_ I OSWER 9200.2-142
S%JJ May 2014
^"a, „ _.,reCo
TECHNICAL REVIEW WORKGROUP
RECOMMENDATIONS REGARDING
GARDENING AND REDUCING EXPOSURE
TO LEAD-CONTAMINATED SOILS
Office of Solid Waste and Emergency Response
U.S. Environmental Protection Agency
Washington, DC 20460
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NOTICE
This document provides technical and policy guidance to the U.S. Environmental Protection
Agency (EPA) staff on making risk management decisions for contaminated sites. It also
provides information to the public and to the regulated community on how EPA intends to
exercise its discretion in implementing its regulations at contaminated sites. It is important to
understand, however, that this document does not substitute for statues those EPA
administrators or their implementing regulations, nor is it a regulation itself. Thus, this
document does not impose legally - binding requirements on EPA, states, or the regulated
community, and may not apply to a particular situation based upon the specific circumstances.
Rather, the document suggests approaches that may be used at particular sites, as appropriate,
given site-specific circumstances.
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U.S. ENVIRONMENTAL PROTECTION AGENCY
TECHNICAL REVIEW WORKGROUP FOR LEAD
The Technical Review Workgroup for Lead (TRW) is an interoffice workgroup convened by the
U.S. EPA Office of Solid Waste and Emergency Response/Office of Superfund Remediation
and Technology Innovation (OSWER/OSRTI).
MEMBERS
Region i
Mary Ballew
Claire Willscher
Region 2
Mark Maddaloni
Julie McPherson
Region 3
Dawn loven
Linda Watson
Region 4
Kevin Koporec
Region 5
Andrew Podowski
Region 6
Ghassan Khoury
Region 7
Mike Beringer (advisor)
Todd Phillips
Region 8
Charles Partridge (co-chair)
Jim Luey
Region 9
Sophia Serda
Region 10
Marc Stifelman
Craig Cameron
OSRTI
Michele Burgess (co-chair)
Steve Jones (ATSDR Liaison)
ORD NRMRL - Cincinnati
Harlal Choudhury
Kirk Scheckel
ORD NCEA - RTP
Jim Brown
State of Utah DEQ
Scott Everett (co-chair)
Advisors
Karen Hogan (ORD NCEA)
Paul White (ORD NCEA)
Larry Zaragoza (OSRTI)
Michele Mahoney (OSRTI)
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OVERVIEW
This document provides an overview of exposure to lead while gardening and consuming
home-grown produce, and, based on currently available information, to provide Best
Management Practices for Gardening in Lead Contaminated Areas to reduce lead exposure in
contaminated soil (see Table i). This document also seeks to identify key data gaps and
uncertainties. These Best Management Practices are based on a review of the literature and
best professional judgment to identify appropriate risk mitigating actions associated with the
varying ranges of soil lead concentrations1 in produce gardens. For further background
information on lead risk assessment, refer to U.S. EPA Technical Review Workgroup for Lead
(TRW) website (http://epa.gov/superfund/lead/trw.htm).
The Office of Solid Waste and Emergency Response (OSWER) recommends using the
Integrated Exposure Uptake Biokinetic Model (IEUBK model) as a risk assessment tool to
support environmental cleanup decisions for residential scenarios at Comprehensive
Environmental Response, Compensation and Liability Act (CERCLA) sites and at Resource
Conservation and Recovery Act (RCRA) Corrective Action sites (U.S. EPA, I994a, b). It is also
useful to support environmental cleanup decisions for other types of sites too. For residential
scenarios, OSWER has established 400 ppm as the screening level for lead in soil (U.S. EPA
i994c). Soil Screening Levels (SSLs) are not cleanup goals. SSLs are guidelines to determine
which sites or portions of sites require further study. While residential areas with soil lead
concentrations below 400 ppm generally require no further action, some actions maybe
appropriate in edible gardens at soil lead concentrations below 400 ppm to reduce the
potential for increased lead exposure. The basis for the 400 ppm SSL is children playing in lead
contaminated soil and some other exposures, with the predominant source of exposure from
direct soil ingestion or ingestion of soil manifested as house dust. Scientific limitations when
the SSL for lead was developed did not allow adequate accounting for consumption of home-
grown produce. In some instances, States or tribal cleanup programs or local governments may
established more stringent standards that require further action at soil lead concentrations
below 400 ppm for cleanup activities they govern, fund, or oversee.
To address public health concerns of potential exposure to lead while gardening, the TRW
extensively reviewed the literature and conducted a feasibility study (i.e., the Spreadsheet
Model, see Appendix A) to develop quantitative, risk-based recommendations for lead
concentrations in garden soil for specific garden-related exposure pathways. The TRW
identified the following four pathways of lead exposure that may be associated with gardening
in contaminated soil and consuming produce as well as additional exposure risks from
contaminated soil tracked into dwellings for inclusion in the model2:
• Direct ingestion of lead in the matrix of produce;
• Ingestion of lead in soil adhered to produce surfaces;
• Incidental ingestion of soil while gardening; and
• Incidental ingestion of soil tracked into residence.
'"Best professional judgment" reflects the collaborative technical expertise of the TRW, as well as other participating Federal and State
Agencies.
2Inhalation and dermal absorption of lead from gardening are believed to be minor routes of exposure, and, consequently, not discussed in this
document.
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Data were not sufficient to derive quantitative, risk-based recommendations for lead
concentrations in garden soil for specific garden-related exposure pathways (see Appendix A).
Nonetheless, the TRW identified that the exposures associated with gardening (both as an
activity and through the consumption of home grown produce) could result in greater exposure
than typically considered as part of the traditional residential exposure pathway. Because of
insufficient data limitations, the TRW recommends that that soil lead concentrations in Table i
be used as guidelines to consider the associated Best Management Practices for Gardening in
Lead Contaminated Areas to reduce lead exposure in contaminated soil.
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Table i. TRW Lead Committee Recommended Best Management Practices for Gardening
in Lead Contaminated Areas
Soil-Lead
Concentration
(ppm)
Category
Recommendation:
Gardening Practices
Recommendation:
Choosing Plants8
100-400'
400-1200
Potential
risk
Increasing use of good gardening and
housekeeping practices as described in
Table 3.
Relocate garden to lower risk garden
areas.
Increasing use of soil amendments (e.g.,
compost, clean fill), barriers (e.g., mulch),
and other remedial measures (see Table
3) up to and including raised beds and
containers.
Ensure gardeners wear gloves and use
tools to reduce soil contact and ingestion.
>12OO
High risk
All of the above good gardening and
housekeeping practices.
Raised beds, soil containers, soil
replacement (i.e., excavate contaminated
soil and replace with soil containing low
lead concentrations) are strongly
recommended.0
Consider finding other locations for
garden.
Restrict child access to only established
safe areas.
Restrict all gardening by or for children in
contaminated soils.
Select plants with shallow roots
for raised beds or areas with
replacement soil to ensure that
roots do not reach
contaminated soil that is left in
place, if any, otherwise, no
restrictions.
a Source: Hemphill et al., 1973; Moir and Thornton, 1989; U.S. EPA, 1995; U.S. DOE, 1998; Jorhem et al., 2000; Heinegg et al., 2000; Finster
et al., 2003; Pichtel and Bradway, 2008; Shayler et al., 2009; Leake et al., 2009; Chaney et al., 2010; Nabulo et al., 2010; U.S. EPA, 2Olla;
U.S. EPA, 2Ollb; Saumel et al., 2012
b While 400 ppm lead in soil is considered an appropriate screening level for residential soil-lead, the TRW recommends that 100 ppm be used
as the low end of the range of soil lead concentrations to mitigate exposure to lead in soil when gardening is an important exposure pathway.
Lacking the information to support a quantitative approach for estimating risk for gardening scenario to support establishing acceptable
concentration of lead in garden areas, best professional judgment was used to establish the low end of the range. This soil concentration is
below the 40 o ppm soil screening level for lead because the gardening exposure pathway includes other sources of lead exposure not
sufficiently accounted for in the soil screening level. The basis for the Soil Screening Level (SSL) is children playing in lead contaminated soil
and some other exposures, with the predominant source of exposure from direct soil ingestion or ingestion of soil manifested as house dust.
Scientific limitations when it was developed did not allow the SSL for lead to adequately account for consuming home-grown produce. In
developing an acceptable concentration of lead in soil for home garden exposures, the same child receptor would be exposed if accompanying
the adult in the garden and also exposed through consumption of lead in and on the produce grown in the soil. Hence, the garden-based level
is lower than the SSL and reasonable steps to mitigate exposure to lead while gardening in soil lead concentrations between 100-400 ppm
would be appropriate. The TRW acknowledges that background soil lead concentrations in some communities may exceed the guidance
values recommended for garden areas. Mitigation may be necessary for those communities.
"Twenty-four (24) inches of clean soil cover is generally considered adequate for gardening; however, site specific conditions should also be
considered. A 24-inch barrier normally is necessary to prevent contact of contaminated soil at depth with plant roots, root vegetables, and
clean soil that is mixed via deep rototilling. Raised garden beds could cost effectively add 24 inches of clean soil (U.S. EPA, 2003).
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INTRODUCTION
The benefits of home- and community-based gardening are widely documented (Green
Institute, 2006; Walsh et al., 2001; van den Berg et al., 2010; Leake et al., 2011; Alaimo et al.,
2008; Burton et al., 1999), yet consuming home-grown produce creates a potential route of
exposure to contaminants in soil (Nolan et al., 2012; U.S. EPA, 2Oiic; Roussel et al., 2010;
Lima et al., 2009; Scheckel et al., 2009; Chaney et al., 2008; Douay et al., 2008; Alloway,
2004; Sams0e-Petersen et al., 2002; Heinegg et al., 2000).
Screening levels are defined as a level of contamination above which there may be enough
concern to warrant site-specific study of risks. Screening levels provide health protection
without knowledge of the specific exposure conditions at a site (U.S. EPA, I994c). The Soil
Screening Level (SSL) for lead is intended to represent children playing in lead contaminated
soil; the predominant source of lead exposure coming from incidental soil ingestion. The
current OSWER residential SSL for lead (400 ppm) was selected as a reasonable value in the
range of candidate preliminary remediation goals (PRG) values and selected as a policy
decision to give a round number for ease of calculations. This value, however, does not account
for consuming garden produce. Thus, the SSL for lead may underestimate the risk of exposure
to lead for garden-related activities and consumption of produce grown in contaminated soil.
The 1994 OSWER Directive states (in the section entitled Derivation of Lead Screening Levels):
"For the purpose of deriving a residential screening level, the background lead
exposure inputs to the IEUBK model were determined using national averages, where
suitable, or typical values. Thus, the estimated screening level of 400 ppm is associated
with an expected "typical" response to these exposures, and should not be taken to
indicate that a certain level of risk (e.g., exactly 5% of children exceeding iop.g/dL
blood) will be observed in specific community (e.g., in a blood lead survey)."
Historically, the TRW has cautioned against gardening in areas or consuming produce grown
in areas of known soil contamination, but the TRW was unable to recommend specific soil lead
concentrations to be avoided for garden areas due to a wide range of recommendations (see
Appendix B). The TRW identified garden-specific exposure parameters that need to be
considered when characterizing risk associated with exposure to lead contaminated soils and
dustss from the following exposure pathways:
• Direct ingestion of lead in the matrix of produce;
• Ingestion of lead in soil adhered to produce surfaces;
• Incidental ingestion of soil while gardening; and
• Incidental ingestion of soil tracked into residence.
The objective of this analysis is threefold: i) review the available literature and determine the
state of the science (i.e., identify data gaps), 2) conduct a feasibility study to develop
quantitative approach for estimating risk associated with and acceptable soil lead
concentrations for gardening (i.e., Spreadsheet Model, see Appendix A), and 3) provide
evidence-based Best Management Practices for limiting potential exposure to lead while
gardening.
3 Inhalation and dermal absorption of lead from gardening are believed to be minor routes of exposure, and was neither discussed in this
document nor included in the analysis.
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TECHNICAL ANALYSIS
A literature search was conducted to identify data for estimating the garden-specific exposure
parameters. PubMed, TOXLINE, and Agricola were searched using various strategies that
incorporated the search terms: lead, uptake, bioaccessible, garden, crops, and plants. The
literature search identified limited quantitative data for the four garden-specific exposure
parameters.
The Spreadsheet Model (see Appendix A) was developed to explore the feasibility of developing
a quantitative risk model given the information available at this time. To simplify the
calculations, daily lead intake rates were calculated for the following types/categories of
produce: dark green leafy, lettuce, tomatoes, root vegetables, and other vegetables. Data
sources, methods, and uncertainty for parameters that were estimated in the quantitative
analysis of the four exposure pathways are provided in Appendix A.
RESULTS
In response to uncertainty and limitations of the available data, the TRW recommended as
Best Management Practices for Gardening to reduce lead exposure in contaminated soil (see
Table i). The results from the feasibility study (i.e., Spreadsheet Model) are provided in
Appendix A.
In addition, four documents were identified that describe Best Practices for limiting potential
exposure to lead while gardening and provide guidance on interpreting soil sample test results
(Table 2). Note: these four well written guidance documents do not constitute an exhaustive
representation of the literature on this subject matter. See Table B-i for a more extensive
listing of guidance documents with accompanying interpretive soil lead values (which vary
from document to document but, collectively, are generally concordant with the
recommendations made in this report).
Table 2. Summary of Selected Guidance Documents that Address Gardening and
Potential Lead Risk
Study
U.S. EPA, 20iia
U.S. EPA, 20iib
Heinegg et al.,
2000*
Shayler et al.,
2009*
Lead Concentration
(mg/kg)
400 mg/kg (residential)
1200 mg/kg (commercial)
-
70 mg/kg (Canada)
50 mg/kg (Quebec province)
63 mg/kg (unrestricted use)
400 mg/kg (residential,
restricted-residential use)
Description
Soil Screening
Level
-
Agricultural
standards for Pb
New York State
Soil Cleanup
Objectives
Study Overview
Provides best practices,
bioavailability, and exposure
pathways
Provides best practices,
interpreting soil sample
results, and current data
limitations
Provides best practices,
compares Canadian National
agricultural soil standards to
provincial standards (Quebec)
Discusses New York
Department of Health and
EPA standards
*While the TRW
different soil lead
;enerally agrees with the best management practices in these documents, the TRW recommends
guideline values for garden areas and the recommendations may not be completely concordant.
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RECOMMENDATIONS
While 400 ppm lead in soil is generally a protective screening level for residential soil-lead, it
may not be adequate for intensive gardening activities and consumption of home grown
produce. The TRW Lead Committee recommends that 100 ppm be used as the low end of the
range of soil lead concentrations to initiate best management practices to mitigate exposure to
lead in soil for gardening-related exposure pathways. Lacking sufficient data to support a
quantitative approach for estimating risk for the gardening exposure pathways to support
establishing acceptable concentration of lead in garden areas, a semi-quantitative weight-of-
evidence and best professional judgment approach was used to establish the low end of the
range. The recommended low-end soil lead concentration (100 ppm) is below the 400 ppm
SSL for lead because the gardening exposure pathway includes other sources of exposure not
sufficiently accounted for in the development of the SSL. The basis for the SSL is children
playing in lead contaminated soil and other gardening exposures, with the predominant source
of exposure from soil ingestion (though it includes contributions from other pathways such as
tap water, air, and store-bought food). Thus, the existing SSL for lead does not explicitly
account for exposure to lead from consuming home-grown produce or the potentially longer
duration of soil contact and potential for ingestion of soil related to gardening activities. In
developing an acceptable concentration of lead in soil for home garden exposures, the same
child receptor would be exposed if accompanying the adult in the garden (and from secondary
soil track-in) and also exposed through consumption of lead in and on the produce grown in
the soil (which can be higher in lead content than store-bought food4). Hence, the garden-
based soil recommendation is appropriately lower than the SSL, and reasonable steps to
mitigate exposure to lead while gardening in soil lead concentrations between 100-400 ppm
would be appropriate. The TRW also acknowledges that background soil lead concentrations in
some communities may exceed the guidance values recommended for garden areas. Risk
management decisions may be necessary for those communities.
Based on the literature review performed for this analysis, as well as utilizing best professional
judgment, the TRW recommends the Best Management Practices for limiting potential
exposure to lead while gardening (Table i). These recommendations may be revisited when
additional data are available.
During the literature search, the TRW identified a variety of additional techniques that could
be used to reduce exposure to lead from garden-related exposure pathways (Table 3).
4 See http://www.epa.gov/superfund/lead for the TRW Lead Committee's current recommendations regarding
dietary exposure from store-bought food.
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Table 3. Additional approaches to reducing exposure to lead while gardening
Techniques
Behavioral
Soil
Remediation
Alternate
Remediation
Approaches
• Discard outer leaves of leafy vegetables
• Wash produce to remove soil
• Peel root crops
• Discourage eating soil
• Wash hands, toys, pacifiers
• Wear gloves
• Keep children from entering the garden if contaminant levels are unknown
• Keep soil outside
• Take off shoes, use doormats, and clean floors
• Provide alternative safe areas, like a sandbox, for children's play
• Locate gardens away from older painted structures, fences or sheds
• Request a soil sample test for metals and agronomic parameters before
beginning gardening
• Adjust soil pH to near neutral (-6.5-7.5), based on findings
• Incorporate clean materials (e.g., compost, manure)
• Apply mulch to reduce dust and soil splash-back onto crops and reduce
exposures
• Add phosphate amendments where appropriate
• Excavate contaminated soil, place geotextile barriers
• Build raised beds with safe materials (i.e., do not use treated lumber or
salvaged painted wood) with a barrier (e.g., landscape fabric) and fill with
clean soil
• Use containers to grow in clean soil (e.g., 5-gallon buckets that do not leach
metals)
• Consider other land/location options
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REFERENCES
Alaimo, K., E. Packnett, R. A. Miles, and D. J. Kruger. 2008. Fruit and vegetable intake among
urban community gardeners. J Nutri Educ Behav 40: 94-101.
Alloway, B.J. 2004. Contamination of soils in domestic gardens and allotments: a brief
overview. Land Contamin & Reclamation. 12 (3): 179-187.
Burton, L.C., Shapiro, S., German, P.S. 1999. Determinants of physical activity initiation and
maintenance among community-dwelling older persons. Preventative medicine. 29 (5):
422-430.
Chaney RL, et al. 2008. Element Bioavailability and Bioaccessibility in Soils: What is known
now, and what are significant data gaps? Proc. SERDP-ESTCP Bioavailability Workshop,
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Chaney, R. L., E. E. Codling, K. Scheckel, and M. Zia. 2010. Pb in carrots grown on Pb-rich soils
is mostly without the xylem [Abstract]. American Society of Agronomy (ASA), Crop Science
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Douay, F., Roussel, H., Pruvot, C., Waterlot, C. 2008. Impact of a Smelter Closedown on Metal
Contents of Wheat Cultivated in the Neighbourhood. Env Sci Pollut Res. 15(2): 162-169.
Finster, M. E., K. A. Gray, and H. G. Binns. 2003. Lead levels of edibles grown in contaminated
residential soils: Afield survey. Sci Total Environ 320(2-3): 245-257. Available online at:
http://pursuitofresearch.org/wp-content/uploads/2Oii/oi/binnspaper2OO3.pdf.
Green Institute. 2006. Multiple benefits of community gardening. Minneapolis, MN. Available
online at http: //www.communitygarden.org
Jorhem, L., J. Engman, L. Lindestrom, and T. Schroder. 2000. Uptake of lead by vegetables
grown in contaminated soil. Commun Soil Sci Plant Anal 31(11-14): 2403-2411.
Heinegg, A., P. Maragos, E. Mason, J. Rabinowicz, G. Straccini, and H. Walsh. 2000. Soil
Contamination and Urban Agriculture: A Practical Guide to Soil Contamination Issues for
Individuals and Groups. Quebec, Canada: McGill University, McGill School of
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http://www.ruaf.org/sites/default/files/guide%20on%20soil%20contamination.pdf.
Hemphill, D. D., C. J. Marienfeld, R. S. Reddy, W. D. Heidlage, and J. O. Pierce. 1973. Toxic
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Leake, J. R., A. Adam-Bradford, and R. Janette. 2009. Health benefits of 'grow your own' food
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Lima, F.S., Nascimento, C.W.A., Silva, F.B.V., Carvalho, V.G.B., Filho., M.R.R. 2009. Lead
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Moir, A. M. and I. Thornton. 1989. Lead and cadmium in urban allotment and garden soils and
vegetables in the United Kingdom. Environ Geochem Health 11:113-120.
Nabulo, G., S. D. Young, and C. R. Black. 2010. Assessing risk to human health from tropical
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Pichtel, J. and D. J. Bradway. 2008. Conventional crops and organic amendments for Pb, Cd
and Zn treatment at a severely contaminated site. Bioresour Technol 99(5): 1242-1251.
Roussel, H., Waterlot, C., Pelfrene, A., Pruvot, C., Mazzuca, M., Douay, F. 2010. Cd, Pb and Zn
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from Two Lead and Zinc Smelters. Arch Environ Contam Toxicol. 58:945-954.
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PAHs by Fruits and Vegetables from Contaminated Soils. Environ. Sci. Technol. 36: 3057-
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124-132.
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APPENDIX A. THE SPREADSHEET MODEL
OVERVIEW
The objective of the Spreadsheet Model is threefold: i) Review the available literature and
determine the state of the science (i.e., identify data gaps), 2) examine the feasibility of
applying a quantitative approach for estimating risk and acceptable soil concentrations for
gardening, and 3) provide evidence-based Best Management Practices for limiting potential
exposure to lead while gardening.
TECHNICAL ANALYSIS
A literature search was conducted to identify data for estimating the uptake of lead from soil by
plants. PubMed, TOXLINE, and Agricola were searched using various strategies that
incorporated the search terms: lead, uptake, bioaccessible, garden, crops, and plants.
Citations in the Spreadsheet Model were also taken from existing EPA risk assessment models.
An EndNote database includes the complete list of relevant citations.
Daily lead intakes were calculated for adults and children (0-7 years of age). Childhood
exposures were calculated for the age-specific groups that are used in the IEUBK model.
Estimates of average moisture content for different types of produce were required because
most of the data on lead concentration in vegetables is provided on a dry-weight basis, while
the consumption data from What We Eat in America (WWEIA) is reported on a wet-weight
basis. Moisture contents were taken from Table 9-37 of the Exposure Factors Handbook (U.S.
EPA, 2011).
The Spreadsheet Model does not make assumptions, nor is intended to, regarding the use of
soil amendments or management strategies to neutralize and control pH, or improve soil
structure or soil covers (such as mulch) that prevent soil deposition on crops.
The literature search identified limited data for the four exposure pathways that are needed to
estimate risk related to gardening in and consuming produce from contaminated soils:
• Direct ingestion of lead in the matrix of produce (including consumption rates for
various types or categories of produce);
• Ingestion of lead in soil adhered to produce surface (e.g., leafy vegetables);
• Incidental ingestion of soil while gardening; and
• Incidental ingestion of soil tracked into residence.
DIRECT INGESTION OF LEAD IN THE MATRIX OF PRODUCE (PB!UP)
Ingestion of lead via uptake from soil by produce was estimated as the concentration of lead in
produce multiplied by the average daily consumption rate for the type of produce. For the
purposes of the preliminary risk assessment, daily lead intake rates were calculated for the
following types/categories of produce: dark green leafy, lettuce, tomatoes, root vegetables, and
other vegetables using Equation i:
Page 14 0/23
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PbIUp = Ingveg x UF x PbS Equation i
Pblup = daily intake of lead (ng Pb/day) from ingestion of vegetables that absorbed lead
from the soil
Ingveg = daily ingestion rate (g/day) of vegetables
UF = uptake factor (unitless; e.g., ppm Pb in vegetable/ppm Pb in soil)
PbS = concentration of lead in garden soil (ng Pb/g soil) (site-specific)
The daily ingestion rates for garden vegetables were estimated using all respondents in the
2003-2008 National Health and Nutrition Examination Survey (NHANES) 24-hour recall
dietary recalls [What We Eat in America (WWEIA) Survey] where recalls were determined to
be reliable and complete (U.S. CDC, 2Oioa, 2Oiob, 2011). Estimates were calculated with the
SurveyMeans procedure in SAS (SAS Institute) using the sampling weights, domains, and
strata provided in the WWEIA data files. Daily ingestion rates were also calculated using the
National Cancer Institute's (NCI) non-linear mixed model (Tooze et al., 2006; Parsons et al.,
2009). The NCI estimates for individual vegetable groups (e.g., dark-green leafy vegetables)
differed from the SurveyMeans estimates by less than 10%; on average, estimates by the two
methods differed by approximately 2%.
Estimates of lead uptake in vegetables were calculated with data from sources identified
through the literature search described above. The uptake factors used in the preliminary lead
intake estimates were estimated using the data from the Sudbury Urban Soil Study (MOE,
2004) for all produce except lettuce. The uptake data for lettuce from Sudbury was at the
higher end of the range of uptakes that were identified from the literature search.
INGESTION OF LEAD IN SOIL ADHERED TO PRODUCE SURFACE (PB!ON)
Ingestion of lead present in soil adhered to the surface of produce was estimated as the
concentration of lead in produce multiplied by the average daily consumption rate for the type
of produce. To simplify the calculations, daily lead intake rates were calculated for the
following types/categories of produce: dark green leafy, lettuce, tomatoes, root vegetables, and
other vegetables using Equation 2:
Pbl0n = lngveg x AdF x PbS Equation 2
Pblon = daily intake of lead (ng pb/day) from incidental ingestion of soil
adhered to surface of vegetables
Ingveg = daily ingestion rate (g/day) of vegetables (see above)
AdF = soil adherence factor (unitless; e.g., mass of soil / mass of vegetable)
PbS = concentration of lead in garden soil (ng pb/g soil) (site-specific)
Data for estimating the adherence factor was provided by Hettiarachchi et al. (2011) as well as
Attanayake et al. (2014). As described by Hettiarachchi et al. (2011) and Attanayake et al.
(2014), the adherence factor was estimated using the concentration measured in produce after
"ordinary kitchen cleaning methods" were used to wash the produce as compared to the
concentration measured after the produce were washed with a more rigorous "laboratory
cleaning method". Differences in measured lead concentrations observed between methods
were attributed to soil lead adherence. The difference in these measured concentrations was
divided by the concentration of lead in the soil to estimate of the mass of soil that remained on
the produce after the kitchen cleaning using Equation 3:
Page 150/23
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AdF = (CKit - CLab~)/PbS Equation 3
AdF = soil adherence factor (unitless; e.g., mass of soil / mass of
vegetable)
at = concentration of lead in/on produce after kitchen cleaning
methods
= concentration of lead in/on produce after laboratory cleaning
methods
PbS = concentration of lead in garden soil (ng Pb/g soil) (site-specific)
INCIDENTAL INGESTION OF SOIL WHILE GARDENING (PB!ING)
The range of lead intake values for children from the incidental ingestion of soil while
gardening (0.05-0.2 g/day) was taken from Table 5-1 of the Exposure Factors Handbook (U.S.
EPA, 2one). The values represent the central tendency (low) and upper percentile (high)
values for the general population; the values do not vary between the age groups. For adults,
the range of values (0.05-0.1 g/day) was based on personal communication with EPA
personnel (Moya, 2011); the range (exposure for typical vs. soil-intensive activities) was also
suggested by the TRW Lead Committee (U.S. EPA, 2003).
INCIDENTAL INGESTION OF SOIL TRACKED INTO RESIDENCE
Daily lead intake from the incidental ingestion of dust containing soil that has been tracked in
from the garden is estimated using the soil/dust ingestion rates and soil dust ingestion ratio
from the IEUBK model (U.S. EPA, I994b, 1999), a track-in factor that represents the fraction
residential dust lead concentration that is attributable to the lead in the garden soil. The track-
in factor is analogous to the mass fraction of soil in indoor dust (Mso) of the IEUBK model
(U.S. EPA, I994b); however, the track-in factor only represents the contribution of lead via
track-in of soil from garden on shoes and clothes while the MSD represents the contribution of
nearby soil via all transport pathways (e.g., including airborne transport of nearby soil
(Equation 4).
PbITr = IRS x PbS x TF x (1 - SDIR~) Equation 4
Pblir = Daily intake of lead (ng Pb/day) from incidental ingestion of dust
containing soil that is tracked-in from the garden
IRs = Soil ingestion rates for children are from the IEUBK model (USEPA,
i994b, 1999); the rate for adults is from the Adult Lead Methodology
(USEPA, 2003)
PbS = Concentration of lead in garden soil (ng Pb/g soil) (site-specific)
TF = Track-in factor (unitless); converts concentration of lead in soil to
concentration of lead in residential dust
SDiR = Soil/dust ingestion ratio (USEPA, I994b)
Page 16 0/23
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RESULTS AND UNCERTAINTIES
The literature provided data that were used to estimate one or more of the parameters included
in the Spreadsheet Model, or provided information that was used to inform the estimates or
the uncertainty in the estimates. In general, the literature search identified data to produce a
reliable estimate, with sufficient precision, for uptake of lead in tomatoes and root vegetables
(e.g., carrots and radish). The data for uptake in lettuce and dark-green leafy vegetables
exhibited much more variability. It is very likely the lead concentrations for lettuce and dark-
green leafy vegetables represented soil adhered to the surface of the vegetables rather than
uptake (Sterrett et al., 1996; Finster et al., 2003; SARA Group, 2008; Nabulo et al., 2010).
Limited data or analyses were found that would provide a basis for estimating the amount of
soil that adheres to the surface of vegetables. Estimates for adherence for dark-green leafy,
lettuce, carrots, and tomatoes are based on Attanayake et al. (2014). Estimates of daily lead
intake are provided in Table A-i.
Table A-i. Current Range in Spreadsheet Estimates of Total Daily Lead Intake (All
Age Group (years)
0.5-lb
l-2b
2-3
3-4
4-5
5-6
6-7
>7
IEUBK with Soil =
400 ppma
29
46
46
46
34
31
29
-
Gardening
Low
11
15
16
17
18
19
18
38
High
777
947
972
1033
1023
1019
1004
-
"Provided for comparison purposes. Calculated with IEUBK model for soil and dust ingestion pathway only; diet (market basket), water and air
not included and assumed to be minor compared to soil and dust ingestion.
b These young children would be exposed while accompanying the adult in the garden and also exposed through consumption of lead in and on
the produce grown in the soil.
DIRECT INGESTION OF LEAD IN THE MATRIX OF PRODUCE
On average this pathway currently represents approximately 50% of the central tendency (low)
total daily lead intake estimated by the spreadsheet model. Along with other data provided by
various published and unpublished study results (Davies, 1978; Chaney et al., 1984; PHD,
1986; Nwosu et al., 1995; Sterrett et al., 1996). The Sudbury Urban Soil Study (MOE, 2004)
identified data to produce estimates with reasonable certainty (i.e., sufficiently high precision)
for uptake of lead by tomatoes and root vegetables (e.g., carrots, potatoes and radish).
Although there is much variability, there is a general trend suggesting that uptake in the matrix
of produce is greater in root vegetables that in the foods where the plant shoots or fruits are
consumed.
In general, the uptake data exhibited high variability. The lettuce uptake data was the most
variable for this data set. A substantial amount of the observed variability maybe explained by
the nonlinear relationship between uptake and soil concentration. The data show uptake tends
to decrease with increasing soil concentration. Much of the Sudbury data for uptake is from
vegetables grown in soil with relatively lower lead concentrations; therefore, the spreadsheet
very likely overestimates uptake for soil concentrations that are encountered in urban areas.
Page 17 of 23
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INGESTION OF LEAD IN SOIL ADHERED TO PRODUCE SURFACE
Another significant source of uncertainty in estimating uptake for leafy vegetables may be due
to the difficulty in removing all soil from the surface of the vegetables before analysis. On
average this pathway currently represents approximately 15% of the total daily lead intake
estimated by the spreadsheet model for the central tendency estimates. The literature search
did not find published data or analyses that provided a basis for estimating the amount of soil
that adheres to the surface of vegetables. Estimates for adherence for dark-green leafy
vegetables (e.g., chard), lettuce, carrots, and tomatoes are based on unpublished data
(Attanayake et a., 2014). While the adherence values may seem small; as discussed below, the
ingestion of lead contained in soil adhered to the surface of vegetables may account for
approximately 15% of the total lead ingestion associated with the gardening scenario.
INCIDENTAL INGESTION OF SOIL WHILE GARDENING (PB!ING)
On average this pathway currently represents approximately 30% of the central tendency
estimates of total daily lead intake estimated by the spreadsheet model for adults and all but
the youngest age group for children estimates. The model estimates this pathway accounts for
approximately 50% for children between 6 months and i-years old.
INCIDENTAL INGESTION OF SOIL TRACKED INTO RESIDENCE (PB!TR)
On average this pathway currently represents approximately 4% of the total daily lead intake
estimated by the spreadsheet model. Given the low contribution and the difficulty with
estimating the track-in factor, additional research is required to better estimate this pathway.
The TRW identified several areas of uncertainty in the data used for the Spreadsheet Model.
According to the current model for estimating daily lead intake for the gardening scenario, the
amount of lead taken up by vegetables and the amount of soil adhered to the surface of
vegetables account for an average of 64% of total daily lead intake; while the amount of lead
taken up by vegetables and incidental ingestion of soil account for an average of 81% of the
total daily lead intake. These pathways should be the focus of best practice recommendations,
intervention efforts, and additional research.
The current spreadsheet model considers uptake as a constant fraction of soil lead
concentration. Some data support a non-linear relationship between the concentration of lead
in vegetables and the concentration in soil. Along with additional uptake data, future work
should include developing non-linear models for uptake that allow the uptake rate to vary with
soil concentration.
The dietary estimates are conservative, preliminary estimates that are biased high because they
do not use recipe files that would provide more accurate consumption estimates. The estimates
should be revised to incorporate recipe files that are available for the 2003-2006 WWEIA
(U.S. CDC, 2Oioa,b). Additional research could be used to identify approaches for estimating
produce consumption that better reflect the population that consumes garden vegetables (e.g.,
WWEIA provides at least one variable that we have used to identify respondents who consume
local produce).
Page 180/23
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These areas of uncertainty could be considered as areas where additional research is needed.
Research on the uptake of lead in plants should focus on collecting more data on the uptake of
lead by produce that is grown in soils containing lead (and possibly other metals) at the range
of soil lead concentrations that are typically encountered in urban areas. Also, additional
information on soil management and gardening best practices as well as food handling that can
reduce exposures is needed. Additional data are needed to estimate the amount of soil that
remains adhered to the surface of vegetables before and after they are washed using typical
residential food preparation methods and based on whether the specific vegetable is commonly
eaten raw or cooked and the nature of cooking. Data are also needed to measure the reduction
of soil contaminants achieved by peeling vegetables (for vegetables that are commonly peeled).
Data that could be used to model the effect of soil pH and soil amendments on uptake would
also be useful. If sufficient, such information could help develop improved models of uptake, as
well as, allow for prediction of efficacy of these as strategies for mitigating exposure.
Page 1C) of 23
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REFERENCES
Attanayake, C.P., Hettiarachchi, G.M., Harms, A., Presley, D., Martin, S. and Pierzynski, G.M.
2014. Field Evaluations on Soil Plant Transfer of Lead from an Urban Garden Soil. J Env.
Qual. 43(2): 475-487.
Chaney, R. L., S. B. Sterrett, and H. W. Mielke. 1984. The potential for heavy metal exposure
from urban gardens and soils. In: J.R. Preer (ed.) Proc. Symp. Heavy Metals in Urban
Gardens. Univ. Dist. Columbia Extension Service, Washington, DC. pp 37-84. Available
online at: http://www.indytilth.org/Links/Chaney Exposure.pdf.
Davies, B. E. 1978. Plant-available lead and other metals in British garden soils. Sci Total
Environ 9: 243-262.
Finster, M. E., K. A. Gray, and H. G. Binns. 2003. Lead levels of edibles grown in contaminated
residential soils: Afield survey. Sci Total Environ 320(2-3): 245-257. Available online at:
http://pursuitofresearch.org/wp-content/uploads/2Oii/oi/binnspaper2OO3.pdf
Hettiarachchi, G. 2011. K-State Project: Gardening Initiatives at Brownfields Sites. Kansas
State University: Manhattan, KS.
Ministry of Environment (MOE). 2004. City of Greater Sudbury 2001 Urban Soil Survey: Main
Study. Ontario Ministry of Environment. Available online at:
http://www.sudburysoilsstudy.com/EN/media/support/reports/2OOiSoilsData/VOL I/M
OE Report.pdf.
Moya, J. 2011. Personal Communication. U.S. Environmental Protection Agency, National
Center for Environmental Assessment, Washington Division.
Nabulo, G., S. D. Young, and C. R. Black. 2010. Assessing risk to human health from tropical
leafy vegetables grown on contaminated urban soils. Sci Total Environ 408(22): 5338-
5351-
Nwosu, J. U., A. K. Harding, and G. Linder. 1995. Cadmium and lead uptake by edible crops
grown in a silt loam soil. Bull Environ Contam Toxicol 54(4): 570-578.
Parsons, R., Munuo, S.S., Buckman, D.W., Tooze, J.A. and Dodd, K.W. 2009. User's Guide for
Analysis of Usual Intakes. May.
Panhandle Health District (PHD). 1986. Kellogg Revisited-igSs. Childhood Blood Lead and
Environmental Status Report. Panhandle District Health Department, Idaho.
SARA Group. 2008. Sudbury Area Risk Assessment, Volume II. Appendix E: Vegetable Garden
Survey Data Report. Ontario Ministry of the Environment. Available online at:
http://www.sudburysoilsstudy.com/EN/media/volume Il.asp.
Sterrett, S. B., R. L. Chaney, C. H. Gifford, and H. W. Mielke. 1996. Influence of fertilizer and
sewage sludge compost of yield and heavy metal accumulation by lettuce grown in urban
soils. Environ Geochem Health 18:135-142.
Page 20 0/23
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Tooze, J.A., Midthune, D., Dodd, K.W, Freedman, L.S., Krebs-Smith, S.M., Subar, A.F.,
Guenther, P.M., Carroll, R. J. and Kipnis, V. 2006. A New Statistical Method for Estimating
the Usual Intake of Episodically Consumed Foods with Application to their Distribution. J.
Amer. Diet. Assoc. 106(10): 1575-87.
U.S. Centers for Disease Control and Prevention (U.S. CDC). 2Oioa. National Health and
Nutrition Examination Survey. 2003-2004 Examination, Dietary, and Demographics Files.
Retrieved October 4, 2010 from http://www.cdc.gov/nchs/nhanes/nhanes2OO3-2OO4.
U.S. Centers for Disease Control and Prevention (U.S. CDC). 2Oiob. National Health and
Nutrition Examination Survey. 2005-2006 Examination, Dietary and Files. Retrieved
October 4, 2010 from http://www.cdc.gov/nchs/nhanes/nhanes2OO5-2Oo6.
U.S. Centers for Disease Control and Prevention (U.S. CDC). 2011. National Health and
Nutrition Examination Survey. 2007-2008 Laboratory File. Retrieved 12/8/11 from
http://www.cdc.gov/nchs/nhanes/nhanes2OO7-2Oo8/labo7 o8.htm
U.S. Environmental Protection Agency (U.S. EPA). 19943. Revised Interim Soil Lead Guidance
for CERCLA Sites and RCRA Corrective Action Facilities, EPA/54O/F-94/O43, Office of
Solid Waste and Emergency Response, Washington, D.C. Directive 9355.4-12.
U.S. Environmental Protection Agency (U.S. EPA). I994b. Technical Support Document:
Parameters and Equations Used in the Integrated Exposure Uptake Biokinetic Model for
Lead in Children. U.S. Environmental Protection Agency, Office of Emergency and
Remedial Response: Washington, DC. Available online at:
http://www.epa.gov/superfund/lead/products/tsd.pdf.
U.S. Environmental Protection Agency (U.S. EPA). 1999. Short Sheet: IEUBK Model Soil/Dust
Ingestion Rates. U.S. Environmental Protection Agency, Office of Solid Waste and
Emergency Response: Washington, DC. EPA 54O-F-OO-OO7. Available online at:
http://epa.gov/superfund/lead/products/ssircolo.pdf.
U.S. Environmental Protection Agency (U.S. EPA). 2003. Recommendations of the Technical
Review Workgroup for Lead for an Approach to Assessing Risks Associated with Adult
Exposures to Lead in Soil. U.S. Environmental Protection Agency: Washington, DC. EPA-
54O-R-O3-OO1. Available online at:
http://www.epa.gov/superfund/lead/products/adultpb.pdf.
U.S. Environmental Protection Agency (U.S. EPA). 2011. Exposure Factors Handbook: 2011
Edition. U.S. Environmental Protection Agency, National Center for Environmental
Assessment Office of Research and Development: Washington, DC. EPA/6oo/R-O9/O52F.
Available online at: http://www.epa.gov/ncea/efh/report.html.
Page 21 0/23
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APPENDIX B. SOIL-LEAD CONCENTRATIONS AND RECOMMENDATIONS FOR
CONTAMINATED GARDEN SOILS
Table B-i. Recommendations for Soil-Lead Concentrations for Contaminated
Garden Soils
Soil Lead
Concentration
(ppm)
0-499
500-999
1000-3000
>3OOO
5000
<15O
150-1000
1OOO-1O,OOO
>10,000
600
>100
<300
300
400
12OO
<300
100-400
>4OO
Recommendation
Low risk
Medium risk
High risk
Very high
Replace soils with clean soils
Lead-free standard
Lead-safe standard
Significant environmental lead hazard
standard
Excavation is required
"Safe" minimized health effects
Should not be used for gardening due
to bare soil exposure to children
through hand-to-mouth activity
If soil exposure to children is not a
concern
Health-based investigation levels for
residential exposure
Residential soil screening levels
Commercial soil screening levels
Safe for growing vegetables
Moderately contaminated sites - used
for gardening with precautions
Should not be used for growing
vegetables or herbs
Source
Traunfeld and Clement, 2001, Lead
in Garden Soils:
http://www.hgic.umd.edu/ media/
documents/hgiS.pdf
University of Rhode Island, 2004,
Lead in Garden Soils:
http://www.uri.edU/ce/factsheets/s
heets/lead.html
Brown University, 2000, Soil &
Lead:
http://www.brown.edU/Research/E
nvStudies Theses /summit /Briefing
Papers/Soil and Lead/index.htm
Madhavan et al., 1989:
recommended maximum
permissible levels
Rosen, 2010, Lead in the Home
Garden and Urban Soil
Environment:
http://www.extension.umn.edu/dist
ribution/horticulture/DG2543.html.
In MN, bare soil standard is 100
ppm, and does not have to be
removed
Australian Government, 2001,
Health-based Soil Investigation
Levels:
http://www.health.gov.au/internet/
main/publishing.nsf/content/66E7
D805ClClAD69CA2573CCooi3EA6
8/$File/env soil.Ddf
U.S. EPA, 1996, Soil Screening
Guidance:
http://www.epa.gov/superfund/heal
th/conmedia/soil/pdfs/ssg496.pdf
National Gardening Association,
2009, Lead Contamination in Urban
Gardens:
http://www.garden.org/urbangarde
ning/index.php?page=sept-lead
Pettinelli, 2013, Lead in Garden
Soils:
http://soiltest.uconn.edu/factsheets
/LeadGardenSoils.pdf
Page 22 0/23
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<1OO
100-400
400-2000
>2OOO
<50
50-400
4OO-12OO
>12OO
63-2OO
>4OO
70 (Canada)
50 (Quebec)
<50
50-300
300-500
>500
<6s
65-180
180-450
450-900
>900
Safe range
Level of concern, use Best Practices
No gardening before contacting
professional gardening group
Gardening not recommended
Little to no lead - no precautions
needed
Some lead present, grow any vegetable
crops, choose best practices to reduce
dust and soil consumption
Do not grow leafy vegetables or root
Not recommended for vegetable
gardening - use clean soil, raised beds,
or containers
Unrestricted use
Restricted use
Agricultural Standards: acceptable
levels
Normal background: no precautions
Slight: wash all vegetables, peel root
crops
Moderate: fruiting vegetables
acceptable, avoid leafy and root
vegetables, wash all produce, maintain
a soil pH (6.5-7.0), organic matter 8-
10%
Heavy: relocate garden area or put a
barrier and bring in clean soil for a
new raised bed garden
Very low: No precautions
Low: wash hands, maintain soil pH
(6.5-7.0), high level of organic matter,
wash vegetables, peel root crops
(remove all soil)
Medium: do not grow leafy or root
vegetables, wash fruiting crops, grow
leafy or root vegetables in containers
with tested clean soil
High: limit child's direct contact,
maintain soil pH, edible plants are not
recommended, limit plants to flowers
or ornamentals
Very high: consider child blood lead
testing
NIH, 2012, Lead Safe Gardening:
httr>://www.niehs.nih.sov/health/as
sets/docs f o/pamphlet lead safe
gardening english.pdf
Angima and Sullivan, 2008,
Evaluating and Reducing Lead
Hazard in Gardens and Landscapes:
http://www.deq.state.or.us/lq/cu/n
wr/MultnomahMetals/OSUEvaluati
ngReducingLeadHazardlnGardensL
andscapes pdf
Shayler et al., 2009, Guide to Soil
Testing and Interpreting Results:
http://cwmi.css.cornell.edu/guideto
soil.pdf
CCME, 1999, Canadian
Environmental Quality Guidelines:
httD://ceas-rcae.ccme.ca/
Hoskins, 2008, General Guidelines
for Soil Lead Contamination:
http://anlab.umesci.maine.edu/soill
ab files/under/lead%2Oguidelines.
Edf
Buob et al., 2012, Lead Screening for
NH Soils: Minimizing Health Risks
University of New Hampshire:
http://extension.unh.edu/resources
/files/Resourceoo2O38 Rep3O2
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