Evaluation of Sampling Methods for Determining Dust Lead Loading on

Residential Carpet Surfaces

Zhipeng Bai, Junfeng Zhang, George G. Rhoads, Paul J. Lioy, David Q. Rich, John L. Adgate, Stella M. Tsai, Lih-ming Yiin, and Peter J. Ashley*

Environmental and Occupational Health Sciences Institute (EOHSI), University of Medicine and Dentistry of New Jersey (UMDNJ)

* Office of Lead Hazard Control, the US Department of Housing and Urban Development

• House dust is a major pathway by which children are exposed to lead.

• Carpets are commonly used in residential buildings.

• Therefore, it is important to obtain measures that are representative of lead exposures resulting from lead-contaminated dust embedded in carpets.

Introduction

Study Design and Strategy

• Between May and November 1998, 33 houses were recruited from homes with children having elevated blood lead levels in Northern New Jersey.

• Five sampling methods were compared to measure dust lead loading (g/m2) on carpet surfaces.

• Lead loading on surfaces is the metric most strongly correlated with elevated blood lead levels in children.

The Five Sampling Methods

• HUD Wipe Method

• EOHSI Vacuum Method

• Technician Hand Rinse Method

• Adhesive Label Method

• C18 Method (Simulated Skin)

Digestion Procedure

Samples are microwave digested (CEM Corporation, MDS-2000) in an acid solution:

a. 20% (v/v) nitric acid (trace metal grade, Pb <0.1ppb) for C18, Vacuum, and Technician Hand Rinse samples.

b. Concentrated nitric acid for Adhesive Label and HUD Wipe samples.

Analysis

• Adhesive label, C18, and Technician hand rinse samples were analyzed using graphite furnace atomic absorption spectrophotometer (GFAA) (Perkin-Elmer Zeeman 5100).

• HUD wipe samples and EOHSI vacuum samples were analyzed using flame atomic absorption spectrometer (FAA) (Perkin-Elmer Model 3100) or using GFAA if the lead levels were below the FAA detection limit.

Method Detection Limit

Area Sampled and MDLs for the five sampling methods.

Sampling methods Area sampled (m2) MDL (ug/m2)Adhesive Label 0.01 20

C18 0.0035 14Vacuum 0.258 0.2

HUD Wipe 0.093 2.7Technician Hand Rinse Both hands area x 5 times

(about 0.035m2 x 5)

0.3

QA: Inter-laboratory Comparison

Relationship between the U. Cincinnati and EOHSI values for the spiked HUD auditing samples

y = 1.377x - 1.763

R2 = 0.962

0

50

100

150

200

250

300

0 50 100 150 200 250

EOHSI values (ug pb/sample)

C

inci

nnat

i val

ues

(ug

pb/

sam

ple)

QA: Correlation (r) between Duplicate Measurements Results within Each Method

Adhesive Label: 0.612

C18: 0.324

Hud Wipe: 0.653

Hand Rinse: 0.213

EOHSI Vacuum: 0.707

Methods Comparison

• HUD wipe results were used to normalize values.

• Ratios were generated for each of the four methods to assess the collection efficiency.

Results

• The descriptive statistical results showed that the vacuum sampling method yielded higher lead loading from carpet surfaces than the HUD wipe did. A total of 90.3% of the vacuum samples had the ratio higher than 1.

• The median ratios of vacuum, technician hand rinse, adhesive label, and C18 were 6.07, 0.52, 0.46, and 0.27, respectively.

Method, Log (ug/m2) C18 HUD TECH Vacuum

r=0.438 r=0.340 r=0.308 r=0.491AD n=32 n=33 n=23 n=31

p=0.012 p=0.021 p=0.153 p=0.005

r=0.0371 r=0.376 r=0.347C18 n=32 n=23 n=31

p=0.84 p=0.084 p=0.060

r=0.479 r=0.476HUD n=23 n=31

p=0.021 p=0.007

r=0.385Tech. n=23

p=0.085

Correlation coefficients of log-transformed lead loading for the five methods

Comparison between the Five Sampling Methods

Method (I) Method (J) Mean Difference (I-J) Std Error P Value Lower bound Upper boundAD C18 0.2437 0.138 0.554 -0.1514 0.6389

HUD -0.3159 0.137 0.279 -0.7345 0.1027Tech. -0.1708 0.152 0.94 -0.5957 0.2541Vac. -1.1348* 0.14 <0.01 -1.6175 -0.652

C18 HUD -0.5596* 0.138 <0.01 -0.9002 -0.2191Tech. -0.4145* 0.153 0.011 -0.7645 -0.065Vac. -1.3785* 0.141 <0.01 -1.7989 -0.958

HUD Tech. 0.1451 0.152 0.954 -0.2314 0.5216Vac. -0.8188* 0.14 <0.01 -1.2609 -0.3767

Tech. Vac. -0.9639* 0.154 <0.01 -1.4118 -0.5161

Based on observed means.*. The mean difference is significant at the 0.05 level

Multiple Comparison of the Sampling Methods

Homogeneous subsets, Multiple comparison

methodStudent-Newman-Keuls a,b,c N 1 2 3

C18 32 1.3656AD 33 1.6093 1.6093

Tech. 23 1.7802HUD 33 1.9253Vac. 31 2.7441Sig. 0.092 0.073 1

Means for groups in homogeneous subsets are displayed.Based on Type III sum SquaresThe error term is Mean Square (Error) = 0.311.a. Uses Harmonic Mean Sample size = 29.834.

c. Alpha = 0.05

Subset

b. The group sizes are unequal. The harmonic mean of the group sizes is used. Type I error levels are not guaranteed.

Conclusions

• General linear model methods were applied to log-transformed lead loading results. The results showed that not all five sampling methods yielded the same level of lead loading (p < 0.001).

• Multiple comparison results showed that the technician hand rinse, adhesive label, and EOHSI vacuum methods were significantly correlated with the HUD wipe method.

Acknowledgement

We are grateful to the families who participated in the study and to Richard Madison and Chen Zhang of the Development and Testing of Lead Exposure Metrics: New Jersey Assessment of Cleaning Techniques (NJACT) Study.

This study was Funded by the Office of Lead Hazard Control, the US Department of Housing and Urban Development through a grant to UMDNJ (Grant # NJLH0023-97).

QUESTIONS & COMMENTS