Mt Todd Fish Surveys 2008 & 2009
Mine Evaluations – Authorisations & Evaluations Division
Authors
M Welch
Contributions
Status
Final
Submission Date
Reviewers
C Edwards, A Frostick, G Robinson, E McGovern, R McDonald & S
Syeda
Mt Todd Rehabilitation Reference Group
Distribution
June 2010
EXECUTIVE SUMMARY
Report Focus
Fish surveys and tissue analyses of heavy metals were undertaken to address
stakeholder concerns regarding the potential impact of the Mt Todd mine site on the
health of fish communities and metal concentrations in fish tissues in the Edith River.
Surveys were conducted over two dry seasons (August 2008 & 2009) and results
were compared with food quality guidelines to provide a first pass assessment of any
potential risks to human health associated with consumption of fish captured in the
vicinity of the mine site.
Major Findings
A total of 20 fish species were recorded during the surveys, with nearly twice the
number of species recorded at a site upstream of the mine compared to a site
downstream. Although it is possible that this may indicate an impact of the mine site
on fish community health, the differences in habitat characteristics between the
upstream and downstream sites make it difficult to make this conclusion with any
degree of confidence.
Results indicated that concentrations of some metals were higher in fish tissues
collected at the downstream site compared with the upstream site, particularly in liver
tissue. This indicates an influence of the mine on metal concentrations in fish tissues.
Further investigation would be required to determine whether the elevated
concentrations of metals are likely to have any physiological effect on fish. However,
prior to undertaking studies into potential physiological effects on fish, tissue samples
should be collected from a more regional perspective (e.g. other catchments), in
order to determine whether the concentrations observed downstream of Mt. Todd fall
within expected concentrations.
Although the human consumption guideline levels are exceeded in several cases, the
actual risk to humans consuming these foods would need to be put into context of the
specific dietary intakes, gender, age and lifestyles of people who would regularly
consume fish from the area. The likelihood that the amounts of fish tissue required to
consistently exceed the guidelines are achievable also needs to be considered, as
capture rates required may not be sustainable in a system such as the Edith River.
However, consideration should be given to informing stakeholders that although likely
to be low, there is some risk to human consumption of significant quantities of fish
livers downstream of the mine site.
It is recommended that the potential mechanisms for transfer of metals from the
water column to fish tissues be further investigated, such as assessing the
bioavailability of sediment-bound metals and whether lower level consumers (e.g.
invertebrates) are responsible for ‘biotransfer’ up the food chain.
Fish surveys and tissue metal analysis should continue on a frequency of every 2-3
years, or more often if there are any substantial increases in concentrations/loads of
metals entering the river from the mine site.
3
Table of contents
1
INTRODUCTION......................................................................................................................... 6
1.1
1.2
2
BACKGROUND ........................................................................................................................ 6
AIMS ...................................................................................................................................... 6
METHODOLOGIES .................................................................................................................... 7
2.1
SAMPLING FREQUENCY & LOCATIONS .................................................................................... 7
2.2
FIELD TECHNIQUES................................................................................................................. 8
2.2.1
Fish collection .................................................................................................................. 8
2.2.2
Environmental data .......................................................................................................... 9
2.3
LABORATORY TECHNIQUES .................................................................................................... 9
2.3.1
Fish samples ..................................................................................................................... 9
2.3.2
Water samples................................................................................................................. 10
3
RESULTS & DISCUSSION ....................................................................................................... 10
3.1
3.1.1
3.1.2
3.1.3
3.2
3.3
3.3.1
3.3.2
3.3.3
3.4
ENVIRONMENTAL DATA ....................................................................................................... 10
Habitats .......................................................................................................................... 10
Water quality .................................................................................................................. 13
Sediment quality ............................................................................................................. 15
FISH COMMUNITY STRUCTURE ............................................................................................. 15
FISH TISSUE CONCENTRATIONS ............................................................................................ 18
Variation between muscle and liver tissues .................................................................... 18
Variation in muscle tissue between sites ......................................................................... 18
Variation in liver tissue between sites ............................................................................ 18
COMPARISONS WITH FOOD STANDARDS ............................................................................... 20
4
CONCLUSIONS & RECOMMENDATIONS ......................................................................... 22
5
REFERENCES ............................................................................................................................ 23
4
Figures
FIGURE 1. LOCALITY MAP OF MT TODD MINE .......................................................................................... 7
FIGURE 2. LOCATIONS OF SAMPLING SITES IN RELATION TO MT. TODD MINE. ........................................... 8
FIGURE 3. UPSTREAM POOL SITE. ............................................................................................................ 11
FIGURE 4. UPSTREAM RIFFLE SITE. .......................................................................................................... 11
FIGURE 5. DOWNSTREAM POOL SITE. ...................................................................................................... 12
FIGURE 6. DOWNSTREAM RIFFLE SITE. .................................................................................................... 12
FIGURE 7. HISTORICAL FIELD PH VALUES FROM 2002 – 2009 ON THE EDITH RIVER UPSTREAM AND
DOWNSTREAM OF MT TODD MINE SITE (DOR DATA). .................................................................... 14
FIGURE 8. HISTORICAL FIELD EC VALUES FROM 2002 – 2009 ON THE EDITH RIVER UPSTREAM AND
DOWNSTREAM OF MT TODD MINE SITE (DOR DATA). NOTE LOG SCALE. ....................................... 14
FIGURE 9. HISTORICAL COPPER (FILTERED) DATA FROM 2002 – 2009 ON THE EDITH RIVER UPSTREAM
AND DOWNSTREAM OF MT TODD MINE SITE (DOR DATA). NOTE LOG SCALE. ............................... 15
FIGURE 10. MEAN MUSCLE TISSUE CONCENTRATIONS AT THE UPSTREAM, DOWNSTREAM AND RAW
WATER DAM SITES (BARS = STANDARD ERROR, VALUES INSIDE BARS = MEAN). ........................... 19
FIGURE 11. MEAN LIVER TISSUE CONCENTRATIONS AT THE UPSTREAM, DOWNSTREAM AND RAW WATER
DAM SITES (BARS = STANDARD ERROR, VALUES INSIDE BARS = MEAN). ........................................ 19
Tables
TABLE 1. FIELD AND LABORATORY PARAMETERS FROM SAMPLES COLLECTED ON 06/08/08 & 12/08/09.
...................................................................................................................................................... 13
TABLE 2. CONCENTRATIONS OF METALS IN SEDIMENTS (DRY WEIGHT) AT THE UPSTREAM AND
DOWNSTREAM SAMPLING SITES. .................................................................................................... 15
TABLE 3. FISH SPECIES COMPOSITION & ABUNDANCE IN EDITH RIVER IN 2008 AND 2009. ..................... 17
TABLE 4. COMPARISON OF MEAN METAL CONCENTRATIONS IN FISH TISSUES WITH FOOD STANDARDS
(MG/KG WET WEIGHT) – VALUES IN RED INDICATE EXCEEDANCES OF GUIDELINE CONCENTRATIONS.
...................................................................................................................................................... 20
TABLE 5. CONSUMPTION RATES OF FISH TISSUES REQUIRED TO EXCEED TOLERABLE WEEKLY INTAKES IN
CASES WHERE FOOD STANDARDS ARE EXCEEDED. ......................................................................... 21
Appendices
Appendix A: Fish tissue metals concentration raw data
5
1
INTRODUCTION
1.1
Background
Mount Todd mine is located 230 km south east of Darwin in the Edith River
catchment, which ultimately flows into the Daly River (Figure 1).
The Northern Territory Government accepted responsibility for rehabilitating the Mt.
Todd Mine site following the collapse of General Gold in 2000 and managed the site
in care and maintenance until December 2006. In 2007, Vista Gold Corporation
formed an agreement with the Northern Territory Government to take on the
management of the site for the purpose of assessing the mineral potential of the
area. As a component of the current agreement, the Northern Territory Government
retains the rehabilitation liability for the long term rehabilitation of conditions on site
predating the agreement. Should Vista choose to mine the site, they will take on the
long term rehabilitation for the site.
The mine site is situated to the north of the Edith River which flows into the Daly
River, an important amateur fishing resource. The mine site operator currently
actively manages an excess inventory of poor quality water with elevated metals
levels resultant from exposure of the mined rock surfaces to water and air and
subsequent acid mine drainage. The water inventory on site is currently reduced by
evaporation and active release to the Edith River at high flow under the stringent
conditions of a water discharge licence (based on dilution rates and ecotoxicity
studies) with the Northern Territory Government. In addition to managed release, at
times of extremely high rainfall the capacity of the retaining pond can be exceeded
resulting in overflow of the Retention Pond 1 Weir to the Edith River.
The observed and potential impacts resulting from elevated levels of metals entering
the Edith River from the Mt Todd mine site have been identified as aspects requiring
more detailed assessment by the Northern Territory Government and mine site
stakeholders (e.g. Jawoyn traditional owners, Amateur Fishing Association of the
Northern Territory – AFANT.
It is likely that a fish kill observed in late 2004 was at least partly due to the toxicity of
first flush water as it entered the Edith River system from the Mt. Todd mine site. To
assess the potential for any health risks of humans consuming fish from the Edith
River, two flesh samples were collected by the Department in January 2005.
Laboratory analysis indicated that metal concentrations were below Australian food
guideline levels. However, it was considered that the low replication of the sampling
was inadequate to draw any firm conclusions regarding risks to human health
associated with consumption of fish. Subsequently, in a presentation to AFANT in
March 2005, a commitment was made by the Department to undertake more
comprehensive sampling.
Surveys of fish communities were undertaken by Mining Evaluations at Mt. Todd
during 2008 and 2009 dry seasons to address Government commitments to
stakeholders and assist in the development of rehabilitation strategies for the site.
1.2
Aims
The aims of this project were to undertake fish sampling in the Edith River
downstream of the Mt. Todd mine site to assist in the evaluation of potential for mine
derived impacts on:

fish community health; and

concentrations of trace metals in fish tissues.
6
Figure 1. Locality map of Mt Todd Mine
2
2.1
METHODOLOGIES
Sampling frequency & locations
Fish surveys were undertaken during the mid dry season, on 5-6 August 2008 and
11-13 August 2009. At this time of the year, although still flowing, pools were formed
in the river channel and this time was chosen as fish were less likely to be actively
migrating between reaches. This reduces the potential for confusion of upstream and
downstream populations. The concentration of the fish assemblages in a smaller
area also made sampling easier. Fish captured in a specific area after isolation for
several months of the dry season, are also more likely to maximise the chances of
potential bioaccumulation of metals for that area.
Two sites were sampled on the Edith River; one upstream and one downstream of
the mine (Figure 2), in both the 2008 and 2009 surveys. The upstream Edith River
site is located about 1 km upstream of the Edith River-Stow Creek confluence at the
bridge crossing of the Edith Falls road. The downstream Edith River site is located
downstream of both the Retention Pond 1 discharge point and the Edith River-Stow
Creek confluence (i.e., downstream of all mine site influence). The sites were chosen
to maximise similarities in fish habitats, although this was constrained to some extent
by accessibility and suitable boat launching locations.
It should be noted that although intended as a reference site, the upstream site
should not be considered a ‘true’ reference site, due to the potential upstream
7
migration of fish from areas influenced by the mine site. To address this possibility,
an additional site was sampled during the 2009 survey at the mine site’s former Raw
Water Dam (RWD), which is artificially stocked with Barramundi. The RWD is located
within a mineralised catchment upstream of any influence of the mine site and
upstream migration of fish is not possible, due to the height of the dam wall.
Both Edith River sites consisted of 50 – 80 metre long pools that had similar depths
and widths. The raw water dam site is a large open water body that is clearly a very
different habitat to the Edith River sites but the objective of sampling this site was to
make additional comparisons of metal concentrations in fish tissues; not fish
community composition.
Figure 2. Locations of sampling sites in relation to Mt. Todd mine.
2.2
Field techniques
2.2.1 Fish collection
The electrofishing technique was used to sample fish, with the assistance of the
Fisheries Research Group (FRG), who have electrofishing equipment (boat-mounted
and backpack units) and the expertise required to operate this equipment. The FRG
are currently involved in research projects in the Daly River catchment that involve
fish sampling, therefore sampling techniques followed their standard procedures so
that data from other sites are comparable. For example, sampling effort is
standardised by the length of time that the electrofishing equipment is operated at
each site.
In the 2008 survey, only the boat-mounted electrofisher was available. Sampling
effort involved a total of 30 minutes electrofishing time with six, five minute ‘shots’
undertaken at each site.
8
In the 2009 survey, both boat and portable backpack units were used. At the
upstream site, the boat unit was used for 25 minutes (5 shots) and the backpack unit
was used for 30 minutes (6 shots). At the downstream site, the boat was used for 50
minutes (10 shots) and the backpack for 25 minutes (5 shots). More sampling effort
was undertaken at the downstream site to ensure there were enough replicates for
tissue analyses. Only the boat unit was used at the raw water dam, as the objective
of sampling fish at this site was to capture fish for tissue analysis and not community
composition.
The effectiveness of electrofishing equipment was markedly reduced by the relatively
low electrical conductivity of the water at sample sites. Additionally, avoidance
behaviour by fish (i.e., escaping from electrode fields) was observed on a number of
occasions. Despite this, a variety of fish species and a sufficient number of replicates
of target species for tissue analysis were captured.
Fish stunned by the electrofisher were scooped up in nets and placed in a holding
tank in the boat or a bucket on the river bank for identification and counting. Fish
retained for tissue analysis were placed in plastic bags on ice and frozen on return to
Darwin. The majority of fish were not required as specimens and were released
unharmed back into the water.
2.2.2 Environmental data
Ancillary environmental data collected at each site included physicochemical water
quality parameters (such as pH, electrical conductivity, metals analyses of water
samples) and descriptions of habitat variables (i.e, depth, substrate, overhanging
vegetation, and snags etc).
Water quality samples were collected by using standard techniques to minimise
potential sample contamination (e.g. nitrile gloves) and samples were filtered and
acidified in the field. Field parameters were measured using pre-calibrated water
quality probes (YSI pH100 & YSI EC300).
2.3
Laboratory techniques
2.3.1 Fish samples
Frozen fish specimens were thawed in preparation for dissections. Strict laboratory
hygiene techniques were observed to prevent cross-contamination between fish
specimens. This involved the washing of trays in Decon 90 solution, rinsing with
demineralised water between samples and the use of sterile disposable scalpels and
gloves.
Muscle tissue samples (without skin) were collected from above the pectoral fin and
anterior to the dorsal fin. Although it is unlikely that most stakeholders would
specifically target liver tissue, samples of this tissue were analysed as a ‘worst case
scenario’ for assessing the risk to human consumption and because many metals are
more likely to accumulate in the liver (e.g. Gbem et al. 2001). For liver tissues,
samples were removed from each specimen by making an incision behind the gill
covers and in most cases, the entire organ removed as a sample.
All tissue samples were placed in sterile vials and re-frozen prior to submission to the
NATA-accredited Northern Territory Environmental Laboratories (NTEL). At the
laboratory, samples were weighed before and after being dried in an oven at 70°C to
allow conversion of data back to wet weights for comparison with food standards.
Dried samples were ground with a mortar and pestle and digested in a concentrated
nitric acid for 2-3 hours at 80-100º C. Samples were analysed for total concentrations
9
of arsenic, cadmium, copper, cobalt, manganese, nickel, lead and zinc using ICP-MS
techniques. These analytes were selected because they have been identified as the
primary contaminants of concern from the Mt Todd mine site, based on water quality
analysis.
2.3.2 Water samples
Water samples were filtered in the field using a syringe and 0.45 µm filters and
preserved by acidification (<1 pH) with concentrated nitric acid. Samples were kept
refrigerated prior to submission to NTEL for analysis of the same metals as for the
fish tissues.
3
3.1
RESULTS & DISCUSSION
Environmental data
3.1.1 Habitats
The channel profile differed between the upstream and downstream sites, with the
downstream site being dominated by a large wide pool and the upstream site
comprising a smaller pool. Average stream depths x widths were 0.8 m x 5.0 m and
1.5 m x 15 m at the upstream and downstream sites respectively. The two sites had
similar riparian canopy cover, overhanging Pandanus habitats and snags. The main
difference between the sites was in bottom substrates and macrophytes (aquatic
plants). The upstream site had a predominantly sand/gravel substrate and large bed
of macrophytes (aquatic plants) in riffle sections above and below the pool, whereas
the downstream site had a predominantly bedrock/cobble substrate with no
macrophytes observed.
In the 2008 survey, only pool habitats were sampled with the boat-mounted
electrofisher, whereas in the 2009 survey, riffles were also surveyed using a back
pack unit. Photographs of sampling habitats are provided in Figures 3 – 6.
The potential influence of these habitat differences on fish communities are
discussed in further detail in Section 3.2.
10
Figure 3. Upstream pool site.
Figure 4. Upstream riffle site.
11
Figure 5. Downstream pool site.
Figure 6. Downstream riffle site.
12
3.1.2 Water quality
At the time of sampling, electrical conductivity (EC) was low and pH was slightly
acidic at both the upstream and downstream sites, which is considered normal for an
upland river in the NT with a sandstone catchment (Table 1). Concentrations of
cadmium were higher at the upstream site, whereas copper, zinc and sulphate
concentrations were higher at the downstream site.
Table 1. Field and laboratory parameters from samples collected on 06/08/08 &
12/08/09.
Site/Year
Upstream 2008
Upstream 2009
Downstream 2008
Downstream 2009
Raw Water Dam
(RWD) 2009
EC
(field)
pH
(field)
As
(ug/L)
Cd
(ug/L)
Co
(ug/L)
Cu
(ug/L)
Mn
(ug/L)
Ni
(ug/L)
Pb
(ug/L)
Zn
(ug/L)
SO4
(mg/L)
15.5
6.57
14.7
7.88
0.15
0.22
0.06
0.19
4.83
0.15
0.06
0.8
<0.10
0.10
<0.20
0.05
0.13
5.31
0.13
0.02
0.9
12.6
<0.10
6.18
0.25
0.1
0.08
0.28
6.36
0.14
0.03
1.3
0.10
15.1
7.83
0.15
<0.20
0.07
0.32
6.09
0.20
0.03
1.5
<0.10
20.6
6.53
3.15
<0.20
0.03
0.57
2.58
0.17
0.04
0.6
<0.10
Water quality data collected by the department at the same upstream and
downstream sites over the past six years are summarised in Figures 7-9, which
demonstrate the historical influence of the Mt Todd mine on water quality in the Edith
River just downstream of the site. This is illustrated by lower pH, higher EC and
higher concentrations of copper, an element that is known to be highly toxic to fish
and other aquatic organisms.
The differences in upstream and downstream water quality are less pronounced over
the past 2-3 years, which may be attributed to improvements in the management of
poor quality water on the mine site associated with improved infrastructure and the
presence of an operator on site. However, it should be noted that the department’s
data is collected less frequently than it was prior to an operator taking responsibility
for the site and samples are not collected during the wet season, when poor water
quality associated with discharges from the site are most likely to occur. The operator
collects samples at a site further downstream (Edith River crossing of Stuart
Highway) and results indicate that there continue to be spikes in copper
concentrations during the wet season when controlled or uncontrolled discharges are
released from the site.
13
pH (field)
Edith R Upstream
Edith R Dow nstream
ANZECC 95% guideline (low er)
ANZECC 95% guideline (upper)
8
7
6
5
4
3
19/04/2001
01/09/2002
14/01/2004
28/05/2005
10/10/2006
22/02/2008
06/07/2009
18/11/2010
Date
Figure 7. Historical field pH values from 2002 – 2009 on the Edith River upstream and
downstream of Mt Todd mine site (DoR data).
EC (field)
10000
Edith R Upstream
Edith R Dow nstream
ANZECC 95% guideline
uS/cm
1000
100
10
1
19/04/2001
01/09/2002 14/01/2004
28/05/2005 10/10/2006
22/02/2008 06/07/2009
18/11/2010
Date
Figure 8. Historical field EC values from 2002 – 2009 on the Edith River upstream and
downstream of Mt Todd mine site (DoR data). Note log scale.
14
Cu (filtered)
Edith R Upstream
Edith R Dow nstream
1000
ANZECC 95% guideline
WDL limit
ug/L
100
10
1
0.1
19/04/2001
01/09/2002
14/01/2004
28/05/2005
10/10/2006
22/02/2008
06/07/2009
18/11/2010
Date
Figure 9. Historical copper (filtered) data from 2002 – 2009 on the Edith River upstream
and downstream of Mt Todd mine site (DoR data). Note log scale.
3.1.3 Sediment quality
Sediment samples were collected as part of a separate study in 2008 (A Frostick
2009, pers. comm.) and results for metals from sediments at fish sampling sites are
presented in Table 2 (where both were analysed). There is an apparent influence of
the mine site on sediment metal concentrations in the Edith River immediately
downstream of the mine, with some metals being substantially higher than the
upstream reference site. However, concentrations were well below sediment quality
guidelines (ANZECC & ARMCANZ 2000).
The potential link between sediment metal concentrations on those in fish tissues is
discussed in Section 3.3.
Table 2. Concentrations of metals in sediments (dry weight) at the upstream and
downstream sampling sites.
Site Location
Sediment guideline*
Upstream site
Downstream site
Mn
Co
Ni
Cu
Zn
Pb
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
-
-
21
65
200
50
31.5
38.2
1.61
2.62
1.97
10.6
1.37
17.8
7.64
21.9
2.15
5.58
* (ISQG Low Trigger Values: ANZECC & ARMCANZ 2000)
3.2
Fish community structure
A total of 20 fish species were recorded during the 2008 and 2009 surveys, including
18 at the upstream site and 10 at the downstream site (Table 3). Western rainbowfish
(Melanotaenia australis) were the most abundant species, with similar numbers
observed at the two sites. Most of the fish species recorded are omnivorous, which
15
means that they are opportunistic feeders and will consume both plant and animal
materials.
The lower species richness at the downstream site potentially indicates an impact of
the mine site. However, there are several confounding factors that make it difficult to
draw any firm conclusions to this effect. Although sites were chosen with the
objective of having similar habitat characteristics, the differences between the sites
outlined in Section 3.1.1 would make it difficult to distinguish between mine impacts
and natural habitat differences that may influence fish communities. For example, the
high primary productivity (and subsequent increase in availability in food resources)
associated with abundant macrophytes beds at the upstream site may result in a
more diverse fish assemblage. The presence of sand/gravel beds at the upstream
site may also contribute to the increased species richness. Other studies have found
that both gravel and macrophytes are important determinants of fish community
structure (e.g. Pusey et al. 1993).
16
Table 3. Fish species composition & abundance in Edith River in 2008 and 2009.
Species
Adontiglanis dahli
Ambassis agrammus
Amniataba percoides
Arius sp.
Craterocehalus stercusmuscarum
Glossamia aprion
Glossogobius sp.
Hephaestus bancrofti
Lates calcarifer
Leiopotherapon unicolor
Megalops cyprinoides
Melanotaenia australis
Mogurnda mogurnda
Nematolosa erebi
Neosilurus ater
Oxyeleotris lineolata
Porochilus rendahli
Strongylura kreffti
Syncomistes butleri
Toxotes chatareus
Common Name
Toothless Catfish
Sail-fin Glassfish
Banded Grunter
Fork-tailed Catfish
Fly-specked Hardyhead
Mouth Almighty
Flathead Goby
Sooty Grunter
Barramundi
Spangled Grunter
Tarpon
Western Rainbowfish
Purple-spotted Gudgeon
Bony Bream
Black Catfish
Sleepy Cod
Rendahls Catfish
Long Tom
Butler's Grunter
Seven Spot Archerfish
Survey Total No. Species
Overall Total No. Species
Diet
Omnivore
Carnivore
Omnivore
Omnivore
Omnivore
Carnivore
Carnivore
Omnivore
Carnivore
Omnivore
Carnivore
Omnivore
Carnivore
Omnivore
Omnivore
Carnivore
Omnivore
Carnivore
Herbivore
Carnivore
Abundance
Upstream
2008
1
1
1
(1)
(2)
1
Abundance
Upstream
2009
1
(2)
4 (1)
1
15 (100+)
2
Abundance
Downstream
2008
Abundance
Downstream
2009
1 (6)
9 (2)
1
1
1
18 (6)
3 (4)
9
2 (20)
21 (250+)
2 (5)
3 (1)
4
10 (20)
4 (2)
15
(30)
43 (600+)
2
4 (20)
35 (100+)
1
1
(50+)
1 (3)
7
(1)
9
1
3
(1)
4
6
14
11
18
10
Note: Counts shown in brackets are from visual observations.
17
3.3
Fish tissue concentrations
Metals concentration data are presented in Appendix A and summarised in Figure 10
and Figure 11. Note that in order to achieve an appropriate level of replication, mean
metal concentrations were calculated by pooling samples from different species at
each of the two sites. However, ideally identical species would have been compared
between the upstream and downstream sites. Note that where concentrations were
less than detection limits, summary data were calculated using values equal to half
the detection limit. Standard error statistics were calculated to investigate the
variability in data and in most cases; standard errors were relatively low, indicating
that concentrations of metals in fish tissue were not highly variable.
Although there may have been a general improvement in water quality downstream
of the Mt. Todd mine site in recent years (Section 3.1.2), there appears to be a an
accumulation of metals in sediments in the Edith River immediately downstream of
the mine (Section 3.1.3). It is possible that the elevated concentrations of metals in
fish tissue at the downstream site are linked to those in the sediments, as uptake of
metals by fish from contaminated sediments has been widely documented (e.g.
Hardy 1996; Moraes et al. 2003).
Fish tissue concentrations are discussed in detail in the sub-sections below.
3.3.1 Variation between muscle and liver tissues
Concentrations of all metals analysed were higher (in some cases, an order of
magnitude) in liver tissues than in muscle tissues in both 2008 and 2009 surveys
(Figure 10 & Figure 11). This would be expected regardless of the level of
anthropogenic impact, as many metals are more likely to accumulate in the liver (e.g.
Gbem et al. 2001).
3.3.2 Variation in muscle tissue between sites
Mean concentrations of As and Cd were very low and below (or close to) laboratory
detection limits at all sites in both 2008 and 2009. Ni and Mn were higher at the
downstream site than upstream site in both years, while Cu concentrations were
higher at the downstream site in 2008 but not in 2009. Concentrations of Pb were
higher at the upstream site in 2008 but similar in 2009, while Zn was similar at both
sites in 2008 but higher at the upstream site in 2009. Concentrations of Co were
higher at the upstream site in both years, particularly in 2009.
For most metals, concentrations in muscle tissue from the Raw Water Dam (RWD)
site were similar to or lower than the upstream and downstream Edith River sites.
However, concentrations of Pb and Zn were higher than both the upstream and
downstream sites. The reason for this is unclear but may be due to differences in
catchment mineralisation.
3.3.3 Variation in liver tissue between sites
Mean concentrations of As were generally low in liver tissue, with higher values
found at the upstream site than downstream site in 2008 but not in 2009 and were
also higher at the RWD site than both the other sites. Concentrations of Cd, Cu and
Zn were higher at the downstream site in both years. Concentrations of Pb were
higher at the downstream site in 2009 but not in 2008. Concentrations of Co and Ni
were higher at the upstream site in both years and Mn was higher at the upstream
site in 2008 but not in 2009.
For most metals, concentrations in liver tissue from the Raw Water Dam (RWD) site
were similar to or lower than the upstream and downstream Edith River sites.
18
However, concentrations of Pb and Cu were higher than the upstream site, which
may reflect differences in mineralisation between catchments.
Figure 10. Mean muscle tissue concentrations at the upstream, downstream and Raw
Water Dam sites (bars = standard error, values inside bars = mean).
Figure 11. Mean liver tissue concentrations at the upstream, downstream and Raw
Water Dam sites (bars = standard error, values inside bars = mean).
19
3.4
Comparisons with food standards
Comparisons of mean metal concentrations (2008 and 2009) in fish tissues with
available Australian food standards are provided in Table 4. ‘Maximum Levels’ are
legally enforceable, whereas ‘Generally Expected Levels’ are only provided as a
guide in the absence of Maximum Levels for some contaminants.
Neither muscle nor liver tissue concentrations exceeded guideline levels for arsenic
at either the downstream or upstream sites. In muscle tissue (most likely to be
consumed by humans), copper and zinc concentrations exceeded guideline levels at
both the upstream and downstream sites and lead concentrations only at the
upstream site. In liver tissue, guideline levels were exceeded at both sites for
cadmium, copper and zinc.
Table 4. Comparison of mean metal concentrations in fish tissues with Food standards
(mg/kg wet weight) – values in blue indicate exceedances of guideline
concentrations.
Guideline/Tissue
Maximum Level
Generally Expected Level
(90th Percentile)
Upstream liver
Downstream liver
Upstream muscle
Downstream muscle
As
2
Cd
0.68*
Cu
Pb
0.5
2
0.477
0.379
0.276
<0.5
1.22
10.5
0.035
<0.05
36.9
113
2.18
2.95
Zn
15
0.34
0.23
0.64
0.36
100
143
25.8
23.1
FSANZ (2001 & 2008)
* In the absence of a specific guideline for Cd concentrations in fish tissues, this
value was calculated by averaging the maximum levels for all other foods.
Although the guideline levels are exceeded in several cases, the actual risk to
humans consuming these foods should be put into context of the average diet and
whether it is likely that the amounts of fish tissue required to consistently exceed the
guidelines are achievable. Table 5 provides a comparison between ‘residual’
tolerable weekly intakes (ie the difference between what is consumed by the average
person and the maximum that they can safely consume) and the amount of each
tissue required to exceed these intakes for a given metal. Calculations were only
performed in cases where metals in tissues exceeded the Maximum Level or
Generally Expected Level guidelines in Table 4.
For muscle tissue, the lowest mass required to be consumed to exceed the Tolerable
Weekly Intakes (TWI) out of all the metals was 2.59 kg for lead (upstream site),
which may be achievable. However, for all other metals, the mass of muscle tissue
required to exceed the TWI is unlikely to be achievable using conventional (and
legal) fishing techniques (Table 5). Also, it is highly unlikely that the capture rates
required could be sustained in a system such as the Edith River, as fish stocks would
quickly become depleted.
In most cases, the amount of liver tissue required to exceed tolerable weekly intakes
is also unlikely, especially given the small size of fish livers (generally < 5 grams
each). However, the lowest amount required for any of the metals was 38 grams for
cadmium in fish liver from the downstream site; which may be possible. Although
possible, it appears unlikely that any individual person(s) would consume the livers of
20
at least 6-8 fish from the downstream Edith River site on a weekly basis, given the
remoteness of the site and limited accessibility.
Table 5. Consumption rates of fish tissues required to exceed Tolerable Weekly Intakes
in cases where food standards are exceeded.
Guideline/Tissue
Mean weekly intake (mg)1
TWI (mg)2
Residual TWI (mg)3
Cd
0.119
0.518
0.399
Cu
7.77
104
95.8
Pb
0.197
1.85
1.65
Zn
77.7
518
440
Consumption required to exceed
Residual TWI (kg):
Upstream liver
Downstream liver
Upstream muscle
Downstream muscle
0.327
0.038
n/a
n/a
2.60
0.849
44.0
32.5
n/a
n/a
2.59
n/a
4.41
3.08
17.1
19.0
1 20th Australian Total Diet Survey (FSANZ 2003)
2 Tolerable Weekly Intake (FSANZ 2003), assuming an average adult body weight
of 74 kg
3 Calculated by subtracting mean weekly intake from tolerable weekly intake
21
4
CONCLUSIONS & RECOMMENDATIONS
A total of 20 fish species were recorded during the surveys, with nearly twice the
number of species recorded upstream of the mine compared to downstream.
Although it is possible that this may indicate an impact of the mine site on fish
community health, the differences in habitats between the upstream and downstream
sites make it difficult to make this conclusion with any degree of confidence.
Concentrations of some metals were higher in fish tissues collected at the site
downstream of the mine than the site upstream of the mine, particularly in liver
tissue. This indicates a very high likelihood of the influence of the mine on metal
concentrations in fish tissues and this was reflected in sediment metal
concentrations. A concurrent sediment study using lead-isotope ratios confirms that
sediments in the Edith River downstream of the mine site contain signatures that
represent the mined host rock (A. Frostick pers. comm.). Further investigation would
be required to determine whether the elevated concentrations of metals are likely to
have any physiological effect on fish. However, prior to undertaking studies into
potential physiological effects on fish, tissue samples should be collected from a
more regional perspective (e.g. other catchments), in order to determine whether the
concentrations observed downstream of Mt. Todd fall within expected concentrations.
Although the human consumption guideline levels are exceeded in several cases, the
actual risk to humans consuming these foods would need to be put into context of the
specific dietary intakes, gender, age and lifestyles of people who would regularly
consume fish from the area. The likelihood that the amounts of fish tissue required to
consistently exceed the guidelines are achievable also needs to be considered, as
capture rates required may not be sustainable in a system such as the Edith River. In
the interim, consideration should be given to the provision of this quantitative
information to stakeholders to ensure that although likely to be quite low, there is
some risk to human consumption of fish livers downstream of the mine site.
It is recommended that the potential mechanisms for transfer of metals from the
water column to fish tissues be further investigated, such as assessing the
bioavailability of sediment-bound metals and whether lower level consumers (e.g.
invertebrates) are responsible for ‘biotransfer’ up the food chain.
Fish surveys and tissue metal analysis should continue on a frequency of every 2-3
years, or more often if there are any substantial increases in concentrations/loads of
metals entering the river from the mine site.
22
5
REFERENCES
ANZECC & ARMCANZ (2000). Australian and New Zealand Guidelines for Fresh
and Marine Water Quality. Australian and New Zealand Environment and
Conservation Council & Agriculture and Resource Management Council of
Australia and New Zealand.
Food Standards Australia & New Zealand – FSANZ (2001). Generally expected
levels for metal contaminants- additional guidelines to maximum levels in
Standard 1.4.1.
FSANZ (2003). 20th Australian Total Diet Survey- a total diet survey of pesticide
residues and contaminants.
FSANZ (2008). Australia New Zealand Food Standards Code. Standard 1.4.1:
Contaminants and Natural Toxicants.
Gbem T. T., Balogun J. K., Lawal F. A. and Annune P. A. (2001). Trace metal
accumulation in Clarias gariepinus (Teugels) exposed to sublethal levels of
tannery effluent. Science of the Total Environment, 271(1): 1-9.
Hardy, R.D. (1996). Dietary exposure to toxic metals in fish. In: ‘Toxicology of Aquatic
Pollution: Physiological, Cellular and Molecular Approaches’. (Ed E.W. Taylor)
pp 29-60. Cambridge University Press, Cambridge.
Moraes R., Gerhard P., Andersson L., Sturve J., Rauch S. and Molander, S. (2003).
Establishing causality between exposure to metals and effects on fish. Human
and Ecological Risk Assessment 9 (1): 149-169.
Pusey B.J., Arthington A.H. and Read M.G. (1993). Spatial and temporal variation in
fish structure in the Mary River, south-east Queensland: the influence of habitat
structure. Environmental Biology of Fishes 37: 355-380.
23
Appendix A:
Fish tissue metals concentration raw
data – 2008 & 2009
24
Table A1. Raw metals data from fish muscle and liver tissues in the 2008 survey (< = less than detection limit).
Analyte:
Units:
Detection Limit:
Site
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Species
L. calcarifer
L. calcarifer
L. calcarifer
S. butleri
S. butleri
A. dahli
L. calcarifer
L. calcarifer
L. calcarifer
O. lineoloata
S. butleri
S. butleri
A. dahli
N. ater
M. cyprinoides
M. cyprinoides
M. cyprinoides
H. bancrofti
H. bancrofti
H. bancrofti
N. ater
M. cyprinoides
M. cyprinoides
M. cyprinoides
H. bancrofti
H. bancrofti
H. bancrofti
As
Cd
Co
Cu
Mn
Ni
Pb
Zn
mg/kg
0.5
mg/kg
0.05
mg/kg
0.05
mg/kg
0.2
mg/kg
0.05
mg/kg
0.2
mg/kg
0.2
mg/kg
0.5
<
<
0.65
1.32
<
1.22
<
<
0.62
<
<
<
<
<
<
<
1.34
<
<
0.63
<
<
<
<
<
<
<
0.36
0.63
3.57
0.86
3.76
1.95
<
<
<
<
<
<
<
21.4
9.58
11.5
8.66
11.1
5.79
7.87
<
<
<
<
<
<
<
0.54
0.63
1.30
32.4
34.3
7.07
<
<
<
<
0.63
0.43
0.24
9.50
1.51
1.55
3.62
3.79
6.63
9.64
0.21
0.13
0.13
0.38
0.06
0.20
0.19
23.0
15.1
46.2
20.3
30.6
179
1.41
1.50
3.47
1.29
3.64
3.97
1.44
144
178
114
119
16.0
15.9
23.4
1.93
1.79
1.79
18.2
1.03
7.90
2.80
4.49
7.18
13.6
156
130
16.7
1.84
2.18
4.09
3.56
8.67
5.89
3.36
18.4
18.1
12.3
20.3
5.42
10.7
11.4
5.52
6.09
3.72
11.1
2.31
5.52
11.6
0.36
<
1.30
2.11
8.67
0.49
<
<
0.50
<
0.28
1.70
0.24
1.00
0.90
0.65
1.07
<
0.52
5.08
<
<
0.26
2.56
<
0.82
0.76
<
<
0.26
0.79
2.04
0.24
<
<
<
<
0.28
7.38
<
1.75
0.60
0.65
0.81
<
<
0.51
<
<
<
2.56
<
1.09
<
56.6
99.7
132
103
108
167
30.4
20.0
23.0
15.5
21.0
15.6
24.6
196
198
145
195
91.4
118
110
24.1
20.5
14.7
18.6
17.3
36.8
28.0
Tissue
liver
liver
liver
liver
liver
liver
muscle
muscle
muscle
muscle
muscle
muscle
muscle
liver
liver
liver
liver
liver
liver
liver
muscle
muscle
muscle
muscle
muscle
muscle
muscle
25
Table A2. Raw metals data from fish muscle and liver tissues in the 2009 survey (< = less than detection limit).
Site code
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Upstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Downstream
Species
L. calcarifer
L. calcarifer
L. calcarifer
H. bancrofti
H. bancrofti
H. bancrofti
H. bancrofti
L. calcarifer
L. calcarifer
L. calcarifer
H. bancrofti
H. bancrofti
H. bancrofti
H. bancrofti
H. bancrofti
H. bancrofti
L. calcarifer
L. calcarifer
L. calcarifer
L. calcarifer
H. bancrofti
H. bancrofti
H. bancrofti
L. calcarifer
L. calcarifer
L. calcarifer
Tissue
liver
liver
liver
liver
liver
liver
liver
muscle
muscle
muscle
muscle
muscle
muscle
muscle
muscle
muscle
liver
liver
liver
liver
liver
liver
liver
muscle
muscle
muscle
Length (cm)
42.3
47.8
65.5
22.5
28.5
29
35
42.3
47.8
65.5
22.5
28.5
29
33
33
35
38.5
47
60
63
26.5
30
38
38.5
47
60
As
mg/kg
0.5
<
<
<
0.631
<
<
<
<
<
<
<
<
<
<
<
<
<
0.621
<
<
<
<
<
<
<
<
Cd
mg/kg
0.05
0.842
13.3
Co
mg/kg
0.05
0.306
1.43
Cu
mg/kg
0.2
39.5
1272
Mn
mg/kg
0.05
3.98
6.13
Ni
mg/kg
0.2
<
0.545
Pb
mg/kg
0.2
<
<
Zn
mg/kg
0.5
59.0
168
0.673
0.504
0.236
0.577
0.327
<
<
<
<
<
<
<
0.258
<
2.57
4.72
9.63
11.9
19.6
16.2
4.00
<
<
<
0.577
7.31
6.54
8.21
3.73
<
<
<
0.193
0.129
0.064
<
5.62
0.063
0.642
3.29
0.972
1.02
6.28
5.94
3.13
<
<
<
21.9
13.1
11.0
15.9
8.10
1.01
1.27
0.770
1.03
1.03
0.771
1.27
12.1
1.26
268
390
269
108
30.5
15.1
8.53
1.25
1.24
0.774
4.33
52.1
5.04
8.46
2.81
0.631
0.951
0.642
2.18
2.13
2.89
2.10
4.97
1.70
3.37
59.0
9.81
4.41
8.59
3.70
3.00
0.938
1.11
0.903
<
1.26
8.82
0.513
1.05
0.252
<
<
<
0.517
<
0.509
0.258
0.503
<
1.24
1.06
0.339
1.28
1.06
0.533
<
0.248
0.258
<
<
<
<
<
<
<
<
<
<
<
0.254
<
<
<
0.745
0.707
<
<
<
<
<
<
0.258
100
87.6
110
106
86.9
17.0
33.6
18.0
32.1
29.7
18.6
17.8
107
20.1
85.1
215
167
126
178
99.1
90.0
20.6
18.6
20.0
26
Site code
Downstream
Downstream
Downstream
Downstream
Raw Water Dam
Raw Water Dam
Raw Water Dam
Raw Water Dam
Raw Water Dam
Raw Water Dam
Raw Water Dam
Raw Water Dam
Species
L. calcarifer
H. bancrofti
H. bancrofti
H. bancrofti
L. calcarifer
L. calcarifer
L. calcarifer
L. calcarifer
L. calcarifer
L. calcarifer
L. calcarifer
L. calcarifer
Tissue
muscle
muscle
muscle
muscle
liver
liver
liver
liver
muscle
muscle
muscle
muscle
Length (cm)
63
26.5
30
38
57
59.5
61
83
57
59.5
61
83
As
mg/kg
0.5
<
<
<
<
<
1.50
<
<
<
0.623
<
<
Cd
mg/kg
0.05
<
<
<
<
0.359
0.451
0.586
0.528
<
<
<
<
Co
mg/kg
0.05
<
0.127
<
<
0.239
0.376
0.293
0.176
<
<
<
<
Cu
mg/kg
0.2
1.01
0.506
0.529
0.775
10.5
38.8
20.5
18.3
1.04
1.74
1.28
1.03
Mn
mg/kg
0.05
0.824
2.47
4.43
1.42
2.03
3.91
5.05
3.96
0.648
0.436
0.702
1.09
Ni
mg/kg
0.2
0.253
0.506
0.794
<
0.957
0.902
0.586
<
0.259
0.249
0.511
0.513
Pb
mg/kg
0.2
<
<
<
<
<
<
0.586
<
<
<
<
14.1
Zn
mg/kg
0.5
20.3
32.9
31.1
16.8
51.4
78.9
89.3
70.4
20.7
69.1
17.2
20.5
Note: Values in red bold were excluded from statistical analysis due to likelihood of sample contamination.
27