ArticlePDF Available

Phosphorus Amendment Efficacy for In Situ Remediation of Soil Lead Depends on the Bioaccessible Method

Authors:

Abstract and Figures

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccessible Pb in P-treated soils. Two Pb-contaminated soils (790-1300 mg Pb kg), one from a garden and one from a city lot in Cleveland, OH, were incubated in a bench scale experiment for 1 yr. Six phosphate amendments, including bone meal, fish bone, poultry litter, monoammonium phosphate, diammonium phosphate, and triple superphosphate, were added to containers at two application rates. Lead IVBA was assessed using USEPA Method 1340 and three modified versions of this method. Modifications included using solutions with pH 1.5 and 2.5 as well as using solutions with and without 0.4 mol L glycine. Soil amendments were ineffective in reducing IVBA Pb in these soils as measured by pH 1.5 with glycine buffer. The greatest reductions in IVBA Pb, from 5 to 26%, were found using pH 2.5 extractions. Lead mineral results showed several soil amendments promoted Pb phosphate formation, an indicator of remediation success. A significant negative linear relationship between reduction in IVBA Pb and Pb-phosphate formation was found only for pH 2.5 without glycine extraction solution. A modified USEPA Method 1340 without glycine and using pH 2.5 has the potential to predict P soil treatment efficacy and reductions in bioavailable Pb.
Content may be subject to copyright.
37
Abstract
A validated method is needed to measure reductions of in
vitro bioaccessible (IVBA) Pb in urban soil remediated with
amendments. This study evaluated the eect of in vitro extraction
solution pH and glycine buer on bioaccessible Pb in P-treated
soils. Two Pb-contaminated soils (790–1300 mg Pb kg−1), one from
a garden and one from a city lot in Cleveland, OH, were incubated
in a bench scale experiment for 1 yr. Six phosphate amendments,
including bone meal, sh bone, poultry litter, monoammonium
phosphate, diammonium phosphate, and triple superphosphate,
were added to containers at two application rates. Lead IVBA was
assessed using USEPA Method 1340 and three modied versions
of this method. Modications included using solutions with pH
1.5 and 2.5 as well as using solutions with and without 0.4 mol
L−1 glycine. Soil amendments were ineective in reducing IVBA
Pb in these soils as measured by pH 1.5 with glycine buer. The
greatest reductions in IVBA Pb, from 5 to 26%, were found using
pH 2.5 extractions. Lead mineral results showed several soil
amendments promoted Pb phosphate formation, an indicator
of remediation success. A signicant negative linear relationship
between reduction in IVBA Pb and Pb-phosphate formation
was found only for pH 2.5 without glycine extraction solution.
A modied USEPA Method 1340 without glycine and using pH
2.5 has the potential to predict P soil treatment ecacy and
reductions in bioavailable Pb.
Phosphorus Amendment Ecacy for In Situ Remediation of Soil
Lead Depends on the Bioaccessible Method
John F. Obrycki, Nicholas T. Basta,* Kirk Scheckel, Brooke N. Stevens, and Kristen K. Minca
D management recommendations for
Pb-contaminated urban soils is necessary to address
public questions regarding best practices for using
urban soils (Kim et al., 2014). Bioaccessible Pb, dened as
the potential for a substance to interact and be absorbed by
an organism, is commonly determined to evaluate potential
exposure risk to Pb-contaminated urban soil. Bioaccessible Pb
is determined by in vitro gastrointestinal (GI) soil extraction
methods (Scheckel et al., 2009; Scheckel et al., 2013). Adding
phosphates to Pb-contaminated soils oers one management
technique for reducing Pb bioaccessibility as measured by in
vitro bioaccessibility tests (Basta et al., 2001; Brown et al., 2007;
Scheckel et al., 2013; Zia et al., 2011). Phosphate soil amend-
ments can react with soil Pb to form Pb-phosphate minerals and
lower Pb solubility. A common urban soil contaminant from Pb
paint, cerrusite (PbCO3), readily dissolves in the human GI tract
and subsequently has a high Pb bioaccessibility (Casteel et al.,
2006). Treatment of cerrusite containing soil with phosphate
amendment has been shown to form insoluble pyromorphite,
which does not completely dissolve in the GI tract (Scheckel et
al., 2013). Because Pb-phosphates have reduced bioaccessibility
relative to some Pb mineral forms in the soil, Pb-phosphate for-
mation can be used as an indicator of remediation success.
Amending soil with phosphate is not always eective in reduc-
ing Pb bioaccessibility (Ruby et al., 1999; Ryan et al., 2004). e
soil Pb may be in a relatively insoluble and unavailable form, such
as the Pb mineral form galena (PbS). Amendment eectiveness
depends on amendment P form, soil Pb form, and soil condi-
tions, such as pH. Soluble P can interact with soil Pb (Basta and
McGowen, 2004) to reduce Pb mobility. Soluble Pb can react
with insoluble amendment P located on soil or amendment sur-
faces (Basta et al., 2005). e ineectiveness of phosphate for
immobilizing Pb has recently been reviewed by Scheckel et al.
(2013).
In vitro GI methods are commonly used to measure in vitro
bioaccessible (IVBA) soil Pb. Several in vitro methods have been
used to evaluate IVBA Pb in contaminated soils and soil-like
material (Drexler and Brattin, 2007; Juhasz et al., 2013; Koch
et al., 2013; Scheckel et al., 2013; Zia et al., 2011). Soil IVBA
Abbreviations: GI, gastrointestinal; IVBA, in vitro bioaccessible; MAP,
monoammonium phosphate.
J.F. Obrycki, N.T. Basta, B.N. Stevens, and K.K. Minca, School of Environment and
Natural Resources, 210 Kottman Hall, 2021 Coey Rd., The Ohio State Univ.,
Columbus, OH 43210; K. Scheckel, USEPA, National Risk Management Research
Lab., Land Remediation and Pollution Control Division, Cincinnati, OH 45224-1701.
Assigned to Associate Editor Benny Chefetz.
Copyright © 2015 American Society of Agronomy, Crop Science Society of America,
and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA.
All rights reserved.
J. Environ. Qual. 45:37–44 (2016)
doi:10.2134/jeq2015.05.0244
Received 28 May 2015.
Accepted 24 Aug. 2015.
*Corresponding author (basta.4@osu.edu).
Journal of Environmental Quality
SOIL IN THE CITY
SPECIAL SECTION
Core Ideas
• The ability of soil amendments to reduce IVBA Pb depended on
the in vitro method.
• Modied USEPA Method 1340 may predict bioaccessible Pb in
P-amended soil.
• Soil amendments were largely ineective in reducing IVBA Pb
using USEPA Method 1340.
Published January 11, 2016
38 Journal of Environmental Quality
Pb can vary between GI methods because of dierent pH and
extraction solution conditions. More Pb is extracted using meth-
ods with lower extraction solution pH, such as pH 1.5, compared
with methods with higher pH, such as pH 2.5 (Attanayake et al.,
2014; Brown et al., 2004; Scheckel et al., 2013; USEPA, 2007a).
Lead compounds are more soluble at lower pH values compared
with circumneutral values (Hettiarachchi and Pierzynski, 2004).
In vitro GI methods are commonly used to measure bioaccessible
Pb in soil amended with phosphates.
However, there is not an in vitro method, including the
standard USEPA Method 1340 (USEPA, 2013), validated for
use with P-treated soils. e USEPA Method 1340 uses 0.4
mol L-1 glycine (C2H5NO2) solution adjusted to pH 1.5 using
hydrochloric acid (HCl). During the development of USEPA
Method 1340, extraction solution pH values of 1.5 and 2.5
were investigated using unamended soils. It is unclear which in
vitro extraction, pH 1.5 or 2.5, is most appropriate to evaluate
Pb bioaccessibility for P-treated soils (Scheckel et al., 2009; Zia
et al., 2011). e USEPA Method 1340 may not be appropriate
for P-treated soils because previous research indicated the pre-
dicted reduction in IVBA Pb using the in vitro method under-
estimated the reduction in swine Pb uptake (Ryan et al., 2004).
For example, 1% P-treated Joplin soils aged for 32 mo resulted in
10% reduction in IVBA Pb using the pH 1.5, 0.4 mol L−1 glycine
extraction. e same soil sample showed an approximately 35%
reduction to the same control soil when a pH 2.5, 0.4 mol L−1
glycine solution was used (Ryan et al., 2004). A similar reduction
of 25% was found using a pH 2.5 solution with other organic
acids as buers (Hettiarachchi et al., 2001). e 1% P-treated
Joplin soil reduced relative bioavailability of Pb 71% (Ryan et al.,
2004). e pH 2.5, 0.4 mol L−1 glycine extraction yielded results
(i.e., 35% reduction), closer to the observed 71% reduction in
relative bioavailability Pb using the in vivo swine model.
e presence of pH buers within the extraction solution
can increase IVBA Pb. Organic acids, including the amino
acid glycine, chelate metals (Furia, 1968), including Pb (Banu
et al., 2012). Using a pH 2.0, 0.4 mol L−1 glycine extraction, a
1% P-treated soil showed 25% reduction in IVBA Pb compared
with the control soil (Ryan et al., 2004). However, using a pH
2.0 extraction solution without glycine buer for the same soil
showed a relative reduction in IVBA Pb of 60% (Yang et al.,
2001). In vitro extraction pH and glycine buer can have a pro-
found eect on IVBA Pb in amended soil. e objective of this
study was to evaluate the eect of in vitro method extraction
solution pH and glycine buer on bioaccessible Pb in P-treated
urban soils.
Materials and Methods
Two soils were selected to represent a historical garden area
(G) and an urban vacant city lot (L). Soils were selected with
Pb concentration above the USEPA screening level for bare soil
areas that will be used by children of >400 mg kg−1 (Table 1).
e soils represented two important types of contaminated sites
encountered in urban areas, a garden and a vacant lot, where
phosphate amendments would likely be considered as a reme-
diation strategy. Surface soils (0–15.24 cm) were collected from
each site, air-dried, and sieved to 2 mm. e soils from the two
sites were separately homogenized by rotating within closed
20-L buckets. Soils were weighed using the air-dried mass into
1.5-L plastic containers for laboratory incubations. For G soils,
500 g of air-dried soil were used in each incubation container;
for L soils, 300 g of air-dried soil were used in each incubation
container. e experimental design included two soils (G and L),
six soil amendments, two application levels (high and low), and
three replicates for each soil-amendment combination (Table 2),
resulting in 72 1.5-L plastic incubation containers.
Amendments were selected to include phosphate fertilizers
used in previous P-Pb solubility studies (Scheckel et al., 2013).
e amendments included the partially soluble phosphate fer-
tilizers bone meal (Scotts Miracle-Gro), sh bone (K. Scheckel,
personal communication), and poultry litter (S. Albro, personal
communication). Readily soluble forms of phosphate fertilizers
used were diammonium phosphate (USA/Interplast Corp.),
monoammonium phosphate (MAP) (USA/Interplast Corp.),
and triple superphosphate (Espoma Co.).
Variability in the P:Pb molar ratios occurred due to variabil-
ity in Pb contamination among the soil pots. e amended soils
were incubated at room temperature (approximately 20–28°C)
in a laboratory from September 2012 until November 2013. e
14-mo incubation time was longer than most previous short-term
studies (3 mo) (Scheckel et al., 2013) to ensure adequate time for
reaction between soil Pb and amendment. Incubation contain-
ers were watered every other day with 18 MW deionized water
to achieve 30% gravimetric water content as determined before
the start of the experiment. Gravimetric water content of 30%
was selected to maintain wet aerobic conditions. Porewater pH
(ibault and Sheppard, 1992; omas, 1996) and Mehlich-3
P (Mehlich, 1984) (Table 2) were evaluated 1 mo aer the start
of soil incubation. Organic carbon (Heanes, 1984) and texture
(Kilmer and Alexander, 1949) were evaluated on the control
soils before the start of the incubations.
Aer the conclusion of the incubation, soil was subsampled
from each container and sieved to <250 mm. Soils were analyzed
for total soil Pb using USEPA Method 3051A (USEPA, 2007b).
Briey, 0.5 g of <250 mm sieved soil was placed in 55-mL Teon
vessels. Samples were digested in a CEM-MARS (CEM Corp.)
using 9.0 ± 0.1 mL of trace metal–grade HNO3 (CAS 7697-37-
2, Fisher Scientic) and 3.0 ± 0.1 mL of trace metal–grade HCl
(CAS 7647-01-0, Fisher Scientic). ree replicates for each soil
type–treatment combination were analyzed. Eight replicates of
the unamended G and L samples were digested to estimate total
Pb in the control soils. Soil extracts from the total digest and
Table 1. Selected properties for the control soils used in this study.
Soil properties Garden site City Lot
pH 6.95 6.75
Organic C, g kg−1 8.0 9.0
Texture loamy sand sandy loam
Mehlich-3 P, mg kg−1 100 110
Total Pb, mg kg−1 911 ± 8.4 807 ± 4.2
pH 1.5 with glycine IVBA† Pb(%) 79 ± 1.0 85 ± 1.0
Total As, mg kg−1 25.1 ± 0.2 12.5 ± 0.1
Total Cd, mg kg−1 2.3 ± 0.0 2.6 ± 0.0
Total Fe, mg kg−1 17,954 ± 79.5 15,572 ± 72.4
Total Zn, mg kg−1 438 ± 3.3 448 ± 3.3
† In vitro bioaccessible.
Journal of Environmental Quality 39
the in vitro extractions were analyzed using inductively coupled
plasma optical emission spectrometry (Varian 720, Varian, Inc.).
Determination of Pb Bioaccessibility by In Vitro
Gastrointestinal Extractions
Samples were analyzed using four in vitro extractions:
USEPA Method 1340 (USEPA, 2013) and three variations of
this method with modied pH and glycine content. Extraction
solution pH values of 1.5 and 2.5 were selected because previ-
ous research indicated the pH 2.5 solution may be better able
to detect reductions in IVBA Pb aer P treatment. Extraction
solutions were produced with and without 0.4 mol L-1 glycine to
determine the eect of the buer on IVBA Pb. e four extrac-
tion solutions evaluated were: pH 1.5 with 0.4 mol L-1 glycine
(Method 1340), pH 1.5 without glycine, pH 2.5 with 0.4 mol
L-1 glycine, and pH 2.5 without glycine.
For the 0.4 mol L-1 glycine-containing extractions, deionized
water was mixed with 60.06 g glycine (Fisher Scientic, CAS
56–40–6) and placed in a covered 2-L volumetric ask. is
ask was placed in a 37°C cabinet overnight. Trace metal–grade
HCl and 37°C deionized water were added to bring the solution
to a volume of 2 L. e trace metal–grade HCl adjusted the nal
solution to pH 1.5 ± 0.05 and 2.5 ± 0.05, respectively. For the
nonglycine solutions, 37°C deionized water was adjusted to pH
1.5 ± 0.05 and pH 2.5 ± 0.05, respectively, using trace metal
grade HCl.
For each in vitro extraction, all soil type–treatment combina-
tions had three replications. Four subsamples of the G control
soil (each subsample was approximately 50 g) were analyzed
from the bulk container of G control soil, and four subsamples
of the L control soil (each subsample was approximately 50 g)
were analyzed from the bulk container of L control soil. Sample
duplicates, duplicate matrix spikes (1000 mg L-1 Pb), blanks,
blank spikes (1000 mg L-1 Pb), and a standard reference mate-
rial, NIST 2711a Montana II Soil, were included in the analysis
as part of quality assurance and quality control measures.
e in vitro extraction process consisted of mixing 1.00 ±
0.01 g of <250 mm sieved soil and 100 ± 0.5 mL of extracting
solution. Samples were placed in 125-mL plastic bottles, sealed,
and secured on a rotating shaker in a 37°C cabinet (Nelson et
al., 2013). Rotations were maintained at 30 ± 2 rotations per
minute. Samples were pH adjusted to 1.50 ± 0.05 or 2.50 ± 0.05
pH at 5 min using 25% trace metal–grade HCl. Samples were
checked and pH adjusted at 30 min. Aer 60 min of rotating,
samples were removed, nal pH was recorded, and samples were
passed through 0.45-mm lters. Final solution pH stayed within
±0.25 pH units of the initial extraction solution pH for all four
in vitro extractions. is met the USEPA 1340 requirement
of the nal solution pH being ±0.5 pH units from the starting
solution pH (USEPA, 2013). Laboratory quality assurance and
Table 2. Overview of study amendments, P content, rate, soils, amount of amendment added, amended soil P:Pb molar ratio, soil pH, and Mehlich-3 P.
Amendment† Amendment P
content Rate Soil‡ Amendment
added§ P:Pb¶ Soil pH Mehlich-3 P
mg kg−1 g molar ratio mg kg−1
BM 40 low G 9.1 4.9 6.4 229
40 low L 11.2 8.6 6.8 335
40 high G 30.2 17.4 7.5 353
40 high L 37.2 30.5 7.5 548
FB 109 low G 3.4 5.0 5.8 233
109 low L 4.2 9.2 6.8 291
109 high G 11.5 17.3 6.1 360
109 high L 14.1 33.6 6.9 545
DAP 202 low G 1.8 4.9 6.2 616
202 low L 2.2 7.6 6.9 239
202 high G 5.9 16.0 6.0 1671
202 high L 7.3 29.0 6.8 1076
MAP 229 low G 1.6 5.1 5.7 736
229 low L 1.9 7.4 6.4 1262
229 high G 5.2 16.1 6.0 1959
229 high L 6.4 29.3 6.4 3680
TSP 202 low G 1.8 5.1 6.3 588
202 low L 2.2 8.4 6.4 1143
202 high G 5.9 17.1 5.7 1624
202 high L 7.3 30.1 5.4 2978
PL 11 low G 32.9 5.1 7.2 397
11 low L 40.6 8.9 7.9 644
11 high G 109.8 16.0 8.2 840
11 high L 135.0 28.9 7.9 1654
† BM, bone meal; DAP, diammonium phosphate; FB, sh bone; MAP, monoammonium phosphate; PL, poultry litter; TSP, triple superphosphate.
‡ G, Garden; L, City Lot.
§ Air-dried mass.
¶ Calculated comparing the amount of P added to the soil and the total Pb content in the soil.
40 Journal of Environmental Quality
quality control measures procedures were followed for each of
the extractions, including using duplicates, blanks, blank spikes,
and matrix spikes. All deionized water used in extractions was
18 MW.
Statistical analysis, including ANOVA tests, matched pairs t
test, and linear regression, were conducted using Minitab (v. 16).
Analysis of variance tests used a post hoc Tukey’s honest signi-
cant dierence (HSD) test with a P value of 0.1. is P value was
used to better capture the variability of the data and to highlight
potential P amendment trends to be evaluated in future stud-
ies. In vitro bioaccessibility for each treatment was calculated
by dividing the in vitro extractable Pb concentration (mg kg-1)
by the total Pb (mg kg-1) measured by USEPA Method 3051A.
For evaluating treatment ecacy, percentage reductions in IVBA
Pb between treated and control for each extraction were calcu-
lated by taking the control soil IVBA Pb minus the treated soil
IVBA Pb. For linear regression, percentage reduction in IVBA
Pb between treated and control soil was calculated by taking the
control soil IVBA Pb minus the treated soil IVBA Pb, and this
quantity was divided by the control soil IVBA Pb.
Pb Mineral Identication by X-ray Absorption Fine
Structure Spectroscopy
X-ray absorption ne structure spectroscopy was used
to evaluate Pb mineral forms using the Materials Research
Collaborative Access Team at the Advanced Photon Source of
the Argonne National Laboratory. Mineral identication meth-
ods are described in Minca et al. (2013). Lead minerals were
quantied using linear combination tting against known Pb
mineral standards. R-factors were reported to indicate variation
that occurred between the standards and the samples.
Various Pb standards were used as reference spectra, including
mineral sorbed Pb [Pb-ferrihydrite, Pb-kaolinite, Pb-goethite,
Pb-gibbsite, Pb-birnessite, and Pb-montmorillonite in which
each mineral was equilibrated with Pb(NO3)2 at pH 6 for a target
surface loading of 2500 mg kg−1 aer dialysis], organic bound
Pb [Pb fulvic acid and Pb-humic acid as reagent-grade organic
acids equilibrated with Pb(NO3)2 at pH 6 for a target loading
of 1500 mg kg−1 aer dialysis and reagent-grade Pb acetate, Pb
cysteine, and Pb citrate], Pb carbonate (Smithsonian Natural
History Minerals Collection specimens of cerussite, hydrocerus-
site, and plumbonacrite with X-ray diraction verication), PbO
(massicot and litharge), Pb phosphates [chloropyromorphite,
hydroxypyromorphite, Pb3(PO4)2, PbHPO4, and Pb sorbed
to apatite at pH 6 and surface loading of 2000 mg kg−1], and
other Pb minerals (leadhillite, magnetoplumbite, plumboferrite,
plumbogummite, plumboyarosite, anglesite, and galena from the
Smithsonian Natural History Minerals Collection with X-ray
diraction verication). All reference spectra were collected in
transmission mode with dilution calculations determined by
XAFSMass (Klementiev, 2012) mixed in binder and pressed
into a pellet. ese spectra were acquired on the same beamline
with identical scan parameters simultaneously with a Pb metal
foil for calibration but on separate occasions to the samples.
Within linear combination tting the sum was not forced
to 1, but the results were normalized to 1 (or 100%) at the end.
e tting required the value for each reference to vary between
0 and 1 so there would be no negative values inuencing the
tting. e R-factor was reported for each analysis. e R-factor
is a measure of the mean square sum of the mist at each data
point: R-factor = sum[(data-t)2]/sum[data2].
Results and Discussion
Determination of Pb Bioaccessibility by In Vitro
Gastrointestinal Extractions
Extractable Pb using USEPA Method 1340 from refer-
ence soil NIST 2711a was 1137 ± 19 mg Pb kg−1 soil. is was
within the range recommended by USEPA Method 1340, which
reports an average of 1114 mg Pb kg−1 soil (980–1249 mg Pb
kg−1 soil 99th percentile prediction interval). Extractable P from
2711a using USEPA Method 1340 was 493 ± 10 mg P kg−1 soil.
Extractable P was 889 ± 9.9 mg P kg−1 from control soil L and
508 ± 4.2 mg P kg−1 for control soil G. Treated soils had extract-
able P ranging from 816 to 7488 mg P kg−1 and a mean of 2857
± 210 mg P kg−1.
Blank spike samples were consistent throughout the four
extractions, with a Pb spike recovery of 103 to 110%. e spike
recovery was within the range recommended by USEPA Method
1340 (85–115%). Matrix Pb spike recoveries at pH 1.5 with and
without glycine (88–102%) were acceptable. e matrix spiked
recoveries ranged from 68 to 90% at pH 2.5 with glycine and
from 22 to 50% at pH 2.5 without glycine. e dierence in the
spike recovery for the pH 2.5 solutions could be due to glycine
chelating Pb or Pb being sorbed to the soil surface. Matrix spikes
were applied to the same treatment subsamples across the four
extractions. is means that glycine and small uctuations in
extraction solution pH were potential explanatory factors when
comparing spiked recovery for a given soil sample at pH 2.5
without glycine and at pH 2.5 with 0.4 mol L−1 glycine.
Bioaccessible Pb determined by the four in vitro extractions
for the G and L soils are presented in Fig. 1. Amendments low-
ered IVBA Pb relative to the controls more frequently in the
pH 2.5 extractions than in the pH 1.5 extractions for both soils.
None of the amendments resulted in Pb IVBA reductions using
the pH 1.5 with 0.4 mol L−1 glycine solution. e ability of soil
amendment to reduce IVBA Pb varied with in vitro method and
soil amendment. A greater number of amendments reduced Pb
IVBA on the L than the G site (Fig. 1).
Table 3 provides an expanded look at the pH 2.5 extraction
solution data to highlight the variation in IVBA Pb reductions
across treatments (P < 0.10). e P treatments consistently
reduced Pb IVBA using the pH 2.5 extractions on the city lot
site. Ten of the 12 treatments demonstrated at least a 10% reduc-
tion in Pb IVBA using either of the two pH 2.5 extractions.
e largest reduction in IVBA Pb (26%) occurred in the “MAP
high” treatment on the city lot using the pH 2.5 with glycine
extraction. e “MAP high” amendment did not demonstrate
this same eectiveness on the garden soil. On the garden soil,
none of the amendments in any of the extractions demonstrated
a greater than 10% reduction in Pb IVBA compared with the
control soil.
e IVBA Pb depended on extraction pH and glycine con-
tent of the in vitro method when comparing the four extractions
by soil (Table 4). e dierences in IVBA Pb due to soil type are
much smaller than the dierences in IVBA Pb due to extraction
method (i.e., the in vitro method used is more important than
Journal of Environmental Quality 41
the soil). e IVBA Pb for both soils decreased in the following
order: pH 1.5 with glycine > pH 1.5 without glycine > pH 2.5
with glycine > pH 2.5 without glycine (P < 0.001). Analysis of
variance with a post hoc Tukey HSD test found statistically sig-
nicant dierences among the four extractions when controlling
for soil type. Within the same pH level, the pH 1.5 with glycine
IVBA Pb was 15 to 20% greater than the pH 1.5 without glycine.
At pH 2.5, the glycine-containing extractions’ IVBA Pb values
were 30% greater than the extraction solution without glycine.
When comparing dierent pH values for the same extractions
(glycine vs. nonglycine), the IVBA Pb between pH 1.5 and pH
2.5 both with glycine was 35 to 40% greater at pH 1.5. Without
glycine, the pH dierence accounted for IVBA Pb values that
were 50% higher at pH 1.5 compared with pH 2.5. Glycine
may be better able to chelate Pb at pH 2.5 because glycine has
an acid dissociation constant of 2.34. ese results support pre-
vious ndings regarding pH 2.5 with glycine showing greater
treatment eects than pH 1.5 with glycine (Ryan et al., 2004).
Fig. 1. Extractable Pb for four in vitro extractions of the
Garden (A) and City Lot (B) sites. * Treatment in vitro
bioaccessible (IVBA) Pb lower than the control soil IVBA Pb
within each soil and each extraction at the p = 0.05 signi-
cance level. † Treatment IVBA Pb lower than the control soil
IVBA Pb within each soil and each extraction at the p = 0.10
signicance level. BM, bone meal; DAP, diammonium phos-
phate; FB, sh bone; MAP, monoammonium phosphate; PL,
poultry litter; TSP, triple superphosphate.
Table 3. Reduction in mean percentage in vitro bioaccessible Pb between control and P-treated soils for pH 2.5 extraction solutions.†
Treatment‡ Garden City Lot
Glycine No glycine Glycine No glycine
BM low 11 ± 2%
BM high 10 ± 2% 9 ± 1%
FB low 8 ± 1% 10 ± 1%
FB high 9 ± 0.5% 8 ± 1.5%
DAP low 9 ± 2.5%
DAP high 19 ± 1% 16 ± 1%
MAP low 5 ± 1% 11 ± 4% 7 ± 1%
MAP high 8 ± 2% 26 ± 3% 18 ± 1%
TSP low 13 ± 0.5% 6 ± 1%
TSP high 5 ± 1% 13 ± 1%
PL low 5 ± 0.5% 13 ± 1% 5 ± 1%
PL high 5 ± 1% 14 ± 2% 7 ± 1%
† Percentage dierence calculated as Mean Control IVBA Pb minus Treatment IVBA Pb. Values listed are those that were signicant at P < 0.10 for each
extraction ANOVA.
‡ BM, bone meal; DAP, diammonium phosphate; FB, sh bone; MAP, monoammonium phosphate; PL, poultry litter; TSP, triple superphosphate.
42 Journal of Environmental Quality
e control soil IVBA was lowest in a pH 2.5 without glycine or
other organic buer solutions.
Pb Mineral Identication by X-ray Absorption Fine
Structure Spectroscopy Results
Spectroscopy results indicated that both control soils
were predominantly mineral-sorbed or organic-bound Pb
(Table 5). Similar amounts of mineral-sorbed (62 vs. 55%)
and organic-bound Pb (29 vs. 31%) were in the control soils
(Table 5). Neither control soil contained Pb-phosphates. e
Pb-phosphate category included Pb pyromorphite, Pb-sorbed
Ca-phosphate, and Pb3(PO4)2. Figure 2 expands on the data
presented in Table 5 by providing the proportion of these three
Pb-phosphate types by treatment and location. As compared
with the control soils, the phosphate amendments increased
Pb-phosphate formation between 6 and 32% for both soils (Fig.
2). Lead phosphate formation ranged from 6 to 27% on the
Garden site and from 8 to 32% on the City Lot site. e high P
application rate led to 10 to 15% greater Pb-phosphate forma-
tion when compared with the low application rate for the same
amendment. Pyromorphite, a more insoluble Pb-phosphate
(Scheckel et al., 2013), was not formed consistently across all
treatments. At the Garden site, the greatest pyromorphite for-
mation was 7% within the Diammonium Phosphate High treat-
ment. At the City Lot site, the “sh bone high” treatment led to
a 16% increase in pyromorphite over the control soil.
ese pyromorphite formation rates are comparable to other
studies that have used similar P treatments and achieved 1 to 16%
pyromorphite formation (Scheckel et al., 2013). is formation
can be increased to 40% if phosphoric acid is used as a treatment
(Juhasz et al., 2014; Scheckel et al., 2013). Juhasz et al. (2014)
included a soil with similar Pb mineral forms compared with the
vacant lot and garden soils in this current study and achieved
Table 4. Percentage in vitro bioaccessible Pb compared with total soil
Pb for each soil location and each extraction.
Soil location Extraction Mean IVBA ± SE‡
Garden† pH 1.5 with glycine 88 ± 1%
pH 1.5 no glycine 69 ± 1%
pH 2.5 with glycine 50 ± 1%
pH 2.5 no glycine 17 ± 1%
City Lot† pH 1.5 with glycine 81 ± 1%
pH 1.5 no glycine 66 ± 1%
pH 2.5 with glycine 47 ± 1%
pH 2.5 no glycine 17 ± 1%
† Calculated as in vitro bioaccessible Pb divided by the total soil Pb and
expressed as a percentage.
‡ Statistically signicant at the P < 0.001 level when the four extractions
are compared within soil location. This analysis did not compare
between the Garden and City Lot soils.
Table 5. Lead mineral types identied in control and treated Garden and City Lot soil using X-ray absorption ne structure spectroscopy.
Location Amendment† Mineral sorbed Organic bound Pb carbonate Pb-phosphate sum‡ R-factor§
———————————————— % ————————————————
Garden control 55 31 14 0 0.002
BM low 60 30 5 6 0.004
BM high 58 25 5 11 0.003
FB low 56 24 4 16 0.003
FB high 54 11 8 27 0.005
DAP low 48 23 18 11 0.003
DAP high 48 22 5 24 0.003
MAP low 48 39 4 10 0.002
MAP high 47 22 7 24 0.009
TSP low 53 21 15 11 0.003
TSP high 51 20 5 24 0.003
PL low 54 24 9 13 0.004
PL high 59 20 3 19 0.004
City Lot control 62 29 9 0 0.002
BM low 52 28 9 11 0.002
BM high 40 23 13 25 0.003
FB low 52 17 10 21 0.006
FB high 47 6 17 30 0.005
DAP low 44 35 10 10 0.002
DAP high 56 13 11 21 0.004
MAP low 27 37 18 18 0.003
MAP high 24 24 20 32 0.007
TSP low 28 36 28 8 0.002
TSP high 37 31 12 20 0.004
PL low 44 36 7 12 0.004
PL high¶
† BM, bone meal; DAP, diammonium phosphate; FB, sh bone; MAP, monoammonium phosphate; PL, poultry litter; TSP, triple superphosphate.
‡ Column includes sum of pyromorphite, Pb3(PO4)2, and Pb-sorbed Ca-phosphate. Data for these three mineral types are shown in Fig. 3.
§ The R-factor is a measure of the mean square sum of the mist at each data point. R-factor = sum[(data-t)2]/sum[data2].
¶ Not determined.
Journal of Environmental Quality 43
43% pyromorphite formation aer phosphoric acid treatment.
is current study did not use phosphoric acid because it is
unlikely to be adopted as a publicly used treatment due to the
potential hazards involved with applying concentrated acid to
residential soils.
e Pb-phosphate formation could not be explained solely by
the variability in the P:Pb molar ratios for the incubation (Table
2). Although L soils had consistently higher P:Pb molar ratios,
the Pb-phosphate formation was not consistently higher across
all treatments. A matched-pairs analysis of Pb-phosphate forma-
tion for the 11 treatments evaluated on both soils found the L
soils did not have consistently higher Pb-phosphate formation
(P = 0.136). e average Pb-phosphate formation in L soils was
approximately 2.8% higher, with a 95% condence interval of
6.69% higher to 1.05% lower. Several other factors, such as incu-
bation pH, extraction solution pH, and soil mineralogy, could be
combined in future studies to better explain how P treatments
react with in situ Pb.
e in vitro results were compared with the percentage
Pb-phosphate formation to evaluate if in vitro solutions could
predict Pb-phosphate formation and, in turn, remediation suc-
cess (Fig. 3). Using the pH 2.5 without glycine extraction data,
we found a linear relationship between the reduction in IVBA
compared with the percentage Pb-phosphate formation (P <
0.001). e percentage Pb-phosphate formation was not related
to IVBA Pb as determined by the other three extractions (Fig.
3). ese results indicate that a pH 2.5 solution without glycine
may be used as a predictor of Pb-phosphate content in soils.
is extraction has the potential to be used in one of two ways.
First, site assessments could incorporate a pH 2.5 extraction
without glycine as an assessment of treatment ecacy. Second,
assessments could use this extraction as a pretreatment test.
is could improve amendment recommendations because if
Pb-phosphate levels are found to be low, there may be a potential
for Pb-phosphate to form during remediation. If Pb-phosphate
levels are found to be higher, adding phosphates to the soils may
not yield additional Pb-phosphate formation. ese results from
this study need to be rigorously tested before widespread adop-
tion for site assessment and remediation.
Soil Management Considerations and Recommendations
Six phosphate amendments showed mixed results regarding
IVBA Pb and soil amendment ecacy. e ability of soil amend-
ments to reduce IVBA Pb depended on the in vitro method.
Soil amendments were ineective in reducing IVBA Pb in these
two urban soils when using USEPA Method 1340. However, P
treatments were more eective when evaluated using modica-
tions of USEPA Method 1340. e greatest number of reduc-
tions in IVBA Pb were found at pH 2.5 without glycine buer.
Reductions in bioaccessible Pb from soil treatment ranged from
5 to 26% for the pH 2.5 extractions. Lead mineral identication
data indicated phosphate treatments were eective in forming
Pb phosphates.
e soils in this study contained Pb at concentrations of 790
to 1300 mg Pb kg−1. ese concentrations are found in urban
soils of industrial cities. Managing these soils gains additional
Fig. 2. Percentage Pb-phosphate formation by Pb-phosphate
type for the Garden (A) and City Lot (B) sites. Control soil had 0%
Pb-phosphates. † Not determined. BM, bone meal; DAP, diammonium
phosphate; FB, sh bone; MAP, monoammonium phosphate; PL,
poultry litter; TSP, triple superphosphate.
Fig. 3. Relationship between in vitro bioaccessible Pb and the amount
of Pb associated with the sum of Pb-phosphate minerals. The percent-
age in vitro bioaccessible (IVBA) reduction was the dierence in IVBA
treatment and IVBA control divided by the IVBA control. X, percent-
age IVBA reduction expressed as a percentage and negative sign
indicates treatment reduced IVBA Pb; Y, percentage Pb-phosphate
sum. (A) pH 1.5 with 0.4 mol L−1 glycine. Regression equation: y =
0.0269x + 17.5; r2 = 0.0016. (B) pH 1.5 without glycine. Regression
equation: y = 0.0630x + 18.1; r2 = 0.0032. (C) pH 2.5 with 0.4 mol L−1
glycine. Regression equation: y = −0.1532x + 15.8; r2 = 0.0622. (D) pH
2.5 without glycine. Regression equation: y = −0.2176x + 11.97; r2 =
0.4165. *** Signicant at the p < 0.001 level.
44 Journal of Environmental Quality
importance because the Centers for Disease Control recently
changed the denition of elevated blood Pb level from 10 to 5
mg dL−1 (CDC, 2012). It is likely this change will lower the soil
screening level below 400 mg Pb kg−1 soil (Henry et al., 2015).
is will result in a much greater demand for bioaccessibil-
ity Pb testing of many more urban soils that exceed the lower
soil screening level. Without an accepted method for screening
P-treated soils and no recommended concentration threshold
for what constitutes a P-treated soil, how will researchers, city
ocials, and the general public evaluate Pb-contaminated soil
remediation eorts? Research is needed to validate an in vitro
method accurate for measuring reductions in IVBA Pb. is
research must include a comprehensive in vitro–in vivo correla-
tion showing the in vitro method is an accurate predictor of in
vivo Pb uptake.
References
Attanayake, C.P., G.M. Hettiarachchi, A. Harms, D. Presley, S. Martin, and
G.M. Pierzynski. 2014. Field evaluations on soil plant transfer of lead
from an urban garden soil. J. Environ. ual. 43:475–487. doi:10.2134/
jeq2013.07.0273
Banu, L., V. Blagojevic, and D.K. Bohme. 2012. Dissociation of deprotonated
glycine complexes with Pb2+ and ve transition-metal dications (Fe2+, Co2+,
Ni2+, Cu2+, Zn2+): e importance of metal bond activation. Int. J. Mass
Spectrom. 330:168–173.
Basta, N.T., J.A. Ryan, and R.L. Chaney. 2005. Trace element chemistry in resid-
ual-treated soil: Key concepts and metal bioavailability. J. Environ. ual.
34:49–63.
Basta, N.T., R. Gradwohl, K.L. Snethen, and J.L. Schroder. 2001. Chemical im-
mobilization of lead, zinc, and cadmium in smelter-contaminated soils
using biosolids and rock phosphate. J. Environ. ual. 30:1222–1230.
doi:10.2134/jeq2001.3041222x
Basta, N.T., and S.L. McGowen. 2004. Evaluation of chemical immobilization
treatments for reducing heavy metal transport in a smelter-contaminated
soil. Environ. Pollut. 127:73–82. doi:10.1016/S0269-7491(03)00250-1
Brown, S., R. Chaney, J. Hallfrisch, J.A. Ryan, and W.R. Berti. 2004. In: situ soil
treatments to reduce the phyto- and bioavailability of lead, zinc, and cad-
mium. J. Environ. ual. 33:522–531. doi:10.2134/jeq2004.5220
Brown, S.L., H. Compton, and N.T. Basta. 2007. Field test of in situ soil amend-
ments at the Tar Creek National Priorities List Superfund site. J. Environ.
ual. 36:1627–1634. doi:10.2134/jeq2007.0018
Casteel, S.W., C.P. Weis, G.M. Henningsen, and W.J. Brattin. 2006. Estimation
of relative bioavailability of lead in soil and soil-like materials using young
swine. Environ. Health Perspect. 114:1162–1171. doi:10.1289/ehp.8852
Centers for Disease Control. 2012. Low level lead exposure harms children: A re-
newed call for primary prevention. http://stacks.cdc.gov/view/cdc/26445
(accessed 28 May 2015).
Drexler, J., and W.J. Brattin. 2007. An in vitro procedure for estimation of
lead relative bioavailability: With validation. Hum. Ecol. Risk Assess.
13:383–401.
Furia, T.E. 1968. CRC handbook of food additives. Chemical Rubber Co.,
Cleveland, OH.
Heanes, D.L. 1984. Determination of total organic- C in soils by an improved
chromic acid digestion and spectrophotometric procedure. Commun. Soil
Sci. Plant Anal. 15:1191–1213. doi:10.1080/00103628409367551
Henry, H., M.F. Naujokas, C. Attanayake, N.T. Basta, Z. Cheng, G.M. Hetti-
arachchi, M. Maddaloni, C. Schadt, and K.G. Scheckel. 2015. Bioavailabil-
ity-based in situ remediation to meet future lead (Pb) standards in urban
soils and gardens. Environ. Sci. Technol. 49:8948–8958. doi:10.1021/acs.
est.5b01693
Hettiarachchi, G.M., and G.M. Pierzynski. 2004. Soil lead bioavailability and
in situ remediation of lead-contaminated soils: A review. Environ. Prog.
23:78–93. doi:10.1002/ep.10004
Hettiarachchi, G.M., G.M. Pierzynski, and M.D. Ransom. 2001. In situ stabi-
lization of soil lead using phosphorus. J. Environ. ual. 30:1214–1221.
doi:10.2134/jeq2001.3041214x
Juhasz, A.L., D. Gancarz, C. Herde, S. McClure, K.G. Scheckel, and E. Smith.
2014. In situ formation of pyromorphite is not required for the reduction
of in vivo Pb relative bioavailability in contaminated soils. Environ. Sci.
Technol. 48:7002–7009. doi:10.1021/es500994u
Juhasz, A.L., E. Smith, J. Weber, M. Rees, T. Kuchel, A. Rofe, L. Sansom, and R.
Naidu. 2013. Predicting lead relative bioavailability in peri-urban contami-
nated soils using in vitro bioaccessibility assays. J. Environ. Sci. Health Part
A Tox. Hazard. Subst. Environ. Eng. 48:604–611. doi:10.1080/1093452
9.2013.731354
Kilmer, V.J., and L.T. Alexander. 1949. Methods of making mechanical analyses
of soils. Soil Sci. 68:15–24. doi:10.1097/00010694-194907000-00003
Kim, B.F., M.N. Poulsen, J.D. Margulies, K.L. Dix, A .M. Palmer, and K.E. Nach-
man. 2014. Urban community gardeners’ knowledge and perceptions of
soil contaminant risks. PLoS One 9(2):9.
Klementiev, K.V. 2012. XAFSmass. XAFSmass a program for calculating the
mass of XAFS samples. http://intranet.cells.es/Beamlines/CLAESS/so-
ware/xafsmass.html (accessed 28 July 2015).
Koch, I., K.J. Reimer, M.I. Bakker, N.T. Basta, M.R. Cave, S. Denys, M. Dodd,
B.A. Hale, R. Irwin, Y.W. Lowney, M.M. Moore, V. Paquin, P.E. Rasmus-
sen, T. Repaso-Subang, G.L. Stephenson, S.D. Siciliano, J. Wragg , and G.J.
Zagury. 2013. Variability of bioaccessibility results using seventeen dier-
ent methods on a standard reference material, NIST 2710. J. Environ. Sci.
Health Part A Tox. Hazard. Subst. Environ. Eng. 48:641–655. doi:10.108
0/10934529.2013.731817
Mehlich, A. 1984. Mehlich 3 soil test extractant: A modication of the
Mehlich 2 extractant. Commun. Soil Sci. Plant Anal. 15:1409–1416.
doi:10.1080/00103628409367568
Minca, K.K., N.T. Basta, and K.G. Scheckel. 2013. Using the Mehlich-3 soil test
as an inexpensive screening tool to estimate total and bioaccessible Pb in
urban soils. J. Environ. ual. 42:1518–1526. doi:10.2134/jeq2012.0450
Nelson, C.M., T.M. Gilmore, J.M. Harrington, K.G. Scheckel, B.W. Miller, and
K.D. Bradham. 2013. Evaluation of a low-cost commercially available ex-
traction device for assessing lead bioaccessibility in contaminated soils. En-
viron. Sci. Processes Impacts 15:573–578.
Ryan, J.A., K.G. Scheckel, W.R. Berti, S.L. Brown, S.W. Casteel, R.L. Chaney,
J. Hallfrisch, M. Doolan, P. Grevatt, M. Maddaloni, and D. Mosby.
2004. Reducing children’s risk from lead in soil. Environ. Sci. Technol.
38:18A–24A.
Ruby, M.V., R. Schoof, W. Brattin, M. Goldade, G. Post, M. Harnois, D.E. Mos-
by, S.W. Casteel, W. Berti, M. Carpenter, D. Edwards, D. Cragin, and W.
Chappell. 1999. Advances in evaluating the oral bioavailability of inorgan-
ics in soil for use in human health risk assessment. Environ. Sci. Technol.
33:3697–3705.
Scheckel, K.G., R.L. Chaney, N.T. Basta, and J.A. Ryan. 2009. Advances in as-
sessing bioavailability of metal(loid)s in contaminated soils. Adv. Agron.
104:1–52.
Scheckel, K.G., G.L. Diamond, M.F. Burgess, J.M. Klotzbach, M. Maddaloni,
B.W. Miller, C.R. Partridge, and S.M. Serda. 2013. Amending soils with
phosphate as means to mitigate soil lead hazard: A critical review of the
state of the science. J. Toxicol. Environ. Health B Crit. Rev. 16:337–380.
doi:10.1080/10937404.2013.825216
ibault, D.H., and M.I. Sheppard. 1992. A disposable system for soil pore-water
extraction by centrifugation. Commun. Soil Sci. Plant Anal. 23:1629–
1641. doi:10.1080/00103629209368692
omas, G.W. 1996. Soil pH and soil acidity. In: D.L. Sparks, editor, Methods of
soil analysis. Part 3. Chemical methods. SSSA Book Series 5. SSSA, Madi-
son, WI. p. 475–490.
USEPA. 2007a. Estimation of relative bioavailability of lead in soil and soil-like
materials using in vivo and in vitro methods. OSWER 9285.7-77. www.
epa.gov/superfund/health/contaminants/bioavailability/lead_tsd.pdf
(accessed 28 May 2015).
USEPA. 2007b. Method 3051A Microwave assisted acid digestion of sediments,
sludges, soils, and oils. www.epa.gov/waste/hazard/testmethods/sw846/
pdfs/3051a.pdf (accessed 28 May 2015).
USEPA. 2013. Method 1340 In vitro bioaccessibility assay for lead in soil. SW-
846 hazardous waste test methods. www.epa.gov/wastes/hazard/test-
methods/sw846/pdfs/1340.pdf (accessed 28 May 2015).
Yang, J., D.E. Mosby, S.W. Casteel, and R.W. Blanchar. 2001. Lead immobiliza-
tion using phosphoric acid in a smelter-contaminated urban soil. Environ.
Sci. Technol. 35:3553–3559. doi:10.1021/es001770d
Zia, M.H., E.E. Codling, K.G. Scheckel, and R.L. Chaney. 2011. In vitro and
in vivo approaches for the measurement of oral bioavailability of lead
(Pb) in contaminated soils: A review. Environ. Pollut. 159:2320–2327.
doi:10.1016/j.envpol.2011.04.043
... To predict Pb exposure risk, in vitro models can be used, which have been shown to be able to predict relative bioavailable Pb in acceptable vivo animal models. In vitro methods vary in their extracting solution composition, and pH can impact their appropriateness for use in certain soil conditions and treatments (Mayer et al., 2022;Obrycki et al., 2016). In vitro bioaccessibility (IVBA) refers to the fraction of the in vitro ingested material that is released from the soil matrix and available to be "absorbed" from the gastrointestinal tract into systemic circulation. ...
... Phosphorus additions to Pb-contaminated soils were promoted as the preferred solution to address contamination without having to excavate soil (Hettiarachchi & Pierzynski, 2004;Hettiarachchi et al., 2001;Scheckel et al., 2013), which can be costly and require further treatment and/or disposal (Karna et al., 2017;Raghavan et al., 1991). However, more recent research has shown the efficacy of P treatments to be variable depending on P source, soil type, and Pb form in soils with urban soils of higher pH showing reduced treatment efficacy (Chrysochoou et al., 2007;Dermatas et al., 2008;Mayer et al., 2022;Obrycki et al., 2016Obrycki et al., , 2017. Phosphorus sources can be inorganic or organic and vary in their solubility and consequent water quality risk. ...
... The intent of this study was to evaluate the reduction of Pb bioaccessibility from various P treatments. However, there is not consensus on which IVBA method should be used to assess treatment effectiveness (Chrysochoou et al., 2007;Hettiarachchi & Pierzynski, 2004;Obrycki et al., 2016). In the current study, two of the commonly used IVBA extraction methods were used. ...
Article
Full-text available
Urban soils contaminated by historical and current anthropogenic activities present an alarming human health risk requiring redress. Federal and state governments continue to lower residential soil lead (Pb) screening standards, which will likely require new risk‐based approaches to address urban soil Pb contamination. Phosphorus (P) soil amendments have long been presented as a solution to sequester Pb, thereby reducing exposure risk. In this study, P‐containing sources (biosolids incinerator ash, poultry litter, biosolids compost, and triple superphosphate) of varying solubilities were assessed as soil amendments to reduce Pb bioaccessibility and serve as an inexpensive remediation strategy for urban soil. Contaminated soil (1624 mg kg−1 Pb, pH 7.43) from Cleveland, OH, was treated with the four P‐containing soil amendments at a 1:5 Pb:P molar ratio and two combination treatments at 1:10 Pb:P molar ratio and incubated for 3 months. A batch equilibration analysis was also conducted to assess reduction in in vitro bioaccessible Pb (IVBA Pb). Pb bioaccessibility was evaluated using US EPA Method 1340 at pH 1.5 and the Physiologically Based Extraction Test pH 2.5 at 1 and 3 months. In general, treatments were ineffective in reducing IVBA Pb regardless of IVBA extraction method, incubation duration, batch equilibration analyses, or P source. The results of this study suggest P‐containing amendments are not suitable to address Pb exposure in the study soil. Site‐specific efficacy testing to determine reductions in IVBA Pb from P‐containing amendments should be performed before making recommendations for remediation of Pb‐contaminated urban soil.
... Although this method has been validated for use to assess Pb RBA in contaminated soil [53], its suitability for assessing treatment efficacy in phosphate-amended soil is debatable. Obrycki et al. [54] contended that USEPA Method 1340 overestimates Pb IVBA owing to the strong acidic conditions of the gastric phase (pH 1.5), which influences Pb solubility. As a consequence, phosphate amendments appear to be "largely ineffective" in immobilizing Pb when assessed using this assay. ...
... As a consequence, phosphate amendments appear to be "largely ineffective" in immobilizing Pb when assessed using this assay. To overcome this issue, Obrycki et al. [54] modified the IVBA assay pH to 2.5 and excluded glycine, which resulted in a significant negative correlation between Pb IVBA and the amount of Pb phosphate in treated soil (r 2 : 0.42, p < 0.001). In studies where assays were conducted at pH 1.5 and 2.5 for the same treated soils [36,[54][55][56], considerably lower Pb TERs were observed at pH 2.5 compared to 1.5. ...
... To overcome this issue, Obrycki et al. [54] modified the IVBA assay pH to 2.5 and excluded glycine, which resulted in a significant negative correlation between Pb IVBA and the amount of Pb phosphate in treated soil (r 2 : 0.42, p < 0.001). In studies where assays were conducted at pH 1.5 and 2.5 for the same treated soils [36,[54][55][56], considerably lower Pb TERs were observed at pH 2.5 compared to 1.5. However, Scheckel et al. [7] cautioned against the use of IVBA assessment at a pH > 1.5 to predict Pb immobilization efficacy because of the potential of assay artifacts (i.e., formation of Pb phosphates in vitro at higher pH), thereby overpredicting treatment efficacy. ...
Article
Full-text available
Purpose of Review The ubiquity of soil contamination by lead (Pb) and arsenic (As) has prompted the development of numerous techniques for its remediation. For human health exposure assessment, oral bioavailability-based methods are the most suitable to assess the efficacy of these treatment strategies, including in vivo relative bioavailability (systemic absorption relative to a toxicity reference) and in vitro bioaccessibility (dissolution in simulated gastrointestinal solutions). This paper provides a critical review of opportunities and challenges associated with the immobilization of Pb and As in contaminated soil. Recent Findings This review identified that the major inorganic and organic amendments used to reduce Pb and As exposure include phosphate, industrial by-products, metal oxides, organic matter, biochar, and treatment with iron sulphate to promote the formation of plumbojarosite in soil. In addition to RBA and IVBA assessment, investigating changes in Pb/As speciation in untreated vs treated soil can provide additional confirmation of treatment efficacy. The results of this review showed that immobilization efficacy may vary depending on amendment type, Pb, and As speciation in soil and the approach used for its assessment. Summary Reducing childhood exposure to Pb and As is a significant challenge, given the variety of contamination sources and treatment strategies. A lines-of-evidence approach using standardized methodologies is recommended for the assessment of immobilization efficacy to ensure exposure and risk reduction Graphical Abstract Bioavailability-based remediation strategies. Popular soil amendments to reduce Pb exposure include phosphate, industrial by-products, metal oxides, organic matter, and biochar; however, these may increase As exposure. The plumbojarosite formation technique has been recently developed to mitigate Pb and As exposure simultaneously. Multiple lines-of-evidence approach is recommended to assess treatment efficacy
... Available examples of field application of P report a variety of P concentrations and addition methods but were, in general, applied to highly contaminated soils. Their effectiveness was mostly measured using in vitro methods mimicking the gastric environment at pH 1.5, evidencing a decrease in bioaccessibility from 10 to 20 % in urban and residential sites (Scheckel et al., 2013;Obrycki et al., 2016) to up to a 100 % decrease in highly Pb-contaminated sites (Bosso et al., 2008). This method has rarely been applied to soils with low or moderate contamination (e.g., according to the Italian legislation, above 100 and below 1000 mg/kg of Pb soils are considered contaminated in residential areas while accepted in industrial areas). ...
... The three soils (RO, MI and SP) were amended with P and incubated for a further six months. Phosphorus was added as KH 2 PO 4 at 2.5:1 (P2.5), 5:1 (P5), and 15:1 (P15) P:Pb molar ratios, which are commonly used proportions in remediation operations (Kastury et al., 2019;Obrycki et al., 2016). After the mixing of phosphate, triplicates of each P treatment plus an untreated control soil (CTR) were prepared. ...
... To overcome this problem, Pb bioaccessibility was assessed using four different methods: US EPA Method 1340 (Ruby et al., 1999;US EPA, 2017) as written, and three modifications (i.e., with or without glycine at pH 1.5 and 2.5). The extraction at pH 2.5 was used, although it could cause an underestimation of the efficacy of the amendment due to artifacts (Scheckel et al., 2013), as earlier investigations suggested that this phenomenon should be limited in the presence of glycine (Barnett et al., 2011;Obrycki et al., 2016). Extracting solutions without glycine were used to assess the effect of the glycine buffer, as in the literature other methods using different organic buffers have been proposed for P-treated soils (Hettiarachchi et al., 2001). ...
Article
Lead (Pb) contamination is one of the most significant exposure hazards to human health. Contaminated soil particles may be eroded and transferred either to the atmosphere (<10 μm) or to streams; or they may be incidentally ingested (<200 μm). Among strategies for the long-term management of this risk, one of the most cost-effective is the reduction of Pb mobility and bioavailability via amendment with phosphorus-containing materials. To clarify the effectiveness of P amendment in reducing Pb mobility and bioaccessibility in different soil size fractions, an experiment was performed by adding a soluble P compound to a historically contaminated urban soil (RO), a mining soil (MI), and an uncontaminated spiked soil (SP) at different P:Pb molar ratios (2.5:1, 5:1, and 15:1). In the <10 μm fraction of soils, P addition reduced bioaccessible Pb only in the SP soil at the highest dose, with little to no effect on RO and MI soils. Similarly, in the coarse fraction, Pb was immobilized only in the SP soil with all three P doses. These results were probably due to the higher stability of Pb in historically contaminated soils, where Pb dissolution is the limiting factor to the formation of insoluble Pb compounds. The bioaccessible proportion of Pb (using SBET method) was higher than 70 % of the total Pb in all soils and was similar in both fine and coarse particle fractions. Due to the enrichment of Pb in finer particles, this implies possible adverse effects to the environment or to human health if these particles escape from the soil. These results call for increasing attention to the effect of remediation activities on fine soil particles, considering their significant environmental role especially in urban and in historically low or moderately contaminated areas.
... Based on the applied in vitro BaPb determination method BaPb amount can vary because of different pH and extraction solution conditions. [34,45,46] The gastric phase was used in both methods. ...
... [43] However, similar to our results, past studies have concluded that IVBA pH 1.5 extracts nearly 100% of total lead as "bioaccessible" due to its low pH. Obrycki et al. [46] found that phosphate treatments where promoted Pb phosphate formation were ineffective in reducing BaPb in treated soils as measured by IVBA pH 1.5, whereas IVBA pH 2.5 showing greater treatment effects in reducing BaPb. As shown in this study, pH 1.5 IVBA appears to dissolve some hardly soluble lead-containing compounds in real gastric conditions like Pbphosphate. ...
Article
Established methods for using standardized dust wipes to collect and measure total lead in household dust are readily available but the use of dust wipes to measure bioaccessible lead (BaPb) is less clear. This study compared two in vitro methods for estimating the proportion of BaPb in dust collected into dust wipes including the US-EPA's in-vitro bioaccessible assay (IVBA) method at two pH (1.5 and 2.5) values; and the physiologically based extraction test (PBET 2.5 pH). Two types of simulated household dust samples (Pb-soil contaminated and Pb-paint contaminated) each with three Pb concentrations were created. Equal amounts of simulated dust were applied to a smooth surface and collected following the standard EPA dust wipe protocol and were analyzed for BaPb and total Pb (ASTM-E1644-17, ICP-OES). Estimated BaPb levels differed significantly by the method of extraction. Mean percent BaPb were IVBA pH 1.5, > 90% (Pb-paint) and 59-63% (Pb-soil); IVBA pH 2.5 78-86% (Pb-paint) and 45-50% (Pb-soil); PBET pH 2.5 56 to 61% (Pb-paint) and 41-50% Pb-soil). Particularly for lead-paint contaminated dust, PBET showed significantly greater discrimination as suggested by the broader range of BaPb values and closer approximation to total lead concentrations in simulated household dust samples.
... EPA Method 1340 is an aggressive assay used to determine untreated soil Pb bioaccessibility to people who ingest contaminated soil under fasting conditions. For treated soils, increasing the extracting solution pH from 1.5 to 2.5 is recommended to improve assay accuracy (Minca et al., 2013;Obrycki et al., 2016;Walraven et al., 2015;Zia et al., 2011). In addition to Pb, Method 1340 at pH 1.5 is also used to determine soil As bioaccessibility (Diamond et al., 2016). ...
... Biochar amendments reduced Pb bioaccessibility to a modest extent in the smelter and ceramics soils, but no treatment reduced Pb bioaccessibility to a threshold that is protective for human exposure. EPA Method 1340 at pH 2.5 is recommended to assess the impact of amendments on soil Pb bioaccessibility (Minca et al., 2013;Obrycki et al., 2016;Zia et al., 2011). In the smelter and ceramics soils, 8 and 9 different biochar amendments significantly reduced Pb bioaccessibility as measured by EPA Method 1340 at pH 2.5 (Fig. 1). ...
Article
Full-text available
Biochar can reduce lead (Pb) bioavailability to plants in metal-contaminated soil, but the ability of biochar to reduce the bioavailability of soil Pb to people and wildlife remains unknown. In this study, 17 biochars were evaluated as in situ amendments for three soils with distinct sources of Pb contamination (smelter emissions, ceramics waste, mining waste), hydrology (upland, well-drained soil vs submerged wetland soil), and biological receptors (human vs waterfowl). Biochars were made from blends of 30% manure (poultry litter or dairy manure) and 70% lignocellulosic material (wheat straw or grand fir shavings) and pyrolyzed at 300, 500, 700, and 900 °C. Soils were amended with 2% biochar (w/w) and incubated for 6 months. A suite of standard (e.g., EPA Method 1340) and experimental soil Pb bioaccessibility assays were used to assess the impact of the treatments. The results showed that biochar amendments to upland soils resulted in modest reductions in gastrointestinal Pb bioaccessibility (maximum reduction from 78 to 68% bioaccessibility as a percent of total, EPA Method 1340 at pH 2.5). In the wetland soil, sample redox status had a greater impact on Pb bioaccessibility than any amendment. Low-solubility Pb sulfides in this soil oxidized over the course of the study and no treatment was able to offset the increase in Pb bioaccessibility caused by this oxidation. The impact of redox status on Pb bioaccessibility was only evident when soil bioaccessibility assays were adapted to preserve sample redox status. This result highlights the importance of maintaining in situ redox conditions when processing/analyzing samples from low-oxygen environments and that soil remediation efforts should consider the role of redox conditions on Pb bioaccessibility.
... Experimentation of phosphorus treatments on soil Pb contamination suggest that soluble P amendments (e.g. H 3 PO 4 , triple superphosphate, ammonium/diammonium phosphate, etc.) and low pH create efficient conditions to reduce the bioavailability of Pb in soils due to the formation of highly immobile Pb-phosphates that can form upon P addition to Pb-enriched soils (Cao et al., 2002(Cao et al., , 2008Huang et al., 2016;Knox et al., 2006;Obrycki et al., 2016;Ruby et al., 1994;Seshadri et al., 2017;Zhu et al., 2004). For example, chloropyromorphite (Pb 5 (PO 4 ) 3 Cl) is a highly stable Pb-phosphate across the typical pH range of most soils [pH ≈ 3-7; Ksp ≈ 10 −25.05 (Lindsay, 1979); pH ≈ 7.21-12 Ksp ≈ 10 −46.9 (Baker, 1964)] that can form from the addition of P amendments (Baker et al., 2014;Moon et al., 2013;Obrycki et al., 2017;Shen et al., 2018). ...
Article
Full-text available
Lead (Pb) is one of the most common heavy metal urban soil contaminants with well-known toxicity to humans. This incubation study (2–159 d) compared the ability of bone meal (BM), potassium hydrogen phosphate (KP), and triple superphosphate (TSP), at phosphorus:lead (P:Pb) molar ratios of 7.5:1, 15:1, and 22.5:1, to reduce bioaccessible Pb in soil contaminated by Pb-based paint relative to control soil to which no P amendment was added. Soil pH and Mehlich 3 bioaccessible Pb and P were measured as a function of incubation time and amount and type of P amendment. XAS assessed Pb speciation after 30 and 159 d of incubation. The greatest reductions in bioaccessible Pb at 159 d were measured for TSP at the 7.5:1 and 15:1 P:Pb molar ratios. The 7.5:1 KP treatment was the only other treatment with significant reductions in bioaccessible Pb compared to the control soil. It is unclear why greater reductions of bioaccessible Pb occurred with lower P additions, but it strongly suggests that the amount of P added was not a controlling factor in reducing bioaccessible Pb. This was further supported because Pb-phosphates were not detected in any samples using XAS. The most notable difference in the effect of TSP versus other amendments was the reduction in pH. However, the relationship between increasing TSP additions, resulting in decreasing pH and decreasing Pb bioaccessibility was not consistent. The 22.5:1 P:Pb TSP treatment had the lowest pH but did not significantly reduce bioaccessible Pb compared to the control soil. The 7.5:1 and 15:1 P:Pb TSP treatments significantly reduced bioaccessible Pb relative to the control and had significantly higher pH than the 22.5:1 P:Pb treatment. Clearly, impacts of P additions and soil pH on Pb bioaccessibility require further investigation to decipher mechanisms governing Pb speciation in Pb-based paint contaminated soils.
... Gardening practice rates are based on suggested rates of application on commercialized amendment packaging. a [58]; b [59]; c [60]; d [61]; e [30]; f [62]; g [63]. ...
Article
Full-text available
Moderately contaminated garden soils can benefit from gentle remediation options such as soil amendments, which improve soil functions and agronomic potentialities while decreasing environmental and human risk. This study aimed to analyze the effects of doses of various common soil amendments generally applied by gardeners on the predicted bioavailability (i.e., extractability) of metal(loid)s (i.e., As, Cd, Pb, and Zn) in contaminated kitchen garden soils. Fourteen different amendment mixes (i.e., a green waste compost with two degrees of maturity used alone and in combination with zeolite, three organic fertilizers, two calcareous amendments, two natural siliceous or alumino-silicate amendments, and one potting soil) were tested on three different garden soils with diverse sources of contamination and physico-chemical characteristics. Chemically extractable metal(loid)s were analyzed using 0.05 M EDTA extraction and 1 M NH4NO3 extraction. In one soil sample, potting soil showed significant potential to reduce the availability of As, as analyzed by both extractants. This amendment also effectively reduced the Pb extractability in the geogenic-contaminated soil, as did other high-organic matter amendments such as various application rates of composts. Zeolite and zeolite-compost mixes demonstrated success on various metal(loid)s and therefore could be a promising emerging amendment mix. Other efficient amendments include crushed horn, which effectively reduced available Zn in all soils, as well as available Pb. The application of bone meal similarly reduced the extractable As, Pb, and Zn in various soils. The two applications of limes were effective against Cd, As, Pb, and Zn in the different soils studied. This study provided evidence that it is possible to reduce the extractability and thus the environmental availability of the metal(loid)s applied with available and affordable amendments. The results depended on the physico-chemical soil parameters and metal(loid)s considered. There is no single solution, which implies that tests must be carried out before any implementation activities on the kitchen gardens.
... These include the application of biochar [17], biosolids [18] and zero-valent iron nanoparticles [19]. Nonetheless, such modifications usually incur high cost and are reversible in certain cases [20]. Excavation of lead contaminated soil for containment or treatment is the preferred option of many regulators but it is cost-prohibitive and logistically challenging. ...
Article
Full-text available
Aims: With lead being one of the most common soil contaminants and phytoextraction has been reported as a prospective method for remediation of lead-contaminated soil, this review aims to examine the feasibility of lead phytoextraction as well as its constraints and concerns. Study Design: This is a literature review. Methodology: Peer-reviewed papers were sourced from scholarly databases. The papers included in the review were mainly those about phytoextraction of lead, particularly with the shoot, soil and root concentrations of lead mentioned as well as the bioconcentration and translocation factors stated. Besides, papers discussing the limits, for instance, the duration of lead phytoextraction, and concerns of the approach were also included. Results: This review found only 11 plants have been reported to accumulate lead in shoots at nominal threshold of near or above 1,000 mg Pb/kg dry weight and in certain cases, soil amendment was required to achieve this. Only two of the plants had bioconcentration factor > 1 and another two had translocation factor > 1. None of the plants fulfilled all three criteria of a successful hyperaccumulator, indicating the constraints and a lack of feasibility of lead phytoextraction. Besides, lead phytoextraction has been predicted to require significant amount of time, hence increasing the risk of exposure to lead. Conclusion: This review highlights that lead phytoextraction may not be feasible for the remediation. It recommends phytostabilization as a more viable alternative to immobilize lead in rhizosphere and reduce lead exposure.
Article
Full-text available
Measuring the reduction of in vitro bioaccessible (IVBA) Pb from the addition of phosphate amendments has been researched for more than 20 years. A range of effects have been observed from increases in IVBA Pb to almost 100% reduction. This study determined the mean change in IVBA Pb as a fraction of total Pb (AC) and relative to the IVBA Pb of the control soil (RC) with a random effects meta-analysis. Forty-four studies that investigated the ability of inorganic phosphate amendments to reduce IVBA Pb were identified through 5 databases. These studies were split into 3 groups: primary, secondary, and EPA Method 1340 based on selection criteria, with the primary group being utilized for subgroup analysis and meta-regression. The mean AC was approximately -12% and mean RC was approximately -25% for the primary and secondary groups. For the EPA Method 1340 group, the mean AC was -5% and mean RC was -8%. The results of subgroup analysis identified the phosphorous amendment applied and contamination source as having a significant effect on the AC and RC. Soluble amendments reduce bioaccessible Pb more than insoluble amendments and phosphoric acid is more effective than other phosphate amendments. Urban Pb contamination associated with legacy Pb-paint and tetraethyl Pb from gasoline showed lower reductions than other sources such as shooting ranges and smelting operations. Meta-regression identified high IVBA Pb in the control, low incubated soil pH, and high total Pb with the greater reductions in AC and RC. In order to facilitate comparisons across future remediation research, a set of minimum reported data should be included in published studies and researchers should use standardized in vitro bioaccessibility methods developed for P-treated soils. Additionally, a shared data repository should be created for soil remediation research to enhance available soil property information and better identify unique materials.
Article
Full-text available
We present a new implementation of the XAFSmass program that calculates the optimal mass of XAFS samples. It has several improvements as compared to the old Windows based program XAFSmass: 1) it is truly platform independent, as provided by Python language, 2) it has an improved parser of chemical formulas that enables parentheses and nested inclusion-to-matrix weight percentages. The program calculates the absorption edge height given the total optical thickness, operates with differently determined sample amounts (mass, pressure, density or sample area) depending on the aggregate state of the sample and solves the inverse problem of finding the elemental composition given the experimental absorption edge jump and the chemical formula.
Article
Full-text available
Trace element solubility and availability in land-applied residuals is governed by fundamental chemical reactions between metal constituents, soil, and residual components. Iron, aluminum, and manganese oxides; organic matter; and phosphates, carbonates, and sulfides are important sinks for trace elements in soil-residual systems. The pH of the soil-residual system is often the most important chemical property governing trace element sorption, precipitation, solubility, and availability. Trace element phytoavailability in residual-treated soils is often estimated using soil extraction methods. However, spectroscopic studies show that sequential extraction methods may not be accurate in perturbed soil-residual systems. Plant bioassay is the best method to measure the effect of residuals on phytoavailability. Key concepts used to describe phytoavailability are (i) the salt effect, (ii) the plateau effect, and (iii) the soil-plant barrier. Metal availability in soil from metal-salt addition is greater than availability in soil from addition of metal-containing residuals. Plant metal content displays plateaus at high residual loadings corresponding to the residual's metal concentration and sorption capacity. The soil-plant barrier limits transmission of many trace elements through the food chain, although Cd (an important human health concern) can bypass the soil-plant barrier. Results from many studies that support these key concepts provide a basis of our understanding of the relationship between trace element chemistry and phytoavailability in residual-treated soils. Research is needed to (i) determine mechanisms for trace element retention of soil-residual systems, (ii) determine the effect of residuals on ecological receptors and the ability of residuals to reduce ecotoxicity in metal-contaminated soil, and (iii) predict the long-term bioavailability of trace elements in soil-residual systems.
Article
Full-text available
Lead (Pb) is one of the most common contaminants in urban soils. Gardening in contaminated soils can result in Pb transfer from soil to humans through vegetable consumption and unintentional direct soil ingestion. A field experiment was conducted in 2009 and 2010 in a community urban garden with a soil total Pb concentration of 60 to 300 mg kg-1. The objectives of this study were to evaluate soil–plant transfer of Pb, the effects of incorporation of a leaf compost as a means of reducing Pb concentrations in vegetables and the bioaccessibility of soil Pb, and the effects of vegetable cleaning techniques on the Pb concentrations in the edible portions of vegetables. The amount of compost added was 28 kg m-2. The tested plants were Swiss chard, tomato, sweet potato, and carrots. The vegetable cleaning techniques were kitchen cleaning, laboratory cleaning, and peeling. Compost addition diluted soil total Pb concentration by 29 to 52%. Lead concentrations of the edible portions of vegetables, except carrot, were below the maximum allowable limits of Pb established by the Food and Agriculture Organization and the World Health Organization. Swiss chard and tomatoes subjected to kitchen cleaning had higher Pb concentrations than laboratory-cleaned plants. Cleaning methods did not affect Pb concentrations in carrots. Bioaccessible Pb in the compost-added soils was 20 to 30% less than that of the no-compost soils; compost addition reduced the potential of transferring soil Pb to humans via vegetable consumption and direct soil ingestion. Thorough cleaning of vegetables further reduced the potential of transferring soil Pb to humans
Article
Full-text available
Although urban community gardening can offer health, social, environmental, and economic benefits, these benefits must be weighed against the potential health risks stemming from exposure to contaminants such as heavy metals and organic chemicals that may be present in urban soils. Individuals who garden at or eat food grown in contaminated urban garden sites may be at risk of exposure to such contaminants. Gardeners may be unaware of these risks and how to manage them. We used a mixed quantitative/qualitative research approach to characterize urban community gardeners' knowledge and perceptions of risks related to soil contaminant exposure. We conducted surveys with 70 gardeners from 15 community gardens in Baltimore, Maryland, and semi-structured interviews with 18 key informants knowledgeable about community gardening and soil contamination in Baltimore. We identified a range of factors, challenges, and needs related to Baltimore community gardeners' perceptions of risk related to soil contamination, including low levels of concern and inconsistent levels of knowledge about heavy metal and organic chemical contaminants, barriers to investigating a garden site's history and conducting soil tests, limited knowledge of best practices for reducing exposure, and a need for clear and concise information on how best to prevent and manage soil contamination. Key informants discussed various strategies for developing and disseminating educational materials to gardeners. For some challenges, such as barriers to conducting site history and soil tests, some informants recommended city-wide interventions that bypass the need for gardener knowledge altogether.
Article
Full-text available
In cities nationwide, urban agriculture has been put on hold because of the high costs of soil testing for historical contaminants such as lead (Pb). The Mehlich-3 soil test is commonly used to determine plant available nutrients, is inexpensive, and has the potential to estimate trace metals in urban soil. The objectives of this study are to evaluate the ability of the Mehlich-3 to estimate total Pb and bioaccessible Pb in vacant residential lots. Total and bioaccessible Pb were determined in 68 vacant residential lots in Cleveland, OH, using standard USEPA Method 3051A and the Relative Bioaccessibility Leaching Procedure (RBALP), respectively. The Mehlich-3 soil test was used to determine extractable Pb, and the results show Mehlich-3 was strongly correlated with total and bioaccessible Pb. The Mehlich-3 soil test could be used as a screening tool to not only estimate total Pb (slope 1.73, = 0.970) but also to estimate bioaccessible Pb when using RBALP at pH 1.5 (slope 1.67, = 0.975) and RBALP at pH 2.5 (slope 1.15, = 0.938). Additional samples were collected from the Thackeray Avenue site in Cleveland, OH, to demonstrate the ability of the Mehlich-3 soil test to screen soil for Pb. The results from the Thackeray site show good agreement between Mehlich-3 and the standard USEPA methods. A screening protocol for urban vacant residential lots using the Mehlich-3 soil test is proposed.
Article
Full-text available
Ingested soil and surface dust may be important contributors to elevated blood lead (Pb) levels in children exposed to Pb contaminated environments. Mitigation strategies have typically focused on excavation and removal of the contaminated soil. However, this is not always feasible for addressing widely disseminated contamination in populated areas often encountered in urban environments. The rationale for amending soils with phosphate is that phosphate will promote formation of highly insoluble Pb species (e.g., pyromorphite minerals) in soil, which will remain insoluble after ingestion and, therefore, inaccessible to absorption mechanisms in the gastrointestinal tract (GIT). Amending soil with phosphate might potentially be used in combination with other methods that reduce contact with or migration of contaminated soils, such as covering the soil with a green cap such as sod, clean soil with mulch, raised garden beds, or gravel. These remediation strategies may be less expensive and far less disruptive than excavation and removal of soil. This review evaluates evidence for efficacy of phosphate amendments for decreasing soil Pb bioavailability. Evidence is reviewed for (1) physical and chemical interactions of Pb and phosphate that would be expected to influence bioavailability, (2) effects of phosphate amendments on soil Pb bioaccessibility (i.e., predicted solubility of Pb in the GIT), and (3) results of bioavailability bioassays of amended soils conducted in humans and animal models. Practical implementation issues, such as criteria and methods for evaluating efficacy, and potential effects of phosphate on mobility and bioavailability of co-contaminants in soil are also discussed.
Article
Recently the Centers for Disease Control and Prevention lowered the blood Pb reference value to 5 µg/dL. The lower reference value combined with increased re-purposing of post-industrial lands are heightening concerns and driving interest in reducing soil Pb exposures. As a result, regulatory decision makers may lower residential soil screening levels (SSLs), used in setting Pb cleanup levels, to levels that may be difficult to achieve, especially in urban areas. This paper discusses challenges in remediation and bioavailability assessments of Pb in urban soils in the context of lower SSLs, and identifies research needs to better address those challenges. Although in situ remediation with phosphate amendments is a viable option, the scope of the problem and conditions in urban settings may necessitate that SSLs be based on bioavailable rather than total Pb concentrations. However, variability in soil composition can influence bioavailability testing and soil amendment effectiveness. More data are urgently needed to better understand this variability and increase confidence in using these approaches in risk-based decision making, particularly in urban areas.
Article
In this study, the effect of phosphate treatment on lead relative bioavailability (Pb RBA) was assessed in three distinct Pb-contaminated soils. Phosphoric acid (PA) or rock phosphate (RP) were added to smelter (PP2), non-ferrous slag (SH15) and shooting range (SR01) impacted soils at a P:Pb molar ratio of 5:1. In all phosphate amended soils, Pb RBA decreased compared to untreated soils when assessed using an in vivo mouse model. Treatment effect ratios (i.e. ratio of Pb RBA in treated soil divided by Pb RBA in untreated soil) ranged from 0.39-0.67, 0.48-0.90 and 0.03-0.19 for PP2, SH15 and SR01 respectively. The decrease in Pb RBA following phosphate amendment was attributed to the formation of poorly soluble Pb phosphates (i.e. chloropyromorphite, hydroxypyromorphite and Pb phosphate) identified by X-ray absorption spectroscopy (XAS). However, a similar decrease in Pb RBA was also observed in untreated soils following the sequential gavage of phosphate amendments. This suggests that in vivo processes may also facilitate the formation of poorly soluble Pb phosphates which decreases Pb absorption. Furthermore, XAS analysis of PA treated PP2 indicated further in vivo changes in Pb speciation as it moved through the gastrointestinal tract resulting in the transformation of hydroxypyromorphite to chloropyromorphite.
Article
The objectives of this study were to modify the Mehlich 2 (M2) extractant to include Cu among the extractable nutrients, retain or enhance the wide range of soils for which it is suitable and minimize it's corrosive properties. The substitution of nitrate for chloride anions and the addition of EDTA accomplished those objectives. The new extracting solution, already designated Mehlich 3 (M3) is composed of 0.2N CH3COOH‐0.25N NH4N03‐0.015NNH4F‐0.013NHN03‐0.001M EDTA. Extractions from 105 soils using M3, M2, Bray 1 (Bl) and Ammonium Acetate (AA) were compared to evaluate the new extractant. The quantity of F extracted by M3 exceeded that by M2 20% and that by Bl 4% but the results from all extractions were highly correlated. Extractions of both K and Mg by M3 were 6–8% higher than those by AA and 3–4% higher than those by M2, but, again, there was high correlation among methods. Addition of EDTA increased Cu extractions by 170%, Mn by 50% and Zn by 25%. Cu extractions by M3 correlated with those from the Mehlich‐Bowling method. High correlations between Mn, as well as Zn, extracted by M3 and M2 were shown.