The Relation of Lead-Contaminated House Dust and Blood Lead Levels Among Urban Children

FINAL REPORT, Volume II, Submitted November 15, 1994
Departments of Pediatrics, Biostatistics, and Environmental Medicine,
The University of Rochester School of Medicine, Rochester, New York,
and The National Center for Lead-Safe Housing, Columbia, Maryland
U.S. Department of Housing and Urban Development Grant
#MLDP T0001-93

Executive Summary

Lead-contaminated house dust was first recognized as an important source of lead for urban
children over 20 years ago. In 1992, the United States Congress passed the Residential
Lead-Based Paint Hazard Reduction Act, which requires the Environmental Protection
Agency (EPA) to promulgate a health-based dust lead standard for residential dwellings
based on exposures that are considered dangerous for children.

Objectives

The objectives of this study were: to determine whether dust lead loading (ug/ft2) or dust lead
concentration (ug/g) is a better predictor of children’s blood lead levels; to investigate
whether dust sampling using vacuum methods or a wipe method is more predictive of
children’s blood lead levels; to identify which interior household surface(s) should routinely
be sampled for dust lead measurements; and to estimate the probability of a child having an
elevated blood lead level on the basis of a known level of lead in house dust, controlling for
other potential exposures.

Methods and Results

Identification and recruitment of eligible subjects was done by using lists of sequential births
between March 1, 1991 and September 30, 1992 from three urban hospitals in Rochester,
New York. Eligible children were in the 1 to 2 ‡ year age range.

Stringent eligibility requirements were imposed to assure that the child’s residential
environment was the principal likely source of lead exposure. A cross-sectional study design
was employed to investigate the relation of lead-contaminated house dust, other potential
environmental sources of lead, and urban children’s blood lead levels. Field work was done
from August through November 1993.

Three dust collection methods were used to obtain side-by-side samples from as many as 12
sampling locations in each house (i.e., a maximum of 36 samples). Two vacuum methods
were used to determine both dust lead concentration and dust lead loading: an in-line filter
method (the Dust Vacuum Method), and a cyclone-type sampler with a much higher flowrate
(the Baltimore Repair and Maintenance study vacuum method). Wipe sampling, which only
measures dust lead loading, was also conducted. Thus, there were five dust collection
method variables (Dust Vacuum Method dust lead concentration, Dust Vacuum Method dust
lead loading, Baltimore Repair and Maintenance vacuum method dust lead loading, Baltimore
Repair and Maintenance vacuum method dust lead concentration, and wipe dust lead
loading).

In bivariate analyses, all five dust collection method variables on window sills, window wells
and carpeted floors, were significantly correlated with children’s blood lead levels. Wipe dust
lead loading and BRM loading on non-carpeted floors was significantly correlated with
children’s blood lead levels.

To determine which of the dust collection method measures was most predictive of children’s
blood lead levels, all five dust collection method variables were entered into the initial multiple
regression model, along with all possible covariates which were significant in bivariate
analyses. A backward selection process was used to eliminate non-significant covariates
while all five dust collection method variables were simultaneously forced to remain in the
model. In addition to the dust collection method, the following covariates were found to be
significantly associated with higher blood lead levels among children: Black race, parental
reports that children put soil in their mouths, single parent household, and a higher ferritin
level.

Each of the five dust collection method variables were then entered individually into separate
regression models along with the significant covariates. Dust lead loading using the Baltimore
Repair and Maintenance vacuum sampler accounted for the largest amount of variation in
children’s blood lead levels compared with all other dust collection method variables. The
partial correlations for the Baltimore Repair and Maintenance vacuum method dust lead
loading and wipe dust lead loading with blood lead was not significantly different. On the
other hand, the partial correlation for Baltimore Repair and Maintenance vacuum method
dust lead loading and blood lead was significantly different than that for both Baltimore
Repair and Maintenance vacuum method dust lead concentration and Dust Vacuum Method
dust lead loading.

To determine which types of surfaces (i.e., interior window sills, window troughs (wells),
non-carpeted floors, carpeted floors), were the best predictors of blood lead for each dust
sampling method, the common covariates were forced into a model and the four surface
variables were then allowed to enter through a forward selection process. For Baltimore
Repair and Maintenance vacuum method dust lead loading, non-carpeted floors and window
troughs were significantly associated with children’s blood lead levels, whereas for wipe dust
lead loading, non-carpeted floors and interior window sills were significantly associated with
children’s blood lead levels.

Using logistic regression to adjust for other significant covariates, the proportion of children
estimated to have a blood lead level exceeding 10 ug/dL (micrograms of lead per deciliter of
blood) was 4.3%, 15%, and 20% at 5 ug/ft2 , 20 ug/ft2 and 40 ug of lead/ft2 respectively, for
non-carpeted floors using wipe sampling. Similar analyses are presented for carpeted floors,
window sills and window troughs.

Conclusions

Dust lead loading is a better predictor of children’s blood lead levels than is dust lead
concentration for the range of lead-contaminated dust and blood lead levels observed in this
study. Any household dust lead standard should be linked to the method by which dust is
sampled, because the relationship between children’s blood lead levels and dust lead levels
varies significantly by method of dust collection. The relationship between blood lead levels
and household dust lead is different for floors, window sills, and window troughs using the
same dust collection method, indicating that different standards are needed for each surface.
To determine if a housing unit is safe for children, non-carpeted floors and interior window
sills or window troughs can be measured using either the Baltimore Repair and Maintenance
vacuum method or wipe sampling method.

Settled, lead-contaminated house dust (at levels observed in this study) is an important
contributor of lead to children who have low level elevation of blood lead levels (i.e., blood
lead levels up to 20 ug/dL). This study suggests that the proportion of urban children having a
blood lead level exceeding 10ug/dL increases at levels lower than current HUD
post-abatement clearance standards and the recently released EPA guidance levels. Future
research should seek to confirm the estimated relationship between children’s blood lead
levels and lead contaminated housedust found in this study. Also, further research should
investigate whether dust control is associated with a meaningful decrease in blood lead levels
of children at today’s lead exposures.


Ordering Information

Copies of Evaluation of the HUD Lead-Based Paint Hazard Control Grant Program
can be obtained from:

The National Center for Lead-Safe Housing
10227 Wincopin Circle
Columbia, MD 21044
Phone: 410-992-0712
Fax: 410-715-2310
E-mail: ebloomer@enterprisefoundation.org