EPA-670/2-74-005 c . . , n . .. T , , r .
January 1974 Environmental Protection Technology Series
FATE AND EFFECTS OF TRACE ELEMENTS
IN SEWAGE SLUDGE WHEN
APPLIED TO AGRICULTURAL LANDS
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-7^-005
January
FATE AND EFFECTS OF TRACE ELEMENTS IN SEWAGE SLUDGE
WHEN APPLIED TO AGRICULTURAL LANDS
A LITERATURE REVIEW STUDY
A. L. Page
Department of Soil Science and Agricultural Engineering
University of California
Riverside, California 92^02
Program Element No. 1B2043
Project Officer
G. K. Dotson
Ultimate Disposal Section
Advanced Waste Treatment Research Laboratory
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION ASENCY
NATIONAL ENVIRONMENTAL RESEARCH CENTER
CINCINNATI, OHIO
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EPA REVIEW NOTICE
This report has been reviewed by the U. S. Environmental Protection
Agency and approved for publication; it is reproduced as received from
the author. Approval does not signify that the contents necessarily
reflect the views and policies of the EPA.
ii
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FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise and other forms of pollution,
and the unwise management of solid waste. Efforts to protect the
environment require a focus that recognizes the interplay between the
components of our physical environment—air, water, and land. The
National Environmental Research Centers provide this multidisciplinary
focus through programs engaged in
studies on the effects of environmental
contaminants on man and the biosphere, and
a search for ways to prevent contamination
and to recycle valuable resources.
This review was prepared for the Ultimate Disposal Section of
the Advanced Waste Treatment Research Laboratory to help evaluate
one of the potential hazards associated with the disposal of
pollutants removed from water. All forms of pollution control
create their own risk of causing pollution in another area. Only
by carefully weighing the benefits of a disposal technique
against the corresponding risk can we make a rational choice
between alternatives.
A. W. Breidenbach, Ph.D.
Director
National Environmental
Research Center, Cincinnati
iii
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CONTENTS
Section Page
I. INTRODUCTION 1
II. RESULTS OF PUBLISHED REPORTS 3
1. Sources of Trace Elements Found in 3
Sewage Sludges
1.1. Uses of Trace Elements 3
2. Concentrations of Trace Elements Found 8
in Sewage Sludges
2.1. Total Concentrations 8
2.2. Organic Acid Soluble 14
2.3. Water Soluble 18
3. Trace Element Composition of Plants, Soils, 26
and Drainage Waters From Soils as Influenced
by Sewage Sludge Applications
3.1. Trace Elements Absorbed by Plants Grown 28
on Sludge-Amended Substrates
3.2. Trace Element Composition of Soils 50
Following Applications of Sewage
Sludge
3.3. Trace Element Concentrations of 60
Drainage Waters From Soils Following
Applications of Sewage Sludge
III. POTENTIAL IMPACT OF SLUDGE APPLICATIONS TO SOIL 62
1. Chemical and Biological Transformations 62
of Trace Elements in Sludge When Applied
to Soil
1.1. Organic Trace Element Transformations 63
1.2. Inorganic Trace Element Transformations 64
iv
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Section Page
III. 2. Evaluation of Criteria Available to Judge 67
Feasibility of Sludge Applications
2.1. Soil and Plant Composition Criteria 68
2.2. Water Quality Criteria 68
3. Consequences of Trace Element Enrichment 69
in Sludge-Amended Soils
3.1. Soil Enrichment 69
3.2. Crop Productivity and Quality 76
3.3. Water Quality 80
IV. SUMMARY 83
V. RECOMMENDATIONS FOR FUTURE RESEARCH 86
VI. REFERENCES 88
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TABLES
No. Page
1 Contents of Trace Elements in Sewage Sludges 9
From 93 Treatment Plants in Sweden
2 Contents of Trace Elements in 57 Sewage Sludges 11
From Locations in Michigan, U.S.A.
3 Contents of Trace Elements in 42 Sewage Sludges 12
From Locations in England and Wales
4 Comparison of Median and Range of Trace Element 13
Concentrations of Sewage Sludges From Michigan,
USA; England and Wales; and Sweden
5 Concentrations or Concentration Ranges of Trace 15
Elements in Sewage Sludges From Various Locations
in the United States and Canada
6 Range of Trace Elements Found in Sewage Sludge in 16
Relation to Treatment Process
7 Extractable Trace Elements in 42 Sewage Sludges 17
From England and Wales
8 Comparison of Saturation Extract Composition of 19
Sludges and California Soils
9 Concentrations of Trace Elements in Sewage Sludge 21
Effluents as Influenced by the Treatment Process
10 Concentrations of Sewage Sludge Effluents as 22
Influenced by Treatment Process
11 Total and Dissolved Concentrations of Trace Elements 24
in Sewage Effluents From 57 Michigan, U.S.A.
Treatment Plants
12 Summary of Trace Element Concentrations of 1577 Surface 25
Waters in the United States
13 Ten Percent HC1 and Hot Water Soluble Trace Elements 30
in Soil Under Healthy and Unhealthy Plants
14 Trace Element Composition of Crops Grown on Soil 32
Treated With Sludge at an Average Rate of 66 m.
tons/ha/year for 19 years
vi
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No. Page
15 Total Concentrations of Trace Elements Typically 33
Found in Soils and Plants
16 Trace Elements Extracted From Soil and Sludge by 34
0.5 N HOAc
17 Trace Elements Normally Extracted From Surface 35
Layers of Arable Scottish Soils
18 Trace Element Composition of Oats and Spinach 37
Grown in Pots Treated With Various Levels of
Sewage Sludge
19 Trace Element Composition of Turnips and Beets 38
Grown in Pots Treated With Various Levels of
Sewage Sludge
20 Copper and Nickel Concentrations in Oat Plants 40
as Influenced by Amount of Sewage Sludge Applied
and Soil pH
21 Effect of Ni Applied to Soils at Different pH Levels 42
on the Ni Content of Spring Wheat
22 Total Contents of Trace Elements in Corn as 44
Influenced by Amounts Applied From a Sewage
Sludge Source
23 Trace Element Concentrations of .Fodder Rape as 45
Influenced by Repeated Applications of Sewage
Sludge
24 Trace Element Composition and Yield of Rye Clippings 48
as Influenced by Sludge Applications to Soils
25 Yields and Concentrations of Zinc for Fescue Forage 51
in Relation to Compost and Lime Applications
26 Concentrations of Various Trace Elements Extracted 53
From Sludge-Amended Acid Spoil Mine Material
27 Concentrations of Trace Elements Extracted With 54
0.1 N HCl From Sludge-Amended Soils
28 Recovery of Trace Elements in the Surface 15 cm 56
of Sludge-Amended Soils
vii
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No.
29 Trace Elements Extracted by 0.5 N HOAc From
Soils Treated With Sewage Sludge for 19 Years
and the Sewage Sludge Applied
30 Changes in the Concentrations of Trace Elements 59
in the Surface 20 cm of Soil Following Application
of 84 m. Tons of Sewage Sludge Over a Period of
12 Years
31 Trace Element Concentrations of Saturation Extracts 61
From Sewage Sludge, Soil Taken From the Bottom of
Sludge Drying Ponds (Treatment Plants A, B, G),
and Soil From Effluent-Irrigated Fields (Treatment
Plants D and E)
32 Surface and Irrigation Water Quality Criteria for 70
Trace Elements
33 Comparison of Amounts of Trace Elements Added to 71
Soil to a Depth of 15 cm From 100 m. Tons of a
Typical Domestic Sewage Sludge With Amounts
Commonly Present
viii
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I. INTRODUCTION
One of the most pressing problems facing metropolitan areas today
is disposal of large volumes of liquid and solid wastes generated by
urban and industrial activities. The need to conserve and re-use water,
problems associated with water pollution resulting from discharging
wastes into surface waters, air pollution resulting from the incineration
of the waste, and the scarcity of suitable sites for landfill operations
have prompted municipalities and other governmental agencies to
investigate alternative means of disposal. One alternative disposal
operation which is currently receiving rather widespread attention is
the disposal of wastes onto agricultural land.
The practice of spreading urban wastes onto agricultural land is
not new, and has been used on a limited scale for decades. Sewage
treatment plant effluents and sewage sludges are currently and have
for many years been used to irrigate field crops and recreation areas
such as parks and golf courses. The settleable solids from sewage
treatment plant works are processed and sold as soil amendments and
low grade fertilizers. Composted sludge and composts consisting of
garbage with or without the addition of sewage sludge also are produced
and marketed. Law (1968) recently reviewed the literature on the
agricultural utilization of sewage effluent and sludge and cited 284
references on the subject.
Although there has been a long history of research on the use of
sewage on agricultural land, these works have been primarily concerned
with the fertilizing value of materials and their effects on crop yields.
There have been very few studies designed to evaluate the long-term
consequences of applying sewage treatment plant wastes on land. One
of the potential problems associated with the long-term (decades)
applications is the accumulation of toxic concentrations of trace
elements. The present study will attempt to evaluate this question
based upon the published information available.
The term "trace element" is rather loosely used in the literature
to designate a number of elements which occur in natural systems in
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small concentrations. As defined in many dictionaries, trace elements
are those chemical elements, especially metals, used by organisms in
minute quantities but believed essential to their physiology. However,
the term is and has been used to designate elements with no known
physiological function. With the recent widespread concern over the
quality of the environment, the term has been used to refer to elements
which are, when present in sufficient concentrations, toxic to living
systems. Other terms which have been used, and which for all practical
purposes can be considered synonyms for the term "trace elements" are
"trace metals," "trace inorganics," "heavy metals," "micronutrients,"
and "microelements." The use of the term "micronutrient" usually has
been restricted to those trace elements known to be essential for the
growth of higher plants, e.g. Cu, Zn, Mo, B, Mn, and Fe. The use of
the term "heavy metals" in the literature is usually, but not always,
restricted to those metals which have densities greater than 5.0. In
the present paper, the elements in sewage sludges considered will be
molybdenum (Mo), manganese (Mn), barium (Ba), copper (Cu), zinc (Zn),
nickel (Ni), cadmium (Cd), cobalt (Co), tin (Sn), chromium (Cr), lead
(Pb), vanadium (V), boron (B), mercury (Hg), arsenic (As), selenium
(Se), and silver (Ag) and are for convenience referred to as trace
elements.
Over the past decade or so, interest in trace elements in the
environment has been rather extensive due principally to discoveries
linking them directly or indirectly with adverse effects on human and
animal health and concomitant observations of excessive trace element
pollution of air, land, and water caused principally by urban and
industrial activities. The extensive research of H. A. Schroeder and
his co-workers at the Dartmouth Medical School serves to illustrate
the current interest of medical researchers in trace elements (see
references cited by Lisk, 1972). A number of reviews have been
published recently on trace element research (Lisk, 1972; Allaway,
1968; Lagerwerff, 1972; Hodgson, 1963; Antonovics, Bradshaw, and
Turner, 1971; and Bowen, 1966).
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II. RESULTS OF PUBLISHED REPORTS
Sources of Trace Elements Found in Sewage Sludges
Trace element concentrations in sewage sludges are related to the
kinds and amounts of urban and industrial discharges into the sewage
treatment systems and to the amounts added in the conveyance and treat-
ment systems. The composition of urban and industrial waste changes
as consumer products, industrial processes, and industrial activity
change, so sewage sludges may vary in their chemical composition from
time to time. .Since the sources of municipal refuse and sewage are the
disposal of consumer and industrial products as well as disposal of
materials used in their production, the trace elements composition of
wastes will depend upon uses of trace elements. For this reason, a
brief review of uses of trace elements is presented in the following
section.
Uses of Trace Elements
Uses of As, Ba, B, Cd, Co, Cu, Pb, Cr, Mn, Hg, Mo, Ni, Se, Ag, Sn,
V, and Zn and their compounds have been extensively reviewed in various
reports (Miner, 1969; Athanassiadis, 1969a, 1969b; Sullivan, 1969a,
1969b, 1969c, 1969d, 1969e; Stahl, 1969a, 1969b; and U. S. Bureau of
Mines, 1971). A summary of findings, by element, follows:
Arsenic. Most forms of arsenic are highly toxic and' its compounds
are used in insecticides, rodenticide, fungicides, and herbicides.
Compounds of As are used in the manufacture of glass, enamels, ceramics,
oil cloth, linoleum, and electrical semiconductors and photoconductcrs.
They are also used as pigments in painting, in fireworks to give an
intense white flame, as wood preservatives, and in the textile and
tanning industries. It is also used in making certain types of bronzes
and other varieties of alloys.
Barium. Barium metal is used as a getter in electronic tubes and
as an alloying agent with Ni for spark plug elements. Its compounds
are used as mordants for printing fabrics and acid dyes, in weighting
and dying textile fabrics, in bleaching, electroplating, synthetic
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rubber vulcanization, lubricants, pesticides, corrosion inhibitors,
pigments, photocells, semiconductors, dielectric and magnetic
amplifiers, computer elements and memory devices. They are also used
in the manufacture of paper, glass, and case hardened steels and
matches. Organometallic compounds of Ba are added in amounts ranging
from 0.075-0.20 percent by weight to diesel fuels as a black smoke
suppressant.
Boron. The principal source of boron in most sewage is the house-
hold use of boron-containing soaps, detergents, and cleaners. Compounds
of boron are used in the manufacture of glazes, cements, crockery,
porcelain, enamels, glasses, alloys, semiconductors, lubricants and
hardened steels. Boron compounds are also used as agricultural
fertilizers, rubber vulcanizers, anesthetics, for fireproof ing and
weatherproof ing wood and fabrics, in the leather and tanning industry,
in printing and dying, paints, photography, and solder.
Cadmium. Principal uses of Cd are in electroplating, pigments
and chemicals, and alloys. Household appliances (vacuum cleaners,
refrigerators, washing machines, television sets, radios, and stoves),
automobiles and trucks, agricultural implements, and airplane parts,
industrial machinery, hand tools (wrenches, pliers, screwdrivers) and
fasteners of all kinds (nuts, bolts, screws, rivets, and nails) are
commonly Cd coated. Compounds of Cd are rather extensively used as
pigments, and as heat and light stabilizers in the plastics industry.
Alloys of Cd are used in the production of bearings for aircraft and
other internal combustion engines, for solders, and for low melting and
brazing alloys. Recent uses of Cd are in the production of automobile
radiators, and batteries. Sealed Cd batteries are used in many con-
venience appliances such as toothbrushes, electric shavers, flashlights,
and knives. Cadmium is also used for luminescent dials, in photography,
lithography, process engraving, rubber curing, and as fungicides.
Chromium. Consumption of Cr falls generally into the categories
of the metallurgical, refractory, and chemical industries. Because of
its chemical inertness and high melting point chromite ore is used in
the manufacture of refractory bricks to line metallurgical furnaces.
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Chromium metal is used in chrome steels and alloys for increasing the
resistance and durability of metals. A number of metals are chrome
plated and most communities have commercial facilities engaged in
plating operations. Compounds of chromium are used in the dying and
tanning industries, in the manufacture of inks, varnishes, glazes for
porcelain, and as abrasives. Chromates also have a variety of appli-
cations as corrosion inhibitors; primer paints and dips for metals
commonly contain chromates; soluble chrotnates are used as rust
inhibitors in cooling towers, industrial coolers, air conditioning
equipment, boilers of many types, and in certain metal pipelines.
Chromates are also used in paper matches, some fireworks, and dry-cell
batteries. Compounds of chromium are used as topical antiseptics and
astringents, defoliants for certain crops, and in photographic emulsions
as hardening agents.
Cobalt. Cobalt is used in the production of high grade steels,
alloys, superalloys, and magnetic alloys. Cutting and other wear-
resistant materials commonly are produced from Co steels and alloys.
It is also used in smaller quantities as a drier in paints, varnishes,
enamels, and inks, as a pigment, and as a glass decolorizer.
Copper. The principal uses of Cu are in the production of wire
and brass. Copper is alloyed with Sn, Pb, Zn, Ni, Al, and Mn. It is
widely used in electrical wires and other electrical apparatus. Because
of its high thermal conductivity and comparative inertness copper is
extensively used in containers such as boilers, steam pipes, automobile
radiators, and cooking utensils. Copper tubing is widely used in water
conveyance systems. It is also used in fungicides and fertilizers.
Lead. The two principal uses of Pb are in the production of storage
batteries and the gasoline additives, tetraethyl and tetramethyl lead.
With the more widespread use of non-leaded and low lead gasolines recently,
amounts of lead used in gasoline have diminished slightly. In 1971 the
average amount of Pb used in gasoline was 2.22 g per gallon, which
compares with an average of 2.43 g per gallon used in 1970 (Ryan, 1971).
Lead is also quite extensively used in ammunition, in the plumbing
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industry as caulking compounds and solders, in pigments, and as an
anti-corrosive agent in exterior paints. Some Pb is still used in
the production of insecticides.
Manganese. The principal uses of manganese are in the iron and
steel industries. Manganese dioxide is used quite extensively in
alkaline batteries, and in the glass, paints, and drying industries.
Other compounds of manganese are used as driers for paints, varnishes,
and oils, fertilizers, disinfectants, and as antiknock compounds for
internal combustion engines.
Mercury. The major uses of mercury and its compounds are in
electrical apparatus, electrolytic production of chlorine and caustic
soda, in paints, industrial and control instruments, pharmaceuticals,
and catalysts. Mercury is used In neon, fluorescent, and mercury-arc
lamps, in silent switches, batteries, rectifiers, oscillators, and
measuring instruments such as thermometers, barometers, manometers,
hydrometers, and pyronometers. In the production of chlorine and
caustic soda, it is used as a floating electrode in electrolysis. It
is used in paints, floor waxes, furniture polishes, fabric softeners
and laundry preparations to prevent mildewing and as an antifouling
agent. It is also used as a fungicide in agriculture and the paper
and pulp industry, and in antiseptics. As a catalyst, mercury is used
in the manufacture of vinyl chloride and urethane.
Molybdenum. The largest single use of Mo is in the production of
molybdenum steels and alloys. It is also used in pigments, filaments
in lamps, electronic tubes, electric contacts and pigments. Molybdenum
disulfide is used as a lubricant. Small amounts of Mo are used in
fertilizers and as catalysts.
Nickel. Nickel is used primarily in the production of stainless
and heat-resisting steels and steel alloys, in Ni-Cu or Cu-Ni alloys,
other nickel alloys, and in electroplating. It is used in the production
of storage batteries, magnets, electrical contacts and electrodes, spark
plugs, machinery parts and as a catalyst for the hydrogenation of oils
and other organic substances. Compounds of nickel are used as pigments
in paints, lacquers, cellulose compounds, and cosmetics.
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Selenium. Most of the Se consumed in the United States is used
in the electronics and electrical industry. Rectifiers containing
0.5-25 g Se are used in electroplating, welding, battery charges,
magnetic coils, arc lamps, and voltage regulators. Approximately the
same amount of Se is used in the production of photoelectric cells
which are used in light exposure meters, electric eyes, detectors,
colorimeters, and pyrometers. Selenium is used with CdS to produce
pigments referred to as lithophones. The pigments impart orange, red,
and maroon colors to materials, and are used to color plastics, paints,
enamels, inks, and rubber. It is also used in stainless steel and in
photocopiers (Xerography). Selenium and its compounds are consumed in
lesser amounts in such consumer goods as pharmaceuticals, deodorants,
plastics, inks, oils (as an antioxidant), insecticides, parasiticides,
bactericides, herbicides, fireproofing agents for textiles, insect
repellants, glue, solid lubricants, and as paint and varnish removers.
They are also used as accelerating and vulcanizing agents in rubber
products, in medicines for animals, and as catalysts for oxidizing,
dehydroginating, and hardening fats used in soaps, waxes, and edible
fats.
Silver. Most silver which enters domestic and industrial waste
water probably has as its source silver used in photographic materials.
Silver is also used in electric contacts and conductors, electroplated
ware, sterling ware, jewelry, and dental and medical supplies. It is
also used in the production of mirrors, bearings, certain types of
storage batteries, and as catalysts in certain industrial operations.
Many low-melting brazes and solders contain silver.
Tin. In 1971 approximately 46 percent of the Sn consumed in the
United States was used in the production of tin cans. Tin is used in
the production of many alloys, babbitt, brass, and bronze and for
galvanizing metals. It is also used in roofing materials, pipe and
tubing, solder- and in collapsible tubes and foil.
Vanadium. The major uses of V are in vanadium steels and non-
ferrous alloys. Vanadium compounds are used as catalysts in many
industrial processes, as driers in paints and varnishes, as developers
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in photography, mordants in drying and printing textiles, and in the
production of colored glass and glazes.
Zinc. Zinc is used extensively as a protective coating on a
number of metals to prevent corrosion and in alloys such as brass
and bronze. Galvanized met ""Is have a variety of applications in the
building, transportation, and appliance industries. Galvanized pipes
are commonly used in domestic water conveyance systems and zinc
solubilized by corrosion is generally thought to make a substantial
contribution to the Zn concentrations observed in waste waters. Zinc
and its compounds are constituents of many household items including
utensils, cosmetic and pharmaceutical powders and ointments, anti-
septics and astringents, insecticide and fungicide formulations, glues,
matches, inks, porcelain products, fabrics, and as a pigment in paints,
varnishes, oil colors, linoleum, and rubber. Zinc and its compounds are
used in the manufacture of parchment paper, phosphors for fluorescent
and electric lights, glass, automobile tires, television screens, dry
cell batteries, and electrical apparatus. They are also used as
hardeners in cement and concrete, in printing, drying, and weighting
textiles, and in agricultural fertilizers. A recent use of zinc which
is increasing dramatically each year is in photosensitive copying paper.
Concentrations of Trace Elements Found in Sewage Sludges
The trace element composition of sewage sludges has been characterized
relative to total concentration, organic acid extractable concentrations,
and water-soluble concentrations. However, most of the data in the
literature pertain to total concentrations.
Total Concentrations
The most complete assemblage of data on the chemical composition of
sewage sludges are those reported by Berggren and Oden (1972), Berrow and
Webber (1972), and Blakeslee (1973).
Berggren and Oden (1972) and Oden, Berggren, and Engvall (1970) have
reported data for the concentration of trace elements in sewage sludges
from many cities and towns in Sweden. A summary of the data of Berggren
s
and Oden (1972) is presented in Table 1. The data show extremely large
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I/
Table 1--Contents of trace elements In sewage sludges from 93 treatment plants in Sweden—'
No. Samples Within
Element
Cd
Co
Cr
Cu
Hg
Mn
Ni
Pb
Zn
Range
2.3
2.0
20
52
<0.1
73
16
52
705
- 171
- 113
- 40,615
- 3300
- 55
- 3861
- 2120
- 2914
- 14,700
Mean
--l^g/g
12.7
15.2
872
791
6.0
517
121
281
2055
Median
6.7
10.8
86
560
5.0
386
51
180
1567
1-10
67
30
0
0
84
0
0
0
0
10-100
24
62
48
1
8
1
65
7
0
100-1000
2
1
39
69
0
82
26
82
11
Ranges
1000-10,000
0
0
2
23
0
10
2
4
81
>10,000
0
0
3
0
0
0
0
1
!_/ Derived from data reported by Berggren and Oden (1972). The values reported are for the means of samples
collected from 1968 through 1971.
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variations in the chemical composition of the sludges from different
treatment plants. Although mean values are reported in Table 1, they
probably have little meaning since the means are highly influenced by
a few abnormally high concentrations. For example, the concentration
of Cr in most sludges falls in the range of 10-100 M-g/g, but 3 of 93
samples had concentrations in excess of 10,000 M-g/g. The median
concentration and distribution of samples within ranges for the Swedish
sludges are also presented in Table 1.
For comparison trace element concentration data for sludges from
57 treatment plants in Michigan, U.S.A., and for sludges from 42
treatment plants in England and Wales are presented in Tables 2 and 3.
Again wide variation in concentrations occur from one treatment plant
to another. Concentrations of Cd most commonly observed in sludges
fall in the range of 1-10 M-g/g. With Cr, the most common range usually
falls within wider limits or from about 50-500 M-g/g. Nickel commonly
occurs in sludges at concentrations ranging from 20-200 M-g/g, and Cu
in the range of 100-1000 M-g/g. The concentration of Zn in sewage
sludges is consistently quite high and normally ranges between 1000-5000
M-g/g. Median concentration, and the most common ranges for the sludges
from Michigan, England and Wales, and Sweden are presented in Table 4.
Except for Cr, variations which occur in concentrations of trace
elements among the treatment plants in the three countries are
reasonably comparable.
Berggren and Oden (1972) analyzed their data relative to the
frequency with which trace elements occurred within certain con-
centration ranges. Extrapolating from their figures shows that
approximately 80 percent of the sewage sludges from Sweden have
trace element concentrations which fall within the following ranges
(in M'g/g dry matter): Zn (800-3200), Cu (200-1600), Pb (100-400),
Mn (100-800), Cr (25-800) and Ni (25-600). Data from other locations
(Tables 1, 2, 3, 5) suggest that concentration of most sewage sludges
will fall within the ranges observed in Sweden. Oden, Berggren, and
Engvall (1970) observed a linear log-log relationship between concen-
trations of Cd and Zn, Zn and Cu, Pb and Cu, and Ni and Cu in sewage
10
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Table 2--Contents of trace elements in 57 sewage sludges from locations in Michigan, U.S.A.
I/
Element
Hg
Cd
Cr
Cu
As
Ni
Pb
Zn
I
0.1
2
22
84
1.6
12
80
72
lange
- 56
- 1100
- 30,000
- 10,400
- 18
- 2800
- 26,000
- 16,400
Mean
pg/g
5.5
74
2031
1024
7.8
371
1380
3315
Median
3.0
12
380
700
7.5
52
480
2200
1-10
49
28
0
0
48
0
0
0
No. Sa
10-100
4
20
19
1
9
33
2
1
mples Within
100-1000
0
8
18
42
0
15
43
9
: Range
1000-10,000
0
1
18
13
0
9
10
44
>1 0,000
0
0
2
1
0
0
2
3
!_/ Derived from data reported by Blakeslee (1973).
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Table 3--Contents of trace elements in 42 sewage sludges from locations in England and Wales—
Element
Ag
B
Ba
Cd
Co
Cr
Cu
Mn
Mo
Ni
Pb
Sn
V
Zn
1
5
15
150
<60
2
40
200
150
2
20
120
40
20
700
Range
- 150
- 1000
- 4000
- 1500
- 260
- 8800
- 8000
- 2500
- 30
- 5300
- 3000
- 700
- 400
- 49,000
Mean
lg/g
32
70
1700
<200
24
980
970
500
7
510
820
160
75
4100
Median
20
50
1500
-
12
250
800
400
5
80
700
120
60
3000
1-10
11
0
0
-
19
0
0
0
35
0
0
0
0
0
No. Sa
10-100
30
39
0
-
22
13
0
0
7
26
0
19
38
0
imples Within
100-1000
1
3
7
6
1
19
33
40
0
12
36
23
4
6
Ranges
1000-10,000
0
0
35
1
0
10
9
2
0
4
6
0
0
34
>10,000
0
0
0
0
0
0
0
0
0
0
0
0
0
2
I/ Fr.om Berrow and Webber (1972).
-------
Table 4--Comparison of median and range of trace element concentrations of sewage sludges
from Michigan, USA; England and Wales; and Sweden—
Median Cone.
Element
Cd
Cr
Cu
Ni
Pb
Zn
USA
(Michigan)
12
380
700
52
480
2200
England
and Wales
-
250
800
80
700
3000
Sweden
6,7
86
560
51
180
1567
USA
(Michigan)
1-10
10-100
100-1000
10-100
100-1000
1000-10,000
(49)
(33)
(74)
(58)
(75)
(76)
2/
Most Common Ranfc£—
England
and Wales
-
100-1000
100-1000
10-100
100-1000
1000-10,000
(45)
(79)
(50)
(85)
(81)
Sweden
1-10
10-100
100-1000
10-100
100-1000
1000-10,000
(72)
(52)
(74)
(70)
(88)
(87)
!_/ Data are from 57, 42, and 93 treatment plants in Michigan, England and Wales, and Sweden, respectively. For
Michigan, England and Wales, and Sweden, data are derived from those published by Blakeslee (1973), Berrow
t
and Webber (1972), and Berggren and Oden (1972), respectively.
2_/ Percentage of samples within the concentration range indicated are given in parentheses.
-------
sludges from Sweden. Their data show the following trace element
ratios as common to most sewage sludges in Sweden: Cd:Zn (1:160),
Zn:Cu (1:0.3), Pb:Cu (1:1.7), and Ni:Cu (1:5).
Less extensive data for trace element concentrations of sewage
sludges from a number of locations in the U.S.A. and Canada are
reported. These data have been compiled and are presented in Table 5.
Generally speaking, the more recent data show concentrations which fall
within the ranges previously discussed. The older data of Anderson
(1955), however, show boron to be considerably lower, probably due to
lesser use of boron in laundry products in 1955 than in recent years.
Data presented by Blakeslee (1973) are sufficiently extensive to
make comparison of concentrations of trace elements in sewage sludges
in relation to the type of treatment process. Ranges observed for
undigested sludge, secondary digestor sludge, and vacuum filter cake
sludge as reported by Blakeslee (1973) are presented in Table 6. The
data show no consistent trends in trace element composition in relation
to treatment process.
Organic Acid Soluble
British workers commonly use the concentration of trace elements
extracted from soils with 0.5 N HOAc as an index of availability to
higher plants. Consequently, Berrow and Webber (1972) determined the
0.5 N HOAc extractable trace element concentrations for a number of
sewage sludges from England and Wales. Their data are reproduced in
Table 7. Ranges of 0.5 N HOAc extractable trace elements from sewage
sludges exceed ranges observed for soils (compare Table 7 with Table 17).
Maximum amounts extracted for the sludges are considerably greater than
maximum amounts extracted from soils. The percentages of the total
content of trace elements in sludge which are extracted with 0.5 N HOAc
vary quite markedly (Table 7). Patterson (1971) also evaluated amounts
of 0.5 N HOAc extractable trace elements from sewage sludges. He
presents data which show that percentages of trace elements extracted from
sludges are not necessarily related to their concentrations. The wide variation
in percentage 0.5 N HOAc extractable trace elements suggests that the chemical
14
-------
Table 5--Concentrations or concentration ranges of trace elements in sewage sludges from various locations in the United States and Canada
Location
Athens, Ga.
Columbus, Ohio
Dayton, Ohio
Cincinnati,
Ohio
Chicago, 111.
Milwaukee,
Wise.
Des Moinas,
Iowa
Houston, Texas
Rochester, N.Y,
Maryland
Connecticut
Southern Calif.
Toronto,
Canada
Oklahoma
Indiana
B Cd
9-18
99-126 5.6-10.5
830
<40
6-67 495
8
7
8
12
4-12
160-360
360-680 1-140
5-45
70-100
3-810
Cr Cu
350-530
282-728
6020
4200
4200 385-1225
435
315
1035
1980
100-490
465-1025
<40-600 135-800
60-16,000 300-2400
Tr-600 800-6000
50-19,600 300-11,700
Element
HI
u,g/g
11-37
17-23
<200
600
425
-
-
-
-
-
-
10-2140
25-170
100-3000
70-3500
Mn
123-268
148-232
-
-
135-250
130
420
65
60
60-790
105-280
260-450
200-1470
Mo Pb Zn
1850-2850
72-88 1605-1764
8390
9000
6.5-6.7 1500 3050-7450
13.5 - 1550
4.9 - 1350
6.7 - 950
5.1 - 3400
2.1-118 - 610-3100
2200-3500
2-25 15-1120 373-3400
185-1425 1100-9400
Tr-1000 3000-7000
450-1900 870-28,400
Reference
King and Morris (l9J2a)
Miller (1973)
Dotaon (1973)
Dotson (1973)
Hinesly, Jones, and
Sosewitz (1972) and
Anderson (1955)
Anderson (1955)
Anderson (1955)
Anderson (1955)
Anderson (1955)
Anderson (1955)
Lunt (1959)
Bradford (1973) and
Dotson (1973)
Van Loon and Lichwa
(1973)
Thompson, Zajic, and
Lichti (1964)
Sommers et al. (1973)
-------
Table 6--Range of trace elements found in sewage sludge
in relation to treatment process—
Element
Hg
Cr
Cu
Ni
Zn
Cd
Pb
As
Undigested ,
Liquid Sludge-'
1.2-3.4
66-7800
200-1740
44-740
900-8400
6-166
150-26,000
3-16
Secondary Digester
Sludge^-'
^g/g
2-56
22-9600
260-10,400
14-1440
1120-16,400
2-1100
240-12,400
4-18
Vacuum
Filter Cake^'
0.6-27
28-10,600
84-2600
12-2800
480-9400
2-480
80-3000
2.8-11
I/ From Blakeslee (1973).
2_/ From 6 treatment plants.
3_/ From 22 treatment plants.
4_/ From 14 treatment plants.
16
-------
Table 7--Extractable trace elements in 42 sewage sludges
from England and Wales—
Element
Co
Cr
Cu
Mn
Mo
Ni
Pb
Sn
V
Zn
B^
Range
0.5-77
<0. 9-170
2.9-1400
39-2300
O.03-1.0
6.8-2400
4.6-150
0.06-1.6
0.88-7.5
230-11,000
3.3-40
0.5 N HOAc Extractable
Median
>"g/g
2.5
4.4
28
190
0.08
25
11
0.5
2.6
1100
8.8
% of Total
6.2-96
<0.7-8.5
0.5-31
17-91
0.4-7.5
15-93
0.5-10
0.1-1.6
1.1-14
15-97
0.9-50
17 From Berrow and Webber (1972).
2/ Hot water soluble.
17
-------
forms of these elements vary in kind and in proportion among sludges.
As far as the author is aware, no data are available on the chemical
forms of trace elements which occur in sewage sludges.
Since the total concentrations of trace elements in sewage
sludges reported by Berrow and Webber (1972) are somewhat comparable
to concentrations in sludges from other locations, it is reasonable
to expect that the ranges presented in Table 7 are representative of
sludges in general.
Jenkins and Cooper (1964) present data on the amounts of Cu, Zn,
and Ni extracted from sewage sludge by shaking 10 g of sludge with 250
ml of 2 percent citric acid. The air-dried sludge contained 6300 ppm
Cu, 1340 ppm Ni, and 8200 ppm Zn. Two percent citric acid (pH 2.18)
extracted the following amounts of trace elements (in percent of total)
Cu (57.8), Ni (72.7), and Zn (75). Buffering the citric acid with
ammonium citrate to higher pH's somewhat reduced the solubility of the
Cu and Zn.
Water .Soluble
Bradford (1973) has determined the concentrations of trace
elements in aqueous saturation extracts of six sewage sludges from
southern California. His data for sludges are compared to data for
soils in Table 8. The values for the concentrations of trace elements
in saturation extracts of soils were obtained from data reported by
Bradford, Bair, and Hunsaker (1971).
Except for V, B, and Mo, the maximum concentrations of trace
elements in saturation extracts from the sludges are greater than
those from soils. Median concentrations of all trace elements in
the saturation extracts of the sludges exceed those of saturation
extracts of soils. It is noteworthy to point out that maximum
concentrations of Cu, Zn, Ni, Pb, and Cd exceed the solubility
products of the hydroxides and carbonates of these elements. This
suggests that the chemical form of these elements which occurs in
solution is in part organic since solubility product considerations
would rule out inorganic forms at the concentrations.observed.
18
-------
Table 8--Comparison of saturation extract composition of
sludges and California soils—*—
Range
Element
Mo
Cu
Zn
Ni
Co
Pb
V
B
Cd
Ag
Sludges
0
0
0
0
0
0
0
2
0
0
.10
.14
.5
.6
.04
.3
.04
.7
.05
.01
- 0.37
- 6.0
- 2.5
-18
- 0.35
- 2.0
- 0.25
-17.0
- 2.0
- 0.30
Soils
<0
<0
0
<0
<0
<0
<0
<0
.01-22
.01- 0
.01- 0
.01- 0
.01- 0
.01- 0
.01- 1
.10-26
<0.01
<0.01
p,j
.0
.20
.40
.09
.14
.30
.20
.0
Mean
Sludges
i- /ml
2;/nu
0.19
1.86
1.35
3.87
0.16
0.61
0.09
7.95
0.60
0.18
Soils
0.73
0.04
0.07
0.02
0.06
0.05
0.07
3.06
<0.01
<0.01
Median
Sludges
0
1
1
1
0
0
0
6
0
0
.18
.30
.25
.15
.16
.35
.05
.80
.12
.20
Soils
<0.01
0.03
0.04
<0.01
<0.01
<0.01
0.01
<0.1
<0.01
<0.01
I/ Derived from Bradford (1973), and Bradford, Bair, and Hunsaker (1971).
2_/ Data for soils represent 68 soil samples obtained from. 30 soil series. Data
for sludges are obtained from six metropolitan Southern California sludges.
19
-------
Stones (1955, 1958, 1959a, 1959b, 1960) has evaluated trace
element concentrations of sewage: fro relation to. treatment process,
and a summary of his results is presented in Table 9. Sedimentation
of tank influent for a period of 12 hours (not reported in Table 9)
yielded concentrations in the supernatant liquor which were lower than
those of the unsettled tank influents by the following amounts (in 7») :
Cu (45), Pb (40), Ni (21), Zn (41), and Cr (28). Sterilization of the
unsettled tank influent using mercuric chloride had no effect on the
trace element concentrations (Table 9). Sterilization also had no
effect on the concentrations of Ni, Zn, and Cr in the supernatant
liquor after 18 hours settling time. However, supernatant liquors
from sterilized tank influents after 18 hours settling time had
slightly greater concentrations of Cu and Pb than similarly treated
unsterilized supernatant; liquors. Chemical precipitation with CaO
(400 ppm) fal'l'owed by an 18 hour settling time produced concentrations
of Cu, Pb, Ni, Zn, and Cr in the supernatant liquors which were con-
siderably less than those; of i. the supernatant liquors from sewage
settled for 18 hours but noxtc treated with CaO. Addition of CaO as
a precipitant reduced trace element concentrations by the following
amounts (in %): Cu (58), Pb (88), Ni (41), Zn (84), and Cr (35).
Addition of Al (SO,)' (400 ppm) to sewage as a precipitant followed
by a settling time of 18 hours produced concentrations of Cu, Pb, Ni,
Zn, and Cr which were 81, 91, 23, 57, and 33 percent lower, respectively,
than those not treated and settled for 18 hours. Sulfuric acid as a
precipitant, under similar conditions as those employed with CaO and
At (SO, ) ,, had no effect on concentrations of Cu and Ni in the super-
natant liquors, but increased somewhat concentrations of Pb, Zn, and
Cr in the supernatant liquors (Table 9)i Biological filtration yielded
concentrations of Cu, Pb, Ni, Zn, and Cr in the unfiltered effluent
which were from about 20 to 40 percent lower than those of the filter
feed (Table 9). One hour settlement of the filter effluent produced
concentrations of Cu, Pb, Zn, and Cr in the supernatant liquor which
were approximately from 35 to 60 percent less than those of the
20
-------
unsettled filter effluent (Table 9). Concentrations of Cu, Pb, Zn,
and Cr in the paper filtrate of unsettled filter effluent were less
(65, 81, 48, and 57 percent, respectively) than those of the unsettled
filter effluent (Table 9). Nickel concentrations of settled (1 hr)
filter effluent and in the filtrate of paper filtered unsettled effluent
were essentially the same as those of the unsettled filter effluent.
This suggests that a substantial percentage of the Ni in the sewage
was in the form of a soluble organic complex. In general, Stones'
results indicate that high percentages of Cu, Pb, and Zn in primary
sewage occur in the settleable fraction. Lesser percentages of Ni
and Cr rapidly settle out from primary sewage.
Argo and Gulp (l972a) recently reviewed the literature on the
subject of heavy metals removal in waste water treatment. Data from
their article, reproduced in Table 10 in a slightly modified and
condensed form, show sand filtration is not nearly as effective in
removing trace elements from sewage suspensions as is carbon adsorption
and lime coagulation and recarbonation. Amounts removed from sewage by
sand filtration were as follows (in %): Cd (6.6), Cr4^ (2.6), Cu (60),
Se (9.5)* Ag (11.6), Zn (76.3)« Carbon adsorption removed more than
96 percent of the Cd, Cr , and Ag, but only 37 percent of the Se.
Generally, lime coagulation and recarbonation removed 90 percent or
20a
-------
Table 9—Trace element concentrations of sewage as influenced by treatment processi'
Trace Element Concentration in |ig/ml oft
Tank Influent
Unsettled
Elegant
Cu
Pb
Ni
Zn
Cr
Unsterilized
0.68
0.60
0.27
1.14
0.52
Sterilized-'
0.68
0.60
0.27
1.13
Supernatant Liquor From
Tank Influent After
18 hrs Settlement
Unsterilized
0.26
0.29
0.22
0.67
0.35
Sterlized-
0.38
0.34
0.22
0.68
0.36
Supernatant Liqaor Frotr. Tank Influent
After Chemical Precipitation and
18 hrs Settlement2/
Feed and Effluent From
Biological Filters
Filter Feed Filter Effluent
CaO
0.12
0.04
0.10
0.09
0.33
K SO,
0.27
0.46
0.21
0.83
0.46
Al (SO )
0.07
0.03
0.17
0.29
0.24
0.32
0.37
0.15
0.57
0.31
Unsettled
0.26
0.26
0.09
0.40
0.21
After l \\T
Settlement
0.13
0.11
0.08
0.26
0.13
Paper
Filtrate
0.09
0.05
0.07
0.21
0.09
!_/ Derived from Stones (1955, 1958, 1959a, 1959b, 1960). Results presented are the mean of 12 or more replications.
2/ CaO, H-SO,, and Al (SO, ), added to unsettled tank influent in amounts to yield concentrations equal to 400 ppm.
3_/ Using mercuric chloride.
-------
I/
Table 10--Concentrations of sewage sludge effluents as influenced by treatment process—'
Sand Filtration Carbon Adsorption
Cone. Before Cone. After Cone. Before Cone. After
Element Treatment Treatment Treatment Treatment
.
~ -mg / 1 -
Cd 0.00075 0.00070 0.00070 <0. 00001
Cr"*5 0.0503 0.049 0.049 0.00017
Cu 0.79 0.32
Mn - <0.1
Ni 0.08 0.1
Se 0.0103 0.0093 0.0093 0.00585
Ag 0.00164 0.00145 0.00145 0.000048
Zn 0.97 0.23
Lime Coagulation
Cone. Before
Treatment
0.0137
0.056
15,700
7
7
302
2.3
21.0
160
5
5
100
0.0123
0.0546
-
and Recarbonation
Cone. After
Treatment
0.00075
0.050
0.79
1.0
0.05
Trace
<0.1
0.05
0.08
0.5
0.5
1.5
0.0103
0.0164
-
I./ From Argo and Gulp (1972a)
-------
:
more of the trace elements studied, except again for Se and Cr^3 of which only
16 and 11 percent were removed. Although line coagulation and recarbonation
removed high percentage concentrations of Cu and Ni, concentrations
after this treatment were generally higher than are commonly observed in
soil solutions (compare data in Table 10 with those in Table 8). Data
reviewed by Argo and Gulp (1972a) also show that trace element concen-
trations of elements in sewage vary considerably. For example, Cu
varies from 0.079-15,700 mg/1 and Ni from 0.08-160 mg/1. Finally, this
recent review article (Argo and Gulp, 1972a) demonstrates the general
lack of detailed and comprehensive published data on trace element
compositions of sewage sludges.
In a follow-up article Argo and Gulp (1972b) reported concentrations
I r
of As, Cd, Cr , Pb, Se, Ag, Hg, Cu, and Zn in effluents from a secondary
treatment plant employing trickling filters. Mean concentrations of
trace elements in the effluent from the trickling filters were as
follows (in mg/1): As (0.01), Ba (<0.02), Cd (0.039), Cr+6 (0.12),
Pb (0.032), Se (0.004), Ag (0.01), Hg (0.0018), Cu (0.168) and Zn
(0.50). The authors report that Cd and Cr in the trickling filter
effluent exceeded the limits for injection waters established by the
California Department of Public Health.
Blakeslee (1973) has reported concentrations of trace elements in
filtered and unfiltered sewage effluents from 57 treatment plants in
Michigan, U.S.A. His data are reproduced in condensed form in Table 11.
The maximum concentrations of dissolved and total trace elements are all
quite high when compared to concentrations observed in surface and well
waters. Kopp and Kroner (1970), Bradford (1971), and Silvey (1967)
have reported extensive data for surface and well waters and their
results show maximum concentrations of trace elements which are usually
less than those reported for sewage treatment effluents by Blakeslee
(1973). To compare concentrations of trace elements in sewage treatment
plant effluents with those commonly observed for surface waters, the
data of Kopp and Kroner (1970) have been reproduced in Table 12. The
median concentration of total and dissolved trace element concentrations
in sewage treatment plant effluents are more or less comparable to median
23
-------
Table ll--Total and dissolved concentrations of trace elements in sewage
effluents from 57 Michigan, U.S.A. treatment plants—
2/
Dissolved—
Element
Range
Mean—
Median
Range
Total-/
Hg
Cr
Cu
Ni
Zn
Cd
Pb
<0
<0
0
<0
0
<0
<0
.02
.01
.01
.02
.01
--pg/mj.
-0.3
-1.0
-0.55
-0.86
-1.7
.005-0.04
.02
-0.08
0.08
0.07
0.24
0.21
0.016
0.038
<0
<0
0
0
0
<0
<0
.2
.02
.03
.04
.10
.005
.02
<0
<0
0
.02 -1
.005-1
.01 -1
<0.02 -5
0
<0
<0
.03 -4
.005-0
.02 -1
.0
.46
.3
.4
.7
.15
.3
Mean—
pg/mi
0.37
0.20
0.14
0".43
0.44
0.027
0.14
Median
<0.2
0.02
0.04
0.02
0.18
<0.005
0.02
_!_/ Derived from data reported by Blakeslee (1973).
2_/ "Dissolved" and "Total" refer to filtered and unfiltered samples, respectively,
3_/ Mean of positive values reported, i.e. removing values reported as less than
the limits of detectability.
24
-------
Table 12--Summary of trace element concentrations of 1577 surface
waters in the United States—
Element
Ag
As
B
Ba
Cd
Co
Cr
Cu
Mn
Mo
Ni
Pb
V
Zn
Detection
Limit!/
mg/1
0.002
0.100
0.010
0.002
0.020
0.020
0.010
0.010
0.010
0.040
0.020
0.040
0.040
0.020
No. of
Positive
Occurrences
104
87
1546
1568
40
44
386
1173
810
516
256
305
54
1207
Frequency
of
Detection
%
6.6
5.5
98
99.4
2.5
2.8
24.5
74.4
51.4
32.7
16.2
19.3
3.4
76.5
Observed
Positive Values
Minimum
0.0001
0.005
0.001
0.002
0.001
0.001
0.001
0.001
0.0003
0.002
0.001
0.002
0.002
0.002
Maximum
0.038
0.336
5.0
0.340
0.120
0.048
0.112
0.280
3.23
1.5
0.13
0.140
0.300
1.183
Mean
0.0026
0.064
0.101
0.043
0.0095
0.017
0.0097
0.015
0.058
0.068
0.019
0.023
0.040
0.064
!_/ From Kopp and Kroner (1970).
2j Detection limits varied with the concentration of total dissolved solids. Those listed
refer to maximum limits of detection.
25
-------
concentrations observed for large numbers of surface and well water
samples. The data reported in Table 11, therefore, suggest that
excessive concentrations of trace elements occur in a lesser per-
centage of treatment plant effluents than more or less normal
concentrations. Means of total concentrations of sewage treatment
plant effluents are approximately 2-4 times greater than dissolved
concentrations (Table 11), suggesting that effective techniques to
flocculate suspended matter in effluents will reduce trace element
concentrations.
Jenkins, Keight, and Ewins (1964) investigated the precipitation
of Cu, Ni, Cr, and Zn by adding these metals to sewage which
contained from 100-360 ppm solids. The data, however, have little
value as they pertain to solubilities of these elements in sludge
because the amounts added on a weight basis (|J-g added per unit weight
of dry solids) were, in most cases, many orders of magnitude greater
than would be observed in sludges. For example, the minimum concen-
tration of Cu added in their studies would produce a concentration
greater than 6000 Hg Cu per gram of dry solids.
The data of Stones (1955, 1958, 1959a, 1959b, 1960), Argo and
Gulp (1972a, 1972b), and Blakeslee (1973) demonstrate that high
percentages of the trace elements which enter sewage treatment plants
are retained in the sludge fraction either precipitated or flocculated
with other solids.
Trace Element Composition of Plants. Soils, and
Drainage Waters From Soils as Influenced
by Sewage Sludge Applications
Published accounts of studies and projects dealing with the
application of sewage sludge and sewage treatment plant effluents to
land as a source of irrigation water, plant nutrients, to reclaim waste
water, and to improve soil physical properties are numerous. Whetstone
(1965) and Law (1968) have published annotated bibliographies on the
subject and each cites approximately 300 references. Very few of the
references, however, deal with trace elements.
26
-------
Results of studies dealing with sludge-created land are expressed
in a variety of ways. Land application rates of sludge are expressed
in terms of English (short) tons of dry matter ,per acre, metric tons
of dry matter per hectare, cubic yards per acre, surface centimeters
of liquid sludge, and surface inches of liquid sludge. Dry matter
weight usually refers to sludges which are air dried. The water
content of the air-dried sludge is variable depending upon the kind
of sewage treatment process, relative humidity, and other factors.
Air dried sludges commonly range from 1-10 percent water when based
upon oven dry weight (HOC) (Dean and Smith, 1973) and 45-76 percent
ash as determined by drying at 500C for 3-4 hours (Thompson, Zajic,
and Lichti, 1964). To evaluate the results of several researchers on
a comparable basis, the author has converted application rates where
convenient and possible, to metric tons per hectare (1 metric ton per
hectare = 0.45 English tons per acre).
Concentrations of chemical constituents in plants (roots and tops)
are expressed in terms of M-g element per g dry weight (70C) or fresh
weight. Unless the water content is given when these are reported on
a fresh weight basis it is not possible to convert to a dry weight
basis; this is because water contents of fresh plant tissue are highly
variable, and depend upon water stress at the time the plant is sampled,
on plant species, relative humidity, and length of time harvested
tissues are permitted to stand until they are weighed.
Trace elements composition of sludges and sludge-treated soils
are evaluated in terms of total amount present per unit weight. This
is commonly accomplished by dry ashing (500-550C for 3-4 hours) or by
wet ashing with a mixture of perchloric and nitric or sulfuric acids.
Empirical measures of availability to higher plants are based upon the
amount extracted from soil by mineral acids (e.g., 0.1 N HCl), organic
acids (acetic, citric), and chelating agents (EDTA, DTPA, etc.). The
results are usually expressed on amount extracted per unit weight of
soil; consequently, these values depend upon the volume of extracting
solution and weight of soil used. 'In certain published papers>
researchers have not specified the details of the methods used; where
-------
this has occurred, I have arbitrarily assumed that the methods conform
to those which I consider commonly employed.
Results are also commonly expressed in terms of part per million
(ppm). The term has been rather loosely used and may be based upon
fresh weight, air dry weight, oven dry weight (70-110C), weight of
ash (500-600C), or on a volume basis usually assuming the density of
the solution is 1.0. With respect to land applications, the term
refers to pounds or kilograms per million pounds or kilograms of soil.
To convert to an acre basis, the weight of soil in the surface 6 inches
(15 cm) is commonly taken as equivalent to 2 million pounds, so pounds
per acre is equivalent to parts per 2 million.
Trace Elements Absorbed by Plants Grown on Sludge-Amended Substrates
Trace elements applied to soils in the form of sewage sludge may
be absorbed by plants. Under conditions where the plant residues are
removed, the trace elements are lost from the soil system, but if
plant residues are not removed, they will decay and the trace elements
will be returned to the soil. The results of studies which deal with
trace element absorption from sludge or compost amended soils are
reviewed in some detail in the following section. No attempt has been
made to review comprehensively all literature on trace element plant
chemistry.
Sludge-amended nutrient solutions. One of the first reports in
the United States on trace elements in sewage sludge was that of Rehling
and Truog (1939, 1940). A commercial product, "Milorganite," obtained
by processing sludge from a Milwaukee, Wisconsin sewage treatment plant
was evaluated as a source of essential trace elements for plants. Corn,
tomatoes, and sunflowers were grown in nutrient solutions which were
supplied with a carbonated water extract as the only source of B, Cu,
Mn, Mo, and Zn. Milorganite extracts added to the nutrient solutions
after plants were grown under trace element stress resulted in resumption
of normal growth and increased amounts of Cu, Mn, and Zn in the plants.
Sludge-amended soils. The work of Rohde (1962) is commonly cited
as an example of one of the few studies on the long-term effects of
28
-------
sewage applications upon soil trace element composition and plant
growth. The research was conducted on the Berlin, Germany and Paris,
France sewage farms where sewage sludges had been spread for from
50-80 years. Trace elements soluble in 10% HCl and hot water for
soils beneath healthy plants were compared to those for soils beneath
unhealthy plants on the Berlin and Paris sewage farms. The acid and
water soluble trace elements were determined by treating 10 g of soil
with 800 ml of 10% HCl or 800 ml of distilled water and refluxing one
hour and 30 minutes, respectively. Results condensed from Rohde's
paper are presented in Table 13. Acid-soluble Cu, Zn, Co, and Mo and
hot water-soluble Cu, Zn, Co, Mo, and B were greater in soil under the
unhealthy plants at the Berlin farm (Table 13). Except for Co, which
is not reported, results for the Paris farm show the same trends.
Acid-soluble Zn and Cu are considerably greater under the unhealthy
plants and based upon these data, Rohde concludes that excessive
amounts of Zn and Cu are mainly responsible for the exhaustion of
sewage irrigated land. The results of Rohde (1962) are difficult
to interpret since concentrations of Zn and Cu in soil beneath healthy plants
are quite high when compared to normal levels observed by others (see
Table 15). Also the depth to which soil samples were taken is not
specified and concentrations of trace elements in sludge-treated soils
are markedly dependent upon depth of sample taken. Copper and zinc are
quite immobile in soils and regardless of source most of that applied
remains within the depth of cultivation. Although the concentrations
are not given, Rohde (1962) also reports higher amounts of Cd, Ba, Pb,
and Ag in soil beneath unhealthy plants.
Le Riche (1968) presents data on the trace element concentrations
of leeks, globe beets, potatoes, and carrots grown on soil treated with
a total of 1260 m. tons of sewage sludge per hectare over a period of
19 years or an average annual rate of 66 m. tons/hectare. The
experiments showed no adverse effects on crop yields, but the
plants accumulated abnormally large amounts of certain trace elements.
Yield results along with major nutrient status were reported by others
(Mann and Patterson,1962; Garner, 1966). Globe beet and potatoes grown
29
-------
Table 13--Ten percent HCl and hot water soluble trace elements
in soil under healthy and unhealthy plants—
Berlin Sewage Farm
Element
Mn
Cu
Zn
Co
Mo
B
Mn
Cu
Zn
Co
Mo
B
Healthy
Plants
116
118
197
1.8
1.7
2.1
6.9
8.7
6.5
0.16
0.25
1.3
Unhealthy
Plants
i na/
lU/o
97
508
609
3
2
2
4
20
19
0
0
1
HC1 S(
.0
.6
.0
Water
.3
.1
.1
.30
.59
.8
Paris Sewage Farm
Healthy
Plants
DIU Die (.M'g/gj
216
132
386
-
2.3
3.3
Soluble (IJ'g/g)--
3.1
8.5
3.4
2.3
1.4
0.40
Unhealthy
Plants
166
291
1032
-
3.1
5.3
2.4
11.2
10.5
3.6
1.5
0.46
!_/ From Rohde (1962). Concentrations are expressed in terms of amount
of element solubilized per unit weight of soil.
30
-------
on the sludge-treated Land contained significantly larger concentrations
of Ni and Zn but not of Cu, Pb, Mo, and Cr. The Ni and Zn were more
concentrated in the tops than in the roots, and there was no evidence
that any of the elements accumulated in potato tubers. Leek plants
from plots receiving the sludge contained significantly higher
concentrations of Cu, Ni, and Zn. Carrots grown on the sludge plots
6 years after treatments were discontinued showed higher concentrations
of Cr, Mo, Ni, and Zn in the tops than carrots grown on untreated plots. The
plant results are summarized in Table ih. The concentrations of Cu, Cr, and Mo
are in the range reported as intermediate for a vide variety of crops, but con-
centrations of Ni and Zn are generally higher than normally found in plant tops
(Chapman, 1966; Allaway, 1968; Jones, 1972). For reference, concen-
tration of trace elements typically found in plants and soils, as
reported by Allaway (1968), are presented in Table 15.
The amount of Cr, Cu, Ni, Pb, and Zn dissolved in 0.5 N HOAc for
the sludge, sludge-treated soils 7 years after the treatments were
discontinued, and untreated soils are also reported by Le Riche (1968).
These results presented in Table 16 show some accumulation of trace
elements in the treated soil. Levels of trace elements normally
extracted from surface layers of arable Scottish soils by 2.57° HOAc
(0.5 N) and 0.05 N ethylenediaminetetraacetic acid (EDTA) as reported
by Mitchell (1964) are reproduced in Table 17- Acetic acid-soluble Cr
and Pb in the sludge-treated soils used in Le Riche's studies are in
the range considered normal by Mitchell (1964), but concentrations of
Cu, Ni, and particularly Zn, are somewhat greater than normal. The
0.5 N HOAc soluble zinc for the sludge-treated soil, 275 M-g/g, is in
excess of the level of 200 M-g/g considered by Purves (1972) to be
indicative of Zn toxicity to a number of crops.
Lunt (1959) studied the influence of applications of six sewage
sludges from Connecticut, U.S.A., on seed germination, plant growth
and composition, and soil properties. Two sludges added to pots at
a rate of 22 m. tons dry matter per hectare (10 tons/acre) caused 20
to 67 percent reduction in germination of lettuce and radish seeds.
Additional studies using aqueous extracts of the sludges on heavy
31
-------
Table 14--Trace element composition of crops grown on soil treated with
sludge at an average rate of 66 m. tons/ha/year for 19 years—
Concentrations of Trace Element in Plants
Treatment
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Untreated
Treated
Cr
0.71
0.54
0.85
1.0
0.3
0.8
1.70
3.0
0.09
0.03
0.41
0.88
0.03
0.06
Cu
5.7
16.0
8.5
10.0
11
18
4.2
8.2
9.5
9.5
8.2
9.9
6.3
4.6
Mo
— M»g/g dry matter™
Leeks
0.50
1.10
Globe Beet Tops
0.45
0.65
Globe Beet Roots
0.1
0.25
Potato Tops
0.37
1.0
Potato Roots
0.40
0.27
Carrot Tops
0.58
0.84
Carrot Roots
0.12
0.12
Ni
2.0
7.0
3.2
16.5
1.65
13.0
1.7
5.2
0.25
0.57
1.28
3.0
-
-
Zn
46
135
169
>505
102
250
90
120
30
27
47
99
34
42
U From Le Riche (1968),
plots. Carrots were
discontinued.
Leeks, beets, and potatoes are means of 2
grown on soil 7 years after treatments were
32
-------
Table 15--Total concentrations of trace elements typically
found in soils and plants—
Element
As
B
Cd
Cr
Co
Cu
Pb
Mi
Mo
Ni
Se
V
Zn
Cone, in
Common
6
.10
0.06
100
8
20
10
850
2
40
0.5
100
50
Soils ft
Lg/g) Cone, in Plants (M-g/g)
Range
0.1
2
-40
-100
0.01-7
5
1
2
2
100
0.2
10
0.1
20
10
-3000
-40
-100
-200
-4000
-5
-1000
-2.0
-500
-300
Normal
0.1
30
0.2
0.2
-5
-75
-0.8
-1.0
Toxic-''
-
>75
-
-
0.05-0.5
4
0.1
15
1
1
-15
-10
-100
-100
0.02-2.0
0.1
15
-10
-200
>20
-
-
-
>50
50-100
>10
>200
I/ From Allaway (1968).
2/ Toxicities listed do not apply to certain accumulator plant species,
33
-------
Table 16--Trace elements extracted from soil and sludge
by 0.5 N HOAc-
Material
2/
Sludge-
Sludge Treated Soil-
Untreated Soil
Trace Element
Cr Cu Ni Pb
|-ig/g dry matter--'
3.5 20 50 3.2
2.6 57 8.1 4.2
0.9 15 3.4 1.6
Zn
800
275
83
U From Le Riche (1968).
2_/ Mean of sludge sampled in 1958 and 1959.
3_/ Treated at a rate of 66 m tons per hectare per year for 19 years.
34
-------
Table 17--Trace elements normally extracted from surface
layers of arable Scottish soils—
Element
Co
Cr
Cu
Mn
Mo
Ni
Pb
Sn
V
Zn
Amount
0.5 N HOAc
0.05-2.0
<0. 01-1.0
<0. 05-1.0
5-100
<0.02
0.1 -5.0
<0.2 -4.0
<0.5
<0. 05-1.0
<2-30
Extracted by:
0.05 M EDTA
M-g/g
<0. 05-4.0
0.1 -4.0
0.3 -10
5-100
<0. 03-1.0
0.2 -5.0
1.0 -10.0
<0.5
0.2 -5.0
<3-20
I/ From Mitchell (1964).
35
-------
blotting paper showed that the principal effect of the sludge was to
delay rather than inhibit germination. In general, as the application
rate increased, the time delay in germination also increased. Hinesly,
Braids, and Molina (1971) also present data which show that sewage
sludge may inhibit seed germination.
The trace element composition of oats, spinach, turnips, and
beets in relation to amounts of sludge applied to soils in pots in
the greenhouse as reported by Lunt (1959) are reproduced in Tables 18
and 19. Levels of Cu, Mn, and Zn reported for plants grown on sludge
treated and control soils are higher than those normally observed for
many crops (Allaway, 1968; Jones, 1972). Boron in the plants does not
appear to be related to sludge application rates (Tables 18 and 19).
Concentrations of Cu appear to be related to plant species and soil
reaction. With oats, spinach, and turnip greens on the acid and neutral
soils, sludge treatment had no consistent effect on Cu concentration in
the plants (Tables 18 and 19). However, in the case of beets, concen-
trations of Cu in tops increased in relation to treatment in both the
acid and neutral soil. Zinc in the tops of all plants tested increased
as the amount of sludge applied to the soil increased, regardless of
the soil pH (Tables 18 and 19). Generally, the increase in Zn in
relation to sludge treatment was more profound in the acid soils. The
results show plant species effects and that concentrations of Zn and Cu
in plant tops can be reduced by increasing soil pH. Similar observations
have been made by others (Chaney, 1973; Terman, Soileau, and Allen, 1973),
Patterson (1971) has reviewed the results of a number of studies on
effects of sewage sludge applications to agricultural land conducted by
the National Agricultural Advisory Service regional soil science
laboratories in England (the results of these studies were reported in
internal reports and as such are not available for general distribution).
According to Patterson (1971), instances of crop damage caused by
accumulations of toxic levels of one or more trace elements in soils
which had repeatedly received annual applications of sewage sludge are
sufficiently common in England so they are known to every agricultural
advisor. Severe damage to vegetable crops was reported on a soil which
36
-------
Table 18--Trace element composition of oats and spinach grown in
pots treated with various levels of sewage sludge—
Treatment
Check
Torrington
Sludge
West Haven
Sludge
Check
Torrington
Sludge
West Haven
Sludge
Rate^
(m. tons /ha)
-
44
88
176
22
44
88
-
44
88
176
22
44
88
B
39
35
35
30
30
31
29
40
42
42
39
47
41
41
Element
Cu
Oat Tops
65
54
57
54
41
43
40
Spinach Tops
23
53
49
65
34
35
46
(M-R/R)-'
Mn
- Acid Soil
240
280
250
400
355
475
665
- Neutral Soil
190
160
140
150
365
825
2280
Zn
240
575
835
1185
245
255
385
525
660
765
815
755
830
1200
I/ From Lunt (1959).
2_/ Approximate - Rate presented by author has been converted from cu
yds/acre to m. tons/ha.
3_/ Although not stated by author, it is assumed results are expressed on
dry wt. basis.
37
-------
Table 19--Trace element composition of turnips and beets grown in
pots treated with various levels of sewage sludge—
__ _^ - __
Rate— Element ftig/g)—
Treatment
(m. tons /ha)
B
Cu
Mn
Zn
Turnip Greens - Acid Soil
Check
Torrington
Sludge
West Haven
Sludge
Check
Torrington
Sludge
West Haven
Sludge
-
44
88
176
22
44
88
-
44
88
176
22
44
88
53
53
53
50
51
51
48
59
36
42
42
58
54
35
62
90
70
80+
46
45
60
Beet Tops
51
54
80+
95+
39
69
100+
70
80
120
120
80
150
190
- Neutral Soil
90
75
100
95
135
130
100
-
385
500
800
185
340
355
-
85
195
230
-
-
160
I/ From Lunt (1959) .
2_/ Approximate - Rate presented by author has been converted from cu
yds/acre to m. tons/ha.
3_/ Although not stated by author, it is assumed results are expressed on
dry wt. basis.
38
-------
had received 45 m. tons of sludge per hectare per year for 30 years.
The surface soil from the treated area had the following trace element
concentrations (in ppm): Zn (5000), Cu (500), Pb (1500), Cr (150), and
Ni (50). No results were reported for the trace element composition
of the sludge applied. Toxicities to sugar beets were recorded on
sludge-treated soils which showed the following amounts of trace
elements extracted from the soil by 0.5 N HOAc (in M-g/g) : Zn (420),
Ni (2.0), Cu (0.24). Twenty-four instances of damage to crops from
sewage sludge applications to soil were observed where 0.5 N HOAc
extractable Zn varied from 66-1500 l^g/g; crop damage, however, was
not necessarily attributed to a Zn toxicity. Poor growth of oats and
potatoes grown on some sewage-treated lands was attributed by Patterson
(1971) to Ni toxicity. In the area of poor growth, concentrations of
Ni extracted with 0.5 N HOAc were 20-34 l-J-g Ni/g. Oats grown in acid
soil (pH 5.3) treated with a sewage sludge high in Ni at rates of 0,
34, 67, and 134 m. tons sludge per hectare showed yield reductions at
the 134 m. ton/hectare rate; but in the same soil adjusted to pH 6.8,
yield was unaffected. The sludge applied contained 920 ppm Cu, 2400
ppm Cr, 8700 ppm Zn, and 6480 ppm Ni, all expressed as total concen-
trations on a dry weight basis. Nickel and Cu analyses of the oat
plants reported by Patterson (1971) are reproduced in condensed and
slightly modified form in Table 20. The rate of sludge application
had no significant effect on the amounts of Cu absorbed by the plants
at both soil pH's. However, Ni was absorbed by the plants in substantial
amounts when sludge was applied to both the acid and neutral soil, with
amounts absorbed by plants grown in the acid soil considerably greater
than those absorbed by plants grown in the neutral soil (Table 20).
At application rates greater than 67 m. tons/ha the Ni concentrations
of the oat plants were greater than levels considered toxic by Allaway
(1968). Additional studies reported by Patterson (1971) show rather
dramatically the influence of pH on Ni toxicity to and absorption by
plants. Wheat was grown on a soil adjusted to various pH values (5.1-
7.5) to which were added increasing amounts of Ni (as NiSO,). Application
rates ranged from 5-160 M-g Ni/g soil. In the soil at pH 5.1 six weeks
39
-------
Table 20--Copper and nickel concentrations in oat plants as influenced
by amount of sewage sludge applied and soil pH—
Amt. Sludge Cone, in Soil O^gA
Applied Cu Ni
(m. tons /ha)
0 -
33 14 97
67 28 194
134 56 389
2/ 3>
*)~ Cone, in Plants (M-g/g) —
Cu Ni
pH 5.3 pH 6.8 pH 5.3
11 13 8
12 12 90
12 12 120
19 14 210
i
pH 6.8
4
28
50
70
!_/- Condensed and modified from Patterson (1971).
2_/ Disregarding amount present initially; concentrations in soil are based
upon air dry weight.
3_/ Concentrations in plants are on a dry matter basis.
40
-------
after sowing, Ni toxicity symptoms and yield depressions were severe,
moderate, and slight on plants grown in soils treated with 80, 40, and
20 Hg Ni/g, respectively. At pH 7.5 Ni treatment had no visible effect
on the plants. Concentrations of Ni in the wheat plants in relation to
treatment and soil pH reported by Patterson (1971) are reproduced in
Table 21. Uptake of Ni in soils at pH 6.5 and 7.5 for Ni application
rates up to and including 80 M-g/g were slight and not substantially
different from the controls (no Ni added to soil), but plants grown in
the Ni treated soils at pH 5.1 and 5.5 absorbed rather large amounts
of Ni (Table 21). According to Patterson (1971), levels of total Ni
greater than 20 M-g/g in soils of pH 5.5 or less may damage several
crops. Toxic levels for neutral, alkaline, and calcareous soils are
much higher. Hunter and Vergnano (1952) report that plants differ
•jiarkedly relative to their susceptibilities to Ni toxicity.
Studies at Wye, England, showed that a single application of
sludge to a soil at pH 7.7 at rates up to 365 m. tons/ha produced
no visible damage to radishes (Patterson, 1971). The sludge contained
200-504 ppm Cu, but the Cu concentration in the tops and roots of the
radishes was unaffected by application rates up to 365 m. tons/ha.
Hinesly, Jones, and Ziegler (1972) have studied the effects of
applications of heated anaerobically-digested sewage sludge from the
Metropolitan Sanitation District of Greater Chicago (MSDGC) on growth
and chemical composition of corn. The sludge was applied during the
growing season as a slurry containing about 3.4 percent solids at rates
of 1/4, 1/2, and 1 inch as frequently as drying conditions of the sludge
would permit. The sludge applications increased yield of corn grain
each year for a four-year period (1968-1971) but yield increases were
significant in only one of the four years. Amounts of trace elements
applied per year in sludge for the maximum rate used averaged the
following (in kg/ha): Zn (510), Cu (132), Mn (44), Mo (0.12), B (4.4),
Cr (316), Co (0.30), Se (0.38), Ni (32), Pb (112), Hg (0.038), Cd (35.8),
and Sn (4.5). Sludge treatments had no significant effect on concentrations
of Cr, Cu, Pb, Ni, and Hg in corn leaves sampled at tasseling stage during
the third year of the study. Similarly, treatments had no significant
41
-------
Table 21--Effect of Ni applied to soils at different pH
levels on the Ni content of spring wheat—
Ni
Applied
M-g/g soil
0
5
10
20
40
80
160
Cone.
5.1
2.5
4.5
3.0
8.0
10.0
74.0
-
of Ni in Plants Grown in
5.5
Hg JNl/g
2.2
2.5
3.7
4.7
6.5
17.2
105.
6.5
dry matter-
1.0
0.75
2.2
2.0
2.75
3.0
8.25
Soil at pH:
7.5
-
0.5
0.5
-
0.75
1.25
3.0
I/ From Patterson (1971).
42
-------
e-ffect on concentrations of Mn, Cr, Cu, Pb, Ni, B, and Hg in corn grain
sampled during the third year. Concentrations of Mn, Zn, Cd, and B in
corn leaves and corn grain from plants grown on soils receiving
the sludge treatments and sampled after the third year of the
study reported by Hinesly, Jones, and Ziegler (1972) are presented in
Table 22. The data show that for the maximum treatments concentrations
of Mn, Zn, Cd, and B in the leaves increased by factors of about 1.4,
3.7, 3.5, and 1.7, respectively. The authors state that corn plants
did not accumulate toxic concentrations of trace elements. However,
accumulations observed apply to a 3-year duration, and if rates of
application were to continue annually at the same levels, since the
plants do absorb certain potentially toxic trace elements, the data
suggest that the soils may build up toxic concentrations of trace
elements, particularly Zn and Cd, in the future years. Evidence that
this may occur is provided by studies conducted in England (Patterson,
1971) and Germany and France (Rohde, 1962).
Andersson and Nilsson (1972) in Sweden have evaluated the influence
of sewage sludge applications to soil on trace element enrichment of
soils and plants. The sewage sludge was applied at an average annual
rate of 7 m. ton dry matter per hectare per year every other year
commencing in 1956. At the time fodder rape plant samples were taken,
a total of 105 m. tons/ha (~47 s. tons/acre) sewage sludge had been
applied. Sludge application rates in this study are somewhat less than
those which have been commonly used in the U.S.A. and England; for
example, the maximum sludge treatment used in the studies of Hinesly,
Jones, and Ziegler (1972) corresponded to a total of 270 m. tons/ha
(118 s. tons/acre) over a 4-year period or approximately 2.6 times the
total amount applied in the Swedish study over a 15-year period.
Concentrations of trace elements in fodder rape plants in relation
to concentration in the sludge applied, and total amount of each element
applied from sludge as reported by Andersson and Nilsson (1972) are
presented in slightly modified form in Table 23. Although plants grown
on sludge-treated soils showed higher concentrations of trace elements,
except for Cd and Se, they were not particularly high compared to plants in
43
-------
Table 22--Total contents of trace elements in corn as influenced
by amounts applied from a sewage sludge source—
Element
Mn
Zn
Cd
B
Amt . Trace Element
Applied From Sludge—'
l_rt. /U f.
kg /ha
0
33
66
132
0
380
760
1520
0
27
54
108
0
3.3
6.6
13.2
Amt . Found
in Leaves
M-g/g
81
83
92
116
58
85
138
212
3.3
3.0
5.3
11.6
26
32
35
44
Amt . Found
in Grain
18
14
11
18
89
93
127
152
0.3
0.6
0.8
1.0
7.1
6.2
5.4
6.6
_!/ Condensed and modified from Hinesly, Jones, and Ziegler (1972)
2_/ Approximate, extrapolated from data presented.
44
-------
Table 23--Trace element concentrations of fodder rape as influenced
by repeated applications of sewage sludge—
Element
Mn
Zn
Cu
Ni
Co
Cr
Pb
Cd
Hg
Mo
As
B
Se
Cone . in
Sludge £
1 1 i-r / rr
Pg/g
373
4890
1960
88
122
176
293
11
12
7.4
6.6
30
7.3
Total Amt.
applied in Sludg
Irrr /Via
Kg/na
39.1
513
206
9.2
1.3
18.5
30.8
1.2
1.3
.78
'.69
3.2
.77
Cone, i
;e Control
I
________ j
36
34
3.9
4.9
1.6
2.6
5.2
0.6
0.033
1.1
0.37
29
0.07
n Vegetation
Sludge Treated
41
114
8.3
9.2
1.9
4.1
7.7
0.6
0.049
1.7
0.73
36
0.06
I/ Condensed and modified from Andersson and Nilsson (1972). Concentrations
are expressed on a dry matter basis.
45
-------
general. Levels of all elements in the plants are in the range reported
as intermediate for many plants (Chapman, 1966), and normal by Jones
(1972) and Allaway (1968). Zinc and mercury were accumulated to the
greatest extent, but the'ir concentrations are still well below levels
considered toxic (Chapman, 1966). The trace element composition of the
sludge is not excessive when compared to sludges from many metropolitan
areas (see Table 5).
King and Morris (1972a, 1972b) have studied the effect of appli-
cations of liquid sewage sludge (mean of 6.3 percent solids) to a sandy
clay loam soil on growth and chemical composition of coastal bermuda
grass and rye. Over a two-year period, the amounts of sludge applied
varied from approximately 42-242 m. tons/ha (oven dry wt., HOC basis).
Dry matter yield of coastal bermuda grass harvested during the second
year of the study for treatments greater than about 40 m. tons/ha/year
were significantly greater than the controls (no sludge or inorganic
fertilizer added) but were not significantly different from treatments
where only inorganic fertilizers (NPK) were added. The effect of the
sludge treatments on the Mn, B, Cu, Mo, and Ni concentrations of the
bermuda grass were slight or insignificant, but the concentration of Zn in
the highest treatment reached levels which were 16 times the levels
in the control and inorganic fertilizer treatments; These high levels
of Zn had no effect on yield or "in vivo" digestibility of the bermuda
grass.
In a follow-up study to investigate residual effects of sludge
applications to soil, King and Morris (1972b) seeded their experimental
plots to rye. Cumulative amounts of trace elements applied in sludge
over the course of the two years were as follows (in kg/ha): Mn (46),
B (5), Cu (116), Zn (612), Mo (3.2), and Ni (6.4). Yields of rye for
the first year's harvest on plots treated with sludge were significantly
greater than those for the controls, and except for the lowest sludge
treatment (42 m. tons/ha), they were not significantly different from
those on plots treated with inorganic fertilizers (NPK). Lower yield
for the low sludge treatment was probably due to a N deficiency. The fertil-
ized (NPK) plots were split at the end of the first year, and one-half of each
46
-------
plot was limed at. a rate equivalent to 6.7 m. tons/ha. Lime was added
because the pH of the soil to a depth of 30 cm for the 121 and 242 m,
tons/ha treatments had dropped from about pH 5.2 to levels, depending
upon depth, of pH 4.2 to pH 4.9. Rye yields for the 2nd planting for
plots treated at the maximum sludge rate on unlimed and limed plots
were about 20 and 50 percent, respectively, of yields of plots which re-
ceived only NPK fertilizer (liable 2k). The differences were highly significant.
Trace element composition of rye clippings sampled from the second
year of the study as reported by King aa|d Morris (1972b) are presented
in a condensed and slightly modified form in Table 24. Concentrations
of Mo in the plants were 4.0-4.8 ppm and not influenced by sludge
treatment. In the sludge-treated soils, lime applications reduced
concentrations of Mn, Cu, and Zn in the rye plants. Concentrations
of Zn and Cu in both limed and unlimed plots which received maximum
sludge applications are in the range reported to reduce yields of many
crops and the authors suggest that reduced yields are associated with
the high levels of Cu and Zn. Zinc extractable with N NH,OAc (pH 7)
— H-
from the maximum sludge-treated soil at a depth of approximately 5 cm
was about 4 times greater than that in the controls (5 compared to 20
kg Zn/ha).
Amounts of trace elements removed from the sludge-treated plots
by bermuda grass and rye are also reported by King and Morris (1972b).
Amounts recovered in the crops for the maximum sludge treatment were
as follows (in percentage of that applied): Mn (14), B (4), Cu (0.3),
Zn (1.0) and Mo (2.0).
Jones, Hinesly, and Ziegler (1973) recently reported the Cd
concentration of soybean plants grown on sewage-sludge amended soils.
Digested sludge containing 129 M-g Cd/g was added to soils at rates up
to 87 m. tons/ha. Soybean plants grown on the treated soils in pots
in the greenhouse absorbed significant amounts of Cd. The concentration
of Cd in the tops of soybean plants grown for 95 days in soil treated at
the maximum rate (87 m. tons/ha) was 18.5 H-g/g dry matter compared to
1.8 M-g/g for the controls (no sludge added). Soybean seeds from plants
47
-------
Table 24--Trace element composition and yield of rye clippings
as influenced by sludge applications to soils—
Sludge Rate- Treatment
0 unlimed
limed
42 unlimed
limed
84 unlimed
limed
121 unlimed
limed
242 unlimed
limed
~ /
Yield-
1_ /l_
kg /ha
2,000
2,120
1,180
1,570
1,540
1,960
1,650
2,090
390
900
Trace
Mn
128
93
84
72
133
89
111
82
227
161
Element
B
1 1 F* 1 ry
M-g/g
5.0
6.2
5.0
6.2
8.8
6.8
6.5
7.5
8.8
6.5
Cone
Cu
10.0
10.2
11.0
10.2
12.5
11.5
14.5
12.0
20.0
16.0
3/
•
Zn
32
30
150
106
232
186
340
251
775
579
I/ Condensed from King and Morris (1972b). All treatments were treated with
~" NFK inorganic fertilizer at recommended rates.
2_/ Total applied on an oven dry weight (HOC) basis over a two year
period.
3_/ Dry weight basis.
48
-------
grown on soils treated at the maximum sludge rate showed Cd concentrations
of approximately 1.0 ^g/g.
Linnman, et al. (1973) report Cd concentrations for wheat grown on
soils adjusted to various pH with CaO and treated with sewage sludge.
The sludge contained 10 p.g Cd/g dry matter and was applied to the soils
at rates up to 175 m. ton/ha. At the maximum rate the Cd added to the
soil was relatively low, 0.84 M-g/g soil. Cadmium uptake by wheat
generally increased with sludge application rate but was also influenced
by the pH of the soil. Maximum uptake, 0.26 M-g Cd/g dry matter, occurred
at pH 5.3 with an application rate of 58 m. tons/ha. Minimum uptake,
0.03 M>g Cd/g dry matter, occurred at pH 7.4 in the control soil.
Compost amended soils. Recently a few studies have been conducted
on the effects of applications of municipal waste composts to soils on
plant performance and chemical composition (Terman and Mays, 1973;
Terman, Soileau, and Allen, 1973; Mays, Terman, and Duggan, 1973). The
composts are prepared by combining dry garbage refuse solids with up to
20 percent sewage sludge. Details of the composting operation cited
above are described by Kochtitzky, Seaman, and Wiley (1969). Additionally,
Hart (1968) has reviewed composting operations in Europe.
Hortenstine and Rothwell (1972) incorporated municipal refuse
(compost) into the top 15 cm of phosphate-mining sand tailings at rates
of 35 and 70 m. tons/ha with and without nitrogen, phosphorus, and
potassium (NPK) fertilizer for a two-year period. Sorghum and oats
were grown on the amended soils. The composts contained approximately
40 M.g B/g and 639 M-g Zn/g. Sorghum and oat plants grown on the compost-
amended soils at the 70 m. ton/ha rate contained significantly higher
concentrations of both B and Zn, demonstrating at least partial plant
availability of these elements from the municipal compost.
Terman, Soileau, and Allen (1973) applied a compost prepared by
combining sewage sludge with municipal refuse (up to 20% sewage sludge)
to an acid soil (pH 4.1) at rates of 0, 45, and 90 m. tons/ha. Fescue forage
was grown in the greenhouse for a period of 10 months on the treated soils with
and without lime and NPK fertilizer. The compost applied contained 1500 ug Zn/g.
Yields of fescue were increased by compost applications where no additional
49
-------
fertilizer was applied, but where NPK fertilizers were applied ad-
ditional increases in yield were observed (Table 25). Liming depressed
the uptake of Zn for all treatments (Table 25). Although Zn levels
were higher in the fescue grown on unlimed soils, they were below
levels considered toxic to fescue.
In another study Terman, Soileau, and Allen (1973) grew corn
and snap beans on an acid soil (pH 4.9) which was limed and compost
treated. Again liming reduced Zn uptake. Corn and snap beans grown
on the compost-treated soil contained more Zn than the control soil
at approximately the same pH, and when the compost-treated soil was
acidulated, zinc absorption by corn and snap beans more than doubled.
Mays, Terman, and Duggan (1973) also have shown that compost appli-
cations increase concentration of Zn in forage sorghum grown in the
field.
A certain amount of data have been published on trace element
compositions of .plants and soils adjacent to mining operations. In
the present study no attempt has been made to review the literature
on soil and vegetation contamination resulting from mining operations.
Recent reviews on this subject have been published by Antonovics,
Bradshaw, and Turner (1971), and Little and Martin (1972).
Trace Element Composition of Soils Following
Applications of Sewage Sludge
Published information on trace element composition of sludge-
amended soils is meager. A few reports cover either the total trace
element composition, or concentrations of trace elements extracted
from soil with various reagents such as mineral acids, organic acids,
buffered salts, and chelating agents. Essentially no information is
available on the chemical form or ion species of the various trace
elements which occur in sludge-amended soils. Reports which deal with
trace element composition of soils as they relate to plant growth and
trace element concentrations have been covered under the section
entitled "Trace Elements Absorbed by Plants Grown on Sludge-Amended
Substrates."
50
-------
Table 25--Yields and concentrations of zinc for fescue forage
in relation to compost and lime applications—
Soil Treatment
Compost
m. tons /ha
0
0
0
45
45
45
90
90
90
Lime
0
6.7
13.4
0
6.7
13.4
0
6.7
13.4
No
Dry
Matter
Yield
g/pot
0
0.5
0.8
3.4
5.1
5.0
8.6
10.3
10.6
NPK
Zn
Cone.
^g/g
-
-
-
141
79
64
110
86
75
NPK
Dry
Matter
Yield
g/P°t
0.2
24.4
28.5
25.6
29.4
28.6
33.4
33.1
34.7
Zn
Cone.
M-g/g
-
78
60
163
92
74
122
102
85
1.1 Condensed and modified from Terman, Soileau, and Allen (1973).
51
-------
Purves (1972) has examined the trace element composition of a
number of sludge-amended soils and soils from urban and rural areas
in Great Britain. Results of these studies show elevated concentrations
of B, Cu, Pb, and Zn in sludge-amended and urban soils. However,
concentrations of these elements in the soil were below those considered
damaging to plants. Purves points out that contamination of soil with
respect to Cu, Zn, and Pb is virtually permanent, and he expresses
concern over potential trace element hazards associated with prolonged
annual applications of sewage sludge.
Peterson and Gschwind (1973) applied sewage sludge to acid mine
spoil material in columns at rates equivalent to 61 and 122 m. tons/ha
and leached the columns with aerated de-ionized water for a period of
110 days. The sludge used was from the Metropolitan Sanitation District
of Greater Chicago (MSDGC) and contained relatively high concentrations
of Cd, Cr, Cu, Ni, and Pb. As indicated by concentrations soluble in
0.1 N HCl following leaching, rather large amounts of Zn, Cu, and Cr
were retained in the spoil columns (Table 26). Sludge applications
at rates of 61 m. tons/ha and 122 m. tons/ha increased the leachate
pH from about pH 2.4 to pH 5.0 and 6.2, respectively. The amounts of
Zn, Cr, and Cu extracted from the sludge-treated acid mine spoil
material with 0.1 N HCl are quite high compared to those of the controls
and soils in general. Concentrations of Zn extracted from agricultural
soils with 0.1 N HCl usually do not exceed 20 P*g/g. It Is also worthy to
note that Peterson and Gschwind's data (Table 26) shov that concentrations
of trace elements in the columns vary with depth. Concentrations in the
profile also vary with rate of application.
Hinesly, Jones, and Ziegler (1972) evaluated the total and 0.1 N HCl
extractable trace element concentration of soils treated with surface applica-
tions of MSDGC sludges at rates equivalent to approximately 44, 88, and 166 m.
tons/ha. In the surface 15 cm of soil, the amounts of Or,. Cu, Pb, Ni, Zn, and Cd
extracted with 0.1 N HCl from the sludge-amended soils are considerably greater
than those in the controls (Table 27). Concentrations of the extractable trace
elements were considerably lower in the 30-45 cm depth increment, indicating
that Cr, Cu, Fb, Ni, and Zn are quite Jbmnobile in soil.
Hinesly, Jones, and Ziegler (1972) also report the total concentra-
tion of trace elements in the surface 15 on of soil following
52
-------
Table 26--Concentrations of various trace elements extracted
from sludge—amended acid spoil mine material—
2/ Spoil
Treatment— Depth
m. tons /ha cm
Control
61 0
10
20
30
122 0
10
20
30
- 10
- 20
- 30
- 40
- 10
- 20
- 30
- 40
0.
Mn
,1 N HC1
Zn
Extractable
Cu
Cr
8.0
7.7
3.5
21
19
12
10
5.5
3.8
54 14
136
145
556
488
404
206
113
70
33
5.5
126
127
80
67
7.1
6.4
4.3
20
3.5
77
78
52
51
5.2
3.8
I/ From Peterson and Gschwind (1973).
2/ Sewage sludge was incorporated uniformly to 2 kgm of spoil
material at rates indicated.
53
-------
Table 27--Concentrations of trace elements extracted with
I/
0.1 N HC1 from sludge'-amended soils—
Application
rate
m. tons /ha
0
44
88
166
0
44
88
166
Mn
304
306.
428
402
45
63
57
61
Cone.
Cr Cu
0 -
0.94 3.9
3.3 8.4
11 19
19 32
30 -
0.6 3.5
0.8 4.9
1.3 5.9
1.6 6.4
in Soil Og/e)
Pb
15 cm
6.
11
17
30
45 cm
2.
2.
4.
5.
Ni
depth
6 2.3
3.5
5.3
7.0
depth
0 2.6
7 3.6
2 3.6
3 3.6
Zn
13
41
98
181
7.8
12
16
18
Cd
0.2
1.5
3.8
7.0
0.6
0.7
0.8
0.9
\J EtowHinesly, Jones, and Ziegler (1972).
54
-------
treatment with up to 166 m. tons per hectare of sludge over a three -
year period (Table 28). From these data and others provided for the
amounts of trace elements applied from sludge, it is possible to
estimate the percentage of trace elements applied which are recovered
in the surface 15 cm of soil. Percentage recoveries in the surface
15 cm, as computed from the data of Hinesly, Jones, and Ziegler (1972),
are presented in Table 28. The data indicate that from 33-56 percent
of the Pb, Ni, and Zn applied are retained in the surface 15 cm of
soil, that Cu retention is slightly lower (27-31%), and that Cr and
Cd are retained to the extent of 17-26 percent. Trace metals not
retained in the surface 15 cm are removed by plants, transported to
depths below 15 cm, or eroded from the surface.
Le Riche (1968) examined the concentrations of trace elements
extracted by 0.5 N HOAc from soils which were treated with a total
of 1260 m. tons of sludge/ha over a period of 19 years. His results,
reproduced in Table 29, show substantial increases of Cr, Cu, Ni, Pb,
and Zn in the sludge-amended soils. Amounts of Zn extracted by 0.5 N
HOAc from the sludge-amended soils (210-430 M-g/g) exceed the level of
150 P-g/g considered by Patterson (1971) to cause yield reductions of
many susceptible crops. Also, Ni and Cu extracted from the soil with
0.5 N HOAc are in the general range considered to be damaging,
particularly to sensitive crops.
The sludge treatments were discontinued after 1961; amounts of
trace elements extracted by 0.5 N HOAc six years after the treatments
were discontinued are also shown in Table 29. The results show that
time (6 yrs.) resulted in some reduction in extractable Ni, Pb, and
Zn. This reduction is possibly due to leaching, plant absorption, and
reversion of these elements to a form less soluble in 0.5 N HOAc.
Extractable Cr remained about the same, and extractable Cu increased.
The change in extractable Cu may be due to sampling and analytical
errors. These results indicate that trace elements applied to soils
in the form of sewage sludge persist in a form considered at least
moderately available to plants for long periods of time.
55
-------
Table 28--Recovery of trace elements in the surface 15
cm
I/
of sludge-amended soils—
Element
Cr
Cu
Cd
Pb
Ni
Zn
Amt .
Sludge
Applied
±- /!_
m. tons /ha
0
88
166
0
88
166
0
88
166
0
88
166
0
88
166
0
88
166
Amt. Trace
Element
Applied
~\f -, /1-, 0
kg/ ha-
0
406
811
0
170
339
0
46
92
0
144
289
0
41
82
0
652
1305
Content in
0-15 cm
Depth
55
118
164
36
64
100
2.1
9.7
16
59
84
114
44
48
53
137
310
596
Recovery in
0-15 cm
Depth
7
10
26
19
-
31
27
-
20
17
-
41
33
-
56
42
_
39
41
!_/ Estimated from data of Hinesly, Jones, and Ziegler (1972).
56
-------
Table 29--Trace elements extracted by 0.5 N HOAc from soils
treated with sewage sludge for 19 years and the
sewage sludge applied—
Description
Sewage Sludge
Applied
Control :
Sampled in 1959
Sampled in 1967
Treated— :
Sampled in 1959
Sampled in 1967
Concentration
Cr Cu
3.5 20
0.3 5
0.9 15
2.8 20
2.6 58
Extracted
Ni
pg/g —
50
4.2
4.4
18
8.1
by 0.5 N HOAc
Pb
3.2
1.2
1.6
5
4.2
•^
Zn
800
88
83
395
275
!_/ From Le Riche (1968). Sewage sludge was applied annually at an
average rate of 66.5 m. tons per hectare per year for 19 years.
2_/ Results are the mean from 2 plots.
3_/ Treatments were discontinued after 1961. In 1959 and 1967 the
total sludge applied was 1260 and 1393 m. tons/ha, respectively.
57
-------
Andersson-and Nilsson (1972) also evaluated accumulations of trace
elements in soils- which had received prolonged application of sewage
sludge. Their results cannot be compared to those of Le Riche (1968)
because the method of extracting the trace elements from soil differed
and amounts applied were considerably lower. Andersson and Nilsson
(1972) determined trace elements extracted by 2 M HCl at 100C, except
for Hg where 2 M HNO was used. The changes which occurred in the
trace element concentration of the surface 20 cm as reported by
Andersson and Nilsson (1972) are presented in the first three columns
of Table 30. The results show that the concentrations of B, Mo, Cd,
Ni, Cr, Pb, and Se are increased by factors of 1.3-2.4 in the sludge -
amended soils, Cu and Zn are increased by ~3.6 times and Hg by ~38
times. Although these rather large increases are observed in the
sludge-amended soils, the concentrations for the treated soils are
still within the range considered normal for soils (see Table 15).
A linear log-log relationship between the log of the concentration
of trace element in sludge and the log of the change in the concen-
tration of trace element in soil was observed by Andersson and Nilsson
(1972). The relationship, log Ac ., = 1.06 log C , --1.53 showed
a correlation coefficient (r) equal to 0.93.
Utilizing the data reported by Andersson and Nilsson (1972), it
is possible to estimate the amount of trace elements applied in sludge
which remains in the surface 20 cm of soil by making the following
assumptions: (a) the trace element concentrations of the sewage sludge
for each application were the same as those reported for a single year;
(b) the bulk density of the soil in the surface 20 cm is uniform and
3
equal to 1.33 g/cm . The percent recoveries of trace elements in the
surface 20 cm, computed from the data of Andersson and Nilsson (1972)
by making the above assumptions, are presented in Table 30. The results
show more -Zn, Ni, Cr, Pb, Cd, Hg, and Se recovered than were applied.
This anomaly may be due to changes in the concentrations of trace
elements of the sludges from one application to another, to an inaccurate
estimate of the bulk density of the soil, or to sampling and analytical
errors. Although the recovery estimates yield data which are questionable,
58
-------
Table 30--Changes in the concentrations of trace elements in the
surface 20 cm of soil following application of 84 m.
tons of sewage sludge over a period of 12 years—
Element
Mn
Zn
Cu
Ni
Co
Cr
Pb
Cd
Hg
Mo
As
B
Se
Control
Soil
476
97.9
25.5
28.2
14.2
36.1
25.7
1.2
0.018
0.53
12.3
0.59
0.238
Treated
Soil
_ j | ,~, / ,*-
M-g/g
480
368.8
90.5
43.3
14.6
61.0
43.9
1.7
0.675
0.68
12.5
0.76
0.569
Total Amt.
Applied2-'
11.8
154
61.9
2.78
0.38
5.56
9.25
0.35
0.38
0.23
0.21
0.95
0.23
Percent
Q /
Recovery—
<7
/o
98
146
104
140
100
146
125
110
170
89
100
49*/
121
l_l Data-are derived from those published by Andersson and Nilsson (1972),
2/ Assuming the bulk density of the soil was 1.33. Except for boron,
percent recovery is based upon concentrations extracted with 2 M
mineral acids.
3_/ Within the surface 20 cm of soil. Losses are due to plant removal,
leaching, and possibly erosion.
4/ Refers to recovery of water soluble boron.
59
-------
they suggest that substantial enrichment of As, Cu, Mn, Mo, Ni, Co,
Cr, Pb, Cd, Hg, Se, and Zn will occur in the surface of soils where
sludges containing these trace elements are applied. Results for B
indicate that the water soluble form in the sludge is lost to the
extent of about 50 percent from the surface 20 cm of soil. This is
as expected since B exists as molecular boric acid, B(OH)_, and as
such is only slightly absorbed.
Trace Element Concentrations of Drainage Waters From
Soils Following Applications of Sewage Sludge
In all studies discussed previously, no data are presented on
the changes which may occur in trace element concentrations of soil
solutions or drainage water from sludge-amended soils. The reason
this seemingly important factor has been ignored may be related to
difficulties in analytical determinations of the small concentrations
of trace elements which occur in soil solutions.
Bradford (1973) has determined concentration of trace elements
in soil solutions (saturation extracts) from fields irrigated with
sewage treatment plant effluents and taken from the bottom of sewage
sludge lagoons. A comparison of the concentrations of trace elements
in the saturation extracts of the soils with those of the sludges
applied is presented in Table 31. The data show substantial reductions
in the concentrations of trace elements in saturation extracts of
sludges once they are mixed with soil. However, generally speaking,
concentrations of all trace elements in the sludge-amended soils exceed
those commonly observed for saturation extracts from soils not treated
with sewage sludges. But, with the exception of Cu, Ni, and Cd, the
saturation extract trace element concentrations for the sludge-amended
soils fall in the range reported for saturation extract concentrations
of a wide variety of soils. (For data on the concentration of trace
elements in a wide variety of soils see Table 8.)
60
-------
Table 31--Trace element concentrations of saturation extracts from sewage sludge, soil taken from the
bottom of sludge drying ponds (treatment plants A, B, C), and soil from effluent-irrigated
fields (treatment plants D and E)—
Element
Mo
Cu
Zn
Ni
Co
Cr
Pb
V
B
Cd
Ag
A
Sludge
0.10
0.14
0.5
18
0.19
-
2.0
0.04
2.7
1.2
0.04
Soil
0.01
0.09
0.11
2.0
0.03
0.40
0.22
0.03
0.40
1.2
0.003
I
Sludge
0.23
1.6
1.0
0.6
0.17
-
0.3
0.05
4.4
0.09
0.01
5
Soil
0.04
0.25
0.27
0.09
0.04
0.01
0.06
0.04
2.0
<0.05
0.05
Treatment
C
Sludge
M-g/mi
0.11
1.1
1.5
0.18
0.04
0.01
0.13
0.10
6.0
0.05
0.25
Plant
Soil
0.05
0.23
0.10
0.07
0.02
0.01
0.05
0.03
0.66
<0.05
<0.002
]
Sludge
0.10
0.14
0.5
18
0.19
-
2.0
0.04
2.7
1.2
0.04
3
Soil
0.01
0.05
0.04
0.30
<0.01
<0.4
0.06
0.01
0.6
0.40
0.002
E
Sludge Soil
(NR)£/
0.04
0.75
0.4
0.05
0.02
<0.01
0.17
0.06
0.5
<0.05
<0.002
!_/ From Bradford (1973). Soils sampled to a 15 cm depth.
2_/ Not reported.
-------
III. POTENTIAL IMPACT OF SLUDGE APPLICATIONS TO SOIL
The literature cited shows that trace element concentrations of
sewage sludges vary from low to modest to extremely high. The evidence
presented suggests that repeated applications of sludges high in Ni, Cu,
or Zn to certain soils will produce toxicities to certain species of
plants. Evidence is also presented which shows that productivity of
soils can be maintained and possibly improved by modest applications
of some sludges to soils for extended but not indefinite periods.
Usually trace element toxicities to plants are more prevalent and acute
where sludges are applied to acid soils. Also plant species exhibit
rather marked differences in tolerance to levels of trace elements in
sludge-amended soils. It thus appears that the amount of sludge which
can be safely applied to soil, from a productivity point of view, will
depend upon the composition of the sludge, the kind of soil to which
it is applied, and the species of plant grown on the soil.
In addition to potential adverse effects on plant growth associated
with trace elements in sludge-amended soils, the trace elements applied
to soils may find their way into surface and subsurface water and there-
by impair water quality. Also foods grown on sewage sludge-amended
soils possibly could absorb trace elements in amounts sufficient to
be hazardous to animals or humans who may consume them.
Chemical and Biological Transformations of Trace
Elements in Sludge When Applied to Soil
Trace elements applied to soil, regardless of the form in which
they are applied, may either pass through the soil unchanged, form
insoluble or sparingly soluble inorganic and organic compounds, be
sorbed by soil colloids as cations, anions, or molecules, be volatilized
from the surface (Hg, As, Se) or be taken up by plants. Leeper (1972)
recently presented a rather detailed review of the specific kinds of
reactions which may occur when trace elements are applied to soil.
The discussion which follows will be more general and attempt to point
out the most probable transformations which occur based upon existing
data and the author's experience.
62
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Organic Trace Element Transformations
Under aerobic soil conditions, the organics in the sludge are
microbially decomposed to CO,., and tLO or partially decomposed with
products being incorporated into the humus fraction of soil. Under
anaerobic conditions organics are incompletely metabolized. Organic
acids, chiefly acetic and butyric, accumulate as end products. Methane
and lesser amounts of hydrogen and other volatile products (sulfides)
are evolved. The organic acids serve as substrates for bacteria.
Under anaerobic conditions, microbial decomposition of organic matter
present or added is much slower than under aerobic conditions. The
microbial processes under both anaerobic and aerobic conditions are
extremely complex and rates and intermediate products are dependent
upon many soil environmental factors. The processes involved in the
decomposition of organics added to soil from sewage sludge would be
quite similar to those which occur with or-ganics from other sources.
Where sludges are incorporated into soils after decomposition had
proceeded for a time, it would be impossible to distinquish between
end products of organic matter added in sewage sludge and organics
initially present or added from other sources.
Trace metals such as Cu, Ni, Co, Pb, Zn, Mn, and others exhibit
rather high affinities for soil organic matter. More or less stable
soluble and insoluble complexes between these elements and soil organic
matter may form. The trace element-organic complexes have not been
characterized in detail, but it is generally known that they involve
binding of the trace element ion through principally carboxyl, phenolic,
and imide functional groups in the organic matter. In situations where
solubilities of trace elements exceed solubility products of inorganic
compounds known or suspected to occur in soils, it is generally thought
that the trace element exists in the soil solution as a soluble organic
complex. Recent reviews of trace element organic complexes formed with
soil organic matter and their relative stability constants have been
published by Schnitzer and Khan (1972), and Stevenson and Ardakani
(1972). Norvell (1972) also has recently evaluated soil systems
63
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relative to competitive reactions between various ions and their
organic complexes. Organics in sludge are somewhat similar to
organics which are added to or occur in soils; thus it would appear
that kinds of trace element organic complexes in sewage sludges may
be similar to those which occur or may be formed in soil. Tan, King,
and Morris (1971) present data which suggest that complexes formed
between Zn and fulvic acid extracted from sewage sludge are similar
to those formed with fulvic acid extracted from soil organic matter.
Inorganic Trace Element Transformations
The total concentration of trace elements in an organic form in
sludges most probably undergoes microbial and chemical transformations
once the sludge is incorporated into the soil. However, a sizeable
percentage of the trace element concentration in sludge which occurs
in an inorganic form may be quite stable, and remain essentially
unchanged once the sludge is incorporated into the soil. To define
inorganic reactions of sludge derived trace elements with soil requires
knowledge of the chemical form of these elements in the sludge.
Presently, our knowledge of chemical forms of trace elements in sewage
sludge is nil.
Following incorporation of sludge into soil, the percentage of
the total trace element concentration in the sludge in stable form
will have a marked effect on subsequent chemical and biological re-
actions. Furthermore, the percentage of stable forms in sludges
probably varies from one sewage treatment plant to another. Thus, for
the same or similar soils, applications of different sludges having
the same total trace element concentrations may not affect soil
properties, water quality, plant growth, and availability to micro-
organisms and higher plants in the same manner. Inorganic stable
solid phases of trace elements in soils have been characterized to
some extent. Studies to characterize these inorganic forms in soils
have involved mainly mineralogical and chemical analyses and solubility
product considerations.
Studies on the solid inorganic phases which control the solubility
of trace elements in soils have involved mainly solubility product
64
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principals. Notable advances in our knowledge of the factors controlling
the solubility of trace elements in soils and natural waters have been
made recently. However, the subject is extremely complex and the science
is not developed to the state that trace element solubilities in natural
systems, including soils, can be predicted. Lindsay and his co-workers
(Lindsay, 1972) have shown that concentration of Cu, .Zn, and Mn in many
soil solutions are less than those predicted from the solubility of the
hydroxides and carbonates of these elements. Hem (1972) arrived at a
similar conclusion regarding the concentrations of Zn and Cd which occur
in surface and ground waters. Generally speaking, these recent works
have served to eliminate several compounds from consideration as
controlling factors in the solubility of trace elements in natural
systems, but have not defined the specific compounds or surface reactions
controlling solubilities.
The trace elements Mn, Ba, Cu, Zn, Ni, Cd, Co, and Pb, if not
complexed with organic matter, most probably exist in soil solutions
predominantly as divalent cations. Many other inorganic complex ions,
molecules, and ion pairs of these elements are known to occur in
equilibrium with the divalent form. These complex ions have the general
formula MX, where M is the divalent cation and X the anion. The
a b
complex can be cationic, neutral, or anionic. Examples of these kinds
of naturally occurring complexes of Hg are listed on page 67. Knowledge
of the equilibria between simple inorganic trace element ions and their
complex forms, in most cases, is not developed to the extent that it
can be applied to soil solutions.
Published data indicate that the concentrations of those trace
elements which exist in solution as cations (Mn, Cu, Zn, Ni, Cd, Co,
Sn, Cr, Pb, and Ag) usually occur in neutral (pH ~7) soil solutions at
concentrations less than 0.05 M-g/ml (Table 8). In acid soils (pH 5-6)
concentrations in solution usually increase and in slightly alkaline
and calcareous soils (pH 7.5-8.5) they usually decrease. In the pH
range common to soils generally (pH 5-8.5), concentrations of the
cationic trace elements do not exceed 0.25 M-g/ml. The precise factors
governing the solubilities of these trace elements in soil solutions
65
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are not known. However, limiting values based upon solubilities of
carbonate, hydroxide, and phosphate forms can be predicted. Generally,
solubility product considerations would limit concentrations in solution
to levels of 1 M-g/ml or less. Under reducing conditions, sulfides of
Mh, Cu, Zn, Ni, Cd, Co, Sn, Cu, and Pb could form. The sulfides of
these trace elements are quite insoluble, so solubilities in anaerobic
soils may be limited by sulfide precipitation. These generalizations
and available published information demonstrate that cationic trace
elements are quite immobile in most soils (possible exceptions are
very acid soils, sandy and organic soils). These trace elements when
applied to soil, regardless of the form, therefore will be retained
largely in the surface soil to the depth of mixing (tillage).
The trace elements As, Mo, and Se occur in solution most commonly
as divalent anions. Arsenic is chemically akin to phosphorus and its
reactions in soils resemble those of phosphorus. In acid soil (pH <5.5)
_2
arsenate (HAsO, ) reacts with active iron and aluminum, if present, and
sparingly soluble iron and aluminum arsenates possibly control the
concentrations of As in solution. In neutral and calcareous soils,
arsenate reacts with calcium to form sparingly soluble calcium arsenates.
The arsenates of calcium are more soluble than those of iron and aluminum.
Consequently, As is usually more soluble in neutral and calcareous soils
than in acid soils. In soils where active iron, aluminum, and calcium
occur, As added to soil is most likely quite immobile and can accumulate;
but in soils where little active iron, aluminum, or calcium occur, As
applied could be leached to lower depths in soil profile.
The behavior of Mo and Se probably quite closely resembles that of
As. Both trace elements are mobile in sandy soils devoid of organic
matter and active iron, aluminum and calcium. Current evidence indicates
that active iron and aluminum in acid soils limits the solubility of
these elements in soil solutions. The elements become more soluble in
neutral and calcareous soils, because calcium forms are more soluble
than the iron and aluminum forms.
Boron, except in highly alkaline soils (pH > 8.5), occurs in soil
solutions as undissociated boric acid [B(OH) ]. It is sorbed by active
-------
oxides of iron and aluminum in soil, but its affinity for these solid
surfaces is low compared to affinities of other trace elements for
surfaces in general. For these reasons B is quite mobile in soils.
In sandy soils low in organic matter and active iron and aluminum
oxides, B in waters passes through soils essentially unchanged.
Organic matter and active iron and aluminum oxides tend to limit
somewhat the mobility of B in soils, but generally the equilibrium
involved is such that substantial percentages of the dissolved B
remain in solution and as such are mobile in soil. Our knowledge of
solubilities of boron in relation to soil organic matter contents is
sparse; consequently, the generalization discussed may be subject to
qualifications dependent upon organic matter contents.
Concentrations of Hg reported to occur in natural waters and
soil solutions are usually less than 0.001 Hg/ml (Lagerwerff, 1972,
and Bradford, 1971). It may occur in solution as soluble elemental
Hg, Hg2Cl2, HgCl2, and Hg(OH)2. In sea water, Bowen (1966) reports
the dominant form of mercury as HgCl. . Under reducing conditions
Hg may precipitate as HgS, which would limit its concentration to
<0.002 M-g/1. Mercury exhibits high affinity for humic substances,
particularly those with S and SH function groups. It is also bound
tightly to sediments such as hydrous oxides of iron and manganese.
In surface soils Hg may be lost as volatile elemental Hg. Because
of high affinity for humic substances and other inorganic constituents
in soil, Hg is not expected to leach from many soils.
Evaluation of Criteria Available to Judge
Feasibility of Sludge Applications
The principal problem associated with attempting to evaluate the
potential impact of sewage sludge applications on soils' capacity to
produce safe consumer crops and upon the quality of waters draining
from soils is the lack of available information upon which one can
base evaluations and recommendations. An analysis of the information
currently available follows.
67
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Soil and Plant Composition Criteria
Most research on trace elements in soils has been concerned with
deficiencies rather than excesses. There are virtually no reliable
soil tests available to diagnose trace element toxicities to plants.
Those which have been discussed under "Results of Published Reports"
serve to demonstrate the inadequacy of the methods currently used.
A few plant analyses criteria for excesses of certain trace elements
in soil have been developed (Table 15), but these are fragmentary and
inadequate. They apply to "normal" soils and may not be applicable
to sewage sludge-amended soils. Also, plant analysis techniques have
the disadvantage that they indicate the problem after it exists, when
what is needed is a technique to predict problems before they occur.
Another means of evaluating consequences of trace element con-
tamination of soils resulting from sewage sludge additions is a
comparison of the amounts of trace elements added to soil in the form
of sludge with the maximum concentrations which normally occur naturally
in productive soils. Although information is lacking to judge maximum
concentrations of trace elements in soils which can be tolerated and
still preserve soil productivity, trace element enrichment beyond
normally maximum natural levels -- particularly within the root zone
of the crops -- should be viewed as potentially damaging until infor-
mation to the contrary is developed.
Water Quality Criteria
Sewage sludges are frequently applied to soil in a dilute
suspension (up to 3%) usually utilizing sprinkler irrigation techniques.
Under these conditions it may seem appropriate to evaluate sludge
applications in this form in terms of quality criteria developed for
irrigation waters. However, by doing this, unnecessary restrictions
may be placed upon the use of liquid sewage sludges since criteria for
irrigation waters are based upon solution as opposed to suspension
concentrations.
In situations where sewage treatment plant effluents (waste waters
as opposed to sludges) are used as supplemental or entire sources of
68
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irrigation water, the water quality criteria developed for irrigation
waters should provide interim guidelines upon which the feasibility of
applying sewage treatment plant effluents to soils can be judged.
Irrigation water quality criteria have been developed by the National
Academy of Sciences (NAS) (1973), U. S. Department of Interior (USDI),
Federal Water Pollution Control Administration (FWPCA) (1968), and
state and regional water quality control boards. McKee and Wolf (1971)
have reviewed state control board water quality criteria and standards.
Water quality criteria for trace elements in irrigation waters developed
by the NAS (1973) and the USDI (1968) are reproduced in Table 32. For
reference, surface water standards which conform to the standards set
by the U. S. Department of Health, Education, and Welfare for drinking
waters (U. S. Dept. Health, Education, and Welfare, 1962) are also
included in Table 32.
Consequences of Trace Element Enrichment
in Sludge-Amended Soils
The review of the literature presented shows that information
upon which one can judge specific consequences of trace element
enrichment in sludge-amended soils is lacking. It is informative,
however, to evaluate the consequences of sewage sludge applications
to soils based upon what is currently known. In the discussion which
follows, amounts of trace elements applied to soils will be compared
to those normally present naturally. Consequences of trace elements
in sludge-amended soils as they relate to productivity and quality of
crops and water quality will also be evaluated.
Soil Enrichment
A hypothetical domestic sewage sludge was selected to evaluate
trace element enrichment in sludge-amended soils in terms of normal
concentrations naturally present. The trace element concentrations
of this hypothetical sludge are presented in column 2 of Table 33.
They represent the author's estimates and are based upon median
concentrations and trace element concentration ratios obtained from
analyses of a large number of sewage sludges.
69
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Table 32--Surface and irrigation water quality criteria for trace elements
Surface Water
Element FWPCA-
As 0.05
Ba 1.0
B 1.0
Cd 0.01
Co
Cr 0.05
Cu 1.0
Pb 0.05
Mn 0.05
Mo
Ni
Se 0.01
V
Zn 5.0
Ag 0.05
Irrigation Water
Continuous Use
FWPCA
Any
Soil
m/> /I .
mg/ 1
1.0
-
0.75
0.005
0.2
5.0
0.2
5.0
2.0
0.005
0.5
0.05
10.0
5.0
-
NAS^
Coarse -Textured
Soil
0.1
-
0.75
0.01
0.05
0.1
0.2
5.0
0.2
0.01
0.2
0.02
0.1
2.0
-
Short -Term Use
FWPCA 21
Fine -Textured
Soil
10
-
2.0
0.05
10.0
20.0
5.0
20.0
20.0
0.05
2.0
0.05
10.0
10.0
-
!_/ U.S. Dept. of Interior, Federal Water Pollution Control Administration (1968).
Surface water criteria are virtually the same as drinking water standards (U.S.
Dept. of Health, Education, and Welfare (1962).
2/ National Academy of Sciences (1973). Recommended maximum concentrations of
trace elements in irrigation waters used for sensitive crops on soils with low
capacities to retain these elements in unavailable forms.
3_/ For short-term use only on fine-textured soils.
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Table 33—Comparison of amounts of trace elements added to soil
to a depth of 15 cm from 100 m. tons of a typical
domestic sewage sludge with amounts commonly present
Element
Ag
As
B
Ba
Cd
Co
Cr
Cu
Hg
Mn
Mo
Ni
Pb
Se^7
Sn
V
Zn
Cone . in
Sludge!/
M-g/g
10
5
50
1000
10
10
200
500
5
500
5
50
500
1
100
50
2000
Amt. Appliec
to Soili/
kg /ha
1
0.5
5
100
1
1
20
50
0.5
50
0.5
5
50
0.1
10
5
200
1 Amt. Present in Soil (kg/ha)-'
Normal Range
0.02-10
0.2 -80
4 -200
200 -6000
0.2 -1.4
2 -80
10 -6000
4 -200
0.02-0.6
200 -8000
0.4 -10
20 -2000
4 -400
0.02-4
4 -400
40 -1000
20 -600
Typical Level
0.2
12
20
1000
0.12
16
200
40
0.06
1700
4
80
20
0.4
20
200
100
!_/ Based upon information presented in Tables 1, 2, 3, and 5.
2_/ Assuming the sludge is mixed to a depth of 15 cm and the bulk density
of the soil is 1.33 g/cnP.
3_/ Derived from data reported by Bowen (1966).
4_/ The Se concentration of the sludge is based upon an estimated from the
~~ content in municipal solid waste as reported by Johnson (1970).
71
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Since applications of sludge are made on the basis of an amount
applied to a unit area and concentrations in soil are expressed on a
weight basis, to make comparisons it is necessary to assume that the
amount of trace elements applied in sludge to the surface will occupy
a certain volume of soil. If it is assumed that the sludge is in-
corporated to the depth of tillage (-0.15 m) the volume of soil in one
hectare is 1500 m3. By specifying a bulk density for the soil of 1330
kg/m (an average value for many textural classes of soils) results of
soil analyses expressed in units of mg element per kg soil (ppm) can be
converted to units of kg/ha. Table 33 shows the amount of trace elements
added to the surface 0.15 m of soil from the application of 100 m. tons
of the hypothetical domestic sludge per hectare and compares them with
amounts of trace elements commonly found in untreated soils. The
rationale behind using a rate of 100 m. tons/ha is that it is a convenient
figure from which one can extrapolate to other application rates, and it
represents a low application rate of 10 m. tons per hectare per year for
a period of 10 years. This annual application rate approximates that
recommended in Sweden (Andersson and Nilsson, 1972).
The data show that 100 m. tons of typical domestic sludge per
hectare (45 s. tons/acre) will add more Zn, Cu, Pb, Cd, Hg, and Ag to
the surface 15 cm than is typically present (Table 33). However, the
amounts added plus amounts initially present fall within the normal
range for many soils. The available evidence indicates that trace
elements applied to most soils are retained in high percentages to the
depth increment of tillage. Management practices involving deep tillage
will serve to reduce concentrations in the surface by mixing with a
larger volume of soil. Thus, employing practices which mix the applied
sludge to greater depths in soil will tend to proportionately increase
the total amount of sludge which can be applied before typical concen-
trations of unamended soils are exceeded. The data, therefore, indicate
that domestic sludges (only slight industrial inputs) could be applied
to soils for a number of years at rates of 10-20 m. tons/ha and not cause
trace element concentrations uncommon to soils in general. Sewage sludges
from metropolitan areas with large industrial inputs contain considerably
72
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higher concentrations of many trace elements than those listed in
Table 33. Each should be evaluated independently to determine the
extent to which soils would be enriched with trace elements by their
application.
Cadmium, Copper, and Zinc. These three elements have been grouped
together since their chemistry is somewhat similar and they commonly
occur in many sludges at concentrations which exceed those normally
found in soil.
As mentioned previously, the data presented in Table 33 show that
application of 100 m. tons/ha of a typical domestic sludge if mixed
uniformly throughout the surface 15 cm would add more Cd, Cu, and Zn
than is typically present in this zone. The Cd concentrations in
natural soils are quite low; consequently, even modest applications
of sludge containing a few mg Cd/kg if applied for a decade or so
would enrich the surface 15 cm of soil to levels beyond those typically
observed naturally. The range of normal values for Cd (0.2-1.4 kg/ha)
in soil is considerably less than the normal range for Cu (4-200 kg/ha)
and Zn (20-600 kg/ha). The maximum values in the normal range for Cu
and Zn in natural soils would be exceeded in the surface 15 cm by
applications of the typical sludge equal to 400 and 300 m. tons/ha,
respectively. For Cd, the maximum value in the normal range would
be exceeded by an application of 140 m. tons/ha.
Lead and Mercury. Application of 100 m. tons of the typical
domestic sludge would also add more Pb and Hg to the surface 15 cm
of soil than is typically present (Table 33). In the case of Hg, the
amount applied in 100 m. tons of sludge is considerably greater than
that typically present, and approaches the maximum soil level in the
normal range. An application of 120 m. tons/ha of the typical sludge
would yield concentrations of Hg in the surface 15 cm equal to the
maximum level observed in the normal range for untreated soils. With
Pb an application of 800 m. tons/ha could be tolerated before the
maximum concentration in the normal range for unamended soils was
reached.
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Nickel and Chromium. Concentrations of Cr and Nl in the typical
domestic sludge are such that applications of 1000 and 1600 m. tons/ha
would be required to produce concentrations in soil which would exceed
those typically present in natural soils (Table 33). It would appear
from the approximations made that sludge enrichment of other trace
elements in soil, namely Hg, Cd, Zn, and Cu in that order, may become
limiting relative to potential hazardous concentration before Ni and
Cr could present problems. However, sludges from metropolitan areas
with large industrial inputs may contain concentrations of both Ni and
Cr considerably in excess of those found in domestic sludges. Concen-
trations of a few thousand mg/kg and even greater are not uncommon in
industrial sludges. Thus, although Ni and Cr may not become controlling
factors in limiting amounts of domestic sludge applied to soil, they may
do so in the case of industrial and metropolitan sludges.
Arsenic, Molybdenum, and Selenium. Concentrations of Se common to
natural soils are somewhat less than those of Mo and As. Representative
concentrations for Se in sludge are rather difficult to deduce from the
published literature because of the very limited number of analyses
available. The concentration used for the hypothetical sludge was
estimated from data reported for municipal solid waste by Johnson
(1970). Andersson and Nilsson (1972) report a value of 7.3 M*g/g in
sludge from Sweden. Using Johnson's data as representative of a
domestic sludge indicates that applications of 400 m. tons of domestic
sludge per hectare could be tolerated before the typical level of Se for
natural soils would be exceeded. In the cases of Mo and As, sufficient
data are available to make what the author considers reasonable estimates
for their concentrations in sludge. The data in Table 33 show that 800 m.
tons/ha of domestic sludge would be required to produce concentration
levels in soils equal to those observed naturally for Mo. Applications
of 2000 and 4000 m. tons of domestic sludge per hectare would produce
concentrations of Mo and Se in excess of the maximum concentrations
normally observed for natural soils. Excessive enrichment of soils
with As by domestic sludge applications appears improbable (Table 33).
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Boron. Boron occurs in both organic and inorganic form in soils.
In inorganic form"in soil solutions, it occurs as undissociated boric
acid. As such it is not retained by soils to the degree of the other
trace elements discussed. Current evidence indicates that soils have
little capacity to retain B in an inert form and that high percentages
of applied B will move with water to lower depths in the profile.
Therefore, the data contained in Table 33 overestimate concentrations
of B in the surface 15 cm of soil. They show that application of 400
m. tons of domestic sludge per hectare would yield a concentration in
the surface 15 cm equal to a typical level for natural soils.
Barium, Cobalt, and Vanadium. Very little direct information is
available on the chemistry of these elements in natural soils. The
data presented in Table 33 show that domestic sludge applications in
excess of 1000 m. tons/ha would be required to produce concentrations
of Ba, Co, and V in the surface 15 cm of soil in excess of those
typically present in natural soils. To reach maximum concentrations
in the normal range of natural soils would require unrealistically
high additions of sludge. Thus, it appears that these three elements
can be removed from consideration as limiting relative-to-excessive
trace element enrichment in soils from domestic sludge applications.
Silver and Tin. The estimated concentration of Ag in the hypo-
thetical domestic sludge given in Table 33 is based upon less extensive
sludge analyses than are concentrations of the other trace elements
(except for Se). It was derived from data presented by Berrow and
Webber (1972). Typical concentrations of Ag in soils are quite low,
so as with Cd, Hg, and Se, modest applications of domestic sludges
containing a few M-g Ag/g will enrich soils beyond concentrations
normally naturally present (Table 33). Silver should be relatively
immobile in soils since it is adsorbed by soil minerals, and forms
sparingly soluble chloride, carbonate, and other salts.
Concentrations of Sn in domestic sludge are such that 200 m.
tons/ha would produce concentrations in soil equal to typical levels
for natural soils. To reach the maximum level in the normal range for
natural soils, however, would require an application of 4000 m. tons/ha
75
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domestic sludge. Tin is generally thought to be quite inert in soils
(Wallihan, 1966). It is unlikely to be damaging when applied to soil
in the form of domestic sludge.
Manganese. Unrealistically high amounts of domestic sludge would
be required to enrich soils beyond the normal maximum concentrations
which occur naturally (Table 33).
Crop Productivity and Quality
The literature reviewed indicates that sewage sludges from most
sewage treatment plants can be applied in modest amounts to most soils
for limited periods of time without causing trace element toxicities
or adversely affecting the quality of most crop species. Continued
applications of most sewage sludges for long period of time (decades),
however; will probably adversely affect plant growth due to trace
element soil enrichment and subsequent plant toxicity. The trace
element composition of the sludge will determine the total amounts
which can be applied to soils over a period of years before adverse
effects on crop yields and possibly quality will occur.
Crop Productivity. It is difficult to generalize about the effects
of trace element enrichment of soils on crop productivity. Trace element
interactions which are dependent upon chemical properties of soils may
indirectly affect plant growth. Plant species exhibit natural variability
and vary markedly in their tolerance to concentrations of trace elements
in soil. Thus, yields of sensitive crops may be drastically reduced by
a particular level of sludge application where yields of tolerant crops
would be unaffected. A detailed treatise of tolerances to trace elements
for a wide variety of plant species is presented by Chapman (1966).
The data published suggest that continued applications of sludge
could produce concentrations of trace elements in soil which may increase
or decrease plant growth. Trace elements in sewage sludge could serve
as a source of plant essential trace elements where they are either
naturally deficient or present in a plant unavailable form in soil.
Studies have shown that most trace elements are toxic to higher plants
if they occur in soil solutions in excessive amounts (Pratt, 1973). Of
76
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those trace elements considered in the present review, it appears that
concentrations of Ag, Mo, Hg, and Sn in all sludges are such that yield
reductions caused by toxicities of these elements in sludge-amended
soils are unlikely. With domestic sludges (small industrial input)
toxicities to higher plants caused by buildup of As, Ba, Co, Cr, Mn,
and V are unlikely. Those most likely to cause toxicities to higher
plants in soils to which large amounts of domestic sludge are applied
over a period of years are B, Cd, Cu, Zn, and possibly Ni, Pb, and Se. With
respect to Cd, Cu, Zn, Pb, and Ni toxicities would probably occur at lower
concentrations and be more acute in acid soils. Concentrations of As,
B, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, V, and Zn may be sufficiently
high in certain sludges from highly industrialized areas to cause yield
reductions of crops when applied in copious amounts to agricultural land.
Sludges from highly industrialized areas must be considered independently
because their trace element concentrations are so highly variable.
Quality of Crops. Quality considerations will be restricted to
those associated with accumulations of trace elements in plants which
produce metabolic imbalances or toxicities to man and animals. Only a
limited number of references to illustrate points discussed are cited.
More complete reviews on the subject are presented by McKee and Wolf
(1971), Lisk (1972), Allaway (1968), and Scott (1972).
Feed and food plants can grow at normal or near normal rates and
still contain sufficient Se, Cd, Mo, and possibly Pb to cause either
direct toxicity or metabolic imbalance in animals that consume these
crops (Allaway, 1968). Other plants, however, may grow normally but
contain insufficient concentrations of Co, Cr, Cu, Mn, Se, and Zn to
meet the dietary requirements of animals. Thus, with respect to
certain trace elements added to soil in the form of sludge, the quality
of feeds and foods could under certain conditions be improved, while
under others detrimental effects may be encountered.
Selenium. Selenium is essential in the diet of livestock at
low concentrations but toxic at higher concentrations. Soils from
widespread regions throughout the United States produce forage without
sufficient Se to satisfy the dietary requirement of animals (Kubota
77
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and Allaway, 1972). In other regions, Se concentrations in soils are
sufficiently high-to produce forage containing concentrations of Se
which are toxic to animals (Ganje, 1966). The range between dietary
deficiency and toxicity is quite narrow. According to Allaway (1968),
concentrations of Se required in the diets of various animals to prevent
Se deficiency range from 0.04-0.20 M-g Se/g depending upon the kind of
animal and the type of diet. Concentrations in excess of 4-5 ^g/g are
toxic to animals. Allaway (1968) suggests that it would be desirable
to control the level of Se in food and feed crops somewhere between
0.1-1.0 M-g/g. Selenium added to soil as selenized superphosphate or
barium selenate at rates of approximately 2 kg/ha produced toxic levels
of Se in the first few cuttings of alfalfa (Gary, Wieczorek, and Allaway,
1967; Carter- Brown, and Robbins, 1969). Very little information is
available on concentrations of Se in sewage sludge. The above information
suggests that if Se were to occur in sewage sludge at concentrations
greater than a few M-g/g, and if it were applied to soil for a number
of years, the concentration of Se in soil could build up to the extent
that forage might absorb sufficient amounts to be toxic to animals.
Molybdenum. Molybdenum, like Se, is an essential element for
animals at low concentrations but is toxic at higher concentrations
(Allaway, 1968). Toxic concentrations of Mo are related to the level
of Cu and SO, in the diet. Where Cu is low in the diet, concentrations
of Mo in forage as low as 5 l^g/g may cause a disorder in animals called
molybdenosis or molybdenum-induced copper deficiency. Ruminant animals
are more susceptible to molybdenosis than are nonruminants. Sewage
sludges contain Mo, so depending upon the concentration in the sludge
and the amount applied, it is possible that soils could become enriched
to the extent that plants would absorb quantities of Mo sufficient to be
toxic to animals. Both Mo and Se are more plant-available in neutral
and alkaline soils than in acid soils. In this respect, Mo and Se are
unique, since they are potentially more damaging in neutral soils, while
the other trace elements are potentially more damaging in acid soils.
Cadmium. Studies in Japan (Yamagata and Shigematsu, 1970), the
U.S.A. (Schroeder, 1971), and Sweden (Friberg, Plscator, and Nordberg,
1971) show that chronic exposure to Cd may result in accumulation of
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levels in man and animals which will cause a serious decline of health
and even death. The Japanese studies (Yamagata and Shigematsu, 1970)
particularly have demonstrated that foods cultured on Cd-polluted soils
irrigated with Cd-polluted waters can accumulate sufficient Cd to be
hazardous to human beings who consume these foods.
Recent data accumulated by a number of workers (John, Chuah, and
Van Laerhoven, 1972; John, 1973; Page, Bingham, and Nelson, 1972;
Haghlri, 1973) show that certain crops accumulate excessive amounts
of Cd from substrates treated with Cd from inorganic sources. Bingham
et al. (1973) present data which show that the leafy portion of plants
grown on soils to which Cd-fortified sewage sludge was applied accumulates
substantial amounts of Cd. Although regulatory agencies have not set
levels for maximum dietary intake of Cd, the current information
indicates that certain foods, if grown on Cd-contaminated soils, will
accumulate amounts of Cd which are potentially hazardous to human and
animal health.
Sewage sludges, particularly those from metropolitan areas, may
contain rather high concentrations of Cd. If these sludges are applied
to soil in modest amounts for a number of years, the Cd concentrations
in soil could become large enough to produce concentrations in foods
grown on the soils which may be toxic. Certain workers (Leeper, 1972;
and Chaney, 1973) suggest that it is not the Cd concentration in soil
"per se" which determines Cd accumulation by plants. They suggest that
the Zn:Cd ratio in the substrate will determine amounts of Cd absorbed
by plants. Chaney (1973) indicates that as long as this ratio (ZnrCd)
is 200 or greater, foods will not accumulate hazardous concentrations
of Cd. The subject is complex and additional research is needed to
resolve potential hazards associated with the Cd-Zn-soil-plant system.
Lead. Lead poisoning of animals and humans caused by excessive
amounts of Pb in foods and beverages consumed, and in air, is well
documented (National Research Council, 1971; Zimdahl and Arvek, 1973).
In those instances where Pb toxicities to animals and humans have
occurred, the sources of Pb in the foods and feeds were not due to
plant absorption from soils but were caused by contamination during
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processing, storage, or deposition from lead in air onto plant surfaces.
The principal source of Fb in air is the combustion of leaded gasoline
by motor vehicles. As far as the author is aware, there are no known
occurrences of Fb poisoning caused by feed and foods absorbing excessive
amounts of Fb from soil.
Sewage sludges may contain rather large quantities of Fb. The
information available indicates that crops absorb relatively small
amounts of Fb when grown on lead-contaminated soils. Except possibly
in certain unique and isolated instances, it is doubtful that sludge
applications to soils will result in enrichment in Fb to the extent
that plants will accumulate hazardous concentrations.
Water Quality
In terms of trace element composition the quality of waters resulting
from sewage sludge applications to soils can be evaluated with respect to
(a) the composition of the solution as it moves through the soil profile
and strata belov and (b) the composition of surface drainage water.
The data reviewed show that the concentrations of dissolved trace
elements, except possibly for B, are reduced once the sludge comes in
contact with soil; the extent of reduction is dependent upon soil
chemical properties. Generally, the capacities of coarse textured
(sandy) soils to reduce trace element solution concentrations of the
applied sludge are less than those of fine textured (clayey) soils.
The extent to which the soluble trace elements in sludge are reduced
is also dependent upon the soil pH. Except for As, Mo, Se, and B, trace
elements are more soluble in acid than neutral soils. Solubilities of
As, Mo, and Se increase slightly with increased soil pH. The solubility
of B is more or less independent of soil pH. Therefore, with respect to
trace elements, except possibly for B, soils have a capacity to "purify"
waste waters.
The trace element composition of soil solutions from sludge-amended
soils should progressively decrease as the depth of percolation within
the soil increases until a composition characteristic of the natural
soil is reached. Data reported by Bradford (1973) (Table 31) show that
the concentrations of Cu, Ni, B, Cr, Mo, and Cd in soil solutions obtained
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from sludge-amended surface soils are greater than those considered
safe for irrigation use (compare data in Table 31 with those in
Table 32). To correct this situation sludge applications could be
discontinued and the soil could be leached with waters which meet the
minimum recommended concentrations for irrigation waters (Table 32).
This practice should displace the trace element-contaminated soil
solution to lower depths in the soil profile and thereby expose it
to more soil and reduce solution concentrations of the trace elements.
Information on the movement of trace elements within soil profiles is
meager. Consequently, critical evaluations of trace element composition
of sludge-amended soils in relation to depth in soil profiles are not
possible at the present time.
The extent to which underground water supplies may become con-
taminated with trace elements from sludges applied to soil is largely
dependent upon the soil's chemical properties and the distance the
percolating solution must move through the soil to the water table.
The potential for trace element contamination would be greatest where
shallow water tables (a few meters) occurred beneath sandy low organic
matter soils. Conversely, where the water table occurs at great
distances from the surface (100 meters) the probability of trace element
contamination of underground water is essentially nil. Of those trace
elements considered in this paper, boron would move in both soil profiles
and the strata below at the greatest rate. Movement of Ba, Cd, Co, Cr,
Cu, Pb, Mn, Ni, Zn, and Ag should be least; Mo, As, and Se should move
at a rate intermediate between B and the cationic trace elements. Pratt
(1972) has developed techniques to compute transit times for drainage
water movement in the unsaturated zone beneath the root zone of crops.
Utilizing the concept of transit time in conjunction with other data,
he was able to predict time lags associated with movement of nitrates
in the alluvial materials of a particular basin. An approach similar
to that used by Pratt (1972) may be feasible to predict the time required
for B, and possible other trace elements, to move from the surface through
an unsaturated zone to the ground water.
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Since trace elements applied to soil are largely concentrated in
the surface, drainage from surface soils into surface waters may con-
tribute to trace element contamination of these waters. Concentrations
of trace elements in water considered to be toxic to aquatic organisms
are, in many cases, less than those considered to be toxic to animals,
man, and higher plants. Wilber (1969) has reviewed trace element
tolerances of aquatic organisms. Concentrations of Ag, Cd, Cr, Cu,
Hg, Mo, Ni, and Pb as low as 0.01 M-g/ml may have serious deleterious
effects on certain species of aquatic life. Since these tolerances
are so low, where sludges are applied to soils, surface runoff of
either sediment or solution into surface water should not be permitted.
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IV. SUMMAHT
Concentrations of trace elements in sewage sludges are related to
industrial and consumer uses. Uses of As, Ba, B, Od, Or, Co, Cu, Fb,
Ma* Hg, Mo, Ni, Se, Ag, Sn, V, and Zn are briefly revieved.
Total concentrations of trace elements in sewage sludges vary widely.
The ranges reported for sludges from approximately 300 treatment plants
from different regions in the U.S.A., Canada, Sweden, England and Wales
were as follows (in jig/g dry matter): Ag (5-150), As (l-l8), B (6-1000),
Ba (150-4000), Cd (1-1500), Co (2-260), Cr (20-40,615), Cu (52-11,700),
Hg (0.1-56), Mn (60-3861), Mo (2-1000), Ni (10-5300), Pb (15-26,000),
Sn (40-700), V (20-400), and Zn (72-49,000). Selenium concentrations
of sewage sludge are difficult to deduce from published literature
because of the limited number of analyses available. Where excessive
concentrations of one or more trace elements occur in sewage sludges,
the source is probably industrial input. Sludges from strictly
residential communities commonly contain concentrations of Cu in excess
of 500 |ig/g dry matter and Zn in excess of 1000 (ig/g dry matter. The
source of Cu and Zn in residential sludges is most likely contamination
from metal pipes and tanks during conveyance, storage, or treatment.
Trace elements in sludges dissolved by acetic and citric acids and
water vary markedly. No apparent relationship exists between the total
concentration of trace elements in sludge and the amount dissolved by
organic acids or water. This indicates that chemical forms of trace
elements in sludges differ among sludges from different treatment plants.
Trace element concentrations in the aqueous phase of sludges may exceed
those predicted from solubility product considerations indicating that
soluble trace element-organic complexes occur in liquid sludges.
Field and greenhouse studies have demonstrated that yields and
trace element concentrations of higher plants grown on sludge-amended
soils are dependent upon the amount of sludge applied, trace element
composition of the sludge, soil pH, and plant species. Leeks, beets,
potatoes, and carrots grew well on a particular soil which had received
annual applications of sludge (66 m. tons/ha) for as long as 19 years.
Although growth was not adversely affected, the tops of plants grown on
sludge-amended soil absorbed more Cu, Zn, and Ni than tops of plants
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grown on the control soil. Corn plants grown on field soils which
received a total of 166 metric tons of sludge per hectare over a 3-
year period grew well and did not absorb significant concentrations
of Cr, Cu, Pb, Ni, and Hg. Concentrations of Mn, Zn, Cd, and B in corn
leaves and Zn and Cd in corn grain were significantly increased by the
sludge applications. Where 105 metric tons of sludge per hectare were
applied to a field soil over a period of 15 years, yield of fodder rape
was unaffected and only the concentrations of Zn in the plant tissue
was increased substantially.
Where sewage sludges have been applied to acid soils (pH < 5.5)
reports in the literature suggest that certain plant species are
damaged by excessive concentrations of available Zn, Cu, or Ni in the
soil. Oat plants were severely damaged when grown on an acid soil
(pH 5.3) treated with 134 m. tons/ha of sludge, but in the same soil
similarly treated with sludge and adjusted to pH 6.8 yield was un-
affected. The sludge applied was unusually high in Ni (6480 M-g/g dry
matter) and growth depression in the acid soil was diagnosed as Ni
toxicity. Nickel absorption by oat plants was decreased by increasing
the soil pH. Yields of rye plants grown on an acid soil which was
treated with sewage sludge at rates of up to 121 m. tons/ha were
significantly reduced. Liming the soil to increase soil pH restored
yields to levels near those of the controls. Concentrations of Zn in
rye increased in relation to sludge application rate, but the increases
were more profound in plants grown on the acid soils. At the higher
application rates on the acid soils, Zn levels in the plant tissue were
greater than those considered to be toxic to many plant species.
In most soils (exceptions are sandy or very acid soils) the
percentage of Ag, Ba, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, and Zn
applied in the form of sludge which moves beyond the depth of tillage
is quite small. Mobility of Mo, As, and Se is also normally quite
limited, but probably exceeds that of the cationic trace elements,
particularly in neutral and alkaline soils. Boron is quite mobile in
most soils and the available information indicates that high percentages
of that applied in the form of sludge will move with water through the
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soil profile. Sludges applied to soils may, therefore, contribute to
B contamination of underground water supplies. Barium, Cd, Co, Cr, Cu,
Pb, Mn, Ni, Zn, Ag, Mo, As, and Se are quite immobile in most soils and
contamination of deep underground water supplies is unlikely. Where
shallow water tables occur beneath sandy soils, the potential for trace
element contamination of underground water supplies from surface appli-
cations of sludge is greatest. Since trace elements are concentrated
in the surface of soil, sediment and solution runoff from sludge-amended
soils could contribute to contamination of surface waters.
Published data show that the surface horizons of sludge-amended
soils are enriched in trace elements. The extent of enrichment is
dependent upon the amount of sludge applied and the trace element
composition of the sludge. Applications of most any sludge equal to
400 m. tons/ha, if mixed uniformly throughout the surface 15 cm, will
add more Cd, Cu, Hg, and Zn to this zone than is normally present in
natural soils.
Molybdenum and Se are absorbed by certain forage crops in amounts
sufficient to cause toxicities to livestock which consume "these forages.
Sewage sludges contain both Mo and Se so depending upon the concentration
in the sludge and the amount applied, it is possible that soils could
become enriched to the extent that forage crops would absorb quantities
of Mo and Se sufficient to be toxic to livestock. Current information
also indicates that certain foods, if grown on Cd contaminated soils,
will accumulate amounts of Cd which are potentially hazardous to humans
and animals. Sewage sludges, particularly those from industrial and
metropolitan areas, may contain rather high amounts of Cd. If these
sludges are applied to soils in modest amounts for a number of years,
the Cd concentrations in soil could become large enough to produce
concentrations in foods grown on the soils which may be toxic.
-------
V- RECOMMENDATIONS FOR FUTURE RESEARCH
1. Fertility of many agricultural soils can be maintained and
possibly improved by finite applications of most sewage sludges, but
in time applications of sewage sludges will produce concentrations of
trace elements in soils which will adversely affect crop productivity,
quality, and possibly the quality of surface and subsurface waters.
The current need is to develop the information necessary to predict
the number of years sludges can be safely applied at modest rates to
agricultural soils. This information needs to be developed for a
variety of soils in various climatic regions and with a variety of
plant species.
2. Diagnostic techniques to predict trace element tolerances of
a variety of plants in relation to trace element concentrations in
sludge-amended soils need to be developed.
3. Feeds and forages accumulate amounts of Mo and Se which are
toxic to animals which consume them.Cadmium is also absorbed by foods
in amounts which may adversely affect the health of humans and animals.
The conditions under which these elements, and possibly other toxic
elements, are absorbed by plants grown in sludge-amended soils need to
be determined. Also research designed to select and breed plant varieties
for tolerance to and exclusion of toxic trace elements should be initiated
4. The manner in which climate may affect plant tolerances to and
accumulations of trace elements in sludge-amended soils needs to be
determined.
5. The effect of trace elements in sludge-amended soils on
metabolic processes and nutritional quality of plants should be
investigated.
6. Sewage sludges should be characterized to determine the
chemical form of the trace elements which occur. Studies should be
designed to determine the fate of trace elements in sludge-amended
soils in relation to the form in which they occur in sludge. These
studies should include the identification of chemical compounds and
their solubility. Considerations should be given to ionic species in
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solution, as well as total concentrations. Organic matter-trace element
studies should identify stable organic soluble and insoluble complexes.
The effect of soil parameters such as redox potentials, pH, and mineral
composition on solubility and immobilization of trace elements in sludge-
amended soils should be examined.
7. Because trace elements may be quite hazardous in minute amounts,
"leakage" of even traces from soils could lead to surface and subsurface
water pollution. The movement and distribution of trace elements in
sludge-amended soil profiles in relation to soil chemical and physical
properties need to be determined. These studies should be designed to
identify soluble and insoluble forms which are retained in soils and
strata above the water table, to establish the rate of movement to
underground aquifers and water supplies in relation to soil properties,
and to determine the conditions under which trace elements are removed
from sludge-amended soils by erosion and volatilization.
8. The influence of trace elements in sludge-amended soils on
microbial populations, activity, and processes should be evaluated.
9. Published data suggest that the response of a particular trace
element in soil will depend upon the concentrations and kinds of other
trace elements as well as other elements present in the substrate.
Since sludges contain a variety of trace elements in concentration
ratios different from those in natural soils, studies designed to
evaluate the effects of trace element interactions on soil chemical
properties, plant response and composition are needed.
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ACKNOWLEDGMENTS
The author is grateful to Dr. Mary Beth Kirkham, Ultimate Disposal
Research Program, Environmental Protection Agency, Cincinnati, Ohio,
for her most thorough review and helpful suggestions for improvement
of the manuscript. Thanks are also due Mr. Michael Elderman, Editor,
College of Biological and Agricultural Sciences, University of Cali-
fornia, Riverside, who edited the manuscript and Ms. Joyce Thompson,
Secretary, Department of Soil Science and Agricultural Engineering,
University of California, Riverside, who typed the manuscript.
Gratitude is also due Professor Parker F. Pratt, Chairman, Department
of Soil Science and Agricultural Engineering, University of California,
Riverside, who encouraged the author to pursue the study.
97
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BIBLIOGRAPHIC DATA 1- Report No.
SHEET EPA-6TO/2-71t-005
3. Recipient's Accession No.
I. Title and Subtitle
FATE AND EFFECTS OF TRACE ELEMENTS IN SEWAGE SLUDGE WHEN
APPLIED TO AGRICULTURAL LANDS—A LITERATURE REVIEW STUDY
>. Report
6.
7. Author(s)
A. L. Page
8. Performing Organization Kept
No.
9. Performing Organization Name and Address
Department of Soil Science and Agricultural Engineering
University of California
Riverside, California 92502
10. Project/Task/Work Urn
1620^-3/21 ACJ-12
11. Contract/Grant No.
12. Sponsoring Organization Name and Address
Advanced Waste Treatment Research Laboratory
National Environmental Research Center, EPA
Cincinnati, Ohio k-5268
13. Type of Report & Period
Covered
14.
15. Supplementary Notes
16. Abstracts Uses of As, Ba, B, Cd, Cr, Co, Cu, Pb, Mn, Hg, Mo, Ni, Se, Ag, Sn, V, and Zn
are reviewed. Total concentrations of trace elements in sewage sludges vary widely.
Ranges are reported for sludges from approximately 300 treatment plants from different
regions in the U.S.A., Canada, Sweden, England, and Wales. No apparent relationship
exists between the total concentration of trace elements in sludge and the amount dis-
solved by organic acids or water. Field and greenhouse studies have demonstrated that
yields and trace element concentrations of higher plants grown on sludge-amended soils
are dependent upon the amount of sludge applied, trace element composition of the
sludge, soil pH, and plant species. In most soils the percentage of Ag, Ba, Cd, Co,
Cr, Cu, Hg, Mn, Ni, Fb, Sn, and Zn applied in the form of sludge which moves beyond
the depth of tillage is quite small. Mobility of Mo, As, and Se is normally limited.
Boron is mobile in most soils. Application of most sludges at a rate of hOO m. tons/h£
if mixed uniformly throughout the surface 15 cm will add more Cd, Cu, Hg, and Zn than
is normally present in natural soils. 107 references.
17. Key Words and Document Analysis. 17a. Descriptors
Metals, trace elements, sewage, sludge disposal, land reclamation, land utilization,
industrial wastes, molybdenum, manganese, barium, copper, zinc, nickel, cadmium, coball
tin, chromium, lead, vanadium, boron, mercury, arsenic, selenium, silver, potatoes,
carrots, oats, beets, corn, rye, spinach, wheat, soil fertility, fertilizers, irriga-
tion, crops, farm crops, forage crops, grain crops, oilseed crops, root crops, tuber
crops, vegetable crops, plant breeding, plant growth, plant nutrients, plant nutrition,
toxic tolerances, ground water, water quality.
17b. Identifiers/Open-Ended Terms
Heavy metals, toxic elements, trace metals, trace inorganics, micronutrients, micro-
elements, sewage sludge, sewage effluent, agricultural land, urban wastes, soil con-
ditioner, leeks, fodder rape, turnips, fescue, trace element tolerance of plants, crop
yield, crop productivity, crop quality, sludge application rate, soil pH, drainage
water, chemical and biological transformation of trace elements in sludge, long-term
trace element enrichment in soils.
17c. COSATI Field/Group
18. Availability Statement
Release to public
19. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
Page
UNCLASSIFIED
21. No. of Pages
108
22. Price
FORM NTIS-35 IREV. 3-721
98
«U.S.Government Printing Office: 1974 — 757-580/5306
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