Transcript Heavy Metals in Soils and Water

Laboratory 14: CRSS/FANR 3060
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
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)
Risk pathways of metals
>Plant uptake (potential for urban gardening)
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.)
10-20 ppm typical
Georgia Childhood Lead
Poisoning Prevention Program
(GCLPPP)
Risk- free – 75 ppm
Loading limits soil – 300 ppm
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
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)
0-1
1-3
3-6
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
Remediation strategy
 One-page paper:
Introduction
Materials and Methods
Discussion – methods of mitigation
Reference
 To reduce exposure to children
 Specify depths and distances