Cu literature review

Cu Lit. Review J. Davis 1 11/09/04
Literature Review -Micronutrient Copper as a Potential Pollutant


I. Background

A listing of heavy metals typically includes Cadmium, Cobalt, Chromium, Copper, Iron, Mercury, Manganese,
Molybdenum, Lead and Zinc. Eighteen elements are considered essential to plant growth. Macronutrients include
Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium
(Mg) and Sulfer (S). Nine elements are required in such small amounts that they are called micronutrients or trace
elements. Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Nickel (Ni), Cobalt
(Co), and Clorine (Cl) are commonly listed. Many crops are fertilized with one or more trace elements to maximize
yields. Micronutrients are increasingly being considered as a pollutant. In general, the levels of these elements is
increasing in soil due to atmospheric deposition; land applications of sludge, manure, and smelter waste; and long
term use of pesticides. The determination of a phytotoxicity level for a specific crop is not a simple task. Soil
properties have a strong influence on crop uptake. (5,29)

II. Federal Regulations

The maximum cumulative loading rates for heavy metals allowed under the original EPA guidelines were relatively
low and varied with the cation exchange of the soil (pH ≥6.5). The Cu loading rate was set at 560 kg/ha (1,2,24).
Subsequent research demonstrated that higher rates of Cu could be applied with no adverse effect on plant growth
(1,14,26). Consequently, the maximum loading rate was revised to 1500kg/ha.


Part 503 -STANDARDS FOR THE USE OR DISPOSAL OF SEWAGE SLUDGE (31).

• Assessments made regarding bio-solid use/disposal practices including: Land application, surface disposal, and
incineration. Procedures established by National Academy of Sciences. (Ch.1:2-5)
• Good discussion of plant uptake and response to metals and associated soil condition.(Ch.1:36-40)
• Criteria used to establish "pollutants of concern", assessment methodologies, and risk-based pollution limits.

Copper is included. (Ch.2, pages 7-18) Public and peer review, proposals, and revisions made. (Ch.2:20-29)
Greater reliance on field studies and less on greenhouse studies. (Ch.2:28)
• Issues regarding highly exposed vs. most exposed individual assessments of potential hazard. (Ch.3:33)
• Final rule: pot/salt studies "greatly overestimate" phytotoxicity and bioavailability of metal pollutants in bio-
solids. References are sited. Good plant uptake and plant response to metals discussion. (Ch3:36-40) Additional
considerations that reduce, or increase, the plants risk to metal toxicity Ch.3:43-44
• Phytotoxicity criteria, thresholds (PT50, PT25), experimental procedures and results related. Cu loading rates
by "calculation approach" is 2500 kg/ha and by "probability approach" was 1500kg/ha so the conservative 1500
kg/ha was designated the appropriate rate for Cu loading. Reference is made to a comprehensive review of
plant metal concentration data and yields from bio-solids field studies including all data reflecting various soil
types and bio-solid sources. Excellent summary of multiple research studies. (Ch.3:48-49)
• Risk assessment Algorithms for human adult/child and for animals for ingestion of crops grown on bio-solid
amended soils Ch.4: 62-70 and land application pollutant limits by exposure pathways Ch. 4:81-83.
• Pollutant limits for land application and 4 types of land application are described. Cu is included as a pollutant
but is excluded from the surface disposal regulation for reasons explained. (Ch.5:99-102) Copper is used as an
example for derivation of pollutant concentration limits (Ch.5:101)
• Rationale for associating specific management practices with Part 503 Rule is listed in tabular format.
(Ch.5:105-106)

III Literature Review

A. Soil Considerations

• Copper Sources:

Cu Lit. Review J. Davis 2 11/09/04
♦ Inorganic sources of Cu

Weathered minerals and resultant sulfides, hydroxyl carbonates, oxides, and commercial fertilizers (5,29).

Some Cu Fertilizers Formulas Elemental Cu % Solubility (water)
Copper metal Cu 100 Insoluble
Copper nitrate Cu(NO
3
)
2
•3H
2
O Soluble
Copper acetate Cu(C
2
H
3
O
2
)
2
•H
2
O 32 Slightly
Copper oxalate CuC
2
O
4
•0.5H
2
O 40 Insoluble
Copper oxychloride CuCl
2

•2CuO•4H
2
O 52 Insoluble
Copper ammonium phosphate Cu(NH
4
)PO4•H
2
O 32 Insoluble
Copper Sulfates (general formula) CuSO
4
•3Cu(OH)
2
13-53 Insoluble
Copper sulfate (Chalcanthite) CuSO
4
•5H
2
O 25 Soluble
Copper sulfate (monohydrate) CuSO
4
•H
2
O 35 Soluble
Chelates
Na2Cu EDTA 13
Soluble
NaCu HEDTA 9
Soluble

Adapted from Gilkes (12)
______________________________________________________________________________________________

Trade and other names: Agritox, Basicap, BSC Copper Fungicide, CP Basic Sulfate and Tri-Basic
Copper Sulfate. The pentahydrate form (CuSO
4
•5H
2
O) is called bluestone, blue vitriol, Slazburg vitriol,
Roman vitriol, and blue copperas. Bordeaux mixture is a combination of hydrated lime and copper sulfate.
Copper sulfate is often found in combination with other pesticides (32).

Regulatory status: Copper sulfate is classed as a General Use Pesticide (GUP) by the EPA. Copper sulfate
is toxicity class I-highly toxic. The label bears the warning Danger-Poison because of its potentially
harmful effects on some endangered aquatic species, surface water use may require a permit in some areas
(32).

Introduction: Copper sulfate is a fungicide used to control bacterial and fungal diseases of fruit, vegetable,
nut and field crops. These diseases include mildew, leaf spots, blights, and apple scab. It is used as a
protective fungicide (Bordeaux mixture) for leaf application and seed treatment. It is also used as an
algaecide and herbicide, and to kill slugs and snails in irrigation and municipal water treatment systems. It
has been used to control dutch elm disease. It is available as a dust, wettable powder, or liquid concentrate
(32)
Cu Lit. Review J. Davis 3 11/09/04
♦ Organic sources of Cu



Manure
(g/Mg dry wgt) (g/Mg dry wgt)

Poultry (broiler) 172
a
473
f

Poultry (layer)-no bedding 155
e

Dairy cow 30
a
30
h

Swine 150
b
150
g

Sheep 30
a

Horse 25
a

Feed lot cattle 2
c

Young rye green 5
a

Spoiled legume hay 10
a

Municipal waste compost 280
d

Sewage sludge 500
a

Wood wastes 50
a


a
Brady and Weil (5) p.629
b
after (5) cited from Zublena, et al.(1993)
c
after (5) cited from Eghball and Power (1994)
d
after (5) cited from He, et al.(1995)
e
after Miller in (29) cited from Edwards and Daniel (1992) and Sims and Wolf (1994)
f
after Miller in (29) cited from Edwards and Daniel (19920 and Brady and Weil (1996)
g
after Miller in (29) cited from Choudhary et al. (1996) and Brady and Weil (1996)
h
after Miller in (29) cited from Brady and Weil (1996)

Cu Lit. Review J. Davis 4 11/09/04

• Natural (Background) levels of Copper in Soils

Holmgren et al. (16) and Huang (17) evaluated previously published data for concentrations of heavy
metals in soil samples collected from around the world.

Copper reported as geometric means
1
for air dried soil samples [adapted from Holmgren et al., (16)]

mg kg
-1

3045 U.S. samples 18 (Holmgren et al., 1993)
1218 U.S. samples 17 (Shacklette et al., 1984)
2276 England samples 18 (McGrath, 1986)
654 Wales samples 16 (Davies et al., 1985)
World samples 59.8 (Ure et.al., 1982)

Copper reported as arithmetic means
2
for air dried soil samples
[Holmgren et.al., (16)]
mg kg
-1

Typical U.S. soil 50 (Sposito et al., 1984)
Minnesota soils 26 (Pierce et al., 1982)

237 Ohio soils 19 (Logan et.al., 1983
296 Ontario soils 25.4 (Frank et.al., 1976)

Considering 3045 U.S. soil samples LRR reported (geometric means)
[Holmgren et.al., (16)]

Mineral Soils
mg kg
-1
Organic Soils
mg kg
-
1

K -Northern Lake States 15.4 K -Northern Lake States 59.6
L -Lake States 18.2 L -Lake States 84.7
N -East and Central Farming 8 R -Northeastern Forage 149
R -Northeastern Forage 34 All Organic Soils 86.9
S -Northern Atlantic Slope 13.5
All Mineral Soils 15.6

Considering 3045 U.S. soil samples by: (geometric means)
[Holmgren (16)]






soil order

mg kg-1
surface texture
mg kg
-1
State
(mineral soils)
mg kg
-
1

Alfisol 10.9 Loamy Sand 6 MD 7.7
Aridisol 25 Sandy Loam 10.8 ME 64.8
Entisol 21.1 Fine Sandy Loam 10.3 NJ 11.0
Histosol 183.2 Silt Loam 18.1 NY 27.0
Inceptisol 28.4 Loam 18.6 PA 28.3
Mollisol 19.1 Silty Clay Loam 28.7
Spodisol 48.3 Clay 37.6
Ultisol 6.2 Clay Loam 22.7
Vertisol 48.5 Silty Clay 33.6
all orders 18.3 Organic muck 75.8
Organic sapric 97.9
All "textures" 18.3



1
It has been observed that element concentrations in natural materials are distributed in a log normal pattern.
Therefore, the geometric mean gives a better estimate of the most probable value in large data sets. (17)
Geometric mean is the antilog of mean for log-transformed data. (16)
2

The arithmetic mean is used for smaller data sets or in cases where the soils are closely related. (17)
Cu Lit. Review J. Davis 5 11/09/04
Huang evaluates the Holmgren et al., (17) data plus an additional 5692 samples from England and
Wales (McGrath and Loveland,1992).
[adapted from Huang (17)]

U.S. Agricultural Soils England and Wales Topsoils (0-15 cm)

Element
Geometric mean (µg g
-1
)
3
Range
Geometric mean (µg g
-1
)
Range
Copper 18 < 0.6-495 23.1 1.2-1,510


Huang sites earlier work relating mean concentrations of metals from mainland China by soil order
(Chang et al., 1991)
[adapted from Huang (17)]
Soil order Geometric means Cu

(µg g
-1
)
Lithosols 26.5

Cold Highland Soils 23.8
Mollisols 10
Aridisols 21.7
Inceptisols 21.8
Alfisols 15.1
Ultisols 17.8
Oxisols 10.9
Vertisols 19.6
Entisols 22.2


• Excess Cu in soils reported

Merry et al. (21) surveyed the distribution of metals in 98 soils from orchards in Australia and Tasmania and
found copper, lead, and arsenic concentrations 25-35 times greater than background levels.

Frank et al. (11) studied apple, cherry, peach orchard and vineyard soils treated with Cu-salts over an 80 year
period in Ontario, Canada. The recommended use of 38 organic and inorganic pesticides used between 1892
and 1975 resulted in the elevation of copper levels over normal background in soils. Crop management tactics,
pesticides used, and duration of application influenced the accumulation of copper in the study area. A high
percentage of apple orchard soils tested had significantly elevated Cu levels from 21ppm to 63ppm over a 70
years period.

• Sludges

Generally accepted concepts:
Research utilizing sludges have established that they are extremely variable in composition and may contain
high levels of Zn, Cd, Cu, Ni, and Pb. Sludge composition, application rates, pH, and CEC are important
factors in plant uptake of metals. Immediately post application Cu uptake is enhanced then reduces as the
organics stabilize. This is probably due to acidifying consequence of organic decomposition and perhaps a

"chelating effect" rendering Cu more available for uptake.

• Feed additives and Cu manure content
4


Copper is added to poultry and swine diets to increase growth rate and promote feed efficiency. On a dry matter
basis: Kingery et al.(18) reported an average of 470 mg kg
-1
Cu in poultry litter, and Anderson et al.(1) 1316 mg
kg
-1
Cu in swine manure when swine were supplemented with an average of 251 mg kg
-1
Cu as CuSO
4
.


3
µg g
-1
and mg kg
-1
are equivalent expressions
Cu Lit. Review J. Davis 6 11/09/04
Soil Organic Matter and Chelation

Generally accepted concepts:
 Soil organic matter

Consists of a wide range of substances, including living organisms, remains of organisms, and organic
compounds produced by metabolism in the soil. The remains of plants, animals, and microorganisms are
continuously broken down in the soil and new substances are synthesized by other microorganisms.
Organic matter comprises only a small fraction of the mass of a typical soil. By weight, typical well-
drained mineral surface soils contain from 1 to 6 percent organic matter. Humus is a collection of organic
compounds that accumulate because they are relatively resistant to decay. The surface charges of humus
attract and hold nutrient ions. Small amounts of humus can dramatically increase the retention and
exchange of nutrients in soils. (5,29)

 Chelates
Are organic compounds that are capable of bonding with positively charged micronutrients (like Cu
2+
and
Cu(OH)
+
). These compounds may be synthesized by plant roots and released into surrounding soil, may be
present in soil humus, or may be synthetic compounds added to enhance micronutrient availability. Many
chelating compounds occur naturally in the soil and numerous synthetics are available. The complexed
form is protected from reaction with inorganic soil constituents. If soluble the complex is available for plant
uptake, if insoluble availability is decreased. Two chelated metal uptake mechanisms are recognized:
Dicots (cucumber, peanuts)-root tissue produces strong reducing agent (NADPH) that strips the chelate
from the metal and allows the reduced metal entry into the root. Monocots (corn, wheat) accept the entire
chelate complex into the root and then remove the metal, reduce it, then expel the chelate to the soil. (5)

Soil metal studies often utilize chemical extractants such as EDTA, DTPA and CaCl
2
to evaluate
concentrations. McBride (19) cites pertinent research and relates that "metals extracted by the chelating
agents, EDTA and DTPA have been reported to correlate well with uptake of metals into plant tops of a
number of crops. Metals extracted by these agents, are largely in exchangeable, organically-complexed, and

carbonate forms, and tend to correlate with metal uptake by plants. It should not be assumed that these
chelating agents actually measure availability".

• Organic matter protection debate

There are several schools of thought regarding the long-term binding, and release, of potentially dangerous
metals by the organic fraction of soils.

"Time Bomb Theory" suggests that the organic matter portion of bio-solids binds metals thus reducing their
bioavailability. However, as soon as the organic matter degrades all accumulated metals are rendered available
(8,19,31).

The EPA response: "Bio-solids are typically about 50% organic and 50% inorganic. Much of the binding that
occurs is attributable to the inorganic part of bio-solids, namely the oxides if iron, aluminum, and manganese,
and also phosphate compounds. The binding effect persists even after the bio-solids have been applied to soils,
except at very low pH situations. Field data suggests that these compounds remain stable for hundreds of years
if pH doesn't drop drastically. The bio-solid has degraded long ago (Beckett et. al., 1979; Johnson et al.,1983)"
(31)

Chaney and Ryan (8) concluded that "all evidence available indicates that the specific metal absorption
capacity added with sludge will persist as long as the heavy metals of concern persist in the soil" They reject
the "time bomb theory".

McBride (19) evaluates the concept that sludge decomposition products can maintain low heavy metal
solubilities for long, perhaps decades, periods of time. He labels the concept the "sludge protection theory".
McBride considers EPA 503 regulations too permissive for most metals because they permit 10 to >100 times
the current background levels for metals in most soils. He notes that while EPA loading limits have not been
Cu Lit. Review J. Davis 7 11/09/04
reached in field experiments, except for a few cases and a few metals, it has yet to be proven that these EPA
levels are safe. Further, mineralization of organic matter in sludge could release metals in more soluble forms.

There is general agreement that a fraction of the organic matter resists decomposition and could protect against
metal uptake for decades (4,8,19), but without additions of sludge the soil would eventually return to near
original organic matter levels and residual metals would have to be rendered unavailable by the inorganic
(mineral) fraction of the soil or be available for uptake.
McBride (19) evaluated long-term orchard studies where soils became increasingly polluted with Cu due to
pesticide applications and concluded that "decades or even centuries of aging pollutants added in inorganic
form to soils is insufficient to convert them to unavailable forms. Consequently, the EPA heavy metal limits
(1500 kg ha
-1
) can be considered safe only if materials in the sludge itself permanently immobilize most of the
metals.

• Organic half-life

♦ The half-life of organic decomposition has been estimated at approximately 10 years (4), but may
overestimate decomposition rate over a period of several decades (30). While some of the organic
complexing ability is lost over several decades, a portion endures for an extended period of time.(4,30)

Bell et al. (4) reported that organic additions from sludge application may still be significant 10 years after
application. The study sites European data suggesting a one-half of the organics added with sludge or
farmyard manure was still present in the soil after 10 years. A similar rate of organic loss could be
expected in the Mid-Atlantic states. Organic matter may have significant impact on Cu availability and
many studies have shown the greater ability of Cu to form complexes with organic matter than Zn or Mn.

• pH
♦ Generally accepted concepts: Micronutrients, including Cu, are most soluble and available under acid
conditions. In very acid conditions one or more trace elements may become toxic to common plants. At
higher pH the nutrients are changed to insoluble compounds that are "fixed" and unavailable for plant
uptake. The exact pH at which micronutrients become "fixed" varies with specific element and valent state.
In soils, Cu is found in more than one valent state. Ion species Cu

2+
dominates under acid conditions and
Cu(OH)
+
at higher pH. In general, high pH values favor oxidation (higher valence), and lower pH the
reduced species (lower valence). The changes in valence are usually associated with decomposition of
organic matter by microorganisms. Cu
2+
is much less soluble than Cu(OH)
+
.(5,29) Most micronutrient
toxicity problems can be avoided by maintaining a pH at neutral or above. Draining a soil is also usually
beneficial , since oxidized forms are usually less soluble and less available for plant uptake than are the
reduced forms (Cr is an exception)(5). It is well established that pH is an important factor in the availability
and uptake of Cu.

Merry et al. (23) Using metal contaminated soils studied the effects of soil pH on uptake of Cu by radish
and beet in a greenhouse study. They noted that Cu concentrations in the plant decreased with increasing
soil pH and that the effect was more marked in the more contaminated soils. Further, soils behaved
similarly no matter what the source of contaminants, but freshly applied Cu appeared to be more
deleterious to plants, especially on poorly buffered soils, then are the same elements accumulated over a
long period of time.

Cavallaro et al.(7) found that sorption and fixation of Cu increased rapidly above pH 4 and 5
respectively. Concluded that acid soil clays show highly pH dependent sorption of Cu. Microcrystalline
oxides seem to be most important for Cu sorption.

• Soil texture, clay type and humus

♦ Generally accepted concepts:

Plant nutrients are released from colloidal surfaces of clay and humus to the soil solution. CEC (or ECEC)
is a measure of the number of charged sites available for capture, or release of nutrients. All soil particles,
organic or inorganic, exhibit the surface charges associated with OH groups, charges that are largely pH
Cu Lit. Review J. Davis 8 11/09/04
dependent. Most of the charges associated with humus, 1:1 -type clays, oxides of iron and aluminum, and
allophane are of this type. In the case of 2:1-type clays a large number of charges are associated with
isomorphic substitution. These charges are not pH dependent and are generally termed permanent charges.
The CEC of most soils increases with pH. To obtain a measure of maximum retentive capacity, the CEC is
commonly determined at pH 7 or above. At neutral, or slightly alkaline pH, the CEC reflects most pH
dependent and permanent charges. (5,29)
Soil texture is significant because of the relative amount surface area available for adsorption of charged
particles including water. The external surface of 1 g of colloidal clay is at least 1000 time that of 1g of
coarse sand. In general, finer textured soils have a higher exchange capacity associated with the mineral
fraction and are therefore less prone to radical changes in pH then are coarser textured soils (5). The
resistance to pH change is referred to as "buffering".

• Micronutrient balance:

♦
Generally accepted concepts:
Plants vary in the amount and species of trace elements required for productive growth. Some plant
enzymatic and biochemical reactions require more than one micronutrient and some are poisoned by the
presence of a second nutrient. Some examples: Mn and Mo are needed for assimilation of nitrates by most
plants, the use of Cu and K is dependent on a balance between the two, and Cu utilization is favored by
adequate Mn which in some plants is assimilated only if Zn is present in sufficient amounts. (5)

"Antagonistic effects" - Some examples: Iron deficiency is encouraged by an excess of zinc, manganese,
and copper; excess phosphate may encourage a deficiency in zinc, iron and copper; heavy N fertilization
intensifies copper deficiency and excess copper or sulfate may adversely affect utilization of molybdenum.
Some antagonistic effects are utilized to reduce toxicities. For example, copper toxicity of citrus groves

caused by residual Cu from insecticide sprays may be reduced by adding Iron or phosphate fertilizers. (5)

"Synergistic effects" -Example: Boron at the root surface increases the uptake of Cu.

McBride (19)- "Because heavy metal toxicity to roots can be somewhat additive and even synergistic when
several metals are present (Hassett et al 1976; Wallace and Berry, 1989), soils approaching the USEPA
limits for several of the phytotoxic elements may show yield reductions at lower concentrations than
expected if a single element is at an elevated concentration. For this reason, there has been debate about the
extent to which the phytotoxic effects of metals such as Zn, Cu, and Ni are additive and whether individual
metal limits should be lowered to reflect this additivity (Saunders et al 1986, Davis and Carlton-Smith,
1984). Antagonism between metals such as Cd, Zn, Mn, and Cu can reduce root and tip growth as well as
reduce micronutrient content in the plants (Jalil et al., 1993), Mn deficiency on old sludge sites (Trocme et
al., 1950), and deficiencies in plants associated w/ high Zn and Cu (Leeper 1978)".

• Organic soils - micronutrient contents depend on the amount and extent of washing and leaching into the bog
area as the soil was formed. The ability of organic matter to bind copper may lead to deficiencies. In
comparison to other trace elements, Cu is especially tightly bound to organic matter (humus) and thus less
available for plant uptake. Cu availability may be very low in organic soils (Histosols). If drained, the rapid
mineralization of the organics and associated reduced pH may enhance Cu uptake (5).

♦ Soil erosion -removes organic matter and thus reduces the soils ability to bind copper in topsoil. Exposed
subsoil horizons may have lower pHs rendering Cu more available for plant uptake.

• Copper mobility

Researchers have established that Cu accumulates mainly in the surface soils with much lower accumulations
below 15 cm (11,21,24,28). Long-term management practices do lead to deeper accumulations: 45 cm from
broiler litter (18), 30 cm after fungicides on citrus (28), and 60 cm after sludge on cropland (24). Copper
leaching is not considered an important process in the soil because Cu is strongly absorbed by oxide minerals
and by organic matter (21,23), but movement of metals in soils has long been known to be associated with

chelation with soluble organic compounds in a process sometimes referred to as cheluviation (18)
Cu Lit. Review J. Davis 9 11/09/04



B. Crop Response/plant uptake/phytotoxicity

McBride (19) summarizes problems in quantifying organic protection and Cu uptake: "There may not be a
strong correlation between metal solubility (or availability to roots) and the concentration in plant tops.
This depends on many factors affecting translocation, including species and cultivar of plant,
environmental conditions, and competing ions. Although the edible portion of the plant may contain
acceptably low concentrations of toxic metals, the true extent of metal bioavailability and toxicity to roots
and soil microbes could be underestimated".

In other words, Cu loaded at high rates, and present in the soil in high concentrations, may not accumulate
in aerial tissues due to factors like the plant's translocation efficiency. Potentially toxic levels of soil Cu
may, due to multiple factors, not have a detectable impact on growing plants. In general, soil extractable Cu
has not correlated well with the amount of Cu found in crop tissues (21,23,24,25). Levels of Cu thought to
be toxic did not produce plant tissue toxicity symptoms (22). The amount of Cu in tissues necessary to
cause toxicity symptoms in plants is independent of growing conditions (10). Soil temperature was found to
be an important factor in uptake of Cu (22).

Minnich et al. (25) relate that "In studies where excess Cu is supplied and concentrations in both roots and
shoots are determined, roots accumulate Cu and only a small fraction of the absorbed Cu is translocated to
the shoots (Dragun et al, 1976; Jarvis and Whitehead, 1981; Struckmyer et al., 1969; Taylor and Fox,
1985)".


Becket et al. (3) reported that even after 12 months the fractions" available" Cu added in sludges were
greater than those native in the soil, but their availabilities to young barley decreased over that period. The

ratio of available/total Cu added to sludge treated soils was 0.8 for Cu. Clearly, then the amounts that can
be taken up/amount present have diminished with time (no difference with sludge types).

McBride (19) "Availability of sludge-borne metals to plants is generally the highest immediately following
application of sludge to the soil, diminishing thereafter (Bidwell and Dowdy,1987; Chang et al., 1987a;
Hinesly et al., 1997). The cause of the initial high bioavailability may be, at least in part, rapid organic
matter decomposition that produces soluble organic carriers of metals (Alloway and Jackson, 1991; Chaney
and Ryan, 1993; Minnich et al., 1987) Organic matter appears to have quite different roles in controlling
trace metal uptake by plants, depending upon whether it is soluble (fluvic acid) or insoluble (humic acid).
Insoluble organic matter very effectively inhibits uptake of metal cations such as Cu
+2
which bind strongly
to organic matter and are thereby prevented from diffusing to roots. Conversely, soluble organics raise the
carrying capacity of soil solutions for Cu
+2
at any particular pH by forming soluble metal-organic
complexes (McBride 1994). Because the plant is able to extract trace metals from these complexes once
they diffuse to the root (Nor and Cheng, 1986), the high level of soluble organics found in soils recently
amended with sludge would promote absorption of trace metals by roots. With time, organic decomposition
rates and levels of soluble organics diminish, total dissolved metals presumably stabilize at lower values,
and bioavailability is reduced".

Crops considered to have high Cu requirement or low uptake efficiency : Wheat, corn, onions, citrus,
lettuce, carrots and crops considered to have low Cu requirement or high uptake efficiency: Beans, Potato,
peas, pasture grasses, pines.(5)




Numerous studies have focused on accumulations of copper, and other metals, in soils affected by long-

stone fruit orchards, vineyards, and on vegetables for about 100 years.

Cu Lit. Review J. Davis 10 11/09/04
In Australia, Merry et al. (22) reported unusually high copper concentrations in plant tissues of sampled
pasture species (20-60mg/kg) and was concerned about the risk to grazing ruminant animals. Additionally,
the study compared tissue concentrations of clover, beet and radish plants grown on Cu contaminated sites
with the same plants grown on uncontaminated sites. Plants grown on contaminated sites contained Cu
levels that exceeded normal values and would likely have been in the toxic range for the plant. However,
no evidence of chlorosis, stunting or other symptoms of Cu toxicity were observed though they suspected
that yield reductions did occur. Mean Cu concentrations of 31±11mg/kg were recorded and literature was
sited that established the plant toxic threshold at 20mg/kg.

Reuther and Smith (28) studied Florida citrus, chlorosis, stunting and yield reduction in orchards that
traditionally yielded well. High concentrations of copper in the 0-6 inches zone correlated well with the
age orchards studied. A 40 years old orchard with pH of 4.9 had 186ppm Cu compared to 0.9ppm Cu at
pH 5.2 for a virgin soil. The study concluded that the level of Cu in many mature orchards on acid, sandy
soil was approaching a point where foliage chlorosis and damage to normal root development would
negatively impact yield.

McBride (19) summarizes the collective experience with Cu-salts applied to orchards, vineyards, and other
agricultural sites and suggests that total soil Cu in the range of several hundred mg kg
-1
caused
phytotoxicity in some crops (22, Lexmond, 1980), but not in all (Payne, ref. 26). As the concentration of
Cu in orchard soil increases with time from cumulative application, a larger fraction of the total Cu can be
extracted by EDTA (Dickinson, 1988) suggesting increased conversion to soluble forms that are available
for plant uptake.
The fact that EDTA, a chelating agent, has rendered adsorbed Cu available for extraction suggests
increased availability for plant uptake. Thus, increased soil-Cu is rendered soluble and thus readily
bioavailable.

Davis et al. (10) found that though the concentration of Cu in tissue of young barley varies with growing
conditions, the minimum concentration of Cu in plant tissue necessary to cause plant toxic reactions are
relatively independent on growing conditions (2,10). Increases in tissue concentration above critical (Tc)
were considered toxic and dry matter yield reduction would be predicted.


Critical Concentrations for Cu (ppm dry matter)
[adapted from Davis (10)]

Barley

Lettuce Rape Ryegrass

Wheat
To Tc To Tc To Tc To Tc To Tc
11 14-25 10 17-21 9 15-22 11 21 11 18
median:19 median:21 median:16
Tc =critical content of plant tissue and To = normal concentration in plant tissue


Minnich et al., (25) compared extracted soil solution Cu
++
with copper accumulation in young snapbeans.
Sludge and Cu-salts were used to supply Cu, and the pH was maintained in the 5.0-5.5 range. Sludge treatments
resulted in non-linear relationships between soil-Cu and Cu-tissue accumulation. Higher shoot Cu occurred
with Cu-salt treatments, but sludge delivered higher root-Cu accumulations at lower Cu-concentrations in the
soil. "This probably reflects the superior ability of the sludge to replenish or maintain the Cu supply in soil
solution". Root toxicity occurred at shoot-Cu levels of 30 mg kg
-1

which equates to a salt addition of 300 mg
kg
-1
(or 600 kg ha
-1
). Significant conclusions: Sludge replenishes Cu faster than the Cu-salts; plants absorb
chelated-Cu as well as free Cu
++
ions; singularly, concentration measurements do not define plant available Cu
in soil; additional study is needed to understand replenishment and interaction factors before accurate
predictions of Cu uptake can be made; Cu concentration in shoot tissue increased linearly with Cu
concentration of sludge; root Cu content is influenced not only by sludge Cu content, but also by the proportion
of sludge in the growth media; the increased root-Cu must reflect either a more labile Cu-Source was present in
the composted sludge or a redistribution of Cu from the high-Cu sludge to more labile forms in presence of
increased additions of sludge.


Cu Lit. Review J. Davis 11 11/09/04

McBride and Bouldin (20) studied long-term copper reactions on calcareous soils and noted that although the
solubility and chemical extractability of metals in sewage sludge might be quite low initially, various reactions
such as oxidation of metal sulfides and organic matter mineralization could serve to increase biological activity
of metals in soils over long time periods.

Evidence suggests that there is a tendency for some heavy metals to transfer into an organically complexed
form. This is particularly true for Cu and Pb as indicated by the large fracton of the total Cu and Pb that can be
extracted by EDTA and the accumulation of these metals in the surface organic rich layer of soils.
The long-term reaction of very high levels of Cu with a calcareous soil failed to convert the soluble metal into a
form unavailable to plants, as evidenced by what appeared to be Cu toxicity in corn. Chemical extraction
revealed that much of the total Cu was present in a non-exchangeable form readily dissolved by the chelating

agent. Greater than 95% of the Cu in soil solution was complexed, probably by soluble organics.


Heckman et al., (14) concluded that sludge composition and soil pH can have a substantial influence on
soybean uptake of metal uptake for at least 9 years after the initial sludge application. The rate of sludge
application strongly influenced the metal content of soybean. Plant tissue concentrations of Cu (and other
metals) exhibited significant linear increases over the rates of sludge application. Payne et al. (26) reported
similar findings post 20 years of applying CuSo
4
on corn. Excessive loading rates did not reduce grain or silage
yields and Cu concentrations remained at normal levels in grain and leaf tissues across all treatments.

Anderson et al. (1) evaluated corn yield response to high Cu levels from Cu-rich swine manure and CuSO
4
applications over an eleven year period. At loading rates of about 600 mg kg
-1
Cu resulted in no reduction in
yield from either Cu-manure or CuSO
4
sources. This loading rate did not increase Cu concentrations in corn
ear leaves or in corn grain. Additional findings: Application of Cu-manure and CuSO
4
increased extractable Cu
from on-site soils; Increases in extractable soil-Cu did not correlate with ear leaf concentrations; This may be
due Cu uptake by roots with a low amount of Cu translocation from roots to shoots.

Cu Lit. Review J. Davis 12 11/09/04

C. Soil flora and fauna

Mycorrhizae appear to protect plants from excessive uptake of micronutrients. Seedlings of birch, pine, and
spruce are able to grow well on sites contaminated by Zn, Cu, Ni, and Al only if the roots are sheathed by
ectomycorrhizae. (5)

Rhee (27) evaluated Cu-accumulation in earthworms after long-term applications of Cu-hog manure (10 years)
to pasture. Worms assessed included: A. caliginosa, A. chlorotica, A. longa, and L. rubellus. No relationship
was found between Cu-contents of the soil and worm numbers. Nevertheless, there was an obvious relationship
between Soil-Cu and Cu levels found in evaluated earthworms.

[
adapted from Rhee (27)]
____________________________________________________________________________________________

Cu-Soil concentration 109.7 98.9 43.7 26.8 25.5 25.4 17.6 14.4 6.7
(ppm dry weight)
Cu-Worms concentration 63 39 20 19 19 16 14 12 10
(ppm dry weight)
Worms densities/m
2
12 239 45 15 64 76 17 84
_____________________________________________________________________________________

Helmke et al (15) evaluated the suitability of using earthworms to monitor the bioavailability of metals in soils,
and to determine the effects of land application of sewage sludge on the concentrations of metals in
earthworms. Worm-Cu and worm cast-Cu increased with increasing rates of sludge application.


Cu Concentrations in earthworms and their casts [adapted from Helmke et al., (ZA)]

0-metric tons/ha manure 15-metric tons/ha manure

1971 1971 1973 1971 1972 1973
worms | casts worms | casts worms | casts worms | casts worms | casts worms | casts
8.8 10.5 9.4 9.5 10.6 12 3 21.2 11.8 18.9 8.3 14.1

30-metric tons/ha manure 60-metric tons/ha manure
1971 1972 1973 1971 1972 1973
worms | casts worms | casts worms | casts worms | casts worms | casts worms | casts
10.0 18.4 13.7 26.3 21.7 36.1 13.3 44.0 12.0 36.9 8.0 9.0
All sludge treatments involved single applications of anaerobically digested liquid sewage sludge.

Hartenstein et al. (13) reported that earthworms (Eisenia foetida) could feed on untreated activated sludges with
up to 1500 ppm Cu for several months without harm. The addition of 2,500 ppm Cu as CuSo
4
to activated
sludge resulted in 100% mortality within 1 week. Additional findings: passage of sludge through the gut did not
result in increased extractable Cu (0.1N HCl); Cu may accumulate or concentrate in the earthworm.











Cu Lit. Review J. Davis 13 11/09/04
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INTERNET REFERENCES

32. EXTOXNET (http://ace/orst.edu/info/extoxnet/pips/coppersu.htm)