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Heavy Metals in Soil and Plants. Martha Rosemeyer IES January 27, 2003. Major points. Heavy metals are forever! We are concentrating them and spreading them in the environment increasing human and animal contact

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heavy metals in soil and plants

Heavy Metals in Soil and Plants

Martha Rosemeyer


January 27, 2003

major points
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
  • What are heavy metals?
  • How are they bound to the soil
  • Food chain
    • Plant uptake of heavy metals
    • Animal uptake
  • Reducing heavy metal contamination
what is a heavy metal
What is a heavy metal?
  • Loose definition- specific density > 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 earth’s crust
heavy metals in the environment
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
contamination vs pollution
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
some heavy metals and their environmental and physiological effects
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!

limits in sewage sludge and metal additions for wa
Limits in sewage sludge and metal additions for WA

0.33 Wa

.089 Wa

.022 Wa


Brady and Weil, 1999 and Labno,2001

forms of heavy metals in soils
Forms of heavy metals in soils

Brady and Weil, 1999

as sources and background levels
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 can’t get tested through class
  • Causes cancer
as regulation
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 < 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
as behavior in soil and plants
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 (<2mm 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
lead pb
Lead (Pb)
  • Sources of lead in soil include: former roadways <100ft., PbAs pesticide, smelter, within 20 ft of buildings, < 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)
lead regulated levels can be contradictory
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
  • 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
cadmium health effects and regs
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)
cd sources of exposure
Cd- Sources of exposure
  • Food- major source of non-occupational exposure, esp. wheat and potatoes
  • Incineration- 71% Pb and 88% Cd due to plastics (vinyland 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”
cd has increased in soils due to p fertilizer use
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
phosphate fertilizers as source of cd pb as western states to 340 mg kg cd
Phosphate fertilizers as source of Cd, Pb, As: Western states to 340 mg/kg Cd

J.R. Simplot’s phosphate mine near ID/WY border

heavy metals in the food chain
Heavy metals in the food chain

Brady and Weil, 1999

  • 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?
uptake of hm by corn from sewage sludge
Uptake of HM by corn from sewage sludge


* not true for wheat

Brady and Weil, 1999

species dependent where it accumulates
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
cd and pb uptake by wheat and potato wsu studies labno and kuo 2001
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
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
cd in tuber yr 2 with tsp
Cd in tuber yr 2 with TSP

Close relationship between soil and plant

levels of Cd (DTPA extractant)

Labno, 2001

message to legislators
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 Kuo’s student’s work, Dec 2001
plant uptake
Plant uptake

Element Crop Uptake

As Root crops Roots

Cd Leafy veges Roots, tuber Grains, tuberleaves

Lead Fruits, grains Surface or in tuber

arsenic and human health
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

arsenic source
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
arsenic soil plant relationship
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 >10000 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 -- --Peryea, 1999
concentration of pb and as in plants
Concentration of Pb and As in plants
  • Roots > leaves> 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
  • Haven’t 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
cd uptake in snails
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
animal uptake of soil not via plant
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

how can we manage pb and as contaminated soil soils
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
organic matter binds heavy metals make sure not contaminated the case of cr
Organic matter binds heavy metals (make sure not contaminated) --the case of Cr

Brady and Weil, 1999

  • 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?
bioremediation by fungi
Bioremediation by fungi
  • Fungi can accumulate from mine tailings and contaminated soil, but then what!?
  • Peryea, F. 1999. Gardening on Lead- and Arsenic- Contaminated soils. WSU Ext. Pub # EB 1884
lab tips
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 45-60°C for at least 24 hrs (WSU)