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 childrens
blood lead levels; to investigate
whether dust sampling using vacuum methods or a wipe method is
more predictive of
childrens 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 childs 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 childrens 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 childrens
blood lead levels. Wipe dust
lead loading and BRM loading on non-carpeted floors was
significantly correlated with
childrens blood lead levels.
To determine which of the dust collection method measures was
most predictive of childrens
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
childrens 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 childrens blood
lead levels, whereas for wipe dust
lead loading, non-carpeted floors and interior window sills were
significantly associated with
childrens 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 childrens 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 childrens 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 childrens 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 todays 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