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Heavy Metals in Soil and Plants

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

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  1. Heavy Metals in Soil and Plants Martha Rosemeyer IES January 27, 2003

  2. 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

  3. 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

  4. 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

  5. Periodic table of the elements

  6. 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

  7. 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

  8. 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!

  9. Reduction of HM in sewage sludge 1976 to 1990 Brady and Weil, 1999

  10. 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

  11. Brady and Weil, 1999

  12. Forms of heavy metals in soils Brady and Weil, 1999

  13. 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

  14. 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

  15. 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

  16. 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)

  17. 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

  18. 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

  19. 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)

  20. 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”

  21. 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

  22. 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

  23. International Pb and Cd limits in foods-- no established US limits Labno 2001

  24. Heavy metals in the food chain Brady and Weil, 1999

  25. 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?

  26. Uptake of HM by corn from sewage sludge * * not true for wheat Brady and Weil, 1999

  27. 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

  28. 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

  29. 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

  30. Cd from TSP in grainNote in yr 2 all levels above stds Labno 2001

  31. Cd in tuber yr 2 with TSP Close relationship between soil and plant levels of Cd (DTPA extractant) Labno, 2001

  32. Where applied Cd goes Labno 2001

  33. 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

  34. Plant uptake Element Crop Uptake As Root crops Roots Cd Leafy veges Roots, tuber Grains, tuberleaves Lead Fruits, grains Surface or in tuber

  35. 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

  36. 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

  37. Arsenic in drinking water in US

  38. 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

  39. 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

  40. HM in earthworms after application of sewage sludge Brady and Weil, 1999

  41. 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

  42. 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

  43. The browse line

  44. Above the browse line!

  45. 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

  46. Organic matter binds heavy metals (make sure not contaminated) --the case of Cr Brady and Weil, 1999

  47. Add lime (make sure source not contain heavy metals) Brady and Weil, 1999

  48. Plant “hyperaccumulation”

  49. 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?

  50. Bioremediation by fungi • Fungi can accumulate from mine tailings and contaminated soil, but then what!?

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