REPORT - Thames-Coromandel District Council... · DETAILED BIOAVAILABILITY STUDY, MOANATAIARI...

November 2012

MOANATAIARI SUBDIVISION, THAMES

Detailed Bioavailability Study

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Report Number. 1278203624

Submitted to: Francois Pienaar Thames-Coromandel District Council Private Bag 515 Mackay St Thames

DETAILED BIOAVAILABILITY STUDY, MOANATAIARI

November 2012 Report No. 1278203624

Summary

The Moanataiari subdivision, Thames, is a contaminated site where arsenic and lead are key risk drivers.

Arsenic and lead concentrations in Moanataiari soils frequently exceed their respective Soil Contaminant

Standards (SCS) incorporated by reference in the National Environmental Standard for Assessing and

Managing Contaminants in Soil to Protect Human Health (NES). While the NES has not been triggered,

these elevated concentrations indicate that further assessment, management or remediation is advisable to

ensure that residents’ health is adequately protected.

One site-specific factor that is relevant to assessment of health risks at Moanataiari is how effectively the

human body absorbs arsenic and lead from these soils – their bioavailability.

At Moanataiari, arsenic and lead are derived from mining sources and were anticipated to be present in

mineral forms, with bioavailability significantly less than the 100 % that was conservatively assumed in the

derivation of the SCS. A realistic characterisation of arsenic and lead bioavailability, based on their

measured bioaccessibility, would produce site-specific soil guideline values greater than the SCS, reducing

or even avoiding the need for costly and intrusive intervention.

The Relative Bioaccessibility Leaching Protocol (RBALP) was developed specifically to estimate arsenic and

lead bioavailability in soils. The USEPA has validated the RBALP for both elements and approved it for use

in health risk assessments. It can appropriately be applied to Moanataiari, as the validation experiments

included similar soils, where contaminants were also derived from mining sources.

In a combined dataset of 32 soil samples analysed using the RBALP from this study, supplementing 16

samples from an initial study, the mean arsenic bioavailability is estimated to be less than 27 %. Lead

bioavailability tends to be higher when total lead is high; for samples with more than 400 mg/kg, the mean

lead bioavailability is estimated to be less than 57 %. These values are recommended for use in site-specific

health risk assessment.


November 2012 Report No. 1278203624 i

Table of Contents

1.0 INTRODUCTION ........................................................................................................................................................ 1

1.1 Purpose ........................................................................................................................................................ 1

1.2 Context ......................................................................................................................................................... 1

1.3 Objectives ..................................................................................................................................................... 1

1.4 Scope ........................................................................................................................................................... 2

2.0 BACKGROUND ......................................................................................................................................................... 3

2.1 Introduction ................................................................................................................................................... 3

2.2 Moanataiari ................................................................................................................................................... 3

2.3 Bioavailability and Bioaccessibility ................................................................................................................ 5

3.0 VALIDATION OF THE BIOACCESSIBILITY METHOD ............................................................................................ 6

3.1 Introduction ................................................................................................................................................... 6

3.2 Regulatory Criteria ........................................................................................................................................ 7

3.3 Regulatory Acceptance ............................................................................................................................... 10

3.4 Application to Moanataiari .......................................................................................................................... 11

4.0 ADDITIONAL SOIL SAMPLING .............................................................................................................................. 11

4.1 Introduction ................................................................................................................................................. 11

4.2 Sampling Locations .................................................................................................................................... 11

4.3 Quality Assurance ....................................................................................................................................... 14

4.4 Supporting Soil Analysis ............................................................................................................................. 14

5.0 RESULTS ................................................................................................................................................................ 15

5.1 Introduction ................................................................................................................................................. 15

5.2 Bioaccessibility ........................................................................................................................................... 15

5.3 Quality Assurance ....................................................................................................................................... 17

5.4 Supporting Analysis .................................................................................................................................... 17

6.0 DISCUSSION ........................................................................................................................................................... 20

6.1 Introduction ................................................................................................................................................. 20

6.2 Bioavailability .............................................................................................................................................. 20

6.3 Supporting Evidence ................................................................................................................................... 21

6.4 Sources of Uncertainty ............................................................................................................................... 22

6.5 Comparison to Other Studies ..................................................................................................................... 22


November 2012 Report No. 1278203624 ii

7.0 CONCLUSIONS ....................................................................................................................................................... 23

8.0 REFERENCES ......................................................................................................................................................... 23

TABLES

Table 1: Arsenic and lead binding phases by relative bioavailability. .................................................................................. 8

Table 2: Particle size distributions. .................................................................................................................................... 19

Table 3: Contaminants of concern in different size fractions of selected samples*. .......................................................... 20

FIGURES

Figure 1: Moanataiari from above. ...................................................................................................................................... 4

Figure 2: Existing and proposed sample location plan. ..................................................................................................... 13

Figure 3: Arsenic bioaccessibility in Moanataiari soils compared to total extractable arsenic. .......................................... 16

Figure 4: Lead bioaccessibility in Moanataiari soils is weakly related to total extractable lead. ........................................ 16

Figure 5: Arsenic bioaccessibility in Moanataiari soils as a function of phosphorus content. ............................................ 18

Figure 6: Arsenic bioaccessibility in Moanataiari soils as a function of phosphorus:iron ratio. .......................................... 19

APPENDIX A Report Limitations

APPENDIX B Relative Bioavailability Leaching Procedure – Standard Operating Protocol

APPENDIX C Relative Bioavailability Leaching Procedure – Validation Reports

APPENDIX D Field Records and Chain of Custody Documents

APPENDIX E Certificates of Analysis and Certification of Reference Material

APPENDIX F Bioaccessibility Analysis Report, Golder Associates, Canada

APPENDIX G Bioaccessibility Datasets and Statistical Analyses

APPENDIX H X-ray powder diffraction spectra


November 2012 Report No. 1278203624 iii

Abbreviations

BARC Bioaccessibility Research Canada

CSM conceptual site model

FS the bioaccessibility feasibility study (Golder 2012b)

Golder Golder Associates (NZ) Limited

Hill Labs R.J. Hill Laboratories Limited

IVBA In Vitro Bioaccessibility Assay

m bgl metres below ground level

pH negative of the logarithm of the hydrogen ion concentration

NES National Environmental Standard

RBALP Relative Bioaccessibility Leaching Protocol

SCS Soil Contaminant Standards

SGV soil guideline value

TCDC Thames-Coromandel District Council

T&T Tonkin and Taylor Limited

UCL95 95th percentile upper confidence limit to the mean

XRD X-ray diffraction analysis


November 2012 Report No. 1278203624 1

1.0 INTRODUCTION

1.1 Purpose

This report1 presents a study of bioaccessibility of arsenic and lead in soils of the Moanataiari subdivision,

Thames, Waikato. It provides scientific justification for the use of bioaccessibility testing at Moanataiari.

It proposes bioavailability values for arsenic and lead to be used in the human health risk assessment for the

site.

1.2 Context

Arsenic and lead concentrations in Moanataiari soils frequently exceed their respective Soil Contaminant

Standards (SCS) incorporated by reference in the National Environmental Standard for Assessing and

Managing Contaminants in Soil to Protect Human Health (NES). While the NES has not been triggered,

these elevated concentrations indicate that further assessment, management or remediation is advisable to

ensure that residents’ health is adequately protected (T&T 2012).

One site-specific factor that is relevant to assessment of health risks at Moanataiari is how effectively the

human body absorbs arsenic and lead from these soils – their bioavailability.

In a recent bioaccessibility feasibility study of Moanataiari soil (‘the FS’: Golder 2012b), 20 soil samples from

around the subdivision were analysed using the Relative Bioaccessibility Leaching Protocol (RBALP), which

evaluates the potential effectiveness of trace element absorption from swallowed soil. Arsenic

bioaccessibility was generally very low at less than 10 %. Lead bioaccessibility was higher in soils with

higher total lead concentrations; approximately 70 % for soils containing more than 300 mg/kg lead.

From a health perspective, it follows that acceptable concentrations of arsenic and lead in Moanataiari soil

may be higher than at other New Zealand sites where arsenic and lead is present in more bioavailable

forms. The SCS for arsenic and lead conservatively assume 100 % bioavailability (MfE 2011a). A realistic

characterisation of arsenic and lead bioavailability, based on their measured bioaccessibility, would produce

site-specific soil guideline values greater than the SCS. If this is appropriate, the potential health risk faced

by many residents may not be as high as it initially appeared from comparison with the SCS; many

properties may not require costly and intrusive management or remediation to achieve a health-protective

outcome.

1.3 Objectives

This detailed bioaccessibility study aims to:

Provide scientific justification supporting the use of the RBALP method to estimate arsenic and lead

bioavailability at Moanataiari.

Collect sufficient additional bioaccessibility data, using the same RBALP method as in the FS, to

accurately determine arsenic and lead bioaccessibility at Moanataiari.

Generate bioavailability parameters for use in subsequent site-specific human health risk assessment.

1 This report is provided subject to the limitations set out in Appendix A.



1.4 Scope

The commissioned scope of this investigation, as set out in Golder proposal 1278203624-007-P and

amplified by Thames-Coromandel District Council (TCDC) instruction, is to:

Summarise the use and role of bioaccessibility in risk assessments by international regulatory agencies

(covered in Section 3.0 of this report).

Summarise the science behind the use of gastric extraction analysis as a means of estimating arsenic

and lead bioavailability to people who ingest soil (Section 3.0).

Summarise bioaccessibility method validation (Section 3.0).

Compare bioaccessibility results from Moanataiari to results from other studies in New Zealand and

internationally (Section 6.0).

Design a detailed investigation that will provide a broader assessment of arsenic and lead

bioaccessibility in Moanataiari soil, meet data quality objectives, and support subsequent site-specific

health risk assessment (Section 4.0).

Carry out soil sampling at Moanataiari, including arranging access to properties (Section 4.0).

Have soil samples analysed for appropriate chemical parameters by RJ Hill Laboratories Limited (Hill

Labs) in Hamilton, including (Sections 4.0 and 5.0):

bioaccessibility analysis for arsenic and lead in the <250 µm fraction of soil samples, via the RBALP

method developed by Ruby and Drexler (Ruby et al. 1996, Drexler & Brattin 2007, USEPA 2008)

that was used in the FS;

total extractable arsenic and lead in the <2 mm, <250 µm and some <63 µm fractions; and

bioaccessible and total extractable arsenic and lead in a standard reference material.

Report duplicate bioaccessibility analyses of approximately 10 samples and the same standard

reference material at the Golder laboratory in Mississauga, Canada, which frequently conducts these

analyses for North American projects, and is a participating laboratory in a bioaccessibility comparative

testing programme (Sections 4.0 and 5.0: Golder 2012d, Appendix G).

Support the geochemical conceptual model of Moanataiari soils developed in the initial bioaccessibility

study by conducting further geochemical analyses (Sections 4.0 and 5.0):

determine total extractable iron and manganese, phosphate, and pH in soil samples, as well as

acid-soluble sulfide and acid-insoluble sulfide in selected samples (Hill Labs);

characterise mineral phases in selected soil samples, using gravimetric separation and powder

X-ray diffraction analysis (University of Canterbury/University of Otago); and

assess the particle size distribution in select samples (down to 63 µm).

Interpret geochemical analyses with reference to the conceptual site model (CSM) (Section 6.0).

Generate bioavailability values for subsequent health risk assessment (Section 6.0).

Identify remaining sources of uncertainty (Section 6.0).



2.0 BACKGROUND

2.1 Introduction

To place this study in context, this section first outlines the CSM for Moanataiari, and then discusses the key

terms bioavailability and bioaccessibility.

2.2 Moanataiari

The Moanataiari subdivision is part of the coastal township of Thames, on the west of the Coromandel

Peninsula in the Waikato. It is a well-known contaminated site that has been subject to several

investigations (summarised in T&T 2012, and see Golder 2012b). Figure 1 presents an aerial view of the

subdivision. The CSM that emerges from previous investigations is outlined below:

Geological sources

The geology of the Thames area is dominated by an epithermal deposit of heavily faulted pyroxene andesite.

Hydrothermal alteration of andesite flows formed a series of quartz veins containing gold and other

chalcophilic elements (those that tend to form minerals in combination with sulfur) such as arsenic and lead.

These veins were the target of historic mining in the area.

The relative concentrations of chalcophilic elements in the faulted system are controlled by the depth at

which hydrothermal alteration occurred. Lead and copper are predominantly present in earlier stage

(deeper) rock, arsenic is associated with middle stage (intermediate depth) geochemical environments that

favour gold, and mercury is restricted to later stage (shallower) mineralisation. As a result of subsequent

faulting in the vicinity of Thames, lead is most common within the Tararu Stream catchment, mercury in the

Kauaeranga catchment, and gold between these two areas.

The land beneath the Moanataiari subdivision was gradually reclaimed from the Firth of Thames between the

1870s and 1970s using wastes from historic mining activities around the Thames township, and to some

extent from other local sources. In the last phase of development, ending around 1980, areas west of

Centennial Avenue were filled up to the desired level using material from the hillside immediately to the east

of the subdivision, which was also part of the mined area (Golder 2012a). Today, soil and rock on this

hillside contains arsenic well above ordinary Waikato background levels (refer T&T 2012).

Contaminants of concern

These geological and anthropogenic processes left Moanataiari soils contaminated with a series of trace

elements. When laboratory data from residential soils (T&T 2012) is subjected to statistical analysis, two

independent groups of trace elements can be discerned: an arsenic-antimony-mercury-thallium association,

found particularly in deeper soils, and a cadmium-chromium-lead-zinc association, found particularly in

surface soils. These most likely reflect materials mined from different locations.

The detailed site investigation (T&T 2012) included 409 laboratory analyses of soil samples, from almost

every residential property in Moanataiari. Key information from this data set included:

Arsenic exceeds its SCS of 20 mg/kg for typical residential use in 86 % of samples, with a maximum of

4,700 mg/kg.

Lead exceeds its SCS of 210 mg/kg in 16 % of samples, with a maximum of 7,200 mg/kg; cadmium

exceeds its SCS of 3 mg/kg in seven samples (<2 % exceedance), with a maximum of 22 mg/kg.

Thallium exceeds a site-specific SGV (soil guideline value) of 1.2 mg/kg (there is no SCS for thallium:

refer Golder 2012c) in 23 % of samples, with a maximum of 26 mg/kg.

Concentrations of all these trace elements are generally higher in the east of Moanataiari than in the west.

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Exposure pathways

The contaminants of concern are elevated in surface soils. Wherever there is no protective cover of turf,

foundations or roadways, or when there are excavations, the contaminants are available in dirt and dust for

incidental soil ingestion, vegetable consumption, skin contact, and soil-derived dust inhalation.

Moanataiari residents are on reticulated potable water supply; groundwater is not used for any purpose.

However, in the immediate vicinity of the site, any contact with groundwater during ground works or sampling

would constitute an exposure pathway.

Receptors

The Moanataiari subdivision comprises just over 200 residential properties and is home to people of all ages.

Children, especially toddlers, are likely to have the highest exposure to contaminants in soil and dust,

through play activities and through putting hands, toys and soil in their mouths.

Water receptors are unlikely to be sensitive in themselves. Groundwater is understood to be brackish and

not suitable for future use. Groundwater contamination generated by impacted soils entering surface water

will be rapidly diluted by tidal action.

2.3 Bioavailability and Bioaccessibility

There are two terms that are central to this report – bioavailability and bioaccessibility. These are properties

of contaminants in soils, ideally equivalent in value but determined in different ways. This subsection

introduces the reader to these concepts.

The chemical relationships between trace elements and soils are complex. Most trace elements can take

many different chemical forms in the soil environment. Depending on the element, these forms can include

oxides and sulfides, carbonates and phosphates, complexes with iron or calcium – coatings on particles of

iron or manganese oxides, associations with humic (organic) materials or sorbed to the surface of clay

minerals.

The actual mix of chemical forms present in any specific soil depends on a host of factors. Key factors

include soil acidity, degree of oxidation, the source of the trace elements, and ongoing biological and

geological processes.

When water comes into contact with soil, some forms of the trace elements that are present dissolve and

leach out, while other forms stay put. Water can be an effective leaching agent but it is very dependent on

water pH. Leaching occurs in natural soils as we often see a downward movement of elements such as iron

in soil profiles. If soils are exposed to stronger leaching agents (e.g., acids of various types), greater

proportions of some elements are leached.

Different leaching agents have been proposed and used to extract specific chemical forms of trace elements

from soils. The scientific literature on the subject is extensive, the classic paper being Tessier et al. (1979).

They proposed a sequential extraction method to operationally distinguish between five increasingly

intractable forms of trace elements – those that were readily exchangeable; those that were bound as

carbonates; those bound to iron or manganese oxides; those bound to organic matter; and the residual trace

elements in mineral form, which would not dissolve in a reasonable time frame under common environmental

conditions.

Which chemical forms are extracted when soils containing trace elements are exposed to the leaching

conditions in the human digestive system? This is a question with practical significance to assessments

such as that undertaken at Moanataiari. Those forms of a trace element that dissolve in digestive fluids can

be absorbed through the linings of stomach and intestines. This ‘bioavailable’ fraction enters the

bloodstream and is transported to different parts of the body. Each element has its own profile of what

happens during its transport around the body in terms of whether it is excreted, stored in a specific location

(e.g., bone, brain etc.). The fraction (in the soil) that is not dissolved and absorbed is eventually expelled

from the digestive system along with other solid waste.



Definition 1. The bioavailability of a trace element is the proportion of that element that is absorbed from

soil in the digestive system into the body.2

However, bioavailability of trace elements is not generally determined directly from measurements in human

body tissues. There are practical collection difficulties, it is hard to attribute findings to a specific source, and

ethical issues can be significant. Bioavailability is typically measured using (in vivo) tests with animals that

are physiologically similar to people; piglets (“juvenile swine”) are considered a particularly good surrogate

for small children. But conducting live animal bioavailability tests on a site-by-site basis is time-intensive and

costly, even for a single test per site, and still poses ethical issues.

Site risk assessment needs accurate measures of exposure that can effectively be applied to large numbers

of samples. Various laboratory-based (in vitro) extraction procedures have been developed by researchers

to mimic biological ‘extraction’ using simulated digestive fluids. Dissolved trace elements in the simulated

biological fluid are then measured by standard analytical techniques. The result is called the ‘bioaccessible’

fraction – the fraction that is ‘accessible’ for absorption into the bloodstream if ingested.

Definition 2. The bioaccessibility of a trace element is the proportion of that element that can be

extracted under simulated digestive conditions.

The leading bioaccessibility test methods are:

The RBALP or In Vitro Bioaccessibility Assay (IVBA), one of the simpler methods, which simulates

stomach action via a 1-hour extraction at 37 °C in glycine buffer at pH 1.5 (see Appendix B for details).

This method has been validated against piglet bioavailability data for both arsenic and lead (see Section

3 on validation).

The Physiologically Based Extraction Test (PBET: Ruby et al. 1996, Rodriguez et al. 1999). This

simulation is more physiologically representative – the digestive solution contains the enzyme pepsin

and several simple organic acids. The stomach extraction phase is followed by an intestinal extraction

phase involving incubation at neutral pH with the addition of another enzyme, pancreatin, and bile salts.

It has been validated against piglet data for arsenic, lead and cadmium.

The unified Bioavailability Research Group of Europe (BARGE) method, which is even more

physiologically representative, has three extraction phases: saliva, stomach and intestine, using

complex extracting agents (Wragg et al. 2009). The BARGE method has also been validated against

piglet data for arsenic, lead and cadmium (Denys et al. 2012).

The RBALP method was selected for this study (and the FS) because it was simple, cheap and functional.

It did not matter that the RBALP could not be applied to cadmium, even though cadmium is a contaminant of

concern. The risk driver for cadmium in residential settings is not soil ingestion but consumption of home-

grown vegetables (MfE 2011a) and bioavailability is not relevant to that pathway.

3.0 VALIDATION OF THE BIOACCESSIBILITY METHOD

3.1 Introduction

One of the objectives of this study is to provide evidence that the bioaccessibility method accurately

simulates bioavailability, so it can be used to develop site-specific soil guideline levels for arsenic and lead at

Moanataiari. This section discusses the scientific evidence to support the bioaccessibility methods for

arsenic and lead, and demonstrates that their use at Moanataiari is appropriate.

2 This definition refers only to human oral bioavailability from soil – the bioavailability of trace elements from food or water, to other animals, to plants, or through skin or lung tissue

may be quite different. Some literature sources may use slightly different definitions.



3.2 Regulatory Criteria

In its ‘Guidance for evaluating the oral bioavailability of metals in soils for use in human health risk

assessment’, the United States Environmental Protection Agency (USEPA) recommends twelve criteria be

met before a test method is considered suitable for regulator use (USEPA 2007a). This section addresses

those criteria for the RBALP method for both arsenic and lead, principally by reference to the following

documents:

‘Estimation of relative bioavailability of lead in soil and soil-like materials using in vivo and in vitro

methods’, USEPA (2007b).

‘Validation assessment of in vitro lead bioaccessibility assay for predicting relative bioavailability of lead

in soils and soil-like materials at Superfund sites’, USEPA (2009).

‘Validation of an in vitro bioaccessibility test method for the estimation of the bioavailability of arsenic

from soil and sediment’, Griffin & Lowney (2012).

Full copies of these documents are provided in Appendix C. Note that the USEPA refers to this method (and

its output) as the ‘IVBA’ rather than the RBALP.

1) A scientific and regulatory rationale for the test method should be available, including a clear

statement of its proposed use.

For many contaminated sites, ingesting soil and dust containing arsenic and lead is a risk driver. Health risk

assessments traditionally assume that these elements have a default bioavailability of 100 %. This

assumption is deliberately conservative, set to provide maximum health protection. There was insufficient

information to support any lower value – while actual bioavailability values in soil are likely to be substantially

less than 100 %, bioavailability can vary substantially between and even within sites, based on soil

characteristics (MoH 2007, MfE 2011b). Contaminated land health risk assessments benefit greatly from

more accurate estimates of exposure, incorporating site-specific bioavailability values for key risk drivers

such as arsenic and lead.

Accordingly, the developers of the RBALP set out to create a simple, inexpensive bioaccessibility test

method from which arsenic and lead bioavailability could be estimated.

2) Relationship of the test method endpoint(s) to the biologic effect of interest must be described.

The RBALP was intended to accurately reproduce the results of existing live animal assays for soil arsenic

and lead bioavailability. In turn, the juvenile swine assay was specifically developed as an experimental

methodology for predicting bioavailability in children, though it can also be used for adults (USEPA 2009).3

For lead, these assays involve intravenous injection of lead acetate solution, followed by lead analysis in

blood, kidney, liver and bone. These four endpoints were considered to have equal reliability, so the overall

bioavailability is the mean of the four.

3) A detailed protocol for the test method is required, including a description of the materials

needed, a description of what is measured and how it is measured, acceptable test performance

criteria (e.g., positive and negative controls), a description of how data will be analysed, a list of

the species for which the test results are applicable, and a description of the known limitations

of the test including a description of the classes of materials that the test can and cannot

accurately assess.

The RBALP protocol is given in Appendix B. Bioaccessibility determined according to the method is related

to bioavailability in piglet assay according to the relationship established in Equations 1 and 2. The resulting

estimate of bioavailability is assumed to represent that in children since the RBALP was calibrated using

data from a piglet study. However, there is no reason not to use the results for evaluating adult exposures.

(USEPA 2009, Griffin & Lowney 2012).

3 For arsenic, validation experiments included a second group of soils for which a cynomolgus monkey assay was carried out. Ultimately, the monkey model was considered

interesting but less compelling, and results from those parts of the experiments were not recommended for use (USEPA 2012). This report does not discuss that model further.



Equation 1. Arsenic. ( )

Equation 2. Lead. ( )

The bioavailability predictions are central tendency estimates; the actual bioavailability will vary and may be

higher or lower than predicted due to inter-sample variability and/or error in measuring either bioaccessibility

or bioavailability. Note the high intercept in the arsenic equation, which means that the minimum

bioavailability that can be predicted is 19.7 %, even if the measured bioaccessibility is very close to zero.

This seems unlikely – the equation appears to have a conservative bias, over-predicting bioavailability at low

bioaccessibility.

The arsenic validation experiments with piglets included 20 soils with total arsenic concentrations ranging

from 181-3,957 mg/kg and arsenic bioavailability ranging from 17-62 %. The lead validation experiments

included 19 soils with total lead concentrations ranging from 1,270-14,200 mg/kg, and lead bioavailability

ranging from 6-105 %. Equations 1 and 2 are expected to apply throughout these concentration ranges.

Validation experiments also included a variety of controls including laboratory blanks and spikes, and NIST

standard reference soils. Responses were satisfactory. Recovery of arsenic from a soil spiked with sodium

arsenate, assumed to have 100 % bioavailability, was 96 %.

The RBALP method may still be applicable to samples with concentrations outside the validated ranges, but

there would be some additional uncertainty. For soluble forms of lead, the extraction fluid may become

saturated with lead at soil concentrations of 50,000 mg/kg or more, which would result in erroneously low

bioaccessibilities. While most of the validation soils were from mining and smelting sites, they constitute a

wide range of different soil types and binding phases. The major phases have been identified and roughly

quantified through electron microprobe analysis, and their relative bioavailability has been ordered as shown

in Table 1. The RBALP method might not predict trace element bioavailability accurately when other binding

phases are present.

Table 1: Arsenic and lead binding phases by relative bioavailability.

Trace element Low bioavailability Medium bioavailability High bioavailability

Arsenic

Mixed lead oxides Arsenopyrite Pyrite Arsenic trioxide Mixed arsenic oxides Slag

Lead arsenic oxides Iron oxyhydroxide Clay

Manganese oxyhydroxide Iron sulfate

Lead

Mixed iron sulfates Anglesite (lead sulfate) Galena (lead sulfide) Mixed lead oxides Mixed iron oxides

Lead phosphate Lead oxide

Cerussite (lead carbonate) Mixed manganese oxides

The RBALP method calls for soils to be sieved to less than 250 µm. This is not considered a limitation on

the method; this sieve size passes the particle sizes that are believed likely to be ingested by children, a

sensitive group targeted in health risk assessments.

4) The extent of within-test variability and the reproducibility of the test within and among

laboratories must have been demonstrated. The degree to which sample variability affects this

test reproducibility should be addressed.

For arsenic, the reproducibility of the RBALP method was evaluated by triplicate analysis of each of 12 soils

for each of three extraction fluids by each of four laboratories. Within-laboratory precision was evaluated by

examining the magnitude of the standard deviation for three replicate extraction results for each of 12 test



materials. Within-laboratory precision was typically less than 3 %, with an average of 0.8 % for all four

laboratories. Between-laboratory precision was evaluated by examining the between-laboratory variability in

the mean bioaccessibility values for each test soil. Between-laboratory variation in mean values was

generally less than 7 %, with an overall average of 3 %.

Experiments undertaken during validations showed that changing some experimental conditions can

significantly affect RBALP results for arsenic (Griffin & Lowney 2012):

Decreasing extraction acidity decreases bioaccessibility for most soils – the method contains

safeguards to ensure that pH does not increase by more than 0.5 units during the extraction.

Increasing extraction time gradually increases bioaccessibility.

Lowering extraction temperature decreases bioaccessibility.

Adding phosphate, which has chemical behaviour similar to arsenate, can have profound effects on

arsenic bioaccessibility for some soils, but hardly any effects on others.

Other variations have little or no effect on RBALP results for arsenic, including:

Adding the enzyme pepsin and a mixture of simple organic acids.

Changing filter pore size, or switching from filtration to centrifugation.

Adding the oxidising agent hypochlorite, or the reducing agent hydroxylamine hydrochloride.

For lead:

An inter-laboratory comparison of performance with four participants applied the RBALP method to

triplicate analyses of each of the 19 validation soils. Average within-laboratory coefficient of variation

ranged from 1.4-6.3 %, and the mean inter-laboratory coefficient of variation was 5.6 %, including two

samples that had coefficients of variation of 18.6 % and 29.7 %.

The University of Colorado at Boulder analysed standard reference material NIST SRM 2710 using the

RBALP method 75 times over several years, and the related NIST2711 83 times during the same

period. The mean coefficient of variation for both standards was 7 %.

These results demonstrate the RBALP method is highly repeatable and reproducible.

5) The test method performance must have been demonstrated using reference chemicals or test

agents representative of the types of substances to which the test method will be applied, and

should include both known positive and known negative agents.

See the discussions above for arsenic and lead concentrations and binding phases in validation soils.

6) There must be sufficient data to permit a comparison of the performance of a proposed

substitute test with that of the test it is designed to replace.

The RBALP developers explicitly related bioaccessibility to bioavailability for all validation soils. In doing so,

they had a data quality objective of a bioavailability-bioaccessibility correlation coefficient R2 of 0.64 or better.

This was achieved in both validation trials: for arsenic R2 was 0.723, for lead 0.924. The RBALP is expected

to yield bioavailability values within approximately 10 % of the values determined by piglet assay.

For lead, as well as the final linear model, the developers also examined power and exponential models

without significantly improving the quality of fit. For arsenic, a complex model which took the principal

binding phases into account was able to achieve R2 = 0.906, but the difficulty of routinely quantifying sample

mineralogy was deemed to be too great for this model to be practically useful. For both lead and arsenic a

predictive linear model was selected to relate bioavailability to the RBALP.



7) Data supporting the validity of a test method should be obtained and reported in accordance

with Good Laboratory Practices (GLPs).

The laboratories involved in the validation studies appear to have been GLP-compliant (see Appendix C).

8) Data supporting the assessment of the validity of the test method must be available for review.

This data is contained in the referenced reports (see Appendix C) and is also maintained on the USEPA

website at www.epa.gov/superfund/health/contaminants/bioavailability/guidance.htm

9) The methodology and results should have been subjected to independent scientific review.

Much of the lead validation study was reported in a peer-reviewed journal, Human and Ecological Risk

Assessment (Drexler & Brattin 2007). The arsenic validation study (Griffin & Lowney 2012) is based on the

same methods. All validation studies were subject to internal USEPA review.

10) The method should be time and cost effective.

The RBALP developers estimate that their method should cost around 5-10 % of piglet assays and take days

instead of months.

These figures assume that multiple samples are analysed by RBALP, but a single material is used for the

animal study, which requires a much larger sample. So RBALP can rapidly and inexpensively provide

information on the bioaccessibility across heterogeneous soils at a site, as well as information on

repeatability and reproducibility.

11) The method should be one that can be harmonised with similar testing requirements of other

agencies and international groups.

All agencies responsible for arsenic and lead contaminated sites face similar issues around bioavailability,

and benefit from an effective means of estimating bioavailability on a site-specific basis.

The RBALP method is not directly comparable with the leading European protocol, the unified BARGE

method, and they have not been formally cross-validated. In a 2010 interlaboratory exercise by

Bioaccessibility Research Canada, three labs used RBALP while one used BARGE. The latter arrived at

rather lower bioaccessibility values (BARC 2011), but when the RBALP results are converted to

bioavailability using Equations 1 and 2, much of the disparity disappears.

The BARGE protocol is superior to RBALP to the extent that it more accurately models physiological

conditions, and in validation experiments it generates bioaccessibility values more similar to bioavailability

measurements in animal tests (Denys et al. 2012). Moreover, the BARGE protocol has been validated for

cadmium, which the RBALP has not. However, by the same token, BARGE is considerably more complex,

which must make it more costly and time-consuming. In the end, the USEPA concluded that a rapid and

simple test with more available data and good validation would better serve the needs of the risk assessment

and regulatory community (USEPA 2009, Griffin & Lowney 2012).

12) The method must provide adequate consideration for the reduction, refinement, and

replacement of animal use.

The RBALP method is intended to replace animal assays in the long term. However, in the process it does

unfortunately require, in the short-term, animal assays for validation studies.

3.3 Regulatory Acceptance

The RBALP method has been validated for arsenic- and lead-contaminated sites where the trace elements

are present at moderate to high concentrations, originating from mining and smelting activities. It is also

applicable to other sites where the trace elements are present in any of the same mineral forms.



The USEPA considers the RBALP method “suitable for international acceptance”. While it is questionable

whether the USEPA has a mandate to make such pronouncements, it is clear that the RBALP method met

all of the USEPA’s internal criteria, without any obvious features that might restrict its use to only the United

States.

The RBALP has been used in several health risk assessments endorsed by regulatory agencies including

the USEPA and California EPA. A very similar protocol was used by the Ontario Ministry of the Environment

in a health risk assessment in 2002 (refer Golder 2012d, Appendix F).

Other bioaccessibility test methods have also found regulatory approval. The BARGE protocol has been

accepted by regulators in the Netherlands, Denmark and the United Kingdom. In two English contaminated

land projects, bioaccessibility testing reduced remedial costs by £7-30M and £3.75M respectively, reassured

residents and restarted the stalled housing market around one site (Cave 2012).

3.4 Application to Moanataiari

Moanataiari is a contaminated site where arsenic and lead are key risk drivers. These trace elements are

considered to be predominantly derived from mining sources. They are anticipated to be present in mineral

forms; sulfur-containing minerals such as arsenopyrite, orpiment and galena, and oxidised minerals such as

scorodite and anglesite. After weathering, arsenic and lead may be associated with iron and manganese-

rich particles (Golder 2012a,b).

The potential health risk faced by Moanataiari residents needs to be realistically assessed. Using generic

health risk assessment criteria – the SCS – would suggest costly and intrusive management or remediation

is likely to be required. However, if arsenic and lead bioavailability is low, intervention could be reduced and

perhaps even avoided.

As such, Moanataiari is precisely the kind of site that the RBALP was developed for. The RBALP has been

developed specifically for assessing arsenic and lead bioaccessibility. Several soils used in RBALP

validation experiments came from mining sites, all the above minerals (except orpiment) have been identified

in validation soils, and arsenic and lead in all these forms are expected to have bioavailability less than

100 % (USEPA 2007b, Griffin & Lowney 2012).

On the other hand, most lead and some arsenic concentrations at Moanataiari are below the validated range

for the RBALP. There is no indication that bias would be introduced into RBALP bioavailability estimates

when it is applied outside the validated range; however there could be an increased level of uncertainty in

the estimates.

4.0 ADDITIONAL SOIL SAMPLING

4.1 Introduction

An important objective of this study was to increase the amount of bioaccessibility data for Moanataiari, in

order to achieve a better spatial coverage, and support development of site-specific bioavailability

parameters for health risk assessment.

4.2 Sampling Locations

In the FS, 20 existing soil samples were analysed by RBALP. However, four of these samples were

collected from as deep as 1.1-1.0 m below ground level (m bgl); site residents are unlikely to be in regular

contact with these soils, and accordingly these samples are not considered further. The remaining 16



samples represent useful data but do not provide representative spatial coverage of the subdivision – there

were no surface soil bioaccessibility data for the western half of the site. Accordingly, additional soil samples

were collected to increase the robustness of the data set supporting RBALP development. The location,

quality assurance and supporting soil parameter data collected are discussed in the remainder of this

section.

The only obvious divisions of the Moanataiari site are the grid of roadways on and around the subdivision.

The grid forms eight blocks, which for the purposes of this investigation are numbered clockwise from the

northeast (see Figure 2). Note that Block 3 is actually a composite of two small blocks separated by

Coromandel Street, and Block 6 is about twice the size of any other block.

For contaminated land management purposes, the block is probably the smallest practical unit within the

subdivision. From a legal perspective, management decisions could be made title by title. But this would

lead to artificial and seemingly inequitable situations where, for example, gardening was acceptable on one

side of a fence but not in an apparently identical property on the other side. And it is difficult to conduct a

remedial excavation across a residential property without impacts to a neighbouring property from dust,

noise, vibration and disrupted utility services.

A key data quality objective for this investigation was to be able to confidently identify a ‘hot block’ – any

block where surface soils had significantly higher or lower bioavailability than the remainder of the site, and

therefore might require different management. Three well separated samples per block were considered to

be the minimum number necessary to achieve this objective. Achieving this sampling density, starting from

existing data, required 21 new locations, as shown on Figure 2.

Golder had no right of access to properties. It was necessary to obtain residents’ permission to enter onto

their land and collect soil samples. Residents living in suitably located properties were contacted by Golder,

using a TCDC community telephone list, to explain why further investigation was required on their property

and to request access. No residents who were contacted refused permission; however, residents often

could not be contacted, and enquiries then proceeded for sampling a neighbour’s property instead. Rental

properties were avoided, as good practice would require informed consent from both landlord and tenant

before entering onto a property, and tenant phone numbers were not available.

A second data quality objective was to restrict sampling to soils that were most relevant to health risk

assessment based upon current residential uses. These included vegetable gardens, flower gardens and

other areas of bare soil – areas that are expected to generate the most dirt and dust, and support the most

gardening/landscaping activity, therefore dominate the soil ingestion pathway. Raised garden beds were not

sampled, as based on discussions with TCDC it appeared that these would most likely be managed

separately from general soils in future. Exact locations of soil samples within a property were determined on

this basis by Golder field staff. At one property, 417 Fergusson Drive, the sample was collected from

underneath the house, where the householder stored wood, and exposure to soil-derived dust would have

been moderately frequent.

For the purposes of this report, soils are considered ‘shallow’ if they are beneath the significant root zone for

common vegetables, which is considered to be approximately 0.15 m bgl (MfE 2011c). Shallow soils are not

likely to be regularly disturbed, but could be exposed when digging holes for young trees, fence or deck

footings, inspecting utility pipework, etc. In this report, such excavations are not considered likely to extend

below approximately 0.6 m bgl.

Shallow soils at Moanataiari typically have higher arsenic and lead concentrations than surface soils, and

might occasionally be exposed by ground works. Arsenic and lead bioavailability in these soils was therefore

of interest. The same sampling density of three samples per block for shallow soils was readily achieved in

most blocks, by hand digging to a nominal 0.5 m bgl at 14 of the sampling locations and collecting a second

sample.

Golder field staff undertook soil sampling at selected locations between 14 and 15 August. The target

samples, 21 surface and 14 shallow soils, were collected without event. Field notes, location photographs

and chain of custody documents are included in Appendix D.

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4.3 Quality Assurance

A third data quality objective was to generate bioaccessibility data that was of demonstrably good quality.

To assess whether bioaccessibility analyses were repeatable, three randomly selected field duplicates were

collected. This achieved the usual industry practice of duplicating one sample in ten.

To assess whether bioavailability analyses were reproducible, a further 10 samples were collected in

sufficient quantity to enable Hill Labs to sieve them, homogenise and split each into two replicates. The

second replicate of each of these samples was sent to the Golder office in Mississauga, Ontario, Canada, for

replicate RBALP extraction. This Golder office frequently conducts RBALP extractions, and participates in

Bioaccessibility Research Canada (BARC) interlaboratory comparison experiments. Elemental analysis of

the resulting extracts was subcontracted to AGAT Laboratories, a nearby accredited analytical laboratory.

To assess whether bioaccessibility analyses were accurate, both Hill Labs and the Canadian laboratories

also analysed a standard reference material, NIST2711a, from near a smelter in Helena, Montana, USA.

This material is certified to contain 107 ± 5 mg/kg arsenic and 1,400 ± 10 mg/kg lead (Appendix E). Lead

bioaccessibility by RBALP for NIST2711a is in the range 85.7 ± 10.5 %. NIST2711a is a recent replacement

of NIST2711, a standard reference material from the same location that is no longer available, which has

been reported to have RBALP bioaccessibility of 58.3 ± 9.4 %. In NIST2710, a standard reference soil from

the same general location but with considerably higher trace element concentrations, arsenic is bound to iron

and manganese oxyhydroxides and sulfates (Griffin & Lowney 2012).

Hill Labs currently hold ISO 17025:2005 accreditation as a testing and calibration laboratory, for services

including environmental monitoring of soils and sludges, specifically including determination of acid-

extractable arsenic, lead and other trace elements by inductively coupled plasma spectroscopy with mass

spectrometry. The accreditation also includes other trace element extraction methods not dissimilar to the

RBALP: the toxicity characteristic leaching protocol and the synthetic precipitation leaching protocol.

4.4 Supporting Soil Analysis

A fourth data quality objective was to support bioaccessibility data with information on Moanataiari soil

geochemistry and physical properties.

All samples were analysed for pH and for total arsenic, lead, cadmium and thallium in the <2 mm particle

size fraction. pH is a measure of soil acidity; cadmium and thallium are minor contaminants of concern.

<2 mm is the particle size fraction used for comparison to the New Zealand SCS.

All soil samples were also analysed for iron, manganese and phosphorus in the <250 µm particle size

fraction. This is the fraction used for RBALP analysis, as it is considered representative of the soil particle

fraction that is likely to adhere to the hands of children and subsequently be ingested. Iron, manganese and

phosphate are common in soils and known to be constituents of minerals to which arsenic and lead can be

bound (USEPA 2007b, Griffin & Lowney 2012).

The 10 samples analysed in Canada were also sieved to <63 µm, and analysed for arsenic, lead, iron and

manganese. These analyses allow for some consideration as to whether trace element content and form

varies with particle size in these soils. This may inform considerations of dust generation and inhalation in

subsequent health risk assessment.

Field duplicates of a further 10 samples were collected in sufficient volume to allow field splits to be sent for

particle size analysis by Opus International Consultants Ltd. This generally comprised particle size

distributions by quantitative wet sieving down to 63 µm. For two soils, a randomly selected topsoil and a

particularly fine soil (logged as a clay), the analysis was continued down to 1.5 µm by hydrometer and solid

density was also determined. Again, this data will inform considerations of dust generation and inhalation in

health risk assessment.



Four samples – surface and shallow soils from one property in the eastern half of Moanataiari and from one

property in the western half – were split and sent to the Geology and Geological Science Department,

University of Canterbury. There these soils were washed with ethanol to remove organic material, then

separated using polytungstate solution (2.60 times heavier than water) allowing the separation of light and

heavy minerals. The bulk of the soil, mostly lightweight silicates, floated on the polytungstate and was

discarded. Particles dense enough to settle were analysed by powder X-ray diffraction (XRD) in an effort to

identify the principal trace element-bearing minerals.

Splits of these four samples were also analysed for acid-soluble and acid-insoluble sulfides. The former

category should include orpiment (an arsenic sulfide) and galena (lead sulfide) if present, while the latter

category should include pyrite and arsenopyrite if present.

Chain of custody documentation is included in Appendix D.

5.0 RESULTS

5.1 Introduction

A second key objective of this investigation was to accurately determine arsenic and lead bioaccessibility at

Moanataiari, and to be confident that they do not vary systematically from block to block. Some supporting

analysis was also required to help determine probable forms of arsenic and lead in these soils, which will

provide further lines of evidence for assessing their bioavailability.

Certificates of analysis are provided in Appendix E. The report from Golder Associates in Ontario, Canada

forms Appendix F. Table A1 in Appendix G compiles all chemical analyses obtained during this

investigation. Appendix H contains raw X-ray diffraction data.

5.2 Bioaccessibility

Arsenic and lead bioaccessibility percentages are calculated by dividing the RBALP extractable

concentration of the trace element, by the total extractable concentration in the same <250 µm soil fraction.

Bioaccessibilities for the following samples were discarded:

1101 Queen St. 0.4-0.5 m bgl, as this sample is a gravel, distinct from all other soils analysed by

RBALP, and only a small fraction of it is material likely to be ingested.

Samples in the FS that had been collected from depths greater than 0.5 m bgl.

Arsenic bioaccessibility values for 110 Centennial Ave. 0.4-0.5 m bgl and 206 Centennial Ave.

0-0.1 m bgl, as the RBALP extractable arsenic in these samples was below detection limit and total

extractable arsenic is also low, so bioaccessibility cannot be estimated with sufficient accuracy.

In the FS, the highest arsenic bioaccessibility value was identified as a statistical outlier, because it was a

garden soil and may have been mixed with material from a different source. However, in this larger dataset it

is not considered an outlier and has not been discarded.

Appendix G presents the bioaccessibility data, calculations and statistics.

Using all remaining data from both this investigation and the FS, arsenic bioaccessibility in these samples

ranges from <1 % to 78 % (Figure 3). The dataset is well described by a lognormal distribution with

geometric mean of 5.4 %; the 95th percentile upper confidence limit (UCL95) for the mean is 7.3 %. For

surface soils alone, the mean bioaccessibility is a little higher (8.3 %).



Figure 3: Arsenic bioaccessibility in Moanataiari soils compared to total extractable arsenic.

Lead bioaccessibility in the same dataset varied widely, from 1.8 %-81 %. Lead bioaccessibility is weakly

related to total lead; no strong mathematical relationship is evident. However, the 10 samples with total lead

greater than 400 mg/kg have a higher bioaccessibility range (50-81 %, mean 62 %). The 41 samples with

total lead concentrations <400 mg/kg have a lower bioaccessibility range (2-62 %, mean 38 %) (Figure 4).4

There were no obvious statistical relationships between arsenic and lead; neither extractable, total nor

bioaccessible arsenic and lead correlated (R2 = 0.00, 0.02 and 0.17 respectively).

Figure 4: Lead bioaccessibility in Moanataiari soils is weakly related to total extractable lead.

4 In the FS, a cutoff of 300 mg/kg was used, but from the larger dataset now available, it is evident that this would be a less coherent group, with a wider range and lower average

bioaccessibility than the group with total lead >400 mg/kg.

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5.3 Quality Assurance

Accuracy

The standard reference material, NIST2711a, has a certified lead content of 1,400 ± 10 mg/kg, and the target

for RBALP bioaccessibility is 85.7 ± 10.5 %. That is, RBALP extractable lead in this material should be

approximately 1,200 mg/kg. In four separate extraction batches, Hill Labs obtained results of 1,171, 1,165,

1,185 and 1,199 mg/kg for samples of NIST2711a. These results are well within the acceptable range. In

the single Canadian extraction batch, extractable lead in NIST2711a was 1,340 mg/kg, just above the target

range.

For arsenic, no approved RBALP extractable value is yet available for NIST2711a, which had not been

issued when the validation study was carried out. For the predecessor material NIST2711, from the same

source, the RBALP has been given as 58.3 ± 9.4 % (Griffin & Lowney 2012). In four separate extraction

batches, Hill Labs obtained results of 58, 54, 54 and 54 mg/kg for NIST2711a. The Canadian laboratories

obtained results of 50.6 mg/kg for NIST2711 and 52.5 mg/kg for NIST2711a.

Repeatability

Field duplicates of three samples were collected: the surface and shallow samples from 202 Kuranui St.

(replicated by samples “Dup A” and “Dup B” respectively), and the surface sample from 104 Margaret Pl.

(“Dup C”). For each of these samples, Hill Labs carried out five analyses on the <2 mm fraction (the usual

fraction for contaminated land investigations) and eight on the <250 µm fraction (the fraction typically

evaluated for bioaccessibility). The root mean square error was 52 % across the 15 duplicated <2 mm

analyses, 21 % for the 24 duplicated <250 µm. The largest differences were generally for lead analyses.

Hill Labs also performed some laboratory duplicate analysis for internal quality control purposes. Hill Labs

advised that arsenic concentrations in the <2 mm fraction of the 437 Fergusson Drive shallow soil sample,

and acid-insoluble sulfide in the <2 mm fraction of the 207 Moanataiari St. shallow soil, “show more variation

than would normally be expected” (Appendix E). Generally, lead concentrations in <2 mm fractions showed

considerable variability on replication (pers. comm. from analyst, 20 September).

Reproducibility

Across nine replicated samples (continuing to discard results for the gravelly soil from 1101 Queen St. 400-

500 mm bgl), root mean square errors between Hill Labs and Canadian results were 9 % for total arsenic

and 7 % for total lead, well within acceptable limits.

For RBALP extraction, reproducibility was less satisfactory. The two sets of results were still very consistent,

but the Canadian bioaccessibility values were on average 42 % less for arsenic and 24 % less for lead.

5.4 Supporting Analysis

Minor contaminants of concern

Cadmium concentrations ranged from less than the 0.1 mg/kg detection limit, to 82 mg/kg in the shallow

sample from 211 Tararu St. This is the highest cadmium concentration encountered at Moanataiari to date,

and substantially above the residential SCS of 3 mg/kg. As in previous investigations, cadmium

concentrations were closely correlated to lead concentrations (R2 = 0.94).

Thallium ranged from <0.2-6.1 mg/kg, occasionally exceeding the site-specific SGV of 1.2 mg/kg, and

correlated with arsenic (R2 = 0.70).



Other soil constituents

The pH of the samples ranged from 4.0-7.9, indicating a wide range of acidic to slightly alkaline soils. There

was no clear spatial pattern in the pH data. Arsenic and lead bioaccessibility were independent of pH

(R2 = 0.00 and 0.06 respectively).

In the <250 µm fraction, iron concentrations ranged from 14,600 mg/kg to 66,000 mg/kg, while manganese

ranged from 20-5,300 mg/kg. Manganese concentrations were moderately well correlated with total lead

(R2 = 0.69). Phosphate in this fraction ranged from 75-5,100 mg/kg: phosphate concentrations were much

higher in surface samples than in shallow soils.

On inspection of the combined dataset from this investigation and from the FS, arsenic bioaccessibility is

statistically related to concentrations of other soil constituents (Figures 4 and 5)

It is moderately correlated to phosphorus in the same <250 µm fraction, with R2 = 0.62

It is strongly correlated to phosphorus:iron ratio: ( ) [ ]

[ ]

However, arsenic bioaccessibility shows little relationship to iron content alone, consistent with most earlier

studies (summarised in Griffin & Lowney 2012). Total arsenic is independent of phosphorus concentration,

iron concentration or the phosphorus:iron ratio (R2 = 0.00, 0.12 and 0.00 respectively).

Sulfide concentrations in surface and shallow soil samples from 207 Moanataiari Street and 103 Fergusson

Drive were low. Acid-soluble sulfides had a maximum of 5 mg/kg, barely above the 3 mg/kg detection limit,

while acid-insoluble sulfides ranged from 18-44 mg/kg in these four samples.

Figure 5: Arsenic bioaccessibility in Moanataiari soils as a function of phosphorus content.

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Figure 6: Arsenic bioaccessibility in Moanataiari soils as a function of phosphorus:iron ratio.

Soil size fractions

Particle size analyses are included in Appendix E. Approximate fractions of interest are summarised in

Table 2.

While only a limited amount of PSD testing has been conducted as part of this study (4 properties across the

subdivision), testing shows that the soils comprise a reasonable amount of fine grained material (<250 µm).

This is an important factor because the arsenic and lead appear enriched in the smaller size fractions, as

shown in Table 3.

Table 2: Particle size distributions.

Property 211 Tararu St. 103 Haven St. 110 Centennial

Ave.

417 Fergusson

Dve.

206 Centennial

Ave.

Sampling depth, m

0-0.1 0.4-0.5 0-0.1 0.4-0.5 0-0.1 0.4-0.5 0-0.1 0.4-0.5 0-0.1 0.4-0.5

Soil description

Silty

SAND SAND

Silty

CLAY CLAY

Silty

SAND

Silty

CLAY

Sandy

SILT

Clayey

SILT

Sandy

SILT SILT

<2 mm 94 % 88 % 65 % 98 % 60 % 83 % 69 % 79 % 93 % 94 %

<250 µm* 61.5 % 42.5 % 42 % 85 % 34 % 60.5 % 38.5 % 52.5 % 68 % 68.5 %

<63 µm 25 % 14 % 29 % 70 % 21 % 45 % 27 % 38 % 45 % 42 %

<10 µm 17 % 45 %

Notes: * Estimated as average of the percentages passing the 300 µm and 210 µm sieves.

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Table 3: Contaminants of concern in different size fractions of selected samples*.

Average arsenic concentration, mg/kg Average lead concentration, mg/kg

<2 mm 209 214

<250 µm 207 256

<63 µm 292 394

Notes: *10 samples included in averages: surface and shallow samples from 103 Ferguson Dve, 1101 Queen St, 409 Ensor St, 207

Moanataiari St, and 209 Kuranui St.

Mineral phases

Few mineral phases could be identified in the soil samples. The powder XRD spectra for the heavy fractions

(density >2.60 g/cm3) of the shallow soil sample from 207 Moanataiari Street, and both 103 Fergusson Drive

were dominated by residual quartz and kaolinite – simple silicate and aluminosilicate minerals. These

minerals are less dense than the cutoff: evidently the polytungstate separation was not completely effective.

Several other peaks were observed in the spectra, especially the two surface soil samples. None have been

unambiguously identified, certainly not as any common arsenic or lead mineral. It appears that arsenic and

lead are present in a variety of minerals and/or in amorphous (non-crystalline) forms.

Mineralogy and bioaccessibility do appear linked. The surface soil from 207 Moanataiari Street is distinct in

that its XRD spectrum is dominated by peaks not seen in the other samples, but also in that it was found to

have higher arsenic bioaccessibility (25 %, others 3-6 %) and lead bioaccessibility (60 %, others 7-41 %).

6.0 DISCUSSION

6.1 Introduction

The final main objective of this investigation was to generate arsenic and lead bioavailability parameters for

use in subsequent site-specific health risk assessment.

6.2 Bioavailability

The arsenic bioaccessibility values determined in Section 5.2 cannot be used directly in health risk

assessment. They must be transformed into estimated bioavailabilities using Equation 1, obtained from

validation experiments (see Section 3.2).

This process yields arsenic bioavailabilities ranging from 20 % to 68 %. The highest value is in the

0-0.1 m bgl sample from 437 Fergusson Drive, which also has much the highest phosphorus:iron ratio in this

dataset, 0.255. This highest bioavailability value is a statistical outlier according to the Grubbs Test, but

there is no obvious justification for removing it from the dataset. The next highest value is 43 %, from a

different location on the same property, then 41 % from 1101 Queen St, on the opposite edge of the

subdivision; both these values pass the Grubbs Test and are not statistical outliers.

The calculated arsenic bioavailability values are well described by a lognormal distribution with geometric

mean of 26 %. The UCL95 for arsenic bioavailability is 27 % and this value is recommended for use in

Moanataiari health risk assessment generally.

This recommended bioavailability value of 27 % is substantially greater than the raw bioaccessibility values

of less than 10 % typically presented in the FS (Golder 2012b). Consequently site-specific soil guideline

values incorporating arsenic bioavailability will be less than the initial indicators presented in the FS.



It would be possible to propose a bioavailability parameter that varied depending on phosphorus:iron ratio.

However, this is not currently practical because iron and phosphorus concentrations from point to point are

not known in sufficient detail, nor have any predictive relationships been identified from which they could be

estimated. To the contrary, total arsenic is statistically independent of total iron, total phosphorus and the

phosphorus:iron ratio. Moreover, a variable parameter is not necessary, because there is no evidence that

there is any large area of the subdivision where bioavailability is generally elevated.

Lead bioaccessibility needs to be transformed into bioavailability using Equation 2 (see Section 3.0).

Resulting lead bioavailabilities range from negligible to 69 %. In this dataset, lead bioavailability tends to be

higher when total lead is high; for the 10 samples where total lead is at least 400 mg/kg, the bioavailability

range is 41-69 % and the UCL95 is 57 %. This value is recommended for use in Moanataiari health risk

assessment.

This recommended bioavailability value of 57 % is less than the raw bioaccessibility values of less than 10 %

typically presented in the FS. Consequently site-specific soil guideline values incorporating lead

bioavailability will probably be higher than the initial indicators presented in the FS. Note that the arbitrary

cutoff indicating ‘high’ total lead has increased from the 300 mg/kg suggested in the FS, to 400 mg/kg here.

This change has been driven by the sample from 103 Fergusson Drive, which had 350 mg/kg lead but only

7 % lead bioaccessibility. Keeping the arbitrary cutoff at 300 mg/kg would reduce the UCL95 for lead

bioavailability to 56 %.

6.3 Supporting Evidence

The bioavailability of arsenic and lead is closely tied to their chemical form (USEPA 2007b, Griffin & Lowney

2012). If the chemical forms of these trace elements in Moanataiari soils can be identified, then Table 1 can

be used to check measured bioavailability against expected bioavailability. However, XRD analysis did not

successfully identify any arsenic- or lead- containing mineral phases.

In this study, only four samples were analysed for sulfides, but sulfide levels were very low in all four, and

many of the other samples have similar descriptions. This strongly suggests that sulfide minerals such as

arsenopyrite, orpiment and galena are now almost absent from Moanataiari soil, indicating extensive

oxidation through exposure to air. Oxidation of sulfides produces acids, which may account for the acidity of

some samples.

For arsenic, the strong correlation of bioavailability with phosphorus:iron ratio suggests that chemical

weathering of Moanataiari surface and shallow soils is well advanced. Phosphorus in the environment forms

phosphates, chemically very similar to arsenates, the oxidised forms of arsenic. Phosphate and arsenate

would compete for binding sites in and on iron minerals, so that when there is less iron and more

phosphorus, arsenic would tend to be more bioavailable.

For lead, one hypothesis might be that lead is chemically bound to manganese oxyhydroxides, since lead

correlates with manganese in Moanataiari soils. However, lead bound to mixed manganese oxides would be

highly bioavailable (Table 1 and USEPA 2007b), whereas the bioavailability estimated here is generally low

when total lead is low, and moderate at higher total lead concentrations. An alternative hypothesis might be

that lead is present in the form of lead oxide, possibly with small amounts of low-bioavailability galena and

anglesite. Further mineralogical studies would be required to settle this question.

Since these soils have been in place at Moanataiari for some decades, and chemical weathering appears

well advanced, further changes in bioavailability are unlikely. Addition of phosphate fertilisers that do not

contain iron, such as superphosphate, may increase arsenic bioavailability over time.

Both arsenic and lead appear to be slightly enriched in the <250 µm particle size fraction, and somewhat

further enriched in the <63 µm fraction. This finding implies that neither arsenic nor lead are predominantly

associated with clays, or the degree of enrichment would be much greater. There are further implications for

risk assessment, not least that a large fraction of the arsenic and lead in these soils may be incorporated in

particles between 2 mm and 250 µm in size, which are unlikely to be ingested, still less inhaled.



Concentrations of arsenic and lead in particles small enough to be suspended in air and inhaled (indicatively

<30 µm) are evidently greater than in bulk soil, and this should be taken into account in any subsequent dust

risk assessment.

6.4 Sources of Uncertainty

The arsenic bioavailability UCL95 of 27 % is recommended for general use in health risk assessments for

Moanataiari. However, it should not be applied to the vicinity of 437 Fergusson Drive where considerably

higher values have been encountered, including one result that is a statistical outlier. This may be

associated with unusually high phosphorus:iron ratios in these samples, and it is also possible that these

results may represent soil or contaminants from a different source. Further investigation is advisable.

There was also some concern about repeatability of lead analyses. However, given that lead is determined

at the same time as the other elements and in the same way, this is most likely to reflect some real

heterogeneity in soils – such as a ‘nugget effect’, some proportion of sand-size lead-rich soil particles that

may or may not be captured in individual subsamples. On this basis, analytical results for <2 mm particle

size fraction that show very high lead concentrations should be treated cautiously during further assessment,

as they may overestimate soil lead concentrations over a wider averaging area. While a concentration effect

has been noted with the finer grained soil, and this is significant for health assessment of ingestion of soil

and dust, the converse situation arises from trace element-rich soil particles that are unlikely to be ingested.

Otherwise, all sources of uncertainty were deemed satisfactory.

Total lead concentrations in this dataset were generally below the range for which the RBALP is validated,

and this could introduce uncertainty as recognised in Section 3. Nonetheless, the value is derived from the

soil samples with higher total lead concentrations, between 450 mg/kg and 7,700 mg/kg, close to or within

the bottom of the validated range beginning at 1,200 mg/kg. Any deviation from the calibrated

bioaccessibility-bioavailability relationship must be small. Accordingly, it is not recommended that the

proposed bioavailability value be raised to allow for extra uncertainty in calibration.

Similarly for arsenic, most of the total arsenic concentrations were below the bottom of the validated range

beginning at 181 mg/kg. However, the mean bioavailability does not change if those concentrations outside

the validated range are discarded, therefore no allowance for uncertainty in calibration is recommended.

The accuracy and repeatability of bioaccessibility analyses were satisfactory. Indeed, the repeatability of

analyses on the <250 µm particle size fraction was better than for the <2 mm fraction usually used for

contaminated land investigations.

Reproducibility of bioaccessibility analyses was only partly satisfactory, as the Canadian results were closely

in line with Hill Labs results, but were consistently lower. The reason for this is unclear and merits further

investigation. For the purposes of this study, it is enough to note that bioavailability parameters determined

from Hill Labs data are not likely to be underestimates.

6.5 Comparison to Other Studies

Arsenic and lead bioavailability in Moanataiari soils are consistent with findings for United States, Australia,

Canadian and UK soils with similar origins that have been reported in validation trials (USEPA 2009, Griffin &

Lowney 2012).

Golder is aware of one earlier application of bioaccessibility testing in New Zealand. Some New Zealand

orchard soils contaminated with arsenic and lead, due to historical use of lead arsenate pesticide. A study of

10 orchard soils using the PBET method found that arsenic bioaccessibility ranged from 12-45 %, and lead

bioaccessibility was between 56-83 % (Gaw et al. 2008).



Some caution should be used in comparing those values to Moanataiari values as they were obtained by

different methods; Equation 1 should not be applied as it is derived for RBALP bioaccessibilities only.

Nonetheless, the values determined by Gaw et al. (2008) are higher than most values measured at

Moanataiari, as would be expected – lead arsenate pesticide, applied in a sprayable form, would be

expected to be highly bioavailable, much more than mineralised arsenic and lead. Furthermore, those

values are also substantially less than the default assumption of 100 % bioavailability, accentuating the

potential value of site-specific assessments for sites such as Moanataiari.

7.0 CONCLUSIONS

The Moanataiari subdivision, Thames, is a contaminated site where arsenic and lead are key risk drivers.

A realistic characterisation of arsenic and lead bioavailability, based on their measured bioaccessibility,

would produce site-specific soil guideline values greater than the SCS, reducing or even avoiding the need

for costly and intrusive intervention.

The RBALP was developed specifically to estimate arsenic and lead bioavailability in soils. The USEPA has

validated the RBALP for both elements and approved it for use in health risk assessments. It can

appropriately be applied to Moanataiari, as the validation experiments included similar soils, where

contaminants were also derived from mining sources.

In this study, 33 soil samples were analysed using the RBALP, supplementing 16 samples from an initial

study. In the combined dataset, the mean arsenic bioavailability is estimated to be less than 27 % (with

95 % statistical confidence). Lead bioavailability tends to be higher when total lead is high; for samples with

more than 400 mg/kg, the mean lead bioavailability is estimated to be less than 57 % (with 95 % statistical

confidence). These values are recommended for use in site-specific health risk assessment.

8.0 REFERENCES

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