SPA United States Office of Water &
3W718 Environmental Protection Waste Management SW718
Agency Washington D.C. 20460 September 1978
Solid Waste
vvEPA Cadmium Additions
to Agricultural Lands -
Via Commercial
Phosphate Fertilizers
A Preliminary Assessment
-------
CADMIUM ADDITIONS
TO AGRICULTURAL LANDS VIA COMMERCIAL PHOSPHATE FERTILIZERS
A Preliminary Assessment
pe.fi
tke, 0^-tae ofi Solved Wa&te, undzfi c-ontnaat no. 6Z-01-4625
and J.A -izpfioduc.e.d an, /lecextved ^fiom the.
The ^x,nd-cngA &koatd be attuJibatid to
and not to tke. 0^-cce ofi Sot
-------
This report was prepared by SCS Engineers, Inc., Long
Beach, California, under contract no. 68-01-4625.
Publication does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental
Protection Agency, nor does mention of commercial products
constitute endorsement by the U.S. Government.
An environmental protection publication (SW-718) in the
solid waste management series.
-------
ABSTRACT
Current literature was reviewed to determine cadmium (Cd)
concentrations in phosphate rock and commercial phosphate
fertilizers. The data were utilized to estimate annual Cd
loading rates and 100-yr Cd accumulations in soil attributable
to the use of phosphate fertilizers. The annual quantity of
cadmium contributed to the environment in the form of phosphate
fertilizers was estimated and compared to other Cd emission
sources. In addition, the probable impacts of Cd loading and
accumulation via phosphate fertilizers and municipal sewage
sludge were compared.
111
-------
CONTENTS
Abstract iii
List of Figures vi
List of Tables vi
Acknowledgements viii
Introduction 1
Sources, Production, and Trends in the 3
Phosphate Fertilizer Industry
Sources of Ore 3
Production and Trends 3
Cadmium in Phosphate Fertilizers 8
Cadmium Concentrations in Phosphate Ores 8
Cadmium Concentrations in Phosphate 8
Fertili zers
Distribution of Phosphate Fertilizers 8
Distribution of Cadmium to Agricultural 12
Land
Assessment 16
Comparison of Cd Loadings from Sewage 28
Sludge and Phosphate Fertilizers
Bibliography 31
V
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FIGURES
Figure Title Page
1 Types and Locations of Phosphate Deposits 4
2 Phosphate Ore Production 6
3 Partitioning of States as to Source of 13
Phosphate Fertilizers
TABLES
Number Title
1 Phosphate Ore Production - United States 5
2 U.S. Phosphate Fertilizer Consumption 7
3 Cadmium Concentrations in Phosphate Ores 9
4 Concentrations of Cadmium in Phosphate 10
Fertilizers (Western and Southeastern Sources)
5 Concentrations of Cadmium in Phosphate 11
Fertilizers
6 Annual Cd Loading Rates Attributable to 14
Phosphate Fertilizers in the Western
Region - 1974
7 Annual Cd Loading Rates Attributable to 15
Phosphate Fertilizers in the Eastern
Region - 1974
8 Estimated Total Cd Contribution to the 17
Environment from the Use of Domestic
Phosphate Fertilizers - 1976
9 Estimated Cd Contribution to the Environment 19
From All Sources, 1974-75
10 Cadmium Concentrations in Selected 21
U.S. Soils
11 100 Year Accumulation of Cadmium in Soil 22
from the Annual Application of Phosphate
Fertilizers from Western and Southeastern
Sources
-------
TABLES (Continued)
Number
Title
12
13
14
Projected Years of Allowable Phosphate
Fertilizer Applications Based on Cd
Loading Limits Recommended By The NC-118
Study Group
Concentrations of
Tissue of Various
Containing 20 ppm
Cadmium in the Edible
Crops Grown in Soils
Cd
Annual Cd Loading Rates at Mine
U.S. Sewage Sludge Spreading Sites
26
29
vii
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ACKNOWLEDGEMENTS
We wish to thank Mr. Alessi Otte and Dr. Albert Page for
their guidance and assistance in the preparation of this docu-
ment.
vi i i
-------
INTRODUCTION
Cadmium has been found to be a potentially toxic heavy
metal. Chronic human exposure and animal studies on cadmium
indicate a positive correlation between the quantities of
cadmium (Cd) intake or accumulation and kidney damage do, 19,
28, 36, 48) .
One source of cadmium entering our environment is phosphate
ore used in the production of phosphate fertilizer. Cadmium
is also present in sludge from treatment plants. When these
fertilizers or sludges are applied to agricultural lands, the
potential exists for cadmium to enter the food chain through
plant uptake or grazing animals.
In the latest market basket studies for Cd, the U.S. Food
and Drug Administration (FDA) determined that teenage male Cd
intake is approaching the recommended maximum (72 ug/gm/day).
In deriving this finding, FDA used maximum weekly Cd intakes
suggested by the World Health Organization. Accordingly, several
states have taken steps to regulate the amount of cadmium applied
to agricultural lands from municipal wastewater treatment plant
siudge.
The requirements and the proposed Cd levels are being
challenged. Accordingly, the U.S. Environmental Protection
Agency (EPA) sponsored this research effort to identify the
fol1 owing:
The range of Cd concentrations present in commercial
phosphate fertilizers,
Annual Cd loading rates to agricultural land via
phosphate fertilizer application,
t Short and long-term Cd additions to agricultural
lands through phosphate fertilizer applications,
0 Potential effects of cadmium in phosphate fertilizers
on groundwater and plants, and
Comparative assessment of potential Cd additions
to agricultural lands from phosphate fertilizers and
sewage sludge.
-------
To perform the research, a review of the literature was
conducted, and data supplied by knowledgeable individuals were
assessed. Where data necessary to the project were lacking,
assumptions were made and are noted.
-------
SOURCES, PRODUCTION, AND TRENDS
IN THE PHOSPHATE FERTILIZER INDUSTRY
SOURCES OF ORE
All of the principal types of phosphate ore deposits are
found in the United States. McKelvey (23) noted that one or
more types of phosphate deposits are found in 30 of the con-
tinental states (Figure 1). The reserves in the U.S.A. are
located in two major geographic locations: the western region,
comprised of mines in Idaho, Montana, Wyoming, and Utah; and
the southeastern region, comprised of mines in Florida, North
Carolina, and Tennessee. The Western states contain the
largest reserves, but most of the mining activity is presently
centered in Florida (30).
PRODUCTION AND TRENDS
Phosphate ore production in the United States for the 1960-
1975 period is tabulated in Table 1 and illustrated graphically
in Figure 2. Major products derived from the ore are phosphate
fertilizers, elemental phosphorus, and phosphoric acid; the
latter is used as a feed stock in the manufacture of phosphate
fertil izer.
Consumption figures for phosphate fertilizers for the years
1960-1975 are presented in Table 2. While total phosphate fer-
tilizer consumption (expressed as P20^)* has increased, led
by concentrated superphosphates and diammonium phosphates, the
production of normal superphosphates has decreased.
*In phosphate fertilizers, P20s is more often used than P. To
convert P to P205, multiply by 2.29.
------- An error occurred while trying to OCR this image.
-------
TABLE 1. PHOSPHATE ORE PRODUCTIONUNITED STATES*
Year
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
Western
Amount
(103 t)f
5,276
4,845
5,519
5,347
5,945
7,182
8,360
7,066
7,462
7,070
6,767
6,109
6,086
6,993
7,896
7,362
Sources
Produced
(X of Total)
29.7
25.7
28.0
26.5
25.5
26.5
23.6
19.6
19.5
20.6
19.3
17.3
16.4
18.3
19.1
16.6
Southeastern Sources
Amount
(103 t)
12,517
14,008
14,170
14,823
17,379
19,558
27,053
28,942
29,952
27,147
28,369
29,161
30,948
31,225
33,541
36,914
Produced
(% of Total)
70.3
74.3
72.0
73.5
74.5
73.1
76.4
80.4
80.1
79.4
80.7
82.7
83.6
81.7
80.9
83.4
* Fertilizer Trends (ii).
t t denotes metric ton; to convert metric ton to ton, multiply by 1.12.
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SOUTHEASTERN
SOURCES
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WESTERN SOURCES
1960
1965
1970
1975
Figure 2. Phosphate ore production (data from Table 1)
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CADMIUM IN PHOSPHATE FERTILIZERS
CADMIUM CONCENTRATIONS IN PHOSPHATE ORES
Several available reports indicate that Cd concentrations
in phosphate ores are highly variable. Table 3 presents data
and appropriate references relating Cd content in phosphate
ore to geographical location. In general, Cd concentrations
in phosphate deposits in the southeastern United States are
low (approximately 10 ppm*); concentrations in western U.S.
phosphate deposits are considerably higher (approximately
150 ppm).
CADMIUM CONCENTRATIONS IN PHOSPHATE FERTILIZERS
Virtually all phosphate-derived fertilizers contain cadmium.
Schroeder and Balassa (36) recognized that phosphate fertili-
zers were a contributing source of cadmium to agricultural
lands. Lee and Keeney (21i) estimated that the amount of
cadmium contained in fertilizers added annually to farmland in
Wisconsin was equivalent to that contained in all sewage sludge
from Wisconsin wastewater treatment plants.
The literature, however, contained little substantive data
on Cd concentrations in domestic fertilizers. Fifty-nine
commercially available phosphate fertilizer samples from western
sources were collected and analyzed by EPA Region X (46).
These data (Table 4) compare with the phosphate ore Cd values
noted above and affirm the difference in Cd concentrations
reported for the western and southeastern region ores. Results
of work by Mortvedt and Giordano (24), presented in Table 5, also
substantiate the previous findings.
Considerably more data would be required to determine how
the Cd content in phosphate ores differs with the phosphate ore
source, method of processing, or fertilizer formulation.
DISTRIBUTION OF PHOSPHATE FERTILIZERS
The proceedings of the 1977 Tennessee Valley Authority
(TVA) Fertilizer Conference (33) provided national and regional
phosphate fertilizer consumption data for 1974. Reported were:
*For the purposes of this report, the terms ppm, ug/g, and mg/kg
are identified by one term - ppm.
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TABLE 4. CONCENTRATIONS OF CADMIUM IN PHOSPHATE FERTILIZERS
(WESTERN AND SOUTHEASTERN SOURCES)
Range of Cd Concentration
(ppm Fertilizer)
Western Region
Fertilizers*
Fertilizer Type
Triple superphosphate
(0-45-0) 40-175
Diammonium phosphate
(11-46-0) 50-160
Monoammonium phosphate
(11-48-0) 40-90
Superphosphate
(various percent mixture) 25-40
Southeastern Region
Fertilizers
12-14
6-14
6-7
5-7
* Unpublished data - EPA, Region X .(46.).
10
-------
TABLE 5. CONCENTRATIONS OF CADMIUM IN PHOSPHATE
FERTILIZERS*
Cd Concentration
Fertilizer ^"ype (ppm Fertilizer)
Diammonium phosphate
(Reagent) 0.9
Diammonium phosphate
(Idaho phosphate rock) 50.0
Diammonium phosphate
(North Carolina phosphate
rock) 30.0
10-15-0
(Idaho phosphate rock) 44.0
10-15-0
(North Carolina phosphate
rock) 17.0
* Mortvedt and Giordano (24).
11
-------
Tons of phosphate fertilizers (as P205) consumed, and
Harvested acreage for major crops (feed grains, wheat,
soybeans, cotton, and tobacco), for which fertilizers
were used.
For this assessment, the various regions denoted in the
TVA Conference proceedings have been classified as
belonging to either the western or eastern regions (Figure 3). The
following assumptions were made to simplify the distribution
analysis:
t Phosphate fertilizers consumed in the western region
were manufactured using western phosphate rock.
Similarly, phosphate fertilizer consumed in the eastern
region were manufactured with southeastern phosphate
rock.
All acreage planted to agricultural crops utilized
phosphate fertilizers.
In 1974, a total of 3,098,550 t*of phosphate fertilizer
(expressed as PgOs) was distributed nationally to a total of
94,015,000 ha under cultivation to the above-noted crops. On
a regional basis, the western region (Figure 3) distributed an
average of 19.6 kg of P205/ha; in the remainder of the United
States, P20c was distributed at an average rate of 37.9 kg/ha
for 1974.
DISTRIBUTION OF CADMIUM TO AGRICULTURAL LAND
Tables 6 and 7 present estimated low, intermediate, and
high Cd loading rates for acreage utilized for the cultivation
of the five crops. The following assumptions were made in
performing the calculations:
t All land identified with a specified crop received equal
application rates of fertilizer.
No losses of cadmium occurred as a
floods, or natural causes.
result of erosion
The low-intermediate-high Cd values of western fertili-
zers were assumed at 25, 100, and 175 ppm, respectively;
corresponding values for southeastern fertilizers were
5, 15, and 30 ppm.
t Phosphate fertilizers were assumed to have an average
content of 50 percent.
*Denotes metric tons.
12
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From the tabulations, the maximum annual average Cd
contribution in the western region would be 0.0162 kg/ha on feed
grain fields. In the eastern region, tobacco fields would receive
the maximum average contribution of 0.0214 kg/ha of cadmium.
ASSESSMENT
A preliminary assessment of the above estimated Cd contri-
butions from phosphate fertilizers follows. Four topic areas
are addressed:
Total Cd contributions from phosphate fertilizers,
Cd effects on soils,
Cd effects on groundwater, and
Cd effects on plants.
For comparison, potential Cd loadings from sewage sludge
applications are also discussed.
Total Cd Contributions from Phosphate Fertilizers
The utilization of phosphate fertilizers results in quanti-
fiable additions of cadmium to the environment, as shown above.
Table 8 presents a breakdown of estimated quantities on a
regional and national basis. Quantities were calculated based
on the following assumptions:
Intermediate Cd concentrations were 100 ppm (western
sources) and 15 ppm (southeastern sources) in the
phosphate fertilizers consumed.
83 percent of the fertilizer consumed was obtained from
southeastern manufacturing sources (derived from 1975
TVA statistics).
In 1976, Cd addition from the use of phosphate fertilizers on a
national basis was approximately 280 t.
To place these quantities in perspective invites further
comparisons between (43) cadmium contributed to the environment
from the utilization of sewage sludges, and (1) total Cd emis-
sions to the environment from all sources.
Estimated Cd Loadings from Sewage Sludge--
An estimated 73 t of elemental cadmium was distributed
to cropland from municipal sewage sludge sources during
1976, based on the following assumptions:
1976 national generation of municipal sewage sludge
was 4.5 million dry t (l).
16
-------
TABLE 8. ESTIMATED TOTAL Cd CONTRIBUTION TO
THE ENVIRONMENT FROM THE USE OF
DOMESTIC PHOSPHATE FERTILIZERS - 1976
Phosphate Fertilizer Production (1976)*
Western Sources 1,614,000 t
Southeastern Sources 7,878,000 t
Intermediate Cd Concentrations
Western Sources 100 ppm
Southeastern Sources 15 ppm
Annual (1976) Contribution of Cd
Western Sources 162 t
Southeastern Sources 118 t
Total 280 t
* Unpublished data - EPA, Region X (46).
17
-------
Average Cd concentration in dry sludge was 81 ppm
(12).
20 percent of all municipal sludge generated was
utilized on agricultural lands (44).
Cadmium distribution from fertilizer sources was slightly
more than four times greater than distribution from municipal
sewage sludge.
The phosphate application rate normally depends on the
soil type, crop to be grown, and method and frequency of
application. Typically, fertilizers are applied prior to
planting and, for some crops, during various stages of crop
growth. Based on which particular fertilizer formulations are
used, application rates may range from 50 to 250 kg P/ha.
Sewage sludge, on the other hand, offers a source of
phosphorus but in a greatly diluted form. Usually, the sludge
is utilized on an available N basis (5) with application rates
ranging from 2 to 50 t/ha (40). If all available sludge were
used as a soil amendment, distribution would approach 2 percent
of available agricultural land (5).
Phosphate fertilizers, on the other hand, are utilized
at much lower application rates - 25 to 250 kg/ha - and are
liberally distributed to a high percentage of the nation's
croplands.
Estimated Cd Loadings from All Sources
Under contract to the EPA Office of Toxic Substances,
Versar (33.) had revised Cd emission estimates based upon data
originally calculated by Fulkerson and Goeller (n ) for all
contributing sources (Table 9). Cadmium from phosphate
fertilizers constitutes approximately 5.5 percent of the total.
If the total estimated 1976 quantity (280 t) shown in Table 8
were substituted, this percentage would increase to approxi-
mately 14 percent. The difference in Cd contributions from
sewage sludge shown in Table 9 and the sewage sludge contri-
butions presented earlier (73 t) is attributed to the follow-
ing:
The Versar study (Table 9) cites all land disposal of
sludge, e.g., landfill, lagooning, and agricultural
utilization.
The 73 t estimate reflects the loading of cadmium from
only those sludges employed for agricultural utiliza-
tion - approximately 40 percent of the total sludge
destined to land (44).
18
-------
TABLE 9. ESTIMATED Cd CONTRIBUTIONS TO
THE ENVIRONMENT FROM ALL SOURCES, 1974-75*
Source
Zinc Ore Mining 4
Beneficiation
Primary Zinc Industry
Total: Extraction,
Pe fining & Production
Electroplating Stoops
Pigment Manufacture
Stabilizer Manufacture
Alloy yanufacture
Battery Manufacture
ratal: Industrial Conversion
Secondary ton-Ferrous Metals
Iron ard Steel Industry
Galvanized Prcd'jcts
Rubber Tire \,'ear
Incineration
Total: Consumption &
Disposal of
Cd-containing products
Phosphate Fertilizers
Phosphate Detergents
Coal Carfcustion
Diesel 1 Fuel Oil
Contxistion
Lubricating Oils
Sewage Sludge
Total: Inadvertent Sources
Grand Totals
Airborne
Dnissions
0.2t
102
102
-1
9.5t
2.7 t
2.3f
0.7 +
15
2.2
10.5
-0
5.2t
16
34
-0
-0
80(1974)
50 t
o.at
20
151
300
Watcrbome
Effluents
-0
2.0(1077)
-7(1974-75)
4.0(1977)
0.75
-0
-o
0.3
-8(1974-75)
-0
-0
-0
-0
-0
-0
-0
10.2
-0
-o
-0
-0
-0
10
15(1074-75)
Land -Destined
Wastes
250
-0
250
80(1977)
16.5
-0
-o
11. 4(1977)
-102(1974-75)
- 75(1980)
20
330
40
-0
70
460
100(1975)
130(1900)
-0
370(1974)
680(1980)
-0
-0
250
720(1974-75)
1,500(1974-75)
Total
Bui ss ions
359(1974-75)
125(1974-75)
93(1980)
494
831(1974-75)
1.800(1974-75
Metric tons per year as elemental cadmium,
"'"Estimates unchanged from Fulkerson-Goeller estimates (H)
19
-------
Calculations within theVersar study- are based on an
annual sludge generation of 10.9 million dry t. In our
study a more conservative figure of 4.5 million dry t
(1) was used.
Cadmium Effects on Soils
To assess the soil effects of cadmium from the use of
phosphate fertilizers, naturally occurring Cd levels in soils
must be considered.
Page and Bingham (28) suggested that soils derived from
igneous rock contain 0.1 to 0.3 ppm Cd and that soils of sedi-
mentary origin contain 0.1 to 1.0 ppm Cd. Page (27) reported
that typical soil Cd concentrations range from 0.03 to approxi-
mately 1.4 ppm, and that a median level for U.S. soils is
approximately 0.3 ppm. Stearns, Lofy, and LaConde (40) reported
naturally occurring Cd levels ranging from 0.24 ppm for a
Morley clay loam to 3.77 ppm for a Salinas silty clay loam
(Table 10).
A preceding section presented estimated annual mass Cd
emissions to the environment. To examine the potential effects
of Cd loading, however, fertilizer application rates must be
examined over longer time frames to determine both net addition
and cumulative effects. Table 11 presents such an approach
showing the hypothetical cumulative Cd loadings for 100 con-
tinuous years of phosphate fertilizer addition. The data in
this table were based on the following assumptions:
Fertilizer was applied annually for 100 yr at the two
rates indicated.
The intermediate values of Cd concentration (western-
100 ppm, southeastern-15 ppm) represented the phosphate
fertilizer used.
The natural Cd concentration of the soil was
0.3 ppm.
Application rates of 100 and 250 kg P/ha represented
the range of typical phosphate fertilizer application
rates .
Phosphate fertilizers contained 50 percent
The Cd loading data in Table 11 are presented in two
forms. The first shows the 100-yr cumulative Cd addition in
kg/ha for two different application rates; the second presents
a factored Cd addition in terms of 1,000 kg/ha fertilizers
added.
20
-------
TABLE 10. CADMIUM CONCENTRATIONS IN SELECTED U.S. SOILS*
Average Cd Concentrationt
Soil Type (ppm )
Congaree sandy loam 0.76
Salinas silty clay loam 3.77
Xenia silty clay loam 0.87
Britwater silt loam 0.73
Burkhardt sandy loam 0.46
Pembroke silt loam 0.83
Morley clay loam 0.24
Ross silty clay 0.78
* From Stearns, Lofy, and LaConde (40).
f HN03-HC104, oven-dry (11QOC) basis.
21
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It is recognized that farming practices may preclude the
continuous addition of phosphate fertilizers. When such addi-
tion is assumed, the above calculations indicate that the annual
amount of cadmium added to soils via phosphate fertilizers is
quite small. However, the long-term (100 years) accumulation
of cadmium from the western fertilizer source could be signifi-
cant. Total Cd additions of 4.6 and 11.5 kg/ha, respectively.
Williams and David (49) performed a similar analysis on
Australian phosphate fertilizers. Soils that had received
regular top-dressing of superphosphate for 30 to 45 yr and
total cumulative dressings of 2,500 to 4,5.00 kg fertilizer/ha
were analyzed for cadmium. The results were expressed in
terms of Cd increase per 1,000 kg fertilizer/ha and ranged
from 0.023 to 0.053 kg Cd per 1,000 kg fertilizer/ha (0.12 to
0.26 kg Cd per 1,000 kg P/ha). The data presented in Table 11,
0.07 to 0.46 kg Cd per 1,000 kg P/ha, are in general agreement
with the Australian findings.
Some state regulatory agencies have .proposed restricting
annual Cd additions to 0.5 kg/ha after 1985. Data from Table 11,
when expressed on an annual basis, indicate that the greatest
possible incremental net increases in cadmium from the use of
phosphate fertilizers are quite small - 0.12 kg/ha for western
and 0.02 kg/ha for southeastern sources, both at fertilizer
application rates of 250 k P/ha. As a result, the use of
typical amounts of phosphate fertilizers, regardless of source,
will not result in annual Cd concentrations greater than those
indicated.
In regard to heavy-metal loading from sewage sludge, it
has been recommended that soils with a cation exchange capacity
(CEC) value less than 5 meq/100 g soil be restricted to a total
cumulative Cd addition of 5 kg/ha; those with CEC's between
5 and 10, to a maximum of 10 kg/ha; and those with CEC's greater
than 15, 20 kg/ha (18). Table 12 extends that data in Table 11
and shows the number of consecutive years that phosphate ferti-
lizer can be applied before the first two limits are exceeded.
The following assumptions were made in calculating these
data:
t Cadmium concentration of western phosphate fertilizer
was 100 ppm; of southeastern phosphate fertilizer,
15 ppm.
Five percent of the cadmium applied in the form of
phosphate fertilizer was removed with the harvested
plant tissues. (Williams and David (49) showed that
plant uptake ranged from 0.4 to 7 percent.
23
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Phosphate fertilizers contained 50 percent
9 Annual applications of phosphate fertilizers were spread
at the suggested rate.
The loading period encompassing the shortest time span
for western phosphate fertilizers would occur at the heavier
application rate of 250 kg P/ha. Even at this rate, an esti-
mated 46 yr would be required to reach a cumulative total of
5.0 kg Cd/ha. Using southeastern fertilizer, more than
1,532 yr would be required to exceed 10.0 kg Cd/ha at the lower
loading rate.
Cadmium Effects on Groundwater
Williams and David (49, 50) examined soils (10 percent
or greater clay) that had received cumulative additions of
superphosphate of up to 4,000 kg/ha over 20 or more years.
They indicated that more than 80 percent of the fertilizer
cadmium was retained in the surface 10 cm of soil. In one
soil containing siliceous sand (2 percent clay), 50 percent
of the cadmium had been retained over a time span encompassing
a 900 kg/ha cumulative loading of phosphate fertilizer.
These data suggest that available cadmium applied to soils
by the use of phosphate fertilizers is chemically precipitated
or retained by the soil matrix (e.g., cation exchange). Thus,
its mobility is greatly reduced.
Cadmium Effects on Plants
The use of phosphate fertilizers on vegetable
crops presents one of the greatest potential hazards of
Cd addition to the food chain. The CAST Report (5) indicated
that crops may contain undesirable Cd concentrations in their
tissues without showing visible symptoms of phytotoxicity.
Further, Bingham et al . (3), CAST (5), Dowdy and Larsen (8),
and others have shown that leafy vegetables take up more
cadmium than other vegetable or grain crops. Table 13 presents
relative Cd uptake by selected vegetables and grains. The
ultimate Cd concentration in plant tissues is dependent upon
many factors, such as application rates, form of applied cadmium,
crop species and variety, CEC, soil pH, texture, organic matter
content, and concentrations of other heavy metals present in the
soil.
Williams and David (49) reported that cadmium in superphos-
phate was soluble in water. The cadmium was associated with both
the phosphate and sulfate compounds of the fertilizer, and
appeared to be as readily available to plants as CdCl2. However,
they found low Cd concentrations (0.012 to 0.036 ppm) in grain
and breakfast-cereal foods made from Australian wheat grown
25
-------
TABLE 13. CONCENTRATIONS OF CADMIUM IN THE EDIBLE TISSUE
OF VARIOUS CROPS GROWN IN SOILS CONTAINING 20 ppm Cd*
Crop species
Rice grain
Zucchini squash
Field bean
Corn grain
Cabbage
Tomato fruit
Radish
Cd
Concentration
ppm t
0.6
1.0
1.0
2.4
3.4
3.6
6.3
Crop species
Red beet
Wheat grain
Turnip
Soybean grain
Carrot
Lettuce
Curlycress
Spinach
Cd
Concentration
ppm t
7.4
8.7
11
17
19
135
154
188
* Derived from Bingham et al. (3); to produce a concentration of
20 ppm Cd in soil, 1% sewage sludge which had been spiked with
CdS04 was mixed with the soil.
t Oven dry weight (70°C) basis.
26
-------
in fields with a long history of superphosphate usage (contain-
ing 44 ppm of Cd). Plant uptake of cadmium from these fields
ranged from 0.4 to 7 percent of total cadmium, and the uptake
was greatly influenced by soil type.
Assuming that only a small percentage of the cadmium from
fertilizer sources is available for plant uptake, the effects
of incremental vs. cumulative Cd loadings will be examined.
The CAST Report (s) , commenting on Cd concentrations in
corn leaves, stated:
"...data 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 cadmium 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."
Recent studies on ryegrass (2) and snap beans ( 9 ) also
suggest that cadmium in plant tissues is more a function of
periodic incremental Cd additions than the cumulative Cd total.
Reuss, Dooley and Griffis (si) recently reported a linear
relationship between Cd additions to soils in the form of
phosphate fertilizers and resultant plant (various species)
uptake. These data, while suggesting a relationship between
total soil and plant Cd concentrations, are seemingly in con-
tradiction with the above referenced studies. Several limita-
tions of the study, however, are noted:
The study entailed greenhouse potting studies conducted
over a one-year period.
t The test conditions may not have been typical of field
conditions.
Extrapolation of one year's data may not be valid,
especially in light of the previously presented
references.
» The fertilizers were "spiked" with cadmium.
The calculations in this study show a range of annual Cd
loading from 0.007 to 0.12 kg/ha, depending on the fertilizer
sources (Table 11). Williams and David (49) presented data
showing that up to 7 percent of cadmium in Australian phosphate
fertilizer was available for uptake by plants. Using this
27
-------
availability as a maximum, the above-cited range would diminish
to 0.00049 to 0.0084 kg Cd/ha/yr.
If cumulative loadings play an important role in plant
uptake, a specific but unknown amount of cadmium in phosphate
fertilizers applied to soil will increase the latter range
somewhat. It should be considered, however, that of the
available 100-yr Cd total, some cadmium will be precipitated or
fixed in the soil matrix. Therefore, it would seem unlikely
that reasonable application rates of phosphate fertilizer con-
taining an average of 100 ppm cadmium would increase the Cd
levels of plant species to any significant degree.
There are not sufficient data which can be used to compare
the plant availability of cadmium in phosphate fertilizers with
that in sewage sludge. Cunningham et al. (7) presented data
which showed that the treatments involving inorganic salts of
heavy metals (Cr, Cu, Zn, and Ni) resulted in lower corn
yields, and in general, higher metal concentrations than the
equivalent sludge treatments. Chemical speciation affects rates
of precipitation and dissolution of metals in soil, thereby
influencing their availability to plants (22). These data
seem to indicate that cadmium in phosphate fertilizers would be
more available for plant uptake than that in sewage sludge,
assuming Cd loadings were the same from both sources. However,
more research is needed to substantiate this speculation.
COMPARISON OF Cd LOADINGS FROM SEWAGE SLUDGE AND PHOSPHATE
FERTILIZERS
A recent study by Stearns, Lofy, and LaConde (40) provided
Cd loading data at nine agricultural locations where sewage
sludge had been utilized for 5 to 17 yrs (Table 14). With the
exception of Site 7, the Cd loading rates ranged from 0.08 to
1.0 kg/ha/yr. It is worthy of note that the Cd concentration
of sludges used at Sites 1, 2, 3, 5, 6, and 9 were of the same
magnitude as Cd concentrations of southeastern phosphate ferti-
lizers. Sites 4 and 8 approximated Cd values of western phos-
phate fertilizers.
Site 8 received an annual Cd application rate of 1.0 kg/ha
when amended with Cd-containing sewage sludge. If this site
were to be treated with an additional western source phosphate
fertilizer (100 ppm Cd) at an annual fertilizer application
rate of 250 kg P/ha (equivalent to 55 kg P/ha), the Cd loading
rate attributable to the fertilizer would be 0.025 kg/ha. By
comparison, therefore, the annual Cd addition from sewage sludge
at Site 8 would be 40 times greater than that from phosphate
fertilizer.
28
------- An error occurred while trying to OCR this image.
-------
Similarly, Lee and Keeney (21) indicated that sludge
additions, compared to phosphate fertilizer additions, had a
greater potential of significantly increasing the soil concen-
tration of cadmium because of the much higher application rates
used. They estimated that 186 yr of continuous (once per year)
phosphate ferti1izer application at 50 kg/ha/yr would be required
to equal one application of sewage sludge at a rate of 9 dry
t/ha (assuming a sludge Cd concentration of 18 ppm).
The largest contributing difference in the above cited
example stems from the application rates of the sewage sludge
compared to those of the fertilizer. On a short-term basis,
therefore, the net addition of cadmium to soil by the use of
phosphate fertilizers is probably not significant. The long-
term cumulative additions are, however, of potential signi-
ficance.
30
-------
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practices, an environmental assessment. 2v. v.2, 1978. (In press.)
41. Stenstrom, T. and M. Vahter (National Swedish Environment Protection
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short report. Ambio, 3(2):91-92, 1974.
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34
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EPA REGIONS
U.S. EPA, Region 1
Solid Waste Program
John F. Kennedy Bldg.
Boston, MA 02203
617-223-5775
U.S. EPA, Region 2
Solid Waste Section
26 Federal Plaza
New York, NY 10007
212-264-0503
U.S. EPA, Region 3
Solid Waste Program
6th and Walnut Sts.
Philadelphia, PA 19106
215-597-9377
U.S. EPA, Region 4
Solid Waste Program
345Courtland St., N.E.
Altanta, GA 30308
404-881-3016
U.S. EPA, Region 5
Solid Waste Program
230 South Dearborn St.
Chicago, IL 60604
312-353-2197
U.S. EPA, Region 6
Solid Waste Section
1201 Elm St.
Dallas, TX 75270
214-767-2734
U.S. EPA, Region 7
Solid Waste Section
1735 Baltimore Ave.
Kansas City, MO 64108
816-374-3307
U.S. EPA, Region 8
Solid Waste Section
1860 Lincoln St.
Denver, CO 80295
303-837-2221
U.S. EPA, Region 9
Solid Waste Program
215 Fremont St.
San Francisco, CA 94105
415-556-4606
U.S. EPA, Region 10
Solid Waste Program
1200 6th Ave.
Seattle, WA 98101
206-442-1260
yal699
SW-718
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