Arsenic in urban air

182 Pages·2015·4.37 MB·English

by  Tamsin Mitchell

Copyright is owned by the Author of the thesis. Permission is given for
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Arsenic in urban air: sources, health
risk and mitigation
A thesis presented in partial fulfilment of the
requirements for the degree of
Master of Philosophy
in
Environmental Health
Massey University, Wellington, New Zealand
Tamsin A. Mitchell
2015

Abstract
Over recent years, several studies have suggested that high concentrations of arsenic
may occur in outdoor air in urban areas of New Zealand on some winter nights. These
spikes in arsenic concentrations are presumed to be caused by some householders
burning copper-chrome-arsenate (CCA)-treated wood as a fuel for domestic home
heating, but detailed examination of the issue has been lacking. The aims of this work
are to examine the concentrations and source(s) of arsenic in ambient air in a
representative New Zealand wood-burning community, identify and quantify potential
health risks linked to both arsenic in air and the activity of burning CCA-treated wood,
and undertake an initial exploration of social factors that may contribute to the issue.
The town of Wainuiomata in the Wellington region was selected as the representative
community.
Concentrations of total arsenic in Wainuiomata outdoor air were measured over two
years, along with a number of other relevant variables useful for source
characterisation, including two size fractions of particulate matter (PM and PM ),
10 2.5
black carbon and other trace elements. Over both years, concentrations of arsenic in
Wainuiomata air were indistinguishable from the national ambient air quality guideline
of 5.5 ng/m3 expressed as an annual average. Arsenic levels were strongly seasonal
and peaked during the winter months, but with significant variability from night to
night. The highest 24-hour concentration recorded during winter was 79 ng/m3.
Results of correlation analysis and source attribution provide strong support for the
idea that the principal source of elevated arsenic in outdoor air is the domestic burning
of wood treated with CCA preservative.
A detailed exposure model was developed and applied to estimate and contextualise
potential arsenic exposures that may be experienced by adults and children living in
the community, and quantify relative health risks. Potential community health impacts
are estimated not to be significant where exposure is limited to outdoor arsenic,
including that which infiltrates into the indoor environment, where “not significant” is
defined as an additional lifetime cancer risk of less than 1 in 100,000 and a hazard
quotient less than 1. Annual average arsenic in outdoor air would need to be around
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15 times higher than the guideline value to increase an individual’s attributable
lifetime cancer risk to 1 in 10,000.
Of more potential concern are health risks arising from indoor exposure for residents
who use CCA-treated timber as supplementary firewood where this may lead to
fugitive emissions of arsenic from the firebox into indoor air. Not only does the
predicted excess lifetime cancer risk approach 7 in 100,000, but there are also non-
cancer health risks to children due to short-term exposure to the relatively higher
levels of arsenic during the winter months. Hazard quotients above 1 were found to
potentially exist for a small number of children (4%) based on the likelihood of living in
a home where CCA-treated timber might be burnt combined with the presence of at
least one adult smoker. However, overall greatest potential for acute health risk for
children was found to be posed by accidental or incidental ingestion of CCA-wood ash,
which contains very high concentrations of arsenic.
Results of focus group sessions and community surveying provided useful contextual
information about the source activity and identification of some potentially modifiable
social factors, along with some understanding about why prohibition of the activity of
burning CCA-treated wood may be ineffective. Findings included an upper estimate of
the proportion of households that may burn CCA-treated timber (approximately 16%),
and identification of the problem that most residents are not able to distinguish
treated from untreated wood.
A number of recommendations are made. Despite the preliminary nature of the
findings due to uncertainties in the modelling and toxicity reference values, it is
recommended that efforts should be made to discourage the practice of CCA-wood
burning as a precautionary measure to protect against inhalation exposure to indoor
sources of arsenic and ingestion of contaminated ash by children. Community
education initiatives would need to be developed from the perspective of local
residents, most of whom cannot identify CCA-treated wood. It would be ideal if this
were complemented with a high-level review of the policy and regulatory framework
which permits the manufacture, use and disposal of CCA-treated wood in New
Zealand, to determine where risks might be best managed.
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Acknowledgements
I would like to thank my supervisor, Dr Nick Kim (Massey University), for his insightful
approach and for sharing his amazing technical knowledge of all things quantitative. I
would also like to thank Dr Terry Parminter (Greater Wellington Regional Council) for
his sage advice and input into the social science investigation that enabled me to
explore the important human dimension of this work. Thank you also to Dr Stuart
McLaren (Massey University) for smoothing the way through the administration
requirements and for supporting my application for to become a post-graduate
student.
This thesis was inspired by Dr Perry Davy (GNS Science) who has been a great mentor
throughout, freely sharing data and technical advice. The project could not have been
completed without Darren Li (Greater Wellington Regional Council), the air quality
instrument guru who was ultimately responsible for ensuring that our monitoring
results were accurate and reliable. Thank you also to Chandar Singh (Victoria
University of Wellington student) for changing the air filters – your efforts are much
appreciated.
I also deeply appreciate the support of Graham Sevicke-Jones (Greater Wellington
Regional Council) and his canny ability to keep me on track to finish the project.
Finally I would like to thank to my family, my wonderful husband, James, who
encouraged and supported me through this long process, and Luca and Charlotte for
being so patient.

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Contents
Abstract .............................................................................................................. i
Acknowledgements ......................................................................................... iv
1 Introduction, aims and structure ........................................................ 1
1.1 Introduction ............................................................................................ 1
1.2 Aims and objectives ............................................................................... 3
1.2.1 Overview of approach ............................................................................ 3
1.2.2 Aims and objectives ............................................................................... 4
1.3 Outline of thesis ..................................................................................... 6
2 Literature review and context ............................................................. 8
2.1 Introduction ............................................................................................ 8
2.2 Arsenic in the environment ..................................................................... 8
2.2.1 Physical, chemical and toxicological properties ..................................... 8
2.2.2 Arsenic sources, environmental fate and partitioning ............................. 9
2.2.3 Arsenic in the New Zealand environment ............................................. 11
2.2.3.1 Drinking water ...................................................................................... 11
2.2.3.2 Food ..................................................................................................... 12
2.2.3.3 Soils and indoor dust ............................................................................ 12
2.3 Arsenic in New Zealand’s air ................................................................ 13
2.3.1 Outdoor air ........................................................................................... 13
2.3.2 Air quality guidelines ............................................................................ 15
2.3.3 Measurement techniques ..................................................................... 16
2.3.4 Source apportionment based on trace elements in air ......................... 17
2.4 Arsenic in wood preservatives .............................................................. 18
2.4.1 History and background ....................................................................... 18
2.4.2 Building industry regulation .................................................................. 19
2.4.3 Identification of CCA-timber ................................................................. 20
2.4.4 Environmental fate of arsenic during CCA-wood combustion .............. 21
2.4.5 Health risks of CCA-wood .................................................................... 23
2.5 Social and regulatory context of domestic wood burning ..................... 23
2.5.1 Air quality regulation ............................................................................. 23
2.5.2 Social understanding of air quality management .................................. 24
2.6 Synthesis .............................................................................................. 27
3 Ambient air monitoring ...................................................................... 29
3.1 Introduction .......................................................................................... 29
3.2 Methodology ......................................................................................... 29
3.2.1 Monitoring site ...................................................................................... 29
3.2.2 Data collection and sampling methods ................................................. 31
3.2.2.1 Overview .............................................................................................. 31
3.2.2.2 Sampling frequency and rationale ........................................................ 31
3.2.2.3 PM gravimetric sampling ................................................................... 32
10
3.2.2.4 PM and PM continuous sampling ................................................... 34
10 2.5
3.2.2.5 Determination of arsenic concentration in PM ................................... 34
10
3.2.2.6 Determination of black carbon and multi-element concentrations ........ 35
3.2.3 Data analysis ........................................................................................ 36
3.2.3.1 Handling of measurements below the limit of detection ....................... 36
3.2.3.2 Graphical presentation and statistical analyses ................................... 36
3.2.3.3 Regulatory guideline comparison ......................................................... 38
3.3 Results and discussion ......................................................................... 39
3.3.1 Numerical summary of arsenic, PM , PM and black carbon
10 2.5
results ................................................................................................... 39
3.3.2 Inter-method agreement for PM and PM :PM ratio ....................... 39
10 10 2.5
3.3.3 Local meteorology at monitoring site .................................................... 42
3.3.4 Comparison with regulatory guidelines and values for health risk
assessment .......................................................................................... 45
3.3.5 Seasonal variation in arsenic, PM , PM and black carbon ............... 47
10 2.5
3.3.6 Relationships between arsenic, PM , PM , black carbon and
10 2.5
meteorology ......................................................................................... 52
3.3.7 Relationship between arsenic and other trace elements for source
attribution ............................................................................................. 56
3.3.7.1 Comparison between arsenic concentrations determined by XRF
and ICP-MS .......................................................................................... 57
3.3.7.2 Relationships between trace elements based on correlations .............. 58
3.3.7.3 Relationship between trace elements based on principal
components analysis ............................................................................ 62
3.3.8 Dependence of arsenic concentration on PM and meteorology ........ 64
2.5
3.4. Synthesis of ambient air monitoring ..................................................... 67
4 Health risk assessment ..................................................................... 70
4.1 Introduction .......................................................................................... 70
4.2 Methodology ......................................................................................... 70
4.2.1 Approach .............................................................................................. 70
4.2.2 Assessment scope and conceptual model ........................................... 71
4.2.3 Exposure assessment method ............................................................. 74
4.2.3.1 Characterisation of exposure setting .................................................... 74
4.2.3.2 Inhalation pathway assessment ........................................................... 74
4.2.3.3 Inhalation exposure characterisation .................................................... 80
4.2.3.4 Background exposure via inhalation .................................................... 81
4.2.4 Ingestion pathway assessment method ............................................... 83
4.2.4.1 Media concentration ............................................................................. 83
4.2.4.2 Scenario evaluation .............................................................................. 84
4.2.4.3 Ingestion exposure characterisation ..................................................... 85
4.2.4.4 Background exposure via ingestion ..................................................... 86
4.2.5 Toxicity assessment method ................................................................ 89
4.2.5.1 Toxicity overview .................................................................................. 90
4.2.5.2 Carcinogenic effects ............................................................................. 90
4.2.5.3 Non-cancer effects ............................................................................... 93
4.2.5.4 Summary of selected toxicity reference values .................................... 96
4.2.6 Risk characterisation method ............................................................... 97
4.2.6.1 Cancer risk estimates ........................................................................... 97
4.2.6.2 Non-cancer risk estimates .................................................................... 98
4.3 Results and discussion ......................................................................... 99
4.3.1 Inhalation exposure and risk characterisation ...................................... 99
4.3.1.1 Cancer risk characterisation ............................................................... 100
4.3.1.2 Non-cancer risk characterisation ........................................................ 101
4.3.2 Ingestion exposure and risk ............................................................... 104
4.3.3 Background exposure and risk ........................................................... 105
4.4 Uncertainty and sensitivity analysis .................................................... 106
4.5 Synthesis ............................................................................................ 108
5 Social behavioural context investigation ....................................... 110
5.1 Introduction ........................................................................................ 110
5.2 Methodology ....................................................................................... 110
5.2.1 Philosophical stance........................................................................... 110
5.2.2 Theoretical lens .................................................................................. 110
5.2.3 Data collection .................................................................................... 113
5.2.3.1 Focus group participant recruitment ................................................... 113
5.2.4 Ethics and privacy .............................................................................. 115
5.2.4.1 Focus group setting and timing .......................................................... 117
5.2.4.2 Focus group facilitation ...................................................................... 117
5.2.4.3 Focus group discussion format .......................................................... 118
5.2.5 Data analysis ...................................................................................... 119
5.2.5.1 Transcriptions of audio recordings ..................................................... 119
5.2.5.2 Coding of verbal transcriptions ........................................................... 120
5.2.5.3 Thematic analysis............................................................................... 120
5.3 Results ............................................................................................... 120
5.3.1 Focus group demographics ................................................................ 120
5.3.2 Themes identified from focus group transcripts .................................. 121
5.3.2.1 Different practices for warming the home and acquiring fuel .............. 121
5.3.2.2 Ash disposal practice ......................................................................... 125
5.3.2.3 Ability to discriminate treated from untreated timber .......................... 125
5.3.2.4 Awareness of practice of burning treated timber ................................ 127
5.3.2.5 Knowledge of emissions, smoke, air pollution and health .................. 129
5.3.2.6 Supporting and discouraging – using treated timber on the fire ......... 133
5.4 Discussion .......................................................................................... 135
5.5 Limitations .......................................................................................... 140
6 Conclusions and recommendations ............................................... 141
6.1 Conclusions ........................................................................................ 141
6.2 Recommendations ............................................................................. 143
7 References ........................................................................................ 146
8 Appendices ....................................................................................... 162
8.1 Focus group invitation letter ............................................................... 162
8.2 Focus group information sheet ........................................................... 163
8.3 Focus group participant consent form ................................................ 164
8.4 Focus group questions ....................................................................... 165
8.5 Focus group ground rules .................................................................. 166
8.6 Focus group demographic questionnaire ........................................... 167
8.7 Focus group transcript release form ................................................... 168
8.8 Focus group facilitator and transcriber confidentiality agreement ...... 169