Lead (Pb) in Urban Soils

Laboratory 14: CRSS/FANR 3060Spring 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 -- PbCO3: bright white, anti-fungal

-- ends up in soil with scraping/repainting

Risk pathways for metals leaching to groundwater (NA: city water…)

Max. in groundwater – 0.015 ppm

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

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)

10-20 ppm typical

Loading limits soil – 300 ppm

Risk- free – 75 ppm

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)

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

Transect

Distance (ft) 0 5 10

Depth (in)

0-11-33-6

Assessment:> sample around older houses

-- distance from house (source)-- depth (paint deposited during

scraping)

> define area/depth that exceeds regulatorylimits:400 mg/kg: “chronic” level1200 mg/kg: “acute” level

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?

Remediation strategy One-page paper: Introduction Materials and Methods Discussion ReferenceTo reduce exposure to childrenSpecify depths and distances