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Relationship Between Total and Bioaccessible Lead on Children’s Blood Lead Levels in Urban Residential Philadelphia Soils Karen D. Bradham, Clay Nelson, Jack Kelly, Ana Pomales, Karen Scruton, Tim Dignam, John Misenheimer, Kevin Li, Daniel R. Obenour, and David James Thomas Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b02058 • Publication Date (Web): 08 Aug 2017 Downloaded from http://pubs.acs.org on August 9, 2017
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Relationship Between Total and Bioaccessible Lead on Children’s Blood Lead
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Levels in Urban Residential Philadelphia Soils
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Karen D. Bradham,*,† Clay M. Nelson,† Jack Kelly,‡ Ana Pomales,§ Karen Scruton,§ Tim
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Dignam,ǁ John C. Misenheimer,† Kevin Li,# Daniel R. Obenour,# and David J. Thomas†
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†
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EPA), Research Triangle Park, North Carolina, 27711, United States
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‡
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United States
Office of Research and Development, United States Environmental Protection Agency (U.S.
Hazardous Site Cleanup Division, U.S. EPA Region III, Philadelphia, Pennsylvania, 19103,
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§
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Registry, Philadelphia, Pennsylvania, 19103, United States
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ǁ
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Health, Centers for Disease Control and Prevention, Atlanta, 30329, Georgia, United States
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#
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University, Raleigh, 27695, North Carolina, United States
Division of Community Health Investigations, Agency for Toxic Substances and Disease
Division of Environmental Hazards and Health Effects, National Center for Environmental
Department of Civil, Construction, and Environmental Engineering, North Carolina State
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*Corresponding Author
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Address: 109 T.W. Alexander Drive, MD-205-05, Research Triangle Park, NC 27711. E-mail:
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[email protected]. Phone: (919) 541-9414. Fax: (919) 541-3527.
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TOC Figure
Blood Pb (µg/dL)
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0
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1000
Soil Pb (mg/kg) :
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Bioaccessible
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Total
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ABSTRACT
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Relationships between total soil or bioaccessible lead (Pb), measured using an in vitro
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bioaccessibility assay, and children’s blood lead levels (BLL) were investigated in an urban
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neighborhood in Philadelphia, Pennsylvania, USA, with a history of soil Pb contamination. Soil
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samples from 38 homes were analyzed to determine whether accounting for the bioaccessible Pb
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fraction improves statistical relationships with children’s BLLs. Total soil Pb concentration
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ranged from 58 to 2,821 mg/kg; the bioaccessible Pb concentration ranged from 47 to 2,567
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mg/kg. Children’s BLLs ranged from 0.3 to 9.8 µg/dL. Hierarchical models were used to
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compare relationships between total or bioaccessible Pb in soil and children’s BLLs. Total soil
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Pb concentration as the predictor accounted for 23% of the variability in child BLL;
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bioaccessible soil Pb concentration as the predictor accounted for 26% of BLL variability. A
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bootstrapping analysis confirmed a significant increase in R2 for the model using bioaccessible
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soil Pb concentration as the predictor with 99.0% of bootstraps showing a positive increase.
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Estimated increases of 1.3 µg/dL and 1.5 µg/dL in BLL per 1,000 mg/kg Pb in soil were
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observed for this study area using total and bioaccessible Pb concentrations, respectively.
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Children’s age did not contribute significantly to the prediction of BLLs.
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INTRODUCTION
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Lead (Pb) is a potent developmental neurotoxin; even low levels of exposure in early life have
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the potential for profound and long-lasting health effects. 1, 2 Lead occurs naturally in soils
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typically at concentrations that range from 10 to 50 mg/kg. Human activity has dispersed Pb in
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the environment, resulting in extensive and persistent contamination of soil and dust.3
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Widespread use of leaded paint until the mid-1970s and leaded gasoline until the mid-1980s, and
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contamination from various industrial sources, resulted in extensive contamination of urban soils
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with Pb. Urban soils often have Pb concentrations much greater than normal background levels.
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These concentrations frequently range from 150 mg/kg to as high as 10,000 mg/kg at the base of
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a home painted with lead-based paint.4 Because Pb does not biodegrade or dissipate over time,
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soil Pb levels remain elevated for many years. Elevated Pb levels in soil and dust represent
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significant sources of exposure for children.5,6
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Earlier studies have evaluated children’s blood lead levels (BLL) in relation to soil Pb
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concentrations. A report released by the U.S. Environmental Protection Agency (1983) estimated
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blood Pb increases of 0.6 to 6.8 µg/dL per 1000 mg/kg of soil Pb. Other published studies have
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reported similar observations.7-11 However, the relationship between childhood blood Pb and soil
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Pb is highly dependent on site-specific variables including soil vegetative cover, frequency and
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duration of soil contact, and behavior, hygiene, and nutritional status of exposed children.12,13
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Although earlier studies evaluated relationships between total soil Pb concentrations and
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BLLs in children, few have considered bioavailability or bioaccessibility of soil Pb when
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evaluating relationships with blood Pb concentrations in urban environments. Soil Pb
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bioavailability is a measure of the fraction of Pb in soil that upon ingestion is released from the
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soil and becomes available for absorption across the gastrointestinal barrier. Accounting for
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bioavailability can improve the accuracy of exposure and risk calculations when assessing
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human exposures to Pb in soil in urban environments. Bioaccessibility is the fraction of the total
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amount of Pb in soil that is soluble in a gastric-like (i.e., low pH) extraction medium,13and can be
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used as an estimate of bioavailability. Ren et al.,14 have reported statistically significant
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relationships between bioaccessible Pb concentration in soil, as measured by the physiologically
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based extraction test,15 and children’s BLLs. However, this study was limited in that it did not
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directly compare total versus bioaccessible Pb with respect to BLLs and measured only eight
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data points per regression analysis. Laidlaw et al’s results from New Orleans indicate that about
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67% of the variation in children’s BLL was explained by independent soil Pb sample location
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variables for samples collected near houses, residential and busy side streets, or open spaces.5,16
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A blood lead study was conducted during June 2014 in several urban neighborhoods in
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Philadelphia, Pennsylvania with a history of soil and household lead contamination. A total of
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122 households and 163 children less than 8 years were enrolled. The current study is a
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randomly selected subset of the original study evaluating the relationship between total or
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bioaccessible Pb and children’s BLLs across 49 data points using an in vitro bioaccessibility
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assay (IVBA) to estimate soil Pb bioavailability. The objectives of this study were 1) to evaluate
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the relationships between total and bioaccessible Pb in soil and children’s BLL’s, 2)to test the
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hypothesis that accounting for the bioaccessible fraction of Pb would improve statistical
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relationships with children’s BLLs, 3) to quantify the effect of child’s age on the relationship
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between soil Pb and children’s BLLs.
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MATERIALS AND METHODS Soil Collection. To evaluate the relationship between total or bioaccessible Pb and
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children’s BLLs, soil samples were collected from yards in selected urban residential homes in
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Philadelphia, Pennsylvania, USA. The majority of the Philadelphia single-family row-style
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homes included in the study were built before 1900. Soil samples were collected from
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neighborhoods (Kensington, Olde Richmond, Port Richmond, North Philadelphia East, and
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Fishtown) with a history of nearby industrial operations dating back to the mid-1800s, several of
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which are known to have released Pb in air emissions. The study area comprised ZIP codes
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19125, 19134, 19145, 19146, 19147 and 19148. During 2015, based on Philadelphia Department
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of Public Health (PDPH) child blood lead surveillance data, the percent of children with BLLs 5-
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9 µg/dL ranged from
