United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-075 May 1984
Project Summary
Effects of Sewage Sludge on Corn
Silage and Animal Products
R.H. Dowdy, R.D. Goodrich, W.E. Larson,
B.J. Bray, and D.E. Pamp
Studies were conducted to document
the impact of sludge-fertilized corn on
the food chain under controlled experi-
mental conditions that eliminated any
direct ingestion of sewage sludge. Spe-
cifically, the studies were to determine
whether sludge-borne heavy metals that
accumulate in corn are secreted into the
milk of dairy goats or are accumulated
in the organs and muscle of goats or
market lambs consuming corn silage
containing up to 5.26 mg cadmium
(Cd)/kg.
Dry matter intake, milk production,
and feed efficiency of dairy goats were
not reduced by feeding a high-Cd corn
silage continuously for 3 years — ap-
proximately half of their productive
lives. Likewise, feed efficiency and daily
gains of market lambs were not reduced
by consuming high-Cd silage.
Cd and zinc (Zn) from corn silage were
not secreted into the milk from lactating
goats, even though some animals were
receiving approximately 5 mg Cd and 100
mg Zn/day. In contrast, Cu concentra-
tions were higher in milk from goats
receiving the control feed.
The Cd concentrations in livers of
both goats and lambs were always
lower in animals receiving the control
feed. These levels increased as the
amount of silage Cd increased. Ac-
cumulations of Cd in animal kidneys
were 5 to 10 times greater than those
observed in livers, but they followed the
same general patterns. Cd concentra-
tions in animal heart and muscle were
low and not affected by treatment. Zn,
the only other element found to ac-
cumulate in silage as a result of treat-
ment, did not increase in animal liver.
heart, and muscle, but it increased
slightly in lamb kidney as a result of
feeding Zn-enriched silage. The concen-
trations of 16 other elements in the
various animal tissues were not con-
sistently affected when the animals
were fed sludge-fertilized corn silage.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Use of municipal sewage sludges as a
source of plant nutrients is of current interest
because of environmental and economic
concerns. Applications of sludge to soil at
rates consistent with the nutrient require-
ments of a crop are believed to be most
beneficial. Use of sludge as a crop fertilizer
would not greatly affect the demand for fer-
tilizer in the United States, since the total
amount of sludge produced would supply
only 1% to 2% of the annual nitrogen (N)
required for crop production. But the impact
of sludge additions to any given land area
is significant where applications are feasible.
Occurring along with the essential plant
nutrients present in sludge are also nones-
sential elements or those potentially toxic to
crops, animals, or humans.
Heavy metals are typically present in mu-
nicipal sludges. Transfer of metals from
sludge to soil and subsequently to plants that
enter the food and feed chain present a
significant health concern. Animals exposed
to subclinical levels of heavy metals are not
easily identified and may be slaughtered or
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used as a source of milk. Limited informa-
tion is available concerning the effects of
feeding sludge-fertilized crops to large
ruminants, though varying degrees of metal
accumulation in animal liver and kidneys
have been shown. Most studies have in-
volved direct ingestion of sewage sludge,
either as a component of the ration or as an
adherent to leaf surfaces of forages.
The purpose of the present studies was
to document the impact of sludge-fertilized
corn on the food chain under controlled ex-
perimental conditions that eliminated direct
ingestion of sewage sludge. Specific objec-
tives were to answer the following questions:
1. Does the feeding of sludge-fertilized
corn silage affect the long-term perfor-
mance of dairy goats and market
lambs?
2. Are sludge-borne heavy metals that ac-
cumulate in corn secreted into the milk
of dairy goats fed the silage for 3 con-
secutive years?
3. Does Cd accumulate in the organ and
muscle tissues of the diary goats and
market lambs that consumed corn
silage containing high concentrations
of Cd?
To accomplish these objectives, corn silage
produced on sludge-amended soil was fed
to dairy goats for 3 consecutive years and
to a group of market lambs in each of the
3 years. Determination of the effects on
human health of consuming food products
from animals that were fed sludge fertilized
corn silage was not included in this study.
Procedures
The soil was a well-drained, Typic
Hapludoll, with a pH of 6.2. Waste-activated
sewage sludge was applied initially at rates
of 0, 30, 60, or 90 megagrams (Mg)/ha.
Before the second and third croppings,
sludge was applied at rates of 0, 15, 30, Or
45 Mg/ha (Table 1). These treatments are
referred to as the control, low, medium, and
high treatments, respectively. Though
sludge metal concentrations varied from year
to year (Table 1), Cd was the only metal that
was atypically high.
Goats and lambs were fed silage ad
libitum. Free choice trace mineral salt that
contained <0.2 mg Cd, 2.4 mg chromium
(Cr), 128 mg copper (Cu), and 125 mg Zn/kg
was offered throughout the study. The corn
silage composition data (Table 1) showed Cd
and Zn as the only elements that increased
consistently as a result of sludge applica-
tions. Cd levels in cornplant tissue showed
the largest relative increases and reached a
high of 5.26 mg/kg during the third year.
These high Cd levels resulted in low Zn:Cd
ratios and enhanced the potential for Cd ab-
Table 1. Sludge Application Hates and Cd, Cu, and Zn Concentrations In Sewage Sludge and
Corn Silage
Item
Control
Treatment
Low
Medium
High
Average
Standard
Deviation
Within
Treatments
Sewage sludge applied (metric tons/ haft
Year 1 0
Year 2 0
Year 3 0
Cd content of sewage sludge (mg/kg)8
Year 1 -
Year 2
Year 3 -
Cu content of sewage sludge (mg/kg)3
Year 1
Year 2 -
Year 3 -
Zn content of sewage sludge (mg/kg)3
Year 1
30
15
15
156
186t>
JOS
703
640C
711
1700
Year 2 - 2065>>
Year 3
Cd content of corn silage (mg/kg)3
Year 1 <0.02°
Year 2 <0.02^
Year 3 <0.06d
Cu content of corn silage (mg/kg)3
Year 1 3.6°
Year 2 3.5
Year 3 4.2°
Zn content of corn silage (mg/kg)3
Year 1 31^
Year 2 44*
Year 3 35<*
1625
0.71
1.84
1.39
3.9
3.7
4.1
40
52
74
60
30
30
161
133
105
712
629
699
1590
2580
1570
1.27
2.68
2.73
4.4
3.8
4.8
50
67
75
90
45
45
156
137
112
717
730
653
1675
2680
1605
1.730
4.25°
5.2&
4.4C
3.6
5.3t>
6(P
113°
J07b
14
7
5
34
53
40
136
123
63
0.29
0.77
0.70
0.36
0.54
0.44
6.1
32.0
14.6
370 C Weight basis.
^Linear effect within sludge levels is significant (P
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Table 2. Concentrations of Cd, Cu, and Zn in Milk Collected from Goats Fed Corn
Silage Grown on Sludge-Amended Soil
Treatment (mg/kg)a
Metal Year
Cd 1
2
3
Cu 1
2
3
Zn 1
2
3
Control
<0.005
0.013
0.011
0.42
0.79
0.64°
35.1
34.1
39.4
Low
<0.005
0.011
0.017
0.32
0.63
0.43
37.2
40.8
40.1
Medium
<0.004
<0.009
0.012
0.29
0.58
0.26
33.8
34.5
34.6
High
<0.003
<0.009
0.009°
0.28
0.53
0.29
30.3d
32.8d
36.9
Average
Standard
Deviation
Within
Treatments
_
-
0.40
0.52
0.42
5.67
7.13
12.86
a70 C Weight basis.
^Linear effect within sludge levels is significant IP<0.05).
cControl versus a/I sludge levels is significant (P<0.01).
dLinear effect within sludge levels is significant (P<0.01).
When averaged across all sludge treat-
ments, the Zn concentrations in milk from
control goats did not differ from those of
goats fed sludge-fertilized corn silage. But
Zn in milk decreased as amounts of applied
sludge increased within sludge treatments
(Table 2), in spite of the fact that Zn con-
centrations in the silage ratio increased with
increasing sludge applications.
Control goats had higher Cu concentra-
tions in milk in each year, but they were
significant only in the third year, as the
amount of sludge used as fertilizer increased.
Possibly the increased levels of Cd and Zn
in the corn silage from sludge-fertilized soil
caused Cu to be less readily absorbed by the
goats.
The concentrations of the other measured
elements in milk were unaffected by treat-
ment. The elemental content of colostrum
was usually higher than that of regular milk,
but it was unaffected by treatment.
Blood Composition
The elemental composition of goat and
lamb blood was essentially unaffected by
feeding sludge-fertilized corn silage. The
significance of no Cd increase in blood is that
blood Cd levels are determined by current
exposure and that exposure is apparently not
high enough to affect blood concentrations.
Organ Composition
Goats
Selected metal concentrations in tissues
collected from goats at necropsy are listed
in Table 3. After 3 years, goats fed corn
silage that received control, low, medium,
and high sludge rates had consumed ap-
proximately <40,1,300,2,200, and 3,900 mg
Cd, respectively. Cd (the element that ac-
cumulated in the corn silage most dramati-
cally) was present at 0.26, 1.72, 2.10, and
2.94 mg/kg in goat livers for the control, low,
medium, and high sludge treatments, re-
spectively. These levels tended to increase
as amount of sludge applied increased.
Kidney Cd concentrations were approxi-
mately 10 times those observed in liver, rang-
ing from 3 to 22 mg/kg for animals on
control and high treatments, respectively.
Kidney Cd levels for control animals were
significantly lower than those in kidneys of
animals fed sludge-fertilized corn silage, and
they increased linearly with increasing sludge
applications. Cd levels in heart and muscle
were minimal and averaged 0.08 and 0.07
mg/kg, respectively.
Zn concentrations in liver and heart did not
differ significantly among treatments. Kidney
Zn ranged from 76.6 to 91.8 mg/kg with con-
trol animals having less Zn than animals fed
sludge-fertilized corn silage. Cu concentra-
tions in livers and kidneys were significantly
lower (approximately 2 mg/kg) in animals
receiving sludge-fertilized corn silage
treatments than in animals fed control silage.
The reason for this result may have been that
the elevated Cd and Zn levels in the sludge-
fertilized corn silage caused Cu to be less
readily absorbed by the goats.
None of the other measured elements had
accumulated in the goat tissues as a result
of fertilizing corn with sewage sludge.
Lambs
Concentrations of selected metals in lamb
tissues are presented in Table 4. For each
year, livers and kidneys from control animals
had a lower concentration of Cd than those
of animals fed sludge-fertilized corn silage.
The latter lambs showed linear increases in
the amounts of Cd in liver and kidney with
increasing sludge applications. Cd concen-
trations in heart and muscle were low and
unaffected by sludge treatments.
Zn concentrations in liver, heart, and mus-
cle were not significantly affected by sludge
treatments. Kidneys from control animals
tended to contain less Zn than those of
animals fed sludge-fertilized corn silage. The
lack of a major dose-related increase in
kidney Zn may be a result of high dietary Cu
(trace mineral salt) and Cd (corn silage) in-
teracting to reduce the absorption of Zn.
Although significant only in the second
year, Cu levels in kidneys from control lambs
were lower than those from lambs fed
sludge-fertilized corn silage. Elemental con-
centrations of Al, B, Ca, Fe, K, Mg, Mn, Na,
Ni, P, and Pb in liver, kidney, heart, and
muscle were not consistently affected by
sludge treatment.
Histological examinations of lamb liver and
kidney tissues showed no observable mor-
phological differences among sludge
treatments.
Table 3. Concentrations of Cd, Cu, and Zn in the Liver and Kidney of Goats Following
3 Years of Feeding with Corn Silage Grown on Slude-Amended Soil
Organ
and
Metal
Liver:
Cd
Cu
Zn
Kidney:
Cd
Cu
Zn
Control
0.26D
16.6°
90.3
3.lb
J5.8°
76. 6b
Treatment
Low
1.72
8.6
91.2
10.8
13.5
82.7
Img/kgP
Medium
2.10
10.3
85.9
24.8
14.9
90.4
High
2.94
10.7
88.8
22.4°
13.5
91.8
Average
Standard
Deviation
Within
Treatments
1.41
4.33
22.4
8.1
1.2
7.7
a70 C Weight basis.
^Control versus all sludge levels is significant (P<0.01).
cLinear effect within sludge levels is significant (P<0.05).
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Table 4. Concentrations of Cd, Cu, and Zn in the Liver and Kidney of Lambs Fed Corn
Si/age Grown on Sludge-Amended Soil
Organ
and
Metal
Liver:
Cd
Cu
Zn
Kidney:
Cd
Cu
Zn
Treatment (mg/kg)a
Year
1
2
3
1
2
3
1
2
3
J
2
3
1
2
3
J
2
3
Control
0.56b
0.29°
0.52°
185
53
164
102
79 ,
105
1.57
2.09°
0.78°
15.3C
16.0°
19.4
109
103°
100b
Low
8.82
1.97
1.13
196
64
163
110
89
105
1.38
5.07
2.70
16.9
16.9
20.5
103
110
103
Medium
1.06
3.56
2.52
215
89
168
103
85
118
1.90
10.89
7.31
15.4
17.8
19.5
109
124
111
High
1.31
5.29d
3.58^
210
66
128
98
84
114
3.Jjd
18.94^
10. 19°
16.8°
18.0
19.6
113
126
113
Average
Standard
Deviation
Within
Treatments
0.53
1.32
1.29
111
50
50
14
21
15
0.97
4.03
3.72
2.31
1.21
1.66
14
7
11
a70 C Weight basis.
b Control versus all sludge levels is significant (P<0.05i.
cControl versus all sludge levels is significant (P<0.01).
dLinear effect within sludge levels is significant IP<0.01).
Conclusions
Total dry matter intake, daily milk produc-
tion, and feed efficiency of dairy goats were
not reduced by feeding a high-Cd corn silage
continuously for 3 years — approximately
half of their productive lives. Similarly, daily
gains and feed efficiencies of market lambs
were not affected by treatment.
Cd from corn silage was not secreted into
the milk from lactating goats, even though
some animals were receiving approximately
5 mg Cd/day. Zn concentrations in milk from
control animals did not differ from those of
goats fed sludge-fertilized corn silage, but Cu
concentrations were higher in milk from the
control goats. The bioavailability of Cu may
have been limited by the elevated levels of
Cd and Zn in silage from sludge treatments.
The elemental concentrations of 15 other
metals and minerals in milk were not affected
by treatment. The composition of goat and
lamb blood was not affected by treatment,
except that Cu was higher in the blood of
control goats.
The Cd concentrations in livers of both
goats and lambs were always lower in con-
trol animals, and they increased with increas-
ing sludge applications. This result was
particularly true for lambs, where Cd con-
centrations as high as 5.29 mg/kg were
found. Accumulations of Cd in animal kid-
neys were 5 to 10 times greater than those
observed in livers, but they followed the
same general patterns. Cd concentrations in
animal heart and muscle were low and not
affected by treatment.
Zn, the only other element found to ac-
cumulate in silage as a result of treatment.
did not increase in animal liver, heart, and
muscle as a result of feeding Zn-enriched
silage. Small but significant increases in Zn
content were observed in lamb kidneys for
animals fed sludge-fertilized corn silage.
Cu concentrations in goat and lamb kid-
neys and goat livers were lower for animals
fed sludge-fertilized silage than for control
animals. The concentrations of 15 other
elements in the various animal tissues were
not consistently affected by sludge fertiliza-
tion of corn silage.
Thus corn silage produced on soil
amended at moderate to high rates with
sewage sludge containing high levels of
bioaccumulated Cd can be fed to dairy goats
and market lambs without impairing their
performance. Trace metals (particularly Cd)
taken up by the corn and ingested by the
animals did not accumulate in milk or mus-
cle tissue — foods consumed directly by
humans. Cd did accumulate in the kidneys
of goats and lambs, reaching concentrations
of 25 mg Cd/kg in goat kidney when corn
silage containing as much as 5.26 mg Cd/kg
of silage (an ingestion rate of approximately
5 mg Cd/day) was consumed continuously
for 3 years. Though Zn is taken up by corn
to a smaller extent than Cd, it did accumulate
in lamb kidneys, but not in goat kidneys or
livers of either species. Histological examina-
tions of lamb livers and kidneys showed no
observable morphological differences as a
result of consuming Cd-enriched silage.
The full report was submitted in fulfillment
of Interagency Agreement No. EPA-80-D-
X0428 by the U.S. Department of Agricul-
ture at the University of Minnesota, St. Paul,
Minnesota, under the partial sponsorship of
the U.S. Environmental Protection Agency.
R. H. Dowdy is with U.S. Department of Agriculture, St. Paul, MN ,55108; R. D.
Goodrich, W. E. Larson, B. J. Bray, and D. E. Pamp are with University of
Minnesota. St. Paul, MN 55108.
G. Kenneth Dotson is the EPA Project Officer (see below).
The complete report, entitled "Effects of Sewage Sludge on Corn Silage and
Animal Products." (Order No. PB 84-168 756; Cost: $10.00. subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/939
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