Heavy Metals in Soil and Plants

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Heavy Metals in Soil and Plants

• Martha Rosemeyer
• IES
• January 27, 2003

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Major points

• Heavy metals are forever!
• We are concentrating them and spreading them in
  the environment increasing human and animal
  contact
• There are methods to manage them as long as there
  is vigilance for the next millenia
• There is some remediation
• Systems thinking is critical to solving
  environmental problems

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Outline

• What are heavy metals?
• How are they bound to the soil
• Food chain
• Plant uptake of heavy metals
• Animal uptake
• Reducing heavy metal contamination

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What is a heavy metal?

• Loose definition- specific density gt 4-7 g/cm3
• Usually associated with toxicity in plants (but
  some micronutrients produce toxicity symptoms as
  well) or animals
• trace metal metals in ppm concentrations in
  earths crust

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Periodic table of the elements
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Heavy metals in the environment

• Most in deposits in earth where safe
• Generally low levels in soil
• By mining and concentrating metals they have
  become more toxic to the biosphere
• Have spread where humans come into contact with
  them
• The toxicity of inorganic contaminants released
  into the environment every year is now estimated
  to exceed that from radioactive and organic
  sources combined. A fair share goes to
  contaminating soil. --Brady and Weil 1999, p740

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Contamination vs. pollution

• Contamination is above the background
• Pollution means concentration above some level
  which is deemed safe
• Pollution levels are not agreed upon and depend
  on who (child or adult), where (soil, water,
  air), over what time (8 hrs or chronic),
  workplace vs. public
• Variability in action levels, recommended
  exposure limits

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Some heavy metals and their environmental and
physiological effects



Brady and Weil, 1999
Canadian HM in soil stds also consider others Co,
Mo, not Cr!
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Reduction of HM in sewage sludge 1976 to 1990
Brady and Weil, 1999
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Limits in sewage sludge and metal additions for WA
0.33 Wa
.089 Wa
.022 Wa
2.2Wa
Brady and Weil, 1999 and Labno,2001
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Brady and Weil, 1999
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Forms of heavy metals in soils
Brady and Weil, 1999
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As- sources and background levels

• Occurs naturally in soil and water (may be toxic
  in water, e.g. Bangladesh and India)
• High As in upper end of Cascade Valleys in WA,
  may be high in volcanic soils and hot springs
• Present in coal burning and dusts from cement
  manufacture
• Smelter- within one mile
• Sprayed in WA state as insecticide on apples for
  codling moth until 1950, forest thinning to 1960s
• May be near Chromated Copper Aresenate treated
  timber- get 25 test kit from EWG if cant get
  tested through class
• Causes cancer

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As- regulation

• Permissible level in water (Bush changed to WHO
  levels of .01 ppm)- 0.01 ppm
• Permissible level in soil in out-of-print WSU
  extension bulletin states 25 mg/kg (ppm) is
  probably not affecting plant growth
• Residential soil cleanup - 250 mg/kg
• Children should be lt 37 ppm, adults with
  occasional exposure to 175 mg/kg acceptable
• Chronic exposure is of concern, e.g in gardening
• Symptoms in humans depend on individual
  susceptibility, form of As in soil, difficult to
  predict

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As behavior in soil and plants

• Background level in soil
• 6 ppm U.S. agricultural soils, but 7 Washington
  state
• Vashon-Maury Soil samples 2.3 - 460ppm (lt2mm
  sieved)
• More soluable and mobile in soil than Pb, so may
  have leached, increases in flooded, wet soils
• Redistributed through tillage, but usually only
  in subsoil if soil is sandy
• If high phosphate in soil may displace As to
  leach
• As in soil can be 10-1000x higher in soil than
  plant
• Can be high enough to stunt plants and reduce
  yield-- binds to energy exchange apparatus

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Lead (Pb)

• Sources of lead in soil include former roadways
  lt100ft., PbAs pesticide, smelter, within 20 ft of
  buildings, lt 1 mile for smelter or fossil suel
  electrical power plants or cement manufacturing
• Background level in soil
• 11 U.S. agricultural soils
• 17 Washington state,
• Vashon-Maury Island 5.3-1300ppm
• Lead in soil usually not high enough to affect
  the plant growth because highly bound to the soil
  unless pH is low (acid)

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Lead- regulated levels- can be contradictory

• OSHA
• blood (adults)- 40-50 ?g/dL
• air- 30-50 ?g/m3 over 8 hours
• CDC
• blood (children)- 10 ?g/dL
• EPA
• soil- 400 mg/kg, sewage sludge accumulated- 300
  kg/ha
• water (drinking)- 15 ?g/L
• air- 1.5 ?g/m3 ambient

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Cadmium

• Background level
• 0.2 ppm U.S. agricultural soils
• 1 ppm Washington state
• 0-15ppm Vashon-Maury soil samples
• Cadmium in wheat grain related to soil salinity,
  esp Chlorides, uptake as CdCl

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Cadmium- health effects and regs

• Health effects carcinogen (respiratory and
  testicular, pancreatic cancer),
• reproductive toxin reduced birthrate, premature
  birth, stillbirth and spontaneous abortion
• Behavioral and learning disabilities
• Regulation air 0.05 ?g/day (1/10th that of Pb)
• Soil maximum 4 ppm Cd (Wa and Canada, FRA 1997)

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Cd- Sources of exposure

• Food- major source of non-occupational exposure,
  esp. wheat and potatoes
• Incineration- 71 Pb and 88 Cd due to plastics
  (vinyl and other) in waste stream
• Cd in fertilizer and food is regulated much more
  strictly by Canadians and Europeans
• Now same as Canada 4 kg/ha max acceptable
  cumulative addition, 0.089 kg/ha max annual
  addition (Fert. Reg Act 1997)
• Canada and Aust. have fertilizer truth in
  labeling

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Cd has increased in soils due to P fertilizer use

• In Columbia basin and around the world where high
  Cd P is applied-- even where low Cd P is applied
• 10 in exchangeable pool in Canadian prairie vs.
  1 in Brady and Weil!
• Concentrated on clays and organic matter

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Phosphate fertilizers as source of Cd, Pb, As
Western states to 340 mg/kg Cd
J.R. Simplots phosphate mine near ID/WY border
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International Pb and Cd limits in foods-- no
established US limits
Labno 2001
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Heavy metals in the food chain
Brady and Weil, 1999
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Message

• Exact relationship between soil and plant depends
  on soil type, climate, management, chemical form,
  plant species and variety
• It is complicated and data is lacking
• Other countries have been able to regulate
  despite this-- why not US?

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Uptake of HM by corn from sewage sludge

not true for wheat
Brady and Weil, 1999
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Species dependent where it accumulates

• Greater accumulation of Pb and Cd in stover than
  wheat grain
• Corn from previous table concerning corn grown
  with sewage sludge grain greater than stover

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Cd and Pb uptake by wheat and potato WSU
studies, Labno and Kuo 2001

• International Cd stds grain 0.1 mg Cd/kg, tuber
  0.05 mg Cd/kg (US mean 0.03 (.06 p 20))
• International stds for Pb grain 0.35 mg Pb/kg,
  tuber 1.5 mg Pb/kg
• Rates of application 1x, 2x, 8x for 2 years
• Used 2 sources of DAP, TSP and RP, one Zn
  fertilizer
• Used a low Cd waste-derived Zn fert. (application
  0.1kg/ha/yr), Pb (5.6 kg/ha/yr at highest level),
  but results not reported for Cd

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• At the yr 1, 1x rate all grain and tubers except
  ID TSP were below international stds for Cd, 8x
  rate above for ID DAP and ID TSP (150ppm Cd)
• At 1x and 8x application rate the levels in the
  grain and tuber were under Pb stds
• Later study looked at Ironite and flue dust (676
  mg Cd/kg, 180000 mg Pb/kg) but plant uptake was
  not performed. Prev study on uptake was
  performed with materials that were lower in Cd
  and Pb

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Cd from TSP in grainNote in yr 2 all levels
above stds
Labno 2001
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Cd in tuber yr 2 with TSP
Close relationship between soil and plant levels
of Cd (DTPA extractant)
Labno, 2001
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Where applied Cd goes
Labno 2001
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Message to legislators

• It was estimated that 1 of total soil Cd is in
  the wheat, indicating that most remains in the
  soil Transfer coefficient .01
• Transfer coefficient (Ratio of uptake over
  applied) was 0.005 for Pb indicating a low
  potential for plant uptake.
• Transfer coefficient for As was small 0.012
  indicating a low potential for plant uptake.
• Report from Dept Ag based on Kuos students
  work, Dec 2001

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Plant uptake

• Element Crop Uptake
• As Root crops Roots
• Cd Leafy veges Roots, tuber Grains,
  tuber leaves
• Lead Fruits, grains Surface or in tuber

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Arsenic and human health

• Food and water major source of exposure for US
  citizens (Yorktimes)
• High concentrations Internal bleeding and death
• Known to cause cancer lung, skin, liver, kidney
  Reproductive damage
• Causes arsenic keratosis
• of skin

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Arsenic Source

• Has been used for centuries (China 900 AD)
• Many different forms of arsenate (200),e.g CaAs
• Form influences mobility and toxicity
• Mined with other minerals esp. Au, Cu, Sn and
  mined, from mine waste or tailings
• Natural or mine waste in water
• Found in hydrothemal deposits

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Arsenic in drinking water in US
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Arsenic Soil/plant relationship

• Exact relationship between soil and plant depends
  on soil type, climate, management, chemical form,
  plant species and variety
• Plant levels tends to increase until some level
  where plateaus
• Significant on alkaline soils where have gt10000
  ppm (Bowell and Parshley)
• As stunts or kills plants by acting as P and
  binding with energy transport mechanisms, green
  beans and legumes most sensitive -- --Perye
  a, 1999

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Concentration of Pb and As in plants

• Roots gt leavesgt fruits and seeds
• Root skin is higher than inner flesh--
• Roots absorb but do not transport Pb
• Apples and apricots contain low Pb and As
• Havent found any regulations on As in food
• Organic As may be less toxic than inorganic
  compounds of As Organic As may be predominant
  in fruits and vegetables, although inorganic As
  more common in grain

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HM in earthworms after application of sewage
sludge
Brady and Weil, 1999
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Cd uptake in snails

• New evidence from France, Renaud Scheifler of
  University of Franche-Comte
• Snails took up 12 of Cd from supposedly bound
  fraction of smelter soil with high Pb and As

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Animal uptake of soil-- not via plant!

• Up to 30 of diet is soil for sheep, goats
• Up to 18 for cattle
• Depends on management how much the animals get
  soil
• Direct ingestion
• of soil particles
• may increase
• uptake of HM

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The browse line
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Above the browse line!
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How can we manage Pb and As contaminated soil
soils?

• Add organic matter (test to make sure low in Pb
  and As)
• Keep pH high with lime (check to make sure not
  contaminated with Pb and As or others)
• Add phosphate to bind with lead (TSP lowest), but
  may increase plant uptake of As. Rock P may have
  Cd.
• Biological remediation

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Organic matter binds heavy metals (make
sure not contaminated) --the case of Cr
Brady and Weil, 1999
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Add lime (make sure source not contain heavy
metals)
Brady and Weil, 1999
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Plant hyperaccumulation
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Hyperaccumulator

• Plant tissue concentrations of 4 Zn can be used
  as ore-- Thalpsi
• Brake fern (Pteris vittata) can accumulate As
• Pb- add chelators, solubilize lead and plant can
  take it up
• Genetic engineering
• moving genes into canola (rapeseed) and Indian
  mustards to accumulate heavy metals!!
• Is this systems thinking?

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Bioremediation by fungi

• Fungi can accumulate from mine tailings and
  contaminated soil, but then what!?

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References

• Peryea, F. 1999. Gardening on Lead- and Arsenic-
  Contaminated soils. WSU Ext. Pub EB 1884

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Lab tips

• Use non-metal soil samplers (WSU)
• May want to sample to 15 cm in ag soils (WSU)
• Sieve soil less that 2 mm (Vashon-Maury)
• Dry plant material at 45-60C for at least 24 hrs
  (WSU)