exhibiting pale yellow stripes running the length of the
leaf. In extreme cases, the entire plant may turn white
with marginal necrosis (burn) of the leaf. In dicots, Ni
toxicity causes an interveinal chlorosis (yellowing) that
looks very similar to manganese deficiency.
I Selenium (5 e)
Natural Occurrence: Only a few rare minerals—
crooksite and clausthalite — contain Se. It occurs in
due dusts remaining from the processing of copper
sulfide ores. Today most of the world’s S ecomes from
electrolytic copper refineries.
Uses: Essential nutrient in animal nutrition; component
of dandruff shampoos and fungal infection treatments;
used in manufacture of ruby-colored glasses and
enamels, photoelectric cells, resistors, photographic
emulsions, stainless steel, pigments, mbber, metal alloys,
textiles, petroleum and medical therapeutic agents
Notes: S e benefits crop production and is essential to
animal nutrition. Deficiency causes muscular dystrophy
in livestock, known as “white muscle disease,” and loss
of hair. S e content in food and feed crops (for livestock)
ranges from 0. 1-1 .0 ppm. Levels above 5 ppm cause
“alkali disease” or “blind staggers.” Too much S e also
causes feather loss in poultry and malformation of
livestock hooves and teeth. Although elemental S e is not
toxic, compounds like hydrogen selenide are extremely
toxic.
Se competes with sulfur in plant uptake. When toxic
levels of S e are found in forage crops, addition of
sulfur is a common remedial treatment. A sulfur rate of
15-25 lb/acre should be sufficient to reduce the toxic
effect in animals. If S e levels are high, consult with an
animal nutrition specialist and submit a forage sample
for analysis.
I Copper (Cu) & Zinc (Zn) _
Natural Occurrence: Cu occurs in rocks, soil, water,
air, plants and animals; Zn is a common element found
in air, soil, water and all foods.
Uses: Cu — Component in metal alloys; electrical
wiring; some water pipes; preservatives for wood,
leather and fabrics; and some agricultural fungicides
Zn — Widely used in industry to make dye, paint, rubber,
wood preservatives and ointments
Notes: Cu and Zn are essential plant micronutrients.
However, at high levels, they may be toxic to plants.
They can also bind to soil organic matter and become
unavailable to plants. Higher availability is usually
associated with low pH.
Plants vary in their sensitivity to Cu and Zn. Based on
field observation, critical toxic levels for plants that are
not unusually sensitive are 60 ppm (NCDA&CS soil
test Cu-I = 3000) and 120 ppm (NCDA&CS soil test
Zn-I = 3000) for Cu and Zn, respectively. Peanuts are
extremely sensitive to Zn, and toxicity has been seen
at levels as low as 12 ppm (Zn-I = 300).
Nutrient management guidelines typically stipulate
finding alternative waste application sites when soil
levels reach 40 ppm Cu (Cu-1 = 2000) or 80 ppm Zn
(Zn-I = 2000), but where peanuts are grown, 20 ppm
Zn (Zn-I = 500) is the limit. Waste applications should
cease when levels reach the critical toxic level as noted
above. Since Cu and Zn availability is highly dependent
on soil pH, a pH of 6.0 should be maintained on mineral
soils.
I Homeowner Concerns
The NCDA&CS soil lab does not test soil samples from
home sites where there are concerns about heavy metals.
Because our analysis is conducted with Mehlich
soil
test extractant, the data obtained may not be comparable
with guidelines established by U.S. regulatory or health
agencies. If health concerns do exist and soil analysis
is desired for this purpose, contact a private lab and
request the approved EPA tests for total metals. For a list
of private labs that may be able to provide assistance,
visit h2o.enr.state. nc. us/lab/nccert.htm.
Specific concerns about metals with regard to human
health should be addressed to
• U.S. Centers for Disease Control and Prevention
— www.cdc.gov
• U.S. Environmental Protection Agency — www.epa.gov
• N.C. Public Health — www.ncpublichealth.com or
• local public health agencies.
Agronomic Division
Heavy Metals
in North Carolina Soils
Occurrences* Significance
www. ncag r. g ov/ag ron
о
mi/
revised September 2008
N.C. Department of Agriculture
and Consumer Services
Steve Troxler, Commissioner
