EPA/600/R-13/222 I September 2013 I www.epa.gov/research
United States
Environmental Protection
Agency
Effectiveness of the Preservation
Protocol within EPA Method 200.8 for
Soluble and Particulate Lead Recovery
in Drinking Water
Office of Research and Development
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EPA/600/R-13/222
December 2013
Effectiveness of the Preservation Protocol within
EPA Method 200.8 for Soluble and Particulate
Lead Recovery in Drinking Water
Prepared by
Chellsie Haas and Lauren Koch
College of Engineering and Applied Science
University of Cincinnati
Cincinnati, Ohio 45221, United States
Keith Kelty and Darren Lytle
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Water Supply and Water Resources Division
Cincinnati, Ohio 45268, United States
Simoni Triantafyllidou
ORISE Post-Doctoral Fellow
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Water Supply and Water Resources Division
Cincinnati, Ohio 45268, United States
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Cincinnati, Ohio 45268
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Notice
The U.S. Environmental Protection Agency, through its Office of Research and Development,
funded and managed, or partially funded and collaborated in, the research described herein. It
has been subjected to the Agency's administrative review and has been approved for external
publication. Any opinions expressed in this report are those of the author (s) and do not
necessarily reflect the views of the Agency, therefore, no official endorsement should be inferred.
Any mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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Abstract
Lead (Pb) is a toxic trace metal that is regulated in drinking water. The U.S. Environmental
Protection Agency (USEPA) issued the Lead and Copper Rule (LCR), which defines the action
level (AL) for lead at the tap as 0.015 mg/L. Researchers and drinking water utilities typically
employ EPA Method 200.8 to quantify lead and other trace metals in drinking water and
wastewaters, using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). EPA method
200.8 instructs how to properly preserve and analyze a water sample after collection. Recently,
researchers have raised concerns about the preservation protocol, and its effectiveness in
recovering actual concentrations of particulate lead in water samples. Specific concerns with the
acidification protocol include bottle types, and occurrence of lead particulates in water samples.
To investigate these concerns, a two-phase study was performed. Phase One investigated the
recovery of dissolved lead in water samples by using the standard preservation protocol of the
method and varying the water source, bottle type, and preservation pH. Phase Two investigated
the recovery of three lead parti culates in water samples, by comparing the standard preservation
protocol of the method to the more rigorous acid digestion of the method and to an alternative
pre-filtration process. Results of Phase One indicated large losses of soluble lead onto glass
bottles in unpreserved samples, while very little loss was observed in unpreserved samples
collected in HDPE bottles. Proper eventual acid preservation rapidly recovered most of the "lost"
lead, in water samples collected in both bottle types. The parti culate findings of Phase Two
indicated that the method's acid digestion procedure was effective, but difficult to consistently
implement with some lead parti culates. These findings aid in determining the effectiveness of the
EPA sample preservation protocol detailed in Method 200.8.
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Acknowledgements
This work was performed under the USEPA's Regional Applied Research Effort (RARE)
program which is administered by the Office of Science Policy and managed by the Regional
Science Liaisons, and is a mechanism that allows innovative research partnerships between the
EPA regions and Office of Research and Development. The authors would like to thank Michael
Schaub and Forrest John of EPA Region 6 (Dallas, Texas) for supporting this project, and
Michael Morton of EPA Region 6 who is the Regional Science Liaison for supporting the
project. Lastly, the authors would like to thank Emily Nauman of Pegasus Technical Services,
Inc. for support with editing of this report.
IV
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Table of Contents
Notice ii
Abstract iii
Acknowledgements iv
List of Figures vii
List of Tables viii
List of Abbreviations xi.
1.0 Background 1
2.0 Introduction 3
3.0 Project Objectives 6
4.0 Experimental (Materials and Methods) 7
4.1 Materials and Reagents 7
4.2 Equipment and Instrumentation 8
4.3 Phase One: Dissolved Lead Recovery 9
4.3.1 Preparation of Sample Bottles 9
4.3.2 Sampling Method 11
4.3.3 Statistical evaluations 11
4.4 Phase Two: Particulate Lead Recovery 12
4.4.1 Preparation of Sample Bottles 12
4.4.2 Sampling Method 12
4.4.3 Heat Digestion Protocol 12
4.5 Analytical Method 12
5.0 Results and Discussion 13
5.1 Phase One: Dissolved Lead Recovery 13
5.1.1 Impact of Bottle Type on Lead Recovery in Dl Water Before and After Acid Preservation 13
5.1.2 Impact of Bottle Type on Lead Preservation in Dl Water with Calcium Before and After
Acid Preservation 16
5.1.3 Recovery of Lead in Drinking Water Samples Before and After Acidification 16
5.1.4 Impact of Sample pH and Acid Preservation pH on Lead Recovery in Dl Water 22
5.1.5 Investigation of Possible Lead Contamination in HOPE Bottles 26
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5.2 Phase Two: Particulate Lead Recovery 27
5.2.1 Total Recoverable Metals using the standard preservation 27
5.2.2 Determination of suspended and/or settled particulate 28
5.2.3 Investigation of accuracy and precision of aliquoting multiphase samples 29
5.2.4 Evaluation of in-situ solubilization of multiphase samples 31
5.2.5 Evaluation of a pre-filtration procedure for the analysis of multiphase samples 33
6.0 Conclusions 35
7.0 References 37
VI
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List of Figures
Figure 1. EPA Method 200.8 (ICP-MS) specifies procedures to quantify total recoverable lead (and other
trace metals) in drinking water samples. A slightly different digestion (not shown) is
recommended if the sample contains >1% undissolved solids. Modified from Triantafyllidou et al.
(2013) 4
Figure 2. Scanning electron micrographs of lead particles added to water samples in Phase Two to
investigate lead recovery: (a) basic lead carbonate, (b) lead oxide, (c) lead orthophosphate 8
Figure 3. Duplicate 2 ml aliquots from each sample bottle (HOPE versus glass) were collected for lead
analysis at specified time intervals in Phase One 11
Figure 4. Lead concentration in Dl water contained in glass and HOPE bottles 15
Figure 5. Lead concentration in Dl water spiked with 100 mg/L calcium and contained in glass and HPDE
bottles 15
Figure 6. Lead concentration in drinking water from (a) ground water, and (b) surface water sources
contained in glass and HOPE bottles 18
Figure 7. Lead concentration in various unpreserved water sources collected in duplicate glass bottles:
(a) surface water unpreserved, and (b) ground water unpreserved 19
Figure 8. Lead concentration in various unpreserved water sources collected in duplicate HOPE bottles:
(a) surface water unpreserved, ground water unpreserved, and deionized water with calcium
unpreserved (100 mg/ L Ca); (b) deionized water unpreserved 21
Figure 9. Lead concentration in HOPE and glass bottles based on initial preservation of (a) pH 4,5, 6, and
7 with a final preservation of pH 4 and (b) pH of 2, 4, 5, 6, and 7 with a final preservation of pH 2.
23
Figure 10. Lead recovery (%) in HOPE bottles preserved to pH < 2, and in one "blank" HOPE bottle
preserved to pH < 2 26
Figure 11. Dissolution of lead orthophosphate, basic lead carbonate and lead (IV) oxide, with standard
preservation to pH < 2 with nitric acid 27
Figure 12. Particulate Pb(IV) oxide recovery with nitric and hydrochloric acid preservation 31
Figure 13. Particulate (PbCO3)2.Pb(OH)2 recovery with nitric and hydrochloric acid preservation 32
Figure 14. Particulate Pb3(PO4)2 recovery with nitric and hydrochloric acid preservation 32
VII
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List of Tables
Table 1. Background elemental analysis of surface water, ground water, and Dl water spiked with
calcium 10
Table 2. Dissolution of basic lead carbonate, lead orthophosphate and lead (IV) oxide, with enhanced
nitric acid and hydrochloric acid digestion 29
Table 3. Particulate PbO2 recovery in acid preserved samples with nitric and hydrochloric acid digestion
30
Table 4. Particulate PbO2 recovery through an alternative pre-filtration procedure 34
Vlll
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List of Abbreviations
AL Action Level
Ca Calcium
Cu Copper
DI Deionized Water
HC1 Hydrochloric Acid
HDPE High Density Polyethylene
HNO3 Nitric Acid
ICP - MS Inductively Coupled Plasma - Mass Spectrometry
IQ Intelligence Quotient
LCR Lead and Copper Rule
LSL Lead Service Line
MCL Maximum Contaminant Level
NaOH Sodium Hydroxide
NTU Nephelometric turbidity units
Pb Lead
PbO2 Lead (IV) Oxide
SDWA Safe Drinking Water Act
USEPA United States Environmental Protection Agency
XRD X-Ray Diffraction
XI
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1.0 Background
The United States Environmental Protection Agency (USEPA) is responsible for establishing
regulations that ensure provision of safe drinking water throughout the country. Regulations
under the Safe Drinking Water Act (SDWA) protect public health by establishing Maximum
Contaminant Levels (MCLs) or other enforceable thresholds for contaminants including
microorganisms, disinfection byproducts, inorganic/organic chemicals, and radionuclides
(USEPA, 2012). Water quality monitoring by drinking water utilities is necessary to demonstrate
regulatory compliance with these enforceable limits.
The Lead and Copper Rule (LCR) (USEPA, 1991) is unique compared to other regulations that
target inorganic contaminants in drinking water. This is because compliance sampling for lead
(and copper) occurs at household taps rather than at the entry point to the distribution system,
acknowledging that premise plumbing materials can be primary sources of lead and copper
contamination at the tap. Furthermore, the LCR established an action level (AL) rather than an
MCL for lead (and copper) (USEPA, 1991). If more than 10% of the water samples (exact
sample number depends on system size) exceed an AL of 0.015 mg/L for lead (1.3 mg/L for
copper), then the drinking water utility is required to implement certain treatment techniques to
control lead corrosion.
Sources of lead in tap water include old lead service lines (LSLs), old lead solders, and brass
plumbing components (Triantafyllidou and Edwards, 2012; Sandvig et al., 2008; Schock, 1990).
If present, LSLs can contribute up to 50-75% of the total lead measured at the tap (Sandvig et
al., 2008). Total lead concentration at the tap consists of particulate lead and dissolved lead.
Particulate lead is operationally defined as the lead fraction in a water sample that is retained by
a 0.45 |im water filter. The fraction of lead that passes through the filter is considered to be
dissolved. Total lead (dissolved and particulate) released from plumbing materials into tap water
can pose health risks when ingested. Although the LCR considers total lead concentration,
knowing the form of lead is useful in identifying the cause of lead release and the type of lead
exposure.
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Lead is a neurotoxin, and lead exposure has long been associated with intellectual impairments
in children (e.g., IQ deficits and behavioral changes) (Health Canada, 2013). Recently, such
neurodegenerative effects in children and other health effects in adults (cardiovascular, renal, and
reproductive) were summarized at much lower levels of lead exposure than previously reported
(Health Canada, 2013). Clearly, assessment of potential human exposure to lead requires
accurate quantification of the total lead concentration (dissolved and particulate) in tap water.
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2.0 Introduction
USEPA Method 200.8 is an accepted method for the determination of total lead and other trace
elements in water (and wastes) by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)
(USEPA, 1994). Among other instructions, the method provides a protocol for acid preservation
of water samples (Figure l),because this step can affect lead quantification. Adding acid
preservative to water samples aims to prevent metal precipitation and reduce metal adsorption
onto the walls of sampling bottles (Sliwka-Kaszynska et al., 2003), thereby rendering all the
metal soluble and thus quantifiable by ICP-MS.
For the determination of "total recoverable" lead, Method 200.8 requires that tap water samples
are shipped to a lab for acid preservation and further processing (Figure 1). The method allows
collection of samples without immediate acid preservation, to alleviate the safety concerns of
handling acids in the field and during sample shipment to the lab. Preservation should therefore
be performed in the lab as soon as practical, but may be delayed up to two weeks following
sample collection. Research conducted by Miller et al. (1985) in support of this time frame,
indicated that acidification of water samples could be performed up to two weeks after collection
without gravely affecting lead recovery. In that work, mean lead recovery after two weeks of
unpreserved sample storage and subsequent acidification was 90% for samples with 70 ug/L
lead, and 94% for samples with 20 ug/L lead (Miller et al., 1985). Feldman et al. (1992) and
Creed et al. (1995) similarly reported that if water samples were held for two weeks unpreserved,
subsequent acidification to pH < 2 re-solubilized the metals that had fallen out of solution.
Standard acid preservation under Method 200.8 involves acidifying the samples to pH < 2, and is
typically achieved by addition of 0.15% v/v concentrated nitric acid (HNOs) in the lab. After a
minimum 16-hour sample holding time from the moment of acid addition, the sample pH is
measured. If the measured pH exceeds the required minimum, the pH is adjusted and the holding
period time frame is repeated. If the measured pH meets the requirement of 2 or less, then an
aliquot is collected to measure turbidity.
A decision tree for further sample processing is based on the turbidity measurement. If the
turbidity is less than 1 nephelometric turbidity unit (NTU) then lead is assumed to have been
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rendered soluble, and a sample aliquot can be directly analyzed by ICP-MS (Figure 1). If the
turbidity is greater than 1 NTU, a sample aliquot must undergo a rigorous heated acid digestion
step, with the addition of specified amounts of nitric acid and hydrochloric acid at 85 °C before
analysis (Figure 1). This additional preservation step aims to ensure that any particulate lead
present (as indicated by increased turbidity) dissolves so that it can be quantified by ICP-MS.
FIELD
Water collection
in sampling bottle
LAB
Standard Acid
Preservation
Acidify with HNO3
(typicallyO.15%)
to achieve pH < 2
Mix sample
Collect 100 mL aliquot
t
Aliquot Digestion
Add 2 mL HNO3 (from 1:1 solution)
and 1 mL HCI (from 1:1 solution)
Heat to 85 °C until volume reduced
to 20 mL (do not boil)
1
r
Analytical Instrument
ICP-MS to quantify
total recoverable lead
1
r
Allow to settle
overnight or
centrifuge until clear
Figure 1. EPA Method 200.8 (ICP-MS) specifies procedures to quantify total recoverable lead (and other trace
metals) in drinking water samples. A slightly different digestion (not shown) is recommended if the sample
contains >1% undissolved solids. Modified from Triantafyllidou et al. (2013).
The standard acid preservation to pH < 2 has been shown to adequately quantify total lead, in
water samples where lead contamination was fairly low and predominantly in dissolved form
(Triantafyllidou et al., 2013; Deshommes et al., 2010), or in the form of very fine lead solder
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powder which had been deliberately introduced to water samples (Lytle et al., 1993). In cases
where water samples were highly contaminated with lead particles, the standard acid
preservation was reported to miss some of the lead present, compared to more rigorous heated
acid digestions (Triantafyllidou et al., 2013; Triantafyllidou and Edwards, 2007). In the presence
of lead (IV) particles in water samples (which are far less soluble in water compared to Pb(II)
particles), lead recovery was reported as low as 20% (Triantafyllidou and Edwards, 2007).
Triantafyllidou and Edwards (2007) suggested increasing the concentration of nitric acid during
sample preservation (2% HNOs instead of 0.15% HNOs), to achieve much lower pH in the water
sample than the method-specified pH < 2, and thus to further increase lead solubility.
Bottle type was shown to affect lead recovery in unpreserved water samples. Issaq and Zielinski
(1974) found that 50% of the lead in unpreserved samples containing 400 |ig/L lead was lost
after 1 hour in glass bottles due to adsorption to the bottle walls, compared to a lower lead loss of
30% in polyethylene bottles after 1.5 hours. Acidification with nitric acid, however, was able to
prevent losses due to adsorption onto container walls (Issaq and Zielinski, 1974). Salim and
Cooksey (1979) noted that the water type could affect lead losses onto container walls, because
presence of other ions in the water (e.g., zinc and calcium) would compete with lead for the
available adsorption sites.
Overall, review of the literature indicated that the extent of lead contamination in water samples,
the form of the lead (dissolved versus particulate), the preservation pH, the type of sampling
container (e.g., glass or HDPE) and the type of water sample (i.e., the sample matrix) are
important factors affecting acid preservation of water samples for lead quantification.
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3.0 Project Objectives
The main objective of this project was to investigate the effectiveness of the sample preservation
protocol outlined in Method 200.8 in recovering lead from water samples. Lead recoveries were
studied in various water samples spiked with lead, by evaluating lead sorption and desorption
from sample bottles using ICP-MS. Specific concerns with the acidification protocol, bottle
types, and occurrence of particulates in water, were investigated in two phases.
Phase One of the study focused on the recovery of dissolved lead within different water sources,
bottle types, and preservation pHs. The lead recovery in glass and high-density polyethylene
(HDPE) bottles was examined in DI water, ground water, surface water, and DI water containing
100 mg/L calcium. Similarly, lead recovery was compared between altered sample preservations
at pH 2, 4, 5, 6, and 7. Phase Two examined the recovery of particulate lead from water samples,
using direct and total recoverable analyses. Specifically, the recovery of lead phosphate, basic
lead carbonate and lead (IV) oxide was evaluated.
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4.0 Experimental (Materials and Methods)
The project was conducted in two phases. The first phase focused on the impact of water source,
bottle type, and preservation pH on the recovery of lead in water samples spiked with dissolved
lead. The second phase focused on what acid preservation and/or acid digestion conditions
would achieve complete solubilization of particulate lead, prior to quantification by TCP-MS.
4.1 Materials and Reagents
Tests conducted during Phase One used 500 mL high density polyethylene (HDPE) bottles
(Nalgene, Rochester, NY) and 500 mL glass media bottles (Wheaton, Millville, NJ) with
polyethylene lined phenolic caps. Glass bottles were acid-washed in a 10% nitric acid (HNOs)
solution before use, whereas HDPE sample bottles were used directly from the package. The
acid wash solutions were prepared with reagent grade HNO3 (GFS Chemical, Columbus, OH).
Tests conducted during Phase Two used 250 mL HDPE bottles directly from the package.
Acid concentrations, unless otherwise specifically stated, were dilutions from "concentrated"
acids. Acids employed were double distilled, "Veritas" nitric acid (HNOs, 15.9 N) and
hydrochloric acid (HC1, 12 N) (GFS Chemical). The pH of water samples was adjusted with
reagent grade sodium hydroxide (NaOH) (GFS Chemical). Dissolved metal standards were
prepared with ICP-MS lead standards (GFS Chemical). The DI water was obtained with a
Thermo Scientific Barnstead B-Pure system, supplied with building reverse osmosis treated
water.
Three different lead particulate compounds were investigated in Phase 2, including a) lead
carbonate basic ([PbCO3]2. Pb[OH]2) (Alfa Aesar, Ward Hill, MA), b) lead oxide (PbO2) (Alfa
Aesar, Ward Hill, MA) and c) lead orthophosphate (PbsfPO^) ( Johnson Matthey, Taylor, MI).
Scanning electron micrographs revealed that the particles ranged from less than 1 |im to
approximately 10 jim in size (Figure 2). The X-ray diffraction (XRD) analysis of the respective
compounds determined that the primary mineralogical makeup of the standards was: a)
hydrocerussite with traces of other Pb(II) carbonate hydroxide oxides, b) plattnerite with traces
of other Pb(IV) oxides, and c) lead orthophosphate.
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Figure 2. Scanning electron micrographs of lead particles added to water samples in Phase Two to
investigate lead recovery: (a) basic lead carbonate, (b) lead oxide, (c) lead orthophosphate.
4.2 Equipment and Instrumentation
Sample pH was measured using an Expandable Ion Analyzer pH meter (EA 940 Orion Research,
Cambridge, MA) and a standard electrode. Three point calibrations were performed daily.
All heat digestions were performed using a DigiPREP Heat Block Jr. and Keypad (SPC Science,
Champlain, NY). Heat digestions were performed at 85°C using 50 mL digestion tubes, a
DigiPKEP Heat Block Jr. and Keypad (SPC Science, Champlain, NY).
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All direct and total recoverable analyses were performed using an Agilent (Santa Clara, CA),
7500cs Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) and a Thermo Elemental
(Franklin, MA) ICP-MS model X7.
Particulate sample filtrations were performed with Fisherbrand™ 0.45 jim nylon luer lock
syringe filters (Fisher Scientific, Pittsburgh, PA). Preliminary determinations revealed the filters
did not impact dissolved metal concentrations when used on nitric acid preserved samples.
4.3 Phase One: Dissolved Lead Recovery
4.3.1 Preparation of Sample Bottles
All tests in this phase were performed in 500 mL HDPE versus 500 mL glass bottles. The four
water sources studied were DI water, DI water spiked with calcium, surface tap water and
ground tap water (Table 1). The DI water spiked with calcium was prepared with 100 mg/L
calcium (CaCb. 2H2O) (Fisher Scientific, Waltham, MA). The surface water was collected from
a faucet in the laboratory, distributed from the Miller Treatment Plant of the Greater Cincinnati
Water Works (Cincinnati, OH). The ground water was collected from a faucet in a home,
distributed from the Bolton Treatment Plant of the Greater Cincinnati Water Works (Cincinnati,
OH). Each water outlet was flushed for ten minutes before water sample collection.
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Table 1. Background elemental analysis of surface water, ground water,
and Dl water spiked with calcium
Element
Lead
Al
As
Ba
Be
Ca
Cd
Cr
Cu
Fe
K
Li
Mg
Mn
Na
Ni
P
S
Sb
Si
Sn
Sr
V
Zn
Surface water
Concentration
(mg/L)
0.0036
0.0260
< 0.004
0.0288
< 0.005
26.83
< 0.0003
< 0.001
0.0046
0.0136
1.822
< 0.005
8.089
< 0.001
18.380
< 0.001
0.1623
18.92
< 0.003
2.676
< 0.001
0.1645
< 0.001
0.0234
Ground water
Concentration
(mg/L)
< 0.002
0.0127
< 0.004
0.0146
< 0.005
17.26
< 0.0003
< 0.001
0.0018
< 0.001
3.304
< 0.005
21.18
< 0.001
32.09
< 0.001
0.1175
19.69
< 0.003
4.366
< 0.001
0.1402
< 0.001
0.0005
DI spiked with Ca
Concentration
(mg/L)
< 0.002
0.0157
< 0.004
0.0027
< 0.005
95.27
< 0.0003
0.0045
0.0017
0.0026
0.3122
< 0.005
< 0.005
< 0.001
0.0341
< 0.001
< 0.005
< 0.003
< 0.003
< 0.020
< 0.001
0.0160
< 0.001
0.00065
Water samples were spiked to 50 |ig/L lead. Each trial included at least one preserved sample
and duplicate unpreserved samples (Figure 3). Preserved samples were adjusted to a pH of less
than two by adding HNOs. Unpreserved sample bottles were adjusted to a pH 7, with the
exception of the investigation of different pH preservation levels, by adding 0.1 NNaOH until
desired pH was reached.
The impact of preservation pH on lead recovery was studied by adjusting water samples to a pH
of 4, 5, 6, and 7. After sample bottle preparation was completed, the sample bottles were stored
and sampled according to the established protocol. After the designated storage time, the
unpreserved samples were acidified using HNOs to obtain either a pH 2 or 4.
10
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4.3.2 Sampling Method
Sampling of the unpreserved water (in HDPE versus glass containers) took place over a one-
week or two-week time frame, with sample collection at 0, 24, 48, 96 hours and one and two
weeks. This was done because according to Method 200.8, water samples can remain
unpreserved for a period of up to two weeks. Duplicate 2 mL aliquots were taken from each
sample bottle for analysis (Figure 3). Following acidification of the unpreserved samples,
sampling continued for an additional one or two weeks, at 24, 48 hours, and one and two weeks.
Each sample bottle was shaken for 10 seconds immediately before sampling. The pH of each
sample bottle was monitored throughout each trial and recorded in a laboratory notebook.
Figure 3. Duplicate 2 mL aliquots from each sample bottle (HDPE versus glass) were collected for lead
analysis at specified time intervals in Phase One.
4.3.3 Statistical evaluations
All statistical comparisons were performed with the two sided t-test and evaluated at the 95%
confidence interval.
11
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4.4 Phase Two: Particulate Lead Recovery
4.4.1 Preparation of Sample Bottles
All tests in Phase Two were performed in 250 mL HDPE bottles. No pre-cleaning of the bottles
was performed. Particulate lead compounds were weighed on a 0.01 mg balance (Model M220D,
Denver Instrument, Bohemia, NY). Aluminum foil weigh boats were employed to minimize
errors frequently encountered with plastic weigh boats and static charge effects.
4.4.2 Sampling Method
Tests were performed in duplicate and individual aliquoting procedures were performed in
triplicate. Results were then averaged. All dissolved lead determinations were performed on
aliquots that had been filtered through 0.45 jim nylon luer lock syringe filters.
4.4.3 Heat Digestion Protocol
Heat digestions were performed at 85°C using 50 mL digestion tubes with elevated watch
glasses. Samples were acidified with nitric and hydrochloric acid, allowed to reduce initial
volumes to approximately 20 mL and then refluxed for a minimum of one hour. Samples were
then reconstituted to original volume and allowed to equilibrate overnight prior to analysis by
ICP-MS.
4.5 Analytical Method
The method employed was EPA Method 200.8 "Determination of Metals and Trace Elements in
Water and Wastes by ICP-MS". Lead determinations were based on a summation of Atomic
Mass Units (AMU) 208Pb, 207Pb and 206Pb. Calibration was based on 4 standards (Spex,
Metuchen, NJ) and periodically verified through second source standards (GFS Chemical,
Columbus, OH). The method detection limit was 0.02 |ig/L.
12
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5.0 Results and Discussion
Lead recovery in soluble lead-containing samples collected in glass and HDPE bottles was
investigated in deionized water first. This was done to determine the effectiveness of EPA
Method 200.8 in the absence of potential chemical interactions present in other investigated
water sources. Lead losses to the glass bottles were observed, but after applying the preservation
protocol detailed in EPA method 200.8, the "lost" lead was recovered. Next, varying the
preservation pH determined the relationship between lead loss and actual preservation pH.
Further investigation was performed to determine the effectiveness of the preservation method,
and the relationship between dissolved lead loss and preservation pH in other water sources,
including deionized water spiked with calcium, and ground and surface-based drinking waters.
These tests identified the lowest recovery of lead in unpreserved glass bottles. Additionally,
particulate lead recovery was investigated within deionized samples collected in HDPE bottles.
Results showed variability in lead recovery depending on particle type, which initiated further
investigation of the preservation method in the presence of lead particles.
5.1 Phase One: Dissolved Lead Recovery
5.1.1 Impact of Bottle Type on Lead Recovery in DI Water Before and After Acid Preservation
Lead losses in DI water to bottles were largely dependent on bottle type, when the water samples
were not acidified (Figure 4). In the case of glass bottles, lead losses, presumably due to sorption
to the bottle surface, were almost immediate and accounted for an approximate 20 ug/L drop in
the measured lead concentration during the first sampling event (at 0 hours). The lead
concentration decreased by another 10 ug/L within the next 24 hours, to approximately 20 ug/L,
where it remained at equilibrium until the samples were acidified. Unpreserved lead
concentration in one glass bottle dropped to as low as 17.1 ug/L, and the unpreserved glass
duplicate dropped as low as 14.7 ug/L. Lead measurements in the duplicate glass bottles were in
reasonable agreement. Average lead recovery in these duplicate unpreserved bottles before
acidification was 19.5 ug/L, or 38.9% of the initial lead spike concentration.
The HDPE unpreserved duplicate bottles did not show such a significant drop in lead recoveries
before acidification. The unpreserved HDPE bottles had an average lead concentration of 44.4
13
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ug/L and 46.9 ug/L by the end of week 2, or 88.9% and 93.8% recovery of the lead spike
concentration.
After being stored unpreserved for 336 hours (i.e., two weeks), the DI water samples were
acidified according to EPA Method 200.8 (Figure 1). The two unpreserved samples stored in
glass bottles yielded reproducible results after acidification. The average lead concentration of
these samples increased from 19.5 ug/L to 47.3 ug/L following acidification, to an average
recovery of 94.7% of the calculated lead spike concentration. The recovery of lead occurred
within 24 hours of acidifying the unpreserved samples. Where sorption losses of lead were
important under un-acidified conditions, lead recovery was rapid, within 24 hours of
acidification.
Lead-containing DI water samples stored in HDPE and glass bottles had similar lead recoveries
after acidification. The lead concentration in the duplicate HDPE preserved samples averaged
47.4 ug/L and 45.2 ug/L after 24 hours of acidification (Figure 4), which is a 94.8% and 90.3%
recovery of the lead spike concentration, respectively. The lead concentration in the duplicate
glass preserved DI water samples averaged 48.1 ug/L, or 96.3% recovery of the lead spike
concentration. Overall, acidifying DI water samples containing 50 ug/L soluble lead according to
EPA Method 200.8 was sufficient to prevent lead losses due to sorption, for both glass and
HDPE bottles studied.
14
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70 n
i
48
T
i
Acid added to
unpreserved sample
•Preserved HOPE
Duplicate Preserved HOPE
•Unpreserved HOPE
Duplicate Unpreserved HOPE
Preserved Glass
Duplicate Preserved Glass
•Unpreserved Glass
Duplicate Unpreserved Glass
96 144 192 240 288 336 384 432 480 528 576 624 672
Time (hours)
Figure 4. Lead concentration in Dl water contained in glass and HOPE bottles.
10
Acid added to
unpreserved sample
•Preserved HOPE
•Unpreserved HOPE
Duplicate Unpreserved
HOPE
Preserved Glass
•Unpreserved Glass
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336
Time (hours)
Figure 5. Lead concentration in Dl water spiked with 100 mg/L calcium and contained in glass and HPDE
bottles.
15
-------
5.1.2 Impact of Bottle Type on Lead Preservation in DI Water with Calcium Before and After
A cid Preservation
Large losses of lead to unpreserved glass sample bottles were observed in the case of DI water
(Figure 4). To test the sorption mechanism of lead loss and the importance of cation charge and
concentration, calcium (100 mg/L) was added to the lead-containing DI water samples. Calcium
was predicted to compete for cation sorption sites on the bottle surface. All HOPE and glass
bottles showed no significant difference between duplicate bottles (Figure 5). The lead
concentration in DI water containing calcium in unpreserved glass bottles averaged 33.5 ug/L, or
67.0% recovery of lead. The unpreserved HOPE samples had an average lead concentration of
42.5 ug/L, or 87.1% lead recovery before acidification. The presence of calcium clearly reduced
lead losses to the glass bottle surfaces (Figures 4 and 5) confirming the importance of charge
interactions and competing cations in the lead loss mechanism. After acidification to pH < 2 at
168 hours (i.e., 7 days), lead levels returned to the initial spike concentration (Figure 5).
5.1.3 Recovery of Lead in Drinking Water Samples Before and After Acidification
The observation that the presence of calcium in DI water impacted lead losses to bottles suggests
that the degree of lead loss in actual drinking water samples would also be impacted. The impact
would likely be water quality specific, given the wide range and complexity of drinking water
chemistries. To test the theory, lead recovery tests were performed in actual drinking waters at a
pH of 7 to 8, having surface or ground water origin (see Table 1) in glass bottles.
There was no significant lead difference between duplicate bottles within each drinking water
source. Greatest losses of lead to the glass bottles were associated with drinking water from the
ground water source. Losses to the bottle all appeared to occur within the first 24 hours of
unpreserved sample storage. Beyond 24 hours, lead levels remained unchanged. The lead
recovery of unpreserved glass bottles containing ground water averaged 26.9 ug/L, or else 53.9%
based on the initial calculated spike of lead concentration (Figure 6a and 7a).
Lead losses in drinking water of surface water origin were considerable (Figures 6b), but not as
large as in drinking water produced from ground water (Figure 6a). And unlike groundwater
trends, lead decreased or sorbed to the bottle exponentially up to 96 hours of standing before
reaching equilibrium (Figure 6b). Measured lead concentrations averaged 36.7 ug/L, or 73.4%
16
-------
recovery of the initial lead level. The unpreserved glass bottles of DI water containing calcium
behaved similarly (Figure 7) and measured lead concentrations averaged 33.5 ug/L or a 67.0%
recovery of the calculated initial lead level.
Lead concentrations in all unpreserved glass bottles showed an obvious difference when
compared to the preserved glass bottles containing water from the same source. However,
appropriate acidification was able to quickly recover lost lead (Figure 6a and 6b). The results
illustrate that lead losses in unpreserved drinking water samples to glass bottles are complicated,
and predicting losses is not straightforward.
17
-------
(a)
Acid added to
unpreserved sample
Preserved HOPE
Unpreserved HOPE
Duplicate Unpreserved HOPE
Preserved Glass
Unpreserved Glass
Duplicate Unpreserved Glass
48 96 144 192
Time (hours)
240
288
336
(b)
£
O
4J
£
4-1
I
o
u
•o
re
0)
40 -
30 -
20 -
10 -
0
Acid added to
unpreserved sample
Preserved HOPE
Unpreserved HOPE
Duplicate Unpreserved HOPE
Preserved Glass
Unpreserved Glass
Duplicate Unpreserved Glass
0 24 48 72
96 120 144 168 192 216 240 264 288 312 336 360
Time (hours)
Figure 6. Lead concentration in drinking water from (a) ground water, and (b) surface water sources
contained in glass and HOPE bottles.
18
-------
(a)
70 n
60 -
.a
a.
10 -
Acid added to
unpreserved sample
I
Surface Unpreserved Glass
Duplicate Surface
Unpreserved Glass
Ground Unpreserved Glass
Duplicate Ground
Unpreserved Glass
•Deionized (lOOmg/LCa)
Unpreserved Glass
•Spiked Concentration
50 100 150 200 250
Time (Hours)
300
350
400
(b)
70 -
60 -
J~ C.[)
-**. M
00
"c 40
o
Concentrati
NJ (JJ
O O
_Q
0- 10
n .
>
•• • . 1
Acid added to
unpreserved sample *•
•l
— ^— Deionized Unpreserved
Glass
Duplicate Deionized
Unpreserved Glass
1^^— Spiked Concentration
100 200 300 400
Time (Hours)
500
600
700
800
Figure 7. Lead concentration in various unpreserved water sources collected in duplicate glass bottles: (a)
surface water unpreserved, and (b) ground water unpreserved.
19
-------
Lead recovery in drinking water was much greater in unpreserved HDPE bottles (Figure 8a and
8b) compared to glass, which was consistent with DI waters. There was no significant difference
between drinking water samples from the ground water source in unpreserved HDPE bottles. The
average lead concentration prior to acidification was 44.5 ug/L or a 88.9% lead recovery. The
variability of the initial (time =0) determinations of the lead in the unpreserved surface samples
in HDPE bottles prevented the ability to perform statistical analysis (t-test). Although statistical
comparisons cannot be made with the unpreserved HDPE bottles, it was calculated that lead
concentrations decreased to as low as 44.9 ug/L and 46.0 ug/L in these bottles which compares
to the ground water results.
20
-------
(a)
E 40
01
u
r°
1 20
10 -
0
(b)
E
4-»
c
01
(J
(0
01
o
70 -
60 -
20 H
10 -
Acid added to
unpreserved sample
Surface Unpreserved HOPE
Duplicate Surface Unpreserved HOPE
Ground Unpreserved HOPE
Duplicate Ground Unpreserved HOPE
Unpreserved HOPE (lOOmg/LCa)
Duplicate Unpreserved HOPE (lOOmg/LCa)
24 48 72 96 120 144 168 192 216 240 264 288 312 336 360
Time (hours)
Acid added to
unpreserved sample
•Deionized Unpreserved HOPE
•Duplicate Deionized Unpreserved HOPE
0 48 96 144 192 240 288 336 384 432 480 528 576 624 672 720
Time (hours)
Figure 8. Lead concentration in various unpreserved water sources collected in duplicate HOPE bottles: (a)
surface water unpreserved, ground water unpreserved, and deionized water with calcium unpreserved (100
mg/ L Ca); (b) deionized water unpreserved.
21
-------
5.1.4 Impact of Sample pH and Acid Preservation pH on Lead Recovery in DI Water
The effect of the initial pH on lead losses was investigated in both bottle types. The impact of
acidification pH at 384 hours (<2 according to EPA 200.8 versus a higher pH of 4) was also
examined. Generally, as the initial sample pH increased from 4 to 7, lead recovery in
unpreserved samples (before preservation) decreased and lead losses increased in the glass
bottles (Figures 9a and 9b). All samples preserved to a pH less than 2 after delayed acidification,
recovered greater than 90% of the original spiked concentration. The greatest lead recovery
occurred in bottles immediately preserved to pH less than 2 (Figure 9b). Furthermore, there was
a significant difference in lead recovery between immediately preserved sample bottles and
sample bottles with a delayed preservation.
Glass and FtDPE bottles preserved immediately to a pH less than 2 showed reproducible results
as also seen in the DI trial (Figure 9b). Preserved FtDPE and glass bottles showed no statistical
difference to one another, when results were averaged for the time frame of the trial. The
preserved FtDPE bottle recovered an average of 50.8 ug/L lead, yielding a 102% recovery, while
the preserved glass bottle recovered an average of 51.5 ug/L lead, yielding a 103% recovery
(Figure 9b). These concentrations were slightly greater than the original 50 ug/L spiked
concentration, suggesting noise within the instrument.
Glass bottles initially preserved to pH 4 showed no significant difference between one another,
even after acidifying one to a pH of less than 2 (pH 4 glass condition in Figure 9a versus 9b).
Although each recovered greater than 90% of the initial spiked lead concentration, each showed
a significant difference to the bottle that was immediately preserved to a pH less than 2. One
FIDPE bottle remained at a pH 4 throughout the entire trial. As seen in Figure 9a, lead recovery
increased for this bottle after 384 hours, even though its pH of 4 remained constant throughout
the trial. The initial average concentration was 46.2 ug/L lead, yielding a 92.4% recovery, and
significantly increased to an average concentration of 47.9 ug/L lead, yielding a 95.8% recovery,
after 384 hours. A possible speculation for this increase is slow dissolution of lead from the
HDPE bottle, contamination problems during sample handling in the lab or sample mixing
effects.
22
-------
(a)
20 -
•a
as
10 -
Acid added to
unpreserved sample
100 200 300 400 500
Time (hours)
600
700
800
pH4HDPE
pH5_HDPE
•pH6_HDPE
•pH7_HDPE
pH 4 Glass
-pH5_Glass
•pH6_Glass
pH7_Glass
(b)
•D
as
01
10
Aad added to
unpreserved sample
100 200 300 400 500
Time (hours)
600
700
pH2_HDPE
pH4_HDPE
pH5_HDPE
•pH6_HDPE
•pH7_HDPE
pH2_Glass
pH4_Glass
pH5_Glass
pH6_Glass
pH7_Glass
Figure 9. Lead concentration in HOPE and glass bottles based on initial preservation of (a) pH 4,5, 6, and 7
with a final preservation of pH 4 and (b) pH of 2, 4, 5, 6, and 7 with a final preservation of pH 2.
23
-------
Although this bottle showed an increase in lead concentration while maintaining a pH of 4, the
duplicate bottle that was eventually preserved to a pH less than 2 after 384 hours showed a
decrease in lead concentration. The initial average concentration was 48.5 ug/L lead, yielding a
96.9% recovery, and after preservation lead significantly decreased to an average of 47.8 ug/L,
yielding a 95.6% recovery (Figure 9a).
This variability was also observed at other preservation pHs. At pH 5, there was no significant
difference between duplicate bottles of each bottle type. There was a significant difference
between samples collected from HDPE bottles preserved at pH 5, when compared to samples
collected from a HDPE bottle immediately preserved to a pH less than 2. This statistical
difference was also seen in the duplicate glass bottle preserved at pH 5, but not in the original
glass bottle. The original glass bottle showed no significant difference to the preserved glass
bottle because the average included skewed results. The averaged concentration included
concentrations as high as 53.8 ug/L lead to as low as 41.6 ug/L lead; therefore, the
concentrations influenced the average to represent an average close to the preserved bottle.
After maintaining the initial pH to a fixed level (pH of 2, 4, 5, 6 or 7) for 384 hours (i.e., 16
days), sample bottles were preserved further to either a preservation pH 4 (Figure 9a) or a
preservation pH less than 2 (Figure 9b). Although preservation was applied two days outside of
the restricted two-week time frame of EPA Method 200.8, a preservation pH less than 2 had
greater lead recovery compared to a preservation pH of 4, for the condition of initial pH 5 in both
glass and HDPE bottles. The glass sample bottle preserved to a pH of 4 recovered 89.39% of the
lead, whereas the duplicate bottle that was preserved to a pH of less than 2 recovered 94.78% of
lead. As seen in Figure 9a, there was a slight decrease in lead recovery after preserving the
HDPE pH 5 bottle to pH 4. At pH 5 the bottle recovered 90.9% lead and decreased to 89.4% lead
recovery after further preservation to pH 4. Whereas after preserving the duplicate pH 5 bottle to
a pH less than 2, an increase in lead recovery was observed from 91.1% to 91.8% lead. Although
an increase was seen in glass and HDPE bottles preserved to a pH less than 2, there was still a
significant difference in lead recovery when compared to the bottles immediately preserved to
pH less than 2.
24
-------
At an initial pH 6, the lowest lead recovery of 86.8% was observed in the glass duplicate bottle
(Figure 9a). After further preserving these samples to a pH 4 or pH less than 2, there was no
significant difference in lead recovery in HDPE bottles by applying either preservation.
However, lead recovery was significantly different in glass bottles based on the preservation
applied. When preserved to a pH less than 2, lead recovery was 96.8%, differing from the 88.6%
lead recovery after applying a preservation pH 4. As seen with the preservation pH 5, a decrease
in lead recovery was observed for pH 6 after applying the preservation pH 4. These lead
recoveries were still significantly different from the recoveries of the immediately preserved
bottle.
Finally, when comparing all initial preservation pHs, the lowest lead recovery was seen in glass
bottles preserved to pH 7. Calculating from Figure 9b, the initial preservation pH of 7 yielded a
42.5 % lead recovery on average. The duplicate bottle (Figure 9a) yielded a 63.5% recovery on
average. After further preservation within the glass bottles, lead recovery increased significantly.
When preserved to pH 4, lead recovery increased to 87.1%. When preserved to pH less than 2,
lead recovery increased to 94.6%. This increase was not observed in FtDPE bottles; both showed
an insignificant decrease in lead recovery after the same preservation was applied. Although
these two FtDPE bottles showed a decrease, they were significantly different from one another
throughout the entire trial. Glass bottles only exhibited a significant difference in lead recovery
after further preservations were applied. These differences indicated that there was variability
among duplicate FtDPE bottles when preserved to pH 7 and a significantly low lead recovery in
glass bottles at this pH in deionized water.
25
-------
5.7.5 Investigation of Possible Lead Contamination in HDPE Bottles
After observing an increase of lead concentrations greater than the 50 ug/L spiked concentration,
an additional trial was performed to investigate lead recovery in "blank" HDPE bottles (i.e., no
lead was added to the water sample). Fifteen HDPE bottles were filled with 500 mL DI water
and preserved to a pH less than 2 using HNOs. Among these HDPE bottles, there was one
occurrence where lead concentrations increased over time to 12.2 ug/L. As seen in Figure 10,
any lead recovery above 100% within the HDPE bottles from the DI, surface and ground trials
was very similar to the increase found in that one blank HDPE bottle. The increase in lead
concentration within these bottles was therefore attributed to random lead contamination.
140.0
24 4S 72 96 12O 144 16B 192 216 24O 264 2SS 312 336 36O
DI Unpreserved HDPE
Surface Preserved HDPE
Ground Preserved HDPE
Spiked Concentration
Blank Preserved HDPE
Pb concentration in Qe ionized Unpreserved (pH 7-3) HDPE sample bottle at336hours; This Earn pie was preserved to a pH < 2 after this col lection
Figure 10. Lead recovery (%) in HDPE bottles preserved to pH < 2, and in one "blank" HDPE bottle preserved
to pH < 2.
26
-------
5.2 Phase Two: Particulate Lead Recovery
5.2.1 Total Recoverable Metals using the standard preservation
The standard approach for determination of metal content on drinking water samples, with
turbidity <1 NTU , is to acidify the sample to pH <2 with 0.15% HNO3, wait 16 hours
(minimum) and then directly analyze the sample by IPC-MS according to EPA Method 200.8.
The effectiveness of this approach was evaluated against the three lead compounds, lead IV
oxide basic lead carbonate, and lead orthophosphate. Approximately 10 mg of each compound
was added to 200 mL DI water, in duplicate, and then acidified to pH < 2 with HNOs. The
solutions were sampled periodically over a one week holding period. The bottles were shaken
prior to sampling. Aliquots were taken in triplicate, filtered through a 0.45 jim nylon syringe
filter and the nitric acid concentration was adjusted to 2% prior to ICP-MS analysis.
Pb3(PO4)2(a)
Pb3(PO4)2(b)
(PbCO3)2.Pb(OH)2(a)
(PbCO3)2.Pb(OH)2(b)
PbO2 (a)
PbO2 (b)
345
Time (Days)
Figure 11. Dissolution of lead orthophosphate, basic lead carbonate and lead (IV) oxide, with standard
preservation to pH < 2 with nitric acid.
27
-------
The lead carbonate and lead phosphate (lead (II) compounds) were solubilized within a one week
period with the standard pH 2 (i.e., 0.15% nitric acid) preservation procedure (Figure 11). The
lead (IV) oxide was only minimally dissolved ( < 2%) over this time period (Figure 11). This is
consistent with the higher-oxidized metal being relatively inert in the dilute nitric acid (0.024 N)
at room temperatures.
5.2.2 Determination of suspended and/or settled paniculate
Section 11.2.2 of USEPA Method 200.8 states that "For the determination of total recoverable
analytes in aqueous samples of >1 NTU turbidity, transfer a 100 mL (±1 mL) aliquot from a
well-mixed, acid preserved sample to a 250-mL Griffin beaker. (When necessary, smaller sample
aliquot volumes may be used)". This approach is recommended for drinking water samples when
undissolved paniculate matter is suspected.
The three lead compounds were used to determine the efficacy of the wet digestion nitric
acid/hydrochloric acid procedure detailed in the method for the dissolution of these solids
(Figure 1). The lead compounds were weighed in triplicate, then directly transferred to the
digestion vessels and processed according to the method with the addition of 2 mL HNOs (from
1:1 solution), 1 mL of HC1 (from 1:1 solution) and 30 mL DI water. They were then covered
with an elevated watch glass and placed on an 85°C hot plate for solution reflux for a minimum
of one hour. Samples were then reconstituted and analyzed by ICP-MS.
28
-------
Table 2. Dissolution of basic lead carbonate, lead orthophosphate and lead (IV) oxide,
with enhanced nitric acid and hydrochloric acid digestion
Compound
Lead Carbonate Basic
(PbC03)2.Pb(OH)2
Lead Orthophosphate
Pb3(P04)2
Lead (IV) Oxide
PbO2
Pb
initial
(mg)
8.2
8.49
8.3
7.87
6.64
5.22
10.1
8.95
9.12
Pb
recovered
(mg)
7.88
8.01
8.1
7.5
6.25
4.88
9.74
8.72
8.98
Recovery
%
95.4%
94.7%
95.5%
95.3%
94.0%
93.6%
92.5%
97.9%
93.0%
The digestion procedure was able to dissolve and quantify approximately 95% of the initial
particulate compound (Table 2). Therefore, if a representative aliquot of the sample can be
obtained, the digestion procedure can, in these cases, achieve dissolution of the target
compounds.
5.2.3 Investigation of accuracy and precision ofaliquoting multiphase samples
The method prescribes the collection of a "well-mixed" sample prior to the digestion procedure.
Depending on the nature of the solids present, this collection may be difficult to achieve. This is
particularly the case if the solids are not well dispersed and/or are significantly massive in nature,
as to preclude homogeneous mechanical dispersion during sampling.
29
-------
The ability to obtain a representative fraction of a sample containing particulate material (i.e. a
"well mixed" homogeneous sample) was evaluated with the standard preservation resistant
compound lead (IV) oxide. Sample agitation can be produced by physical shaking of the bottle
prior to sampling or use of magnetic stir bar during sampling. Tests with a magnetic stir bar
proved problematic when utilized for agitation of a lead (IV) oxide and DI water preserved with
0.15% HNOs. This was because PbC>2 was found to have been incorporated into the Teflon
coating of the stir bar, with the inevitable impact on sample integrity. Further studies employed
physical shaking of the bottle for sample dispersion.
20 mg of lead (IV) oxide (i.e., PbC^) was dispersed in 200 mL of DI water preserved with 0.15%
HNOs, held for 24 hours and then sampled. The bottles were agitated and six aliquots were
taken, three of which were filtered (0.45 jim nylon) and three remained unfiltered. All were then
processed through the acid digestion procedure as detailed in Method 200.8.
Table 3. Particulate PbO2 recovery in acid preserved samples with nitric and
hydrochloric acid digestion.
Sample ID
digest 1
digest 2
digest 3
digest 4
digest 5
digest 6
Process
unfiltered
unfiltered
unfiltered
filtered
filtered
filtered
Pb (mg/L)
25.6
24.5
29.4
1.52
1.52
1.64
Recovery
30.7%
29.4%
35.3%
1.82%
1.82%
1.96%
The replicate sampling yielded reasonably consistent determinations for suspended particulate
but the total recoveries were low (Table 3), consistent with the observation that settling occurred
during the aliquoting procedure. The collection of a well mixed sample was determined to be not
feasible under these conditions. This observation points to a larger concern; that a sample may
contain only one particle, or a few, or a large number with a wide size and specific gravity range.
Any of these situations would make the collection of a representative sample difficult. A new
approach would be required.
30
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5.2.4 Evaluation ofin-situ solubilization of multiphase samples
One approach would be to determine the effect of increasing the acid concentration of the
preservation procedure in the original sample bottle, thereby affecting digestion in-situ. This
would eliminate the difficulty encountered when attempting to analyze a subset of the original
sample. The ICP-MS analytical procedure requires the sample matrix to be adjusted to 2% nitric
acid prior to analysis, to ensure sample stability and eliminate memory effects in the sample
introduction pathway. Therefore 2% nitric acid addition was chosen as a base concentration for
this series of experiments. Hydrochloric acid was added to the sample in varying concentrations.
Approximately 10 mg of lead (IV) oxide (PbO2) was dispersed in 200 mL DI water with 2%
nitric acid. Hydrochloric acid was added at three concentrations of 0, 1 and 2%. Samples were
prepared in duplicate. The solutions were sampled periodically over a one-week holding period.
The bottles were shaken prior to sampling. Aliquots were taken in triplicate, and filtered through
a 0.45 |im nylon syringe filter to determine the dissolved lead component. The samples were
then analyzed by ICP-MS.
2%HNO30%HCI
2%HNO30%HCI
2%HNO3 1%HCI
2%HNO3 1%HCI
2%HNO32%HCI
2%HNO32%HCI
0123456
Time (Days)
Figure 12. Participate Pb(IV) oxide recovery with nitric and hydrochloric acid preservation.
31
-------
I 70°/° -
8 60% -
•a 50%
40% -
30%
20%
10%
0%
0
345
Time (Days)
•2%HNO30%HCI
2%HNO30%HCI
2%HNO3 1%HCI
2%HNO3 1%HCI
•2%HNO32%HCI
2%HNO32%HCI
Figure 13. Participate (PbCO3)2.Pb(OH)2 recovery with nitric and hydrochloric acid preservation.
2%HNO30%HCI
2%HNO30%HCI
2%HNO3 1%HCI
2%HNO3 1%HCI
2%HNO32%HCI
2%HNO32%HCI
345
Time (Days)
Figure 14. Participate Pb3(PO4)2 recovery with nitric and hydrochloric acid preservation.
32
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The results for the lead carbonate (Figure 13) and lead phosphate (Figure 14) were similar to the
results with the 0.15% HNOs preservation experiments. Both exhibited recoveries in the 90 -
100% range after one week. These compounds are easily solubilized in low pH waters. The lead
(IV) oxide was solubilized only in a hydrochloric acid matrix (Figure 12). The reduction of Pb
(IV) to Pb (II) and the oxidation of chloride to chlorine in an acid matrix, are well documented
thermodynamic principles1:
PbO2 + 4 HC1 -> PbCl4 + 2H2O
PbCl4 -> PbCl2 + C12
5.2.5 Evaluation of a pre-filtration procedure for the analysis of multiphase samples
A pre-filtration approach, where the sample is filtered to allow processing of the particulate
matter in a separate digestion procedure, would constitute a viable alternative to the problems
associated with obtaining a "well mixed" representative aliquot for lead determinations. The
procedure would require the sample to be filtered through a 0.45 jim filter, after which the
filtered particulate and the filtrate portions would be digested according to the nitric/
hydrochloric acid procedure in EPA Method 200.8.
Approximately 10 mg of lead (IV) oxide (PbO2) was dispersed in 200 mL DI with 0.15% nitric
acid and was allowed to equilibrate for one week. The samples were then filtered through
0.45|im, 47mm HA filters (Millipore, Billerica, MA). The filter and filtration apparatus, stainless
steel pressure vessels (Gelman Sciences, Ann Arbor, MI), were pre-cleaned with 250 mL, 0.15%
nitric acid prior to each sample filtration. The filtered particles were then processed through the
nitric/ hydrochloric acid digestion process along with a 30 mL aliquot of the filtrate solution. The
1 Descriptive Inorganic Chemistry, Third Edition - Geoff Rayner-Canham, Tina Overton, Macmillan,
2003
33
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samples were then reconstituted with DI water and analyzed by ICP-MS. Digestion blanks and a
dissolved lead standard were concurrently processed.
Table 4. Participate PbO2 recovery through an alternative pre-filtration procedure.
Sample
ID
1
2
3
PbStd
Blank
Blank
PbO2
(mg)
13.08
11.27
10.25
0
0
0
Pb
Initial
(mg)
11.33
9.76
8.88
2.00
0.00
0.00
Filter
(mg)
10.155
8.139
7.812
0.024
0.022
0.013
Filtrate
(mg)
0.177
0.171
0.123
1.953
0.016
0.013
Pb
Total
(mg)
10.332
8.310
7.935
1.977
0.038
0.026
Pb
Recovery
91.2%
85.1%
89.4%
98.8%
The results indicate that the total Pb recoveries for the PbC>2 samples averaged 88.6% recovery
(Table 4). The relatively low recoveries were attributed to losses within the filtration hardware.
The parti culate was observed to adhere to the sides of the metal jacket during filtration and was
difficult to remove quantitatively. The dissolved lead standard recovery of 98.8% indicates the
dissolved lead component of a sample is not significantly impacted by the filtration process. The
background level of lead contamination in the blanks, 26-38 jig (Table 4), points to a larger
concern with the approach in general. While this process could be ultimately enhanced to allow
improved recoveries, the additional sample handling provides an opportunity for increased
exposure to laboratory contamination.
34
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6.0 Conclusions
Phase One
Unpreserved glass bottles showed a significant decrease in lead concentration prior to
acidification in all water sources. After acidification to a pH less than two, the lead recovery
increased and showed no significant difference to the immediately preserved bottle in the DI,
surface, ground and DI spiked with Ca trial. Within these glass bottles, DI water showed the
greatest decrease, followed by ground water, surface water, then DI water spiked with Ca.
In the trials investigating the relationship between lead recovery and preservation pH in DI water
samples, as pH increased, lead recovery decreased. As also seen within the other water source
trials, the lowest lead recovery occurred in glass bottles preserved to pH 7 in this trial.
It was also determined that pH 4 was not an optimal preservation pH, because it did not always
yield as high of a lead recovery as pH less than 2. In some cases, there was a significant
difference between preservation to pH 4 and to a pH less than 2. This difference was seen in DI,
surface and ground water samples collected in glass bottles. However, this difference was not
seen in the bottles containing DI water spiked with 100 mg/L Ca. It is suspected that the high
concentration of Ca present within the matrix influences lead recovery. Lead and calcium
compete for the active sorption sites on the bottle's surface. It can be inferred from the results
that calcium occupied the sorption sites, forcing lead to remain in solution at both preservation
pHs.
Overall, all samples preserved to pH less than 2 recovered greater than 90% of the initial spiked
dissolved lead concentration of 50 |ig/L, independent of sample container type and delays in
acidification.
Phase Two
Recovery of lead particulates was more problematic than recovery of dissolved lead. A "well
mixed" acid preserved sample was not always attainable, due to particulate inhomogeneity even
if samples were vigorously agitated prior to aliquoting. A concentration of 2% HNOs and 1%
35
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HC1 provided complete solubilization of the three investigated lead compounds. This techniqu
would require the addition of large amounts of reasonably expensive high purity acids (i.e., 20
mL nitric and 10 mL hydrochloric acid) to the 1L water samples mandated in the LCR. An
alternative pre-filtration procedure offers advantages over the digestion procedure, specifically
given the lower cost associated with the acid requirements. However, recovery of lead was not
complete at 88.6% on average after the pre-filtration procedure.
36
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7.0 References
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Shock, M. R. Causes of Temporal Variability of Lead in Domestic Plumbing Systems.
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