IJERD – International Journal of Environmental and Rural Development (2022) 13-1

Research article
erd

Utilizing Lead Isotope Tracing to Investigate Sustainable
Agriculture Practice in the Burdekin Catchment, Australia
FIONA HENDERSON*The University of Queensland, St Lucia, Australia
Email: uqfhend1@uq.edu.au

BARRY NOLLER
The University of Queensland, St Lucia, Australia

TATIANA KOMAROVA
Queensland Health Forensic Scientific Services, Brisbane, Australia
Received 31 January 2022

Accepted 25 April 2022(*Corresponding Author)

Abstract The Burdekin delta is the largest sugarcane producing region in Australia (85,000ha) and a major coastal output to the Great Barrier Reef (GBR). Run-off from cultivation
areas contain heavy metals from fertilizers, contributing to elevated Cd, Hg, and Pb inwaterways. Validating the efficacy of sustainable agriculture practice is necessary to
determine if current strategies protect ecosystems and uphold environmental standards. The
objective of this study is to utilize Pb isotope tracing (207/206Pb and 208/206Pb) and elevatedtrace-elements (Cd, Hg, and Pb) as a monitoring tool, to detect residual heavy metals fromfertilizers and alternative pollutant sources in the Burdekin catchment. Lead-isotope ratiosfrom dry-season samples of embankment soils/sediment (n=15, 2016, 2019) and water(n=35, 2016-2020), reveals sources of natural forest soils, cane soils (fertilizer enriched),
ambient dust, and historic coal fly-ash (Collinsville Power Station). Pb isotope
compositions and low levels of heavy metals (soil/sediment: TCd 0.11 mg/kg, THg 0.03
mg/kg and TPb 11.02 mg/kg; estuary: THg 0.011 μg/L and TPb 4.99 μg/L) indicate that
fertilizers applied to soils have minimal impact on Burdekin waterways during the dryseason, suggesting effective agricultural practice and sustainable irrigation control.
Keywords agriculture, sustainability, sustainable practice, lead isotope, source-tracing

INTRODUCTION
The GBR is the largest reef ecosystem on the planet (344,400 km2) and a World Heritage site
located off the coast of Queensland (QLD), Australia (Coggan et al., 2021). Land-runoff fromcoastal catchments can adversely impact the GBR (Lewis et al., 2021). Agricultural
mismanagement, (i.e. fertilizer overuse and uncontrolled irrigation run-off) contributes to water
quality risk through the accumulation of heavy metals in soil and remobilization to waterways(Table 1; Alengebawy et al., 2021; Coggan et al., 2021). In literature, research has conventionallyused elevated heavy metals to establish pollutant presence and Pb-isotopes to trace pollutant source
by providing a measure of geologic age (Table 1; Diaz-somoano et al., 2009; Lottermoser, 2009;
Alengebawy et al., 2021). Following ~10 years of sugarcane cropping, Rayment (2007) noted Cdand Hg were elevated in QLD cane soils. Davis, et al. (2008) detected sugarcane pesticides in
Burdekin waterways. Extended fertilizer use is known to degrade soil fertility and productivity(Ping et al., 2020). Fertilizer overuse burdens the environment, economic and social value of boththe GBR and the sugarcane industry (DAE, 2017). Sugarcane production is $1.33 billion AUD(gross); the Burdekin represents 31% or $4.12 million AUD (DAE, 2017). Aboriginal and Torres
Strait Islanders have maintained cultural ties to the GBR for ~ 60,000 years. There are over 70
identified clans in the GBR; 16 of which reside in the Burdekin (DAE, 2017). Coastal communitiesⒸ ISERD

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with high fish intake risk methyl-Hg and Cd (neurotoxins) exposure; illustrating community
dependence upon ecosystem health (Haswell-Elkins et al., 2006; Russell et al., 2015).
Table 1 Summary of mean cadmium, mercury and lead concentrations (mg/kg) incontaminated soils, fertilizers, sugar cane soil, and sugarcane by-products
loading to soil
Description
Fertilizer Derailment
Contaminated soil (n=7)
Contaminated soil (max)Fertilizer type (N-K-P)
0-9-0, (n=4)
TSP, 0-21-0
DAP, 18-20-0 (n=3)
13-14-12 plus
Sugarcane soil (± SD)
Sugarcane by-product
Filter Mud
Mill Ash
Biosolids
Soil loading limits

Cd (mg/kg)

Hg (mg/kg)

Pb (mg/kg)

4.21
45

n.a.
n.a.

53.7
790

0.5
0.5
0.5
0.5
0.069
Hg (kg/ha)
n.a.
n.a.
n.a.
n.a.

5.43
6.68
0.33
132
27
Pb (kg/ha)
n.a.
n.a.
n.a.
260

22
6.67
1.18
0.85
0.05
Cd (kg/ha)
0.011
0.003
0.11
2

Reference
Noller, 2021
Noller, 2021
Lottermoser, 2009
Lottermoser, 2009
Lottermoser, 2009
Lottermoser, 2009
Rayment, 2007; 2011
Rayment, 2011
Rayment, 2011
Rayment, 2011
NWQMS, 2000

Note: N-K-P nitrogen, potassium, and phosphorus; SP, superphosphate; TSP, triple superphosphate; DAP, Diammonium phosphate; sugarcane by-products load to soil (0-10 cm depth).

OBJECTIVE
This study investigates utilizing analytical indicators (Pb isotopes: 207/206Pb and 208/206Pb and heavy
metals: Cd, Pb, and Hg) to monitor sustainable agricultural practice and identify impacts offertilizer to Burdekin waterways. Alternative pollutant sources are also investigated. In this study,
appropriate fertilizer use and irrigation run-off control defines sustainable agricultural practice.
METHODOLOGYThe Burdekin catchment (area ~130,400 km2) resides in the seasonally dry tropics of NE QLD (Fig.
1). The Upper Burdekin is bordered by coastal ranges (750-1070 m height) < 50 km from thecoastline and feeds into the largest dammed catchment in QLD, Lake Dalrymple, impounded by the
Burdekin Falls Dam (BFD). In the dry-season, lower catchment flow is driven by allocated releases
from the BFD (mean ( ) minimum flow volume ± standard error (se): 4715 406 ML/month) anduncontrolled irrigation run-off (QLD Government, 2017). Approximately 75% of surface water
diversion schemes go to irrigation of sugarcane agriculture (Lewis et al., 2021). Monsoonal rains
govern flow volumes during the wet season ( se: 1535476 ML 255826). Extreme flooding
events occur annually, resulting in overspill at BFD, dislodging fertilized material, and dispersing
heavy metals to waterways. Monitoring of Burdekin River environment health is carried out during
the dry season (May-November se:101672 ML 36104) when vehicle access is possible, andsamples are safe to collect. Wet season volumes also cause dilution ( :15 times, 1986-2021) often
resulting in undetectable heavy metal concentrations (WMIP, 2022). As a consequence, heavy
metal concentrations from the run-off events are likely to pose greatest environmental risk during
the dry-season, when perennial river volumes have returned to “steady-state” flows. Embankment
soils/sediments (n=15, 0-100 mm depth, 2016, 2019) and water (n=35, unfiltered, 2016, 2018,2019 and 2020) were sampled in the Upper and Lower (estuary) sub-catchments of the Burdekinwatershed during the dry season. Water and sediment samples in 2016 and 2018 (Fig. 1) werecollected in June and July to demonstrate dry-season sources of heavy metals, and input of soil
seepage, representing concentrations coinciding with fall of the hydrographic curve. Samples in
x

x

x

x

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2019 and 2020 were collected in late November and early December (increase in hydrographic
curve). Thus, sample collections in 2019 and 2020 (Fig. 1) captured first flush and post run-off
heavy metal concentrations from the start of the wet-season, including any input from agricultural
fertilizers.

Fig. 1 Study area and sample site location map
Water and soil/sediment were analyzed at the NATA accredited laboratory (ISO/IEC 17025,
2017) Inorganic Chemistry, Queensland Health and Forensic Scientific Services, Coopers Plains,
QLD 4108, Australia. Agilent 8800 triple quadrupole inductively coupled plasma mass
spectrometer (ICP-QQQ; Agilent Technologies, Santa Clara, CA, USA) measured heavy metal
concentrations. Internal standards, spikes and certified reference materials (CRM, TM-28) wereused for quality assurance and quality control (QA/QC). QC for Hg analysis used 5% Hg (v/v)
HNO3 solution (SRM ID 3133, SRM Lot # 060204; High Purity Standards, Charleston, SC 29423,
USA). Pb isotope ratios (207/206Pb and 208/206Pb) in water, soil and sediment digests were determinedby Agilent 8800 ICP-QQQ (CRMs: GXR-1, JG-2, JR-1, JSD-1, JSD-2). Soil/sediment (includingCRMs) were prepared following the standard operating procedure (SOP 18191). Water samples
were analyzed directly after addition of 0.2 mL High Purity HNO3 to total 10mL. Pb isotope stock
standard solution was used from Choice Analytical and prepared via serial dilution. Ratios were
calculated using instrument software. Blank corrections were made with 0.5mL High Purity HNO3
in 10mL of deionized water. The ICP-QQQ is tuned following manufactures recommendations(Ref 11.3) and QIS: 30638 Operational Guidelines – ICP-MS. Total Hg measurements in soil wereanalyzed by National Measurement Institute Department of Industry, Innovation and Science,
Sydney, Australia.
RESULTS AND DISCUSSION
Mean se of total (T) Hg (0.016 ±0.002 μg/L) and TPb (0.15 ±0.02 μg/L) in freshwater remain
below ANZG (2018) default guideline values (DGVs) (Table 2). Mercury ( se: 0.011 ± 0.001) inthe estuary are below marine DGVs. In one estuary sample, TPb (4.99 μg/L) is above a marine
DGV of 4.4 μg/L (Table 2). At < 2 mm size fraction, embankment soil/sediment samples reflectse of TCd (0.11 0.10 mg/kg), THg (0.03 0.004 mg/kg) and TPb (11.02 1.65 mg/kg), allxxⒸ ISERD

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below soil and sediment DGVs throughout the upper and lower catchments (Table 3). The majority
of Burdekin soils/sediments (80%) and water (72%) samples, reflect isotopic compositions of canesoil (fertilizer enriched) and natural forest soils (Lottermoser, 2009; Fig. 2A and B). Isotope tracing
also suggests TPb Burdekin soils/sediments and waters are reflective of residual coal fly ash andambient-background dust (Turull et al., 2018). NSW coal fly ash signatures (Fig. 2; Diaz-somoana
et al., 2009) identified in Burdekin samples likely reflect historic contributions from a nearby
powerplant. A nearby coal-electricity generation station is the Collinsville Power Plant (Fig. 1).
Based on current flow statistics, the Burdekin River is highly variable, considerably influencing
annual sediment and nutrient loads (Brodie and Bainbridge, 2008). This is apparent in Pb isotope
compositions that vary with sample years (Fig. 2B). In 2016, isotope ratios trend toward phosphatefertilizers and are very similar to ratios found in fertilizer-enriched cultivation areas of the Tully
catchment (QLD; Turull et al., 2018). In 2018 and 2019, ratios in fresh and estuarian waters reflecta mixture of sources: NSW coal fly ash, dust, natural forest soils and leaded petrol (1996) (Fig. 2
B).
Table 2 Total Hg and Pb (μg/L) in the Burdekin River from 2016, 2018, 2019, and 2020.
Freshwater
N
Mean
SD
SE
Min
Median80 percentile
95 percentile
99 percentile
Max
Toxicant DGV

THg (μg/L)
24
0.016
0.01
0.002
0.005
0.013
0.022
0.027
0.044
0.048
0.06a

TPb (μg/L)
24
0.146
0.079
0.018
0.053
0.111
0.149
0.204
0.372
0.414
3.4b

THg* (μg/L)
11
0.011
0.004
0.001
0.004
0.011
0.011
0.015
0.018
0.019
0.1a

Saltwater
N
Mean
SD
SEM
Min
Median80 percentile
95 percentile
99 percentile
Max
Toxicant DGV

TPb (μg/L)
1
4.99
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
4.4b

Note: N, count; SD, standard deviation; SE, standard error, *Collected in 2019 and 2020 n=11,
a 99% level of protection for Hg. b 95 % level of protection of species for Pb (ANZG-water, 2018)

Table 3 Total Cd, Hg and Pb (mg/kg), <2mm size fraction soil/sedimentfrom 2016 and 2019
Summaryn
No < values
Mean
SD
SE
Min
Median80 percentile
95 percentile
99 percentile
Max
Toxicant DGV*

TCd (mg/kg)
14
4
0.11
0.37
0.10
0.00
0.02
0.04
0.53
1.23
1.40
1.5

THg (mg/kg)
15
9
0.03
0.01
0.004
0.02
0.03
0.04
0.05
0.05
0.05
0.15

TPb (mg/kg)
14
0
11.02
6.16
1.65
2.40
9.13
16.00
21.10
24.22
25.00
50

Note: * No defined level of protection available (ANZG-sediment, 2018)

BFD stores are replenished during the wet-season from moonsoonal rains (cf. Townsvillerainwater se: pH 6 0.1; Na 1  4 mg/L, Cl 17 7 mg/L, from seawater) and released in the dry
season for irrigation (Crosbie et al., 2012). Site 7-19 samples, taken below BFD, captures wetseason water stores from dam releases. This is evident in 7-19 water characteristics, where pH andelectrical conductivity (EC) are influenced by wet-season rains ( se pH 7.4 0.01, EC: 193 1.1
µS/cm). Upstream (dry season) waters ( se pH 8.5 0.02, EC: 558 21.1 µS/cm) have higherxxxⒸ ISERD

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alkalinity/hardness and EC demonstrating differences between wet/dry waters. In the dry season,
heavy metal re-mobilization from sugarcane areas has low environmental, economic and social
risk; with one sample, TPb of 4.99 μg/L (2019), above DGVs of 4.4 μg/L (Table 2). Isotope tracing
reveals that fertilizer signals remain low throughout the catchment, suggesting sustainble irrigtion
practice and run-off control. The impact of fertilizer use in this study is likely minimized due to adelayed start to the wet season in 2019 and 2020 resulting in reduced rainfall run-off events. It is
recommended that on-land investigations should be carried out to further inform on fertilizer rates.

A

B

Fig. 2 Pb isotope ratios, 207Pb/206Pb and 208Pb/206Pb, suggest natural andanthropogenic sources (A) soil/sediment (2016 and 2019) and(B) water (2016, 2018 and 2019)
CONCLUSION
This study informed on baseline heavy metal concentrations and provides new insights ofalternative anthropogenic sources impacting Burdekin River water quality (i.e. Collinsville Power
Plant). Pb isotope tracing and elevated trace elements is effective at monitoring irrigation control.
Fertilizer use has no impact on the Burdekin River in the dry season, suggesting low environmental,
economic and social risk. Future land-based investigations could further inform on fertilization
rates and impact.
ACKNOWLEDGEMENTS
I acknowledge the University of Queensland, QHFSS and the Inorganic Chemistry team forproviding facilities, funding and access to their laboratory. A special thank you to my supervisors
Barry Noller and Tatiana Komarova for their support and mentorship.
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