vvEPA
United States
Environmental Protection
Agency
Office of Water
Program Operations (WH-547)
Washington, DC 20460
November 1976
430/9-76-013
Water
Application of Sewage
Sludge to Cropland:
Appraisal of Potential Hazards
of the Heavy Metals
to Plants and
AGENCY
DAUAS.tEXAS 75202
X
MCD-33
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EPA REVIEW NOTICE
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not signify
that the contents necessarily reflect the views and policies of
the Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recom-
mendation for use.
NOTES
To order this publication, MCD-33, "Application of Sewage Sludge
to Cropland: Appraisal of Potential Hazards of the Heavy Metals
to Plants and Animals", write to:
General Services Administration (8FFS)
Centralized Mailing List Services
Bldg. 41, Denver Federal Center
Denver, CO 80225
Please indicate the MCD number and title of publication.
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EPA-430/9-76-013
November 1976
APPLICATION OF SEWAGE SLUDGE
TO CROPLAND:
Appraisal of Potential Hazards of the
Heavy Metals to Plants and Animals
By
Council for
Agricultural Science and Technology
Report No. 64
November 15,1976
Prepared at request ot
Office of Water Program Operations
U.S. Environmental Protection Agency
Washington, D.C. 20460
MCD-33
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EPA Comment
This report is one of a series planned for publication by the U.S.
EPA Office of Water Program Operations to supply detailed information
for use in selecting,developing, designing, and operating municipal
sewage sludge management systems. The series will provide in-depth
presentations of available information on topics of major interest and
concern related to municipal sewage sludge management. An effort will
be made to provide the most current state-of-the-art information available
concerning sewage sludge processing and disposal/utilization alternatives,
as well as costs, transport, and environmental and health impacts.
These reports are being prepared to assist EPA Regional Administrators
in evaluating grant applications for construction of publicly owned
treatment works under Section 203(a) of the Federal Water Pollution
Control Act as amended. They also will provide designers, municipal
engineers, environmentalists and others with detailed information on
municipal sewage sludge management options.
Harold P. Cahill, Jr., Director
Municipal Construction Division
Office of Water Program Operations
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ABSTRACT
This report examines the present state of knowledge regarding the potential effects
on agricultural crops and animals by heavy metals in sewage sludges applied to cropland,
as well as some consideration of possible groundwater and surface water contamination.
Other potential effects associated with land application of sewage sludge are not addressed
in detail.
The potential effects of metals in sewage sludges applied to cropland are discussed
within a national perspective based upon the volume of sludge being produced (present and
projected), the concentrations of heavy metals in sludges, the total acreage of cropland
potentially affected and resulting impacts on the crops grown. The problem is also
addressed in terms of its localized variability, emphasizing the differences in observed
effects as dependent upon the characteristics of the sludge applied, the application site
characteristics, the method, rate and duration of application and other agricultural
management practices (such as pH control), the particular metal of concern, and the crops
and animals involved. Various approaches that could be used singly or in combination to
reduce the potential impacts are discussed.
As a current state-of-the-art report, recent research results are summarized and
the many gaps in data and understanding are identified. Where possible, the importance
of missing data is indicated. The report addresses some of the problems associated with
monitoring metals concentrations in sludge, soil and plant tissues as well as with
determining toxicity under widely varying circumstances.
The report concludes that the overall impact of sewage sludge use on agricultural
practices is very small. Even if all the sewage sludge currently produced were applied
to cropland, the actual acreage affected would still be very small and would continue to
be so even with the anticipated increase in sludge production after full implementation of
P.L. 92-500. Nevertheless, in certain localities (e.g., the Northeast) the percentage of
cropland affected could be quite significant. The report further concludes that many
metals are probably not a significant potential hazard, either because they are generally
present in low concentrations, are not readily taken up by plants under normal conditions,
or are not very toxic to plants and/or animals.
Two unanswered questions are identified as crucial in determining the potential
hazards of applying sewage sludges to croplands. First, and possibly most important to
determining hazards to humans, what percentage of an individual's diet is composed of
foods affected by heavy metals from sewage sludge? Second, for determining the relation-
ship between plant uptake and transfer to farm animals as well as to humans (about which
relatively little is known) what are the cumulative effects of repeated applications of
metals in sewage sludges over time?
The committee-prepared report indicates that most heavy metals are susceptible to
control through choice of appropriate application sites, limiting the .sludge application
rate to that required to meet crop nutrient demands, and applying the sludge to well-aerated
soils with pH controlled by sound management practices. Several metals (particularly
Cd, Zn, Mo, Ni, Cu) are labeled as posing a potential serious hazard under certain
circumstances, however, with cadmium presently being the metal of most concern.
Robert K. Bastian
Municipal Construction Division
Office of Water Program Operations
U.S. Environmental Protection Agency
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APPLICATION OF SEWAGE SLUDGE TO CROPLAND:
APPRAISAL OF POTENTIAL HAZARDS
OF THE
HEAVY PETALS TO PLANTS AND ANIMALS
Council for
Agricultural Science and Technology
Report No. 64
November 22 , 1976
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COUNCIL FOR AGRICULTURAL SCIENCE AND TECHNOLOGY
Member Societies
American College of
Veterinary Toxicologists
American Dairy
Science Association
American Forage and
Grassland Council
American Meteoro-
logical Society
American Phytopathological
Society
American Society for
Horticultural Science
American Society of
Agricultural Engineers
American Society of
Agronomy
American Society of
Animal Science
Association of Official
Seed Analysts
Council for Soil Testing
and Plant Analysis
Crop Science
Society of America
Poultry Science
Association
Rural Sociological
Society
Society of
Nematologists
Soil Science Society
of America
Southern Weed Science
Society
Weed Science
Society of America
Headquarters Office: Agronomy Building,
Iowa State University, Ames, Iowa 50011
Telephone 515-294-2036
-i-
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TASK FORCE MEMBERS
Leo M. Walsh (Chairman of the task force), Department of Soil Science,
University of Wisconsin at Madison
Dale E. Baker, Department of Agronomy, Pennsylvania State University
Thomas E. Bates, Department of Land Resource Science, University of Guelph
Fred C. Boswell, Georgia Agricultural Experiment Station
Rufus L. Chaney, Agricultural Research Service, U. S. Department of Agriculture
Lee A. Christensen, Economic Research Service, U. S. Department of Agriculture
James M. Davidson, Department of Soil Science, University of Florida
Robert H. Dowdy, Agricultural Research Service, U. S. Department of Agriculture
Boyd G. Ellis, Department of Crop and Soil Sciences, Michigan State University
Roscoe Ellis, Department of Agronomy, Kansas State University
Gerald C. Gerloff, Department of Botany, University of Wisconsin
Paul M. Giordano, Soils and Fertilizer Research Branch, Tennessee Valley
Authority
Thomas D. Hinesly, Department of Agronomy, University of Illinois
Sharon B. Hornick, Agricultural Research Service, U. S. Department of Agricul-
ture
L. D. King, Department of Soil Science, North Carolina State University
Mary Beth Kirkham, Department of Agronomy, Oklahoma State University
William E. Larson, Agricultural Research Service, U. S. Department of
Agriculture
Cecil Lue-Hing, Metropolitan Sanitary District of Greater Chicago
S. W. Melsted, Department of Agronomy, University of Illinois
Harry L. Motto, Department of Soils and Crops, Rutgers University
W. A. Norvell, Department of Soil and Water, Connecticut Agricultural Ex-
periment Station
A. L. Page, Department of Soil Science and Agricultural Engineering, Uni-
versity of California at Riverside
James A. Ryan, Municipal Environmental Research Laboratory, U. S. Environmental
Protection Agency
-ii-
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R. P. Sharma, Department of Veterinary Science, Utah State University
Robert H. Singer, Central Kentucky Animal Disease Diagnostic Laboratory
R. N. Singh, Division of Plant Sciences, West Virginia University
Lee E. Sommers, Department of Agronomy, Purdue University
Malcolm Sumner, Department of Soil Science, University of Wisconsin
Jack C. Taylor, Bureau of Veterinary Medicine, Food and Drug Administration
John M. Walker, Region 5, U. S. Environmental Protection Agency
-iii-
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FOREWORD
On June 3, 1976, a proposed EPA technical bulletin entitled "Municipal
Sludge Management: Environmental Factors" was published in the "Federal
Register" for public comment. During the development of this document by an
interagency workgroup, considerable concern and conflicting opinions were
expressed regarding the merits and potential hazards of applying sewage sludge
to agricultural lands. The fate of heavy metals and other potentially toxic
elements in sludge in terms of soil contamination and the uptake of these
elements by crops has been expressed as one of the most serious potential
problems.
As a possible aid in addressing questions concerning heavy metals, EPA
requested that CAST constitute a task force to review the most recent research,
especially field research, on the application of sludge to cropland and to
prepare a consensus statement on the current understanding of the relation-
ships among the metals applied in the sludge, the chemical and physical pro-
perties of the soils, the soil and crop management practices, and the plant
growth and uptake of these metals by plants. The report emphasizes these sub-
jects. Implications concerning animal health are dealt with to some extent
but not in depth. Possible problems connected with the presence of industrial
organic compounds, pathogens, and viruses are not considered.
The report that follows was prepared by a group of 30 scientists, most
of whom have been actively engaged in research on the application of sewage
sludge to agricultural land. Members of the task force met in St. Louis from
September 15 to September 17, 1976, and prepared a preliminary draft of the
report. This draft was revised by the chairman of the task force, with
special assistance from Dr. Malcolm Sumner, a member of the task force. The
revised draft was reviewed by each task force member and was then revised
again, edited, and reproduced for transmittal.
-iv-
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CONTENTS
Summary 1
Introduction 5
Assessing the impacts 6
Sludge production 6
Cropland requirements 10
Metal content of crops 11
Controlling the impacts 15
Limiting the rate of application 15
Nitrogen basis 16
Metal basis 17
Phosphorus basis 18
Boron basis 18
Soluble salt basis 19
Accessory criteria 19
Soil properties 19
Drastically disturbed lands 19
Ground-water protection 20
Surface-water protection 20
Crop selection 20
Monitoring 21
Analytical problems 23
Sampling 23
Sample preservation 23
Analysis 23
Hazard of heavy metals and other elements to plants
and animals 24
Elements posing relatively little hazard 24
Manganese, iron, and aluminum 24
Chromium 25
Arsenic 26
Selenium 26
Antimony 27
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Lead 27
Mercury 28
Elements posing a potentially serious hazard 29
Cadmium 29
Copper 32
Molybdenum 33
Nickel 34
Zinc 35
References 36
Appendix Tables 43
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SUMMARY
Application of sewage sludge to cropland usually benefits agriculture
because of the value of sludge as a soil conditioner and as a source of many
essential plant nutrients. However, there is also the possibility that the
heavy metals applied in the sludge might be toxic to crops and might increase
the heavy-metal concentrations in edible crops sufficiently to have deleter-
ious effects on animals and humans. This report summarizes current knowledge
on plant uptake of heavy metals from sludge-treated soils and the implications
for the food supply.
At present, only 25% of the sludge produced is applied to land, and not
all of this land is used for production of edible crops. Economic and en-
vironmental considerations, however, may increase substantially the percent-
age of the sludge applied to cropland in the future. At the same time, in-
creases in sewered population and upgrading of treatment plants will result
in increases in the total amount of sludge available.
If all the sludge produced in the United States were to be applied to
cropland at a rate suitable for purposes of nitrogen fertilization, the es-
timated proportion of the total 1970 cropland required to accept the sludge
would be less than 1%. The proportion of the cropland required could in-
crease to 2% by 1985. This land requirement is relatively small, and the
nationwide impact would be even smaller because some sludge will always be
disposed of by other means. However, where the population is concentrated
(e.g., the Northeast), the ratio of sludge produced to available land ex-
ceeds the national average. In New Jersey, for example, about 27% of the
cropland would be required in 1970, and 55% would be required in 1985. Thus,
in localized areas the amount of land available for sludge application could
be a limiting factor.
Semiquantitative estimates indicate that application of all available
sludge to cropland would not appreciably increase the total amount of heavy
metals in crops harvested in the United States. However, significant amounts
of some heavy metals might enter the food supply over a period of several
decades. This eventuality could be largely circumvented by designating
certain lands as "sludge farms" on which repeated applications would be made.
The limited area of land on the sludge farms could be properly managed more
easily than could the much larger area needed if the sludge were applied in
small quantities on many farms. In general, the increase in metal content of
plants is greater from the initial sludge application than from subsequent
applications. The long-term impact of repeated applications of sludge on
metals in the food supply could be substantially reduced by growing corn and
other selected crops harvested for their edible seeds or fruits in place of
forages or leafy vegetables. On the other hand, in areas in which the pro-
duce from sludge-treated land constitutes a large part of the diet, accumu-
lations of some metals may pose a hazard. Industrial pretreatment of waste-
water from highly industrialized areas could decrease substantially the
heavy-metal contents of sludges, and this would considerably reduce the
hazards associated with use of the sludges.
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Several criteria, including the nitrogen content, phosphorus content,
and heavy-metal content, may be used in determining the quantities of sludge to
apply. If sludges are not excessively high in heavy metals, the applications
might be oased initially on the quantities needed to supply the crop with
adequate nitrogen or phosphorus and, with time, on permissible metal levels
in the soil. In this way, the life of the application sites would be extended,
and the food supply would be protected.
Suggestions have been made to limit the application of metals in sewage
sludge to land on the basis of (1) a "zinc equivalents" equation which attributes
to nickel and copper a certain toxicity to plants relative to that of zinc and
which assumes that the several toxicities are additive; (2) a zinc-to-cadmium
ratio which presumes that zinc will become toxic to plants before excessive
levels of cadmium can accumulate in the plants; and (3) the cumulative amounts
of the metals supplied. Each of these methods has its limitations. None of
the methods, if used alone, is universally applicable.
The impact of heavy metals in sludges on plants, animals, and humans may
be limited by using rational management methods intelligently. When sludge
is applied to land, special attention must be paid to good management of the
site. For example, if the soil is allowed to become acid, the solubility of
a number of the heavy metals increases, and this could result in their toxicity
to plants and in unnecessary accumulation of some of these metals in the food
supply. Moreover, adequate steps must be taken in site management to ensure
the protection of both ground water and surface water from contamination.
The impact of heavy metals in sludges applied to cropland can be reduced
considerably by proper selection of the crops. The benefits of growing non-
edible (fiber) or subsequently processed crops such as sugar beets and sugar-
cane are obvious. In addition, however, considerable flexibility can be achieved
by proper selection of edible crops. For example, the entry of heavy metals
into the seeds of some crops is limited, and the potential hazard can be reduced
by harvesting only the grain for consumption. In general, leafy vegetable
tissues accumulate higher levels of heavy metals than do grain crops.
The heavy metals and other potentially toxic elements present in sludges
can be divided into two categories, based on whether or not they present a po-
tentially serious hazard to plants, animals, or humans. This subdivision
assumes that correct management practices are implemented at the application
site. (The classification used here applies to sludge-borne metals that enter
plants through the roots and not to metals that may be ingested directly by
grazing animals from sludge present on plant foliage or on the soil surface.)
Manganese, iron, aluminum, chromium, arsenic, selenium, antimony, lead,
and mercury pose relatively little hazard to crop production and plant accumu-
lation when sludge is applied to soil because all either have low solubility
in slightly acid or neutral, well-aerated soils or, as with selenium, are
present in such small amounts that the concentration is low in soils. As a
result, the availability of these elements to plants is relatively low, and
little uptake by plants occurs. Even though many sludges, particularly those
from tertiary treatment plants, contain considerable quantities of iron and/or
aluminum, these elements will not pose a problem provided that the application
site is well managed. In addition to having low solubility in soil, chromium
and lead are not readily taken up by plants, and this also limits their entry
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into the food supply. Addition of sludge to soil seldom increases the chromium
concentration in plant tissue; however, because there is evidence that chromium
may be deficient in the diets of animals and humans, such small increases in
concentration of chromium in plants as might result from application of sewage
sludge are not to be viewed with alarm. Most sludges are relatively low in mer-
cury, and very little increase in mercury concentration in plants ₯a,s resulted
from sludge application. Considerable quantities of arsenic can be^'added to
soil in the form of sludge; but, because most plants tend to exclude arsenic
from their aerial tissues, little hazard arises from this element. In the case
of selenium, very few reports are available to indicate the quantities likely to
be applied to land in sludge. Data now available indicate that selenium does
not present a hazard. In some cases it is deficient in animal diets, and so
somewhat elevated levels in plant tissue could be an advantage. Research is
lacking on antimony, but on the basis of present evidence antimony is unlikely
to be a potential hazard to plants or animals.
The remaining heavy metals cadmium, copper, molybdenum, nickel, and
zinc can accumulate in plants and may pose a hazard to plants, animals, or
humans under certain circumstances. Because of the potential problems asso-
ciated with these elements, they will be dealt with in greater detail than the
preceding group which poses less hazard.
Cadmium is a nonessential element which can be a serious hazard to animals
and humans if dietary levels are increased substantially. Median concentrations
of cadmium in sludge are low, but some sludges contain appreciable quantities
of cadmium. The chemistry of cadmium in soil is not well understood, but its
lability in soil is reduced by organic matter, clay, hydrous iron oxides, high
pH, and reducing conditions. Annual cadmium application rates, soil pH, and
crop species and varieties have a major influence on the cadmium concentra-
tion in plant tissue. Many crops may contain undesirable concentrations
of cadmium in their vegetative tissues without showing symptoms of cadmium
toxicity. The literature on cadmium is replete with seemingly contradictory
findings which no doubt result from incomplete knowledge of the systems and
reactions involved. The following management options are, nevertheless,
available to limit cadmium accumulation in the food supply to a relatively low
level on sludge-treated land: (1) maintain soil pH at or above 6.5; (2) grow
crops which tend to exclude cadmium from the whole plant or from reproductive
tissue; (3) apply low annual rates of cadmium, and use sludges which have a
low cadmium concentration; and (4) grow nonedible crops. The last option may
be useful in instances in which problems have occurred. Because the greatest
detrimental impact of applying sludge to agricultural land is likely to be
associated with the cadmium content of the sludge, the potential for limiting
the entry of cadmium into the sewage system and methods for removal of cadmium
from sludge prior to application to the soil are worthy of investigation.
Copper, although essential to plants, can become toxic to them at high
concentrations. Sludges often contain appreciable levels of copper, but
application of sludge to soil results in only slight to moderate increases
in the copper content of plants. In general, animal diets are deficient in
copper; hence, slightly elevated concentrations in animal feeding could be
advantageous. Under good management practices, copper in sludges will
seldom be toxic to plants and should not present a hazard to the food supply.
Copper toxicity in animals would be expected to occur only when copper tox-
icity is severe in the plants used as feed.
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Molybdenum is not particularly toxic to plants, even when applied at rela-
tively high levels. As a result, molybdenum may accumulate in plants at con-
centrations sufficient to cause molybdenosis in ruminant animals without prior
warning from plant behavior. The recommended practice of maintaining the soil
pH at 6.5 or higher at sludge application sites results in greater solubility
and availability of the molybdenum than would occur at lower pH values. However,
since sludges are usually very low in molybdenum, it is doubtful that molybdenum
in sludge would present a serious hazard to the health of grazing animals except
for the unusual circumstances in which forages from sites receiving high-
molybdenum sludge form the major part of the animal diet.
Nickel is not essential to plant growth but seems to be required for
poultry. Sludges often contain substantial quantities of nickel, which appears
to be more readily available from sludges than from inorganic sources. Never-
theless, toxicity of nickel to plants occurs only on acid soils. If the soil
pH is maintained at 6.5 or above, nickel should not cause toxicity to plants
or pose a threat to the food supply.
Zinc, an essential element for both plants and animals, is often found
in sludge at relatively high concentrations. Additions of sludge to soil may
cause substantial increases in the zinc content of plants, but toxicity seldom
occurs. Many animal diets are deficient in zinc, and a wide margin of safety
usually exists between normal dietary intakes of zinc and those that produce
toxicity in birds and animals. Slightly elevated levels of zinc in plants
may, therefore, be regarded as beneficial. In general, if the pH of sludge-
treated soils is maintained at 6.5 or greater, zinc should not be a hazard to
plants or to the food supply unless exceptionally high amounts are added in
the sludge.
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-5-
INTRODUCTION
At present, disposition of most sewage sludge is made in landfills and
lagoons, by incineration and dumping in the ocean, and by application to land.
Applications to land include those for purposes of disposal, reclamation of marginal
or drastically disturbed land, and improvement of cropland. Because of environ-
mental and economic considerations, particularly those associated with incin-
eration, application of sewage sludge to land often appears to be the most
feasible method of disposition.
Several beneficial effects may result from application of sludge to land.
Since sludge contains considerable quantities of organic matter, it acts as
a soil conditioner. When applied at high rates, it is effective in improving
the physical properties of marginal or drastically disturbed lands and in
supplying the plant nutrients such areas almost invariably need. When applied
to cropland, sludge has the same beneficial effects in smaller degree. Even
though the nutrient concentrations in sludge are low, sludge can be applied
at rates which will supply all the nitrogen and phosphorus needed by most crops.
Based on current fertilizer prices, the nutrient value of sewage sludge ranges
from 15 to 30 dollars per metric ton on a dry-weight basis.
Since sewage sludge is a low-analysis material, the cost of transportation,
handling, and application may place sludge at an economic disadvantage in com-
parison with high-analysis, commercial fertilizers if the distance of transport
is great. On the other hand, projected natural gas shortages and increased
production costs will probably keep fertilizer prices relatively high and may
maintain sludge as an economically attractive source of nutrients. In addi-
tion to supplying significant quantities of most of the essential plant nutrients,
sludges may increase the concentration in plants of certain elements which
are at or near deficiency levels for animals. For instance, animal diets are
often deficient in trace elements such as zinc, copper, nickel, chromium, and
selenium. Crops grown on sludge-treated land usually contain slightly elevated
contents of some of these nutrients. Application of sludge to land may thus
improve the quality of feeds and forages used for animal consumption.
On the other hand, there are also several problems or potential hazards
associated with application of sludge to land. These include public acceptance,
odor, pathogens, parasites, contamination of surface or ground waters, toxicity
to plants, and increased concentration of potentially toxic elements in the
food supply.
Long-term soil contamination, toxicity to plants, and accumulation of toxic
elements in the food supply are thought to be the most serious potential problems
resulting from application of sludge to cropland. Since conflicting opinions
are held among scientists and within regulatory agencies regarding these issues,
the principal objective of this report is to summarize current research infor-
mation on the impact of heavy metals in sewage sludge on crop productivity,
the metal content of plants, and the consequences for livestock that consume
these plants. Principal emphasis throughout is on low rates of application
of sludge commensurate with meeting the nitrogen fertilizer requirements of
the crops. Additional objectives are to review the factors which influence up-
take, translocation, and accumulation of potentially toxic elements by plants.
Plant factors include differences in selectivity among plant species and varie-
ties and plant parts. Soil factors include pH, content of clay and sesquioxides,
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cation-exchange capacity, redox potential, and texture. As long as the toler-
ance for heavy metal addition to cropland is not set at zero, better management
decisions can be made for the application of sludge if the underlying plant
and soil factors which affect accumulation of these metals in plants are well
understood.
The interpretations presented are, of course, based on the data now avail-
able. As more information is obtained, understanding will be improved, and
more specific interpretations can be developed for different circumstances
and different sewage sludges.
ASSESSING THE IMPACTS
It is important to maintain a reasonable perspective of the potential
impact of heavy metals and other potentially toxic elements in sludges
applied to cropland. The analysis presented in this report overestimates
the impacts. The analysis is based on the assumptions that (1) all sludge
is applied to cropland, (2) the area of land required to accept the sludge is
relatively high because the rate of application of the sludge is not in
excess of the amount needed to meet the nitrogen fertilizer requirements of
the crop, and (3) all sludge-treated land is used to produce crops for food
or feed. Qualifying explanations are then presented as an aid to developing
qualitatively realistic and reasonable interpretations of the numerical esti-
mates .
In this portion of the report, we develop first some estimates of sludge
production under certain assumptions. Then we estimate the amounts of cropland
required to accept the sludge. Then we estimate the background levels of cer-
tain metals in crops and the increases in the metal content of these crops due
to application of sludge. Selected for special consideration are cadmium, a
metal for which an increase in crops is undesirable, and zinc, a metal for
which an increase in crops could be desirable.
Sludge Production
Table 1 gives the human population and sludge production for a densely
populated state (New Jersey), for an agricultural state (Illinois), and for
the United States. Included also are estimates of the cropland that would be
needed if all sludges were applied at annual rates to supply the nitrogen re-
quirements of the crops. Reference to these figures on cropland requirements
will be made in the next section. Analogous data by states are given in
Appendix Tables 1 and 2.
Sludge production in the United States is influenced by many factors.
Basic to any estimation are the present and projected numbers of people served
by municipal sewers. The portion of the population served by sewers is es-
timated to be 67% in 1970 and 75% by 1985. On the basis of population estimates
of 204 million people in 1970 and 235 million in 1985 (Water Resources Council,
1972), the sewered population will increase from 135 million in 1970 to 176
million in 1985.
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Production of sludge on the dry-weight basis per person per day by the
sewered population is estimated at 0.055 kg for primary sludge, 0.091 kg for
combined primary and secondary sludges (Farrell, 1974), and 0.11 kg for com-
bined primary, secondary, and tertiary sludges. The corresponding figures on
an annual basis are 20, 33, and 40 kg. Implementation of advanced wastewater
treatment increases sludge production by additional removal of suspended and
dissolved solids. The type of sewage treatment employed may thus have great-
er impact on sludge production than will increases in population. Production
of municipal sludge in the United States in 1970 is estimated at approximately
3.6 million metric tons on the dry-weight basis (Appendix Table 1). With
projected improvement of wastewater treatment, sludge production is estimated
to increase to 7.3 million metric tons per year by 1985 (Appendix Table 2).
Production of sludge would be increased still further by pretreating combined
sewer overflows to remove 50% of the biological oxygen demand.
The heavy-metal content of sewage sludges, which is of principal concern
in this report, is a consequence of the affinity of the organic material in
the sludge for the metals and the presence of the metals in the wastewater from
which the sludge is developed. The most obvious way to reduce the level of
metals that might enter the food supply through application of sludge to crop-
land is to reduce the amount of metals entering the sewage by pretreating in-
dustrial wastes. Although metals will always be present in sludge as a result
of their natural content in food and human wastes, leaching from plumbing sys-
tems, surface runoff, etc., an effective industrial pretreatment program could
significantly reduce the concentrations in many sludges. Principal emphasis
could reasonably be placed on metals which could present a potential hazard
to animals and humans.
A specific case in point is the experience of the Metropolitan Sanitary
District of Greater Chicago, where an industrial pretreatment ordinance has
been in effect since 1969. To evaluate the effects of this ordinance, the
metal content of anaerobically digested sludges from the Calumet Plant which
were placed in storage lagoons before 1969 were compared with sludges from
this same plant through the summer of 1974 (Table 2). It is clear from the
data that the metal content of the sludge was lower after passage of the ordi-
nance than before. The concentrations of metals of greatest environmental con-
cern (nickel, copper, lead, and cadmium) were reduced in the digested sludges
by 92, 81, 73, and 72%, respectively, during the period from 1969 to 1974. Data
for 1976 are similar to those for 1974, which indicates that this level of in-
dustrial pretreatment has reached its limits of effectiveness for this plant.
Although an industrial pretreatment program can effect substantial reduc-
tions in the metal content of sludges in industrial areas, it must be emphasized
that each sewage treatment plant or the area served by one has an indigenous
concentration for all metals which may not be further reduced by more stringent
industrial pretreatment. For example, Chicago's industrial waste control or-
dinance has had no appreciable effect on the metal content of sludge from the
Hanover Park Plant, which serves a nonindustrial area. Digested sludges from
this plant had a cadmium content of 60 ppm in 1969 and 56 ppm in 1975. The
cadmium content of the Hanover Park sludge before and after the 1969 ordinance
is similar to that of the Calumet sludge in 1974.
An industrial pretreatment program implies the existence of effective
monitoring and enforcement procedures. In view of the political ramifications
-------
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10
of these procedures, the effectiveness of an industrial pretreatment program
cannot be generalized from one area to another unless the monitoring and en-
forcement are federally mandated and implemented.
Tertiary treatment of wastewater may entail chemical precipitation of
phosphate and coagulation of additional solids with lime, ferric chloride,
or alum. Tertiary treatment could remove additional metals, but only a
slight increase would be expected since the secondary sludge already contains
most of the metals found in the influent. Since tertiary treatment generates
additional sludge, the metal concentration in the combined primary, secondary,
and tertiary sludges probably will not change appreciably from the concentration
in the combined primary and secondary sludge before advanced wastewater treat-
ment. Care is needed to ensure that the sources of ferric chloride and alum
used in tertiary treatment do not contribute significantly to the content of
metals in the sludge. Some sources of these chemicals contain appreciable
levels of heavy metals.
Finally, because in this report the nitrogen content of sludge will be
used as a basis for calculating the appropriate quantity of sludge to apply
to cropland, comment on the nitrogen content is appropriate. The processing
to which the sludge is subjected has a marked influence on the nitrogen content,
particularly the available nitrogen, which represents the portion of the total
nitrogen that is available to plants. Available nitrogen is the inorganic nitro-
gen plus the mineralizable portion of the organic nitrogen. The total nitrogen
content of a liquid sludge on a dry-matter basis may decrease from 6% to less
than 3% after composting, with little change in metal content. To provide equal
amounts of total nitrogen, therefore, the amount of composted sludge required
would be more than twice that of liquid sludge, on a dry-matter basis, resulting
in the addition of more than twice as much of the metals per unit area and
affecting less than half as much cropland.
Cropland Requirements
The disposition of municipal sewage sludge in the United States in 1975
has been estimated to be 15% in the ocean, 25% in landfills, 35% by inciner-
ation, and 25% by application to land (Bastian, 1976). Environmental regu-
lations and economic forces are placing restrictions on all disposal methods.
Elimination of ocean dumping and pipe discharges in 1981 will make available
an increasing amount of sludge for disposition in other ways. The greatest
relative increase is expected to occur in application to land.
Increasing attention is being given to the application of sewage sludge
to cropland for use in agricultural production because the sludge is indeed
a valuable resource for this purpose. This section of the report contains
estimates of cropland required to accept all the sludge at rates of application
sufficient to meet the nitrogen requirements of the crops.
Gross acreage requirements for agricultural utilization of municipal sludges
can be estimated on the basis of sludge production, generalized application
rates, and assumed values for the average nitrogen percentage in the sludge.
If the sludge contains 1% nitrogen, the proportion of the total U.S. cropland
required to accept all U.S. sludge at rates low enough to provide for efficient
-------
11
use of the nitrogen by the crops may be estimated at 0.24% in 1970 and 0.49%
in 1985. Cropland requirements on this basis thus seem negligible. Even so,
the estimates of cropland requirements are inflated because the figure used
for the nitrogen percentage in the sludge is low. Moreover, the
assumption is made that the nitrogen percentage in the sludge will be the
same in 1985 as in 1970. This assumption also tends to overestimate the
cropland requirement in 1985. As municipalities increasingly adopt tertiary
treatment of wastewater, the amount of sludge produced will increase, but
the nitrogen percentage in the sludge will decrease because the tertiary
sludge contains a lower percentage content of nitrogen than do the primary
and secondary sludges.
Estimates of the type given in the preceding paragraph do not tell the
whole story, however, because the centers of greatest sludge production are
the major metropolitan areas. Population centers in the Northeast, for
example, are not in close proximity to extensive agricultural land. If the
sludge produced in such areas is to be applied close to the source, therefore,
the proportion of the total cropland needed for sewage sludge application
will be far above the national average.
Population, sludge production, and cropland estimates are given in Table
1 for a densely populated state (New Jersey), an agricultural state (Illinois),
and the United States as a whole, along with estimates of cropland needed if
all sludges were applied at annual rates to supply the nitrogen requirements
of the crops. The table indicates the variability of cropland needs among states
and the importance of the ratio of sludge production to cropland availability.
Figures by states are given in Appendix Tables 1 and 2.
Another factor of importance in application of sewage sludge to cropland
is the transportation cost. The limited availability of cropland for appli-
cation of sludge near urban centers increases the distance the sludge must be
transported and the cost of the transportation. Although these costs may be
relatively high, they may nevertheless be considered acceptable in light of
the economic and environmental costs of the next best alternative. It seems
likely, however, that, to save on transportation costs, an appreciable propor-
tion of the sludges in such areas will be applied to nonagricultural land near
the municipality.
Metal Content of Crops
As a basis for assessing the potential impact of sludge on metals in crops,
average background levels of cadmium and zinc (from such sources as native
levels of the metals in soil, additions of phosphate fertilizer, and air
pollution) were estimated for most agronomic crops in Illinois, New Jersey,
and the United States. These values are found in Table 3.
The estimates of the increases in cadmium and zinc content of the crops
due to application of sludge were based on the assumption that the recovery
of these metals applied in the sludges would not exceed 1 and 3%, respectively.
This approach, based on field data from Wisconsin (Appendix Table 3), was
used to calculate the values in Tables 4 and 5. Crop recovery of metals varies
with many factors, including the pH and cation-exchange capacity of the soil,
crop species, plant part harvested, and number of years of cropping over which
-------
12
Table 3. Background levels of cadmium and zinc in crops grown in Illinois, New
Jersey, and the United States
Crop
Corn grain
Small grain
Soybean grain
Forages
TOTAL :
Corn grain
Small grain
Soybean grain
Forages
TOTAL:
Corn grain
Small grain
Soybean grain
Forages
TOTAL:
Total ,
yield,-7
millions
of metric
tons
31.56
2.23
7.94
3.22
0.17
0.08
0.06
0.28
146.50
75.88
41.43
120.70
2/
Cadmium
Zinc'/
Mg per kg Total kg
of crop in crop
Illinois
0.05
0.1
0.1
0.5
New Jersey
0.05
0.1
0.1
0.5
United States
0.05
0.1
0.1
0.5
1578
223
794
1613
4208
8.6
7.7
5.5
136.4
158.2
7325
7588
4143
60350
79406
Mg per kg Total metric
of crop tons in crop
25
40
25
25
25
40
25
25
25
40
25
25
789
89
199
81
1158
4.3
3.0
1.4
6.9
15.6
3662
3035
1036
3017
10750
Total yields are for 1975 crops (Crop Reporting Board, SRS, USDA); small grains
include oats, barley, and all wheats.
2 /
Based on average cadmium and zinc contents of crops derived from currently available
data. Sources of the metals include natural contents in soils and additions from
fertilizers and other sources.
-------
13
Table 4. Potential impact of the application of sewage sludge on the cadmium content
of crops grown in Illinois, New Jersey, and the United States on the basis
of recovery of the applied cadmium in crops and on the assumption that all
the sludge produced is applied to cropland
Area
Illinois
New Jersey
USA
Sludge
produced,
thousands of
metric tons
197
127
3,602
Total Cd
in sludge ,i'
kg
3,940
2,540
72,040
Background
Cd in crops
presently
grown?./ ,
kg
4,220
160
79,406
Increase in Cd content
in all crops , assuming
1% recovery of Cd applied
in sludge^/
Kg Percent
39.4 1.0
25.4 15.9
720.4 0.9
_L/ Based on an average concentration of 20 mg of Cd per kg of sludge (dry-weight basis)
_2_/ Based on 1975 crop yields and levels of 0.05, 0.1, 0.1, and 0.5 mg of Cd per kg in
corn, soybeans, small grains, and forages, respectively. Values are for the grain
of the grain crops and for the total above-ground parts of the forages.
3/ See Appendix Table 3.
Table 5. Potential impact of the application of sewage sludge on the zinc content of
crops grown in Illinois, New Jersey, and the United States on the basis of
recovery of the applied zinc in crops and on the assumption that all the
sludge produced is applied to cropland
Area
Illinois
New Jersey
USA
Sludge
produced,
thousands of
metric tons
197
127
3,602
Background
Zn in crops
Total Zn presently
in sludge ,±.' grown^.' ,
metric tons metric tons
394 1,160
254 16
7,204 10,750
Increase in Zn content
in all crops, assuming
3% recovery of Zn
applied in sludge "L'
Metric
tons
11.8
7.6
216.1
Percent
1.0
47.5
2.0
_!_/ Based on an average concentration of 2,000 mg of Zn per kg of sludge (dry-weight basis)
2_l Based on 1975 crop yields and levels of 25 mg of Zn per kg in corn, soybeans, and
forages, and 40 mg of Zn per kg in small grains. Values are for the grain of the
grain crops and for the total above-ground parts of the forages.
3/ See Appendix Table 3.
-------
14
the recovery is determined. Nevertheless, the 1 and 3% maximum recovery levels
for cadmium and zinc were not exceeded in the Wisconsin work, in which the soil
pH averaged about 5.5 (Appendix Table 11), even with cropping for several years
after application of the sludge.
The values in Tables 4 and 5 indicate a considerably greater impact of
application of sludge on the metal content of crops in New Jersey than in
Illinois. The reason is that, although the production of sludge in Illinois
in 1970 is estimated to be 56% greater than that in New Jersey (Table 1) , there
is far more cropland in Illinois than in New Jersey. A 16% increase in cadmium
content is estimated for the crops in New Jersey and a 1% increase in cadmium
content for those in Illinois. A 48% increase in zinc content is estimated for
the crops in New Jersey and a 1% increase for those in Illinois. Values for
the United States as a whole are similar to those for Illinois.
The values for cadmium and zinc in Tables 4 and 5 are based on the assumption
that all sludges applied have concentrations of cadmium and zinc slightly above
the 16 and 1,890 ppm median values found in over 200 different U.S. sludges by
Sommers (1976). If the cadmium and zinc values were twice as high in the sludges,
the estimated increases in metal content of the crops would be twice as great
as those given in Tables 4 and 5.
Soil reaction has an important influence on the absorption of heavy metals
by crops from sludge-treated soils. Almost a ten-fold reduction in zinc, cad-
mium, and manganese content may be achieved by liming acid soils (pH 4.5 to 6)
to a nearly neutral condition (pH 6 to 7). Because of this fact, pH control
is recognized as a fundamental requirement for proper management of sludge-
treated soils, and the estimates of heavy-metal uptake by crops in this sec-
tion apply to soils that are in a nearly neutral condition.
The data in Tables 3, 4, and 5, showing the impact of sludge on metal
uptake by crops, are based on estimated levels of metals present in the grain
of grain crops and the total above-ground parts of forages. The total use of
grains for food and industrial purposes as a percentage of total production
has been estimated at 7.5% for corn, 35% for wheat, 28% for barley, and 5% for
oats. The remainder is used for livestock feed, exports, and seed (U.S.
Department of Agriculture, 1971). Therefore, only a minor part of the grain
and none of the forages are used for direct consumption by humans. If humans
consume meat from animals raised on crops grown on sludge-treated soils, the
heavy-metal content will be lower in the muscle meat than in the crops used
as animal feed. In the liver and kidneys, however, the heavy-metal levels may
be above those in the feed.
If the total diet were derived from sludge-treated cropland, the increase
in intake of heavy metals over the background level would thus be greater if
the persons in question were vegetarians than if they consumed some animal
products. In metropolitan areas, where the ratio of sludge production to
available cropland is greatest, there might be a few agricultural producers
whose diet would come mostly from sludge-treated land. Because of the modern
food system, however, the major part of the diet of most of the population
would be derived from areas that have not been treated with sludge. The
excess of metals from sludge-treated soils would thus be diluted with food from
soils that have not been treated.
-------
15
CONTROLLING THE IMPACTS
Limiting the Rate of Application
The quantities of sludge applied to agricultural land will be limited
in many respects by regional agronomic practices. Guidelines proposed
by USDA and various states are based upon fertilizer recommendations for
nitrogen. Nitrogen is the fertilizer element applied in greatest amount to
soils, and it is found in sludge in substantial amounts. Therefore, there
is good reason to base the application of sludge on its nitrogen content.
In addition to application rates based upon the nitrogen fertilizer value
of sludge, constraints have been placed on other constituents in the sludge
which may adversely affect crop productivity or may result in concentrations
in the edible part of the plant which may adversely affect the health of
animals or humans. In Pennsylvania, for example, applications of sludge are
based on the nitrogen requirement of the crop, the nitrogen and heavy-metal
content of the sludge, and the toxicity of the sludge to plants as estimated
by chemical analysis and biological assay (Baker and Chesnin, 1975). The con-
stituents in sludge generally considered to be toxic to plants when they occur
in soils at elevated levels are boron, cadmium, copper, molybdenum, nickel,
and zinc. The tolerance of plants to levels of these elements in soils varies
widely with plant species as well as soil chemical and physical properties.
Consequently, it is not possible to select a single level of an element or
combination of elements which would be suitable for all crops and soils.
Limiting the concentration of potentially toxic metals in the sludge was
one of the first methods suggested for limiting the application of sludge-
borne metals to land. Such a limitation would have the salutary effect of
encouraging industrial pretreatment and other programs which would lower the
concentration of heavy metals in the sludge. Although lowering the heavy-
metal content would improve the acceptability of many sludges for applica-
tion to cropland, the concentration of sludge-borne metals in plants is
related more closely to the total amount of the metals applied than to the
concentration of the metals in the sludge, fertilizer, or other sources.
Thus, a limit on the concentration of metals in sludge would not necessarily
protect plants and animals from the hazards that might result from applying
excessive amounts of metals to land.
Recently, guidelines for maximum permissible metal application have been
developed by several state agencies. These have included recommendations based
upon maximum amounts of single metals which can be applied (Sommers and
Nelson, 1976) and on the maximum amount of zinc, copper, and nickel which
can be applied together. The latter is the so-called zinc equivalent (Zn +
2Cu + 4Ni), where 2 and 4 are coefficients to express the toxicity of copper
and nickel relative to that of zinc. The various alternatives for limiting
sludge application to land based on recent research information and our best
judgment will now be evaluated.
-------
16
Nitrogen Basis
*
Sludges typically contain from 1 to 6% nitrogen (Sommers, 1976; Keeney
et al., 1975), which is partly in inorganic form and partly in organic form.
Generally 30 to 60% of the total nitrogen in anaerobically digested fluid
sludges is present in the ammoniacal (NH+) form, and the remainder is present
in the organic form (King, 1976). If fluid sludges are applied directly to
land, a certain percentage of the ammoniacal nitrogen is lost by volatilization
as ammonia as the sludge dries. The actual amounts of loss vary, depending
upon soil and sludge properties and environmental conditions, but they will
range from about 30% to essentially complete loss. Amounts of this form of
sludge-borne nitrogen which will be available for utilization by plants must
be determined for the conditions under which the sludges are applied. Incor-
poration of fluid sludges below the soil surface by injection or by immediate
incorporation following application minimizes the amount of nitrogen lost by
volatilization.
Nitrogen in organic forms is unavailable to plants and is not lost follow-
ing surface application. In soils, organic nitrogen must undergo minerali-
zation (i.e., conversion from the organic to inorganic state) before it can
be utilized by plants. The rate of this microbially related conversion depends
upon a variety of soil environmental factors such as water content, aeration,
pH, temperature, and level of nitrogen in the inorganic state. Although pre-
cise rates for the various climatic regions are not completely worked out,
the available data indicate that from 15 to 40% of the organic nitrogen is
mineralized in the year of application (Pratt et al., 1973; Keeney et al.,
1975) . Lesser percentages of the remaining nitrogen are mineralized in
succeeding years. So-called decay series have been worked out for a few
regions, and these can be utilized to approximate the proportion of the
nitrogen which will become available each succeeding year. For example, Keeney
et al. (1975) suggest 15% availability in the first year, 6% of the remaining
nitrogen in the second year, 4% in the third year, and 2% in the fourth year.
Generally, the quantities of sludge required to satisfy nitrogen fertili-
zer requirements of crops will range from 5 to 40 metric tons per hectare.
Techniques to compute the quantities of a particular sludge needed to supply
specific amounts of available nitrogen have been worked out (Keeney et al.,
1975; Sommers and Nelson, 1976).
It is well known that nitrogen which leaches below the root zone will be
in the nitrate form, and eventually this nitrate may contaminate ground-water
supplies. For this reason, it is advisable to gear sludge applications to
supply sufficient but not excessive nitrogen for crop needs.
Basing sludge application rates on the needs of the crop will often be a
safeguard in that use of this criterion will limit the application of potentially
toxic heavy metals to levels that are of no concern except for sludges that have
an excessively high content of metals. However, when applications are made
continually to the same tract of land over a long period of time, metals could
eventually accumulate to toxic levels.
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Metal Basis
Metal concentrations in sludges vary over wide limits. Recent information
on the composition of more than 200 sludges from the North Central Region of the
United States has been compiled by Sommers (1976). The literature contains
numerous references which show that, when concentrations of certain metals
build up in soils from application of inorganic salts of these metals, growth of
a wide variety of crops is affected (Baker and Chesnin, 1975; Chaney and Gior-
dano, 1977; Page, 1974). For this reason, some guidelines for the application
of sewage sludge to agricultural land have suggested limits on the quantities of
metals, particularly copper, nickel, zinc, and cadmium, which can be safely
applied.
Early attempts to limit metals applied to soils in the form of sludges
were based upon the zinc-equivalents concept. Briefly, this concept assumes
that toxicities of copper and nickel can be expressed in terms of some multiple
of zinc and that the toxicities of these three elements to plants are additive.
The zinc-equivalents equation was based upon a limited amount of data. Infor-
mation developed since its introduction shows that the toxicity of these ele-
ments generally is not additive and that use of the equation greatly underesti-
mates the amounts of sludge-borne metals which can be safely applied to near
neutral, neutral, and calcareous soils. Furthermore, the equation does not
apply uniformly over a broad spectrum of plant species.
During the past two years, the NC-118 and W-124 Cooperative State Re-
search Service Technical Committees have been working on the development of
suggested maximum rates of metal application to land (Sommers and Nelson, 1976).
They recognize that the maximum safe applications of individual metals may
differ among soils as a consequence of differences in cation-exchange capacity
of the soils and differences in relative toxicity of the various metals. They
have eliminated the concept of additivity of the toxic effects of the metals
that appeared in the zinc-equivalents equation and instead have made sugges-
tions based on the total limits of addition of the heavy metals on an individual
basis. It should be pointed out, however, that the rates of application sug-
gested by these committees cannot be considered definitive and that the rates
are likely to be changed as additional research information becomes available.
To judge from studies of the effects of adding inorganic salts of metals
to soils and studies of soils contaminated with metals from mining and smelt-
ing activities, it is certain that there is a limit to the extent to which
soils can be enriched in heavy metals and still maintain their normal crop
productivity. Data currently available are not sufficient to determine the
maximum amounts of heavy metals that can be tolerated in additions of sludge.
The information at hand strongly suggests that the maximum additions tolerated
will depend upon interactions with other constituents in the sludge and soil.
These interactions will depend upon soil chemical and physical properties and
regional factors such as climate and water quality. The question of maximum
rates of application is complex and cannot be answered with certainty without
additional research.
It has also been suggested that rates of application of sludge should be
limited by the ratio of zinc to cadmium in the sludge. This concept has as
its basis two premises. First, the ratio of zinc to cadmium averages 500 for
parent rocks and 100 for soils, which means that, during weathering, cadmium
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18
has not been lost as rapidly as has zinc. Second, regulation based on the
ratio of zinc to cadmium would result in high enough zinc concentrations in
soil to kill plants before cadmium could accumulate to levels in foods considered
hazardous to animals and humans. More recent research results (Chaney et al.,
1976b; Giordano and Mays, 1976b; Page, 1976) show that this premise often is
not correct and that many plants grown on nearly neutral to calcareous soils
will tolerate high levels of zinc in the soil and will still show an increase
in the concentration of cadmium. Furthermore, at a given ratio of zinc to
cadmium, the concentration of cadmium in plants increases with increasing cad-
mium applications (Appendix Tables 19, 20, and 21). Hence, it seems advisable
to abandon the ratio of zinc to cadmium in sludges as a criterion for limiting
or regulating applications of sludge to soil, especially if the pH is above
6.5. In these soils, cadmium limits can be based solely on annual and total
or "lifetime" rates of application. In acid soils, use of a combination of
the ratio of zinc to cadmium in the sludge and annual and total rates of appli-
cation may be advisable.
If sludge applications are based initially on supplying the crop with ade-
quate nitrogen and safe annual applications of toxic metals and, subsequently,
as metals accumulate with time, on permissible metal levels in soil, the life
of the site will be extended, and the food supply will be protected. The impact
of heavy metals in sludges on plants, animals, and humans may be limited by
using rational management methods intelligently, making adjustments with time
as may be appropriate.
Phosphorus Basis
Sludges generally contain from 1 to 3% phosphorus. If sludge is applied
in amounts sufficient to satisfy the nitrogen requirements of crops, more than
adequate amounts of phosphorus will nearly always be added. The nutrients in
sludge could thus be used more efficiently if the sludge were applied in quan-
tities to meet the phosphorus needs of the crops instead of the nitrogen needs.
This practice, however, would result in a low rate of sludge application, perhaps
1 to 2 metric tons per hectare, and the cost of application would be increased
accordingly.
If sludge applications are based on the phosphorus needs of the crop, the
additions of heavy metals will be even less than those applied if nitrogen is
used as the base. This management option will nearly always require the appli-
cation of supplemental nitrogenous fertilizer to nonleguminous crops.
Boron Basis
Boron may limit the amounts of sludge which can be applied in irrigated
regions. Concentrations of boron in sludges typically range from 100 to 1,000
ppm. If application of sludge causes the concentration of boron in the soil
solution to reach 1 ppm, damage to boron-sensitive crops may occur. In humid
regions and in irrigated regions where the irrigation water is low in boron, the
boron added in the sludge will be diluted below the threshold toxic concentration
and will present little hazard.
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Soluble Salt Basis
Fluid sludges contain a variety of soluble salts. In irrigated arid and
semi-arid regions where the soils and/or irrigation water contain relatively
high concentrations of salts, practices to maintain salinity levels in the root
zone at acceptable levels are required for successful sludge utilization in
agriculture.
Accessory Criteria
Soil Properties
Many soil properties are important in considering the use of sewage sludge
on land. Among these are pH, texture of the surface soil, cation-exchange cap-
acity, organic matter, and profile characteristics. Of these, the pH is per-
haps the most important. Most heavy metals are more soluble under acid condi-
tions than under neutral to alkaline conditions, molybdenum being the main ex-
ception. It is important that the soil pH be maintained at 6.5 or above follow-
ing sludge application.
The cation-exchange capacity of a soil is a reflection of the content of
organic matter and of the nature and content of clay and sesquioxides. The
cation-exchange capacity thus gives an integrated value that relates to the
chemical behavior of a soil. In general, the higher is the cation-exchange
capacity, the more sludge a soil can accept without potential hazards.
Although little information is available, application of sludges to Histosols
(organic soils) does not seem desirable. Organic soils often have low pH values,
high nitrification rates, and high water tables. Application of sludge may re-
sult in increased nitrification and loss of nitrates. Even though organic soils
have high capacities for metal sorption, excessive amounts of these metals may
become available in acid soils.
Care should be exercised not to apply sludges on wet soils with heavy appli-
cation equipment such as tank trucks or tank wagons. The heavy equipment may
compact the soil, causing later problems in tillage and in plant growth. Com-
paction may also enhance runoff. Equipment with large flotation-type tires has
been developed which may reduce this problem.
Drastically Disturbed Lands
Sewage sludge is an excellent soil amendment for renovating drastically
disturbed lands. For plant establishment, it is often desirable to apply
larger amounts of sludge than would be recommended on productive soils. The
sludge will usually raise the pH of acid soil material, improve its physical
properties, and supply nutrients long enough to establish plant growth. If
large amounts of sludge are applied, transport of metals to surface waters may
present a hazard. Because of the wide range of soil materials and landscapes,
recommendations for application of sludges on drastically disturbed lands must
be considered on a site-by-site basis.
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Ground-Water Protection
Although long-term studies have not been completed, those working on the
subject agree that soils readily remove heavy metals from the soil solution and
prevent them from reaching the ground water. Contamination of the ground water
with metals, therefore, is not likely to result from application of sewage
sludge to soils.
Sludge application at rates supplying more nitrogen than the crop requires
on very permeable soils or on soils with water tables or bedrock within a few
feet of the soil surface can result in ground-water contamination with nitrate.
When selecting sites for sludge application, the permeability and drainage of
the soil and the depth of the water table and bedrock should be considered.
Surface-Water Protection
Because heavy metals can be transported in surface runoff waters, good
engineering and soil management practices to limit runoff and sediment transport
are appropriate. Factors affecting runoff include land slope, distance from re-
ceiving waters, rate of sludge application, water content of the sludge, exist-
ing vegetation, soil permeability, and weather conditions. The steeper is
the slope of land receiving sludge and the shorter is the distance to re-
ceiving waters, the greater is the potential for surface-water contamination.
Use of conservation tillage practices and engineering designs available from
the Soil Conservation Service for sloping land will help reduce transport
of metals by erosion and runoff.
Fluid sludges are more prone to loss in runoff shortly after application
than are dried sludges. If surface-applied to cultivated land, fluid sludges
should be worked into the soil as soon as practicable after application. Trans-
port in runoff is a distinct possibility where sludges are applied to frozen
and snow-covered soils.
With fluid sludges low in available nitrogen, which would otherwise be
applied in relatively large quantities on the basis of their nitrogen content,
the amount of any single surface application should preferably be limited to
surface layers no more than 0.8 to 1.2 cm (1/3 to 1/2 inch) in thickness to
avoid undue runoff.
Crop Selection
Crops differ in their ability to absorb heavy metals such as cadmium from
the soil. They differ, moreover, in their tendency to exclude certain metals from
particular organs. In many crops, the seeds contain lower concentrations of most
heavy metals than do the vegetative tissues. Hence, the potential hazard from
heavy metals is reduced if only the grain is harvested. The foliage of pastures
sprayed or surface-treated with sludge may have surface coatings of sludge (Chaney
et al., 1976a). Ingestion of sufficient quantities of such forage by grazing
animals could result in animal-health problems due to heavy metals or other con-
stituents. Thus, in general terms, grain crops present a lesser heavy-metal
hazard to the food supply than do forages, pastures, and leafy vegetables.
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Little or no hazard to the food supply from heavy metals applied in sewage
sludge would be presented by crops that are processed to supply refined sub-
stances such as sugar and distilled alcohol. If absolutely no hazard is to
be permitted from occurrence of heavy metals above the background level, sewage
sludge could be applied only to nonagricultural land or to land used only for
production of crops that are grown for their nonedible products.
Monitoring
When sewage sludge is applied to soil, the heavy metals it contains may be
retained by the soil or removed by erosion. Losses by transport in water moving
downward through the soil are negligible. Uptake by crops is small. The major
part of the metals added normally remains in the upper part of the soil with
which the sludge is mixed. With repeated applications of sludge, therefore, the
content of heavy metals in the soil gradually increases.
The strong retention of the heavy metals by soil is a consequence of their
low solubility. In almost all instances of soils and heavy metals, the
availability of the metal to plants is expected to decrease with time after
application because of reactions the metal undergoes in the soil.
The capacity of soil to react with substances that are added to it is of
great importance where the potentially toxic elements applied in sewage sludge
are concerned. Two general situations may be discerned. With elements such
as aluminum, which may be inactivated merely by pH control, the capacity of any
soil for inactivating the element is infinite as long as the pH is maintained
in the proper range by additions of limestone or otherwise. Aluminum may react
with specific soil constituents as well, but such interactions are not essential
to inactivation as long as proper pH control is practiced. With elements such
as arsenic, which are inactivated by interaction with soil constituents such as
hydrous iron oxides and not by pH control as such, the capacity of the soil to
react decreases with each succeeding application of the element until, in the
limit, no reaction capacity remains. At the limit, the soil will have accumu-
lated considerable arsenic and will be highly toxic to plants. The amount of
arsenic accumulated will depend on the nature of the soil.
Now under investigation is the extent to which the hazard of the metals to
crops and to the food supply increases with cumulative additions of sludge
under different conditions. Further research is needed to clarify the trends
in availability of the various potentially toxic elements that are added to
soils in sewage sludges and to provide some explanation for the trends and for
the differences among soils.
If sludges are applied to cropland at rates sufficient to meet the nitrogen
fertilizer requirement of the crop, the initial addition of heavy metals to
the soil will be small. No measurable detrimental effect of the metals on
the crop is expected, and the heavy metal content of the plants will be in-
creased only a little above the background level normally present in the plants
without sludge addition. In the view of most members of the task force, there
is no hazard at this stage, and monitoring is unnecessary. However, a few mem-
bers consider that some monitoring is needed even when low rates of sludge are
applied.
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If additions of sludge at these low rates were to be repeated indefinitely,
however, all would agree that there would be some time at which monitoring of
soil and plant tissue would be desirable to ensure that the accumulation is not
producing toxic effects on the crop and that the increases in metal content of
the crop are not sufficient to represent a hazard to the use of the crop as
food for animals or humans. Exactly when this time might be cannot be foretold
because too little is known at this stage. There is no question, however, that
periodic monitoring would signal an undesirable build-up of heavy metals before
irreparable damage results. The warning provided by timely monitoring would
enable the operator to introduce corrective measures or, if necessary, to dis-
continue sludge application.
It is to be expected that, as research proceeds, the kind of guidance
needed to develop effective but reasonable monitoring programs will gradually
unfold. The prognosis at present is that little monitoring of soils and crops
would be needed if sludges were monitored, heavy-metal levels were controlled,
and good soil and crop management practices were followed.
If and when agricultural monitoring is necessary, plants are to be re-
garded as the most appropriate evaluator of the system. Analyses of the har-
vested portions of plants at intervals will, in most instances, indicate the
rate of increase of availability of the metal to the plants and will signal
the approach of harmful levels well in advance of permanent damage to either
soil or crop. Interpretations of such analyses must recognize normal seasonal
differences in plant composition and possible sampling errors. As further
toxicological information is obtained, the plant analyses can be interpreted
with increasing precision in terms of potential toxicity of the plants to ani-
mals and humans.
Plant analyses have three main limitations where monitoring of heavy metals
and other toxic elements is concerned. First, although the analyses indicate
the approach of a hazardous level for the crop analyzed, the level attained
may already be toxic to another more sensitive crop. Second, both tops and
roots must be analyzed to diagnose all toxicities. Third, plant analyses
usually cannot be used to indicate the level of soil nitrogen that may lead
to ground-water contamination.
Soil analyses can be used to monitor fields being treated with sludge.
When properly correlated over a wide range of soils and crops, soil tests
can indicate a potential metal hazard for any crop. Such extensive testing
and correlation has not, as yet, been done. Regardless of the rate and fre-
quency of sludge application, soils should always be routinely tested for pH
and available phosphorus and potassium. Proper site management requires that
recommended amounts of limestone and nutrients such as potassium be applied.
Soil analysis can also be used as an index of potential ground-water
pollution.
Because the properties of the soil in the rooting zone of crops vary with
depth, there is always some question about where the samples should be col-
lected and, if samples from different depths are collected and analyzed, how
the results should be interpreted. For agricultural purposes, soil samples
are usually collected from the plowed layer only. Use of the same convention
for monitoring the effects of applications of sewage sludge would have the
advantage that analyses of this layer should indicate the build-up of heavy
metals well in advance of permanent damage.
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Analytical Problems
Soils, plants, and sewage sludges are extremely diverse and complex,
and methods for sampling, sample preparation, and analysis have been in-
adequate in many instances. Sensitive, accurate, analytical methods have not
been available for some of the metals until recently. Therefore, data from
some of the earlier investigations are questionable. In some instances, high
levels of certain elements can interfere in the determination of other elements,
resulting in values which are either too high or too low if the problems are
not taken into proper account. Difficulties of this kind often result in a
lack of confidence in reported work. Use of a common set of standard samples
by analysts in different laboratories can be a valuable aid to accuracy (Ellis
et al., 1975).
Sampling
Sludge materials are extremely variable in composition (Sommers, 1976).
In addition, sludge from a given source varies in composition with time. A
coefficient of variation as great as 50% may occur over time for some of the
metals (Baker and Chesnin, 1975). This variability emphasizes the need for
obtaining samples over a fairly long period of time when characterizing the
composition of sludge from a given source.
The concentration of metals in plants varies with the plant part sampled
and the stage of growth. The concentration of metals in sludge-treated soils
may vary considerably from sample to sample due to variation in the sludge
and poor mixing of the sludge with the soil. Obviously, great care must be
taken in sampling plants and soils if the analyses are to be used to identify
or predict heavy-metal problems. Sampling plants and soil for quantitative
analysis is discussed in detail by Ellis et al. (1975).
Sample Preservation
Preservation of soil and plant samples is not a major problem in most
cases, but preservation of sludge samples is a major problem. Methods for
preservation are outlined in a publication by the Environmental Protection
Agency (1974).
Analysis
Plant materials and sludges are normally digested and analyzed for total
content of metals. Dry ashing (<500°C) and wet digestion methods have both
been used in preparing plant and sludge samples for analysis. Dry ashing is
not satisfactory for mercury, selenium, iron, and copper.
For soils, a total analysis for the metals seldom correlates with uptake
by plants or leachability of the element in soils. Better correlations with
uptake of elements by plants in the deficiency range are obtained by use of
appropriate equilibrium extraction solutions that remove a labile fraction
of the element from the soil, but with most extractants the quantities ex-
tracted have not been correlated with uptake by plants in the toxic range.
Further research is needed to establish more precisely the relationships in
the toxic range.
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Once metals are in" solution, a competent analyst can obtain reliable results
for many of the metals by any one of several analytical procedures. Atomic
absorption is used in most laboratories, but some of the new techniques, such
as neutron activation and plasma-source emission spectroscopy, offer good
precision and provide lower limits for detection for some of the metals.
Analyses of sludge, plant material, and soil extracts by atomic absorption
and flame emission methods are subject to problems because of high salt content
and interference by similar ionic species in the matrix. The deuterium back-
ground corrector seems to be the best method for correcting "background" prob-
lems. Background correction is very critical for the accurate determination of
cadmium.
HAZARD OF HEAVY METALS AND OTHER ELEMENTS
TO PLANTS AND ANIMALS
When the chemistry of the heavy metals and other potentially toxic ele-
ments in sewage sludges is considered in conjunction with their uptake by
plants, it is possible to subdivide the elements into two categories depending
on whether or not they represent a potentially serious hazard to plants or
animals. In allocating the various elements to the low-hazard category, certain
management constraints were taken for granted. These are mentioned in the
relevant sections to follow. It should be clearly understood that if poor
management is practiced at a sludge-treated site, some of the elements rated
here as relatively innocuous could constitute a hazard.
Elements Posing Relatively Little Hazard
Manganese, Iron, and Aluminum
Manganese, iron, and aluminum form sparingly soluble oxides and hydroxides
in soils. Those of iron are the least soluble. Most soils contain large quan-
tities of iron and aluminum, and so the addition of sludge containing high
amounts of iron or aluminum will not appreciably increase the concentration of
these elements in the soil. Under good soil management practices (i.e., soil
pH greater than 5.5), little of either element remains in solution.
Aluminum and iron added to soil in sludge should rapidly precipitate as
the hydroxides. Later the ferric hydroxide may be expected to revert to less
soluble oxide-hydroxide mixtures. A small quantity of each element may remain
in the soil as iron or aluminum organic complexes.
Under well-aerated soil conditions, added manganese should rapidly revert
to one of the insoluble tetravalent manganese oxides. Manganese may also form
stable organic complexes.
The major soil property to affect the solubility (and availability to
plants) of aluminum, iron, and manganese is soil pH. But both manganese and
iron may be rendered more soluble by reducing conditions in soils. Good manage-
ment would include applying sludge only to well-aerated soils because this
would prevent solubilization of manganese.
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25
At soil pH values above 5.5, uptake of manganese, aluminum, and iron is
restricted, and plants will not accumulate these elements to toxic levels.
But below pH 5.0, aluminum toxicity is common, and excessive manganese may
accumulate in plants if the soil contains large quantities of manganese. Al-
though iron does not accumulate in plant tissue to a great extent, it has been
reported that relatively high availability of iron in the soil will induce
manganese deficiency.
The levels of iron, manganese, and aluminum in sludge usually will not
be of any environmental concern. Even though many tertiary sludges may be
high in iron, aluminum, or manganese, these elements will not be a limiting
factor in determining the quantity of sludge that may be applied to agronomic
crops if the soil pH is maintained above 5.5 and the soil receiving the sludge
is well aerated.
Chromium
Little soluble chromium is found in soils. If soluble trivalent chromium
is added to soils, it rapidly disappears from solution and is transformed into
a form that is not extracted by ammonium acetate or complexing agents. How-
ever, it is largely extractable by strong acids, indicating the formation of
insoluble hydroxides or oxides. Hexavalent chromium remains as such in a solu-
ble form in soil for a short time but is eventually reduced to trivalent chro-
mium and then changed to forms of low solubility. Hexavalent chromium is
toxic to plants, but sludges contain little, if any, hexavalent chromium because
it is reduced to the trivalent state during the sewage digestion process.
There have been few studies of the chemistry of chromium added in sludge
to soils. The concentration of chromium in sludges ranges from very low values
to well over 20,000 ppm. Decomposition of sludge in soils is likely to pro-
gress at a sufficiently slow rate so that the released chromium will change
to insoluble compounds without build-up of appreciable levels of soluble chro-
mium in the soil.
Most crops absorb relatively little chromium, but some species can contain
levels up to 10 ppm. Schueneman (1974) found chromium concentrations less than
0.5 ppm in leaf tissue of corn grown on sandy soils treated with inorganic
chromium up to the rate at which growth was reduced (200 ppm on a dry-soil
basis). However, a few crops can take up appreciably higher levels of chromium.
Field bean tissue reached a chromium concentration of 30 ppm when chromium was
applied to the soil at 200 ppm. This addition produced a 25% reduction in
yield. Chromium accumulated in tomato tissue to a concentration of 35 ppm,
but yield reductions were associated with tissue concentrations as low as 5 ppm.
Clapp et al. (1976) found a chromium concentration of 4 ppm in corn tissue
with no increase due to application of 135, 270, or 530 kg of chromium in
sludge per hectare (Appendix Table 4). The concentration of chromium in the
grain was less than 0.1 ppm, indicating little translocation of chromium
from the leaf tissue into the grain. Other researchers (Appendix Table 5)
found low concentrations of chromium in leaf and stover tissue of corn grown
on soil treated with sludge supplying 833 kg of chromium per hectare.
Although it is generally considered that chromium is not essential for
plant growth, there have been several reports of slight yield increases due
to chromium additions. These increases may be associated with release of other
ions (for example, manganese) that plants require as nutrients.
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Chromium is not expected to be a limiting factor in determining the
quantity of sludge that may be applied to soil producing agronomic crops
because (i) plants can tolerate relatively high levels of chromium applied in
sludge, (ii) plants do not accumulate chromium even when it is present in the
soil at high levels, and (iii) there is evidence that chromium is required by
humans and animals and that diets are deficient in chromium in certain areas
(Underwood, 1971).
Arsenic
Inorganic arsenicals have been used as agricultural pesticides and defol-
iants for many years, and they have seriously polluted soils in certain areas.
Since the banning of inorganic arsenicals in 1967, the application of arsenic
to soil has decreased very markedly.
Sludge is known to contain arsenic in concentrations ranging from 10
to 1,000 ppm. The form of combination of arsenic in sludge is unknown. Re-
search studies with inorganic sources of arsenic have shown that rates in
excess of 90 kg of arsenic per hectare must be applied before toxicity to
plants is observed, even on sandy soils (Jacobs et al., 1970). To judge from
these results, approximately 90 metric tons of a high-arsenic sludge would
have to be applied to cause toxicity to plants.
Once incorporated into the soil, arsenic reverts to the chemical form
of arsenate, which is strongly held by the clay fraction of most soils. As
a consequence, arsenic has a low availability to plants on soils which have
an appreciable clay content. Because of the low clay content of sandy soils,
arsenic toxicity to plants could develop if high-arsenic sludge were applied
at high rates.
Although plants take up arsenic, they tend to accumulate it in the roots,
and the arsenic content of most of the edible portions of plants is well be-
low the critical concentration of 2.6 ppm (U.S. Department of Agriculture,
1968) considered safe for animal or human consumption. Hence, arsenic is
not readily passed on to animals and humans. Since sewage sludge generally
contains low levels of arsenic, application of sludge usually will not be
limited by its arsenic content.
Selenium
Little evidence exists to suggest that selenium is an essential element
for plants, but it is definitely required by certain animals. Despite its
seeming nonessentiality, selenium is taken up by plants, which serve as
carriers of selenium from soil to animal. The range between deficiency and
toxicity in animals is fairly narrow. At levels of 0.05 ppm in the diet,
degeneration of muscle tissue results; when the diet contains more than 4 ppm,
selenium toxicity may occur.
Furr et al. (1976b) found the selenium concentration in sludge from 16
U.S. cities to range from 1.7 to 8.7 ppm. Bates et al. (1976) analyzed nine
Ontario sludges and found a selenium concentration of 0.86 ppm in one, 0.73
ppm in another, and less than 0.05 ppm in the remaining seven. Data from
greenhouse trials showed that application of up to 8.8 kg of selenium in
sludge per hectare to a sandy loam soil did not increase the uptake of selen-
ixim by ryegrass. Furr et al. (1976a), on the other hand, found that selenium
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27
uptake by a variety of plants was greater from sludge-treated than from control
soils but that, in all instances, the selenium content of the tissue was well
below hazardous levels.
Selenium in soil is least soluble under acid conditions, which would be
in conflict with the general requirement that the soil be near neutral in
reaction for appliction of sludge. Under neutral to alkaline conditions,
selenium occurs as the selenate ion, which forms neither highly insoluble salts
nor stable sorption complexes with the clay fraction of soil. It is under
such conditions that selenium poses the greatest hazard to animals. Selenium
toxicity to livestock is known to occur under certain conditions in dry regions
of the United States where the soils have developed on seleniferous parent
materials. Before the potential hazard of selenium applied in sewage sludges
can be properly evaluated, more needs to be known about the selenium content
of sludges and the rate of loss of selenium from soils in humid regions.
Antimony
Antimony is not known to be essential to the growth of plants but has
been reported to be moderately toxic. Significant amounts of antimony can be
taken up by plants from contaminated soil, and plant leaves tend to contain
more antimony than do stems. Soil investigations have shown that antimony is
sorbed very strongly by kaolinite and sesquioxides under acid conditions, but
under neutral to alkaline conditions it appears to move readily. Antimony
generally occurs in sewage sludge in very low concentrations; one value of
900 ppm has been reported. Although antimony could be a potential hazard to
plants and animals if applied in large amounts, no evidence of hazard is
currently available.
Lead
Lead is a nonessential element that exhibits a low degree of potential
toxicity to plants and a high degree of potential toxicity to animals. Sewage
sludge contains lead in significant amounts. Sommers (1976) gives the median
concentrations as 540 ppm for anaerobically-digested sludges and 290 ppm for
aerobically digested sludges. Additions of 20 metric tons of these sludges
per hectare would supply 10.8 and 5.8 kg of lead per hectare or approximately
4.4 and 2.6 ppm in the soil.
Soluble lead added to soil reacts with clays, phosphates, carbonates,
hydroxides, sesquioxides, and organic matter, and these reactions greatly
reduce the solubility. Jurinak and Santillan-Medrano (1974) concluded that
lead is retained as the hydroxide or hydroxy-phosphate in acid soils and as
the carbonate in calcareous soils. Hassett (1974) found that the lead
sorption capacity of Illinois soils could reach several thousand kg per hec-
tare and was related to the cation-exchange capacity, pH, and extractable
phosphorus content of the soil.
Plants take up lead in the ionic form from soils. The amount of lead
taken up from soil decreases as the pH, cation-exchange capacity, and available
phosphorus of the soil increase. Miller et al. (1975a,b) observed an inverse
relationship between the lead uptake by corn and soybeans and the lead sorption
capacity of soils. Lead taken up by five plant species from lead-contaminated
soil was reduced by liming (Cox and Rains, 1972).
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28
Studies on the effect of lead on plant growth are limited; however, the
effect appears to be minor. Baumhardt and Welch (1972) applied up to 3,200
kg of lead per hectare to a soil having a pH of 5.9 with no effects on corn
growth or grain yield. In general, the lead content of roots is higher than
that of plant tops, with fruits and seeds showing the lowest content. It ap-
pears that the lead content of soils would have to approach 1 percent and
that the soil pH would have to be below 5.5 before significant effects on
plant growth would be encountered.
Investigations by Sabey and Hart (1975), Haze et al. (1975), and Clapp
et al. (1976) (Appendix Tables 4 and 6) indicate that, when sewage sludge is
incorporated in the soil, the lead content of the above-ground portion of the
plants or seeds is not significantly changed. If the sludge is applied as a
surface dressing when a crop is growing (Boswell, 1975; Chaney et al., 1976a),
there may be an increase in the lead content.
Most soils treated with sewage sludge have a pH above 5.5 and a high
labile phosphorus content. Under these conditions, movement of lead from
treated soil into plant tops and seeds is not found. Accumulation of lead in
crops thus would seldom be a cause for limiting the application of sludge to
cropland. One may ensure that lead does not become a problem, however, by
maintaining the pH of sludge-treated soils above 5.5, by avoiding the growth
of root crops, and by avoiding repeated application of sludges with very
high lead content.
Mercury
The mercury contents of soils not receiving additions of sewage sludge
lie in the range from 0.01 to 0.5 ppm. In soils receiving sludge for pro-
tracted periods, the concentration could approach 1.0 ppm. Once in the soil,
mercury enters into reactions with the exchange complex of the clay and organic
fractions, forming both ionic and convalent bonds.
Many mercurial compounds, both organic and inorganic, decompose to yield
elemental mercury, which may volatilize or be converted to HgS, HgCl ~, or
HgCl,2-. xhe last of these forms may be adsorbed by sesquioxide surfaces or
may move freely in soils (Newton et al., 1976). Organic mercurial compounds
can be sorbed on clay minerals by molecular forces, and there is evidence
that mercury can be chelated by organic matter. Chemical and microbiological
degradation of mercurials can take place side by side in the soil, and the
products ionic or molecular are retained by organic matter and clay or
may be volatilized if gaseous. Because of the high affinity between mercury
and the solid soil surfaces, mercury persists in the upper layer of soil and
is not a threat to ground water.
Mercury can enter plants through the roots, it can be translocated, and
it has been reported to cause injury to plants (Smart, 1964; Stewart and
Ross, 1967). Once absorbed, it appears to be readily translocated through-
out the plant. In many plants, mercury concentrations range from 0.01 to 0.20
ppm, but when plants are supplied with high levels of mercury, these concen-
trations can exceed 0.50 ppm. Mercury ingested in food undergoes "biological
magnification" in animals, indicating a lower rate of excretion than of intake.
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29
In sludges the mercury contents may be high if industrial sources of
mercury contamination are present. Little is known about the forigin which
mercury occurs in sludge. Mercury may undergo biological methylation in
sediments (Jernelov, 1972), but no methylation has been observed in soils,
mud, or sewage sludge (Rissanen et al., 1970).
Most sludges are relatively low in mercury, and very little increase in
concentration of mercury in plants has resulted from application of sludge.
However, Van Loon (1974) found mercury concentrations up to 12.2 ppm in
tomato fruit after application of a high-mercury sludge to an alkaline soil.
Nevertheless, sludge application would seldom be limited because of concern
over mercury.
Elements Posing a Potentially Serious Hazard
Cadmium
During the past decade, there has been increased concern over cadmium
in the environment because cadmium has been linked to certain health problems.
Because of the cumulative characteristics of cadmium in animals and humans
from low-level exposure, there is much greater concern about the possible hazard
to humans from elevated concentrations of cadmium in plants than there is for
possible toxicity to the plants.
Sewage sludge may contain cadmium concentrations from 3 to over 3,000
ppm, with a mean value of 106 ppm and a median value of 16 ppm (Sommers,
1976), whereas soil contains from 0.01 to 7 ppm with 0.06 being common
(Allaway, 1968). Therefore, the addition of sewage sludge to soil usually
results in an increase in concentration of total cadmium in the soil. To
maintain perspective, it is important to note that superphosphate can also
add cadmium to soil. For example, Lee and Keeney (1975) have shown that
cadmium added to land in Wisconsin as a contaminant in fertilizer is equivalent
to that produced in sludges from all Wisconsin treatment plants. However, be-
cause of a wide difference in the rate of application, cadmium addition to a
given tract of land will be much less from fertilizer than from sludge. In
either case the amount of cadmium added is low (about 2000 kg for Wisconsin).
The chemistry of cadmium in soil is not well understood, but cadmium
appears to be influenced by soil organic matter, clay content and type,
hydrous oxide content, soil pH, and redox potential. The assumption has been
that the total amount of cadmium added to the soil would ultimately control
the amount of soluble cadmium present and thus the uptake of cadmium by
plants. Soils must have some "saturation" limit for cadmium at which the
addition of a quantity of soluble cadmium results in a nearly equivalent
increase in soluble cadmium in the soil. However, data in Appendix Table 7
on repeated annual applications of sludge to soil cropped to corn show
that the amounts applied in a given year influenced the cadmium content in
the leaves to a greater extent than did the total cumulative amounts of cad-
mium applied. The implication of these results is that, at the rates used,
most of the applied cadmium was being converted to forms of relatively low
availability to plants.
The observations just made point to the importance of an understanding
of the chemistry of cadmium in soil-water systems. Soil properties and
their importance to the removal of cadmium from the soil solution need fur-
ther study and quantification.
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30
In investigations in which cadmium addition was discontinued, there
was a decrease in cadmium uptake by corn in the first year with a smaller
decrease in the second year (Hinesly et al., 1976b). The number of years
after termination of sludge application required for plant uptake to approach
background levels has not been established.
Field plots have been established on several farms in the northeastern
United States on which sewage sludge containing cadmium concentrations of
5 to 800 ppm had been applied over a period of 7 to 25 years. The period
after cessation of sludge application ranged from 1 to 12 years. Although
the total amount of sludge or cadmium applied could not be definitely estab-
lished, the cadmium content of crops grown on these plots reflected the influence
of pH on the availability of the cadmium to plants as well as the importance
of agronomic practices, including crop selection. Many farms were managed
without the benefit of pH control during sludge applications. Subsequent
additions of lime to these acid areas showed that cadmium was thereby rendered
less available to crops (Appendix Table 8). This decrease in cadmium uptake
with increasing pH was noted for both low and high cadmium application
levels. In one set of observations (Appendix Table 9), the effect of applica-
tion of cadmium-bearing sludge on the cadmium content of plants was evident
5 years after application of sludge had ceased.
Annual cadmium application' rates, soil pH, and crop species and varieties
have a major influence on the cadmium concentration in plant tissue. To a
lesser extent, soil temperature, nitrogen and phosphorus fertilization, and
addition of metals such as zinc and copper may also influence the cadmium
content of crop tissues.
In experiments in which soil pH was varied (Anderson and Nilsson, 1974 ;
Chaney et al.,1976b; Giordano and Mays, 1976b), an increase in soil pH
usually markedly reduced the cadmium content of crop tissues and grains (Appendix
Tables 8 and 9). However, raising the pH of sludge-treated soils probably
will not reduce the content of cadmium in plants to the same level as that on
untreated soils. Moreover, differences in cadmium uptake by plants from dif-
ferent soils at a given pH may conceivably exceed the differences in uptake
from a given soil at different pH values.
Research studies (Bingham et al., 1975; Giordano and Mays, 1976a; Dowdy
and Larson, 1975) have shown that different plant species, varieties, and
plant tissues contain different cadmium concentrations from similar rates of
application (Appendix Tables 4, 6, 8, 12, 13). Cadmium concentrations in
corn grain are usually only 3 to 15% of those in the leaf, whereas in the grain
of soybeans, wheat, oats, and sorghum, cadmium reaches 30 to 100% of the foliar
levels.
Interactions of other metals with cadmium have been observed in soybeans
and corn. Application of copper increased the cadmium content of corn and
rye shoots (Cunningham et al., 1975a). As shown in Appendix Table 21, appli-
cation of zinc or zinc plus copper plus selenium plus molybdenum reduced the
cadmium content of soybean grain (Chaney et al., 1976b; Baker et al., 1975) even
though foliar cadmium content increased (Haghiri, 1974). On phosphorus-deficient
soils, phosphorus application appears to decrease the cadmium content of corn
leaves. Ammonium fertilizer applications may increase cadmium uptake.
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31
Bingham et al. (1975, 1976) found that cadmium concentrations in the
dry matter of edible tissues of various crops ranged from 1.7 to 80 ppm at
cadmium additions to soils which caused 25% yield reduction (Appendix Table
12). It appears that crops may contain undesirable concentrations of cadmium
in their tissues without showing visible symptoms of toxicity of cadmium to
the plants. Leafy vegetables such as lettuce, chard, spinach, and turnip
greens may contain cadmium concentrations exceeding 100 ppm without showing
any toxicity symptoms.
Crops grown on different soils were found by John et al. (1972) and
Miller et al. (1976) to differ widely in cadmium uptake from equal cadmium
additions as inorganic cadmium salts. Cadmium uptake was related to the ratio
of cadmium added to the cadmium sorbing capacity of the soil. Where cadmium
salts were added in sludge, some work showed no influence of the clay content
of the soil on cadmium absorption by plants (Kelling et al., 1976), and some
showed a significant influence of soil clay content (Singh et al., 1976).
An increase in soil temperature leads to an increase in uptake of cadmium
by crops whether the added cadmium is inorganic (Haghiri, 1974) or sludge-borne
(Shaeffer et al., 1975; Giordano and Mays, 1976a). Sludge processing may
affect subsequent availability of the cadmium to the crop. For example, appli-
cation of high-lime sludge cake may cause soils to become alkaline, thus re-
ducing cadmium availability, and anaerobic digestion may be necessary to pro-
duce the lack of additivity of cadmium uptake by plants grown on soils that
have received repeated applications of cadmium in sludge. Clapp et al.
(1976), however, have not observed this phenomenon with an aerobically stab-
ilized sludge. As shown in Appendix Table 10, composting of digested or
raw sludge appears to reduce the crop uptake of cadmium in field studies
during the first and subsequent years (Chaney et al., 1975).
Field experiments involving use of anaerobically digested sewage sludge
(single application) for corn production have led to conflicting results.
Kelling et al. (1976) found that the application of 4.3 kg of cadmium per
hectare did not change the cadmium concentration in corn grain, Decker et al.
(1976) found that application of 2.0 kg of cadmium per hectare increased the
cadmium concentration five-fold, and Baker et al. (1975) found that application
of 24.8 kg of cadmium per hectare increased the concentration eight-fold
(Appendix Table 11). The same treatments, however, gave a twenty-fold increase
in cadmium concentration in sorghum grain. Findings with sweet corn (Giordano
et al., 1975; Singh et al., 1976) also show conflicting results (Appendix
Table 11). The inconsistency in results obtained by the various investigators
cannot be explained on the basis of existing knowledge of the systems involved.
In summary, several management options are available to keep the concen-
tration of cadmium in food and feed crops at a low level on sludge-treated
land: (1) Maintain the soil pH at or above 6.5. (2) Grow crops which accumu-
late relatively low concentrations of cadmium or, for crops harvested for grain,
those which have a low concentration of cadmium in the grain. (3) Make only
small annual applications of cadmium when food or feed crops are to be grown.
(4) Use sludges low in cadmium on cropland. (5) Grow nonedible crops.
Inadequate information is available to set forth either specific soil
properties other than pH or specific sludge processing methods which may lead
to lower availability of cadmium to crops. Because cadmium is the heavy
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32
metal which is likely to have the greatest impact on the food produced on
land treated with sewage sludge, the potential for limiting the entry of
cadmium into the sewage system and for removing cadmium from sludge prior to
application is worthy of investigation.
A specific metal-binding protein called metallothionein, which has
been characterized in several animal species and microorga isms, is responsible
for the accumulation of cadmium in animals. The content of this protein in-
creases following continued exposure to cadmium.
Williams et al. (1976) found that the liver, kidney, and muscle of meadow
vole contained lower concentrations of cadmium than were present in the diet
supplied by corn or sorghum grown with or without application of sewage sludge
as a source of cadmium (Appendix Table 16). Concentrations of cadmium in
the liver and kidney considerably exceeded those in the muscle. The maximum
concentration of cadmium in the diet in this work was 2.76 ppm.
In research by Baker et al. (1975) on chickens, shown in Appendix
Table 15, the cadmium content of eggs and muscle was lower than that in the
diet at all levels of cadmium feeding, but the cadmium content of liver and
kidney exceeded that in the diet. In this work, the lowest concentration of
cadmium fed was 3 ppm and the highest was 48 ppm.
Doyle et al. (1974) found that, with lambs, the muscle and the fat
had much lower concentrations of cadmium than did the diet, and the liver and
kidney had much higher concentrations than did the diet (Appendix Table 17).
Dietary concentrations of cadmium supplied in this work ranged from 5 to 60
ppm. Up to 5.3% of the cadmium supplied in the diet was absorbed by the
lambs.
In all the investigations mentioned, the cadmium content of all tissues
analyzed increased with the cadmium content of the diet. The poorest corre-
lation observed was between cadmium in the diet and in the wool of the lambs
fed by Doyle et al. (1974).
Preventive effects of zinc in cadmium toxicity suggest that a simultaneous
increase of zinc intake may prevent cadmium absorption or accumulation (Pari-
zek, 1957). Interactions with other elements are not well known.
As the foregoing discussion has indicated, there are many gaps in our
knowledge of the behavior of cadmium in soils, plants, animals, and humans,
and much more research is needed to clarify the relationships which control
the fate of cadmium in the environment. Under some circumstances, cadmium
could represent a very real hazard in the food supply, and so caution should
be exercised whenever cadmium is applied to land used for producing food
crops. The hazard is greatest when sludges high in cadmium are applied at
high rates to limited tracts of land and where the produce from such land
constitutes a considerable portion of the diet.
Copper
Copper is found in all soils, and its concentration is usually from
10 to 80 ppm. In soils, copper occurs in association with hydrous oxides
of manganese and iron and also as soluble and insoluble complexes with
organic matter. Keeney and Walsh (1975) found that the extractable copper
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33
content of sludge-treated soil decreased with time, which suggests that
a reversion of the copper to less soluble forms was occurring.
Copper is essential to the growth of plants, and the normal range of
concentrations in plant tissue is from 5 to 20 ppm. Copper concentrations
in plants normally do not build up to high levels when toxicity occurs.
For example, Walsh et al. (1972) found that the concentrations of copper in
snapbean leaves and pods were less then 50 and 20 ppm, respectively, under con-
ditions of severe copper toxicity. Even under conditions of copper toxicity,
most of the excess copper accumulates in the roots; very little is translocated
to the aerial portion of the plant.
Copper toxicity may develop in plants from application of sewage sludge
if the concentration of copper in the sludge is relatively high. Copper toxi-
city to plants from sludge applications was reported by Cunningham et al.
(1975a), who suggested that copper is about twice as toxic as zinc. Corn
and rye. took up more copper from soil treated with an inorganic salt of copper
than from soil treated with sewage sludge supplying an equal amount of copper
(Cunningham et al., 1975c).
Sheep are most susceptible to copper toxicity, followed by cattle, swine,
and poultry, in that order. Swine, sheep, and cattle are capable of accumulat-
ing high concentrations of copper in the liver under some conditions. Accum-
ulation of copper in animal livers with resultant copper toxicity may occur
with rations having normal levels of copper if the molybdenum intake is extremely
low. This toxicity can be prevented by controlling the molybdenum content of the
ration. Relatively high concentrations of copper can be tolerated in ruminants
when an adequate amount of molybdenum is available. Copper poisoning of animals
associated with consumption of certain plants such as Heliptropium species is
considered to be due to liver damage caused by hepatotoxic agents of the plant
in which the injured animal hepatic cells also accumulate copper.
High levels of copper in the diet are beneficial for chickens and pigs
and have been widely used in feeding these animals. Modern research with
pigs followed from the observation that pigs have a craving for copper. The
optimum level for pigs seems to be a copper concentration of 250 ppm in the
diet. The dietary copper is supplemented with extra zinc and iron. Pigs
fed the high-copper rations gain weight more rapidly and use less feed per
pound of gain than do control pigs. The physiological effect of the copper
overlaps that of antibiotics and often seems to be a substitute for anti-
biotics. Although feeding copper at a concentration of 250 ppm increases the
concentration of copper in the liver of the pigs, the accumulations do not
seem harmful if the copper is properly supplemented with zinc and iron. Liter-
ature on this subject was reviewed by Braude (1965) and Wallace (1967). An-
other review by Braude is in publication. The principal issue surrounding the
feeding of high levels of copper has not been the possible detrimental effects
on the animals but the possibility that toxicity of copper to plants may de-
velop over a period of years if the animal wastes are applied in large quanti-
ties to limited areas of land.
Molybdenum
Molybdenum is required in very small amounts by plants. It does not
appear to be very toxic to plants, even at levels of a few hundred ppm in
plant tissues.
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34
Sorption of molybdenum by acid soils depends on the iron oxide and phos-
phorus status of the soil, iron oxide having a great affinity for molybdenum.
If phosphorus is present in large quantities, some molybdenum bonded to iron
oxide will be replaced. Maximum molybdenum sorption in soils occurs at pH
values near 4.2. The availability of molybdenum increases as the soil pH in-
creases, a behavior the reverse of that observed with copper, nickel, and
zinc. The practice of keeping soils at pH values near neutrality to limit
the availability to plants of heavy metals applied in sludge thus is ineffective
in limiting molybdenum availability.
The molybdenum content of sewage sludges has been found to vary from 5
to 39 ppm with a mean of 28 ppm (Sommers, 1976). If sludge with a molybdenum
concentration of 39 ppm were applied at the rate of 60 metric tons per hectare,
the molybdenum application would be about 2.3 kg of molybdenum per hectare,
an addition that would not pose a threat to the health of grazing animals.
However, repeated applications of high-molybdenum sludge over a long period
of time might cause animal health problems, especially on soils of high pH
which are not subject to leaching (Hornick et al., 1976). It is doubtful
that molybdenum in sludge would present a serious hazard to the health of
grazing animals except where forages from sites treated with sludge high in
molybdenum form the major part of the animal diet.
The tolerance of animals to molybdenum varies with species and age, and
is dependent upon the copper status and copper intake of the animal, the
inorganic sulfate and organic sulfur oxidizable to sulfate in the diet, and
the intake of other metals such as zinc and iron. Cattle are considered the
most susceptible of the farm animals to molybdenum toxicity. Sheep are less
susceptible, and horses and pigs are least susceptible. Forages containing
molybdenum concentrations exceeding 10 to 20 ppm may produce molybdenosis in
ruminants. The symptoms of molybdenosis are essentially those of copper de-
ficiency. Cattle provide the most overt clinical signs. Excessive molybdenum
in the diet causes copper deficiency accompanied by phosphorus deficiency.
The condition is correctable by supplementing the diet with copper sulfate and
phosphorus.
Nickel
Nickel is found in nearly all soils, plants, and waters. The content of
total nickel in soils is commonly in the range from 10 to 100 ppm, with higher
values in soils derived from serpentine. The concentration of extractable
nickel in soils seems to be governed by the surfaces of iron and manganese
hydrous oxides, which act as a "sink" for nickel, as well as by organic chelates,
which complex nickel less strongly than copper.
Sludges vary greatly in their nickel content from 2 to over 3,500 ppm
with a mean of 300 to 400 ppm (Sommers, 1976). Considerable quantities of
nickel can be added to soil in sewage sludges, but whether the nickel becomes
toxic to plants depends on several soil factors, the amount of nickel applied,
and the contents of other metals in the sludge. Unlike copper and zinc, which
are more available to plants from inorganic sources than from sludge, nickel
uptake by plants seems to be promoted by the presence of the sludge organic
matter (Cunningham et al., 1975c).
Nickel has no known essential function in plants. It is toxic to plants
at concentrations above 50 ppm in plant tissues. No significant plant toxicity
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35
due to nickel was observed by Cunningham et al. (1975b), however, when nickel
in quantities of 81 ppm in sludge and 100 ppm as nickel sulfate was added
to sandy loam and silt loam soils, respectively. Thus far, toxicity of nickel
to plants has been observed only on acid soils.
The daily ingestion of nickel by grazing sheep is approximately 2 mg
per day. Nickel ingested as the sulfate or acetate has a very low toxicity
to rats, mice, monkeys, and chickens (nickel may be required by chickens).
Nickel salts in quantities to supply nickel at 700 ppm in the diet of
chicks suppressed growth and nitrogen retention. This effect was not observed
at lower levels. Soluble nickel salts in quantities to supply nickel at 1,000
ppm in the diet did not affect the growth rate or reproduction in rats.
Soil treatments such as liming that reduce the solubility of nickel reduce
the toxicity. Thus far, toxicity of nickel to plants has been observed only
on acid soils. If sludge-treated sites are well managed, nickel is not likely
to be taken up by plants in quantities sufficient to cause toxicity to the
plants or to pose a threat to the food supply.
Zinc
Zinc is essential for both plants and animals, being an essential component
of a number of enzyme systems. Under acid conditions, zinc occurs in solution
as the Zn ion. The most important mechanisms for zinc retention in soils
are sorption on clay and hydrous iron oxide surfaces and chelation by organic
matter.
Zinc is taken up by plants as Zn^"*" and, in excessive quantities, can be
toxic. However, few records of toxic effects of zinc are available in the
literature. Heavy dressings of zinc (up to 1,390 kg of zinc per hectare) had
little or no effect on the growth of a number of crops (Murphy and Walsh,
1972; Walsh et al., 1972). When zinc toxicity does occur, the tissue of most
crops will contain zinc at concentrations of several hundred ppm.
Giordano and Mays (1976a) found, in studies with string beans and sweet
corn, that zinc in zinc sulfate initially was more available to plants than
zinc in sludge. However, in residual studies, more zinc was taken up from
sludge-treated plots than zinc-sulfate-treated plots. The pH was the same,
and the difference in uptake, therefore, was not due to a pH effect. Accord-
ing to research by Giordano and Mays (1976a) and Touchton et al. (1976), the
availability of zinc is reduced more by liming than is that of cadmium, copper,
and nickel.
Touchton et al. (1976) found a marked decline of heavy metal content of
grass with time. Three years after the last addition of sludge to Coastal
bermudagrass, copper was at normal levels, and zinc levels were decreased by
almost half. In contrast, where zinc sulfate was applied, Giordano et al.
(1975) found that the reduction in yield of snapbeans and the increase in
zinc content of the plants grown on Sango silt loam of pH 4.9 were almost
as marked in the second year following application as in the first. There
was little evidence of reversion of the zinc to forms not extractable by
0.5IJ hydrochloric acid. Walsh et al. (1972) similarly did not find reversion
of zinc added as zinc sulfate at high rates. In this work, however, the toxicity
to plants was not studied. To what extent and under which conditiors reversion
of zinc to forms of low availability in soils can decrease the long-term po-
tential for uptake by plants and toxicity to plants remains uncertain. If
the soil pH drops, the availability of the zinc will increase.
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36
A wide margin of safety exists between normal dietary intakes of zinc and
the higher intakes that may produce toxicity in birds and mammals. Pigs show
no ill effects when they receive either zinc sulfate or zinc carbonate in
quantities to supply a zinc concentration of 1,000 ppm in the diet. Sheep and
cattle are less tolerant than other species. Dietary zinc levels of 500 ppm
do not cause signs of toxicity or other detrimental effects, but levels of
900 ppm cause reduced gains and lowered feed efficiency. Excessive zinc intake
decreases the copper content of the liver in sheep and cattle.
In general, if the pH value of sludge-treated soils is maintained at the
recommended level, zinc should not be a serious hazard to plants or to the
food supply unless exceptionally high levels are added in the sludge. In many
instances, a moderate increase in the zinc content of the food supply should
be beneficial because there is evidence that diets are often deficient in zinc.
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-------
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-------
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42
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-------
Appendix Table 1.
43
Estimated production of sewage sludge in the continental U.S.A. in 1970 and annual
cropland requirements for utilization of the sludge in agriculture!'
State
AL
AR
AK
CA
CO
CN
DE
FL
GA
ID
IL
IN
IA
KS
KY
LA
ME
MD
MA
MI
MN
MS
MO
MT
NB
NV
NH
NJ
NM
NY
NC
ND
OH
OK
OR
PA
RI
SC
SD
TN
TX
UT
VT
VA
WA
WV
WI
WY
USA
Population,
millions
3.45
1.79
1.93
19.99
2.22
3.04
0.55
6.85
4.60
0.72
11.14
5.21
2.83
2.25
3.22
3.64
1.00
3.94
5.70
8.90
3.82
2.22
4.69
0.70
1.49
0.49
0.74
7.20
1.02
18.26
5.09
0.62
10.69
2.57
2.10
11.88
0.95
2.60
0.67
3.93
11.25
1.07
0.45
4.65
3.41
1.75
4.43
0.33
203.90
Sludge
9 /
produced ,ZJ
thousands of
short tons
67
35
38
389
43
59
11
133
90
14
217
101
55
44
63
71
19
77
111
173
74
43
91
14
29
10
14
140
20
356
99
12
208
50
41
231
19
51
13
77
219
21
9
91
66
34
86
6
3971
Cropland required to accept the sludge having
the indicated content of nitrogen!/
Cropland,
thousands of
acres
3550
1210
8010
9700
5700
150
500
1380
4870
4290
22820
12260
24160
21660
4700
3660
420
1530
150
6270
20030
5560
13240
9090
17710
500
110
420
1240
4080
4750
18960
10730
10380
2640
4480
20
2740
15400
4610
23150
1160
580
2850
4820
760
9160
1810
328270
1% Available nitrogen
Acres
13
7
8
78
9
12
2
27
18
3
43
20
11
9
13
14
4
15
22
35
15
9
18
3
6
2
3
28
4
71
20
2
42
10
8
46
4
10
3
15
44
4
2
18
13
7
17
1
794
Percent of
total cropland
0.38
0.58
0.09
1.21
0.15
7.89
0.43
1.93
0.37
0.07
0.19
0.17
0.05
0.04
0.27
0.39
0.93
1.00
14.80
0.55
0.07
0.16
0.14
0.03
0.03
0.38
2.62
6.68
0.32
1.74
0.42
0.01
0.39
0.10
0.31
1.03
18.50
0.37
0.02
0.33
0.19
0.36
0.30
0.64
0.28
0.90
0.19
0.07
0.24
4% Available nitrogen
Acres
54
28
30
311
35
47
9
107
72
11
174
81
44
35
50
57
15
61
89
139
60
35
73
11
23
8
12
112
16
285
79
10
167
40
33
185
15
41
10
61
175
17
7
72
53
27
69
5
3177
Percent of
total cropland
1.51
2.30
0.38
4.85
0.61
31.58
1.71
7.73
1.47
0.26
0.76
0.66
0.18
0.16
1.07
1.55
3.71
4.01
59.21
2.21
0.30
0.62
0.55
0.12
0.13
1.53
10.48
26.71
1.28
6.97
1.67
0.05
1.55
0.39
1.24
4.13
74.01
1.48
0.07
1.33
0.76
1.44
1.21
2.54
1.10
3.59
0.75
0.28
0.98
' 1970 population estimates and harvested crop acreages for 1975.
_/ Sludge production estimates assume that 67% of the population was sewered and produced 0.16 Ib of sludge
per capita per day.
' Sewage sludge containing 1% or 4% available nitrogen (i.e., inorganic nitrogen) plus an additional 15 to
20% of this amount in organic form. Acreages are calculated on the basis of application of the sludge at
rates to supply 100 Ib of available nitrogen per acre.
-------
44
Appendix Table 2.
Estimated production of sewage sludge in the continental U.S.A.
requirements for utilization of the sludge in agriculture^/
in 1985 and annual cropland
State
AL
AR
AK
CA
CO
CN
DE
FL
GA
ID
IL
IN
IA
KS
KY
LA
ME
MD
MA
MI
MN
MS
MO
MT
NB
NV
NH
NJ
NM
NY
NC
ND
OH
OK
OR
PA
RI
SC
SD
TN
TX
UT
VT
VA
WA
WV
WI
WY
USA
Population,
millions
3.91
2.45
2.18
23.66
2.73
3.53
0.66
9.90
5.51
0.72
12.56
6.07
2.95
2.25
3.79
3.84
0.98
4.86
6.56
10.18
4.33
2.39
5.25
0.67
1.53
0.68
0.88
8.49
1.09
20.13
6.09
0.57
12.12
2.88
2.43
13.03
1.07
2.97
0.65
4.86
12.85
1.23
0.50
5.70
3.68
1.84
4.87
0.33
234.50
Sludge
produced ,_'
thousands of
short tons
134
84
75
810
93
121
23
339
189
25
430
208
101
77
130
131
34
166
224
348
148
82
180
23
52
23
30
291
37
689
208
20
415
99
83
446
37
102
22
166
440
42
17
195
126
63
167
11
8024
Cropland required to accept the sludge having
the indicated content of nitrogen'
Cropland ,
thousands of
acres
2500
1220
7280
8390
6060
120
470
2400
3870
4140
21200
10990
22500
23320
3180
3770
400
1370
150
6100
18460
5100
11880
11660
18640
450
90
410
830
3640
4110
20610
8740
8640
3420
3850
20
1330
14950
3590
21680
740
400
2210
6760
510
8810
1440
312410
1% Available nitrogen
Acres
27
17
15
162
19
24
5
68
38
5
86
42
20
15
26
26
7
33
45
70
30
16
36
5
10
5
6
58
7
138
42
4
83
20
17
89
7
20
4
33
88
8
3
39
25
13
33
2
1605
Percent of
total cropland
0.75
1.39
0.19
2.52
0.33
16.11
0.90
4.91
0.77
0.11
0.38
0.34
0.08
0.07
0.55
0.72
1.60
2.17
29.93
1.11
0.15
0.29
0.27
0.05
0.06
0.93
5.48
13.83
0.60
3.38
0.88
0.02
0.77
0.19
0.63
1.99
36.61
0.74
0.03
0.72
0.38
0.73
0.59
1.37
0.52
1.66
0.36
0.12
0.49
4% Available nitrogen
Acres
107
67
60
648
75
97
18
271
151
20
344
166
81
62
104
105
27
133
180
279
119
65
144
18
42
19
24
232
30
551
167
16
332
79
67
357
29
81
18
133
352
34
14
156
101
50
133
9
6419
Percent of
total cropland
3.02
5.54
0.75
10.09
1.31
64.42
3.61
19.64
3.10
0.46
1.51
1.36
0.33
0.28
2.21
2.87
6.39
8.70
119.72
4.44
0.59
1.18
1.09
0.20
0.24
3.72
21.90
55.34
2.41
13.51
3.51
0.08
3.09
0.76
2.52
7.96
146.46
2.97
0.12
2.89
1.52
2.90
2.36
5.48
2.09
6.63
1.46
0.50
1.98
i/ 1985 population estimates for population and cropland projections (Water Resources Council, 1972).
I Sludge production estimates assume that 75% of population is sewered and produces 0.25 Ib of sludge per cap!
per day.
/ Sewage sludge containing 1% or 4% available nitrogen (i.e., inorganic nitrogen) plus an additional 15 to
20% of this amount in organic form. Acreages are calculated on the basis of application of the sludge at
rates to supply 100 Ib of available nitrogen per acre.
-------
45
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-------
46
Appendix Table 4.
Metal content of corn grown in the field on sandy soil in
Minnesota treated with different quantities of sewage sludge
(Clapp, Dowdy, and Larson, 1976)
Sludge 1 .
applied
per hectare,
metric tons
Yield of
grain per
hectare,
metric tons
Metals
Zinc Copper Cadmium Nickel Lead Chromium
2/
Applied to soil, kg per hectare'
119
237
466
14.9
15.2
15.6
555
1110
2175
290
580
1135
1.3
2.6
5.1
42
84
165
325
650
1275
3/
Present in dry leaf tissue, yg per g'
135
270
530
0
119
237
466
0
119
237
466
9
14
15
15
9
14
15
15
.1
.9
.2
.6
.1
.9
.2
.6
19
132
160
182
Present
20
38
40
42
6
11
13
12
in
1
0
0
2
dry
.0
.7
.8
.0
0.04
0.12
0.19
0.25
grain
<0.04
<0.04
<0.04
<0.04
0
0
1
3
tissue,
0
1
2
.3
.8
.4
.0
Ug per
.3
.5
.6
4.0
1.5
1.3
1.0
0.7
g3/
0.14
0.14
0.14
0.14
0
0
0
0
<0
<0
<0
<0
.4
.4
.4
.5
.1
.1
.1
'l
Anaerobically digested sewage sludge applied over a four-year period.
2 /
105°C weight basis; total metals applied over a four-year period.
3/
70°C weight basis; metal concentration of tissue grown after final sludge
application.
-------
47
Appendix Table 5. Content of chromium in corn leaf and stover tissue from
field plots on Blount silt loam in Illinois with and
without application of sewage sludge (Hinesly, 1976)
Chromium in dry tissue with indicated
sludge treatment, ppm
No sludge 1/2 Maximum Maximum 1 ,
Year Tissue applied sludge application sludge application
1971 Leaf 1.2 1.3 1.2
1973 Leaf 1.5 1.2 1.2
1973 Stover 1.0 1.2 1.2
Digested sludge was applied annually on replicated plots. By 1971, the maximum
treatment had received 700 kg of chromium per hectare in 280.5 metric tons of
sludge. By 1973, the maximum treatment had received 833 kg of chromium per
hectare in 368.6 metric tons of sludge.
-------
48
Appendix Table 6.
Heavy-metal concentrations in vegetable crops grown in the field
on Sango silt loam (pH 6.4) in Alabama with and without appli-
cation of sewage sludge (Giordano and Mays, 1976a)
Crop
Lettuce
Broccoli
Potato
Tomato
Cucumber
Egg Plant
String Beans
Cantaloupe
Treat-
ment!'
C
S
C
S
C
S
C
S
C
S
C
S
C
S
C
S
Concentration in dry mat-
ter of fruit or rootr./ ppm
Zn
86.8
99.4
15.7
19.4
25.7
40.4
40.4
67.5
14.8
22.5
45.4
60.5
~"~
Cu
__
7.5
12.2
7.8
8.6
5.0
9.6
7.7
14.4
25.1
26.5
8.1
8.9
~~^
Ni
__
3.3
2.1
0.8
0.9
1.3
1.3
3.4
2.2
1.1
1.0
7.6
2.8
___
Cd
0.3
0.5
0.1
0.1
0.5
1.2
0.1
0.4
0.5
1.6
0.4
0.4
^
Pb
2.4
2.6
1.3
1.4
1.6
1.7
2.6
2.6
1.2
1.3
2.5
2.7
__
Concentration in dry matter
of leaves , ppm
Zn
47.5
74.2
26.7
33.4
37.5
47.1
39.2
80.0
20.9
22.1
32.9
49.2
44.4
40.0
Cu
5.2
9.6
14.9
31.3
20.7
22.5
17.1
12.0
14.4
17.7
8.6
7.6
10.2
9.2
Ni
2.4
1.7
4.1
2.3
2.5
2.0
6.2
3.9
2.3
1.8
4.3
3.0
4.8
3.1
Cd
0.9
3.6
0.8
0.7
1.1
3.6
7.8
10.9
0.8
2.0
0.4
0.5
1.1
2.3
Pd
2.4
3.1
5.1
4.6
7.3
8.1
0.5
0.9
4.7
4.6
5.0
6.8
8.2
8.4
C = control. S = Anaerobically digested sludge from Decatur, Alabama, applied in
the fall of 1974 at a rate equivalent to 224 metric tons of dry matter per hectare,
The heavy metal concentrations in the sludge were as follows: Zn = 1800 ppm, Cu =
730 ppm, Ni = 20 ppm, Cd = 50 ppm, and Pb = 530 ppm.
21
The plant samples were taken in the summer of 1976.
-------
49
Appendix Table 7.
Cadmium concentrations in corn leaves in different years
and in successive ryegrass cuttings within a single year
as influenced by applications of sewage sludge
Cadmium
applied per
hectare in
sewage sludge,
20
29
4
7
13
7
(48)-'
(77)
(81)
(88)
(101)
(108)
0.00 (O.OO)-/
1.08 (4.33)
8.64 (34.2)
Cadmium in dry matter of corn leaf
tissue in indicated years,
ppm
Cadmium in dry matter
of ryegrass in indica-
ted cuttings,
kg
0
2
4
.0
.2
.5
(0.
(8.
(18
1970 1971 1972 1973
0>±'
8)
.0)
0
0
1
.05
.45
.07
1974
0.
1.
2.
20
30
25
1975 1st 2nd 3rd 4th
0.
1.
1.
10
19
62
17.1
25.4
21.9
22.1
10.09
13.5
0.46 0.36 0.45 0.63
1.16 0.93 0.90 1.08
3.30 3.68 2.70 3.12
Research by Baker et al. (1976) in Pennsylvania. The applications of sludge
indicated were made in 1973, 1974, and 1975. The values in parentheses
are cumulative amounts applied through 1975. The crops were grown on soil
in containers in the greenhouse.
2/
Field research by Hinesly et al. (1976) in Illinois. The first application
of sludge was made in 1968, and it supplied 11 kg of cadmium per hectare.
The second application in 1969 supplied 17 kg of cadmium per hactare. The
third application in 1970 supplied 20 kg of cadmium per hectare, a cumula-
lative total of 48 kg. The values in parentheses are cumulative total
amounts of cadmium applied.
3/
Field research by Bates et al. (1975) in Ontario. The cadmium applications
indicated in the first column were made in applications of sludge in indi-
vidual years, and the cumulative values in parentheses are the total appli-
cations by the time the ryegrass was planted. The four cuttings of ryegrass
were all made in a single year.
-------
50
Appendix Table 8.
Cadmium content of swiss chard, soybeans, and oats grown on
limed and unlimed soil with and without prior application of
sludge from three cities (Chaney, Hornick, and Simon, 1976a)
Site
designation
City 4
City 9
City 13
Soil
PH
5.7
6.7
5.2
6.2
5.3
6.7
4.8
6.6
5.3
6.4
5.6
6.6
Sludge
treat-
men tZ/
Control
Control
Sludge
Sludge
Control
Control
Sludge
Sludge
Control
Control
Sludge
Sludge
Extractable
cadmium
in soil
ppm
0.13
0.14
0.53
0.57
0.13
0.10
1.13
1.19
0.93
0.96
7.15
5.45
Cadmium in dry matter of crops, ppm
Swiss
chard
leaves_£/
0.6
0.5
1.9
0.6
3.6
1.2
73.0
5.5
0.89
0.49
70.4
17.7
Soybeans^./
Leaves
0.27
0.26
1.04
0.55
10.7
1.87
0.24
0.17
5.70
2.38
Grain
0.17
0.15
0.36
0.28
3.70
1.51
0.16
0.13
2.64
0.65
Oat
grain_L/
0.05
0.04
0.23
0.07
0.22
0.04
2.12
0.38
0.11
0.07
3.38
0.54
/Applications of sludge were made from 1962 to 1975 at the City 4 site, from
1961 to 1973 at the City 9 site, and from 1967 to 1974 at the City 13 site.
'Extractable by diethylenetriaminepentaacetic acid.
I/Grown in 1975.
I/Grown in 1976.
-------
51
Appendix Table 9.
Cadmium and zinc content of soils and swiss chard grown
in the field (Site City 39) five years after the appli-
cation of sludge with a cadmium concentration of 100 ppm
(Hornick, Chaney, and Simon, 1976a)
Soil
PH
Total content of
metals in soil,
ppm
Metals extractable
from soil,A/
ppm
Metals in dry matter of
of swiss chard leaves,
ppm
Cd
Zn
Cd
Zn
Cd
Zn
5.68
5.87
6.37
6.66_.
6.12-2/
13.3
16.4
16.5
14.8
0.06
458
501
563
583
57
6.38
8.53
7.56
6.41
0.04
140
156
135
127
1.6
5.88
5.43
3.39
2.88
0.43
287
216
103
84
28
Extractable by diethylenetriaminepentaacetic acid.
2/
Control, no sludge applied.
-------
52
Appendix Table 10.
Cadmium content of crops grown on Woodstown silt loam treated
with digested sludge or composted digested sludge (Chaney,
Simon, et al., 1976)
Treatment
designation
Control
Sludge
Sludge
Compost
Compost
Sludge
or
compost
applied 1/
per hectare,
metric tons
0
40
80
160
240
80
160
240
40
80
160
240
80
160
240
Extract-
able
cadmium
in soil,
ppm
0.03
0.27
0.40
0.75
0.98
0.42
0.74
1.08
0.10
0.11
0.19
0.33
0.14
0.16
0.25
Tests in
1973
Soil
pH
5.5
5.2
5.6
6.5
6.4
6.4
6.3
6.9
5.8
6.0
6.5
6.8
6.8
6.9
7.0
Cadmium in
dry matter
Corn
seedlings
2.1
3.6
6.6
5.9
5.1
4.5
5.9
4.6
3.2
2.8
2.9
2.8
1.2
2.3
2.2
, ppm
Swiss2 ,
chard
2. Ode
5.9ab
6.3a
3.8cd
4.3bc
2.9cde
3.5cde
3.5cde
2.9cde
2.1de
2.3de
2.3de
1.5e
1.6e
1.6e
Soil
pH
5.8
4.9
4.9
4.4
4.4
6.4
6.6
6.4
5.0
4.9
4.4
4.6
6.6
6.7
6.6
Tests in
1976
Cadmivm in
dry matter of ,
corn seedlings
ppm
0.41h
3.0cd
4.9b
6.2a
6.3a
l.Sfg
2.7cd
3.2c
1.6g
2.1ef
2.5cdc
2.8cd
0.5h
0.8h
l.lgh
The sludge or compost were mir.ed with the soil by tillage in 1973. In 1976,
sulfur was added to plots on which the desired low pH had not been achieved
due to soil pH alteration by the sludge or compost.
2/
Values not followed by the same letter or letters differ significantly at the
5% probability level.
-------
53
Appendix Table 11.
Zinc and cadmium content of soil and corn grain with different
applications of sewage sludge in field experiments by various
investigators
Sludge
applied
per hectare,
metric tons
<,!/
3.7
7.5
15
30
60
c£7
55
100
220
O17
5
10
20
O^7
50
100
200
c£7
45
90
145
Time from
sludge
application Soil
to sampling pH
1 year 5.8
5.5
5.4
5.3
5.3
5.3
2 years 5.2
5.4
5.3
5.3
1 year 6.6
6.7
6.9
6.8
6 months 4.9
5.3
5.3
5.6
4 months
-
-
Total zinc
in soil
per hectare
kg
11.2
22.5
45
90
180
-
64
129
258
5.6
56
113
221
_
90
180
360
_
79
158
267
Zinc in
dry corn
grain,
ppm
20.1
20.3
20.6
22.0
26.3
26.9
22
34
49
60
28.5
30.8
36.3
39.9
37
43
49
44
44
55
46
74
Total
cadmium
in soil
per hectare,
kg
0.26
0.53
1.07
2.15
4.30
_
0.5
1.0
2.0
0.2
6.2
12.4
24.8
_
2.5
5
10
0
0.23
0.46
0.76
Cadmium in
dry
corn
grain,
ppm
0.09
0.08
0.10
0.09
0.09
0.10
0.12
0.41
0.59
0.68
0.015
0.025
0.065
0.120
0.3
0.9
1.0
1.2
0.18
0.26
0.31
0.93
Kelling et al. (1976). Data are for field corn.
2/
Decker, Chaney, and Wolf (1976). Data are for field corn.
3/
Baker et al. (1976). Data are for field corn.
4/
Giordano, Mortvedt, and Mays (1975). Data are for sweet corn.
Singh et al. (1976). Data are for sweet corn.
-------
54
Table 12a. Cadmium extracted from calcareous Domino silt loam and cadmium content
of various crops associated with a 25% yield depression from addition
of cadmium in sewage sludge in greenhouse tests (Bingham et al., 1975)
Crop
Spinach
Soybean
Curlycress
Lettuce
Corn
Carrot
Turnip
Field bean
Wheat
Radish
Tomato
Zucchini
squash
Cabbage
Rice
Plant
part
harvested
and
analyzed
Shoot
Dry bean
Shoot
Head
Grain
Tuber
Tuber
Dry bean
Grain
Tuber
Ripe fruit
Fruit
Head
Grain
Cadmium per
with a 25%
crop yield,
Cadmium
added in
sludgei'
4
5
8
13
18
20
28
40
50
96
160
160
170
>640
gram of soil
reduction in
yg
Cadmium
extracted
by DTPA!/
2.4
3.0
4.8
7.8
10.8
12.0
16.8
24.0
30.0
57.6
96.0
96.0
102.0
>384.0
Cadmium per
matter with
reduction,
Diagnostic
leaf
75.0
7.0
70.0
48.0
35.0
32.0
121.0
15.0
33.0
75.0
125.0
68.0
160.0
3.0^'
gram of plant dry
a 25% yield
yg
Edible plant
part
harvested
75.0
7.0
80.0
70.0
2.0
19.0
15.0
1.7
11.5
21.0
7.0
10.0
11.0
2.CF-7
The sludge used was obtained from a treatment plant that served a residential
community and was low in cadmium. This sludge was enriched to different levels
with cadmium as cadmium sulfate before addition to the soil. The cadmium-treated
sludge was added at the rate of 10 g of dry sludge per kg of soil. An additional
quantity of fertilizer containing nitrogen, phosphorus, and potassium was added
to all cultures.
o /
Cadmium extracted by a technique involving shaking 10 g of soil for 2 hours with
20 ml of diethylenetriaminepentaacetate (DTPA)-triethanolamine (TEA) solution
of pH 7.3 for 2 hours.
3/
These are the values measured with the maximum addition of 640 yg of cadmium per
gram of soil. No yield depression was noted with this addition of cadmium.
-------
55
Appendix Table 12b. Cadmium content of crops grown in the greenhouse on calcareous
Domino silt loam with and without treatment with sewage sludge (Chaney and
Siordano, 1977)
Cadmium per gram of dry plant tissue, ug
Crop
Paddy rice
Upland rice
Sudangrass
White clover
Alfalfa
Bermudagrass
Field bean
Wheat
Zuchinni squash
Soybean
Tall fescue
Corn
Carrot
Cabbage
Radish
Swiss chard
Table beet
Romaine lettuce
Tomato
Curlycress
Spinach
Turnip
Control
Diagnostic
leaf
0.4
0.2
0.2
0.3
0.3
0.6
<0.1
0.6
0.4
1.4
3.9
1.4
0.7
4.2
1.4
0.8
0.8
2.6
2.4
3.6
1.8
soil
Edible
tissue
-------
56
Appendix Table 13. Cadmium content of vegetable crops grown in 1974 and 1975
on field plots of Sango silt loam with an initial pH value of 6. 4 with
and without application of sewage sludge from two sources in Alabama
(Giordano and Mays (1976a)
Cadmium in dry plant tissue, ppm
Crop and
plant part
Bean leaf
Bean pods
Okra leaf
Okra pods
Pepper leaf
Pepper fruit
Tomato leaf
Tomate fruit
Squash leaf
Squash fruit
Turnip leaf
Turnip globe
Radish leaf
Radish globe
Kale leaf
Lettuce leaf
Spinach leaf
Control, no
sludge applied
1974 1975
0.46
0.04
0.59
0.13
0.71
0.09
0.66
0.12
0.34
0.03
0.59
0.42
0.92
0.29
0.63
1.00
1.00
0.67
0.42
1.04
0.04
1.70
0.33
0.70
0.27
1.20
Treated with
Decatur sludgeJV
1974
1.70
0.23
2.00
0.60
2.70
0.40
2.10
0.39
0.63
0.20
2.60
1.30
3.10
0.92
2.30
8.60
2.80
1975
^
3.10
1.20
2.92
0.60
6.70
1.12
2.15
0.72
-
7.00
*-,^-
Treated
Tuscumbia
1974
0.55
0.07
0.59
0.16
0.76
0.14
0.75
0.20
0.36
0.15
0.59
0.42
0.88
0.33
0.63
3.00
0.84
with
sludgei'
1975
__
0.44
0.39
0.78
0.12
1.70
0.40
0.87
0.19
_-
2.60
"~
The sludges were applied in the fall of 1973 in quantities to supply 112 metric
tons of dry matter per hectare. The Decatur and Tuscumbia sludges supplied
2.45 and 1.75 kg of cadmium per hectare and had pH values of 6.6 and 6.1.
The heavy-metal concentrations in the sludges were as follows: Cd = 49ppm,
Zn = 1840ppm, and Cu = 740ppm in the Decatur sludge; and Cd = 35ppm, Zn = 3640ppm,
and Cu = 516ppm in the Tuscumbia sludge.
-------
57
Appendix Table 14. Cadmium content of the grain of corn grown in the field in
Illinois on three soils receiving different amounts of sewage sludge
(Hinesly et al., 1976b)
Soil type
Cumulative amount
of sludge applied per
hectare, 1968-1971,
metric tons
Cumulative amount
of cadmium applied in
sludge per hectare,
1968-1971, kg
Cadmium in
dry matter
of corn grain
in 1972, ppm
Blount silt
loam
0
40
80
160
0
12.9
25.7
51.4
0.10
0.21
0.57
0.96
Elliott silt
loam
Plainfield
loamy sand
0
40
80
160
0
40
80
160
0
12.9
25.7
51.4
0
12.9
25.7
51.4
0.17
0.49
0.53
1.29
0.22
0.27
0.87
0.94
-------
58
Appendix Table 15. Content of cadmium in various tissues of chickens at
the end of a 12-week feeding trial with various levels of dietary
cadmium supplied as an inorganic cadmium salt (Baker et al., 1975)
Cadmium
in the Cadmium in dry
diet,
ppm
0
3
12
48
matter of
Laying hen
Egg
0.047
0.075
0.071
0.12
Liver
1.6
9.0
26.5
91.8
Kidney
8.5
30.7
92.6
305.9
indicated
tissues ,
ppm
Broiler chicken
Muscle
0.07
0.15
0.26
0.75
Liver
0.2
4.7
15.1
87.2
Kidney
0.4
9.3
49.7
239.0
Appendix Table 16. Content of cadmium in meadow vole tissues at the end
of a 40-day feeding trial with corn and sorghum forages grown on soil
with and without application of sewage sludge (Williams, Shenk, and
Baker, 1976)
Forage
Corn
Corn!/
Sorghum
Sorghumi/
Sludge
treatment
Control
Sludge
Control
Sludge
Cadmium in dry matter ', ppm
Diet
O.lOa
1.09b
0.23a
2.76c
Liver
O.OSa
0.43b
0.03a
1.86c
Kidney
0.09a
0.42b
0.09a
2.84c
Muscle
0.02a
0.05a
0.03a
0.03a
' The material fed was a composite of produce from plots receiving 10 and
20 metric tons of sludge per hectare (Appendix Table 11).
' Values not followed by a common letter differ significantly at the
5% level of probability.
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59
Appendix Table 17. Content of cadmium in various tissues of lambs at
the end of a 191-day feeding trial with different levels of dietary
cadmium supplied as an inorganic cadmium salt (Doyle et al., 1974)
Cadmium
added to
the diet,
ppm
0
5
15
30
60
Cadmium concentration in indicated tissue { ppm
Liver
1.7a
14.9ab
51.7ab
62. 7b
276. Oc
Kidney
4.4a
58. 9a
187. 6b
426. 8c
468. 8d
Muscle
0.025a
0.047a
0.091a
0.170a
0.428b
Fat
O.Olla
O.OlOa
0.012a
0.021a
0.113b
Wool
0.55a
1.20a
0.84a
1.22a
0.70a
' Values for fat are on the wet-weight basis. All others are on the dry-
weight basis. Values in a given column not followed by the same letter
differ significantly at the 5% probability level.
-------
60
Appendix Table 18. Heavy metal content of sorghum grown in the field
in Georgia in two years on soil at different pH values and with
different additions of inorganic fertilizer and sewage sludge
(Boswell, 1976)
Treatment^'
Metal concentrations in dry tissues/
in indicated year, ppm
Cu
1974
Mn
Zn
Cu
1975
Mn
Zn
Lime level,.
Control 5.7 28 16.4 5.6 28 20.7
N-P-K (140-25-93)!/ 7.1 50 15.8 8.7 53 27.2
Sewage sludge, 5.6 mt/ha 5.7 53 19.6 5.4 28 32.9
Sewage sludge, 11.2 mt/ha 5.3 39 20.6 6.8 29 66.0
Lime level-^
Control 5.2 30 14.1 4.8 19 15.3
N-P-K (140-25-93) 6.0 36 13.4 8.3 34 33.1
Sewage sludge, 5.6 mt/ha 5.7 24 17.5 5.6 20 31.3
Sewage sludge, 11.2 mt/ha 6.1 22 23.1 5.6 24 49.7
Lime level2
Control 5.9 35 15.7 5.1 26 17.1
N-P-K (140-25-93) 5.9 32 12.9 6.8 32 25.0
Sewage sludge, 5.6 mt/ha 5.4 28 14.6 5.4 22 35.4
Sewage sludge, 11.2 mt/ha 5.2 29 17.2 6.1 22 38.5
'The treatments were applied annually. The numerical values for the
inorganic fertilizer are kilograms per hectare. The concentrations
of heavy metals in the sewage sludge were as follows: Cu = 656ppm,
Mn = 1040ppm, and Zn = 8930ppm. Soil pH values at lime levels 0, 1,
and 2 were 6.0, 6.6, and 6.9, respectively, in 1974.
2/
The tissue analyzed was the third leaf down from the flag leaf.
'The numerical values are kilograms of nitrogen, phosphorus, and
potassium per hectare.
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