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Practical Project - Carolyn Sonter
Assessment of lead and zinc levels of sediments in
Cockle Creek - New South Wales, Australia
Cockle Creek in New South Wales (NSW), Australia, flows into Lake Macquarie (Fig 1) and
is of significance in the investigation of lead and zinc levels in sediments due to its close
proximity to a now discontinued lead and zinc smelter. Constructed in 1897 the Pasminco
Cockle Creek Smelter (PCCS) was a major lead processing plant until its closure in late
2003. During the smelter’s operation, stack and fugitive emissions and dust from ore and
slag covered an area extending to Glendale in the north, Macquarie Hills in the east,
Speers Point in the south with the adjoining suburbs of Boolaroo and Argenton to the west
receiving the greatest contamination (NSW Health Department 1991). Cockle Creek flows
through the suburbs of Argenton and Boolaroo before entering Lake Macquarie (Fig 1).
Creeks act as contamination ‘sinks’ due to the fine silt and clay component which is washed
into creeks during rain events from run off thus making the creek sediments an accurate
indicator of the persistence of contaminants in an area (Encyclopedia of Water Science
Fig 1. Map of Pasminco Cockle Creek Smelter and Cockle Creek (NSW), showing the
geographical relationship to the surrounding suburbs and Lake Macquarie (Willmore
et al. 2006).
Lead (Pb) is a metal, bluish grey in colour and found in the earth’s crust in small amounts
usually in ore which also contains zinc, silver and copper (Geoscience Australia 2014).
Lead may take several forms depending on the pH, salinity and humic content of the
medium (Agency for Toxic Substances and Disease Registry 2014). Exposure to Pb can
occur from the inhalation or ingestion of lead dust, particles or exhaust emissions from lead
being burnt (Australian Government Department of the Environment 2014). Lead is found in
air, water and soil in a range of compounds with the bioavailability and persistence largely
determined by the compound formed, with organic lead the most toxic (Alloway and Ayres
1997). The health effects of exposure to Pb can be both acute and chronic (Australian
Government Department of the Environment 2014). In children, exposure to Pb can result
in reduced intelligence, slowed growth and hearing problems while in adults, increased
blood pressure, brain and kidney damage and damage to the reproductive organs is
common (Agency for Toxic Substances and Disease Registry 2014).
Zinc (Zn) is a relatively abundant bluish-white, lustrous, diamagnetic metal, often found in
association with other base metals such as lead, silver and copper (Geoscience Australia
2014). Zinc may take several forms depending on the pH of the medium and temperature
with acidic conditions increasing availability. Due to an electrochemical reaction known as
galvanic action, Zn is commonly used as an anti-corrosion coating in the construction,
transport and appliance manufacturing industries (Geoscience Australia 2014). Zinc is also
used to create alloys such as bronze, pigments, salts, oxide additives to rubber and in
fertilizers (Geoscience Australia 2014). While Zn is a mineral essential for human, animal
and plant health, the absorption of excessive Zn in humans results in Iron (Fe) and Copper
(Cu) deficiencies which cease with a reduction in exposure (Harmaza & Slobozhanina
2014; Department of Human Services 1997). Excess Zn in soil water results in plants
exhibiting Phosphorous (P) and Fe deficiencies and eventual death if exposure is not
reduced (Reichman 2002).
A 1973 survey of ceiling dust, room dust and soil in Boolaroo and Argenton revealed that
Pb levels ranged from 2759-30,764 parts per million (ppm), 23-35,870 ppm and 8-26,794
ppm respectively (NSW Health Department 1991). As Zn was not a focus of the 1973
survey, no information is provided by the 1973 survey. The Australian guidelines for the
assessment of contaminated sites recommend further investigation if soil levels are above
300 ppm (former Standing Council on Environment and Water 2014). Information regarding
if the sediments of Cockle Creek were tested at this time is not available. Since 1973
regular testing has occurred in the suburbs surrounding the PCCS largely related to a Lead
Abatement Strategy (LAS) which was developed in conjunction with Department of
Environment, Climate Change and Water New South Wales and Lake Macquarie City
Council Health in response to the high levels found in humans and soil (Pasminco 2014).
The LAS concluded in February 2013. Kim, Owens and Naidu (2009) conducted an
independent heavy metal distribution, bioaccessibility and phytoavailability study of the
suburbs considered contaminated and others further afield. Lead levels of between 79
mg/Kg and 58,000 mg/Kg were found in the suburbs previously tested in 1973 and levels
between 8 mg/Kg and 235 mg/Kg were found in those areas outside of the 1973 test area
(Kim et al. 2009). Zinc levels of between 310 mg/Kg and 90,000 mg/Kg were found in the
suburbs tested for Pb in 1973 and levels of between 5 mg/Kg and 660 mg/Kg were found
outside of the 1973 Pb test area (Kim et al. 2009).
The NSW Department of Public Works and Services conducted a study in 2002 which
involved the testing of Pb and Zn levels from sediment cores taken from 21 sites
surrounding PCCS, including Cockle Creek, Cockle Bay and Lake Macquarie. That study
provided Pb levels of 326 to 1360 mg/kg and Zn levels of 1003 to 2700 mg/kg (NSW
Department of Public Works and Services 2002) which are in excess of the Australian
guidelines (former Standing Council on Environment and Water 2014). Chariton, Maher
and Roach (2011) tested sediment pore water from Cockle Bay in Lake Macquarie. Their
results indicated Pb of 260 mg/kg and Zn of 550 mg/Kg, however, these levels do not
indicate the Pb and Zn level of the sediment particles but rather the Pb and Zn available for
extraction by water from the sediment (Chariton et al. 2011).
The proposed study will test the Pb and Zn levels in sediment cores from five sites in
Cockle Creek. Testing will be performed upstream from PCCS and the remainder at evenly
distributed points between PCCS and Cockle Bay. It is expected that the Pb and Zn results
will be consistent with results of the studies performed by the NSW Department of Public
Works and Services (2002), Kim, Owens and Naidu in 2009 and Chariton, Maher and
Roach in 2011.
Sampling site and procedure
Samples were collected from five sites, upstream from (Site 1 (control site)), level with (Site
2) and downstream from (Sites 3, 4 and 5) the smelter site (Figure 2). Sampling was
performed by the author and an assistant during clear weather on Sunday 27 July 2014,
between 1.00 pm to 3.00 pm. Each sample was collected at least 100 cm from the bank
and from submerged sediments. When collecting the sampler would walk into the creek,
find a location free of rocks and thrust the sediment core sampler into the creek bed until
the sampler reached an impenetrable surface. After excess water was allowed to drain from
the sediment core sampler, the sampler was opened and the sediment core was halved
using a stainless steel trowel with the upper and lower halves placed in a labelled plastic
collection containers. On collection samples were immediately placed in an esky with
icebricks for transportation to refridgeration where they were stored until analysis.
Fig 2. Map showing the location of sample collection for the testing of Pb and Zn levels
from sediments of Cockle Creek, NSW (Google Maps 2014).
GPS coordinates and general site details were recorded for each site (Appendix A, Table
1). All equipment was decontaminated prior to collection at the first site and after collection
at each site by rinsing any visible debris from the equipment with creek water, then rinsing
with Decon 90 followed by rinsing with distilled water. One field and two rinsate blanks were
taken during collection.
Sample preparation for analysis
Samples were kept refridgerated for a period of one week prior to processing for analysis.
To ensure analysis of a representative sample the contents of each of the ten samples
collected were mixed prior to sample removal and weighing.
To prepare samples for analysis by x-ray fluorescence spectroscopy, approximately 10
grams of each sediment sample was measured into labelled beakers and oven dried at
110oC (Figure 3) for a period of one week.
Fig 3. Oven drying of sediment samples.
Following dessication large debris was removed and each sample ground to a fine powder
by mortar and pestle (Figure 4).
Fig 4. Grinding of oven dried soil.
Labelled x-ray cannisters (Figure 5) were filled with sufficient sample to cover the bottom of
the cannister for analysis.
Fig 5. Sediment samples in x-ray canisters
ready for analysis.
For analysis by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES),
approximately 10 grams of each sediment sample was measured into labelled beakers for
digestion (Figure 6).
Fig 6. Weighed sediment samples ready for
Additions of 5 mL each of concentrated nitric acid and concentrated hydrochloric acid were
made to each sample. Beakers were covered with watchglasses and placed on a hotplate
and boiled approximately 18 hours (Figure 7). During the digestion process further additions
were made of nitric and hydrochloric acid and of concentrated hydrogen peroxide. Each
hour the condensation on the watchglasses were rinsed into the beakers using distilled
water. Sulfuric acid (18 M) was added to samples from Site 4 to digest the remaining
Fig 7. Digestion of samples on a hotplate.
Following digestion the samples were cooled and then filtered through 45 filter paper to
remove sediment (Figure 8).
Fig 8. Filtering of sediment from samples.
To ensure all sediment was removed from the samples they were vacuum filtered through
Millepore (Figure 9).
Fig 9. Vacuum filtering samples through
Following filtering, samples were placed into volumetric flasks and made up to 100ml with
distilled water (Figure 10). Standards of 1 mg/L, 10 mg/L and 100 mg/L of Pb and Zn were
prepared from 1000 mg/L Pb and 1000 mg/L Zn (Figure 10) and analysed to obtain the
standard curve of absorbancy.
Fig 10. Standards of 1 mg/L, 10 mg/L and
100 mg/L of Pb and Zn in the
foreground with filtered samples
ready for ICP analysis.
X-ray fluorescence analysis of oven dried sediment was performed on an X-ray MiniPal4
PANalytical (Figure 11).
Fig 11. Sediment prepared for x-ray
ICP analysis of the digested sediment samples and Pb and Zn standards was performed on
a Varian Liberty AX Sequential ICP-AES (Figure 12).
Fig 12. ICP analysis of sediment samples
and Pb and Zn standards.
Data obtained from the analysis of the samples by x-ray fluorescence was initially reviewed
to determine the presence and identity of metals. As x-ray fluorescence is a quantitative
rather than qualitative analysis tool the presence of each element identified can only be
reported as present and it’s quantity in relation to the other elements present.
Data obtained from analysis of the standards by ICP was entered into an excel spreadsheet
and graphed to find the standard curve. The absorbancy equation obtained for Pb: y =
1350.1x - 580.85 (R2 = 1) and for Zn: y = 9562x - 53963 (R2 = 0.9924). Following analysis
of the sediment samples, this equation was used to determine the concentration of Pb and
Zn and the results calculated (Appendix B, Table 1) and graphed in Excel (Figures 13 and
Analysis by x-ray fluorescence indicates that the number of elements present in the
sediments increased in both number and readable amount with the progression of the creek
from Site 1 to Site 5 (Appendix B, Figures 1 to 10). The elements identified are displayed in
Table 1. Elements identified in Cockle Creek sediments.
Element Site 1 Site 2 Site 3 Site 4 Site 5
B T B T B T B T B T
B: Bottom of sediment core
T: Top of sediment core
: Element not present
: Element present
No Pb was detected by x-ray fluorescence spectroscopy in any of the samples.
Analysis by ICP of Pb concentration indicates that on average higher levels were retained
in the deeper sediments of Cockle Creek (Figure 13). The mean concentrations of Pb found
cores were 284.68 mg/kg in the bottom half of the sediment cores and 226.12 mg/kg in the
top half of the sediment cores.
Fig 13. Concentration of Pb found in sediment of Cockle Creek, NSW, as determined by
Analysis by ICP of Zn concentration indicates that on average higher levels were retained in
the deeper sediments of Cockle Creek (Figure 14). The mean concentrations of Zn found
cores were 683.86 mg/kg in the bottom half of the sediment cores and 587.96 mg/kg in the
top half of the sediment cores.
Fig 14. Concentration of Zn found in sediment of Cockle Creek, NSW, as determined by
1 2 3 4 5
1 2 3 4 5
Differences were also found in the concentration of Pb and Zn between sites. From the
samples taken, Sites 1, 2, 3 and 4 contained Pb concentrations below the 600 mg/kg
Health Investigation Level (HIL) maximum recommended by National Environment
Protection Measures (NEPM) 2013 for open space areas (Appendix C, Table 1). Lead
concentration of the sediment in the top half of the core sample taken from Site 5 was
below the NEPM HILs, however sediment in the bottom half of the core exceeded the
NEPM HILs at 848.31 mg/kg. Zinc levels across all sites were within the maximum NEPM
HILs with Site 3 providing the lowest concentration and Site 4 the highest.
The aim of this study was to determine if Pb and Zn concentrations in Cockle Creek are
consistent with the results of the studies performed by the NSW Department of Public
Works and Services (2002), Kim, Owens and Naidu in 2009 and Chariton, Maher and
Roach in 2011. As expected our study found that sediments analysed by ICP-AES
displayed the lowest Pb levels at Site 1 (control site) and highest at Site 5. The variation
found at Sites 2, 3 and 4 could be due to the thickness of the riparian vegetation trapping
sediments prior to entry to the creek, the side of the creek sampled in relation to creek flow
and the taking of one sediment core only from each site. However, while zinc levels did not
exceed the NEPM HILs at any of the sites, Site 3 provided the lowest concentrations and
Site 4 the highest. The reasons for this variation could be similar to the findings for Pb such
as riparian vegetation, the side of the creek sampled and the taking of one sediment core
from each site.
Analysis by x-ray fluorescence spectroscopy did not provide results consistent with previous
studies or the results of this study from ICP-AES analysis with regards to Pb levels. This
inconsistency may be due to the amount of energy employed during x-ray analysis or the
broadness of the spectrum used. A different result may have been obtained if the x-ray
analysis was repeated with a spectrum specific to Pb at a higher energy level.
Of note is the variation in sampling that occurred between this study and previous studies.
The NSW Department of Public Works and Services did not conduct sampling but drew
from previous studies which had utilised a range of sampling techniques at a range of
locations. Kim, Owens and Naidu (2009) collected surface soil samples while Chariton,
Maher and Roach (2011) collected the top 10 cm of creek sediment from Cockle Creek
which they considered representative of sediment deposition over the past 15-20 years.
This study collected sediment samples to a depth of 25 cm at Sites 1, 2 and 3 and to a
depth of 50 cm at Sites 4 and 5. At each site the corer was sunk to the deepest depth
permitted by the underlying bedrock. This method was considered appropriate due to the
underlying bedrock restricting the depth of the sediment profile.
However, overall the study results are consistent with previous studies when considered in
context with the sampling locations and methods. The NSW Department of Public Works
and Services refers to the Pb and Zn concentrations in sediments taken from Cockle Creek.
While it is not known the exact location or the depth of sampling and the levels reported,
are greater than our study obtained, the studies referred to were conducted between 1982
Of the locations sampled by Kim, Owens and Naidu (2009), two were closely located to the
creek sediments collected in this study. Surface soil collected upstream from Site 4 and 5 of
this study, provided Pb concentration levels that were much higher than the NEPM HILs.
Creek sediments collected from Site 4 were close to the maximum NEPM HILs permitted
for residential use with soil access but below the levels permitted for open area use. The
top of the sediment core for Site 5 was within the maximum NEPM HILs permitted for open
area use but would have exceeded the levels for residential use with soil access if it had still
been surface soil. Of note is the high level of Pb found in the bottom of the sediment core
for Site 5 which exceeded both the maximum NEPM HILs permitted for open area use and
residential use with soil access.
Chariton, Maher and Roach (2011) sampled sediment from Cockle Bay which is the inlet
area where Cockle Creek flows into Lake Macquarie, close to Site 5 of our study. The high
results obtained in our study may have two explanations. Sampling in the 2011 study may
have occurred further into the lake where the sediment from the creek may have been
deposited over a greater area and so was thinner at any one point, thus providing a lower
concentration per kg of sediment. Secondly, the sediment core collected was to a depth of
50 cm and does not appear to have been mixed prior to analysis which could potentially
result in only the top of the core being tested. With the expected rate of deposition into lake
Macquarie being between 1 to 7 mm per year (Hollins et al. 2011), the sediments tested
may have been deposited after the smelter closed.
Sediment deposition rate explains the higher concentration of Pb and Zn in the bottom half
of almost all of the sediment cores across Sites 2, 3, 4 and 5. Riparian vegetation reduced
at each site which would explain the reduction in sediment with the progression of the creek
towards Lake Macquarie. It is likely that the bottom half of the sediment cores represent
deposition from over 25 years ago (Hollins et al. 2011), prior to a reduction in contaminants
released by the smelter. As the top half of the sediment cores contained lower levels of Pb
and Zn it would appear that less contaminated sediments have entered Cockle Creek in the
past 25 years.
Our results are consistent with previous studies and with what would be expected eleven
years after the smelter ceased operation. While Pb levels are in excess of the NEPL HILs
for open space in the bottom half of the sediment core from Site 5, it is unlikely that the Pb
is bioaccessible unless the deep creek sediments are dredged or the creek develops an
acidic environment. However, without any further addition of contaminants and or
disturbance of the creekbed, Cockle Creek can be considered environmentally safe and
stable after 106 years of contamination.
Table 1. Site specific information for sampling of sediments from Cockle Creek, NSW.
The Weir Rd
Northern end of
Speers Point Park
at junction of
Cockle Creek and
GPS Coordinates 32o56’7” 151o35’44” 32o58’38” 151o32’27” 32o57’11” 151o37’1” 32o57’11” 151o37’1” 32o58’1” 151o36’48”
Distance from bank 200 cm 100 cm 150 cm 200 cm 250 cm
Water flow rate Slow Medium Medium Medium Medium
Depth of sample 25 cm 25 cm 25 cm 50 cm 50 cm
Sample colour Black Black Black Black Black
Sample texture Clayey fine gravel Fine clay Fine clay Fine silty clay with
Sandy with large
Sample odour Strong sulfur Sulfurous and oily Slightly sulfurous Slightly sulfurous None
Riparian vegetation Thick vegetation of
river ash, she oaks
and reeds approx 2
metres thick along
oaks, reeds and
grasses approx 2
metres thick along
and grasses approx
2 metres thick along
Features of site Inside curve of
Near railway line Close to Lucky’s
Across from the Five
Inner edge of
Fig 1. X-ray fluorescence analysis of the bottom of the sediment core from Site 1.
Fig 2. X-ray fluorescence analysis of the top of the sediment core from Site 1.
Fig 3. X-ray fluorescence analysis of the bottom of the sediment core from Site 2.
Fig 4. X-ray fluorescence analysis of the top of the sediment core from Site 2.
Fig 5. X-ray fluorescence analysis of the bottom of the sediment core from Site 3.
Fig 6. X-ray fluorescence analysis of the top of the sediment core from Site 3.
Fig 7. X-ray fluorescence analysis of the bottom of the sediment core from Site 4.
Fig 8. X-ray fluorescence analysis of the top of the sediment core from Site 4.
Fig 9. X-ray fluorescence analysis of the bottom of the sediment core from Site 5.
Fig 10. X-ray fluorescence analysis of the top of the sediment core from Site 5.
Table 1. Health Investigation values in mg kg-1 for soil from NEPM 2013
Health Investigation Levels
values in mg kg-1
A B C D
Arsenic2 100 500 300 3 000
Beryllium 60 90 90 500
Boron 4500 40 000 20 000 300 000
Cadmium 20 150 90 900
Chromium (VI) 100 500 300 3600
Cobalt 100 600 300 4000
Copper 6000 30 000 17 000 240 000
Lead3 300 1200 600 1 500
Manganese 3800 14 000 19 000 60 000
Mercury (inorganic)5 40 120 80 730
Methyl mercury4 10 30 13 180
Nickel 400 1200 1200 6 000
Selenium 200 1400 700 10 000
Zinc 7400 60 000 30 000 400 000
Cyanide (free) 250 300 240 1 500
A Residential use with garden/accessible soil
B Residential with minimal opportunities for soil access
C Parks, recreational open space and playing fields
D Commercial/industrial use
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