 1 mile north of Mack, Mesa County, Colo

Surface drainage near Loma, Mesa County, Colo

New drain, 4 miles north of Mack, Mesa Countv, Colo. (1934)

p.p.h.

700

1,050

320

630

7

3

1, 980

B-15202 New drain, 4 miles north of Mack, Mesa Countv, Colo. (1935) 2, 680

Data from 206, table 1.

TABLE 7.- -Selenirtm content of salt crusts on drainage ditches of irrigated areas along the Gunnhnn

and Colorado Rivers ^

Laboratory

No.

Field

No.

Location Se

B-14412

B-14442

B-14439

B-15085

18

28

25

4

Near main lateral, 1 mile south of Chipeta, Montrose County, Colo

Main drain, 1.5 miles east of Loma, Mesa County, Colo

6.5 miles east of Fruita, Mesa Countv, Colo

Sec. 15, T. 9S., R. 103W., Mesa County, Colo

p.p.m.

100

16

260

52

1 Data from 206, table
SELENIUM IN AGRICULTURE 11

TABLE 8.—Selenmm, in water from 4 f<t(ttion-s on the ( 'alorado and Gunnhon Hirers

Laboratory

No. "

Stream Location Composite water sam- '

pie for dates shown

Runoff in

acre-feet of

water '

Se 2

Se per

month

(calculated)

B-20269___

B-20270

B-20271

Colorado River

do

do

Cameo, Colo

do

do

do

do

do

Apr. 11-.30, 1936

May 1-31, 1936

.June 1-30, 1936

.July 1-31, 1936

Aug. 1-31, 1936

Sept. 1-30, 1936

Apr. 11-30, 1936

May 1-31, 1936

June 1-.30, 1936

July 1-31, 1936

Aue. 1-31, 1936

Sept. 1-30, 1936

Apr. 1-30, 1936

May 1-31, 1936

June 1-30, 1936

.July 1-31, 1936

Aug. 1-31, 1936

Sept. 1-30, 1936

329, 400

1, 168,000

942, 500

347, ,500

234, 800

122,200

(')

{')

{')

{')

{')

P)

291, .500

629, 300

301, 900

72, 680

79, 370

53, 470

P.p.h.

0

0

0

0

1

1

5

2

0

1

5

10

15

5

10

25

25

55

Tons

B-20272

B-20469

B-20470

do

do

do -

Ü,'.32

17

B-20273 do Grand Junction,

Colo.

do

do

do

B-20274

B-20275

B-20276

do

do

do

B-20467

B-20468

B-19565

B-19566

B-19567

B-20277

B-20465

B-20466

do

do

Gunnison River

do

do

do

do

do

do

do

do

do

do

do

do

do

.5.'9

4.4

4. 1

2. 4

2. 7

4.0

1 Calculated from data given in 195, p. 222. 2 Data from 27, table 13. ^ No record.

tern from tlie lar<re areas of seleiiiferous lands

drained by the Missouri River and its tributaries.

^Movement of selenium in other areas is given

by De Salas {IfS), who has examined a number of

ground and surface waters in Argentina and

found selenium ranging from 1 to 67 p.p.b. Surface waters were generally free of selenium; the

highest value reported was 19 p.p.b. In the provinces of Cordoba and Catamarca, ground waters

contained, respectively, 16 to 39 p.p.b. for the ?>

samples examined, and T to 67 p.p.b. for 5 samples.

BEHAVIOR OF SELENIUM IN

THE ZONE OF WEATHERING

The presence of water-soluble compounds of

selenium in Western united States is demonstrated by its presenc« in water of rivers, wells,

and springs. In Hawaii and Puerto Rico, however, selenium, although present, seems to be fixed

in certain soils and unavailable to plants.

The behavior of selenium in various environments may best be determined by an examination

of the oxidation potentials for its various oxidation states as a function of pH. Krauskopf [99)

calculated the oxidation potentials at varying pll

for selenium ions at a concentration of 10"" mole

per liter. These data are given in figure 2.

Krauskopf {99) states:

"Each line on tlie diagram represents equilibrium

between the oxidized form written above the line

and the reduced form written below it * * *. The

space between two lines * * * ig the stability field

of the ion or molecule shown on the upper side

KssñQO—61 2

of the lower line and the lower side of the upper

line. The area enclosed by heavy lines shows

the normal range of surface conditions." The

lower line for Se"-Se= is taken from Chariot {34)

and is for molar solutions. The sign of the redox

potential is given according to the European conA'ention and is opposite to that of Latimer {Hi'/).

These data show that ILSe is unstable in the

presence of moist air. When it is liberated from

FeSe by hydrochloric acid, it decomposes to elemental selenimn and water (Trites and Lakin,

191). The presence of selenium as a pink halo

1.4 -

1.2

\_ "^-H?

-

10

0.8 "* ^"^"""^---^ -

,,.__^ ^^^ SeOV ^~^^ ___

06 r^^^^- ""----.

sT^^ ^^~^^ ■■" --.

0.4 --^^ SeO,* ^""^ ^^^

02

0.0

-02

Se

-04 ^5^^^ ^^^

^^-~~^~~^,Se ^"~^ ^

-0 6 ^?sr^-^__

~^^SepH

From Krauskopf 1955 and Chorlot 1954

Figure 2.—Variation of oxidation potentials of the oxidation states of selenium as a function of pH.
12 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

around oxidizing sulñde bodies is due to tliis instability. The presence of elemental selenium in

volcanic sulfur is another example of ready oxidation of the Sulfide.

Selenium is also oxidized from Se" to Se**

(SeOr) ^vith relative ease. Selenites may be

readily formed in alkaline to mildly acid conditions; thus, selenites should be found in nature.

Williams and Byere {W7) demonstrated that

when extremely dilute solutions of selenites react

with ferric chloride, a very insoluble precipitate

is formed that approximates the composition of

basic ferric selenite (Fe2(OH)4Se0.i) ; the ratio

of iron to selenium, however, is not constant.

Byers and coworkers give numerous examples of

the association of selenium with ferruginous precipitates. The presence of 12 p.p.m. of seleniimi

in Hawaiian soils under an annual rainfall of

about 100 inches is considered by Byers and others

{27) as an example of the occurrence of this ironselenium complex.

In strongly acid conditions—one molar with

respect to H+—the oxidation potential for SeOl"

to Se04° is + 1.15 volts. In acid solution, therefore, very strong oxidants are required to oxidize

selenimn to selenic acid; concentrated nitric acid

does not oxidize it quantitatively. But at pH

values of about 7 and greater, the diiïerence between the SeO,°—SeOr couple and TIoO—On

couple is almost 0.4 A^olts, a difference large

enough to permit the oxidation of SeOz to SeOf

by oxygenated water. If the selenite selenium

were distributed in porous alkaline moist materials, its oxidation by air might proceed at a

measurable rate.

Although Goldschmidt and Strock (7^) repoited the presence of selenates in Chilean nitrates and Williams and- Byers demonstrated

their presence in South Dakota soils in 1936, it

is still tacitly assumed in some current literature

that selenates are very unstable in nature and

that selenium rarely occurs in this foiTii. The

ready reduction of selenates by halogen acids is

more fi'equently mentioned than is the fact that

dilute selenic acid solutions do not react appreciably with such relatively strong reducing agents

as HjS, SO2, and Fe*^ in the absence of halogen

acids (Latimer, 107). Eecently Sindeeva (165)

stated that the selenates iije very easily I'educed

to selenites and to free selenium in nature. The

fact is, however, that in an alkaline oxidizing

environment selenates are stable.

From these considerations one might make

the following predictions : ( 1 ) In regions of alkaline soils—and particularly in regions of low

rainfall—the selenium would occur, in part at

least, as selenate; this selenate selenium would be

soluble, available to vegetation, and readily transported in ground waters; (2) in regions of acid

environment, selenium, if present, would be found

in ferric hydroxide ¡precipitates—quite stationary,

and presumably of low availability to plants.

Vertical and Lateral Distribution of Selenium in

Sedimentary Rocks of Western United States '

By H. W. LAKIN

In an investigation of the so-called "alkali

disease'' of livestock, a prelimiiuiry field survey

was made in the summer of 1!)31 by Kurt, W.

Franke, chemist, T. D. Eice, soil scientist, A. G.

Johnson, ¡jlant pathologist, and II. W. Schoening,

veterinarian (59), to evaluate the economic importance of the disease, its geographical distribution, and possible soil and plant relationships.

Every case of the disease investigated by them

in the central and southwestern parts of South

Dakota, parts of northern Nebraska, and the

eastern part of AVyoming occurred on soils called

Pierre clay or Pierre clay loam that were developed from the Pierre shale. This significant observation directed the attention of all workers

interested in the alkali disease problem to the

importance of the parent material from which

seleniferous soils are developed. It was soon

' Publication authorized by the Director, U.S. Geological

Survey.

found that in addition to the Pierre shale, numerous other geologic formations are sufficiently

seleniferous to form soils that are potential hazards to farm and ranch animals.

The Pierre shale is of Cretaceous age and has

an enormous extent, cropping out in North Dakota, South Dakota, Nebraska, Montana, Wyoming, Colorado, and New Mexico; rocks of equivalent age and similar lithology ai'e known in

Utah. Byers ('23) reported on about 500 samples

representing strata in the recognized subdivisions

of Pierre shale that crop out in Nebraska and

South Dakota. Selenium was found in evei^

sample; Byers published only a small part of

the analytical data but stated that the quantities

of selenium found ranged upward through 100

p.p.m. This early concej^t of the relation of the

selenivuii content of the soils to that of the geologic

formation from which the soils are derived has

been developed and expanded by workers who followed Byers. The work in South Dakota of A. L.
SELENIUM IN AGRICULTURE 13

INfoxon find his associates at the South Dakota

Agricultural Experiment Station is the most complete study of these relationships, and the data

from their investigations fonn the chief bases of

the generalizations made in this revieAv.

SELENIUM ANOMALIES IN

WESTERN UNITED STATES

Data in geologic literature SIIOAY that the selenium content of various rock types, sediments,

and soils is locally variable. The average values

given in table 1 oti'er useful standards, nevertheless, for recognition of anomalous concentrations

of selenium in specific rock types. Some unusally

high selenium values for certain geologic materials

in Western United States are given in table 9.

Comparison of the data in table 9 with the estimated abundance for similar materials in table 1

reveals marked enrichment of selenium in some

of the tutï's, shales, limestones, sandstones, and

soils of Western United States. Thus the tuffs

described by Beath and others (16) as containing

a maximum of 187 p.p.m. of selenium are enriched

by a factor of 2,00(.) in comparison with Goldschmidt's average of 0.09 for the lithosphère.

Similarly, concentrations of selenium have been

found in shales and limestones 260 and 300 times,

respectively, the average values of Rankama and

Sahama; and in soils, 14,000 times Vinogradov's

values. (See tablet.)

Special attention has been given to Cretaceous

formations because of the early observations by

Byers and because of the large area of fannlands

on which soils were derived from these formations.

Many soils in the plains extending eastward from

the Eocky Mountains to the eastern borders of

North Dakota, South Dakota, and Nebraska, to

the middle of Kansas, and to the eastern border

of New Mexico, as well as soils comprising many

thousands of acres of range and irrigated land in

northwestern New Mexico, western Colorado, and

Utah, are derived from Cretaceous sedimentary

rocks. Because of the agricultural importance of

these sedimentary rocks and the relative abundance of data on them, the formations of the Cretaceous period will be considered first and at

greatest lengtli, in the discussion that follows, and

will be followed by a discussion of the data available on the rest of the geologic column.

SEDIMENTARY ROCKS OF CRETACEOUS AGE

During the Cretaceous period an inland sea

invaded the western plains from the Gulf of

JNIexico northward into Canada; it covered an ai'ea

bounded roughly by the present position of the

iMississippi River on the east and the eastern

borders of Nevada and Idaho on the west

( Eardley, .^G). Sediments accumulated in this inland sea for 55 million years and later became the

chalks, shales, and sanclstones that are the parent

materials of many soils in the same region today.

Moxon and his associates have published the

most data on the selenium content of Cretaceous

formations, but their data are restricted to South

Dakota. ]3eath and his associates, who relied

almost wholly on the occurrence of selenium indicator plants to evaluate the seleniferous nature

of the geologic formations on which plants grow,

have published a moderate amount of data on the

selenium content of Cretaceous formations. Bj'ers

and his coworkers have publislied data on numerous random samples of Cretaceous sedimentary

rocks from 10 Western States and from the eastem coast in New Jersey and Maryland. Because

the results of the work of these people are

scattered through many State and Federal publications and in journals of scientific societies, it is

TABLE 9.—Some anomaloitnly high kelemum contents in materials from. Western Z^vited States

Sample

No.

Material Location Reference Se

content

Bed No. 2___ TuflFs of Eocene age

do

Fremont Countv, Wvo

do

Beath and others (16)

Everett and Bauerle (.5/)

Bvers {'2d)

P.p.m.

187

890

B-3321 Pierre shale, Cretaceous age _ _

Shale, Niobrara formation

Phosphate rock in the Phosphoria formation, Permian

age.

Vanadiferous siltstone, Phosphoria formation, Permian

age.

Bentonite, Niobrara formation. Cretaceous age.

Chalk, Niobrara formation

Sandstone, Tertiary age

Surface soil, depth 0-6 inchesSoil, depth 26-32 inches

Boyd County, Nebr

Pueblo County, Colo

Lincoln County, Wyo

Lincoln County, Wyo

Ziebach County, S. Dak

Custer County, S. Dak

Carbon County, Wyo

Logan Countv, Kans _

103

B-18344

4

Byers and others {27)

Beath and others {13)

Beath and others (16)

Moxon and others {130)

Bvers {23)

156

212

680

113

B-3075 - 30

Beath and others {16)

Bvers {24)

112

B-16689 140

B-19650 Fremont County, Colo Byers and others {27) 98
14 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

considered desirable by the autlior to compile these

data for easy reference and access; the compilation is given in tables 10 throuo-h 14.

Table 10 gives the data available on sections of

the Pierre, Niobrara, Carlile, and Greenhorn formations. The data on the Cretaceous formations

and discussion of these data are presented in a sequence from youngest to oldest, contrary to common usage, because the youngest formations, the

Pierre and the Niobrara, are the most seleniferous

and are the parent materials of soils over vast

areas of agricultural importance. The weighted

average of the last column of table 10 was obtained by applying the following equation to the

data :

Parts per million Se X thickness repreWeighted sented by each composite

average Thickness of measured section

The thickness of the section examined in most

cases does not represent the thickness of the member or formation.

A correlation chart of the Cretaceous rocks discussed here is given in figure 3. This chart is

particularly helpful in comparing data in table 11

with those in table 10.

Only a few Cretaceous formations have been

studied, and even for these, detailed studies of the

selenium content are scanty (see tables 10 and 13) ;

thus, broad generalizations about the selenium

content of the Cretaceous sedimentary rocks of

Western United States are not warranted from the

data available. One can conclude, however, that

parts of the Niol^rara and Pierre formations are

locally unusually seleniferous. These seleniferous

parts are potential parent materials of exceptionally seleniferous soils.

The bulk of the data available on measured

sections is on the Pierre shale and is largely from

the work of Moxon and his associates. In South

Dakota, six members of the Pierre shale are recognized, according to Moxon and others {WS).

These, youngest to oldest, are Elk Butte, Mobridge, Virgin Creek, Sully, Gregory, and Sharon

Springs.

No data are available on the selenium content

of the Elk Butte member.

The weighted average selenium content of the

Mobridge member ranges from 0.2 p.p.m. selenium in a 70-foot section in Pennington Cotuity,

S. Dak., to 20.9 in a 50-foot section in Boyd

County, Nebr. Moxon and othere {WS) pointed

out that the selenium content of the Mobridge is

highest in the southeastern exposures along the

Missouri River near the South Dakota-Nebraska

State line and that it decreases westward and

northward. They stated, in this connection, that

selenium in unusual quantities seems to be associated widi calcareous sediments. H. A. Tourtelot, geologist, U.S. Geological Survey, who is engaged in geochemical in\'estigations of the Pierre

sliale (oral communication, 1960), considers that

the Mobridge, whicii he has identified as a marl

along the Älissouri River where it is high in selenium, grades into a shale to the westward, where

it is low in selenium. Within very small areas,

the Mobridge member is the parent material of

very seleniferous soils; but it is important to note

that many soils derived from the Mobridge are

practically nonseleniferous. Nimierous illustrations of this variation in selenium content both

within formations and in the soils derived from

them are in the literature.

Tlie weighted average selenium content of the

Virgin Creek member of the Pierre shale ranges

from 0.9 p.p.m. in a section 140 feet thick in

Dewey County, S. Dak., to a maximum of 22.7

p.p.m. selenium in a section 25 feet thick in Gregory County, S. Dak. The same geographic trend

in the distribution of selenium is shown by the

Virgin Creek membei' as that shown by the Mobriclge member.

The Sully member of the Pierre, which is 486

feet thick at the Irish Creek Well in Ziebacli

County, S. Dak. (Moxon and others, 130), is

generally low in selenium. Its content is 0.5

p.p.m. selenium in a 100-foot section in Dewey

County, S. Dak., 1.3 in the Irish Creek Well section, and 2.3 in a 20-foot section in Stanley

County, S. Dak.

The data compiled on the Sharon Springs

member show it to be the most uniformly seleniferous of the members of the Pierre shale, and

yet the data also demonstrate the great variation

in selenium content common both areally and vertically within single members of the Pierre. To

illustrate: In Butte County, S. Dak., only 1 of

4 composite samples representing a 35-foot section gave a positive test for selenium; but 6 composite samples representing a 235-foot section in

Ziebach County, S. Dak., ranged from 4.5 to 18

p.p.m. and gave an average value of 11.6 p.p.m.

selenium.

The Niobrara formation, which directly underlies the Pierre shale (fig. 3), occurs in Nebraska,

South Dakota, North Dakota, central and southeastern Montana, eastern Wyoming, eastern Colorado, northeastern New Mexico, Kansas, and

southern JMinnesota. The upper part is a leadgray calcareous marl, called the Smoky Hill member, that weathers to yellowish chalk; the lower

part is a medium-gray limestone called the Fort

Hays limestone member. Although the Niobrara

formation is of great areal extent, the areas in

which it crops out to form the parent material of

soils are relatively small.

Tlae Smoky Hill member of the Niobrara is

selenifez'ous, like the overlying Sharon Springs

member of the Pierre shale. Composite samples

of a 100-foot section, collected in Butte County,

S. Dak., averaged 5.4 p.p.m. selenium and contained one 10-foot composite that gave no test for

selenium. In this same region the Sharon Springs

member of the Pierre shale also is low in selenium
SELENIUM IN AGRICULTURE 15

STANDARD CLASSIFICATION

Reference sequence for

Western Interior

If)

O

LÜ

O

<

IÜJ

ce

O

CL

CL

3

CO

Z)

o

o

<

ce

o

ce

LiJ

O

Hell Creek fornnation

Virgin Creekmbi

Verendrye mbr

De Grey mbr

Crow Creek mbr

Gregory mbr

Sharon Springs

member

Eag le

sandstone

Telegropti Creek

formation

o t

Smoky Hill

ctidlk

member

Fort Hoys Is mbr

Sage Breoks mbr

Turner sdy mbr

Blue Hillsh mbr

Foirportchymbf

Pfeifer Is mbr

Jetmore cfik mbr

Hartland sfi mbi

mb

Belle Fourcfie

sfiole

r^owry stiele

Newcostle sondstone

Skull Creek shole

Fall River sandstone

Red shale

Draney

limestone

Bechler

conglomerate

Peterson

limestone

Ephraim

conglomeróle

Northeostern part

of San Juon Basin

New fi/lexico

Animos

formation

Lewis shole

Lo Ventono

ss member

Gibson

cool

member

Hosta ss mbr

N iobrora

shole

member

Juono Lopez ss

Greenhorn Is mbr

Grane ros

shale member

Wallace

County

Kansas

Pliocene

Beecher Island

shole member

Unnamed

member

Salt Gross

shole member

Lake Creek

shole member

Weskon

shale member

Shoron Springs

shole member

Smoky Hill

chalk

member

'¿ Fort Hoys Is mbr ZTuiiirCalcareous

member

Noncolcoreous

member

Dokoto ss

Purgatoire formation

Cosper

region

Wyoming

Centrol

port

South Dokoto

Poleocene

Lance

formation

Poleocene

Hell Creek formation

Timber Lake ss mbr

Lewis shole

Teopot ss mbr

Porkman

sandstone

member

Shannon

sondstone member

Greenish ss mbr

Banded member

Trail City sh mbr

Elk Butte sh mbr

Mobridge sh mbr

Virgin Creek sh mbr

Verendrye sh mbr

lUocomo

De ñrpybent mbr

mbr Agency

sh mbr

Crow Creek mbr

Gregory marl mbr

Sharon Springs

shale member

Niobraro

shale Niobroro

formotion

Carlile

shale

Woll Creek ss mbr Carlile

shale

Dork shole member

contoining locolly

several sandstone

members

Greenhorn

limestone

Groneros

shole

Mowry shole

Thermo- Muddy ss 7ñ5r

polls sh

Dokoto ond other

sondstones not

clearly distinguished

7

Upper ss membber

Stiele

member

Conglomeratic

sandstone

member

Jurassic Jurassic (? )

Big Horn

County

Montona

Poleocene

Hell Creek

formationBearpow

shole

Porkman

sondstone

Eogle

Te 1er graph

Cr mbr

Cloggett

shole member

Virgelle

Elk Basin

ss

Member

equivotent to

Niobroro and

Carlile formotions

Mowry shole

Thermopolis sh

Birdheod"ss"

Grevbull ss mbr

Shole

member

Pryor cgl mbr

Jurassic

Vertical lines indicóle a hiatus* bent, bentonile-, cgl.conglomerote-, chk,cholkjChy,ctialkyj fm^formotion; Isjimestone mbr, me m be rsdy, sondy-, sh,shQle¡ss, sondstone .

Figure 3.—Correlation of cretaceous rocks in certain areas of the western interior of the United States. (Adapted

from Cobban and Reeside (36, chart 10b)).
16 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

TABLE 10.—Selenium content of sections of some sedimentary rocks of Cretaceous age

PIERRE SHALE-MoBRtor.E MEMBER

Location Reference Thickness

Composite

samples

Se range

Weighted

average

NEVi sec. 31, T. 2 N., R, 13 E., Pennington

County, S. Dak.

NEJÍ sec. 16, T. 1 S., R. 19 E., Jackson County,

S. Dak.

NE>i sec. 16, T. 1 S., R. 19 E., Jackson County,

S. Dak.

Center sec. 7, T. 1 S., R. 30 E., Jackson County, S. Dak.

Sees. 13 and 14, T. 5 N., R. 21 E., Haakon

County, S. Dak.

Irish Creek well, SE14, sec. 17, T. 15 N., R. 20

E., Ziebach County, S. Dak.

NW'4NEJi sec. 33, T. 3 N., R. 31 E., Stanley

County, S. Dak.

Hill north of Midland, U.S. Highway No. 14,

Haakon County, S. Dak.

NWKi sec. 3, T.' 10 S., R. 9 E., Fall Riyer

County, S. Dak.

Sec. 29, T. 18 N., R. 30 E., Corson County,

S. Dak.

1.8 mi. south of junction of U.S. Highway No.

14 and S. Dak. Highway No. 63 on U.S. 14,

Stanley County, S. Dak.

Sec. 2, t. 107 N., R. 78 W., Lyman County,

S. Dak.

Roadcut, 8 mi. east of Stamford on U.S. 16,

Jones County, S. Dak.

ji mi. west of junction, U.S. Highway No. 16,

U.S. Highways Nos. 16 and 83, on U.S. 16,

Jones County, S. Dak.

SEMNE1/Í sec.'29, T. 3 N., R. 31 E., Stanley

County, S. Dak.

Sec. 17, t. 100 N., R. 72 W., Gregory County,

S. Dak.

NEJ^NWM sec. 15, T. 106 N., R. 76 W., Lyman

County, S. Dak.

Sec. 22, T. 100 N., R. 72 W., Gregory County,

S. Dak.

Sec. 30, T. 33 N., R. 11 W., Boyd County, Nebr.

High bare hill, sec. 3, T. 96 N., R. 67 W.,

Gregory County, S. Dak.

Sec. 3'3, "T. 98 Ñ., R. 68 W., Charles Mix

County, S. Dak.

Sec. 30, "T. 33 N., R. 11 W., Boyd County,

Nebr. portion of zone D (iden. as Mobridge

by Searight).

Moxon and others (Í38).

do

_do_

-do.

_do_

Moxon and others (ISO)

Moxon and others (128)

Moxon and others (130)

Moxon and others (lêS)

do

Moxon and others (130)..-

Moxon and others (138)

Moxon and others (130)...

do

Moxon and others (128).

do

_do_

_do_

_do_

Moxon and others (ISO).

Moxon and others (1:28).

Byers (23)

Feel

70

157

35

38

135

334. 5

25

15

40

120

70

72

5

10

60

52

15

90

105

90

68

50

Number

7

18

4

4

14

12

3

1

4

12

4

7

1

1

6

5

3

9

11

6

7

27

P.p.m.

0-1. 2

0-1. 0

0-1. 5

0-1. 5

0-8. 5

0-5. 0

0-1. 8

0. 6-1. 6

0-3. 0

0-2. 3

0-3. 0

1. 5-5. 0

1. 2-10. 0

1. 8-10. 0

2. 0-17. 0

1. 3-40. 0

10. 0-23. 0

2. 1-32. 5

1. 5-103. 0

P.p.m.

0. 2

. 3

.5

.95

. 9

1. 0

1. 0

1. 1

1. 24

1. 3

1. 5

3. 0

3. 3

4. 2

5. 8

9. 2

15. 1

18. 5

20. 4

20. 9

PIERRE SHALE—VIRGIN CREEK MEMBER

(Type section) Sec. 29, T. 16 N., R. 29 E.,

Dewev County, S. Dak.

Irish Creek well, SE% sec. 17, T. 15 N., R. 20

E., Ziebach County, S. Dak.

24.85 mi. west of Fort Pierre on U.S. Highway

No. 14, Stanley County, S. Dak.

Midland Hill, north of Midland, Haakon

County, S. Dak.

Roadcut sec 10, T. 96 N., R. 67 W., Charles

Moxon and others (lê8)

Moxon and others (130)

do

do

do

140

289

25

10

10

25

13

4

2

1

1

3

0-2. 5

1. 0-1. 5

2. 0-3. 0

0. 9

1. 1

2. 4

3. 0

6. 0-52. 0

3. 5

Mix County, S. Dak.

Sec. 22, T. 100 N., R. 72 W., Gregory County,

S. Dak.

Moxon and others (128) 22. 7
SELENIUM IN AGRICULTURE 17

TABLE 10.—Selenium content oj sections of some sedimentary rocks of Cretaceous age—Continued

PIERRE SHALE—SULLY ME.MBER

Location Reference Thickness

Composite

samples

Se ran ge

Weighted

average

(Agency zone, Type sec.) NWJ4 sec. 6, T. 12

N., R. 32 E., Dewev Countv, S. Dak.

(Verendrve zone) see. 36, T. 7 N., R. 17 E.,

Moxon and

do

others {12S)

Feet

100

40

78

486

30

6

20

Nil Trlb er

10

4

6

15

2

1

2

F.p.n

0-2.

. .5-1.

0-2.

0-.5.

. 3-2.

.

1

2

0

0

0

p.p.m.

0. 5

8

Meade County, S. Dak.

(Verendrye zone) Fort Pierre, Stanley County,

S. Dak.

Irish Creek well, SE>i sec. 17, T. 15 N., R 20

M jxon

Ho

and others (Í30)„__ 1. 0

1 3

E., Ziebach County, S. Dak.

(Agency zone) Railway cut. Fort Pierre, do 1. 15

Stanley County, S. Dak.

(Gregory zone) Ôacoma Hill, Lyman County, do 2. 2

S. Dak.

(Oacoma zone) Fort Pierre County, S. Dak. do 2. 2-2. 5 2 3

below Verendrye monument.

PIERRE SHALE—SHARON STHIXGS MEMBER

SE^iSWK sec. 8, T. 11 X., R. 3 E., Butte

County, S. Dak.

Sec. 32, T. 103 N., R. 72 E., Lyman County,

S. Dak.

Sec. 23, T. 3 S., R. 8 E., Cu.ster County, S.

Dak. (Iden. as Sharon Springs by Searight).

SEK sec. 13, T. 1 S., R. 8 E., 'Pennington

County, S. Dak.

Sees. 5 and 8, T. 7 S., R. 7 E., Fall River

County, S. Dak.

Irish Creek well, SEM sec. 17, T. 15 X., R. 20

E., Ziebach County, S. Dak.

N. 1/2 sec. 19, T. 10 S., R. 3 E., Fall River

County, S. Dak

Rosebud Bridge, Gregory County, S, Dak

Moxon and others {128).

do

Byers [23)

Moxon and others {128).

do

Moxon and others {130).

Moxon and others {128).

IMoxon and others {130).

35

126

4. 5

58

80

235

95

20

4 0-1. 3 0.3

14 . 7-24. 0 5. 8

G 2. 0-8. 0 7. 3

G 3. 0-21. 0 8. 2

8 . 6-13. 0 9. 1

6 4. ,5-18. 0 11. 6

10 8. 5-24. 0 14. 3

7

IG. 0-21. 0 18. 5

NioBRARA FORMATION

SW14 sec. 32, T. 8 S., R. 1 E., Fall River Moxon and others {128) 30 3 1. 6-7. 0 4. 0

Countv, S. Dak.

SWK sec. 16, T. 4 S., R. 8 E., Cu.ster Countv, do 57 G 2. 7-16. 0 5. 7

S. Dak.

Irish Creek well, SEJl sec. 17, T. 15 X., R. 20 Moxon and others {130) 270 9 10. 0-22. 0 14. 8

E., Ziebach County, S. Dak.

XWM sec. 26, T. 10 X., R. 2 E., 8.5 mi. north Moxon and others {128) 25 3 16. 0-21.0 18. 1

of Mobile Station at Belle Fourche, Butte

Countv, S. Dak.

Sec. 17, T. 104 X., R. 71 W., railroad cut at do 82 S 1 G. 0-45. 0 33. 5

Oacoma, west end of Missouri River bridge,

Lyman County, S. Dak.

XlOBRARA FOR.MATIO.V SMOKY HILL MEMBER

NEM sec. 6, T. 8 X., R. 5 E., Butte Countv,

S. Dak.

Spillway, Lake Henrv, Bon Homme County,

S. Dak.

8.5 mi. west of Pine Ridge, Shannon Countv,

S. Dak.

SEYi sec. 33, T. 8 S., R. 1 W., Xiobrara

County, Wvo.

SEYi sec. 35, T. 1 N., R. 8 E., Pennington

County, S. Dak.

Moxon and others {128).

Moxon and others {ISO).

Moxon and others {128).

do

do

100

5

25

120

86

10

1

3

12

9

0-8.

7. 0-11. 6

. 6-24. 0

5. 7-21. 0

5. 4

6.5

8. 0

11. 8

12.6
18 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

TABLE 10.—Selenium content qf sections of some sedimentary rocks of Cretaceous age—Continued

NiOBRARA FORMATION—SMOKY HILL MEMBER—Continuerl

Com- WeightLocation Reference Thick- posite Se range ed

ness samples average

Feet Nu. mher P.p.m. P.p.m.

SWi-iSWJ^, see. 18, T. 10 S., R. 3 E., Fall Moxon and others {128) 44 5 8. 0-24. 0 15. 0

River County, S. Dak.

Eads, Colo- _ - - Williams and others (208) _ _ 80 8 8. 0-16. 0 12. 0

NE}^ sec. 17, T. 93 \., R. 56 W., Yankton Moxon and others (130) 90 9 2. 0-16. 0 6.5

Coiintv, S. Dak.

SE^i sec. 31, T. 7 N., R. 6 E., Meade County, Moxon and others (128) 6.5 / 0. 3-27. 0 17. 0

S. Dak.

Sec. 23, T. 3 S., R. 8 E., Custer County,

S. Dak.

Byers (33) 34 12 0. 0-30. 0 17. 1

Railroad cut, Oacoma, Lyman County, S. Dak_ Moxon and othei-s (ISO) 25 2 24. 0-28. 0 26. 4

XluBRARA FoR.MATION FoRT H.\YS MEMBER

NW)i sec. 9, T. 93 N., R. 52 W., Clay County,

S. Dak.

Spillway Lake Henry, Scotland, S. Dak

Quarry, Spirit Mound, Clay County, S. Dak__.

Spirit Mound above quarry, Clav County,

S. Dak.

Lake Henry S]3ilhyay, Scotland, Bon Homme

County, S. Dak.

Moxon and others (l-iO).

do

_do_

_do.

_do^

10

9

10

10

0

. 3

1. 0

1. 5

3. 0

CARI.ILE FORMATION

Irish Creek ^yell, SEU .sec. 17, T. 15 N., R. 20

I']., Ziebach County, S. Dak.

Moxon and others (l:iO) 384 0. 0-3. 0 0.84

CREEMHORN FORMATION

Irish Creek well, SEJi sec. 17, T. 16 N., R. 20

E., Ziebach County, S. Dak.

Sec. 18, T. 22 S., R. 66 W., Pueblo County,

Colo.

SWYi sec. 13, T. 9 S., R. 2 E., south of Edgemont, Fall River County, S. Dak.

KE}i sec. 27, T. 9 X., R. 2 E., Butte County,

S. Dak. (Se content was reported as 0.0 Se

p.p.m. for 7 of these lO-ft composite

samples.)

Moxon and others (130).

Byers and otliers (27)

Moxon and others (128).

do

346

39

44

110

15

32

5

11

0--6. 0

1--8. o'

0--3. 2

1--1. 0

1. 3

1.6

.2

content. A remarkably uniform 25-foot section

of tlie Smoky Hill member from Lyman County,

S. Dak., contained 26 p.p.m. seleniuuL Some

seleniferous soils are derived from tlie Smoky Hill

member of the Niobrara in eastern Colorado,

southwestern Kansas, eastern Wyoming, northwestern Nebraska, southwestern South Dakota,

and adjacent to the ^lissouri River in the southern portion of South Dakota and northeastern

Nebraska.

Only a few samples of the Fort Hays member

of the Niobrara formation Avere analyzed by

Moxon and others (13(>), and th.ey were found to

contain little selenium. The highest A'alue reported is o p.p.m. for a 5-foot composite sample

in Bon Honuue County, S. Dak.

The Carlile formation, underlying the Niobrara

formation in South Dakota, is notably IOAV in selenium content. In western South Dakota it is a

medium- to dark-gray noncalcareous shale that is

slightly sandy in places (Moxon and others, 130).

The highest selenium content found in 13 composite samples representing its entire thickness of 384

feet Avas 3 p.p.m.; two of these composites contained no selenium, and the weighted average seleniiuii content for the formation was 0.84.

The (Ireenhorn formation, which underlies the

Carlile formation, occurs in eastern Colorado and

Wyoming, northeastern New Mexico, southeastei-n Monrana, Nebraska, South Dakota, and Kansas, and consists of beds of chalk, shale, and lime-
SELENIUM IN AGPJCULTURE 19

stone. A 346-foot section at Irish Creek Well in

Ziebach County, S. Dak., averaged 2.2 p.p.m.

selenium. Samples of 60 feet of this section contained no detectable amount of selenium ; one composite of 23 feet contained only 0.8 ; the remaining

12 composites ranged from 1 to 6 p.p.m. Moxon

and others {128) were of the opinion "that the

selenium content of the Greenhorn formation in

South Dakota is so low that toxic soils are not

likely to be developed from it." Selenium-indicator plants found growing on the formation were

of relatively low selenimn content. Byers and

others {27) report 32 composite samples representing a section 39 feet thick in Pueblo County,

Colo., contained 0.1 to S p.p.m. selenium with a

weighted average of 1.3. Byers stated that these

values for the (íreenhorn are about the same as

his unpublished values for the upper portions of

the Pierre shale in South Dakota and for the

upper portions of the Mancos shale in western

Colorado.

In table 11 are listed grab samples of various

Cretaceous formations from nine Western States.

The interpretative value of these samples is limited

because of their inadequate numl^er and the fact

that, except for the Xorth Dakota samples, tlie

stratigrapliic position within the formation is

unknown.

TABLE 11.—Selenium content of gratj f^aniples< from xome Heâîmentnnj rocha of CretaccouH age

COLORADO

Sample

No.

Lot-atioii Formation or

member

Reference Se

B-11382

B-11383

B-11380

B-11381

B-11397

B-11399

B-18361

14 mi. north of Fort Morgan, Morgan Count}-

9 mi. north of Fort Morgan, Morgan County"-

12 mi. north of Sterling, Logan Count.v

9 mi. north of Sterling, Logan County

19 mi. south of Fort Morgan, Adams County

2314 mi. south of Fort Morgan, Adams Couiity

38 mi. south of Pueblo, Huérfano County

Pierre

do

do

do

do

do

do

Bvers (23)

__:^-do

do

do

do

do

Byers and

others {27).

do

do

P.p.m.

0

.5

0

2. 0

. 2

.5

. 8

B-18123

B-18342

Ji mi. south of Haswell, Kiowa Countv

1 mi. west of Pueblo—U.S. Highway No. 150, Pueblo

Niobrara

do

54. 0

3. 5

B-18344

B-11415 __

County.

3 mi. west of Pueblo, Pueblo County

3 mi. south of Aver, Otero Countv

do

do

do

Bvers {2S)

Byers («'4)

do

156. 0

5

B-15103

B-15065

3 mi. north of Whitewater, Mesa County

8 mi. north of Delta, Delta Countv

Mancos

do_

3. 0

2. 0

KA.XSAS

B-16523_.

B-5298-_.

B-16176-

B-16l77-_

B-16892_,

B-16697_.

B-16184_-

B-16191_.

B-16696A

B-l7367_-

B-16718_.

B-17128__

B-17434_.

B-17166__

B-17177__

B-5271_-_

Sec. 32, T. 13 S., R. 36 W., Logan County, at contact with

Ogallala.

Sec. 11, T. 13 S., R. 42 W., Wallace Countv

Center of sec. 13, T. 12 S., R. 37 W., Logan Countv

Center of .sec. 13, T. 12 S., R. 37 W., Logan Countv

Sec. 1, T. 14 S., R. 35 W., Logan Countv "^

Sec. 28, T. 14 S., R. 31 W., Grove Countv

SE corner, sec. 24, T. 13 S., R. 37 W., Logan County

NE corner, sec. 1, T. 15 S., R. 37 W., Logan Countv

SE Yi, sec. 21, T. 13 S., R. 35 W., Logan Countv---"

Sec. 29, T. 8 S., R. 20 W., Rooks County

East of Trego Center, Trego Countv

Sec. 10, T. 15 S., R. 24 W., Trego Countv

Sec. 13, T. 10 S., R. 17 W., Rooks Countv

Sec. 2, T. 15 S., R. 22 W., Trego Countvl

Sec. 8, T. 15 S., R. 21 W., Trego County

4 mi. south of Belvedere, Comanche County

Pierre

Weskan

Pierre

do

Niobrara

do

Smokv HilL

do

do

do

Fort Havs_

do_:-_

do_

Carlile_

do_

Kiowa_

Byers {24).

Bvers (23).

Bvers (24)_

do

do

do

^do_

_do-

_do_

_do_

.do_

_do_

do

do

do

Bvers (23).

6.0

. 5

10. 0

22. 0

18. 0

18. 0

16. 0

8. 0

22. 0

8. 0

. 5

. 3

6. 0

. 7

. 5

1. 5

MONTANA

B-15447

B-15505

B-15503

B-1553I

B-15533

2 mi. northeast of Nashua, Valley County

3 mi. north of Leedy, Phillips Counts'

6y2 mi. north of Leedy, Phillips County

5 mi. west and 2.4 nor1;h of Phillips, Phillips County

5 mi. west and }i mi. north of Phillips, Phillips County

Bearpaw.

do._

do,_

_do-

-do.

Bvers (24).

__'_.do

.do.

-do.

2.0

2.0

2.0

1. 0

1. 5
20 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

TABLE 11.—Selenium content of grab samples from, some sedimentary rocks of Cretaceous age—Con.

MONTANA—Continued

Sample

No.

Location Formation or

member

Reference

B-15535

B-1.5540

B-15459

B-15466

B-15509

B-15678

B-15682

B-6295_

6.3 mi. south of Brookside, Phillips County

24 mi. north of Dodson, Phillips County

4 mi. northeast of Cottonwood Creek Bridge, Phillips

County.

Cottonwood Creek Bridge, Phillips County

6 mi. west of Leedy, Phillips County

11.4 mi. east of Ethridgc, Toole County

1.8 mi. north of Shelby, Toole County

18 mi. east of Ridge, Carter County

Bearpaw

do

Judith River_

Byers {24).

do

do

Claggett-.

äo_._

Colorado _

do_--

Graneros _

do

do

do

do

Byers {23).

NEBRASKA

B-4374.

B-4375-

B-7745.

B-7746.

B-7750-

B-14619

B-14680

B-7739_

B-7741_

B-7742..

B-7743-

B-7747.

B-4373_.

B-14673

B-14672

Sec. 2, T.

Sec. 21, T

Sec. 17, T,

At bridge

Sec. 3, T.

Southwest

County,

Sec. 22, T,

Sec. 16, T,

Sec. 2, T.

1 mi. west

Sec. 5, T.

Sec. 23, T.

Sec. 15, T.

Sec. 28, T.

Sec. 34, T,

1 N., R. 17 W., Piarían County

1 N., R. 17 W., Piarían County

, 1 N., R. 17 W., Harlan County

south of Alma, Harlan County

1 N., R. 37 W., Dundy County

corner, sec. 13, T. 33 N., R. 52 W., Dawes

15-ft. composite.

35 N., R. 47 W., Dawes County

. 1 N., R. 9 W., Webster County

1 N., R. 11 W., Webster County

of Riverton, Franklin County

1 N., R. 14 W., Franklin County

, 2 N., R. 21 W., Furnas County

, 1 N., R. 17 W., Harlan County

, 35 N., R. 47 W., Dawes County

, 35 N., R. 47 W., Dawes County

Pierre __

do.

do_

_do_

_do_

.do_

do___

Niobrara.

do_._

do___

do___

do._.

do___

Carlile,__

Graneros.

Byers

do

do

do

do

Byers {24).

do

Byers {23).

do

do

do

do

do

Byers {24).

do

NEW MEXICO

B-18150_

B-20251-

On U.S. Highway No. 85 at Raton

2 mi. northwest of Colfax, T. 28 N., R. 21 E., Colfax

County.

Pierre__

do.

Byers and others

do

NORTH DAKOTA

B-26420 Workings of former Northern Cement & Plaster Co., on

Olson farm, 2 mi. Southwest of Concrete, Cavalier

County, N. Dak.; bentonite 4 ft. above limonite layer

at contact of Pierre and Niobrara formations.

Pierre Lakin and Byers

{102).

L6

B-26421 Same as above, fissile shale immediately above limonite

layer at contact of Pierre and Niobrara formations.

do do 32.0

B-26422 Same as above, limonite layer at contact of Pierre and

Niobrara formations.

do do 34.0

B-26423 Same as above, nodule in Niobrara 6 inches below limonite layer at contact of Pierre and Niobrara formations.

Niobrara do 36.0

B-26424 Same as above, "cement rock," 5 ft. below limonite layer

at contact of Pierre and Niobrara formations.

do do 14.0

B-26425 Same as above, yellow seam 3 inches thick immediately

below "cement rock."

do do 28.0

SOUTH DAKOTA

B-15157.

B-15155.

Sec. 4, T. 8 S., R. 6 E., Shannon Countv 10-ft. composite...

Sec. 33, T. 7 S., R. 6 E., Shannon County 10-ft. composite..

Graneros.

do...

Byers {24).

do
SELENIUM IN AGRICULTURE 21

TABLE ll.Selenium content of grab sampler from Home Hedimentary rocha of Cretaceous age—Qoxv.

UTAH

Sample

No.

Location Formation or

member

Reference Se

B-12137

B-12135

B-12539

B-12520 __

1 mi. east of Jensen

5 mi. east of Jensen

6 mi. west of Cisco

xy^ mi. west of Desert Switch _ . .

Mancos

do

do

do

Byers (¿.S)

do___

do

do

5. 0

3. 0

8.0

2

WYOMIING

B-4834

B-4831

B-5668

B-6317

B-4801

Sec. 16, T. 16 N., R. 74 W., Albany Countv^

Sec. 16, T. 16 N., R. 74 W., Albany CountvSec. 16, T. 27 N., R. 76 W., Albany County.

3^/2 mi. southeast of Upton, Weston Countv-.

Sec. 21, T. 14 N., R. 74 W., Albany CountySteele

Niobrara_

do__-

Graneros _

Benton

Byers {2S).

do

do

Byers {2A).

Byers {23).

6. 0

4 0

55. 0

1. 0

1. 0

The Pierre shale in Kansas, as represented by

three samples, appears to be erratically seleniferous. The Smoky Hill member of the Niobrara is seleniferous in Kansas, at least in part;

however, the underlying Fort Hays limestone

member is relatively free of selenium. The samples of the Pierre and Niobrara formations collected in Nebraska range from 1.5 to 30 p.p.m.

Very little selenium was found in the Pierre formation in Colorado ; the Niobrara formation seems

to be very seleniferous, but perhaps the highly

seleniferous areas are small and local. In Wyoming the Niobrara formation and the Steele formation, which is partly equivalent to the Pierre,

are also variably seleniferous. Six samples collected near the contact of the Pierre and Niobrara

formations in northeastern North Dakota contain

from 1.6 to 36 p.p.m. of selenium; this is about

the same range as that found in these formations

in South Dakota, Wyoming, and Kansas. In

contrast, the Cretaceous shales that have been sampled in Montana are low in selenium content ; the

maximum was 2 p.p.m. The two samples from

the Pierre shale in New Mexico are likewise low.

The Niobrara formation and lower part of the

Pierre shale found east of the Rocky Mountains

are correlated with the upper part of the Mancos

shale west of these mountains (see fig. 3). The

Mancos shale occurs in western Colorado, northwestern New Mexico, eastern Utah, and southern

and central Wyoming; it ranges in thickness from

1,200 to 2,500 feet. Soils derived from the Mancos

shale cover large areas in eastern Utah and western Colorado. Neither the Mancos shale nor the

soils derived from it have been studied sufficiently

to evaluate either the existence or extent of seleniferous beds within the formation, or the selenium content of tlie soils derived from tliese beds.

Tlie six samples of Mancos shale that have been

analyzed for selenium—four in Utah and two in

Colorado—contained 0.2 to 8.0 p.p.m. Trelease

and Beath {185) reported the collection of 17

selenium-indicator plants growing on Mancos

shale in Utah; the plants contained 54 to 2,210

p.p.m. selenium ; 13 seleniferous plants growing on

the Mancos in New Mexico contained 84 to 1,640;

and 26 selenium-indicator plants growing on the

Mancos in Colorado contained 65 to 2,148 p.p.m.

Some soils in Mesa, Montrose, and Delta Counties,

Colo., derived in part from Mancos shale, were reported by Byers {21^) to contain 0.2 to 10 p.p.m.

selenium.

The data available on the selenium content of

the Graneros, Benton, and Carlile formations are

inadequate. The few available analyses range

from 0.5 to 7.0 p.p.m. selenium.

Samples of Cretaceous shales were collected by

Lakin and Byers {101) at outcrops from the

coastal bluffs near Los Angeles and northward, for

approximately 400 miles, to the vicinity of Maxwell, Colusa County, Calif. Part of the data

obtained in this reconnaissance is given in table

12; the selenium content of these samples ranged

from 0.1 to 25.0 p.p.m. These results contrast

strongly with those obtained on Cretaceous materials collected along the eastern coast of the

United States (table 13). The 28 samples of eastern materials range in seleniiim content from 0

to 5 p.p.m.; only 3 contained as much as 1 p.p.m.

selenium.
22

TABI.E 12.-

AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

-Seleniuin content of >>onie CretaceouH

xluiles in Californ'ni '

Sample No. Local ion Se

B-25440___

B-25441

2 mi. north of Santa Monica on

U.S. Ilifihway No. lOlA, Los

Angeles County.

do._

P.p.rn.

18. 0

22. 0

B-25444.__

B-25453.._

B-25472___

B-25474___

B-25475___

B-25479

B-25480

2 mi. west of Jiuiotion with rente

27 on U.S. Highway No. lOlA,

at base of bluff above beach, Los

Angeles County.

2Y2 mi. up La Brea Creek from

Spanish ranch, Santa Barbara

County.

2 mi. we.st of Pozo on route 178,

San Luis Obispo County.

6.3 mi. west of Pozo on route 178,

San Luis (_)bisj)o County.

8.2 mi. west of Pozo on ro\ite 178,

San Luis Obispo County.

5.5 mi. northeast of Cholame, San

Luis Obispo County.

^ do

24. 0

1.0

2

2

1. 0

. 1

1. 0

B-25488_._

B-25545___

B-25547_^_

B-25548__^

B-25550_

ly-, mi. east of Kern County line on

rollte 41, Kern County.

15 mi. south of Tracy on Hospital

Creek, San Joaquin County.

14!.L' mi. south of Tracy on Hospital

Creek, San Joaquin Countv.

100 yds. from sample B-25547

do

2

5. 0

8. 0

2.0

28. 0

B-25584__.

B-"25590_^_

10 mi. southwest of Williams on

route 20, Colusa County.

7 mi. west of Maxwell, up Coral

Creek canyon, Colu.sa County.

. 2

6. 0

' Data from Lakin and Byers (101).

TABLE 13.—Selenium content of some CvetaceouH

rochn in eaxtern T'nited Sfiitex '

Sample

No.

Location Se

B-25998___

B-25999

0.7 mi. east of White Horse, Raritan formation, Mercer Countv,

N.J.

___do

p.p.rn.

0. 4

. 2

B-26005___

B-26006^_^

B-26007___

B-26008-__

B-26029__-

0.5 mi. west Crosswicks, Woodbury formation, Burlington

County, N.J.

Highway intersection Kinkora,

Merchantville formation, Burlington County, N.J.

1 mi. southwest of Morristown, red

sand, Englishtown formation,

Burlington County, N.J.

1 mi. southwest of Morristown,

yellow and gray sand, Jinglishtown formation, Burlington

County, N.J.

Permutit Co. pit, Burmingham,

green sand, Hornerstown formation, Burlington County, N.J.

. 6

.8

. 1

.04

2. 4

TABLE 13.—Selenium content of. some Cretaceous

I'ock.s in eastern United States ^—Continued

Sample

No.

B-26Ü23.

E-26028_

B-25921_

B-25922_

B-25923^

B-25924_

B-25925_

B-2.5927_

B-25948_

B-25928,

B-25047_

B-25929_

B-25930.

B-25949_

B-25950_

B-25951-

B-25952_

B-25931_

B-25932_

B-25953_

B-2o933_

Location

0.5 mi. north of Crawford's Corner,

green sand, Hornerstown marl,

Monmouth C!ounty, N.J.

0.25 mi. west of railroad station at

Highlands, green sand. Navesink marl, Monmouth Countv,

N.J.

Orloff sand pit, District of Columbia, top portion of Magothy

formation.

Orloff sand pit, District of Columbia, Magothy formation, 12 ft.

above base.

Orloff sand pit. District of Columbia, probably basal Monmouth

formation.

Orloff sand pit. District of Columbia, undoubtedly Monmouth

formation.

Branch .\ve., just east of District

line. District of Columbia, Monmovith formation.

On Crystal Springs Ave., 300 yd.

south of Centra) Ave. in Seat

Pleasant, Md., top of Potomac

formation.

On Crystal Springs Ave., 300 yd.

south of Central Ave. in Seat

Pleasant, Md., variegated redyellow-gray clay.

On Benning Road, ^4 mi. southeast

of District Line, clay from

Potomac formation.

On Benning Road, }{ mi. southeast

of District Line, ferruginous

concretion, Potomac series.

do

29th and Adams Streets NE,

District of Columbia, clay,

Potomac series.

29th and Adams Streets NE,

District of Columbia, red clav.

29th and Adams Streets NÈ,

District of Columbia, iron concretion.

29th and Adams Streets NE,

District of Columbia, pyriteo

and lignite.

29th and Adams Streets NE,

District of Columbia, iron concretion.

Daniels sand pit, Mount Rainier,

Md., lenticular mass of sand,

Potomac series.

Daniels sand pit. Mount Rainier,

Md., purple and pink concretions.

do

Piney Branch Road and Ray

Road, Takoma Park, Md',

sandy clay, Patuxent.

1 Data from Lakin and Byers (if/).
SELENIUM IN AGRICULTURE 23

ROCKS AND SEDIMENTS OF

VARIOUS AGES

Less is known about the selenium content of

rocks of other geologic periods than about the

selenium content of Cretaceous rocks. Part of the

data available is given in table 14. These rocks

and sediments are described in order of increasing

age. The Manning Canyon shale of IMississippian

and Pennsjdvanian age, the Phosphoria formation

of Permian age, and certain tuffs of Tertiary age

are noticeably high in selenium.

The glacial tills of northeastern South Dakota

contain appreciable amounts of selenium, undoubtedly because of the relatively seleniferous

Cretaceous beds from which they are deri^-ed in

part. According to Searight and others {1G3),

selenium is leached from these Pleistocene deposits, transported downslope, and deposited at

lower levels. Maximum amounts of selenium in

these enriched areas are about the same as the

average amounts of selenium in toxic soils (toxic

soils, as here used, are those that produce seleniferous vegetation toxic to animals) derived directly from Cretaceous formations. Lakin and

Byers (102) rejiorted a similar system of leaching

of till and enrichment in lacustrine beds in Xorth

Dakota. Ivocal enrichment by deposition from

ground waters probably has occurred in widely

differing: times and areas.

The selenium content in the rest of the material listed in table 14 differs little from the

average for the rock types, as shown in table 1.

In addition to these data, indirect evidence of

the presence of seleniferous rocks is gi\-en by the

gi-owth of seleniferous vegetation on i-oils derived

from the rocks. Trelease and Beath (J85) reported finding seleniferous plants growing on .55

formations in 15 Western States, but very seldom

confirmed the seleniferous character of these formations by analysis. The formations range in

age from Pennsylvanian through Quaternary ; 22,

hoAvever, are of Cretaceous age.

The presence of appreciable amounts of .selenium in the uranium deposits of the Colorado Plateau is often indicated by the growth of seleniumindicator plants over the ore. Helen L. Cannon

(oO, 31) and Cannon and Kleinhampl {32) have

developed a useful method of prospecting for

uranium based on the distribution of seleniumindicator plants.

DISCUSSION

The selenium content of samples of sedimentary

rocks in the Western United States ranges from

less than 0.02 p.p.m. to more than 1,500 p.p.ni.

Individual formations vary in selenium content

between wide limits, both vertically and areally.

TABLE 14.—Selenium content of some non-Cretaceoim rocks and sediments in u'estern United States

Period Formation Reference Location Samples Se range

Quaternary_

DoDo.

Do_

Tertiary

Do.

Do_

De Smet tilL

Mankato till

Arlington glacial till

Kansan and lowan tilL

Brule shale

Bridger shale

Eocene tuflfs

Do

Do

Do

Jurassic

Do

Do

Triassic

Do

Permian

Do

Pennsylvanian and

Mississippian.

Do

Mississippian

Do

Ordovician

do

do

Green River.

Alorrison

do

Gunnison

Spearfish

Dinwoody

Phosphoria

do

Manning Canyon shale.

do

Great Blue limestone..

Pahasapa limestone

Whitewood Limestone.

Searight and Moxon

{164).

do

do

do

Bvers {24)

Byers {23)

Everett and Bauerle

{51).

do

South Dakota

.do.

.do.

.do.

Nebraska

Wyoming

Lvsite, WvoBeath and others {16),

Beath and others {11)-

Byers {23)

Knight and Beath {97).

Bvers {24)

Byers {2S)

Beath and others {13)-

do

....do...

Wyoming.

.."-.do...

Beath and others (16) _.

Beath and others {14).

Lakin and Bvers {102) ^

do :

South Dakota.

Wyoming

Colorado

South Dakota.

Wyoming

..". do..

do

Utah

Moxon and others {12S)

do

..do.

..do.

South Dakota.

do

Nu mber

23

1

104

i;5

1

2

245

11

5

1

3

1

1

1

' 1

30

11

20

7

1

1

1

P.II.m

27-5. 38

. 86

. 2-4. 92

31-3. 7

40. 0-1, 000. 0

12.

160. 0

5-187. 0

. 32

0-4. 8

. 23

5. 0

1. 0

1. 0

8-2. 2

0-680. 0

4-96. 0

4-54. 0

1. 2

.25

.8

' Composite sample.
24 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

Certain formations, however, contain abnormal

amounts of selenium (greater than 2 p.p.m.)

throug-liout large portions of their stratigraphie

tliickness over large areas. Certain zones in the

Maiming Canyon shale and Pliosplioria formation

of Paleozoic age contain 1ÜÜ to 600 times as nnich

selenium as the average of the 36 European Paleozoic shales reported by Minami (Jí21). The

Niobrara and Pierre formations of Mesozoic age

also contain mucli selenium, but the selenium

content of samples ranges from less than 0.1 to

more than 100 p.p.m. and is erratically distributed vertically. A high selenium content is characteristic of the rocks of the upper part of the

Niobrara and the lower part of the Pierre: an

average of 20 p.p.m. was found above and below

the contact of these two formations in northeastern North Dakota, northeastern Nebraska, and

west-centi'al Kansas. Some extremely seleniferous tufi's of Cenozoic age occur in Wyoming, containing as mucli as 187 p.p.m. selenium, mucii of

which is water soluble according to Beath and

others (Iß).

Numerous accounts in the literature describe

areas wliere selenium has been concentrated locally by precipitation from seleniferous waters.

One can expect that after ancient seleniferous beds

have been eroded away, local concentrations will

form again in resultant younger beds. Sediments

high in selenium have existecl in Western United

States ever since the Manning Canyon shale was

laid down approximately 250 million years ago.

Thus, it is not surprising that Trelease and Reath

{185} liave found seleniferous plants growing on

55 different sedimentary formations in Western

United States.

The seleniferous soils of the Great Plains region

in Montana, North Dakota, South Dakota, Wyoming, Nebraska, Kansas, and Coloi'ado are deri\'ed

primarily from sedimentary rocks of Late Ci^etaceous age. The rocks of the formations are horizontal throughout the area and are extremely

variable in selenium vertically. Such valuation

in parent material makes possible a wide range of

the selenium content of tlie soils in a single field.

Tlius, in gently rolling topography the wide range

in selenium content of the parent material gives

rise to relatively large areas of mildly seleniferous

soils spotted with small markedly seleniferous

areas.

Chemical Determinations of Selenium

By M. S. ANDERSON

Precise methods for the determination of selenium are basic for investigations of this element

in agriculture. Qualitative methods for the determination of selenium have been available for

a long time. Quantitative methods have also been

used, but their precision Avas not adequate for

a study of the small quantities often present in

potentially dangerous vegetation. Even smaller

quantities must also frequently be determined in

soils. The quantities present in these materials

are best expressed as parts per million. In water

and in a few other materials where the quantities

present are normally very small, the results are

expressed as ¡larts per billion. The methods used

must of necessity be highly sensitive.

OLD METHODS

An analytical procedure found in older textbooks of quantitative chemical analysis calls for

fusion with sodium car])onate and potassium nitrate. The resulting alkali selenate that is soluble

in water is dissolved and acidified with hydrochloric acid. The selenium is then precipitated

with hydrazine hydrate.

A later method was used to some extent in the

first selenium investigations at the Wyoming

Agricultural Experiment Station (11,178). This

invoh'es treatment of dry plant tissue with sodium

hydroxide solution followed by ignition at a low

temperature. The residue is treated with hydrochloric acid, filtered, and the clear solution treated

with hydroxylamine to reduce selenium to elemental form.

A qualitative method that was used to some

extent for detection of organic selenium compounds was one devised by Horn (79). A dried

sample of plant or animal material was placed

in a Kjeldahl flask with 40 ml. of concentrated

sulfuric acid and 0.2 gram of mercuric oxide,

digested, diluted, and treated with a few drops

of an aqueous solution of codeine sulfate. A

green color changing to blue indicates the presence

of selenium.

When it was demonstrated by the then available

methods that selenium was present in such vegetation as wheat, the need for more precise and

reliable analytical methods was urgent. The

chemical methods must be adequately precise, flexible as to detail, and involve no great difficulty

of operation.

CURRENT METHODS

A method that meets the varied requirements

of an agricultural chemist was developed by
SELENIUM IN AGRICULTURE 25

Robinson and associates {155). The metliod specifies details of iDrocedure for soils, pyrites, and

other Sulfides, water, vegetable matter, and animal

tissue.

This method with only minor modifications has

been used in the U.S. Department of Agriculture

for making about 10,000 determinations. The

selenimn contents ranged fI'oni less than one-tenth

part per million to more than 1 percent. A detailed description of the method was published by

Williams (304-) after it had been in use several

years. The method is based on the fact that selenium tetrabromide is volatile under the conditions of distillation with liydrobromic acid and

bromine, whereas tellurium is not volatile. The

distillation apparatus used is shown in figure 4.

THISTLE TUBEh''i

Figure i.—Apparatus employed in the distillation

procedure.

This is copied from an earlier description of the

method by Robinson and associates {155).

Dlistillation.—Place 50 grams of air-dry soil

that has passed a 2-mm. sieve in the distilling

flask. Add to the contents of the flask, slowly and

with constant shaking, 100 ml. of -iS-percent HBr

containing 2 to 3 ml. of Br2.

After any frothing due to decomposition of

carbonates has subsided, connect the still so that

the adapter is below the surface of the 5 ml. of

Bra water in the receiving flask. [The success of

the distillation depends on the saturation of the

organic matter in the soil with Br, so that it will

not reduce the SeBr.j during the distillation.]

Apply heat gradually. When the mixtui'e begins

to boil, adjust the flame so that the distillation

proceeds very slowly ( approximatelj^ 20 minutes

for 1 to 2 ml. of bromine), thereby giving time for

the Br2 and soil organic matter to react. If insufficient Br2 was added to the soil to give 1 to 2

ml. in the distillate, remove the flame and add

more Bro in HBr solution tlirough the tliistle tube.

[After this period of In-omination, the distillation

niay be finished rapidly.] Collect 50 to 60 ml. of

distillate. To check tlie complete distillation of

the selenium, add more HBr and V>Y, to the residue

and collect a second distillate. Remove the receiving flask, dilute the distillate to 80 to 00 ml.

with distilled water, and i^ass in SO2 until the Br2

is reduced and the solution Ijecomes essentially

saturated with the SO2. [If the reduction is made

in concentrated acid and the amount of selenium

is small, it often precipitates as a yellow, finely

divided form that is exceedingly hard to retain on

a filter mat.] Keep the solution cool during the

reduction witli SO2 to avoid possil:)le loss l)y volatilization just as the reduction of the Bi-o is completed. Add 0.3 to 0.5 gram of hydroxylamine

hydrochloride (XHsOH-HCl) and'warm on the

steam bath for 10 minutes.

Entimation.—Set the distillate aside for 48 hours

to allow complete reduction and coagulation of

the selenium. Examine the distillate for selenium ; if the amount is small, employ the Tyndall

efïect, using either direct sunlight or a strong,

well-focused, artificial light. As little as 0.005

mg. may be easily seen by this method. Filter

the selenium on a tight asbestos mat in a Gooch

cracible, wash with cold water, then with alcohol

to remove the oily material always present in

soil distillates, ancl again wash with cold water.

If the amount of selenium is 0.5 mg. or less, dissolve on the pad with 10 ml. of water-white 48-

percent HBr to which has been added 3 ml. of

Brj per liter. Filter into a 25-ml. volumetric

flask and wash the pad with cold water until the

volume reaches 24 ml. Pass in SO2 until the solution is essentially saturated. Add 1 ml. of a

fresh solution of NIIaOH-HCl containing 10

gi'ams per 100 ml. of solution. Shake well. Heat

on the steam bath for 20 minutes, bringing the

temperature to 45° to 50° C. Cool to room temperature, shake well, and compare in Kessler tubes

with Ivnown amounts of selenium precipitated in

the same manner. Prepare fresh standards each

time. [In routine work it is convenient to accumulate 25 to 50 samples for estimation.] Then

prepare standards containing 0.01, 0.025, 0.05,

0.10, 0.15, 0.20, 0.30, and 0.50 mg. of selenium

from a standard stock solution of Na2Se03 or

NaaSeOi. [By treating each sample and the

standards exactly alike in the manner described,

the colored turbidities can be readily matched.

Despite all precautions, an oft'-colored one will

be obtained from time to time. Such samples

must be refiltered and determined with the next

set.]

If moi'e than 0.5 mg. of selenium is present,

dissolve it into a 100-ml. beaker, using 30 ml. of

HBr containing 0.2 to 0.3 ml. of bromine, and
26 AGRICULTURE HANDBOOK 20 0, U.S. DEPARTMENT OF AGRICULTURE

wash with 30 ml. of cokl wiiter. Precipitate as

before and heat on the steam hath for 20 minutes,

bringing the temperature to 45° to 50° C. [Tiiis

second precipitation is necessary to free the selenium from sensible quantities of impurities.]

Allow to stand 48 hours. Gather the selenimn

on an asbestos mat in a Gooch crucible and wash

with cold water. Prepare a tare in a similar

manner. Dry at 85° to 90° C. overnight, cool in

a vacuum desiccator, and weigh against the tare.

Special Treatmerif w'/fh Siilfuric Acid.—If the

soil contains 0.1 p.p.m. or less of selenium, use preferably the integration method. In order to accomplish this, add the distillate to a fresh charge of

the soil with additional HBr and Brg. [This procedure may be repeated until any desired amount

of the sample has been used.] If the soil is calcareous, lateritic, or of high colloid content, add

H:,S04 to the charge so that the water liberated in

the reaction will not dilute the acid distillate and

thereby fail to carry over tlie selenium. [A sim-

¡ile, small hydrometer may be made for use in the

receiving flask and calibrated with HBr and

water.] If the distillate is less than 42 percent

HBr, take a second distillate and mcrease the

amount of HoSOj correspondingly. If too mucli

H2SO4 has been added and hydrogen bromide gas

passes as a fog through the Bra water trap, add

water through the thistle tube to correct this. In.

the regular distillation of lateritic soils, add

H2SO4 to the charge to produce a distillate of 42

percent HBr, or stronger.

The method, essentially as described, has played

a great part in selenium investigations. AYith

slight modifications its usefulness has been greatly

expanded. A few of the modifications frequently

utilized by analysts include these :

1. The so-called integration concept mentioned

above involves the combining of distillates from

two or more individual samples {164) If distillates from as many as 10 separate samples are

combined, the final determination will be based on

a quantity increased tenfold from that of an indiviclual sample. This procedure is often used for

analysis of waters and other materials of very

low" selenium content.

2. A mixture of concentrated sulfuric and nitric

acids is preferable to hydrobromic acid and bromine for preliminary digestion, when such organic materials as vegetation and animal tissues

are being analyzed.

3. In certain cases titration of recovered selenium has been recommended as a final step in the

determination instead of a colorimetric comparison (39). This procedure has been used successfully, particularly when the contents of selenium

are relatively high. This involves use of a sodium

tliiosulfate iodine titration with starch as

indicator.

Selenium determination as normally carried out

leads to results dependable to about 0.01 part per

million in soils, minerals, and vegetation and about

0.25 part per billion in the case of liquids and

other materials where the integration principle is

applied. As a rule, analytical results are reported

in accordance with tlie limits indicated.

The method described above with its several

modifications is widely used where selenium toxicity problems are being investigated. Since the

recent discovery of selenium-deficient animal diets

(see p. 52), it becomes desirable to determine

even smaller quantities of this element than those

noted above, particularly in feeds and feeding

stuii's, than heretofoi'e has been possible. Probably the most sensitive of all procedures consists

of neutron activation by conventional methods,

followed by measui'ement of the radioactivity induced in the selenium. The practical limit of

sensitivity is reported to be i).01 microgram of

selenium. Leddicotte and Eeynolds published a

general discussion of activation analysis in 1951

\W8).

In recent years another method of high sensitivity has been developed. This method is essentially a colorimetric one, depending upon a

spectrophotometric measurement of a yellow derivative of selenious acid and 3,3'-diaminobenzidine as described by Cheng (35). This is said

to Ije sensitive to 50 parts per billion with a 1-cm.

cell.

Very recently a fluorometric method using

3,3'-diaminobenzidine has been developed by Watkinson (ßOß) for determining as little as 0.02ftg.

of selenimn in plants and other materials. The

method appears to have promise as a means of

determining small quantities of selenium. The

procedure has not, however, been tried in our

laboratories.

Marked progress has been made in the development of a satisfactory method for determination

of extremely small quantities of selenium. However, most chemists feel that more work is necessary before a method can be recommended as

sufficiently sensitive and reliable for use in studies

currently underway and projected. A method

of this type is needed very much because of the

important shift in interest from studies of selenium as a toxic element to studies concerned with

threshold values in feeds for normal animal

nutrition.
SELEN:-¡'m^ IM AGRICULTURE 27

Selenium Content of Soils

By H. W. LAKIN

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.

Data on the selenium content of soils were summarized by Swaine in 1955 (176). This section is

not intended to duplicate Swaine's work, but to

point out the significance of various aspects of soil

chemistry in the availability of selenium to plants.

The relations between the selenimii content of

soils and that of the plants grown on them are

complex. For some complexities, explanations

are available in the literature; for others, the

causes are unknown. The nontoxic seleniferous

soils, although their selenium content may be high,

yield no selenium to plants; yet the toxic seleniferous soils jie\d enough selenium to plants to

make the vegetation very toxic, in spite of the fact

that the total selenium content of these soils may

be appreciably lower than that of the nontoxic

soils.

Studies made of toxic and nontoxic seleniferous

soils have revealed that climate and soil-development processes are major factors in the availability to plants of the selenium in soils. The

alkaline seleniferous soils of semiarid "Western

States produce toxic vegetation, whereas the acid

seleniferous soils of the humid interior of Puerto

Rico produce vegetation free of detectable

amomits of selenium. In general, seleniferous

Pedocals are toxic and Pedalfers are nontoxic.-^

The selenium content of plants grown on the

Pedocals of Western United States has no direct

relation to either the total or the Avater-soluble selenium content of those soils. Plants grown in sand

cultures that contain the same amount of watersoluble selenium as that contained by our western

seleniferous soils absorb more than 10 times as

much selenium from their growth medium as the

same species of plant absorbs from the soil whose

water-soluble selenimn content approximates the

sand culture. Other factors than the presence of

selenium in the soil solution must be operative;

* Publication authorized by the Director, U.S. Geological Survey.

"Pedocals and Pedalfers are defined by Marbut (111).

5SS590—61 3

but adequate knowledge of these factors is still

lacking.

TOXIC SELENIFEROUS SOILS—

PEDOCALS

The toxic soils of the united States are Pedocal soils; they are alkaline in reaction, they contain free calcium carbonate, and they lie in regions of low rainfall—less than 20 inches mean

annual precipitation. Toxic seleniferous soils of

Canada, South America, and Israel are similar.

The major wheat-producing areas of the world

are regions of Pedocals, and commercial wheat

from various parts of the world examined by

Robinson [15Jf) contained from 0.1 to 1.9 p.p.m.

selenium.

That a small pasture may yield grass ranging

in selenium content from less than 1 p.p.m. to

as much as 50 p.p.m. demonstrates the fact that

the seleniferous soils of our "Western States are

not uniformly toxic. Although the erratic variation of selenium content in the surface soil yields

little or no information on the toxicity, variation

of selenium content with depth may provide some

guide in the matter (surface in this text means

from 0 to G or 8 inches in depth).

Byers and his coworkers {23, 2Ii., 27) reported

the selenium content of thousands of surface soils

in North Dakota, South Dakota, Montana, Wyoming, Nebraska, Kansas, Colorado, New ^léxico,

T^tah, and Arizona. The amounts of selenium

in these surface soils showed no correlation with

tlie amounts of selenium found in the vegetation

sampled, other than that when selenium was present in the plants, it was present in the soils in

amounts of 0.1 p.p.m. or more. Byers {23) investigated the variation of selenium content of

the surface soil within a square mile area of gently

rolling land in Gregory County, S. Dak. The

underlying seleniferous shales were horizontal,

and it Avas expected that the variation of the selenium in the soils might reflect vertical variations

in the parent rocks. A topographic map with a

10-foot contour inter\'al was prepared of the area

and on this was plotted the selenium content of

the soil (fig. 5). No relation was apparent between the selenium content and the topography—

nor was there any grouping of high and low

selenium concentrations. A soil containing 0.5

p.p.m. lay between soils containing 5 and 8 p.p.m.
28 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

Num 3er of samples

20

10

0

4 5 6 7 8 9 10

Selenium content in parts per million

13

Figure 5.—Selenium content of the 122 samples of surface soils (0 to 7 inches) from sec. 21, T. 100 N., R. 72 W., Gregory

County, S. Dak.

selenium. Selenium contents range from 0.5 to

13 p.p.m., the average content is 4.5, and the

median 4.0; yet 45 samples contained only 2.0

to 3.5.

When the surface soil is analyzed, it does not

give a true picture of the selenium content of

the soil in which even shallow-rooted plants feed,

because the selenium content may vary considerably within the soil profíle. This variation is

illustrated by a few representative profiles from

Western United States (table 15). In some areas

the selenium content is low near the surface and

increases considerably with depth. Two trends

may be seen in the data here listed: One is the

increase in selenium content of soils with depth;

and the second is the slight tendency for selenium

to accumulate in the upper parts of some profiles—most pronounced in the profile from Fremont Comity, Colo., but also evident in the Boyd

County, Nebr., and Pueblo County, Colo., profiles.

NONTOXIC SELENIFEROUS

SOILS—PEDALFERS

No acid soils are known to produce toxic seleniferous vegetation. The nontoxic seleniferous

areas are Pedalfer soils; they usually have a pH

range of 4.5 to 6.5; they are characterized by a

zone of accumulated iron and aluminum compounds and are developed under humid conditions.

The selenium present in these soils is associated

with the iron and is probably in the form of a

very insoluble basic ferric selenite. If the selenium occurred as selenate, it would normally be

leached out of the soil. The selenimn content of
SELENIUM IN AGRICULTURE

TABLE 15.—Variation off^eleniuminsoilprofles of Wei^tern TJniferlStates

PROFILE 1, BOYD CLAY, SEC. 1, T. 33 N., R. 10 W., BOYD COC.VTY, NEBR. (BYERS, iS)

PROFILE 8, BOYD CI..\Y LOA-VI, SEC. 35, T. 2 N., R. 30 E., JONES COI'NTY, S. DAK. (BYERS, 2Í

29

Laboraton- No. Depth Se Laboratory No. Depth Se

B-843 _ _

In ck s

0-6

6-12

12-18

18-24

24-30

30-36

P.p.m

3. 0

3. 0

2. 0

2.0

2. 0

2. 0

B-829

Inches

36-42

42-48

48-54

54-60

61-72

P.p.m.

3. 0

B-844 B-830 3 0

B-845

B-846

B-827

B-840

B-841

B-842

12.0

28.0

24.0

B-828

B-12089

B-12090

0-12

12-24

24-36

2. 5

4.0

4. 0

B-12092

B-12093

36-48

48-60

60 +

3.0

3 5

B-12091 B-12094 3 5

VALE FINE SANDY LíIAM, SEC. .30, T. 8 N., R. 7 K.. BTTTE COI-NTY, S. DAK. (BYERS, SS)

B-11786

B-11787

0-10

10-24

24-35

0.2

. 2

. 3

B-11789

B-11790

35-46

46-60

0.4

5

B-11788 ____._.

PROFILE 17, NIOBRARA SILT LOAII, PUEBLO COUNTY, S. DAK. (BYERS AND OTHERS,

B-19616

B-19617

0-6

6-12

12-24

24-36

5.0

5. 0

4. 0

5.0

B-19620 _-

B-19621

B-19622

36-48

48-58

58-62

3.0

3 0

B-19618 -- ._ ^ 12. 0

B-19619

PROFILE 18, NIOBRARA SILT LOA.M, SEC. 9, T. 18 S., R. 70 W., FREMONT COUNTY, COLO. (BVERS AND OTHERS, ê7)

B-19644 0-1

1-4

4-6

6-10

38. 0

26. 0

22. 0

24.0

B-19648

B-19649

10-14

14-26

26-32

36-40

42 0

B-19645 . .. 54 0

B-19646 _ B-196.50 98 0

B-19647 B-19651 48. 0

Pedalfers lias not been studied extensively. Only

two areas of seleniferous Pedalfers are known—

one in Hawaii and the other in Puerto Rico.

The selenium content of samples from six soil

profiles from the Hawaiian Islands—three from

the island of Mauii, and three from the island of

Kauai—are given in table 16. In these, the selenimii content decreases with depth and with decreased rainfall. Byers and others (ß7) postulated that the selenium in these soils is brought

down by rain from volcanic emanations and dust

and is fixed as a basic ferric selenite. Certainly

soils containing as much as 26 p.p.m. of selenium

under an annual rainfall of 100 inches do not contain selenium in a very soluble form. The pH of

these soils is between 4.5 and 5.5 (Hough and

Byers, 8.^). Although the soils contain as much

as 26 p.j).m., 3 p.p.p. is the highest reported selenium content of plants grown in them (Byers and

others,^'/).

Another illustration of the unavailability of

selenium to plants in acid soils is provided by the

soils developed from the seleniferous Fajardo

shale (Roberts and party, Jo2) in the moujitainous interior of Puerto Rico (table 17). One

of these soils, the Yunes clay, was developed o»

a steep slope under an annual precipitation of 80

inches; another, the Yunes silt loam, was developed under an annual rainfall of 55 inches. Selenium content of soils from this area ranges from

1.0 to 12.0 p.p.m., and of the underlying Fajardo

shale from 2.5 to 8.0 p.p.m. ("Williams and others,

208). J. I. Otero collected and classified every

type of vegetation growing in the Yunes silt loam

on a 40-acre tract (Lakin and others, JOS). None

of tliese plants contained as much as 1 p.p.m. of

selenimii.
30 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

TABLE 16.—Vaiiation of selenium content in soil profiles, Hatoaiian Islands ^

Island and

laboratory No.

Island of

Mauii:

B-5787

B^5788

B-5789

B-5790

C-938_

C-939_

C-940_

C-941_

B-5791

B-5792

B-5793

B-5794

Island of

Kauai:

B-3717

B-3718

B-3719

B-3720

B-3721

C-784_

C-785_

C-786^

C-792_

C-793_

C-794_

C-795_

Location

156°39'40" W., 20°56'20" N.; elevation, 2,500

feet.

\b mi. N. by NE. of Lahaina; elevation, 2,550 feet_

>156°40'24" W., 20°58'24" N.: elevation, 450 feet.

>159°27'48" W., 22°12'36" N.; elevation, 500 feet.

)2 mi. south of Kalihiwai_

0.75 mi. north of Hanapepe.

Rainfall

Inches

100

100

20

100

90

25-30

Material

Texture

{Red clay

Red clay

Red clay

Lava and soil__

iSilty clay loam.

Silty clay loam.

Silty clay loam.

Silty clay loam.

IClay loam

Clay loam

Clay loam

Clay loam

Red clay

Red clay

Red clay

Red clay

Red clay

{Kalihikai suty clay,

Kahhikai silty clay.

Kalihikai .silty clayIHanapepe

Hanapepe

Hanapepe

Hanapepe

Depth

Inches

0-6

6-9

9-30

30-40

0-7

7-15

15-22

22-30

0-2

2-7

7-28

28-50

0-4

4-16

16-33

33-50

2 20

0-6

12-20

20-54

0-8

8-14

14-32

35-42-

Se

p.p.m.

7

15

18

26

3

2

1

3

15

15

12

12

10

6

2

1

1

1

1

1 Data from Byers and others [27).

^ In feet.

TABLE 17.—pH and selenium content of nontoxic

Puerto Rican soil profiles ^

Soil type Soil

Survey No.

Depth pH Se

Inches P.p.m.

Yunes clay 5802141 0-6 4. 6 1.0

Do 5802142 6-9 4 1 1. 5

Do 5802143 9-30 3. 9 1. 5

Yunes silt loam 5803115 0-4 5. 1 1. 5

Do 5803116 4-14 4.3 2.0

Do 5803117 14-28 4 2 10.0

1 Data from Roberts and party (162, tables 36 and 56).

PROPERTIES OF TOXIC SELENIFEROUS SOILS

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 water-soluble selenium; the

others do not. From the pliysical chemistry of

seieniuiii one finds that it may be oxidized to selenates in a moist alkaline environment; tlie 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 CaSeOj, 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.

The seleniferous soils of Ireland lie between these

two extremes and are an interesting example of

the mobility of selenium in a liumid climate. In

addition to water-soluble selenates, water-soluble

organic selenium has been found in our "Western

States.

Sulfates decrease the uptake of selenates by

plants, and sulfates are usually present in the

seleniferous soils; however, the addition of more

sulfur to these soils has no discernible elî'ect. Soil

colloids have practically no effect on the availability of selenates to plants, although these

diminish the availability of selenites.

The relatively low annual rainfall in seleniferous areas of the United States minimizes the

leaching of selenates from the soil. A Pierre clay

profile—pH 8.1 to 8.5—from Gregory County, S.

Dak., where the mean annual rainfall is 14.54

inches, was examined by Brown and Byers [22)

(table 18). They found calcium sulfate accumulating in the 60- to 74-inch horizon and com-
SELENIUM IN AGRICULTURE 31

TABLE IS.—Soluble salts, pH, and selenivtn content of a toxic soil profile (Pierre day), Gregory County, S. Dal:}TABLE 19.—Relation of solvhle selenium in soils

to selenium in vegetation ^

Sample Xo. Depth pll Soluble

salts

Se

B-858

Inches

0-8

8-18

18-40

40-60

60-74

8. 3

8.5

8. 4

8. 1

8. 2

P.p.m.

860

760

780

1, 260

9, 800

p.p.m.

5. 0

B-895

B-894

B-857

B-893

6. 0

4. 0

5. 0

6. 0

1 Data from Brown and Bj^ers {23, table 14}-

mented : "In the general run of the Pierre soils the

zone of sulfate accumulation is nearer the surface

than in the present profile. It may be remarked

that while the zone of carbonate accumulation may

be regarded as marking the maximum mean penetration of water, the zone of sulfate accumulation

marks the maximum depth of penetration of

moisture." Certainly the 9,800 p.p.m. of soluble

salts that these authors found in the 60- to 7-1-inch

horizon suggests that little leaching is taking place

beyond this depth. In this environment selenium

could be oxidized to selenate and the soluble selenates could remain in the soil.

To ascertain how much selenium is soluljle in

seleniferous soils, "Williams and Byers (£07) determined the selenium in water extracts of a hundred samples of seleniferous soils, and found that

the soils contained from less than 0.1 to 38 p.p.m.

water-soluble selenium. They concluded that

j^robably most of the soluble selenium was in the

form of calcium selenate.

Olson and others (138) studied the occurrence

of soluble selenium in soil profiles from sec. 2, T.

107 K, E. 78 ^y., South Dakota (table 19).

These authors stated that the water-soluble selenium is almost entirely selenate, because it was

nat a^jpreciably reduced by SO2 in 6 N sulfuric

acid. They concluded that the weathering processes in this region oxidize a large part of the

selenium to the selenate form, which maj^ then be

leached from the near-surface soil and moved to the

subsoil or removed by runoff waters and redeposited at lower elevations. These workers observed

a relationship between the apparent leaching of

selenium in the soils and the selenium content

of the plants and stated: "With few exceptions,

where plants of the higher selenium contents

are found the amount of the element in the soil

increases witli depth." PIurd-Karrer (88) found

tenfold as much selenium (350 p.p.m.) in wheat

grown in a sand culture containing 2 p.p.m. selenium as is reported for A. smithii (35 p.p.m.) in

tal)le 19, soil No. 14. These data and other data

in the literature strongly suggest that solul^ility

of selenium is not the only factor involved.

Soil No. and depth -

Total Se

content

of soils

Soluble Se

content

of soils

Se content

of

Agropyron

smithii '

6: 1st foot

P.p.m.

2. 7

5. 5

11. 5

4 3

15. 8

29. 0

3.0

4 5

11. 5

4 4

28. 4

38. 4

4 4

4. 8

6. 4

5. 9

46

6.0

P.p.m.

0. 12

2. 76

. 58

. 43

.5. 00

10. 85

1.43

. 48

2. 66

0. 91

17. 00

18. 99

. 08

. 10

. 12

. 11

.05

. 11

P.p.m.

18

2d foot

3d foot -_

7: 1st foot.

2d foot

79

3d foot

8: 1st foot

2d foot

3d foot

8

14: 1st foot 35

2d foot

3d foot

21: 1st foot 2

2d foot

3d foot

32: 1st foot

2dfoot___

2

3d foot

1 Data from Olson and others (1S8).

2 Soil location was an area in sec. 2, T. 107 X., R. 78 W.,

South Dakota.

' Results of analyses of composited samples taken over a

5-j'ard radius from the sampling point of each soil sample.

As annual rainfall increases, the movement of

selenium in gi'ound waters liecomes more evident

(195). In western South Dakota, northwestern

Nebraska, and eastern Colorado, selenium enrichment in the subsoil sometimes results from leaching of the topsoil. In northeastern South Dakota

and north-central North Dakota, evidence of removal from the soil is found. Depressions in

soils developed on Pleistocene deposits in northeastern South Dakota, as reported by Searight

and ^loxon (16^), and soils formed from Pleistocene lacustrine deposits in North Dakota, as reported by Lakin and Byei-s (102), contained more

selenium than did the adjacent glacial drift.

Lakin and Byers suggested that selenium leached

from the surrounding drift had enriched the lowlying lacustrine materials. The most impressive

example of selenium enrichment of low-lying lacustrine soils by ground waters is found in the

most highly seleniferous soils reported in the literature—those of Limerick, Tipperary, and Meath

Counties, Ireland (Walsh and Flem'ing, 200. 201;

O'AIoore, 139; and Fleming and Walsh, 55).

Fleming and Walsh reported soils containing as

much as 1,200 p.p.m. selenium, a figure tenfold

that of the selenium content of the most seleniferous soils reported in the United States.

Fleming and Walsh (55) observed that the highest selenium concentrations found in the Irish

soils are associated with tlie organic-rich horizons.

Data selected from the work of these authors are

given in tables 20 and 21. In all three areas ex-
32 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

TABLE 20.—Selenium content of toxic and ncmtoxic soil profiles in relation to pH and organic matter,

County Tipperary, Ireland'^

Toxic profile Non toxic profile

Depth

(inches)

pH Se Organic

matter

Depth

(inches)

pH Se Organic

matter

0-6

C-12

7. 2

6. 5

7. 7

7. 1

7. 3

7. 9

J'.p. m.

19. 6

175. 0

0. 9

100. 1

2. 1

. 6

Percent

31. 0

75. 0

6. 6

62. 6

3.0

1. I

0-6

6-12

5. 4

5. 7

5. 9

8. 1

P.p.m.

1. 27

1. 46

. 74

. 56

Percent

9, 5

3. 5

12-20 12-18 1. I

20-24

24-34

>18 0. 7

>37

Data from Fleming and Walsh {55, table 6).

amined by Fleming iind Walsh the highest selenium contents were found in low-lying, poorly

drained, highly organic soils; the adjacent welldrained Brown Earth soils were relatively low in

selenium, were acid in reaction, and did not produce toxic vegetation. The data in table 20 show

a marked correlation between selenium and organic matter in the toxic ¡profile. The highly organic horizons are also the least alkaline; and,

as ijiight be expected, the data in table 21 show

that water-soluble selenium constitutes a smaller

percentage of the total selenium in organic horizons than is found in presumably more alkaline

horizons of lower selenium and organic content.

These extremely seleniferous areas in Ireland

apparently have resulted from transportation of

water-soluble selenium into a poorly drained organic reducing basin. The selenium in the area

has been redistributed by ground water as a result

of alternate oxidation and reduction. Although

these soils are very high in total selenium, they are

low in water-soluble selenium as compared to the

soils of South Dakota (table 19) and of Israel

(table 22). The Irish soils are unique in being the

only known seleniferous soils producing toxic

vegetation in a humid climate. The toxic vegetaTABLE 21.—Total and loater solulAe selenium in

toxic soil profiles from County Limeiick,

Ireland ^

Profile

Depth Total Se

Water soluble Se

No.

P.p.m. Percentage

of total

3

•

4

Inches

\ 0-6

6-12

( 24-36

/ 0-6

1 12-24

P.p.m.

63. 4

207. 0

225. 0

53. 5

850.0

1. 48

1. 29

1. 41

. 25

2. 81

2. 34

.62

.63

.46

.33

' Data from Fleming and Walsh {65, table 7).

tion, however, is confined to soils of alkaline

I'eaction.

Water-soluble selenium makes up as much as 30

percent of the total selenium in some toxic soils of

Israel (talkie 22) studied by Kavikovitch and JNIargolin {150). These are calcareous alluvial soils

with a pH 7.8 to 8.2. Although the maximum

selenium content found in the soils in the Huleh

Valley is 6 p.p.m.,-alfalfa grown there contained

from 1.4 to 44 p.p.m. selenium. Alfalfa that

grew on soils containing only 0.1 to 0.3 p.p.m. of

total selenium accumulated up to 14 p.p.m. A

native deep-rooted plant, Prosopis farcta (Euss.)

Macbr., growing in the Huleh Valley, contained

136 to 311 p.p.m. of selenium. The seleniiun content of plants growing on these soils serves to

demonstrate that high total selenium in soils is not

the determining factor for toxicity of vegetation

in seleniferous lands. In contrast, the highest

selenium content in vegetation from the highly

seleniferous Hawaiian soils reported by Byers and

others {27) is 3 p.p.m.

Not all water-soluble selenium in soils occurs

as selenates. In soil containing 40 p.p.m. selenium, Williams and Byers {207) found about 10

p.p.m. of water-soluble selenium that was neither

selenate nor selenite selenium. They postulated

that this fraction was composed of organic selenium compounds, since the selenium in green

vegetation is largely water-soluble. BeatliT and

others {16) reported on a sample of the top 20

inches of soil in northeastern Niobrara County,

Wyo., that contained 22 p.p.m. total selenium, 2.6

as selenate, and 6.0 as soluble organic selenium. A

sample of the soil from a depth of 20 to 40 inches

contained 32 p.p.m. total selenium, 9.5 as selenate,

and 3.4 as soluble organic selenimn. The highest

selenium content reported for any vegetation is

14,920 p.p.m. in Astragalus racemosus Pursh found

by Beath on this soil (Beath and others, 16). A

water leachate of such seleniferous plant material

would indeed be rich in selenium.

Beath and his associates {11) have attached

much significance to the part played by "con-
SELENIUM IN AGRICULTURE

TABLE 22.—Total and v:ater Holuljle i^eleninm in fo:e!r Inraeli !<oil¡< ^

33

Soil No. Depth Total Se

Water soluble Se

Location

P.p.m. Percentage

of total

Naot-Mordechai (Huleh Valley) 6

Feel

1

2

1

3

1

2

P.p.m.

4. 0

2. 0

6.0

2.0

3. 8

.4

0.3

.4

. .5

.6

.3

.0.5

7 5

Do . 20 0

Do

Do --

12 8.3

30 0

Do - --- 68

57

7 ')

Nir David (Beit Shan Valley) 12 ,5

1 Ravikovitch and Margolin (Í43, tahle S).

verter" plants in making selenium available to

other types of vegetation. HoAvever, Olson,

Whitehead, and Moxon {138)^ in their study of

South Dakota soils, state: "The importance of

converter plants in the soils studied here is not

known, but it appears quite probable that weathei'-

ing has played the dominant role in the freeing of

seleniiun from its insoluble forms."' Although

soluble organic selenium compounds no doubt

play a part in supplying selenium to crops, Beath

and others {16) concluded that in the toxic areas

investigated by them selenate selenium is the

dominant water-soluble form and that this form

is more toxic to nonaccumulator plants than is

the organic form.

REDUCTION OF TOXICITY BY

SOIL AMENDMENTS

A means to inhibit the absorption of selenium

by plants has been sought to permit safe utilization of seleniferous soils for agricultural purposes.

In a study of Belle Fourche irrigation project,

Butte County, S. Dak., Byers {23) observed that

if the sulfur-selenium ratio is 50 or more, the

selenium content of the vegetation is low. HurdKarrer and Kennedy {90) showed that the addition of sulfur or gj'psum to the Keyport clay,

made seleniferous by the addition of 2 p.p.m. selenium as sodium selenate, reduced the uptake of

selenium by young winter wheat to one-tenth the

amount absorbed in the absence of sulfur or

gypsum. Further experiments with wheat grown

in nutrient solutions (Hurd-Karrer, 89) showed

that sulfur inhibited the uptake of selenate seleniiun but not of selenite selenium. Numerous

greenhouse experiments have confirmed these observations (Hurd-Karrer, 88, Gile and Lakin,

69,Treleaseand Beath, ]8o).

The effects of soluble sulfates upon the selenium

nptake of plants in natural surroundings are

difficult to evaluate. Franke and Painter (67)

tested the effect of adding sulfur to plots in a

12-acre field in Gregory County, S. Dak., where

surface soil contained an average of 446 p.p.m. of

sulfur before am' additions were made. Enough

sulfur was added, both as native sulfur and as

gypsum, to ti'iple the sulfur content of the ui)per

6 inches of soil. Xo decrease in the selenium content of corn or wheat grain was noted following

the treatment. The total selenium content of the

surface soil (0-6 inches) ranged from 2.0 to 3.7

p.p.m. No data are presented on the watersoluljle selenium nor on the selenium content of

lower horizons. The authors concluded that sulfur applications failed to inhibit the absorjition

of selenium by plants. Brown and Byers {22)

give data on the soluble salts (presumed by these

authors to be sulfates) and selenium content of

a Pierre clay from Gregory County, S. Dak. The

soluble salts in this profile range from 760 to

9,800 p.p.m., and selenium from 4 to 6 p.p.m.

(table 18). The sulfur-selenium ratio in this

profile ranges upward from about 30. Most of

the controlled experiments have been at lower

ratios. Beath (5) concludes that the "sulfurselenium antagonism theory has not been found

generally applicable to farm and range practices

of the Rocky Mountain region."

In greenhouse experiments, Ravikovitch and

Margolin {U^d) supplied monocalcium phosphate,

calcium sulfate, and barium chloride to Israeli

soils containing 4.0 and 0.5 p.p.m. selenium, in

order to determine their inhibitoiy etïect. The

monocalcium pliosphate had little effect, which

confirms the results of Gile and others {OS) on

the growth of millet in soils made seleniferous

with sodium selenate. Considerable quantities of

gypsum caused a significient reduction in the selenium uptake by alfalfa. The effectiveness of

barium chloride in small quantities was exceptionally pronounced; it stopped completely the

absorption of selenium by alfalfa from the soil of

lower selenium content.

The generally high sulfur-selenium ratios prevalent in our western soils preclude the possibility

of determining what the selenium content of vegetation might be in the ;il'-ence of abmidant sulfates. The seleniferous Irish soils, however, may

give some insight into the beneficial effects of the
34 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

presence of plentiful sulfates in our seleniferous

soils. As noted earlier, the Irish soils are high in

total selenium but low in water-soluble selenium;

the maximum water-soluble selenium (Fleming and Walsh, 65) is 2.81 p.p.m. In South Dakota soils, Olson and others (137) reported 19

p.p.m. of water-soluble selenium; and Williams

and Byers {207) found 38 p.p.m. However, a

survey of wheat grain from Western United States

(Williams and others, 2(li)) showed a maximum

of 25 p.p.m., as contrasted to \M p.p.m. in wheat

grain from the Irish soils reported by Fleming

and Walsh {65). The fact tliat grasses aljsorb

selenium only in small quantities in the Western

States is commented on as follows by Fleming

and Walsh : "Our experience does not agree with

this as can be seen from the relatively high levels

pi-esent in some of the hei'bage species from our

pot experiments, while in addition * * * levels

up to 500 p.p.m. have been obtained on mixed

herbage samples." Because of the high rainfall

one would not expect to find an appreciable

amount of sulfates in the Irish soils and nothing

in the literature indicates high sulfate content.

It is probable that the abundant sulfates in the

seleniferf)ns soils of the United States have greatly diminished the selenium uptake by cultivated

crops.

Occurrence and Significance of Selenium in Plants

BY K. C. BEESON

The detection of selenium in plants was announced in 1932 by the French chemist Taboury

{177), and the first quantitative determination of

this element in plants was i-eported by Robinson

in 1933 {153). As early as 1880", however,

Cameron (^5), after the addition of selenium to

a soil, noted a chlorosis in the plants growing

thereon. He postulated tlnit selenium was absorbed by the plant and might be substituting for

sulfur in some of the sulfur compounds in the

plant. The literature now contains reports of

thousands of analyses of a wide variety of both

native and crop plants, indicating that selenium

must indeed be readily absorbed by all members

of the plant kingdom. Of special interest in this

respect is the occurrence of selenium in food

plants Avith the possible detrimental effects on

public health. With this aspect of the problem

in mind a numter of reports have appeared on the

selenium content of wheat grown in many parts

of the world {10, 91^, 100, 123, 11^3, 16k, 183, '208).

Robinson {153) and Lakin and Byers {100),

from their extensive work on this crop, suggest

that selenium is present in all wheat in detectable

amounts. Tliere appears to be no basis for concern, however, for very few samples analyzed have

contained toxic quantities and the dilution of these

crops with nonseleniferous wheat minimizes any

danger. Of the samples reported by Robinson

{153), two contained levels of selenium toxic to

rats—5 and 11 p.p.m. Lakin and Byers {100) reported that 82.5 percent of 951 samples of wheat

examined by them contained 1.0 p.p.m. or less of

seleniiun, 10 percent contained 2 to 3 p.p.m., 7.5

percent contained 4 p.p.m. or more selenium, and

of these only 8 samples contained as much as 10

p.p.m. or more. Thorvaldson and Johnson {183)

reported a mean value of 0.4-1 p.p.m. of selenium

in 2.230 samples of Avheat from Canada. The

maximum was 4.0 p.p.m. Robinson {153) found

26 p.p.m. of selenium in one sample of toxic

wheat, but reported 0.1 to 1.5 p.p.m. in 29 samples

from various parts of the world. Although a

human tolerance for selenium is not known, it appears doubtful that any substantial quantity of

selenium occurs in our food supply from this crop.

Williams, Lakin, and Byers {209) have published analyses of a numl^er of crops grown in the

seleniferous soils of Western United States. In

general the levels in the majority of samples collected range from 0.1 to 4 p.p.m. Very few values

as high as 15 p.p.m. are reported. One sample of

rye, 25 p.p.m., and one of corn, 30 p.p.m., were

notable exceptions. There appears to be little

evidence that alfalfa will absorb large quantities

of selenium. Both ]\Ioxon {123), at the South

Dakota Agricultural Experiment Station, and

Beatli, Eppson, and Gilbert ( 12), at the WyomingStation, have conducted surveys of this kind.

Beath and coworkers harvested a crop of alfalfa

from a field formerly containing two "indicator"

or "converter" plants, Antragalus pectmntus

Dougl. and A. 'bhulcaiuH (Hook.) Gray. Selenium

Avas not detected in the alfalfa, and when it was

fed to rabbits no toxicities were observed. While,

in general, conclusions that alfalfa is not ordinarily seleniferous are probably valid, a few high

values in alfalfa have been reported by Byers(^.^).

SPECIES DIFFERENCES IN THE

ABSORPTION AND ACCUMULATION OF SELENIUM

The first indication of a species difference in

the absorption of selenium was that made by

Taboury {177), who detected selenium in only

two of three plants collected from one locality.

Beath and coAvorkers {8) had observed early in

their studies that not all plant species growing

on certain shales and other geological formations

Avere toxic to animals. HoAvever, evidence that
SELENIUM IN AGRICULTURE 35

significant quantitative differences do occur among

species growing in the same soil was first presented by Hurd-Karrer (56'), who studied the

problem under unifonn conditions in the greenhouse. Her data show tliat the greatest accumulation of selenium occurred in the two representatives of the Cruciferae—mustard and broccoli.

This family also accumulates large quantities of

sulfur. All plants studied under these conditions

absorbed more selenium than is normally absorbed

by similar plants in seleniferous areas.

As field surveys became more extensive, many

workers observed this difference in the abilitj' of

plants to absorb selenium. Beath, Eppson, and

Gilbert {11) noted that different species of

Astragalus were not at all uniform in this respect, even when grown in close proximity to

one another. Miller and Byers {119) collected

a number of plants from a small seleniferous area

in Colorado, unfortunately, at least four soil

types appear to be represented, but the data indicate that wide differences may be expected in

the selenium content of different plant species.

Astragalus pecthiatus contained about 4,()00 p.p.m.

of selenium, whereas blue gramagi-ass contained

only 2 p.p.m. Stanleya p'mnata (Pursh) Biitt.

and Haplopapfus fremontii Gray were also absorbers of excessive quantities of selenium. Other

studies by Byers {23) and Williams, Lakin, and

Byers {209) show that the grasses are relatively

poor selenium accumulatoi-s as compared to many

other plants. Thus, in a soil wliere the selenium

concentration in buckbrush was 12 p.p.m., little

bluestem contained only 1 p.p.m. Also, in another soil, wild aster contained 120 p.p.m. and

associated grasses contained only 6 p.p.m. of selenium {23). Fourteen plant species collected from

another area 100 feet square showed a range in

selenium concentration of 0.5 to 20 p.p.m. The

lowest values were found in the grasses.

Hence, Byers, Miller, Williams, and Lakin {27)

decided that plants may be grouped with reference to their relation to selenium absorption.

Those absorbing little selenium included the

grasses—buffalograss and gramagrass, in particular. Those able to absorb moderate amounts

of selenium included the common cereals and a

number of such native plants as wreath aster, blue

aster, turpentineweed, and the .sunflower. The

third group included plants that absorb selenium

readily. These include Astragalus racemosus, A.

pectinatus, A. bisulcatus, A. caroUnixmus L., A.

grayii Parry, Stanleya p'mnata, S. pinnata A'ar.

hipinnata (Greene) Eollins, Haploppapus fremontii, and Xyloi^-hiza parryi (Gray) Greene.

Moxon, Olson, and Searight {129) sampled several species within an area of about 4 square rods

on the same geological formation. Their data

show clearly the magnitude of the differences that

may be expected in absorption of selenium by

différent species. Thus, ArtemUUi ranaden.sis

Michx. contained 6.8 p.p.m. of selenium as compared to 2,880 p.p.m. in KtanJeya pinnata var.

hipinnata. In anotlier area the contents ranged

from zero in western wheatgrass to 500 p.pan.

in Astragalus racemosus (figs. 6 and 7).

SELENIUM INDICATOR PLANTS

The most useful tools foi' study of the selenium

problem have been the development Ijy Robinson

{153) of chemical methods of analysis for minute

quantities of the element and the concept of inclicator plants first advanced by Beath and coworkers in 1934 {8). These workers noted that

certain species invariably showed the presence of

selenium and occurred oid}- on certain seleniferous

geological formations. After extensive field observations on the occurrence of these and other

plants (-5, 6, 11, 119), Beath and coworkers published a series of reports {8, -9, 10, 11), outlining

their concepts much more fully. The following

list is their selection of the seleniferous Astragalus and other indicator plants :

Genus Group Species

agalus Bisulcati Astragalus bisulcatus

(Hook.) Gray

Do do A. haydemanus Gray

Do do A. oocalycis M. E.

.Jones

Do do A. scohinatulus Sheld.

Do do A. urceolatus Greene

Do Galegifonnes A. racemosus Pursh

Do Inflad A. ariemisiarum M. E.

Jones

Do Lonchocarpi A. oslerhoulii M. E.

Jones

Do Ocreati A. alhulus Woot.

Standl.

Do do A. argillosus M. E.

Jones

Do do A. conferliflorus Gray

Do do A. flaviflorus (O.

Ktze.) Sheld.

Do do A. flavus Xutt.

Do do A. moencoppensis

M. E. Jones

Do do A. sophoroides M. E.

Jones

Do Podo-scle rocarpi. A. grariii Parry

Do do A. peclinatus l)ongl.

Do do .1. pecdnatus var.

platyphf/Uus M. E.

Jones

Do do A. rafaelensis ]M. E.

Jones

Do do A. ioanus M. E. Jones

Do Pretissii A. asclepiadoides

M. E. Jones

Do do A. beaihii Porter

Do do A. easiwoodae M. E.

Jones

Do do A. ellisiae (Rydb.)

Porter

Do do A. limalus Sheld.

Do do A. paliersonii Gray

Do do A. praclongus Sheld.

Do do . 1. preussii Gray

Do do .1. preussii var. lalus

M. E. Jones

Do do A. sabulosus M. E.

Jones
36 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

Figure 6.—Legume plants of the genus Astragalus are among the highest absorbers of selenium: A, A. bisulcatus;

B, A. canadensis L.; C, A. pectinatus; and D, A. racemosus. (Courtesy U.S. Geological Survey.)

Figure 7.—Plants of different botanical groups are sometimes strong absorbers of selenium: A, Xylorrhiza venusta

(M. E. Jones) Heller (woody aster) ; B, Grindelia squarrosa (curlycup gumweed) ; and C, Stanleya pinnata (desert

princesplume).
SELENIUM IN AGRICULTURE 37

Genua Group Species

Stanleya Stanleya alhe-icens

yi. E. Jones

Do S. elaia M. E. Jones

Do S. pinnata

Do S. pinnata (PuTsh)

Britt. var. gihherosa

Rollins

Do S. pinnata var.

hipinnata

Do «S. pinnata var.

inteyrifolia (James)

Rollins

Do S. tomentosa PsLTTy

Do S. viridiflora Nutt.

Xylorrhiza Xylorrhiza

glahrinscula Nutt.

Do X.parryi

Do X. venusta

Do A', villosa Nutt.

Oonopsis Happlopappns

fremontii var.

wardii Gray

Do Oonopsis argillacea

A. Neis.

Do 0. condensata A. ^els.

Do 0. engelmannii (CxrsLy)

Greene

Do 0. foliosa (Gray)

Greene

The fact that not all species of AstnigaJus are

selenium absorbers has led several workers to use

this property as a basis for group reclassificatioii

of the Astragali. Beath (G) found that Astragalus lonchocarpus Torr, did not absorb selenium

in toxic amoimts and was not confined to seleniferous soils. ^1. osterhoiitii is associated only with

seleniferoits soils. Lakin and Hermann {lOJ^)

found that ..4. artemisiarum M. E. Jones.classified

in the Irifati group, contained large quantities of

selenium and was found only on seleniferous soils.

They note that this species has several morphological characteristics in common with the seleniferous

Preusii gi'oup and they suggest its inclusion in that

group. Trelease and Trelease {100), pursuing

this problem further, studied the effect of selenium

in a nutrient solution on Astragalus racemosiis,

an indicator plant, and A. crassicarpiis Nutt., a

nonindicator. The growth of A. racemosus Avas

greatly stimulated by selenium, whereas A. crassicarpus was retarded. They concluded that these

experiments indicated a physiological basis for

the differences noted in the field. Perhaps this

means an actual need of relatively large quantities of selenium by certain species of Astragalus.

Other criteria based on selenium have been devised to improve the classification of Astragalus. Trelease {18-í) has suggested a germination

test as an aid to classifying the 218 species in North

America and the 1,200 species in the rest of the

world. He found that the addition of 20 p.p.m.

of selenium (as sodium selenite) to the culture

solution has no observable effect upon the earl}'

seedling growtli of an indicator species of Astragalus, wliereas it completely inliibits I'oot development of a nonindicator species. Vilkomereon

(lOfí) has correlated chromosome numbers of 26

species of Astragalus witli selenium absorption

data. Eleven species, all selenium absorbere, had

24 chromosomes. Thirteen had 22 chromosomes,

and of these, nine are nonabsorbers. It appeared

that the Lonchocarpi and Podo-sclerocarpi groups

should be subjected to further study, since these

groups include species of like chromosome number

and unlike reaction to seleniimi.

Byers and Lakin (;26') suggest, on the basis of

of selenium content, that IlornaJohus tenellus

(Piu-sh) Britt. [A. tenellus Pursh) and

Cliamaerhodos nuttalli are selenium indicators.

However, more extensive experience with these

species will be necessary before this observation

can be fully accepted, iloxon and others {120)

have suggested ilentzeliu decapetala (Pursh)

Urb. & Gilg. as a possible indicator plant.

A somewhat different concept of an indicator

plant has been utilized by Olson, Jornlin, and

Moxon {1S7), who emplo^-ed Agropyron smithil

in an intensive study of a small area in South

Dakota. This grass, common to the area, absorbs

more selenium than do other grasses and appears

to be a better indicator of available selenium in

the soil than other species. It is not, however",

restricted to seleniferous soils.

SELENIUM CONVERTER PLANTS

In 1934 Beath, Draize, and Gilbert (.9) observed

that crop and forage plants growing on seleniferous shales most frecpiently absorb toxic quantities

of selenium in those cases where indicator plants

are or have been growing. To study this further,

a composite sample of raw Steele shale was placecl

in two large pits (-5, 12). Seeds of Astragalus

racemosus, A. grayi, A. hisulcatus, A. pectinatus,

and Oonopsis condensata were sown in one pit.

The resulting plants were permitted to grow

normally and eventually they died, decomposed,

and wei-e leached. After ?> years the surface soil

in this pit produced a toxic wheat, whereas wheat

grown ni the control was not toxic. Hence, the

authors refer to most of the indicator plants as

also being "converter' plants in that they are

able to absorb selenium from relatively insoluble

compounds and convertit to forms readily available to other plants, including crop plants such

as corn and wheat.

DISTRIBUTION OF SELENIUM IN

THE PLANT

It is strange that of the thousands of plants

analyzed for selenium there should be such a

paucity of information on tlio selenium content

of the different parts—tin leaves, stems, Hower,

seed, etc. Beath, Eppson, and Gilbert {12) sepa-
38 AGRICULTURE HANDBOOK 2 00, U.S. DEPARTMENT OF AGRICULTURE

rated the wheat phiiit into o-raiii, steins and leaves,

and roots. The stems and leaves contained abont

one-half to two-thirds as nuich selenium as did the

grain and roots. The distribution varied in different samples, however, and it is diflicult to arrive at valid conclusions from tlie data presented.

Byers, Miller, Williams, and Lakin (S7) fomid no

difference in selenium content in the tops and

roots of onions or sugar beets. Williams, Lakin,

and Byers (208) reported about twice as much

selenium in a sample of radish tops as in the roots

in one case, and no dill'erence in the second case.

The selenium content of the first sample was much

higlier than that of the second. Taboury and

Manceau (179) and Taboury and Coudray-Viau

(178) have reported on the selenium content of

mustard and rape, separated into roots, stalk, seed

pod, and oil. The concentration in the seed pod

was high in both species. Williams (205) has

reported on the analysis of five samples of Asfmr/alus and one of Stanleya. Although the separations of the plants into their parts differed in

each case, the seed, with or without the pod, contained the highest concentration of selenium.

With one exception, the leaA^es contained more selenium than the stem or the root. The flower also

contained relatively large quantities of selenium.

Hurd-Karrer (85) made the rather interesting

observation that the relative distribution of selenium between the roots and tops of the wheat

plant depended on the source of selenium. Plants

supplied with a selenite contained a higher percentage of selenium in the roots than in the tops.

The reverse condition was obtained for plants

supplied with selenate. Similar results were reported by Gile and Lakin (69). Hurd-Karrer

(85) postulated that selenites are more easily reduced to elemental selenium than selenates in plant

cells and, hence, transport to the leaves was retarded. The reduction did not occur when selenates were absorbed by roots. Johnson and

Whitehead (94) reported on the distribution of

selenium in the mature wheat plant in relation

to the supply in the soil. At low levels of supply

the concentration in the kernel and the stem was

about equal. At high levels of selenium supply

the concentration in the stem exceeded that iii

the kernel by substantial amounts. The lowest

concentrations of selenium were found in the hull.

Somewhat more information is available concerning the distribution of selenium in milled

seleniferons Avheat. Eobinson (153) reported in

1933 that the gluten of a toxic wheat contained

90 p.p.m. of selenium as compared to 11 p.p.m.

in the whole wheat grain. Franke (57) reported

in 1934 that the toxicant in toxic wheat and corn

was carried in the protein fraction. A subsequent publication (60) indicated that the toxicant

was selenium. In a later publication, Eobinson

(15J^) reported the following distribution of selenium in a toxic wheat (26 p.p.m. Se) : gluten, 121

p.p.m.; bran, 22 p.p.m.; starch, 5 p.p.m., and

soluble and suspended matter, 16 p.p.m. of selenium.

Thus, early in the attack on the selenium problem a keen interest developed in the natural plant

compounds containing the element. Much effort

was expended on the fractionation of proteins and

the isolation of individual amino acids that might

contain selenium as a substitute for sulfur. The

possibilty of such a substitution was first suggested by Cameron in 1880 (20). Painter and

Franke '(1^0) reported in 1935 that most of the

selenium appeared to be in a compound very

similar to cystine. However, their data indicated

that selenium was not restricted to any one amino

acid but was rather widely distributed throughout

the protein fraction. Horn, Nelson, and Jones

reported in 1936 (81) that the principal centers

of the toxic selenium compounds were the proteins

gliadin and glutenin. Upon hydrolysis it was

found that tlie leucine fraction contained most

of the selenium. In a later publication (95) it

was repoi-ted that peptized gluten adjusted to pH

6.2 and with the precipitate removed the gluten

contained most of the selenium and was high in

cystine . In further work, Honi and Jones (80)

isolated and crystallized from Astragalus fecHnatus an amino acid complex containing both selenium and sulfur and agreeing in chemical properties and composition to the following isomorphic

amino acids: HOOC—CH (NH^)—CH,—S^-

CH,—CH.—CH (NH)—COOH, and HOOC—

CH (NIL)—CTL—S—CH,—CH,—CH (NH)—

COOH in the ratio of 2:1. The amount of selenium contained in the isolated ciystalline material

represented only a small part, of that contained

in the total plant material.

The knowledge that wheat grown in seleniferous areas would absorb selenium and accumulate

it in the grain led to several studies of wheat

byproducts and flour, particularly since public

health might te involved. Robinson (151f) examined samples of flour from Maryland and

North Dakota. Both contained a minimal quantity of selenium. Lakin and Byers (100) and

Williams, Lakin, and Byers (209) reported on a

large number of samples of flour and wheat byproducts, all obtained from Western United

States. Of 66 samples of flour only 5 contained

selenium in excess of 1 p.p.m. and 3 samples contained 4 and 5 p.p.m. The samples of bran, shorts,

and middlings ranged from 0.2 to 5 p.p.m., with

no significant difference among the three fractions. These authors suggest that selenium may

be present in small amounts in all wheat and

wheat products.

Moxon and others (126) examined four samples

of wheat grown in seleniferous areas of South

Dakota. The selenium content of the grain ranged

from 4.8 to 63 p.p.m. About 35 ¡Dercent of the
SELENIUM IN AGRICULTURE 39

selenium was found in the bran. The other fractions of the milled wlieat did not vary materially

from each other or the whole wheat grain in the

concentration of selenium.

The inorganic forms of selenium in plant tissue

have been investigated by Beath and Eppson ( 10).

Although the method used for extracting the

inorganic selenium compounds is empirical in

nature, it represents a good means of accomplishing an approximation of such compounds. No

selenate selenium was fovmd in representative

species of the seleniferous Astragalus and Sfunleya, although a large portion of the selenium

present was soluble in water. An examination

of several native plants, including Xylorrhiza

spp. and other selenium-indicator plants, showed

that all contained large quantities of selenium as

selenate. Only organic forms were found, however, in alfalfa, young wheat plants, and yellow

sweetclover or in barley, com, and oat grains.

These workers showed that species of Asfmgalvs

and Sianleya and possibly some forages and

cereals were capable of converting selenate or

selenite selenium entirely to organic compounds.

The situation with respect to grasses was not so

clear, however.

EFFECT OF STAGE OF GROWTH ON

SELENIUM CONTENT

Changes in the concentration of selenium as the

plant matures have received only casual attention

from most workere, whose jirimary aim has been

to determine only the presence or absence of the

element. Beath, Eppson, and Gilbert. {12) reported some selenium values in plants of diiîerent

size, but these authoi's ha\-e confounded size, stage

of maturity, and age. Hence, some of their data

are not interpretable. Other data {12, 127) indicated a smaller concentration in plants collected

late in the fall than in young plants. As pointed

out by Byers {2S), an important criterion in the

interpretation of field data is the variation that

may be expected as a result of the age and stage of

growth of the plant collected as the indicator of

soil and animal nutritional relationships.

Moxon, Olson, and Searight {128) studied

Agropyron smithii, Aster multiforus, GrhideJia

squarrosa (Pursh) Dunal, MelUotus ofßcinaJis

(L.) Lam., and several cereal plants. There was

considerable variation in the trend of the selenium

concentration as the plants matured, although in

general it appears that the highest concentrations

occurred in the very j'oung jolant. Johnson and

'\Aniitehead {91^) have examined this problem further by growing wheat plants in soils containing

different levels of selenimn as sodium selenite. At

low levels of selenium supply the more matixre

plants had a lower concentration of selenimn than

did their corresponding younger plants. The opposite trend occurred at high levels of selenium

supply. At intermediate levels of supply little

change occurred as the plant matured. In all

cases there was a constant increase in the total

uptake of selenium as the j^lant matured.

EFFECT OF SELENIUM ON

GROWTH OF PLANTS

The experience with indicator plants had suggested to several workers the possibility that

selenium was essential to the growth of these

plants. This supposition was based on the observation that such plants as certain Astragalus

species, the Stanleya, and others were not found

execpt on seleniferous soils.

Criteria for determining the essentiality of an

element as generally accepted liave been .stated Ijy

Arnon {S) as follows: "The criterion of the foremost physiological significance is the requirement

of an inorganic element for the successful completion of the life cycle of a plant. This is, of course,

different from merely demonstrating a favorable

effect on growth.'' Secondly, he states that it

must be shown that this effect is peculiar to the

specific element and that other elements cannot be

substituted. And finally, according to Arnon, the

direct effect of the element, as distinguished from

its possible influence on the root environment, must

be established. The toxicity of very low concentrations of selenium to certain plants had been

reported in earlier work {29. TJlj.. 192). Hence,

the report of Levine {111) of an increased growth

of lupin .seedlings in a nutrient solution containing

1 to 10 p.p.m. of selenium was received with interest. According to this investigator, higher

concentrations were toxic and the degree of toxicity was greatest when a selenite was used and

lesser for a selenate. Hurd-Karrer {85) reported,

however, that as little as (M p.p.m. of selenitim in

nutrient solutions was toxic to the wheat plant

when no sulfur was present in the nutrient solution, although her data indicated that this could be

prevented hy adding sulfur. Thus, witli 192

p.p.m of sulftir, injtiry was prevented when the

concentration of selenium was as high as 16 p.p.m.

Martin {118), however, was not able to confirm

these observations. In his experiments 2.5 p.p.m.

of sulfur in the nutrient solution prevented the

toxicity of wheat plants caused by 1 p.p.m. of selenium, but even the highest le\'els of sulfur (80

to f)40 p.p.m.) failed to counteract growth retardation at levels of 2 p.p.m. or more of selenium. In Martin's data the root developinent

appeared to be stimulated by 1 p.p.m. of selenium and 2.5 to 5.0 p.p.m. of sulfur but not by

higher levels of selenium at any level of sulfur.

It- was not shown whether or not quantities of selenium much smaller than 1 p.p.m. would have

stmiulated plant growth. In a later report, Hurd-
40 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

Karrer {87) claimed a growtli stimulation in

wheat seedlinf^s with 4 p.p.m. of selenium as the

selenate and 36 p.p.m. of sulfur in the nutrient

solution. The difference in weiglit—0.65 vs. 0,71

gram—is hardly significant, however.

Quite different responses of Astragalus to selenium have been reported by Trelease and Trelease

{189). Seeds of Astragalus racemosits containing 2,125 p.p.m. of selenium were germinated in

sand culture and transferred to water culture.

Seedlings that were given no added selenium made

slow growth in comparison with tliose grown in

a nutrient solution containing this element as selenite. In this experiment 81 p.p.m. of selenium

was definitely toxic at all levels of sulfur. Additions of 1, 3, and 9 p.p.m. of selenium stimulated

growth if 3 p.p.m. or more of sulfur were present,

and the stimulation increased with increase of

sulfur in the nutrient solution up to 81 p.p.m.

Sodimn selenite and potassium selenate were about

equally effective as sources of selenium. In common with Hurd-Karrer's obsei-vations (55, 89, 90),

the accumulation of selenium by the plant varied

inversely with the concentration of sulfur in the

nutrient solution. In a later report Trelease and

Trelease {190) studied the response of an indicator plant Astragalus racemosus with AstmgaJvs

crasslcarpus Nutt., a nonindicator. Selenium as

selenite was added to the nutrient solution in both

cases. Tlie two species of Astragalus responded

entirely ditTerently to selenium. The growth of

A. racémosos was stimulated, whereas that of A.

crass/carpus was I'etarded as the quantity of selenium was increased. No marked ditl'erence in the

accumulation of selenium by these plants was

noted.

Perkins and King {H-S) have reported some

effects on growth of Avheat from additions of selenium to the soil. Levels of 0.4, 1.0, and 2.6

p.p.m. stimulated growth, whereas 6.4 p.p.m. was

toxic. Stanford and Olson {173) have also noted

some stimulation of growth in wheat, oats, and

sorghum plants but not in corn plants as a result of adding 0.001 to 0.05 p.p.m. of selenium

as sodium selenate to culture solutions. Sharrer

and Schropp {159) reported that 1.3 p.p.m. of

selenium in a culture solution containing 25 p.p.m.

of sulfur was toxic to wheat, Ijarley, and oats.

No stimulation of growth was obtained with even

extremely low levels of selenium. Corn, however, appeared to respond to concentrations up to

0.013 p.p.m. of selenium.

Stoklassa {17Jf) showed in 1922 that 4 p.p.m.

of selenium as selenite was slightly toxic to

barley plants, but selenate at the same concentration was not. An indication that these concentrations of selenium accelerated growth in corn

and buckwheat was reported. He also observed

that radiation from radium seemed to accelerate

the germination of all seedlings and to limit the

toxicity of selenium as selenite. This effect of

radiation was also observed on plants growing

in nutrient solutions with or without selenium.

It is obvious from the foregoing that Arnon's

criteria {3) for essentiality of an element have

not been met in any experiment cited here. In

no case has the selenium-free seed been used. In

fact, under the conditions described this would

have been highly impractical to accomplish. In

no case was the life cycle of the selenium-free

plant studied, and it is obvious that there is a

selenium-sulfur interaction either in the root environment or within the plant that prevents any

interpretation of the evidence produced in these

experiments of the effect of selenium alone.

Hence, no evidence is available that selenium is

an essential element for plant growth even for

the selenium indicator plants such as the Astragalus species.

MISCELLANEOUS FACTORS AFFECTING THE ABSORPTION OF

SELENIUM BY PLANTS

The effect of sulfur in inhibiting the absorption

of selenium by wheat has already been discussed.

In 1937 Beath', Eppson, and Gilbert [12) reported

that decomposed seleniferous range plants (indicator and converter plants) were the chief source

of selenium to farm crops. They claimed that

these latter crops were incapable of absorbing

enough selenium from seleniferous shales to become toxic. In greenhouse experiments Trelease

and Di Somma {186) found tliat corn seedlings

absorbed and accumulated from 5- to 14-fold more

selenium from the organic compounds in a water

extract of seleniferous Astragalus hisulcatus than

from a sodium selenite solution of equal selenium

concentration. Furthermore, a marked increase

in the accumulation of selenimn from sodium

selenite occurred after the addition to the nutrient

solution of an extract of dried, ground nonseleniferous string beans. Tlie nonseleniferous

plant extract appeai'ed to have a protective action

to the corn seedlings against selenium toxicity.

Further work by Trelease and Greenfield {187)

indicates that several proteins and amino acids

added to the nutrient solution will enhance the

uptake of selenium by the corn plant. These

authors suggest that inorganic seleniimi is less

toxic when entering the plant in company with

these organic compounds than when entering

alone.

Taboui-y and Coudray-Viau {178) have studied

the effect of selenium in the nutrient culture on

the absoi'ption of a number of elements by mustard and radishes. The data indicate that the

concentration of iron, manganese, magnesium,

and lithium is higher in the normal plant than

in the seleniferous plant. Calcium, strontium, and

barium were lower in the normal plant.
SELENIUM IN AGRICULTURE 41

Use and Limitations of Selenium as an Insecticide

By FLOYD F. SMITH

Selenium compounds as possible insecticides

were first investigated by Gnadinger in 1933 {71).

Selenium was investigated because of its close

relationship to sulfur, one of the better miticides

available at that time, and because these two elements form analogous compounds. Tlie compound best suited for mite control on greenhouse

plants was fonned by dissolving selenium in potassium ammonium sulfide solution in proportions

corresponding to the formula (K(XH4)S)s Se.

A 3ü-percent solution designated as Selocide at

a 1 to 200 dilution with a soap spreader destroyed

Tetranychus telarais L. on greenhouse plants, also

Paratetranychus citri ]\IcG. and Phyllocopten

spp. on citrus in the field. At 1 to 800 dilutions

it killed 95 percent of T. ¡xtc'ifcuH McG. on grapes.

In furtlier tests with P. clfr'i^ Selocide was used at

1 to 600 dilution in combination with spreaders

and with lime-sulfur and a light spray oil with

blood albumen emulsifier. The highest kill obtained was with the oil combination, which destroyed over 99 percent of the older mites but

which was less efi'ective against the eggs.

Gnadinger {71) discussed the toxicity of selenium-spray residues and considered the toxic

action of selenites and selenates to be similar to

that of arsenites and arsenates. He further

pointed out that Selocide in a spray at a dilution

of 1 to 500 contains only one-fifth the quantity

of selenium as compared to arsenic found in the

standard lead arsenate sprays then in use. Furthermore, Selocide would lie applied only once or

twice a year as compared to the usual four to

nine applications of lead arsenate. Pie considered

selenium residues from such a schedule to be less

dangerous than residues from arsenical sprays

in an established program.

The reports bv Xelson and others {13fj) in 1933

and "White {2C)S) in 1934 pointed out the dangerously poisonous qualities of selenium compounds as discussed later under Health Hazards

(p. 45). This, no doubt, influenced the thinking

of subsequent research workers on the limitations

of this insecticide.

Boyce {20) in 1936 found Selocide at 1 to 800

dilution to be the most promising material other

than oil sprays for red mites on citrus. He found

the effectiveness was increased by addition of limesulfur (1 to 300), wettable sulfur (2 Ib./lOO gal.),

or light mineral oil (1 to 300). The seleniumsulfur compounds killed only those eggs in which

the embryo was well develoi^ed, but the residue on

foliage destroyed young hatching mites. The

Selocide-oil combinations gave high initial kills

of mites but lacked the residual effect.

After Hoskins (52) found residues of selenium

in fruits of treated grajjes and citrus, Boyce and

Prendergast {21) considered it inadvisable to use

selenium substances on citnis and discontinued

further studies with this compound in Califoniia.

Taylor (181), reporting on investigations in

New Zealand, found Selocide more elfective

against ParafetrnnyckuH piloHun C. & F. than

HETP, TEPP, Parathion, or karathane. One or

two sprayings after blossoming gave protection

for most of the season. Analyses of the fniits

indicated selenium residues of 0.3 p.p.m. or less.

However, he pointed out that a diet containing 3

p.p.m. could be consumed without ill effects.

Compton and Kearns {38) in 1937 found tliat

T. telariuH mites on rose were much harder to

kill than on snapdragon, which may be the first

report of resistance in this species. These authors

found that by use of a wetting agent such as

Aresket 240 a l-j:)ercent Selocide solution, was

equal to a 2-percent solution without a wetting

agent.

In the investigations reviewed above the nature

of the insecticidal action of selenium in Selocide

was not discussed. It was compared with other

insecticides on the basis of immediate kill and

residual action. In 1936 Hurd-Karrer and Poos

{91) first demonstrated that selenium was a systemic insecticide in plants. They showed that

selenium was absorbed by the roots of wheat plants

from tlie substrate and translocated to the foliage

where it killed aphids {RhopaIos¡¡)hum -prunifolhie Fitch.) at concentrations too low to ciiuse

visible effects on the plants themselves. The

aphids did not distinguish lietween treated and untreated plants in their feeding preferences. Thus,

a purely physiological study provided the suggestion for a fresh approach to pest control on plants.

Luekel {lOO) in 1940 protected sorghiun plants

in the greenhouse from attack bj^ Aphis /D nidis

Fitch and T. telnr-ius by applying water solutions

of sodium selenate at the rate of 4 p.p.m. by

weight to the soil. Lower dosages at 2 or 3 p.p.m.

were ineffective, and higher dosages 5 to 15 p.p.m.

stunted the growth.

In 1940 Xeiswander and Älorris {135) added

sodium selenate to nutrient solutions in which

chrysanthemums were growing; at a 2-p.p.m.

rate the concentration in the leaves Avas 45 p.p.m.,

which eliminated MacrosiphonieVa sanhorni

(Gill.) : and at a 4-p.p.m. rate the foliage contained

90 to 100 p.p.m. selenium, which destroyed T.

telnriuA. Tomato plants growing in solutions

containing 1.5 p.p.m. seleniuui concentrated suiScient selenium in the leaves to kill T. telarius.

Carnations required 6-p.p.m. concentrations in
42 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

the soil to kill mites; they failed, however, to absorb toxic amounts of selenium wlien grown in nutrient solutions. Roses growing in solutions containing 0.5 p.p.m. selenium were defoliated by

mites but at a 2.5-p.p.m. level they were protected

from mite attack and grew well.

Speyer and coworkers {172) found that insufficient selenium was taken up by tomato seeds

soaked in sodium selenate solutions for 24 lionrs

before sowing to immunize the seedling plants

from attack by T. telarlus. Seedling tomatoes

grown in soil or compost containing more tlian

50 p.p.m. of sodium selenate were severely injured.

Plants grown in soil at lower levels of selenate

were immunized from mite attack, but plants

grown from seed from these treated plants were

severely damaged by mites. These authors pointed

out the risk of rendering tomato fruits unsuitable

for consumption and of the contamination of the

soil for other crops.

English {50) prevented attack of aphids, spider

mites, and the Mexican mealybug {Phemirorcus

gossypii T. & (\) on chrysanthemum and of spider

mites and grape mealybugs {Pseudococciis m/iritinus Ehrh.) on carnation by a single 0.25 gram

dosage per square foot of soil application of sodium selenate. Five varieties of clirysanthemum tolerated the treatment but a sixth one was injured.

Carnation shoots were stunted, but flower production was not reduced. Farrar (5,'3) found that

vigorously growing clirysanthemum plants tolerated higher dosages of sodium selenate in the

soil than did weak-growing varieties; also tliat

mites, mealybugs, and thrips were destroyed by

the standard dosage of 0.25 gram per square foot,

but not the chrysanthenumi midge as reported by

Blauvelt {19). In field trials a 0.25-gram dosage

per square foot of soil controlled gladiolus thrips

{TaeniofhripH s'niiplex Morison). In 1945 Blauvelt {19) publislied the first practical recommendations for applying sodium selenate, in solution

or impregnated on pelleted phosphate rock, to the

soil of greenhouse flowering crops for the control

of spider mites and aj^hids on clirysanthemunis

and carnations; chrysanthemum midge {D'tarthronomy'/a chrynanfhemi Ahlberg) ancl foliar

nematodes on chrysantliemum ; and cyclamen mite

{SteneofarHonemus pallUhiH (Banks) ) on chrysanthemums and African-violets. His procedures for

application and his dosage rates for various crops

are still used.

TOLERANCE OF INSECTS TO

SELENIUM

Of the insects tested, aphids Avere probably the

most susceptible to selenium in plants. On clirysanthemums in nutrient solutions containing sodium selenate, Macrosiphoniella sanborni and

TtrtrrniyclxvH felariu-'i were killed by leaf concentrations of 45 p.p.m. and 90 to 100 p.p.m., respectively. Tests by Morris and coworkers (-?2S)

in 1941 showed that Aphh vmidis Fitch did not

survive on corn plants containing 25 p.p.m. of

selenium. On other plants with selenium content of 50 p.p.m., occasional sluggish T. telarius

mites were found, and at 100 p.p.m. all mites

were killed. That mites can change in their susceptibility was indicated by Quayle {1^6), who

reviewed the increased resistance in insects to insecticides and stated that Selocide had ceased to

be effective against 7'. telarius in greenhouses of

Eastern States, although it was of outstanding

value for a few years.

Fox {5G) reported on the tolerance to and possible preference for high levels of selenium by

several sj^ecies of insects in their choice of food

plants. Afitragalv-'i pert'maMü (Hook.) G. Don

{Cri.emldophacos pecthmtua (Dougl.) Rydb.),

a milkvetch growing in selenium-bearing soils in

Saskatchewan, contained 58 to 969 p.p.m. of selenium in the roots and 162 to 4,190 in the foliage;

another vetch {A. hisvlcatus (Hook.) Gray

(Diholf'Oft hhvlrnfiiH (Hook.) Rydb.)) contained

as much as 3,640 p.p.m. A Cerambycid AnovJodera hiMahilis Hald. and the Tineid WaJshia

amorplxelln Clem, bred in the roots of both of

these vetches. Larvae of A. insfahUis occurred in

roots of A. pectinatvs containing 154 to 969 p.p.m.

selenium, whereas the selenium content of roots

of uninfested plants contained only 58 p.p.m.

Other insects that fed on the neai-by roots of

these plants included larvae of Corymhites

{Ludiusi) aeripenvJ-^ denfrucior Jirovrn, Dra^sterius

{Aeolva) m^llillv^ Say, and Brneliyrlxmus ovatus

L. Three Meloids fed on the foliage of both

species, and Bnirhv.9 sem'/nvlvm Horn and a

Euryfomid near Brvchophagus gihhvs Boh. occurred in the seeds of lioth.

Other studies in Wyoming {188) showed that

Bruchiis fraterciihifi Horn completed its life cycle

in seeds of Af^fingalns^ hi!<iucahi,<< that contained

1,475 p.p.m. selenium: also that two parasites

Brurhophagvs me.vicanus Ash. and Eutelus

hruehophagi Sah. were present.

In experiments by Bennett and Martin {17) in

1948 mature grain from wheat plants grown in

soil treated with sodimn selenate was infested with

adult granary weevils {Calandra granaría). The

grain was not toxic to the adults, but no eggs or

larvae developed in the infested seeds." The

absence of eggs suggests the possibility that

certain vitamins or proteins containing sulfur are

concerned in the reproductive process and that

these become deranged in the presence of analagous

selenium compounds {17).

COMPATIBILITY WITH OTHER

INSECTICIDES

As mentioned earlier {18,. 71, 8J), several workers found increased kill of mites and insects wlien

lime-sulfur, wettable sulfur, or light sjiray oil
SELENIUM IN AGRICULTURE 43

«•ere combined with the Selocide. Selocide was

also compatible with nicotine sulfate, zinc oxide,

and zinc sulfide, but not with zinc sulfate and

hydrated lime (5^).

In 1936 Lilly [113) obtained increased kills of

the cherry case bearer {Coleophora prunleUa

Clem.), the bud moth {Evcosma ocellan/i Schiff.),

and the fruit tree leafroller {Tortrix argyrospila

Wlk.) by adding Selocide to the usual dormant

oil sprays applied for control of these apple pests.

Hoskins reported {82) in 1938 that Selocide

(1 to 800) in combination with a medium oil in

emulsion successfully controlled PorotetninyeliuH

citri and Tetranychua sexnuM-uJatiis Riley; and

Selocide plus wettable sulfur controlled citiais

thrips Scirtothiips cit/i Moult, and Phyllocoptnita oleivorus Ashm. Results of comparative

tests with Selocide alone were not included.

Taylor (181) reported that adding sulfur to

Selocide sprays had a synergistic effect, but that

in combinations witii lead arsenate Selocide severely damaged foliage.

Fuller {65) obtained excellent control of aphids

oil chi-ysanthemum with 0.2-gTam dosage of

sodium selenate in dry mixtures witli limestone

but obtained onlj- partial control with g;V'psum.

However, best aphid control and least plant injury

was obtained with 0.4-gram dosage of sodium

selenate in gypsum. Plant analysis indicated that

gj'psum reduced plant absorption of selenium and

of toxicit}' to the aphids, probably owing to the

available sulfur content of the gj^psum. Moxon

(125) pointed out that grasshopper damage was

equally severe in seleniferous and nonselenifei-ous

soils of South Dakota. A direct correlation occui-s

between tlie selenium content of tlie grasshoppei-s

and that of the vegetation upon which they fed.

Because arsenic is rendered more or less nontoxic by selenium, Moxon believes the effectiveness

of arsenic for poisoning grasshopi^ers in seleniferous areas is questionable.

KINDS OF PLANTS TREATED

. In 1941 Morris and coworkers (122) prevented

attack of Tetranychu^ telarhii^ on young apple,

elm, legumes, and wheat plants growing in sand or

soil cultures by adding sodium selenate at rates of

1 to 10 p.p.m.

Wolfenbarger (210) reported that Selocide

spraj^s on avocado and mangos were ineffective

again.st Paratetranychus yothersi (McG.) in

Florida.

FORMS OF SELENIUM

INSECTICIDES

Sodium selenate as crystals and usually dyed

blue or red is available in bulk to florists and

nurserymen who make up solutions for soil

drenches.

588590—61 4

Capsules containing one-fourth gram of sodium

selenate are packaged for shipping through the

mails or for sale in seed stores and garden supply

houses. They are mostly used in tlie home or

small greenhouses for the control of cyclamen

mites on African-violets or other plants. Each

package of capsules is accompanied by directions

for preparing .sodium selenate solutions and the

quantity to be used for each plant according to the

size of the pot. Four capsules containing"a total

of 1 gram of the chemical will make 1 gallon of

solution, which is sufficient for 64 4-inch pots or

256 2-inch pots.

Capsules of sodium selenate diluted with an

inert carrier are also a\'ailable for a one-capsuleper-plant treatment. Lindane is added by .some

firms to provide a combined foliage and soil insecticide.

SiJecially prepared phosphate rock, in pellets

and treated with a hot solution of sodium selenate

to give a 2-percent sodium selenate content, is

packaged in 25- to l(>0-pound drums for sale to

florists. The material is broadcast over the soil

surface at rates of ly^ to 3 pounds per 100 square

feet to give an approximate application rate of

one-eighth to one-fourth gram per square foot.

Selocide containing 30 percent potassium ammonium selenosulfide has been tlie most widely

used selenium formulation for foliage sprays.

Schrader (IGO) synthesized compounds of phosphorus and selenium—including diethyl ethylmercaptoethyl selenophosphate, a selenium analogof demeton—which were toxic to insects. However, Schrader found all of his analogs had unpleasant odors, were expensive to produce, and

were highly toxic to wai'm-blooded animals.

Xone have been made commercially.

Anthony (2) obtained complete control of the

black cherry aphid (Myzus ce rau F.) on cherries

and the green peach aphid and spider mites on

peach by foliage sprays containing 1.2 ounces of

Schrader's selenium analog in an emulsion concentrate.

In studies by Kiplinger and Fuller (90) selenates of copper or potassium were more toxic to

aphids than were selenates of calcium or sodimn.

METHODS OF APPLICATION

Soil applications.—To be successful with sodium selenate as a systemic poison, rather exacting

conditions must be observed to attain the desired

concentrations in the plant for insect kill and to

avoid excessive quantities that would be phytotoxic. In practical applications of sodium selenate to soil in greenhouse benches, plant-gro\Ytli

conditions conducive to luiiiorm translocation enhance the systemic action. Best kills are obtained

on vigorous, young, well-established plants^
44 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

Young seedling plants are more susceptible to injury, and selenium uptake in older plants or in

those injured by insects or mites is sometimes

too slow to be effective. Tlius, Kiplinger and

Fuller (96) obtained no control of mealybugs on

gardenia, a woody-stemmed plant, or on the

fleshy-stemmed Begonia, socotrana Hook, f., apparently because of its extreme susceptibility and

leaf drop. Also aphids and spider mites were

controlled by soil applications of sodium selenate

on tender current season growth of recently ¡iropagated hydrangea, but no control was obtained

on older woody-stemmed plants.

Treatments are not made when temperatures

are excessively high, because of increased transpiration rate and the buildup of phytotoxic concentrations of selenium in the leaves. Treatments

during November through January are avoided,

because selenium uptake is slow during the short

winter days. The ill effect of overdosage can be

corrected by leacliing the soil with water and by

applications of gypsmu or sulfur.

The danger of plant injin'y from a single Ingram application is reduced by making two applications of sodium selenate at a %-gram rate in

solution or in fertilizer mixtni-e, with a 4- to 6-

week interval between applications.

One series of treatments is required for shortterm crops such as chrysanthemums, but cai-nations are usually treated at G-month intervals to

replace the selenium taken \\\> by the ])lants lost

through leaching or chemically transformed in the

soil.

Foliage applications.—Selocide containing 30

percent potassium ammonium selenosulfide has

been the most widely used formulation for foliage

sprays on citrus and apple trees and was used on

roses and other greenliouse crops until resistance

of mites developed. The usual application rate

is 1 pint per 100 gallons. Foliage applications of.

Selocide appear to have short residual action and

systemic qualities are not shown as exhibited by

selenium in soil applications.

QUANTITY MARKETED

Although a large number of individuals who

irrow ornamentals benefit from selenium in its

various forms for insect control, the total quantity of selenium compounds actually marketed as

insecticides is small.

One small-scale formulator indicated approximately 2,000 annual mail order sales of sodium

selenate in 25,000 14-gram capsules, chieñy to

growers of African-violets for cyclamen mite control. He requires approximately 14 pounds of the

chemical to fill these orders. The same formulator

has an increasing demand for capsules containing

lindane plus 1.3 percent sodium selenate for use

as a capsule-per-pot treatment. Larger concerns

have made wide distribution of diluted sodium

selenate in capsules for treating individual pots

through retailers of seeds, flowers, and garden

supplies.

There is a small but steady demand by florists

for bulk crystalline sodium selenate for application to the soil as a water solution to control

spider mites, aphids, and certain foliar nematodes;

also for the phospliate fertilizer-selenate mixture

in 25- to 100-pound drums for broadcast applications. The florists' demand for selenium in Selocide for use as foliage sprays has practically

ceased, because of its failure to control resistant

spider mites.

Information is not available on the quantities

of sodium-.selenate or Selocide used in sprays on

citrus or other crops in California, the only

State in which seleniferous insecticides have been

registered for use on food crops.

DANGERS OF TREATED PLANTS

AND SOILS TO ANIMALS

Plants take up A^arylng amounts of selenium

from the soils in whicli they gi'ow. Food plants

grown in naturally seleniferous soils or in .soils

treated with selenium compomids for pest control

are a threat to the health of man or animals

ingesting tliem.

Hurd-Karrar {S8) reported that plants with

higli sulfur requirement also store relatively large

quantities of selenium. Such crops are broccoli,

(•al)bage, cauliflower, mustard, and onions.

Kiplinger and Fuller {9G) found that the uptake of selenium in chrysanthemum plants varied

with the rate of soil application of sodium selenate; at a Vy-gram-per-square-foot application an

equilibrium of 70 p.p.m. was reached in 3 weeks,

wiiereas with 14- or i^-gram applications tlie uptake in the plant increased for aljout 7 weeks to

an equilibrium of 425 or 690 p.p.m., respectively.

When the workers added sodium selenate in

nutrient solution to corn plants at 2-week intervals

at rates ranging from 0.5 to 3 p.p.m., they found

selenium contents of the foliage rang-ing; from 25

to 150 p.p.m., respectively {122).

Fuller (Gif.) investigated the selenium content

of vegetables grown on greenhouse soils treated

with sodium selenate. Carnations were grown in

the soil and treated with sodium selenate at the

rate of 0.25 gram per square foot. The carnations

were removed 7 months later and vegetables planted. Leaf lettuce and onions from sets planted in

the same soil contained 0.24 and 3.4 p.p.m.

selenium, respectively, when harvested. In another experiment lettuce contained 4.2 p.p.m.
SELENIUM IN AGRICULTURE 45

seleniiun at harvest when it followed a chrj'santhemum crop that had been grown in soil treated with

0.5 gram of sodium selenate per square foot. In

these experiments the selenium content available

to plants was depleted only by reaction with soil

and by tlie growing chrysanthemums ; it was not

leached out by excessive watering or other treatment. Cabbage and onions contained 6.1 and

5.6 p.p.m. of selenium, respectively, when grown

in soil treated with 0.5 gram sodium selenate

per square foot, then kept fallow for 61/2 months

without watering until planting time.

Fuller {61^) ako conducted experiments to deplete the selenium contents of the soil or inhibit the

selenium uptake. Lettuce grown in soil treated

with one-fourth gram of sodium selenate per

square foot (or 24 lb. per acre) after tlie crop was

established contained ?)5 p.p.m. of selenium at

harvest. Lettuce planted in similarly treated soil

that was leached with water at 21/2 or 5 gallons

per square foot before planting had a selenium

content of 13 and 2 p.p.m., respectively. A 21/0-

gallon leach per square foot plus 10 pounds of

gjq^sum or 2 pounds of sulfur per 100 square feet

reduced the selenium content in the succeeding

lettuce crop to 3 and 1 p.p.m., respectively. Fuller

{GJt) concluded that drastic leaching alone or moderate leaching plus addition of sulfur or g\'psum

offers an effective method for reducing danger of

.selenium in food crops grown on soils previously

treated with sodium selenate.

HEALTH HAZARDS FROM

SELENIUM RESIDUES

In a summary of spray residue problems in IDoi,

"White {20S) stated that care is needed in the exploitation of new potentially dangerous insecticides such as those containing selenium.

In 193?) Xelson and others (ISO) warned against

the use of selenium as an insecticide. Quantities

as small as 1 p.p.m. in the soil permitted growth

and maturation of wheat, but when the grain that

contained 8 to 10 p.p.m. selenium was fed to rats

and guinea pigs it retarded their gTowth and

death followed after a few weeks. These authors

further stated that selenium can be absorbed from

the soil by at least some and possibly all plants.

Even the complete removal of surface-spray residue from an edible product might be no safeguard ; and the degree of toxicity of the compound

used in spraying is not a measure of the toxicity

of the compounds formed in the plant. Moreover, there is evidence that selenium compounds

may be reduced by soil organisms, so that spray

residues ordinarily considered innocuous may be

made available to the plant and be converted to

highly toxic combinations.

in 1938 Hoskins {82) found residues of 0.6

p.p.m. selenium in fruits of vinifera grapes from

plots sprayed for several years with Selocide at

1 to 600 dilution for control of Tetrnnyrhiis parifcuH McG. The residues were less wlien the sprays

had been applied in jjrevious years only.

In tests on citrus fruits from trees spraved with

Selocide at 1 to 800 dilution, Hoskins {82) also

found residues of 0.21 and 0.06 p.p.m. in the skin

and pulp, respectively, whereas the corresponding

parts of untreated fruits averaged 0.10 and 0.05

p.p.m., respectively. The selenium content was

0.25 p.p.m. in untreated soils and was alwaj^s less

than 1.0 p.p.m. in soils of plots treated up to 6

times.

In New Zealand Taylor {181) stated that the

maximum amount of .selenium in the wliole diet

that man can consume without ill effects is l)elieved to be 3 p.p.m. He reported that analysis

of apples at harvest showed less than 0.08 p.jj.m.

selenium in fresh fruit from trees sprayed twice

with 1 pint of Selocide per 100 gallons 4 months

previously. He found 0.3 p.p.m. in fruits sprayed

1 or 2 months before harvest : and fruit from unsprayed trees contained 0.04 p.]).m. Xo evidence

was obtained of any tendency for ap]:)]e trees to

assimilate increased amounts of selenium after

having l^een sprayed for three successive years

with Selocide.

Fuller (i?4) and Kiplinger and Fuller (OG)

found 0.24 p.p.m. selenium in fresh lettuce and

3.44 p.p.m in green onions, or 3.8 and 31.3 p.p.m.

respectively on dry-weight basis. They state that

the best estimate tliev can get is from a study of

the T'.S. Pulilic Health Reports l)v Smith and associates {IGT. 1G8. Ujn. 170). They also reported

that a daily intake of 1 mg. of selenium in food is

prol)ably not harmful to an adult i:)erson. On this

basis 0.5 lb. of any vegetable that contains not

more than 4.5 i^.p.m. of selenium wouhl be entirely

safe for normal inclusion in the daily diet, provided that other constituents of the total food sup-

])ly were not seleniferf)us.

In a later paper Fuller (6'6')points out that by

adding sodium selenate to the nutrient medium

of some ornamental crops they can be ]5rotected

from attack by certain pests. He emphasized that

selenium or its compounds should in no case be

used on crops which may ultimately be used as

food for humans or domestic animals or on land

that might Ije used for growing such ci-ops. This

is in keeping with the present lecommendations

for use of selenium ; it has a zero tolerance on all

food crops anil has been registered for use only on

ornamentals, except for the rcgi&tered use on citrus

in California.
46 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

Effect of Selenium on Animals

By E. J. TiiACKER

The effects of selenium on animals have been

discussed in the comprehensive reviews by Moxon

and coworkers (]2?3, 123. Í27) and in the oi'iginal

description by Franke and associates (-5.9, G'2).

Moxon and Rhian {Í31) state "The chronic type,

'alkali disease' is predominant in South Dakota

and in other States where seleniferous soils are

formed extensively. It results from the consumption of vegetation, grains and forages containing

up to approximately 25.0 p.p.m. of selenium for a

period of several days or weeks." Dullness and

lack of vitality is a general symptom. Tlie animals become emaciated, stiff, and lame, and fail

to respond to good care and selenium-free feed.

A prominent symptom in horses and mules is the

loss of the long hair from the mane and tail. This

loss often takes place within a month after horses

are moved to seleniferous areas.

"The loss of long hair from the mane and tail

in horses and mules, and the loss of the long hair

from the switch of cattle is usually accompanied

or followed shortly by lameness and soreness of

the feet [fig. 8]. Swelling appears at the coronary band. In very mild cases there may be no

further change although the animals may be lame

for some time. In severe cases a gradual separation of the wall of the hoof occurs below the coronary band, and a new growth of hoof starts at the

coronary band. In some cases the old hoof is

sloughed off and in others it remains attached to

the new growth until the new hoof has gro^vn to

normal length. In cattle the old hoof usually remains attached to the new growth and in eases

where there have been several attacks the old

ragged hoofs may be 8 or 10 inches long and

turned upward at the end [fig. 9]. During the

time the animals are sloughing the old hoofs and

growing new ones they are very lame and often are

in severe pain. TTsually the_y do not move about

much and miless feed and water are within easy

reach, death may result from starvation and

thirst."

' -^- ,i •' ^-//»v i; •/•'*,^/4~^^, *,/,*&....^V^iîù'

Figure 8.—Seleiüzed animals frequently rest on their knees to relieve the pain of standing on sore, deformed feet.
SELENIUM IN AGRICULTURE 47

Figure H.—Severely selenized cattle frequently lose portions of their hoofs and the general body condition becomes

severely emaciated.

"In hogs the sj-mptoms of 'alkali disease' are

emaciation, lameness, loss of hair from the bocl}^

and irreoailar growth of the hoofs with occasional

slonghing of the hoofs similar to the condition in

cattle and horses [fig. 10]. "When yonng pigs are

fed corn containing 10 p.p.m. to 15 p.p.m. of selenium, the symptoms appear within 2 or 3 weeks."

In Wyoming a more acute ty])e of selenium

poisoning has been observed. Beath and coworkers (5) state : "The animals, particularly

cattle, exhibit early in the stage of poisoning a

dullness and a lack of vitality. It is evident early

in the stage of poisoning that there is a stasis of

the gastrointestinal tract. There is considerable

abdominal pain, with grunting, grating of teeth

and salivation. Shortly before the paralytic stage

animals exhibit excitement, with a tendency to

constantly wander, often aimlessly in circles. The

animal may or may not show impairment of vision.

Prior to death the animal exhibits varying degrees of paralj^sis, which becomes serious when it

involves the swallowing mechanism."

Pathologically, the lesions of selenium poisoning may be those of an acute, subacute, or chronic

reaction. Acute poisoning was experimentally

produced by Miller and "Williams {LiU) in the

horse, mule, cow, and swine, and death followed

within hours the administration of lethal doses of

selenium as sodium selenita. These authors dése ribed the clinical symptoms of an acute toxicity

ill horses as follows: "There is first a lack of appetite and refusal to drink water, and the animal

stands quietly in the stall. The pulse is slightly

accelerated and the respii'ations are fast. The

temperature may be normal or slightly higher. A

few hours before death, the animal stands as

though fixed to the floor, eyes staring, nostrils dilatecl, and the breathing is convulsive, fast, and

very labored. The temperature has a tendency to

rise, and the pulse is fast and weak or imperceptible in some animals. A blood sample taken at this

time is almost black in color, but there is no

hemolysis."

Necropsy revealed small, black hemorrhages,

few in number, on the surface of the lungs and

visceral pleura, along the coronary groove, and

on the pericardiiun, with multiple hemorrhages

under the endocardium extending into the myocardium. Subcajjsular hemorrhages were noted

on the spleen and kidney, and the kidney was soft

and friable. Severe gastritis and enteritis were

present, frequently with ulcération. Cloudy

swelling, fatty degeneration, and small hemorrhagic areas indicated liver injury. Acute nephritis and cortical hemorrhages were seen, as well

as cystitis, which was manifested as a diffuse, ulcerative or catarrhal lesion. Death in acute poisoning probably follows a marked reduction in

the respiratory capacity of the blood or asphyxiation {11).

The pathology of "blind -laggers" is characterized by the presence of acute and chronic lesions,

with death attributed to physiological anoxia.
48 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

Figure /O.—The lower portion of hogs' legs frequently

lose hair, and the hoofs show a gradual separation of

the walls below the coronary band.

The followins; description is paraphrased from

Draize and Beath (4-5) and Eosenfeld and Beath's

study {157) of this disease. Acnte congestion,

hemorrhaii'es, and fibrosis were firossly evident in

the luno-s. Fibrolthistic proliferation, lymphocytic infiltration, hemorrhajres, and edema thickened the alveoli walls to the extent of alveoli obliteration. The heart was atro])hied and fibrotic,

with all layers showinfj hemorrhages. On section

fibrosis, conp'estion and necrosis, with a serofibrinosis exúdate around the coronary vessels, were

observed.

The principal patholofrical changes in the liver

were varying degrees of fatty degeneration, necrosis, and early fibrosis. Large amounts of fat,

bile duct proliferation, necrosis around the central vein, and initial fibrotic changes destroyed

the normal architecture of the liver. The gastrointestinal tract showed desquamation of e]nthelium, congestion, hemorrhage, and frequently

ulcération of the stomach mucosa.

In the kidney, the cortical-medullary boundary

was indistinct and contained petechial hemorrhages. Microscopically, glomerulonephritis and

tubular changes were evident. Endothelial proliferation, fatty infiltration, and epithelial crescents were noted in the glomeruli and coagulation

necrosis of the tubules. The spleen tended to be

enlarged and firm with the cut surface mottled

with red and grayish-red areas. The sinusoids

were dilated and the pulp appeared congested

with red blood cells. Many malpighian corpuscles appeared hyperplastic. lîeticular fibrosis

and thickening of the trabeculae and of the blood

vessel walls were evident. Congested and hemorrhagic lymph nodes also showed fatty and variable fibrotic changes. The reproductive organs

were congested. In some animals necrosis and

edema were observed in the anterior pituitary.

No specific pathological lesion has been associated with the apparent impairment of vision observed in many cases of "blind staggers." Since

blood plasma vitamin A levels are reduced in subacute selenium poisoning (156), the suggestion

was advanced that the impaired vision was a result of a physiological vitamin A deficiency.

Confirmatory evidence for this has not been reported. The a])]:)arent blindness may be a manifestation of physiological anoxia associated with

the acute phase of the toxicity.

The pathologic changes observed in "alkali

disease" reflect the progressive degenerative

changes of chronic selenium toxicity. Swelling

and i)iflamation of the hoof coronary band and

the possible erosion of the articular surface of the

long bones would explain the painful lameness

seen in this condition.

The heart was soft, flabby, and atrophied, with

obvious areas of myocardial fil)rosis. INficroscopically, muscle fiber atrophy, myocardial fibrosis,

edema, and foci of lymphocytic infiltration were

noted. The normal histological sti'ucture of the

lung was destroyed by the atelectatic interstitial

tissue and fibroblastic proliferatioji. Liver damage was pronounced, with the normal lobule architecture of the liver disturbed by a fibrotic replacement of the parenchymal tissue. Typical portal

cirrhosis was seen in the advanced cases.

Atro{)hy, hyaline degeneration, and tubular

calcification were seen in the kidneys, Avith increased interstitial tissue, fibrosis, and thickening

of the blood vessel walls. In the spleen the reticulum and trabeculae were ]:)roliferated, and the

JNIalpighian corpuscles may be either hyperplastic

or fibrotic. The testes and ovaries were atrophied

and fibrotic.

A polioencephalomalacia (forage poisoning) in

feedlot and pastured cattle and sheep has been reported {93) from Colorado in which the clinical

symptoms were identical to those ascribed to blind

staggers in Wyoming. The significant lesions

were limited to the brain in which foci of necrosis

were observed throughout the cerebral cortex.

The condition was demonstrated to be noncontagious. Attempts to reproduce the disease by feeding vegetation and water collected from the areas

associated with the disease were unsuccessful.

Analysis of tissues from the afflicted animals indicated a variable selenium content.

The cause of forage poisoning is unknown and,

in the absence of information on the possible brain

damage in the blind staggers of alkali disease, the
SELENIUM IN AGRICULTURE 49

relationship of forage poisoning to blind staggers

is uncertain.

Maag, Orsborn, and Clopton (77-5) have recently reported from Colorado an experiment in which

an attempt was made to develop chronic selenium

poisoning by feeding an inorganic soui'ce of selenium for periods extending for 28 weeks. Sodium

selenite was fed by capsule to 8 steers at the rate

of 0.25 to 0.50 mg. selenium for each pound of

body weight three times a week. No symptoms

of poisoning Avere evident when selenium was fed

at a rate that resulted in a selenium blood level

of 3.0 p.p.m. or less. Sjanptoms of toxicosis were

observed when blood levels exceeded 3.0 p.p.m.

and inappétence and depression of the animals appeared when blood selenium exceeded 4.0 p.p.m.

Polioencephalomalacia was obseiwed clinically and

confirmed pathologically in two steers fed selenium for 8 and 22 weeks. Rumenitis, abomasitis,

and enterocolitis wei'e noted in six steers that died

during the experiment. Two animals slaughtered

after 28 weeks were free of lesions attriljutable to

selenium. Prolonged feeding of inorganic selenium did not result in the steers exhibiting the

classical symptoms of chronic selenium poisoning—deformed hoofs, lameness, roughened hair

coat, shedding of the long hair, emaciation, or

anemia. "Whether or not the incidence of

polioencephalomalacia in this experiment should

be attributed to selenium feeding is equivocal.

The Colorado workers have eifectively demonstrated that the prolonged ingestion of subacute quantities of selenium as an inorganic salt

does not induce the syndrome attril)uted to chronic

selenosis, which results when seleniferous plants

are fed to animals. The etiological factors involved in the development of chronic selenosis or

alkali disease would appear to be more complex

than simple selenium intoxification. Among the

factors that may be involved are one or more of

the alkaloidal constituents of certain seleniferous

plants, specific organic compounds of selenium,

and minor-element concentrations of unknown

biological significance in the vegetation. These

and other factors may be acting alone, together, or

interacting physiologically in the animal to produce the syndrome of alkali disease presently

ascribed to selenium poisoning. The apparenth'

still obscure etiolog;\' of alkali disease presents a

challenging problem for investigation in the interrelationships among the soil, plant, and animal as

well as those of a metabolic nature, biochemical

and physiological, essential to the etiological description of alkali disease.

Rosenfeld and Beath (7.57) have described a

congenital malformation in a gi'oup of 250 lamljs

born in a band of 2,100 ewes grazed on a seleniferous area. Seventy-five percent of the malformed

1:1 mbs died at birth and 10 percent died between

the ages of 3 to 5 months. The animals that survived showed a reduced rate of gain, thickened

and nodular joints of the extremities, deformities

of the eye, and hypoplasia of the reproductive

organs. The gross and histological changes in

the cystic malformed eyes were reported in detail.

The eye abnormalities indicated that developmental arrest occurred early in ge.station and the

capacity for differentiation, growth, and proliferation was impaired or lost. Arrested gTowth,

cellular proliferation, and lack of differentiation

at certain developmental stages resulted in microl^hthalmia, rudimentary development, microcornea, and colobomas of the various structures.

These observations have not been confirmed with

exi^erimental feeding of selenium.

Injury to poultry by ingestion of selenium has

been extensively studied at tlie South Dakota

Agricultural Experiment Station (123). Feed

consumption and growth is reduced in the chick

when the ration contains 8 p.p.m. selenium. As

little as 3.5 p.ji.m. in the ration of the hen results

in the fertile eggs carrying deformed embryos.

Eggs from hens fed selenized rations showed a

poor hatchability. The chicks that do hatcli are

weak and carry a wiry and greasy ajopearing down

(fig. 11). Fertility of the eggs was high, but

hatchability was reduced by the high incidence of

malformations. ^Many of the monster embryos

died before the 21st day, others were unable to

pip the shell because of a deformed upper beak.

Other terata included microphthalmia, abnormal

legs and wings, otocephaly, anencaphaly, and any

combination of the.se defects. The left side of the

embrvo was more severelj- affected than the right

side '(lOG).

A disease in wild ducks similar to the syndrome

produced by Clostridium hofullnium was believed

by Towmey and coworkere {19.!f. 193) to be caused

by selenium poisoning. However, Lakin, Quortrup, and Hotchkiss (7(9-5) were unable to confirm

this from observations made in the vicinity of

areas in which losses from western duck sickness

were known to occur. Similar levels of selenium

were found in livers of birds that died of botulism

or that were shot in flight. The level of selenium

in the liver was less than that reported as found in

apparently healthy hens. The marsh vegetation

and waters in affected areas were too low in selenium to be toxic. Furthermore, no deformities

in young waterfowl in the affected areas were

found. The possibility that fish in their native environment might be affected by seleniferous water

is suggested by the work of Ellis, Motley, Ellis,

and Jones [Iß). Goldfish kept in water containing 2 p.p.m. of selenium showed definite signs

of toxicoses. A typical sj'mptom was protruding

eyes, loss of color or scales, ijn oordination with

spasmodic movements.
50 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

Figure 11.—Selenized embryo chicks are frequently unable to pip the shell because of deformed beaks. The

chicks also carry a wiry, greasy appearing down. Fertility of eggs may be high, but hatchability is low because of a high incidence of malformation.

EXPERIMENTAL WORK WITH

LABORATORY ANIMALS

The rat assay of toxicants in plant foodstuffs

was reported by Franke in 1934 {57. 6£), although

it was not until a year later that he related the

trouble to selenium. He found that elemental

selenium added to the diet of the rat ajDpeared to

be harmless, whereas the different salts of selenium were about as toxic as a seleniferous Avheat

of equal selenium routent. The symptoms were

identical in all cases. In 193G, Maiisell, DeVaney,

and Kennedy {J33) reported on rat assays of a

seleniferous wheat begun in 1931 after Robinson

(löj) reported the presence of this element in

wheat. Unfortunately there is some confusion in

the report of Munsell and coworkers (133), and

it is not certain as to which rat in their pairedfeeding experiment was fed the toxic grain. In

further woi-k these authors were able to establish

that 0.25 milligram of selenium per 100 grams of

body weight per week resulted in retarded growth,

failure to reproduce, and the development of the

characteristic symptoms of selenium poisoning.

In view of recent findings (161. 162) it is interesting to note that Munsell and coworkers reported

that the female rats of the first generation on the

diet containing 0.75 p.p.m. of selenium and those

of the second generation on 0.75 and 1.5 p.p.m.

showed an apparent superiority over the control

group in i he number of young born and the percentage reared. Rosenfeld and Beath (lo7) reported normal litters from mothers receiving 1.5

to 2.5 p.p.m. of selenium in their diets.

The pathology of selenium poisoning seen in

small animals—rat, rabbit, cat, and dog—is amazingly similar to that seen in farm animals—cattle,

horse, and swine. Smith, Stohlman, and Lillie

(169), in a detailed study of the pathology in

selenized rat, found that the iiijui-y to the gastrointestinal tract, heart, spleen, kidney, and liver

was similar to that seen in the large animal. They

also observed a severe hyj^ochromatic and microcytic anemia, bone-marrow hypoplasia with compensatory myeloid metaplasia of the liver and

spleen. The histogenesis of liver cirrhosis, the

most prominent lesion in selenium poisoning,

was studied by Lillie and Smith (113). These

authors observed that capillary congestion, focal

and diffuse, developed into a hemorrhagic condition that was often periportal in location. These

areas gradually became organizing hemorrhages

with fibroblastic proliferation occluding clumps

of surviving liver cells. Eventually dense fibrosis

developed with the isolated parenchymal cells

proliferating to form nodular cirrhosis.

Rhian and Moxon (151) reported that the hair

of dogs fed selenium was coarse and loose, that

walking was difficult and painful, that response to

commands was slow, that the eyes were dull and

lifeless, and that the dogs stumbled over objects

blindly. The pathological findings were comparable to those seen in subacute poisoning of

cattle.

Moxon and Rhian (131) have summarized the

experiments conducted with small animals and

reported through 1943. Some of the tolerances

and characteristics of species other than the rat

follow :

Chicks.—In the ration of young chicks 8 p.p.m.

of selenium as sodium selenite retarded growth,

but 4 p.p.m. had no effect. Selenium injected into

fertile eggs in amounts as low as 0.0005 milligram

per egg caused typical deformed embryos. Ra-
SELENIUM IN AGRICULTURE 51

TABLE 23.—Levels of selenium in the ration associated loith different degrees of toxicity in various

animals

Animal

Amount of selenium and source of data forAoute toxicitv Subacute toxicitv Chronic toxicit\

Chicken.

Cow

Dog

FroK

Horse...

Mule...

Rat

Sheep

Swine

4.5 to 5 me:. {120)^

2U p.p.m. (ÍSÍ)2

0.1 mg. (;.3;)

1.5 mg. (120Y

1.5 mg. (120Y

4 mg. Í118Y

20 to 30 mg. (1.56Y per dav.

6 to 8 mg. {l20Y

5 to 8 p.p.m. (13Ï)?

5 to 40 p.p.m. (/,>,3).3 4

7.2 to 10 p.p.m. (131)?

15 to 25 p.p.m. (ISiy15 to 20 mg. per day {156V^.

5 to 15 p.p.m. (131)?

10 mg. per dav (lóñ).

10 to 15 p.p.ni. (131)?

1 Generally lethal within 24 hours.

2 In the ration.

3 Per pound of body weight; sodium selenite administered orall}'.

* Over a period of several days to weeks.

ä Death within 5 days.

^ Dependent upon protein level, death in 13-30 days.

' Dependent upon protein level.

tions containing seleniferous grains (15 p.p.m.

selenium in the ration) restilted in low hatchability of the eggs.

Rahhit.—By subcutaneous, intraperitoneal, or

intravenous injection, the fatal dose of sodiimi

selenite for the rabbit is from 0.9 to 1.5 milligrams of .selenimn per kilogram of body weight.

The quantity of sodium selenate required is somewhat larger, 2.0 to 2.5 milligrams.

Dog.—The lethal dose for the dog is about 2

milligrams of selenium jier kilogram of body

weight by subcutaneous, intraperitoneal, or intravenous injection.

EXPERIMENTAL WORK WITH

LARGE ANIMALS

Miller and Williams {120) have shown that the

single minimum lethal dose for horses and mules

is al)out 1.5 milligrams of .selenium per pound of

body weight. The selenium as sodium selenite

was administered orally. The minimum lethal

dose for cattle was between 4.5 to 5 milligrams

per pound of body weight, and for swine 6 to 8

milligrams. Other data on the quantities of selenium associated with degrees of toxicity in different animals are presented in table 23.

PROTECTIVE MEASURES

AGAINST SELENIUM

Supplements of calcium, phosphorus, cod liver

oil, orange juice, and yeast had no effect on selenium toxicity in experiments reported by Moxon

{123). Additions of cystine, fat, and sulfur to

the diet were also without effect. In a diet containing 55 percent of protein plus 37.5 p.p.m. of

.selenium, however, rats made slightly better gains

than those on a 10-percent protein diet. On the

basis of work by a number of workers, Moxon and

Khian {JJl) concluded that the jirotein content of

the diet was of considerable importance as affecting toxicity of selenitnn to animals. They noted

that proteins producing definitely favorable effects are casein, lactalbumin. ovalbumin, gelatine,

and proteins derived from wheat, dried brewers''

veast, de-ssiccated liver, and zein. Rosenfeld and

Beath {lófí. 157.158) studied further the effect of

protein, using sheej^ with controlled diets but

similating held conditions. Even at the high level

of protein (20 percent digestible protein), only

partial protection against selenium toxicity was

obtained. Thus, 10 and 15 milligrams per day of

selenium resulted in greatly decreased food intake.

Toxic symptoms appeared in the high and medium

protein-diet groups after the administration of 20

milligrams of selenium for 25 days, and in the low

l^rotein group (1.5 percent digestible protein)

after 15 milligrams of selenium for 6 days. In the

high and medium protein-diet gTotip, death occurred after feeding 2(1 milligrams of selenium

daily for 40 days, with a decrease of food intake

of 00 percent or over. In these animals {157)

there was a gradual decrease in the vitamin A and

total jirotein content of the blood and a more rapid

decrease in ascorbic acid. An increase of nonprotein nitrogen in the blood wa.s ob.served in all

animals that died from selenium poisoning.

Rosenfeld and Beath postulated that the increased

resistance against selenium poisoning in animals

fed high ])rotein diets may lie caused by the more

complete saturation of tlie liver cells with protein

producing a protection against injury of the cell

by the toxic action of selenium. Moxon and Rhian

{IJl) had noted that linseed meal and crude casein
52 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

^vere the more effective protein materials in reducing selenium toxicity. Plalverson, Heudrick, and

Olson (75) have reported, however, that the active

principle of linseed oil meal may not be the protein. A hot 50-percent ethanol extract of linseed

meal contained much of the protective principle.

It was found to be volatile and water soluble, and

an excess of lead did not precipitate it from solution.

Arsenic administered in the drinking water

completely inhibited the toxicity of selenium to

rats, according to Moxon (J2.í). Subsequent

work with the chick showed this treatment less

successful than with rats and dogs (131). Moxon

and Wilson (133) reported that 2.5 p.p.m. of arsenic counteracted in part the effect of selenium on

the hatchability of eggs, 5 p.p.m. was somewhat

better, but complete elimination of the effects of

selenium was not obtained. Further work by

Hendrick and Olson (70) indicates that sodium

methyl arsenate and calcium methyl arsenate have

no protective effect to rats fed a seleniferous diet.

The arsenics were administei'ed through the drinking water at the rate of 15 p.p.m. arsenic. In a

later report (33) Olson and coworkers reported

that 3-nitro-4-hydroxyphenylarsonic acid added to

a basal diet of seleniferous corn fed to chicks resulted in greatly improved growth. The addition

of Bi2 (20 micrograms per pound) resulted in a

nearly doubled growth in chicks, and selenivmi

added to this diet had a much more pronounced

toxic effect than it did on chicks fed the basal diet.

Arsenicals added to the B12 diet did not protect

against selenium. Experiments with pigs (199)

showed some protective effect of both 3-nitro-4-

hydroxyphenylarsonic acid and arsanilic acid

when added to a diet containing 10 p.p.m. of

selenium. At higher levels of selenium (13 p).p.m.)

the arsenicals clid not entirely prevent toxicity

symptoms unless linseed oilmeal was the source of

protein. However, use of this protein supplement

resulted in poorer growth and feed efficiency than

did the use of soybean oilmeal.

FAVORABLE EFFECTS OF SELENIUM IN THE DIET

An early reference, indicating a favorable effect

of selenium on reproduction in rats, has been cited

(133). Poley (1^5) claimed an indication of improved growth in chicks when 2 p.p.m. of selenium

liad been added to the diet. Recently, Pattei-son,

Milstrey, and Stokstad (H'B)., ScliAvarz, Bieri,

Briggs, and Scott (161), and Schwarz and Foltz

(16'S) have presented evidence that selenium will

prevent exudative diathesis in chicks or liver damage in rats on a diet deficient in vitamin E and

low in cystine. Selenium in the form of selenocystathionine (isolated by Horn and Jones (80)

from Afifragalus pectinatus in 1941) or as sodium

sek-nite were equally effective. About 10 micrograms of selenium as the seleno-cystathionine, 13.3

micrograms as sodium selenite, or 4 micrograms of

elemental selenium per 100 grams of diet all appeared to be effective. The preventive dose is

about 1 percent of the chronic toxicity dose of

300-400 micrograms per 100 grams of ration. Under these conclitions selenium appears to be about

500 times'as active as vitamin E. There is no

evidence that the need for selenium can be replaced by vitamin E, but diets very low in selenium and containing vitamin E are effective in

preventing exudative diasthesis. Patterson and

coworkers (1^2) point out that Poley's favorable

results with selenium in chick diets might have

been due to the vitamin E present.

It is well known that some confusion exists regarding the relationship between metabolism of

vitamin E and traces of selenium.

Muth, Oldfield, Renmiert, and Schubert (13If)

have demonstrated that muscular dystrophy

("white muscle disease") in lambs can be prevented by supplementing the eAve's ration (legume

hay and oats) with 0.1 p.p.m. selenium. Moreover, it was shown that treatment, orally or parenterally, of the ewe Avith alpha tocopheral (vitamin E) preparations at approximately physiological levels did not prevent a myopathy developing. Hogue (77) also presents evidence for the

efficacy of selenium supplements in prevention of

"stiff' lamb disease." In this study vitamin E supplements at similar levels to those used by Muth

Avere partially effective in protecting against the

dystrophic condition.

SELENIUM AND HUMAN

NUTRITION

Selenium toxicity in humans has been carefully

considered by the U.S. Public Health Service,

W'hose members Avorked in seA^erely selenized areas

of Western States (167, 171). Conclusions are

neither definitely positi\"e nor certainly negatiA^e.

Symptoms comparable to those of selenized domestic animals are essentially lacking. On the other

hand, cases of arthritis appear to be associated

with selenium in the diet. DegeneratiA^e processes

in the liver may have been hastened. There is

some suspicion that other features, such as discoloration of skin, bad teeth, dermatitis and

gastrointestinal disorders, may be aggi-avated by

the intake of small amounts of selenium. In the

Irapuata area of Mexico strongly seleniferous

vegetation is sold in local markets. Among the

items collected at a market wer-e radish roots—15

p.p.m. Se; spinach—7; and cabbage—70 (25).

This area of Mexico was suggested as one especially suited for study of human ailments in relation

to selenium. Such studies, hoAvever, haA^e not been

made. Tradition in the area indicates that human

ill health has been related to outwash from silver

mines. Since mercury Avas used in recovering

silver, the presumption was that this element Avas
SELENIUM IN AGRICULTURE 53

re.s]:>onsible for the trouble. As a matter of fact,

seleniferous vegetation probably has caused some

trouble there.

CONCLUSIONS

Wliereas the conditions for producino; selenium

toxicity in the laboratoiy animal and the chick

haA"e been faii'ly well established, the relationships

in the grazing animal are less clear. The various

degrees of toxicity in cattle encountei-ed on the

range are the results of the quantity of selenium

ingested as well as the proportion and length of

time that seleniferous vegetation is eaten. It

would appear, howevei', that ;"> ]:).]).m. or more

selenium in vegetation should be considered as

dangerous when ingested by any animal species

over a period of several weeks.

The mechanism of the protective action of protein feeds against selenium is not clear, since considerable variability in results with différent species and different sources of ¡n-otein have been

experienced. Furthermore, more recent work indicates that the protein in one of the more protective materials, linseed oilmeal, may not be the

active ingredient.

Likewise, the mechanism and effectiveness of the

arsenicals needs further clarification. Experimentation with the less toxic organic compounds

of arsenic has met with some success, although the

results with different compounds are quite variable.

Of considerable interest are the recent experiments indicating the need for selenium by the rat

and the chick when fed a vitamin Í] deficient diet

and the effectiveness of selenium in preventing

muscular dystrophy in lambs. Although this fact

in itself does not establish selenium as an essential

element for these species, it does suggest a s]:)aring

action of this element for vitaminE.

Management of Sekniferous Lands

By M. S. ANDERSON

Investigations of selenium in soils as related to

quality of vegetation and to animal sickness were

well underway by the mid-1930's. At that time

it had been shown that lands in certain "Western

States frequently produced forage and sometimes

grain crops that were a hazard to the health of

domestic animals. Such conditions reacted seriously against the economic welfare of local farmers and ranchers using these soils. Certain areas

in South Dakota had been clearly delineated as

having extensive seleniferous lands. It was established, also, that currently followed agricultural practices Avere not conducive to soil conservation nor did they give satisfactory economic

return to the local fann operators over a period

of years. It seemed desirable, therefore, to consider purchase of an extensive tract of these lands

by Federal agencies for the purpose of establishing field practices in accordance with the best

methods then known for the area. Furthermore,

there seemed to be widespread advantages from

possession of a large continuous area in which

experiments might be conducted, if so desired, by

Federal and State agencies.

ACQUISITION OF LANDS

In 1935, at the request of local people, the recently organized Resettlement Administration of

the Federal Government initiated proceedings

for the purchase of farm and ranch lands then

privately owned. The area lies south and a little

west of Pierre, S. Dak. Average annual rainfall

ol the area is approximately 17 to 20 inches. Certain kinds of vegetation grown on the soils are

frequently seleniferous and injurious to farm

animals. The soils are mostly of high clay content, difficult to work, and known locally as

"gumbo." A discussion of Federal land projects

in South Dakota is given by Glover {70).

In 1936 purchase of a large area of these lands

in three counties of South Dakota by the Federal

Government was accomplished. These lands are

located as follows : In Lyman County 60,285 acres;

in Stanley County 35,823 acres: and in Jones

County 19.711 acres; total 115,819 acres. The

area is known as the South Central South Dakota

LU Project No. 2. Figure 12 shows the location

of the lands in the State with respect to certain

landmarks included for identification of the area.

The average purchase price was $5.80 per acre.

During succeeding years a little more than the

original purchase price has been expended for improvements in the ai'ea, primarily for cross fences

and stock-water reservoirs.

The land purchased had been partly open-range

country and partly fenced for farm use. About

75 homes had been established in the area, but only

about 40 were occupied at the time of purchase by

the GoA'ernment. 1"\lien the Federal Government

took over the lands, it was during a period of unusuallj' low rainfall in much of the Great Plains

area. The T'nited States, as a whole, was then in

a period of deep economic depression. A number

of the local farmers of these counties had moved

away, and those remaining had no funds from

current income to carry out «oil conservation practices. "Wind erosion was i luipant, A photoirraph

of a landscape within this area is shown in fifrnre

13. *
54 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

Figure 12.—Area SD-LU-2 shows the location of federally owned seleniferous lands in South Dakota. The total area

of 115,819 acres is administered by the Forest Service.

Figure IS.—Landscape, showing an extensive seleniferous area in South Dakota.
SELENIUM IN AGRICULTURE 55

LAND MANAGEMENT PRACTICES

Initial supervision of the newlj' acquired lands

was assi<rned to different (rovernmental agencies,

particularly to the former Bureau of Afrricultural Economics and the Soil Conservation Service

of the U.S. Department of Af2:riculture. In 1954

responsibility for administration of the entire

area was transferred to the Forest Service, which

agency has extensive responsibility for the supervision of Federal lands for multiple-use management, including grazing.

Initial management practices consisted of removal of all farm buildings and some of the

fences. Land that had once been plowed was

properly treated for abatement of wind and water

erosion. It was then put in proper condition and

seeded with crested wheatgrass or other adajjted

forage vegetation. The cost of soil-improving

practices since purchase has been moderately in

excess of the original purchase price of the land.

Although the lands have not been used to any

great extent for formal experimentation, much has

been learned from continued operation of the

practices initiated there. Some of these accomplishments are summarized bj^ Dinkel and associates (44)- These have led to a better understanding of desirable field management methods

within the area. Seeding and grazing ]>ractices

have increased the production of good-fiualitj'

foi'age, the selenium contents of which appear not

to interfere with normal animal health and weight

gains as much as was the case before ]:)ublic ownership and management took place. Plant pojjulation counts have not been reported, but troublesome species of Astragalus plants presumablj"

constitute a smaller portion of the total vegetation

than was the case before the present management

program was undertaken.

GRAZING LEASE PRACTICES

It has been the custom of Federal agencies in

charge of land utilization projects to lease the

areas for immediate supervision by a local grazing

district that handles the grazing contracts. During the fiscal year 1957 rentals for grazing privileges were reported to be approximately 18 cents

per acre on the South Central Dakota Laud utilization Project. Counties where land is located

receive 25 percent of the rental fees in lieu of taxes.

THE EXAMPLE AND THE FUTURE

The management of Government-owned seleniferous lands in South Dakota has served as a demonstration ground rather than an intensively experimental one. Farmers and ranchers located on

seleniferous lands elsewhere can now come to this

great area in South Dakota to observe what may

be accomplished by good range practice applied

to seleniferous lands. Animal disease troubles incident to selenium are not entirely eliminated, but

conditions are greatly improved.

One cannot look to this area for substantial agricultural profits; such was never the case. Low

rainfall, stiff clay soils, cold winter temperatures,

and the presence of excessive contents of selenium

in a considerable portion of the soils all add to

difficulties of profitable livestock production.

The foregoing discussion pertains only to three

counties in South Dakota. Other areas within the

State have seleniferous soils, as do certain areas

in other Western States. The land acquired by

the Federal Government probably represents one

of the largest continuous areas where selenium

troubles are pronounced. But even here not all of

the soils are sufficiently seleniferous to make trouble for farmers.

Summary

Selenium in certain soils of the Great Plains

and other areas of the West is recognized as the

cause of so-called alkali disease of domestic animals in the region. Range animals are most likely to be affected, particularly when the supply of

good forage is limited and there is little opportunity for the animal to make any selection of

forage types.

Soils associated with selenium trouble are

derived, for the most part, from rocks of the

Cretaceous age. Geology and mineralogy are

related in important ways to the occurrence of

selenium in rocks, soils, and plants. Highly

seleniferous rocks are often of tuff, shale, or limestone groups. A vertical section of rock often

sliows wide variation of selenium content with

¿epth. Considerable quantities of selenium are

transported in the drainage waters of certain western streams.

Rainfall in excess of al)out 25 inclies aj^pears

to be suiffcient to leach out the readily soluble and

available selenium. Likewise, irrigation after

several years will leach substantial quantities of

the element from the soils, thus reducing the

hazard.

Although the presence of selenium in plants has

long been suspected, it was not until 193-3 that

quantitative estimations were made in the U.S.

Department of Agriculture. Many thousands of

analyses have since been reported in the literature

for the purpose of detenuining the presence of

quantities toxic to either man or animals. In the

course of such survey studies it was soon learned
56 AGRICULTURE HANDBOOK 200, U.S. DEPARTMENT OF AGRICULTURE

that typical selenium accumulator plants such as

some meml)ers of the Astragulitf: ^cnus (a le<>'ume),

woody aster (a composite), and l:^tanle;ia phmata

(a mustard) were commonly found on seleniferous

soils. Other plants, such as the cereals, also take

up appreciable quantities of selenium if the element is in an available form in the soil.

The form of selenium in plants has never been

clarified, although some of the early work indicated that it was present as a seleno-amino acid

similar to cystine and leucine. The quantities of

selenium reported range from 0.1 p.p.m. to several

thousand p.p.m.

Extensive studies of the effects of toxic quantities of selenium on animals have been made.

Horses, cattle, swine, and poultry are all susceptible to selenium poisoning. Both chronic and

acute conditions have been recognized. The pathology of these conditions are described. Symptoms of toxicity may appear in a few hours or

after several weeks, depending upon the quantity

of selenium ingested. Death generally occurs in

the acute cases, but, lameness, loss of hair, refusal

to walk, and consequent troubles are seen in the

milder cases. Congenital malformations in lambs

and chicks are commonly found. Lethal doses

for several animals have been established.

No practical protective measures are available

except to limit grazing in certain areas. On federally owned lands in South Dakota, enough diy

forage is left in the late fall to provide early pasturage for animals the next spring. Avoidance

by grazing animals of early-growing toxic plants

is thus made reasonably effective. The use of

arsenic as a drench will counteract the eiïects of

selenium, but this method requires careful control.

Some current inve.stigations of certain diseases,

such as muscular dystrophy ("white muscle disease") in lambs and calves, exudative diathesis

in clucks, and liver damage in I'ats. indicate that

small quantities of selenium will prevent such

troubles. Extensive investigations must be made,

however, before the essentiality of selenium is

proved.

Methods for the chemical determination of

selenium in different kinds of materials are given.

These methods have been successfully u.sed for

more than 25 years as a means of determining

selenium in soils, vegetation, and other materials.

Methods for evaluating traces of the element are

being currently investigated at several laboratories.

Selenium compounds as insecticides are discussed and the dangers arising from their use

noted.

Literature Cited

'(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

ANCIZAR-SORDO, .J.

1047. OCCURRENCE OF SELENIUM IN SOILS AND

PLANTS OF COLOMBIA, SOUTH AMERICA. Soil

Sei. 63: 437-438.

ANTHONY, E. W.

1951. NEW INSECTICIDES, INCLUDING SYSTEMIC INSECTICIDES, FOR CONTROL OF BLACK CHERRY

APHiDS. Jour. Econ. Ent. 44 : 1012.

ARNON, D. I.

1951. GROWTH AND FUNCTION AS CRITERIA IN DETERMINING THE ESSENTIAL NATURE OF INORGANIC

NUTRIENTS. Ill Mineral Nutrition of Plants

(Emil Truog, editor), pp. 313-341. Madison, Wis.

BEATH, O. A.

1921. POISONOUS PLANTS OF WYOMING. Wyo. Agr.

Expt. Sta. Bui. 126, 35 pp'., illus.

1937. SELENIFEROUS VEGETATION OF WYOMING.

PART II. In Knight, S. H., and Beath, O. A.,

The Occurrence of Selenium and Seleniferous Vegetation in AVyoming, Wyo. Agr.

Expt. Sta. Bui. 221, 64 pp., illus.

1939. THE SELENIFEROUS ASTRAGALUS OSTERHOUTH

JONES. Amer. .Jour. Bot. 26: 729-730.

1943. TOXIC VEGATATION GROWING ON THE SALT

WATER SANDSTONE MEMBER OF THE MORRISON

FORMATION. Amer. Jour. Bot. 30: 698-707,

illus.

DEAIZE, J. H., EPPSON, H. F., and others.

19.34. CERTAIN POISONOUS PLANTS OF WYOMING ACTIVATED BY SELENIUM AND THEIR ASSOCIATION WITH RESPECT TO SOIL TYPES. Amer.

Pharm. Assuc. Jour. 23 : 94-97.

(9)

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(211)

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Appendix

BY K. C. BEESON

The extensive investin^ations by the U.S. Department of Agi-iciiltnre and several State Experiment Stations of the occurrence of seleniferous

areas are rejiorted in many bulletins and papers.

To au^nent the search for work done in a particular area, references have been compiled in

taljle "24 by States and counties. No interijretation of the data in terms of toxic or normal areas

has been made. This information can best be obtained by a study of the original report.

TABLE 24.—Lorationn hy States and counties where the concentration of selenium in vegetation has

been investigated

State und county

Arizona:

Apache__

Cochise.-

Coconioo_

Gila

Greenlee_

Mohave _.

Navajo _ _

Pima

Final

Yavapai _.

California:

Alameda.

Colusa

Fresno_

Reference and page

iU, p. S98; S3, p. 35)

{14, p. 298; 1.5, p. 892)

{14, p. 298)

{14, p. 298)

{14, P- 298; 16, p. 892)

{14, P- 298; 27, p. 10)

{14, P- 298: 15, p. 892; 23, p. 35)

{15, p. 892)

{14, p. 298; 15, p. 892)

{101, p

{101, p

{101, p

Glen ; {101, V

Kern.

Los Angeles

Merced

Napa

Orange

San Bernardino. _.

San .Joaquín

San Luis Obispo..

Santa Barbara

Solano

Stanislaus

Tehama

Yolo

Colorado:

Adams

Archuleta

Bent

Cheyenne.

Crowlev.-

Delta--...

El Paso...

Fremont..

Garfield...

Grand

Gunnison.

Huérfano.

Kiowa

La Plata

Larimer

Las Animas.

Lincoln

{101, p

(101, p

{101, p

{101, p

{101, p

{101, p

{101, p

{101, p

{101, p

{101, p

{101, p

{101, p.

{101, p.

5)

5)

4)

6)

4)

S)

4)

5)

3)

299)

5)

4)

4)

5)

4)

6)

5)

{23, p. 31)

{14, P- 301; 16, p. 892)

{27, pp. 6, 16, 27, 42; 209, pp. 8,

32, 42)

{27, p. 6; 209, pp. 32, 42)

{27, pp. 6, 18; 209, pp. .32, 42)

{24, p. 21)

{14, p. 301; 27, pp. 6, 21, ^5; 205,

p. 200)

{14, p. 301; 27, pp. 6, 22)

(16, p. 893; 23, p. 31)

(14, p. 301; 16, p. 892; 23, p. 31)

{23, p. 32)

(14, p. 302; 27, pp. 6, 19, 44)

(27, pp. 6, 16, 63; 119, p. 65; 206,

p. 200; 209, pp. 32, 42, 6,3)

(14, p. 301)

{14, p. 301; 16, p. 892; S3, p. 31)

{14, p. 302; 23, p. 31; 27, p. 19)

{14, p. 301; 23, p. 31; 27, pp. 6, 18)

State and countv

Colorado—Cont

Logan

Mesa

Moffat

Montezunia. _

Montrose

Morgan

Otero

Ourav

Park".

Prowers

Pueblo

Rio Blanco

Routt

San Miguel

Washington _ _

Idaho :

Ada

Bannock

Caribou

Clark

Ehnore

Gem

Gooding

Owvhee

Power

^Twin Falls...

Kansas:

Barber

Clark

Comanche

Gove

Graham

Hamilton

Lane

Logan

Ness

Norton

Phillips

Rooks

Scott

Trego

Wallace

Montana:

Big Horn

Reference and page

, p. 31)

, p. 301; 16, p. 892; 23, p. 32;

'h p. 1-J)

p. 302; 16, p. 892; 23, p. 32)

p. 301; 27, p. 66)

p. 32; 24, p. 21)

p. 31; 27, p. 6)

p. 31; 27, pp. 6, 17, 28; 205,

200; 209, pp. 8, .^2, 42)

p. 301; 23, p. 32)

p. 302)

(23,

(14

2

(14,

(14,

{23,

(23,

(23,

P-

(14,

(14,

(27,

(27,

{14,

(14,

(23,

{27,

(14. p. 304)

(14, p. 304)

(106, p. 24)

(14. p. 304)

(102, pp. 23,

(102, p. 23)

p. ÖUZ)

pp. 15, 26; 20'.>, pp. 8, .32, 42)

p. 20)

p. 301; 15, p. 892; 23, p. 32)

p. 302; 23, p. 32)

p. 32)

p. 6)

U; 209, p .62)

(102, p. 23)

(14, p. 304; 102, p. 24; 209, p. 62)

(14, p. 304; 102, p. 23; 209, p. 62)

(14, p. 304)

(102, p. 23)

(23, p. 34)

(23, p. 34)

(23, p. 34)

(23, p. 34; 24, p. 40; 206, p.

209, p. 8)

{24, p. 46; 209, p. 8)

(23, p. 34)

(208, p. 8)

(23, p. 34; 2.

42, 64)

(209, p. 9)

(24, p. 48)

(24, p. 48; 209, p. 9)

(24, p. 46; 209, p. 9)

(24, p. 43)

(24, p. 43; 209, p. 9)

{23, p. 34; ^4- P- S7; 209, pp. 9, 32)

(14, p. -306; 15, p. 8.93; 208, p. 9;

209, pp. 9, S3, 42)

i 63

200;

(208, p. 8)

(9.a. -n a/,- 9.4, p. 29; 209, pp. 8, S2,
64 AGRICULTURE HANDBOOK 2 0 0, U.S. DEPARTMENT OF AGRICULTURE

TABLE 24.—Locationx by tStatefi and coimtieH inhere the concentration of seJeniv/m, in vegetation has

been invefitir/ated—Continued

State and county

Montana—Con.

Blaine

Carter

Cascade

Chouteau

Daniels

Dawson

Deer Lodge

Fergus

Gallatin

Garfield

Glacier

Hill

Jefîerson

Judith Basin

Lewis and Clark

Liberty

McCone

Musselshell

Petroleum

Phillips

Pondera

Roosevelt

Rosebud

Sheridan

Teton

Toole

Treasure

Valley

Wheatland

Yellowstone

Nebraska:

Boyd

Cedar

Dawes

Dundy

Franklin

Furnas

Harlan

Hitchcock

Knox

Nance

Red Willow

Sheridan

Sioux

Webster

Nevada:

Clark

Douglas

EIko

Humboldt

Lincoln

Lyon

Mineral

Nye

Pershing

White Pine

New Mexico :

C'alron

Cîolfax

De Baca

Reference and page

', 42)

•. 24; 209, pp. 11,

.. 12, 4S)

12,

(14, p. S06; 209, pp. 10, S3)

(14, p. 306; 15, p. 893; 23, p. 28; 24,

p. 15; 209, pp. 10, 33, 4^)

{14, p. 306: 15, p. 894; 208, p. 28

209, pp. 10, 33, :""

(14, p. 306; 208, p

33)

(16, p. 893; 209, pp

(14, p. 307)

(14, p. 306)

(15, p. 894: 208, p. 26; 209, pp.

S3)

(14, V- 306)

(15, p. 893: 209, p. 63)

(14, p. 306: 209, pp. 13, 33, 43)

(14, p. 306; 15, p. 893; 208, p. 29;

209, pp. 13, 33, 43)

(14, p. 306)

(15, p. 894: 208, p. 29; 20.9, p. IS)

(208, p. 28)

(15, p. 894; 209, pp. 13, 43)

(14, p. 306; 15, p. 893)

(15, p. 893)

(209, pp. 14, 33, 63)

(24, p. 58: 209, pp. 14, S3, 4S)

(14, p. 306: 15, p. 894: 208, p. 21;

209, pp. 14, 34, 43, 64)

(14, p. 306; 15, p. 893; 209, p. 14)

(16, p. 893: 208, p. 14)

(15, p. 893; 209, pp. 15, 34)

(14, p. 306; 15, p. 894; ^08, p.

209, pp. 15. 3.( ¿3 ,T7^

(14, p. 306;

(15, p. 893)

(14, p. 306;

44)

(15, p. 893)

(14, p. 307; 15, p. 8.93; 208, p. 12;

209, pp. 16, 34, 44)

(15, p. 894; 23, p. SS; 129, pp. 49,

209, pp. 15, 34, 43, 57)

4, p. 306; 16, p. 894; 209, p. 15)

5 -n R9X\

15;

24, p. 68, 209, pp. 15;

oy; zun, pp. iv, S4)

(23, p. 33: 209, pp. 35, 63)

(24, p. 6; 209, pp. 17, 35, 44, 6¿

(15, p. 894; ^3, p. S3)

(15, p. 894; 23, p. 33)

(23, p. SS; 209, pp. 17, 36)

(16, p. 894; ^S, p. S3; 209, p. 17

(15, p. 894; 23, p. S3; 209, p. 17

(23, p. SS; 209, pp. 18, 36)

(209, p. 63)

(15, p. 894; 209, p. 18)

(24, p. 6; 209, pp. IS, 36)

(24, p. 9; 209, p. 18)

(15, p. 894; SS, p. 33)

(14, p. 307; 101, p. 10; 102, pp.

23)

(14, p. 307)

(14, p. 307; 102, p. 22)

(14, p. 307)

(14, p. 307)

{14, p. 307)

{14, P.- 307)

(14, p. 307)

(14, p. 307)

(14, p. 307; 102, p. 22)

(14, P 309; 15, p. 894)

(t'l. p. 309: 16, p. 894; 27, pp. 8, 32)

(14, p. 309)

22

State and county

New Mexico—Con

Dona Ana

Harding

Hidalgo

Lincoln

Luna

McKinlev

Mora___l

Otero

Quay

Rio Arriba

Sandoval

San .Juan

San Miguel

Santa Fe

Sierra

Socorro

Taos ,

Torrance

Union

North Dakota:

Bottineau

Burke

Burleigh

Cavalier

Dickey

Divide

Golden Vallev--

McHenry

McKenzie

McLean

Mountrail

Pierce

Renville

Sheridan..

Stutsman

Ward

Williams

Oklahoma:

Bryan

Caddo

Cleveland

Custer

Grady

Kiowa

Washita

Oregon:

Harney

Malheur

Puerto Rico

South Dakota:

Beadle

Brookings

Brule

Butte

Charles Mix

Codington

Corson

Güster

Day

Dewey

Fall River

Gregory

Haakon

Hughes

Hyde

Reference and page

(14,

(H,

(14,

{14,

(14,

{14,

{27,

{14,

(14,

(14,

(14,

(14,

(27,

(14,

(14,

(14,

(16,

(IS,

(15,

(102

(102

(209

(102

(102

(102

(H,

(102

(1.02

{102

(102

(102

(102

(102

(15,

(102

(102

p. 309)

p. 309; 27, p. 34)

p. 309)

p. 309)

p. 309)

p. 309; 15, p. 894)

vv. 8. 33)

15, p. 894)

pp. _,

p. 309,

p. 309)

p. 309

p. :309,

p. 309; _ _

pp. 8, 34)

p. 309; 16,

p. 309)

p. 309;

p. 894)

p. 894)

p. 894)

15, p. 894; 27,

15, p. 80.Ç)

16. V. 894:

p. 8)

to, p. OU-'i-l

16, p. 894; 27, p. 8)

i, p. 894; 27, p. 8)

16, p. 894)

4)

5; 209, p. 66)

18)

6)

6)

6)

310)

7)

P7)

7)

8; 207, pp. 18, 35, 44, 65)

9)

9)

10)

894)

10; 209, pp. 19, 36, 44, 66)

11; 209, pp. 19, 44, 66)

(101, p. 14)

(23, p. 34; 101, p. IS)

(23, p. 34)

(101, p. 13)

(23, p. 34; 101, p. 14)

(101, p. 13)

(101, p. 13)

(14, p. 310)

(102, p. 24)

(27, p. 65; 208, p. 49)

(163, p. 461; 164, p. 28)

(163, p. 461; 164, p. 28)

(15, p. 896; 23, p. SO; 209, pp. 20, 36)

(15, p. 894; 23, pp. 29, 36; 24, p. 16;

129, pp. 31, 38, 79; 204, V- ^03;

209, pp. 20, 36, 44)

(23, p. SO; 129, p. 50)

(163, p. 461; 164, P- ^8)

(129, p. 54)

(24, p. 16; 129, p. 38; 209, p. 36)

(163, p. 461; 164, P- ^8)

(23, p. 29)

(14, P- 311; 24, p. 12; 129, pp. 30,

37, 66, 79; 209, pp. 21, 36, 45)

(14, p. 311; 16, p. 894; 23, pp. 13,

42; 24, p. 66; 129, pp. 49, 70; 209,

pp. 21, 36, 62)

(14, p. 311; 129, p. 53; 209, p. 21)

(14, P- 311; 23, p. SO; 209, pp. 22,

37)

(23, p. 30)
SELENIUM IN AGRICULTURE 65

TABLE 2-t.—Lorations hy States and eoanHes ichere the concentration of selenium in vegetation has

been in vestigated—Continued

State and county

South Dakota—Con

Jackson

Jones

Kingsbury

Lawrence

Lyman

Meade

Pennington

Shannon

Stanley

Sully

Tripp

\Vahvorth_.

Yankton

Ziebach

Texas:

Brewster__.

Dallas

Hill

Utah:

Beaver

Box Elder..

Cache

Carbon

Duchesne_.

Emery

Garfield___.

Grand

Reference and page

{IJf, p. 311; 129, pp. 53, 81; 209,

p. 22)

{14, p. 311; 23, p. 39; 209, pp. 22,

37)

(163, p. 461; 164, P- ^8)

{16, p. 896)

(14, p. 311; on; 23, ZÖ pp. 17I /, at/; 24, p. 62:

101, p. 17; 129, pp. 36, 42, 61, 71,

77- W8, p. 66; 209, pp. 22, 37,

. . 2)

(23, p. 29; 24, p. 10; iz'd, pp.

69, 79; 209, pp. 23, 38)

312; 23, p. 29; 24, p. 16;

77; 208, p. „„, .„„, ,.,.. .., „,,

45, 62)

23, p. 29; 24, p. 16; 129, pp. 36,

69, 79; 209, pp. 23, 38)

(14, p. 312; 23, p. 29; 24, p. 16

129, pp. 36, 81; 209, pp. 23, 38)

, „ o<,. a/ ^ 11 . i2g^ p. S4)

129, pp. 36, 81; 209, pp. 23, 38)

(14, p. Sll; 24, p. 11; 129, p. 34)

(14, P- Sll; 129, pp. 62, 69, 79;

209, vp. 23, 38, 45, 63)

(23, V- SO)

(209, pp. 23, 38)

(23, p. 29)

(14, P-311)

(23, p. 29; 129, p. 38; ISO, p. SOS)

(14, P- 312)

{15, p. 896)

(15, p. 896)

(78, p. 299)

(U, p. SIS)

(78, p. 299)

(14, p. 313; 27, p. 10; 102, pp. 21,

22)

(14, P- SIS; 15, p. 897)

(14, p. 313; 15, p. 896; 27, p. 10;

102, p. 22)

(7, p. 70S; 27, p. 10)

(7, p. 703; 14, p. 313; 15, p. 896;

23, p. 35: p. 27, 10)

State and couiily

Utah—Continued

Iron

Juab

Millard

Piute

Rich

Salt Lake

San Juan

Se vier

Summit

Tooole

Uintah

Utah

Washington

Wayne

Wyoming:

"Albany

Big Horn

Campbell

Carbon

Con\'erse

Crook

Fremont

Hot Springs

Johnson

Xatrona

Niobrara

Platte

Sheridan

Sweetwater

Teton

Uinta

Washakie

Weston

Reference and page

(14, p- 313)

(14, p. 31S; 78, p. 299; 102, p. 21)

(14, p. SIS; 78, p. 299; 102, pp. 21,

22)

(102, p. 22)

(14, P- 31.i)

(102, p. 21)

(14, p. SIS)

(102, pp. 21, 22)

(102, p. 31)

[14, P- SIS; 102, p. 21)

(14, P- 313; 15. p. 896; 102, p. 21)

(14, p. 313; 102, p. 21)

(14, P- SIS)

(16, p. 896)

(15, p. 897; 23, p. 22)

(206, pp. 23, 38, 45)

(2S, p. 27; 209, pp. 24, 38, 46)

(16, p. 898; 23, p. 25)

{209, pp. 24, 38)

(23, p. 27; 24, p. 15; 209, pp. 24,

39, 46, 64)

(15, p. 897; 23, p. 26)

(23, p. 27)

(209, pp. 24, 39)

(23, p. 26; 209, pp. 24, 39, 45)

(16, p. 898; 24, p. 14; 129, pp. 32,

39; 209, pp. 24, 39, 4.3)

{15, p. 898)

(23, p. 27; 209, pp. 25, 39)

(15, p. 898)

(15, p. 898)

(15, p. 898; 23, p. 27)

(23, p. 27; 209, pp. 25, 39, 4-5)

(24, p. 14; 209, pp. 25, 39, 46)

U.S. GovEP.'i''^NT pfilNTIHG OFFICE: 1961
Sroxtüi Tbtougi) Agricultural Progress