### Environmental Health Perspectives

• volume 117 | number 3 | March 2009 

### 461 

# Research 

# | Children’s Health

The U.S. Centers for Disease Control and Prevention (CDC) estimates that 310,000

children between 1 and 6 years of age in the

United States have blood lead (PbB) levels > 10 micrograms per deciliter (CDC 2005). The

health effects associated with PbB levels at or

above this level of concern have been well doc

umented, including learning and behavioral problems (National Research Council 1993). Evidence suggests that children with PbB < 10 μg/dL also experience notable adverse effects and that no safe level of lead exposure exists (Canfield et al. 2003; CDC 1991; Lanphear

et al. 2000, 2005b; Schwartz 1994). In this study we identified factors associated with childhood residential dust lead (PbD) exposure. Lead exposure can occur through a variety of sources, including air, bare soil, home rem

edies, drinking water, toy jewelry

, and others (Levin et al. 2008). However, the major path

way of exposure for children is from deterio

rated lead-based paint and lead-contaminated dust in the home that is ingested during nor

mal hand-to-mouth behavior (CDC 2007; Lanphear et al. 1998). The importance of

PbD from lead paint was recognized very early (Gibson 1904)

, and work was done sub

sequently in an attempt to quantify its expo

sure contribution (Sayre et al. 1974). Although lead-based paint was banned from residential use in 1978, approximately 38 million older housing units in the United

States still contained lead-based paint, and an estimated 24 million housing units contain sig

nificant lead hazards as of 2000 (Jacobs et al. 2002). Although intact paint does not gener

ally result in significant immediate exposure, all paint eventually deteriorates; lead-based paint that is chipping, peeling, or flaking or other

wise separating from its substrate presents a hazard. In addition, lead-contaminated settled dust, which is often found in houses with dete

riorated lead-based paint, is a significant lead hazard (Lanphear et al. 1998). PbD can also begenerated from the friction and impact of leadpainted surfaces (Dixon et al. 2007) and during housing renovation and repair projects where lead-based paint is present and proper precau

tions are not in place (Lanphear et al. 2005a;

Reissman et al. 2002). The use of leaded gaso

line, which peaked in the early 1970s, has also contaminated soil around the home (Mielke 1999). Many studies, employing a variety ofresearch designs, have demonstrated that soillead concentrations are a significant contribu

tor to PbD and children’s PbB (Bornschein

et al. 1987; Clark et al. 2004; Dixon et al. 2007; Lanphear et al. 1998). Numerous cross-sectional (Lanphear et al. 1998) and longitudinal studies [U.S. Department of Housing and Urban Development (HUD) 2004] have firmly established the correlation

of settled PbD and children’s PbB. In an effort to protect young children from adverse effects of lead, current federal health-based hazard

standards indicate that floor and window PbD should not exceed 40 μg/ft 2 

### and 250 μg/ft 2



### , respectively [U.S. Environmental Protection Agency (EPA) 2001]. Through an interagency agreement with the CDC, the U.S. HUD Office of Healthy Homes and Lead Hazard Control sponsored

the collection of PbD wipe samples and housing-related data through the National Health and Nutrition Examination Survey (NHANES) from 1999 through 2004, mark

ing the first time that NHANES has collected both health and housing environmental data. Using these national survey data, we investi

gated PbD in homes to explore the feasibility of lowering PbD standards. Here we present the demographic and housing characteristics

associated with floor and windowsill PbD. We used linear regression modeling to predict nat

ural log-transformed floor and windowsill PbD and logistic regression modeling to predict the log odds of PbD at various levels. A compan

ion article in this issue (Dixon et el. 2009) presents the analysis of NHANES data with respect to childhood PbB levels. Together these data identify the important risk factors and the relationship between PbD and children’s PbB

in the United States in recent years.



## Methods

Study population. We examined three waves of NHANES (1999–2000, 2001–2002,

Address correspondence to S.L. Dixon, National Center for Healthy Housing, 10320 Little Patuxent Parkway, Suite 500, Columbia, MD 21044 USA. Telephone: (443) 539-4156. Fax: (443) 539-4150. E-mail: sdixon@nchh.org

We thank R. Kaufman, D. Brody, and M.J. Brown of

the U.S. Centers for Disease Control and Prevention.

The U.S. Department of Housing and Urban Development funded this project under contract

C-PHI-00931.

The opinions expressed in this paper do not neces

sarily represent those of the U.S. government.

D.E.J. is paid as director of research at the National Center for Healthy Housing, a nonprofit agency dedicated to decreasing children’s exposure to hazards in the home. The other authors declare they have no competing financial interests.

Received 10 July 2008; accepted 13 November 2008. 

# Exposure of U.S. Children to Residential Dust Lead, 1999–2004: I. Housing and Demographic Factors

Joanna M. Gaitens, 1 

### Sherry L. Dixon, 2 

### David E. Jacobs, 2 

### Jyothi Nagaraja, 3 

### Warren Strauss, 3 

### Jonathan W. Wilson, 2


### and Peter J. Ashley 4

1 Healthy Housing Solutions, Inc., Columbia, Maryland, USA; 2 National Center for Healthy Housing, Columbia, Maryland, USA; 3 Battelle Memorial Institute, Columbus, Ohio, USA; 4 U.S. Department of Housing and Urban Development, Washington, DC, USA



### B ackground 

### : Lead-contaminated house dust is a major source of lead exposure for children in the

United States . In 1999–2004, the National Health and Nutrition Examination Survey (NHANES)

collected dust lead (PbD) loading samples from the homes of children 12–60 months of age.

O b jectives 

### : In this study we aimed to compare national PbD levels with existing health-based stan

dards and to identify housing and demographic factors associated with floor and windowsill PbD.

M ethods 

### : We used NHANES PbD data ( n = 2,065 from floors and n = 1,618 from windowsills) and covariates to construct linear and logistic regression models.

R

esults 

### : The population- weighted geometric mean floor and windowsill PbD were 0.5 μg/ft 2 

### [geometric standard error (GSE ) = 1.0 ] and 7.6 μg/ft 2 

### (GSE = 1.0), respectively. Only 0.16% of

the floors and 4.0% of the sills had PbD at or above current federal standards of 40 and 250 μg/ft 2



### , respectively. Income, race/ethnicity, floor surface/condition, windowsill PbD, year of construction, recent renovation, smoking, and survey year were significant predictors of floor PbD [the propor

tion of variability in the dependent variable accounted for by the model ( R 2 

### ) = 35% ] . A similar set of predictors plus the presence of large areas of exterior deteriorated paint in pre-1950 homes and the presence of interior deteriorated paint explained 20% of the variability in sill PbD. A compan

ion article [Dixon et al. Environ Health Perspect 117:468–474 (2009)] describes the relationship

between children’s blood lead and PbD.

C onclusion 

### : Most houses with children have PbD levels that comply with federal standards but may put children at risk. Factors associated with PbD in our population-based models are primarily

the same as factors identified in smaller at-risk cohorts. PbD on floors and windowsills should be kept as low as possible to protect children.

K ey words 

### : dust lead, housing, lead, National Health and Nutrition Examination Survey,

NHANES. Environ Health Perspect 117:461–467 (2009). doi:10.1289/ehp.11917 available via http://dx.doi.org/ [Online 14 November 2008]

### Gaitens et al.



### 462 volume 117 | number 3 | March 2009

• 

### Environmental Health Perspectives 

### 2003–2004) data for children 12 to 60 months of age with measured PbB. Included in this population were homes of 2,155 children, of which 2,065 had floor PbD data and 1,618

had windowsill PbD data. NHANES is a nationally representative cross-sectional house

hold survey that uses a complex, stratified, multistage probability sampling design to track

the health of the noninstitutionalized civilian U.S. population. Details of the NHANES protocol, survey and analytical procedures, and handling of samples are available else

where [National Center for Health Statistics (NCHS) 2006a, 2006b, 2006c]. Demographic and housing characteristics. NHANES interviewers collected demographic and housing information through a structured

household interview. Characteristics included child’s race/ethnicity, household and family income, type of home (e.g., mobile home or trailer, one- family house detached, one- family house attached to one or more houses, apart

ment, or “other”), number of apartment units in building, year of construction, number of years the family had lived in the home, owner

ship status, and smoking in the home. Parents of participants reported the race/ethnicity

of their child based on lists that included an open response. We used a composite race/eth

nicity variable for this analysis: non-Hispanic white, non-Hispanic black, Hispanic (com

posed mostly of Mexican American because

of

oversampling), or other race or ethnicity. The poverty-to-income ratio (PIR) is the ratio of income to the family’s appropriate pov

erty threshold (Office of Management and Budget 1978). PIR values < 1.00 are below the poverty threshold

, whereas PIR values

of ≥ 1.00 indicate income above the poverty level. Variables on smoking behavior included the presence of smoking in the home, num

ber of smokers, and the number of cigarettes smoked in the home per day. An adult mem

ber of the household reported the presence of peeling, chipping, or flaking paint (i.e., deteriorated) inside and outside the home. The household member categorized the paint

condition inside the house as follows : no dete

riorated paint, deteriorated paint but no large areas, large areas of deteriorated paint in one room, or large areas of deteriorated paint in more than one room. Similarly, the house

hold member classified the exterior paint con

dition as no deteriorated paint, deteriorated paint but no large areas, or large areas of dete

riorated paint. Large areas inside the home were defined as areas larger than one sheet of a newspaper and large areas on the outside of the home as areas larger than a door. The household member also reported whether the home had been repainted, whether they had scraped old paint or whether there had been renovations of windows, cabinets, and/or walls in the preceding 12 months.

PbD measurements. Interviewers collected separate single-surface floor and windowsill PbD samples from the room where the fam

ily member reported that children spent most of their time while awake, typically the living room or play room. Floor PbD wipe samples

were collected from a measured 1 ft 2 

### area in 2,065 homes using a standard procedure for moist wipes (ASTM E-1728-03; ASTM International 2003). Floor PbD was measured using graphite furnace atomic absorption spectroscopy and reported in micrograms per square foot . Windowsill PbD in 1,618 homes was also reported as micrograms per square
foot using information on the length and width dimensions of the windowsill wiped area. The laboratory detection limits (DL s ) for the moist wipe samples were 0.16 μg for

floors and 2 μg for windowsills. Blank samples were collected in 10% of the sampled homes. Robust laboratory quality control procedures were followed (NCHS 2006d, 2006e, 2006f).

Floor and sill PbD values that were below

the DL s were assigned the value of DL/ √ – 2 in the NHANES dust analysis data set. Forty-four percent of the sill loadings and 12.5% of the floor loadings were below the DLs. Although sill loadings are generally higher than floor PbD, the surface area of windowsills is typically

less than the 1 ft 2 

### sampled on floors, resulting in more sill loadings below the DL. The effects of the high percentage of sill loadings below

the DL in the linear model are limited because the surface areas of sills sampled varied and consequently the loadings varied. We categorized the floor’s surface and condition as uncarpeted smooth and clean

able, uncarpeted not smooth or not clean

able, low- pile carpet, or high- pile carpet.

Windowsill conditions were characterized

as either smooth and cleanable or not. The modeling presented here also examined room cleanliness, presence of clutter, and room location as reported by the individual collect

ing the wipe sample.

Statistical methods. We analyzed data using SAS (SAS System for Windows, ver

sion 9.1.3; SAS Institute Inc., Cary, NC) and SUDAAN software (version 9.0.0; RTI International, Research Triangle Park, NC). We used linear regression models to pre

dict natural log-transformed PbD and logistic regression models to predict the probability

that a home’s PbD exceeds various thresholds ( 10 μg lead /ft 2 

### for floors and 100 and 250 μg/

ft 2 

### for windowsills ) . Models for 10 μg/ft 2 

### for floors and 100 μg/ft 2 

### for windowsills were selected because analyses in the companion article indicate that 95% of children 1–5 years of age would have PbB ≤ 10 μg/dL at these dust lead levels. Because only three homes in

the data set had floor PbD exceeding the fed

eral hazard standard of 40 μg/ft 2 

### , we could not use logistic regression modeling to predict the probability that floor PbD exceeded the standard. The models adjusted the parameter estimates for the clustering and unequal sur

vey weights within NHANES. The modeling employed Taylor series expansion theory with

out degrees of freedom adjustments. Backward elimination of insignificant independent vari

ables ( p > 0.10) was followed by additional steps to allow addition and/or removal of vari

ables. For certain variables, there was a high percentage of missing values (e.g., 28% of the study sample did not have year of construction documented). We fit an intercept term for the study participants who had a missing value

so that we could include these homes in the analysis. For categorical variables, we reported

the p- value for the test for a significant differ

ence in the dependent variable between the category of interest and the comparison cat

egory, where the comparison category is the category with parameter estimate of zero. The

overall p- value is the type 3 F -test that cap

tures the overall statistical significance of each variable included in the model. For categorical variables with missing values, the missing level was not included in this hypothesis test. **Table 1.** Descriptive statistics for continuous housing and demographic variables, NHANES 1999–2004.

Weighted

Variable Levels No. of units GM (GSE) AM (SE)

Floor PbD by floor Missing 90

— — surface/condition Smooth and cleanable 453 0.99 (1.11) 3.16 (0.56)

Not smooth and cleanable 25 1.70 (1.47) 4.92 (2.11) Carpeted, low pile 1,381 0.46 (1.06) 0.91 (0.11) Carpeted, high pile 206 0.35 (1.10) 0.62 (0.08) All nonmissing 2,065 0.52 (1.05) 1.34 (0.14) Windowsill lead loading by Missing 537

— window surface condition All nonmissing 1,618 7.64 (1.07) 57.79 (9.42)

Smooth and cleanable 1,453 6.98 (1.07) 47.57 (5.30)

Not smooth and cleanable 165 16.9 (1.24) 146.6 (69.35)

PIR a Missing 136

— — Nonmissing 2,019

— 2.07 (0.05)

Years lived in home a Missing 23

— — Nonmissing 2,132

— 2.64 (0.04)

Abbreviations: AM, arithmetic mean; GSE, geometric standard error.

a GM and GSE are undefined because of zero values.

### Dust lead in homes of U.S. children

Environmental Health Perspectives

• volume 117 | number 3 | March 2009 

### 463 Because the surface area and concentra

tion of lead paint is higher in pre-1978 and particularly pre-1950 housing (Jacobs et al. 2002), our models allowed the effects of paint deterioration, renovation, repainting, and paint scraping in the preceding 12 months to be modified by the year of construction. This allowed paint deterioration, renovation, repainting, and paint scraping to have effects

on PbD only in homes constructed before
1978 or before 1950. Model diagnosis is complex for the analy

sis of data from a clustered multiframe survey with unequal weights, such as NHANES. Thus for the linear models, residual analysis to assess the validity of the assumption of nor

mality of the error was based on models with the same predictors but ignoring the cluster

ing and survey weights. For the logistic model, we used analysis of deviance (McCullagh and Nelder 1989) to assess the goodness of fit of the model. Although this measure accounts for the survey weights, it does not account for the effects of clustering.



## Results

Characteristics of the study population. Tables 1 and 2 provide descriptive statistics for the continuous and categoric variables that were significant in predicting floor and window

sill PbD in the linear and logistic regression models. The geometric means (GMs) for floor
and windowsill PbD were 0.52 μg/ft 2 

### and

7.64 μg/ft 2 

### , respectively. Only 0.16% of the weighted floor dust samples and 4.00% of the windowsill dust samples were at or above the

current federal hazard standards. Most floor and sill samples (84.3%) were collected in family rooms, living rooms

, or dens. Nearly

10% of the samples were collected in bed

rooms, 1.7% from kitchens, 1.4% from din

ing rooms, and 3.10% from another room. Floor dust samples were primarily from carpeted areas (80.12%). Only 1% of floor dust samples and 10% of windowsill sam

ples were from nonsmooth or noncleanable hard surfaces. However, uncarpeted floor sur

faces that were not smooth or not cleanable had higher GM PbD than did smooth and cleanable surfaces (1.7 μg/ft 2 

### vs. 1.0 μg/ft 2 

### ).

Floor PbD from smooth and cleanable sur

faces were more than double PbD on low -pile and high-pile carpeted surfaces (1.0 μg/ft 2



### vs. 0.46 μg/ft 2 

### and 0.35 μg/ft 2 

### , respectively). Approximately 21% of homes had smoking occurring inside the home, 22% of homes had reported areas of deteriorated paint inside the home, 52% of homes were built before 1978, and 4% of homes were constructed before 1950 and had recent renovations. Only 1.7% of homes reported exterior deteriorated paint, possibly because of the large surface area required for this category. **Table 2.** Descriptive statistics for categorical housing and demographic variables, NHANES 1999–2004.

Weighted percent

No. Missing Missing

Variable Levels of u nits included excluded

F loor PbD loading ≥ 40 μg/ft 2 Missing 90 3.68

— No 2,062 96.17 99.84

Yes 3 0.15 0.16 Floor PbD loading ≥ 10 μg/ft 2 Missing 90 3.68

— No 2,006 94.40 98.00

Yes 59 1.93 2.00
Floor surface/condition Missing 90 3.68

— Smooth and cleanable 453 18.18 18.87

Not smooth and cleanable 25 0.96 1.00 Carpeted, low pile 1,381 66.08 68.60 Carpeted, high pile 206 11.1 11.52

Windowsill PbD Missing 537 24.17

—

loading > 100 μg/ft 2 No 1,465 69.07 96.00

Yes 153 6.75 4.00

Windowsill PbD Missing 537 24.17

—

loading ≥ 250 μg/ft 2 No 1,538 72.8 91.10

Yes 80 3.03 8.90

Window surface condition Missing 537 24.17

— Smooth and cleanable 1,453 68.00 89.67

Not smooth and cleanable 165 7.83 10.33 Room dust sampled Missing 90 3.68

— Living room, family room, or den 1,700 81.20 84.30 Dining room 29 1.31 1.36

Kitchen 33 1.66 1.73

Bedroom 250 9.17 9.52

Another room 53 2.98 3.10

Year of construction Missing 840 28.1

— 1990–present 287 19.61 27.28

1978–1989 265 14.84 20.64

1960–1977 304 14.35 19.96

1950–1959 168 7.43 10.34

1940–1949 82 4.27 5.94

Before 1940 209 11.39 15.84
Window, cabinet, or wall Missing 174 5.97

—

renovation in pre-1950 home Yes 70 3.98 4.23

No 1,911 90.05 95.77 Anyone smoke Missing 23 1.50

—

inside the home Yes 430 20.78 21.09

No 1,702 77.73 78.91 Year of survey 1999–2000 624 30.23 30.23

2001–2002 765 34.08 34.08

2003–2004 766 35.69 35.69 Extent of peeling, flaking, or Missing 392 15.88

— chipping paint outside No deteriorated paint 1,376 64.57 76.75 Deteriorated paint but no large areas 309 15.98 18.99 Large areas of deteriorated paint 78 3.58 4.26 Presence of large area of deteriorated Missing 283 10.42

— paint outside in pre-1950 home Yes 27 1.55 1.73

No 1,845 88.03 98.27 Extent of paint deterioration inside Missing 28 1.45

— No deteriorated paint 1,596 76.73 77.86 Deteriorated paint but no large areas 439 18.75 19.03 Large areas of deteriorated paint 65 2.33 2.36

in one room Large areas of deteriorated paint 27 0.74 0.75

in two or more rooms Presence of paint deterioration inside Missing 28 1.45

— Yes 531 21.82 22.14

No 1,596 76.73 77.86 Paint scraped when home Missing 1,423 59.59

—

repainted in preceding 12 months Yes 197 10.63 26.44

No 535 29.57 73.56 Race/ethnicity Non-Hispanic white 618 57.09 57.09 Non-Hispanic black 634 15.32 15.32 Hispanic a 837 23.82 23.82

Other 66 3.77 3.77

a Sixty-six percent of Hispanics are Mexican Americans.

### Gaitens et al.



### 464 volume 117 | number 3 | March 2009

• 

### Environmental Health Perspectives 

### Floor PbD linear model. Table 3 provides the parameter estimates and associated SEsfor the linear model that predicts natural logtransformed floor PbD. Floor PbD was not significantly different between housing built from 1978 to 1989
and that from 1990 to present, although the difference between pre- and post-1978 was significant ( p < 0.001). The difference in PbD by race/ethnicity was also significant, with non-Hispanic blacks having significantly higher levels than non-Hispanic whites ( p

< 0.001). PbD in Hispanic homes was not significantly different than non-Hispanic white homes ( p = 0.864). A higher PIR was significantly associated with lower PbD ( p = 0.021). Higher windowsill PbD was sig

nificantly associated with higher floor PbD ( p < 0.001). Floor PbD in the 1999–2000 NHANES was significantly higher than floor
PbD in the 2001–2002 or 2003–2004 waves (both p < 0.001). The presence of a smoker in the home was associated with significantly higher floor PbD ( p < 0.006), as was window,

cabinet

, or wall renovation in pre-1950 homes ( p = 0.056). Although floor PbD on uncarpeted nons

mooth or noncleanable floors was higher than on smooth and cleanable floors, this difference was not statistically significant ( p

= 0.170), per

haps because only 25 homes had uncarpeted

floors that were not smooth and cleanable. This multivariate statistical model explains 35% of the variability in floor PbD of a

home . If a variable was significant in either the linear or logistic model but not the other model, the cells for that variable in the model
that did not contain the variable in Table 3 contain a dash (—). Floor PbD logistic model. Only 1.92% of

homes had floor PbD ≥ 10 μg/ft 2 

### (Table 2). The parameter estimates for the log-odds that floor PbD is ≥ 10 μg/ft 2 

### are shown in Table 3. Our results indicate that PbD from high -pile

or low- pile carpet is much less likely to exceed

10 μg/ft 2 

### than PbD from smooth and clean

able floors ( p < 0.001 and 0.024, respectively). Floor PbD in homes of non-Hispanic blacks was higher than in homes of non-Hispanic whites ( p = 0.088). Year of construction, type of home or apartment, and sill PbD were also significant predictors of floor PbD ≥ 10 μg/

ft 2 

### . Several variables, including PIR , smok

ing in the home, renovation, and survey year

, were significant in the linear regression model but were not significant in the logistic model.

Windowsill PbD linear model. Table 4 provides the parameter estimates and associ

ated SE s for the linear model that predicts

natural log- transformed windowsill PbD.
Homes built after 1950 had lower win

dowsill PbD compared with those built before 1950 ( p < 0.001). The presence of

**Table 3.** Model results for floor PbD.

Linear model for log PbD ( R 2 = 35%) Logistic model PbD ≥ 10 μg/ft 2 ( R 2 = 7% a )

Variables Overall p- value Estimate (SE) p- Value Overall p- value Estimate (SE) p- Value

Intercept 0.235 –0.239 (0.199) 0.235 < 0.001 –6.179 (0.834) < 0.001 Floor surface/condition

Smooth and cleanable < 0.001 0.000 < 0.001 0.000

Not smooth and cleanable 0.354 (0.254) 0.170 0.449 (0.740) 0.547 Carpeted, low pile –0.634 (0.094) < 0.001 –2.147 (0.401) < 0.001 Carpeted, high pile –0.868 (0.110) < 0.001 –2.868 (1.229) 0.024 Log windowsill PbD loading

Intercept for missing < 0.001 0.409 (0.090) < 0.001 < 0.001 0.000 Slope 0.172 (0.027) < 0.001 0.732 (0.106) < 0.001 Race/ethnicity

Non-Hispanic white < 0.001 0.000

— 0.009 0.000

— Non-Hispanic black 0.373 (0.086) < 0.001 0.900 (0.516) 0.088 Hispanic –0.015 (0.087) 0.864

— — — Other b –0.194 (0.129) 0.140

— –0.492 (0.581) 0.402

PIR

Intercept for missing 0.028 0.036 (0.120) 0.768

— — — Slope –0.047 (0.020) 0.021

— — — Year of construction

Intercept for missing < 0.001 –0.136 (0.141) 0.338 < 0.040 –0.032 (0.665) 0.962 1990–present –0.795 (0.128) < 0.001

— — 1978–1989 –0.714 (0.149) < 0.001

— — 1960–1977 –0.410 (0.137) 0.004

— — 1950–1959 –0.366 (0.177) 0.044 0.872 (0.723) 0.234

1940–1949 –0.393 (0.242) 0.118 1.284 (1.015) 0.213

Before 1940 0.000

— 0.000

— 1960–present

— — –1.519 (0.775) 0.056 Anyone smoke inside the home

Intercept for missing 0.006 –0.352 (0.344) 0.312

— — — Yes 0.253 (0.087) 0.006

— — No 0.000

— — Window, cabinet, or wall renovation in a pre-1950 home

Intercept for missing 0.056 –0.113 (0.116) 0.334

— — — Yes 0.355 (0.181) 0.056

— — No 0.000

— — Year of survey

1999–2000 < 0.001 0.429 (0.093) < 0.001

— — — 2001–2002 0.067 (0.091) 0.470

— — 2003–2004 0.000

— — Home-apartment type One-family house, detached

— — 0.042 1.032 (0.550) 0.067 One-family house, attached

— — 1.397 (0.739) 0.066 Apartment (1–9 units)

— — 1.964 (0.604) 0.002 Apartment (≥ 10 units)

— — 0.000

a Estimated using Cox–Snell methodology. b “Other” includes Hispanics for the logistic model.

### Dust lead in homes of U.S. children

Environmental Health Perspectives

• volume 117 | number 3 | March 2009 

### 465 deteriorated interior paint was associated with higher sill PbD ( p = 0.028). Pre-1950 homes that had large areas of deteriorated paint on the outside of the home also had higher sill PbD than other homes ( p = 0.076). Homes of non-Hispanic blacks had significantly higher sill PbD than homes of non-Hispanic whites ( p < 0.001). Sill PbD in homes of Hispanics were not significantly different from that in homes of non-Hispanic whites ( p = 0.298). Smoking inside the home was also positively associated with sill PbD ( p = 0.001). Samples taken from surfaces that were not smooth or not cleanable had significantly higher PbD compared with samples taken from smooth and cleanable surfaces ( p = 0.009), as was the

case for floors. Similar to the linear floor PbD model, the year of the survey was statistically significant. The sill PbD in 1999–2000 was higher than in the 2001–2002 or 2003–2004 waves ( p = 0.006). The multivariate statistical model explains 20% of the variability in natural-log trans

formed windowsill PbD. Windowsill PbD logistic regression mod

els. Only 8.90% of the homes had window

sill PbD ≥ 100 μg/ft 2



### , and 4.00% of homes yielded windowsill PbD ≥ 250 μg/ft 2 

### (Table 2). The parameter estimates for the log-odds

that a windowsill PbD is ≥ 100 μg/ft 2 

### and

≥ 250 μg/ft 2 

### are shown in Table 5. In both logistic models, smoking in the home and year of construction were sta

tistically significant predictors. If someone smoked inside the home, the odds that the sill

PbD was ≥ 100 or ≥ 250 μg/ft 2 

### were nearly 90% higher than if no one smoked inside the

home. Interestingly, in the logistic model for

PbD ≥ 100 μg/ft 2 

### , the odds that sill PbD was

≥ 100 μg/ft 2 

### for homes with large areas of exterior deteriorated paint was about three times higher than for homes with no exterior deteriorated paint. In the logistic model for **Table 4.** Linear model results for log windowsill PbD ( R 2 = 20%).

Variable Levels Overall p- value Estimate (SE) p- Value

Intercept < 0.001 2.670 (0.190) < 0.001 Race/ethnicity Non-Hispanic white 0.001 0.000

— Non-Hispanic black 0.521 (0.114) < 0.001 Hispanic 0.145 (0.138) 0.298

Other –0.234 (0.241) 0.338

Year of construction Intercept for missing < 0.001 –0.777 (0.234) 0.002 1990–present –1.616 (0.249) < 0.001

1978–1989 –1.442 (0.216) < 0.001

1960–1977 –1.332 (0.221) < 0.001

1950– 1959 –1.072 (0.315) 0.001

1940–1949 –0.715 (0.410) 0.088

Before 1940 0.000

— Window surface condition Smooth and cleanable 0.001 0.000

— Not smooth and cleanable 0.759 (0.213) 0.001 Anyone smoke inside the home Intercept for missing 0.001 0.664 (0.824) 0.425

Yes 0.460 (0.130) 0.001

No 0.000 Presence of large area of Intercept for missing 0.076 –0.422 (0.200) 0.040 deteriorated paint outside Yes 0.992 (0.545) 0.076 in pre-1950 home No 0.000

— Presence of paint Intercept for missing 0.028 –0.413 (0.649) 0.528

deterioration inside Yes 0.361 (0.159) 0.028

No 0.000

— Year of survey 1999–2000 0.020 0.330 (0.144) 0.027

2001–2002 –0.100 (0.114) 0.382

2003–2004 0.000

—

**Table 5.** Logistic model results for windowsill PbD. a

PbD ≥ 100 μg/ft 2 ( R 2 = 7% a ) PbD ≥ 250 μg/ft 2 ( R 2 = 4% a )

Variable Levels Overall p- Value Estimate (SE) p- Value Overall p- Value Estimate (SE) p- Value

Intercept < 0.001 –1.289 (0.385) 0.002 < 0.001 –2.502 (0.352) < 0.001 Race/ethnicity Non-Hispanic white

— — — 0.002 0.000

— Non-Hispanic black

— — — 1.127 (0.297) < 0.001

Other b

— — — 0.049 (0.569) 0.932

Year of construction Intercept for missing 0.005 –1.162 (0.354) 0.002 < 0.001 –1.161 (0.386) 0.004 1990–present –2.194 (0.805) 0.009 –3.201 (0.812) < 0.001

1978–1989 –1.852 (0.542) 0.001 –2.038 (0.895) 0.028

1960–1977 –1.603 (0.365) < 0.001 –1.705 (0.464) 0.001

1950–1959 –1.045 (0.507) 0.045 –1.009 (0.624) 0.113

1940–1949 –0.193 (0.521) 0.713 –0.121 (0.576) 0.834

Before 1940 0.000

— 0.000

— Anyone smoke Intercept for missing 0.041 –0.336 (1.046) 0.749 0.059 10.472 (0.895) < 0.001

inside the home Yes 0.623 (0.296) 0.041 0.625 (0.323) 0.059

No 0.000 0.000

— Extent of paint Missing

— — — 0.005 –10.017 (0.385) < 0.001

deterioration inside No deteriorated paint

— — 0.000

— Deteriorated paint but no large areas

— — –0.044 (0.417) 0.916 Large areas in one room

— — –1.402 (1.058) 0.192 Large areas in two or more rooms

— — 1.458 (0.669) 0.035 Extent of peeling, Intercept for missing 0.005 –0.530 (0.456) 0.251

— — — flaking, or chipping No deteriorated paint 0.000

— — — paint outside Deteriorated paint but no large areas –0.317 (0.364) 0.389

— — Large areas of deteriorated paint 1.303 (0.586) 0.031

— — Paint scraped when home Intercept for missing 0.053 0.433 (0.293) 0.146

— — —

repainted in last 12 months Yes 0.899 (0.451) 0.053

— — No 0.000

— — — Years lived in the home Intercept for missing 0.076 0.000

— — — — Slope –0.227 (0.124) 0.076

— — Year of survey 1999–2000 0.050 0.534 (0.229) 0.024

— — — 2001–2002 –0.087 (0.306) 0.776

— — — 2003–2004 0.000

— — — —

a Estimated using Cox–Snell methodology. b “Other” includes Hispanics.

### Gaitens et al.



### 466 volume 117 | number 3 | March 2009

• 

### Environmental Health Perspectives 

### PbD ≥ 250 μg/ft 2 

### , if the interior paint dete

rioration was large in two or more rooms,

the odds that sill PbD was ≥ 250 μg/ft 2 

### were about three times higher than if there was no interior paint deterioration.

Most variables that achieved statistical significance did so in more than one of the three sill PbD models, making these findings robust. For example, smoking and year of building construction were significant in all three models. Paint scraping in the preceding 12 months and the years lived in the home were only significant in the logistic model for

PbD ≥ 100 μg/ft 2 

### . Window surface condition was only significant in the linear model.



## Discussion

Consistent with other national data (Jacobs

et al. 2002), we confirm that the year of con

struction is a strong predictor of PbD and that post-1978 housing has significantly lower PbD than older housing. Housing units built after 1950 have significantly lower floor PbD than older housing. Furthermore, floor PbD
in houses built between 1940 and 1949 are not significantly different than in the pre1940 houses. This is consistent with the concentration of lead in paint. Before 1940, this concentration typically ranged from 10

to 50% (Rabin 1989; U.S. HUD 1995). However, in 1955, a voluntary paint industry standard limited the concentration to 1%, although the degree of compliance with this standard is unknown (American National Standards Institute 1955). In 1978, the Consumer Product Safety Commission and Congress banned the use of lead paint for res

idential use, limiting lead in new house paint to 0.06% by weight (Consumer Products Safety Commission 1977). Pre-1950 homes with window, cabinet, or wall renovation within the preceding 12 months had higher floor PbD than other homes. Renovation activities completed with

out using lead-safe work practices can gener

ate significant amounts of PbD (Jacobs et al. 2003). The U.S. EPA recently promulgated a final regulation in an attempt to control exposures from renovation (U.S. EPA 2008). Replacing windows in a lead-safe manner can help control PbD and may have large eco

nomic benefits (Nevin et al. 2008). Compared

with other housing components, windows are known to have the highest levels of lead-based paint and lead-contaminated dust (Jacobs

et al. 2002). We found that dust wipe samples taken from homes with chipping, peeling, or flaking (i.e., deteriorated) paint had higher windowsill PbD than homes without deteriorated paint, which is consistent with other research (U.S. HUD 2004; Wilson et al. 2006). Although we expected to see similar findings for floors,

we did not. This could be attributable to other factors included in the model. For example,

PIR and recent renovation were significant in the floor model, but not in the windowsill model, which could have masked the effect of deteriorated paint. In addition, it is more likely that floors are more regularly cleaned

than windowsills. The homes of non-Hispanic blacks had significantly higher PbD than the homes of non-Hispanic whites, even after controlling for other factors. Many prior studies have shown

that African- American children are at higher risk compared with white children (U.S. CDC 2005). For example, similar to our findings, other studies (Lanphear et al. 1996, 2002)

found that African- American children were exposed to higher PbD loadings and worse housing conditions than white children. Previously published studies suggest that rental units were more likely to have lead-based paint hazards than owner-occupied housing (Jacobs et al. 2002; Lanphear et al. 2005a). Although we found that homeownership sta

tus was a significant predictor of floor PbD in bivariate analysis, after controlling for other fac

tors such as PIR , renovation, and the presence of deteriorating paint, it was not significant in

the final models. Because low-income fami

lies are more likely to rent, the fact that home ownership was not significant in the model (but poverty was) is not surprising. Moreover, the type of home had a significant association with PbD in bivariate analysis, but not in the final models, again probably because of the confounding influence of poverty. A prior study found a relationship between exposure to environmental tobacco smoke exposure and the PbB levels of young chil

dren who were included in the NHANES III (1988–1994) (Mannino et al. 2003). Because lead is a component of tobacco smoke, such a relationship between PbB levels and tobacco smoke exposure is not surprising. That smok

ing in the home was a significant predictor of floor and windowsill PbD, even when control

ling other factors, suggests that lead in second

hand smoke is a significant contributor to lead on interior surfaces, at least at the relatively low surface loadings documented in this study.

We found that the surface condition from which the PbD samples were taken signifi

cantly influences the reported PbD. Other studies have found that uncarpeted smooth and cleanable surfaces have significantly lower PbD after cleaning compared with rough uncarpeted surfaces (Dixon et al. 1999; Ettinger et al. 2002). Although our results indicated that floor PbD on uncarpeted non

smooth or noncleanable surfaces was not sig

nificantly higher than floor PbD on smooth and cleanable surfaces, the trend was in the expected direction. It is possible that our find

ings were not statistically significant because

of

the small number of dust samples taken from nonsmooth or noncleanable floor sur

faces in this data set. The presence of carpeting also influ

enced reported PbD. We found that PbD on carpeted floors was significantly lower than lead loadings on hard- surfaced floors. This observed difference in lead loading by flooring type is likely attributable to the fact that wipe sampling was the methodology used in this study. Wipe sampling captures only dust adhering to the tops of the carpet fibers, whereas most of the dust in the carpet matrix is located deeper in the pile. A study that reported much higher PbD in vacuum samples from carpet compared with adja

cent wipe samples (Bai et al. 2003) supports this idea. The significance of this observation with respect to children’s lead exposure is not well understood. Our findings do not clarify whether or not carpet contributes to higher or lower exposures. The NHANES survey year was signifi

cantly associated with PbD. Although PbDshould decline with time as the ratio of post1978 to pre-1978 homes increases, the mag

nitude of the decline (14%) for the floor PbD

between the first and second waves was much larger than expected. Similarly, the magnitude of the decline (43%) between the first and second waves for windowsill PbD is unlikely to be explained only by temporal changes in national PbD. Although many housing characteristics were included in the model, other significant factors that we were unable to control for may exist ( e.g., different waves of NHANES sampling may occur in different geographic regions). Thus, the year of survey variable may reflect geographic differences in the three study wave locations that could

account for the observed trend in floor PbD. We used data from a large national sur

vey that combined housing and environmen

tal data, which is a strength of our study. However, the housing data included in this study may not be representative of the national housing stock. The sampling and weighting methodology used in NHANES is population based, not geography based; thus, the survey includes a nationally representative sample of the U.S. population but not a representa

tive sample of U.S. housing. Integrated health and housing surveys that are representative of both the population and the housing stock are

needed in the United States; such surveys were completed recently in eight European cities (Bonnefoy et al. 2003). Finally, a limitation of the NHANES PbD data is that they are based on a single floor and a single windowsill PbD measurement in a given home. The HUD Guidelines for the Evaluation and Control of Lead-Based Paint Hazard in Housing recom

mend that six to eight floor and sill samples be taken to help reduce spatial variability, which could not be assessed here (U.S. HUD 1995).

### Dust lead in homes of U.S. children

Environmental Health Perspectives

• volume 117 | number 3 | March 2009 

### 467 Despite these potential limitations, the study results presented are largely consistent with earlier findings.

Levels of PbD on floors and windowsills should be kept as low as possible to protect children from lead exposure. The current stan

dards for floor and windowsill PbD were set in 1999–2001 to protect 95% of children from developing a PbB level > 15 μ g/dL [the envi

ronmental intervention level established by the CDC (2005)], in light of feasibility and mea

surement limitations. These findings show that in most children’s homes, the average level of PbD is well below the current standards, mak

ing it feasible to lower the current standards and thus afford more protection for children.

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