Cadmium accumulation in agricultural soils

192 Pages·2017·6.51 MB·English

by  Maddie Zadeh

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thesis.
Cadmium accumulation in agricultural soils
A thesis
submitted in fulfilment
of the requirements for the degree
of
Doctor of Philosophy in Environmental Science
at
The University of Waikato
by
MAHDIYEH SALMANZADEH
2017

Abstract
Cadmium (Cd) has accumulated in New Zealand (NZ) soils as a result of phosphate
fertiliser application. Cadmium is a biotoxic heavy metal and can be adsorbed by
soil and enter the human food chain. Three objectives were investigated in this
thesis: 1. Determine if the distribution of Cd varies between soils with contrasting
mineralogy and drainage characteristics, but the same phosphate fertiliser history,
2.Evaluate the utility of Cd stable isotope ratios (δ114/110Cd) to trace the sources of
Cd in NZ soils through time and distinguish the contribution of different sources of
Cd in NZ soils, and, 3. Determine whether there is a difference in the concentration
of Cd in irrigated and unirrigated soils within the same paddock.
The concentration of Cd was measured in three soils, with contrasting mineralogy
and drainage characteristics within the same paddock, and thus same fertiliser
history. The mean concentration of Cd in topsoil (0-7.5 cm) samples was
0.77 mg kg-1 (range 0.56-0.99) in the Horotiu soil (Orthic Allophanic Soil in NZ
soil classification, Typic Hapludand in US soil taxonomy), 0.83 mg kg-1 (range
0.60-1.11) in the Bruntwood soil (Impeded Allophanic Soil in NZ soil
classification, Aquic Hapludand in US soil taxonomy) and 0.78 mg kg-1 (range 0.46-
0.96) in the Te Kowhai soil (Orthic Gley Soil in NZ classification, Typic
Humaquept in US soil taxonomy). There were no significant differences in the
concentration, and/or the total mass of Cd between the three soils. Cadmium was
mainly adsorbed to the near surface soil regardless of soil mineralogy and drainage
characteristics. Thus, it was concluded that it is appropriate to apply the same Cd
management approach (The Tiered Fertiliser Management System) to the
investigated soil types.
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Isotope ratios of Cd (δ114/110Cd) were used to trace the sources of Cd in a long-
term irrigation and fertiliser trial at Winchmore, Canterbury, New Zealand. The
isotopic composition of pre-2000 fertilisers (δ114/110Cd = 0.10 ± 0.05 to 0.25 ±
0.04) was comparable to the Nauru source rocks used in fertiliser manufacture
(δ114/110Cd = 0.22 ± 0.04), but distinct from the control subsoil (δ114/110Cd = -0.33
± 0.04) and post-2000 fertilisers (δ114/110Cd range of -0.17 ± 0.03 to 0.01 ± 0.05).
The isotopic compositions of fertilised soil samples ranged from δ114/110Cd = 0.08
± 0.03 to δ114/110Cd = 0.27 ± 0.04, which were comparable to pre-2000 fertilisers.
Thus, it becomes possible to distinguish the sources of Cd within the soil using
isotopes. The fractional distribution of Cd sources confirmed the main
contribution of Nauru-derived phosphate fertilisers (pre-2000 fertilisers) in
increasing the amount of Cd in soils at the Winchmore research farm.
The concentration and distribution of Cd in adjacent irrigated and unirrigated soils
with the same phosphate fertiliser history were investigated. Twenty-two pairs of
soil samples from 4 depths (0-10, 10-20, 20-30 and 30-40 cm) were taken from
irrigated and unirrigated areas in the same paddocks on different dairy farms from
three regions of New Zealand (Bay of Plenty, Manawatu-Wanganui, and
Canterbury). The mean concentration of Cd (depth of 0-10 cm and 10-20 cm)
and the cumulative mass of Cd (depths of 0-20, 0-30, and 0-40 cm) were higher
(P < 0.05) in unirrigated soil than in irrigated soil. Total Cd was about 10% less
abundant in the 0-40 cm depth range in irrigated soil (mean of 0.63 kg ha-1) than
unirrigated soil (mean of 0.73 kg ha-1), with the average difference of 7.2 g ha-1yr-1
for the 0-40 cm depth. The significant difference (P < 0.05) in the cumulative mass
of Cd between irrigated and unirrigated soils demonstrated that irrigation may have
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enhanced the mobility of Cd. However, overall the results demonstrate that Cd was
generally immobile and mainly absorbed to the near surface of the soils studied.
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Acknowledgements
My PhD journey would not have been possible without the support of supervisors,
co-workers, friends and family.
I would like to first acknowledge my chief supervisor, Dr Megan Balks, for
providing the opportunity to come to New Zealand as a young scientist and work
on an exciting project. Thanks for the great company and support. Your patience
and never-tiring eye for looking over drafts was invaluable.
It has been a privilege to work with my co-supervisors, Dr Adam Hartland and Prof
Louis Schipper. Working on novel isotope tracers was a great opportunity and many
thanks to Adam for his creativity and continues support. Whether it was a quick
chat or long meeting, I always enjoyed our discussions and learned a lot from you.
It was great to be a part of your group (Waikato Environmental Geochemistry,
WEG).
I especially wish to thank Prof Schipper for providing the opportunity to join the
Waiber (Waikato Biogeochemistry and Ecohydrology Research) group. It was a
pleasure to work with such a friendly and knowledgeable group. Thanks also for
funding support, which made my PhD research easier and relieved financial
stresses.
I would like to acknowledge DairyNZ and The Fertiliser Association of New
Zealand for funding my research and The University of Waikato for the PhD
scholarship.
Dr Claudine Stirling, thank you for providing the opportunity to work in your
isotope laboratory at The University of Otago. Without your helpful guidance and
comments, the isotope research would have been impossible.
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I also want to acknowledge Dr Ejin George for his help to complete my isotope
experiments, even when he was really busy with his own PhD.
Special thanks to Dr Ray Littler for statistical consultations and also Dr Chaitanya
Joshi for his advice on my Matlab codes amendments. Carli. A. Arendt is also
acknowledged for helpful guidance on using the Bayesian mixing model.
Thank you to Dr Paul Mudge for providing the soil samples for the last part of my
PhD research.
Thanks to Ray Moss, Richard McDowell and Ian Power for providing soil and
fertiliser samples.
Thanks also to my thesis examiners for their useful suggestions and comments.
I am grateful to Prof. David J. Lowe for the helpful comments on Chapter 3 of my
thesis.
Aaron Wall, thank you for answering patiently my Matlab questions.
Many thanks to the chemistry laboratory technician, Annie Barker. Life was easier,
because you were always there and provided all the lab-wares promptly.
Thank you to Janine Ryburn for all the help during my work in the soil laboratory.
I would like to thank Steve Cameron for analysing my samples using ICP-MS and
providing the results quickly.
Special thanks to Huma Saeed, one of my group-mates at WEG. Thanks for your
patience with my chemistry questions and letting me steal your lab-wares! I wish
you all the best with your PhD.
Heartfelt thanks go to my best friend and office-mate, Femke Rambags, for your
support and assurance. You were always there and made my PhD journey more
exciting.
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I also want to thank my other office-mates, Doreen Huang, Jack Pronger, Sheree
Balvert, Joss Ratcliffe, and Liyin Liang. It was great to get to know you all, hope
to meet you again somewhere in the world!
Many, many, thanks to my lovely parents, my supportive sister, and her daughter.
Your kindness and motivation were always with me, even though you were far away
from me. I hope to always make you proud.
Last, but not least, thank you to my amazing husband, Mannan. I can’t imagine this
journey without you. Thanks for your help during my soil sampling, which I
couldn’t have done without your powerful hands. We made it as a team.
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