Assessing The Appropriate Particle Size Fraction To Use For The Analysis Of Soil And Dust Samples For Lead

 

S. Roda1, S. Clark1, W. Friedman2,

J. Buchanan1, S. Spalding1

 

1University of Cincinnati; Dept. of Environ. Health

 

2U.S. Dept. of Housing and Urban Development

 

 

 

This work was funded by The U. S. Dept. of Housing and Urban Development, Office of Lead Hazard Control

SOIL AND DUST PREPARATION PROCEDURES

 

PARTICLE SIZE SIEVE NO.

 

 SOURCE

 

< 2 mm

 

 

 

 

No. 10

HUD1

 

< 500 um

No. 35

ASTM2

 

< 250 um

 

No. 60

EPA-Three City Urban Soil-Lead Demonstration Project3

< 125 um

No. 120

Literature

 

 

 

1United States Department of Housing and Urban Development, Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing, Washington, DC, June, 1995, Appendix 13.3-3.

 

2American Society for Testing and Materials. Standard practice for Sample digestion of soils for the determination of lead by atomic absorption spectrometry. Designation E1726-95.

 

3Three City Urban Soil-Lead Demonstration Project. Protocols for samples and analysis of soils, dusts, and handwipes. Environmental Criteria and Assessment Office, October 1991.

STUDY DESIGN

 

 

 

5 Geographic Collection Sites

x

40 Total Samples* per Geographic Collection Site

(20 soil samples + 20 dust samples)

x

4 Particle Fractionation Procedures

x

3 Replicate Analysis/ Particle Fractionation Procedures

 

 

 

= 2400 samples analyzed for Pb

 

 

*Samples were collected as part of the exterior dust and soil project in the Evaluation of the HUD Lead/Based Paint Hazard Control Grant Program in Private Housing

 

STUDY OBJECTIVES

 

 

PRIMARY:

To determine the appropriate particle size fraction to use for the determination of lead (Pb) in soil and exterior bulk dust samples for use in risk assessment. Considerations include: bioavailability, the size of particles adhering to the hands of children, and the homogeneity of the sample.

SECONDARY:

  1. To determine variability as a function of the particle size range.
  2. To determine if the variability of the replicate analysis of various fractions is the same for soil and dust.
  3. To analyze the Pb concentration of all particle size fractions.
  4. To evaluate if differences exist in sample results due to geographic location.

 

Variance1 of ln-Transformed Soil and Dust Sample Aliquots2

 

SAMPLE PARTICLE SIZE

 

SAMPLE

< 125µm

< 250µm

< 500µm

< 2mm

SOIL

(GSD)

N = 100

1.0006

1.0011

1.0025

1.1472

DUST

(GSD)

N = 100

1.0051

1.0362

1.0726

1.1154

 

 

1Squared Residuals [(s.d.)2]…ln (Pb)

23 subsamples were analyzed from each of the 4 fractions for each sample

 

 

 

Per Cent of Samples Exceeding + 25% Relative Per Cent Difference

for

Soil and Dust Sample Aliquots1

 

SAMPLE PARTICLE SIZE

 

SAMPLE

< 125µm

< 250µm

< 500µm

< 2mm

SOIL

% >+25% RPD

N = 100

1%

2%

4%

35%

DUST

% >+25% RPD

N = 100

6%

16%

39%

48%

 

13 subsamples were analyzed from each of the 4 fractions for each sample. For the RPD calculation this analysis assumes samples were analyzed in duplicate.

 

 

Geometric Means of All Dust Sample Aliquots for Each Site

Removing Subsample Outliers > 2 S.D. from the Fraction Mean (n=1151)

 

SAMPLE PARTICLE SIZE

SAMPLE

COLLECTION SITE

< 125µm

< 250µm

< 500µm

< 2mm

% Pb Concentration Increase between

< 2mm and < 125µm

CHICAGO

399

283

241

235

70%

CLEVELAND

553

437

398

401

38%

MILWAUKEE

504

456

424

379

33%

RHODE

ISLAND

385

277

230

186

107%

WISCONSIN

108

100

82

62

74%

 

Geometric Means of All Soil Sample Aliquots for Each Site

Removing Subsample Outliers > 2 S.D. from the Fraction Mean (n=1135)

SAMPLE PARTICLE SIZE

SAMPLE

COLLECTION SITE

< 125µm

< 250µm

< 500µm

< 2mm

% Pb Concentration Increase between

< 2mm and < 125µm

CHICAGO

1845

1485

1423

1524

21%

CLEVELAND

2505

2142

 

2202

2618

-4%

MILWAUKEE

1843

1770

1715

2047

-10%

RHODE

ISLAND

876

827

778

597

47%

WISCONSIN

610

484

326

268

128%

 

STUDY RESULTS

   

  1. Excess variability exists for the analysis of both soil and dust samples when using fractions < 2mm and < 500µm in particle size.
  2. Analysis of the < 2mm fraction of higher concentration soil samples is more variable and higher in Pb than the <125µm portion of the sample. Paint chip contamination is suspected in this fraction.
  3. Pb concentration increases in the smaller particle size fraction (<125µm).
  4. Site differences exist in the absolute concentration of Pb but not in the general overall pattern of increase to the < 125µm fraction.

 

 

 

STUDY CONCLUSIONS

 

 

1. Due to the imprecision of the results, the bioavailability of lead from smaller particles, and the bioassessability of smaller particles to children the analysis of soil and dust samples sieved to < 125µm is recommended.

2. Conclusions derived from past studies may be affected and dependent on the preparation and analysis procedures used for soil and dust.

3. A consistent and universal procedure for the laboratory preparation of soil and dust samples is critical for both risk assessment and subsequent remediation of contaminated areas.