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Lead ( Pb ) in Urban Soils

Lead ( Pb ) in Urban Soils

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Lead ( Pb ) in Urban Soils

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

  2. Urban soils often contaminated with metals (Pb) Refining, smelting (aerial deposition) Plumbing (Pb solder) • Before 1973 – additive in gasoline; emitted in exhaust • Before 1978 – white pigment in paint -- PbCO3: bright white, anti-fungal -- ends up in soil with scraping/repainting

  3. Risk pathways for metals > leaching to groundwater: not major threat --Pb is quite insoluble at normal pH --small % of watershed is contaminated --well water not used in urban areas : drinking water limit: 15 ppb (ug/L)

  4. Risk pathways of metals >Plant uptake (potential for urban gardening)

  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. SOIL PB LEVELS: Background: 10-30 ppm (mg/kg)—naturally occurring : present in rocks that form soils “Safe for all uses”: < 75 ppm EPA Pb advisory levels (child soil ingestion): <400 ppm: minimal impact 400-1200: some impact >1200: acute impact

  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 strategy • One-page paper: Introduction Materials and Methods Discussion – methods of mitigation Reference • To reduce exposure to children • Specify depths and distances