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Lead ( Pb ) in Urban Soils

Lead ( Pb ) in Urban Soils. Laboratory 14: CRSS/FANR 3060 Spring 2011. Urban soils often contaminated with metals ( Pb ). Refining , smelting (aerial deposition ) Plumbing ( Pb solder) Before 1973 – additive in gasoline Before 1977 – white pigment in paint

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Lead ( Pb ) in Urban Soils

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  1. Lead (Pb) in Urban Soils Laboratory 14: CRSS/FANR 3060 Spring 2011

  2. Urban soils often contaminated with metals (Pb) Refining, smelting (aerial deposition) Plumbing (Pb solder) • Before 1973 – additive in gasoline • Before 1977 – white pigment in paint -- PbCO3: bright white, anti-fungal -- ends up in soil with scraping/repainting

  3. Risk pathways for metals leaching to groundwater (NA: city water…) Max. in groundwater – 0.015 ppm

  4. Risk pathways of metals Plant uptake (maybe– “urban agriculture”…)

  5. Risk pathways for metals Soil ingestion --all kids eat some dirt; some eat a lot… --accumulates in brain: neurological effects (synapse damage, behavioral, learning disabilities, etc.) Georgia Childhood Lead Poisoning Prevention Program (GCLPPP) Risk- free – 75 ppm Loading limits soil – 300 ppm 10-20 ppm typical

  6. Nutrients – Cu, Zn, Co Toxic – (higher concentrations) Cd, Pb, Hg Lead in paint – Lead Carbonate (PbCO3) Soluble dilute acid (to make insoluble above 7 pH)

  7. Nine sample: (3 distances x 3 depth) Extract with acid to dissolve Pb -- 1.0 g soil + 30 mL 0.1 M HNO3 (centr. tube) --shake 5 min; filter --analyze Pb by flame AA mg/L x 0.03 L/0.001kg = mg/kg

  8. Transect Distance (ft) 0 5 10 Depth (in) 0-1 1-3 3-6

  9. Assessment: > sample around older houses -- distance from house (source) -- depth (paint deposited during scraping) > define area/depth that exceeds regulatory limits: 400 mg/kg: “chronic” level 1200 mg/kg: “acute” level

  10. Remediation: Bioremediation - Indian Mustard (Lead and chromium) What is the risk pathway? What is the extent of contamination? What are possible fixes for problem? What are costs vs. benefits of alternatives?

  11. Remediation strategy • One-page paper: Introduction Materials and Methods Discussion Reference • To reduce exposure to children • Specify depths and distances

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