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Introduction
Contrary to the historical belief that the ocean is
immune to pollution due to its vastness, anthropogenic
activity has made oceans susceptible to pollution [1].
Commercial wastes from industries are considered the
major potential source of pollutants nding their way
into the sea – particularly heavy metals and petroleum
hydrocarbons [2]. Heavy metals can bioaccumulate to
toxic concentrations in aquatic food webs, resulting in
serious environmental and ecological consequences [3].
In the aquatic food-web, sh stand at the higher levels and
may accumulate high concentrations of some toxic metals
from both seawater and the food they eat [4-5].
Fish, however, is considered a healthy food in the
human diet because of its high nutritional benets related
to proteins of high biological quality, attractive lipid
composition, benecial minerals, and useful vitamins
[6]. Due to the lipid solubility of heavy metals and their
resistance to several degenerative processes in animal
tissue, different organs of sh can bioaccumulate trace
metals to considerably higher concentrations than those
Pol. J. Environ. Stud. Vol. 27, No. 3 (2018), 1-6
Short Communication
Assessing Toxic Elemental Concentrations
in Marine Fish Trachurus capensis (Cape Horse
Mackerel) and Implications for Public Health
Sanjeev Debipersadh, Ramganesh Selvarajan*, Timothy Sibanda, Richard Naidoo
Department of Environmental Sciences, UNISA Florida Campus, P.O Box 1710, Florida, South Africa
Received: 23 March 2017
Accepted: 18 July 2017
Abstract
While sh is considered a healthy component of the human diet, consumption of sh with high levels
of trace metals in their esh constitutes a public health risk as trace metals have been proven to be toxic.
We investigated the concentrations of toxic elements in seawater and also in different body parts of the sh
Trachurus capensis caught near Durban, South Africa, using inductively coupled plasma-atomic emission
spectrometry (ICP-AES). The highest metal concentration in sh body parts was observed for Pb, followed
by Zn. Signicantly higher levels of Mn were observed in sh gills as compared to the tissue (muscle) and
sh frame. With respect to bioaccumulation, signicantly higher Pb levels were observed in sh tissues
compared to As, Cr, and Mn. In the frame, signicantly higher Pb levels were observed compared to all
other metals except Ba. There were no signicant differences in the concentrations of different metals in
sh gills. Overall, the toxic metal concentrations in the muscle of cape horse mackerel were below levels
of concern for human consumption as dened by the FAO and WHO.
Keywords: Trachurus capensis, public health, toxic metals, bioaccumulation
*e-mail: ramganesh.presidency@gmail.com
DOI: 10.15244/pjoes/75965 ONLINE PUBLICATION DATE:
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Debipersadh S., et al.
found in the water around them [7]. Accumulated toxic
metals from sh could easily interact with human genetic
materials and other bio-macromolecules, leading to
organ distortion, mutation, nervous disorder, kidney
malfunctioning, bone diseases, and cancer [8]. Arsenic,
cadmium, chromium, copper, lead, nickel, and zinc
are the most commonly found toxic trace elements in
nature, which enter water sources by natural means and
through human activities such as wastewater discharge
[9] and are the most likely to accumulate in sh organs.
Consequently, determining heavy metal accumulation in
commercial sh is an important task in order to calculate
the viable risk to human health due to sh consumption
[10].
Trachurus capensis is a pelagic sh species commonly
called mossbunker or cape horse mackerel that forms a
large population in the surface layers of the ocean (pelagic
zone). They are common along the entire coast of South
Africa and Namibia, with the highest population between
the west coast and the Agulhas Bank. It is a common
“by-catch” species that is a high source of protein and
is exported to rural South Africa and other African
countries. While bioaccumulation of toxic elements in
edible sh tissues remains a health concern, relatively
few studies have investigated the levels of metals in some
sh species from the Durban coast [11-12]. The main aim
of this work, therefore, was to estimate the concentration
of toxic trace elements (Al, As, Pb, Cr, Mn, Zn, and Cu)
in seawater and the bait sh T. capensis collected from
selected popular shing spots off the Durban coast, since
they are an important component of the human diet in
this area.
Materials and Methods
Three sites were chosen in and around the harbour of
Durban, South Africa:
– Harbour mouth (S 29°52.017’ - E 31°03.961’)
immediately outside the harbour
– Container (S 29°49.478’ E 31°04.535’), situated about
5 km north of the harbour mouth
– Cuttings (S 29°58.404’ - E 30°59.287’), situated about
10 km south of the harbour where the southern outfall
waste pipes are connected to the ocean (Fig. 1)
Trachurus capensis were caught by rod and reel.
Immediately after shing, all the sh were washed with
seawater and then with fresh tap water, placed on ice,
and brought to the laboratory on the same day for further
analysis.
The sh were dissected into three sections, namely
tissue, frame, and gills. The samples were then dried at
105ºC for 8 h, preceded by ash drying at 650ºC for 6 h.
Triplicate 0.5 g ash samples were then digested with di-
acid (30 ml of HCL and 10 ml of HNO3 in 3:1 ratio) on
a hot plate maintained at 100°C until all materials were
dissolved completely. Samples were then cooled at room
temperature and transferred into 25 ml volumetric asks
containing 2.5 ml of indium (internal standard) for metal
analysis. The samples were subjected to analysis for
various trace metals using inductively coupled plasma-
atomic emission spectrometry (ICP-AES).
The bioaccumulation factor (BAF) in this study was
predicted using the equations of Vaseem and Banerjee
[13]. The EDI was calculated by factoring in the average
metal concentration in a whole sh (this study), the
average daily consumption of sh by an adult person
[14], the average weight of an adult African [15], and the
permissible tolerable daily intake of heavy metals [16].
The statistical package for social sciences (IBM SPSS
Statistics 23) was used for data analysis. Analysis of
variance (ANOVA) was used to determine statistically
signicant differences in the concentrations of metals in
water and in sh body parts at a 0.05 level of signicance
using the least signicant difference (LSD) as the post
hoc test.
Results and Discussion
The concentration of metals in seawater averaged
0.3 mg/L for all metals and in all study sites. The only
slight but statistically insignicant deviation (P>0.05)
was noted for Zn, whose concentration in seawater
was 0.38 mg/L at the site container. The average metal
concentration in different sh body parts is presented
in Fig. 2. This average combines values for sh caught
in each of the sampling sites off the Durban coast. The
highest metal concentration in all body parts assessed
was observed for Pb, followed by Zn, while the lowest
metal concentration in any body part was observed for
Fig. 1. Map of Durban Coast in South Africa (Sampling sites are
marked) Source: CSIR, South Africa.
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Assessing Toxic Elemental Concentrations ...
Mn. Compared to other studies that evaluated metal
concentrations in mackerel, higher metal concentrations
were observed in our study than in previous studies
(Table 1). Reported results in literature showed that metal
accumulation in sh muscle varied widely depending on
location [17], season [18], behavior, and feeding habits
[19].
When the selective tendency of sh body parts
to bioaccumulate metals was analyzed, signicantly
higher levels of Mn were observed in sh gills as
compared to the tissues (muscle) (P = 0.005) and sh
frame (P = 0.008). The differences in the concentration of
the rest of the metals in various sh body parts were not
signicant (P>0.05).
The average concentration of metals in sh tissue
(muscle) in this study was far greater than the average
recorded by Elnabris et al. [14] in a range of sh collected
from different points of the Gaza Strip. Metals have also
been shown to have varying afnities for adsorption to
sh tissues mainly based on varying uptake, deposition,
and excretion rates [20]. When the bioaccumulation
of various metals with respect to sh body parts were
compared, signicantly higher Pb levels were observed
in sh tissue compared to As (P = 0.048), Cr (P = 0.05),
and Mn (P = 0.044). The differences in the concentrations
of other metals in sh tissue were not signicant. In the
sh frame, signicantly higher Pb levels were observed
compared to all other metals (P<0.05) except Ba (P>0.05).
Other signicant metal concentration differences were
between As and Zn (P = 0.03), Cr and Zn (P = 0.027), Cu
and Zn (P = 0.037), and Mn and Zn (P = 0.025). There
were no signicant differences in metal concentration
in the gills. Overall, there was signicantly higher Pb
concentration in all sh body parts compared to all other
metals (P = 0.003), with the exception of Zn (P = 0.185).
The calculated bioaccumulation factor for each metal
conrmed these statistical assertions.
The overall average metal bioaccumulation in this
study was found to be in the order of Pb > Zn > Ba >
Al > Cu > As > Cr > Mn. These ndings contrast with
the ndings of Elnabris et al. [14], who reported higher
concentrations of Zn, Ni, Cu, and Mn as compared to Pb,
and the ndings of Alam et al. [21], who reported higher
concentrations of Cu, Cr, and Zn compared to Pb.
Fish are an important part of a healthy diet because of
their richness in omega-3 fatty acids, essential minerals,
and vitamins [22]. However, because of their trophic level,
sh normally bioaccumulate toxic metals – especially
pelagic sh [23] – from their food, sediments, and water,
as shown by the results of this study. In this regard, the
negative health effects of heavy metals in sh tissue may
outweigh the positive health effects of sh consumption
in the long term. The estimated daily intake (EDI) of
heavy metals (µg/day/person) were calculated (Table 2) in
order to estimate the risk of heavy metal toxicity among
people who consume sh caught off the Durban coast on
a regular basis.
Table 2 shows that the EDI values for As, Ba, Cr, Cu,
Pb, and Zn were within the permissible tolerable daily
intake (PTDI) for an adult weighing 60.7 kg who consumes
an average of 11.66 g of sh a day. Such calculations are
necessary to preserve public health because the toxicity of
metals is dose-dependent [24]. The value of 11.66 g used
for EDI calculations is rather conservative as people are
likely to consume more than 11.66 g of sh per day. The
advantage, however, with using a conservative gure is
that the risk is not overestimated, which may likely cause
unnecessary panic among consumers and unwarranted
loss of revenue for the shing industry. However, it still
remains a fact that aquatic organisms may bioabsorb
toxic metals to levels that might affect even their own
physiological state [20].
The EDI for As was 5.09 µg/day for an adult African.
The main form of As found in sh is the organic As
Figure 2: Log10 average trace metal concentrations in different sh body parts.
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Debipersadh S., et al.
Table 1. Average trace metal concentrations in mackerel caught from different places around the globe.
Metal concentration (µg/g)
Fish Fish body part Cu Zn Pb Cd Fe Mn Cr Reference
Cape horse mackerel (Durban coast,
South Africa)
Muscle 69.3±48.32* 375.66±57.98* 719.01±132.54* ND ND 12.35±0.4* 31.75±16.52* This study
Frame 32.9±27* 274.8±28.5* 67.9±59.5* ND ND 13.7±1.4* 18.1±1.0*
Gills 54.46±45.35* 283±16.97* 403.1±319.71* ND ND 24.33±5.56* 33.316±16.57*
Horse mackerel (Egypt) Muscle 0.77 ± 0.14 4.21 ± 0.19 0.40 ± 0.17 0.2 ±0.02 6.25 ± 0.46 0.18 ± 0.02 ND [20]
Gills 2.26 ± 0.04 39.8 ± 8.16 4.03 ± 1.06 0.56 ± 0.15 168.9±38.69 6.31 ± 0.50 ND
Canned mackerel (Turkey) Muscle 1.01± 0.54 14.54± 7.31 0.31 ±0.87 0.02± 0.03 5.88± 9.44 ND ND [27]
Horse mackerel Muscle 1.6 42 ND 0.04 ND ND ND [28]
Atlantic horse mackerel (Turkey) Muscle 0.95 ± 0.04 37.4 ± 2.9 0.68 ± 0.05 0.50 ± 0.03 74.3 ± 6.1 7.40 ± 0.60 0.95 ± 0.07 [28]
Horse mackerel (Turkey) Muscle 0.4 7.76 0.0001 ND 8.52 0.58 ND [29]
Indian mackerel (Persian Gulf) Muscle 8.86±0.86 35.97±5.33 6.46±0.01 0.17±0.06 ND ND ND [30]
Horse mackerel (southeastern Black Sea) Muscle 1.7 ± 0.04 18.1± 0.95 0.02 ±0.01 0.25 ±0.03 ND 0.56 ± 0.03 0.68 ± 0.05 [31]
ND - Not done *Metal concentration values for the present study were obtained using ash-dried samples
Average metal concentration in whole sh
(AMC µg/g wet weight)
Daily sh consumption rate
(DFC)**
Average adult weight
(AAW)*
Estimated daily metal
intake***
Permissible tolerable daily intake
(PTDI)aPTDIb
60.7
Al 117.32 11.66 60.7 13.31 1,000 60,700
As 26.52 11.66 60.7 5.09 1 60.7
Ba 99.33 11.66 60.7 19.08 20 1214
Cr 31.75 11.66 60.7 6.09 5 303.5
Cu 69.3 11.66 60.7 13.32 140 8,498
Mn 12.35 11.66 60.7 2.37 140 8,498
Pb 719.02 11.66 60.7 138.11 3.6 218.52
Zn 375.67 11.66 60.7 72.16 500 30,350
*Average African adult weight as cited in [15], **DFC value as cited from [14]
***Estimated daily metal intake (EDI) calculated as EDI =
aPTDI values were cited from [16]
bPTDI60.7: permissible tolerable daily intake for 60.7 kg person (µg/day) = PTDIa × 60.7 kg
Table 2. Estimated daily intake of trace elements (µg/day/person) through consumption of the sh T. capensis caught off the Durban sea coast.
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Assessing Toxic Elemental Concentrations ...
compounds such as arsenobetaine [25]. While the
calculated EDI gure for As may have been lower than
the permissible tolerable daily intake for a 60.7 kg adult
African (PTDI60.7), which is 60.7 µg/day, consistent intake
of low levels of As are known to cause adverse health
effects, especially skin ailments [26]. If consumed in high
quantities, As is known to be acutely toxic and has been
linked to an array of ailments including gastrointestinal,
cardiovascular and neurological disturbances [25].
Additionally, As has been reported to result in reduced
growth and reproduction in both sh and invertebrate
populations, and furthermore reduced migration in
sh [27]. The type and severity of adverse effects are
dependent on the life stages of the sh, with the juveniles
more affected than adult sh. Arsenic accumulation may
be higher in benthic sh than in epipelagic or photic
feeders. However, humans are more sensitive to As
than are aquatic organisms, which increases the risk of
adverse health effects in the event that contaminated food
products are consumed.
The EDI value for Cr was 6.05 µg/day, and while this
result may suggest insignicant effects on human health,
Cr has been observed to variably exert toxic effects at
different concentrations in different groups of aquatic
organisms, with sh being more resistant compared to
invertebrates, especially daphniids [28]. For Cu, the EDI
was 13.32 µg/day compared to the estimated PTDI60.7
of 8,498 µg/day. While Cu is an essential micronutrient
that is involved in redox reactions, it is rapidly accu-
mulated by plants and animals and is toxic at low
concentrations in water, where early life stages of
organisms appear to be more sensitive than adults to
copper pollution [27].
In this study, the EDI of Pb as a result of sh
consumption was lower than the estimated PDTI value
for an adult human. However, regular consumption of sh
containing trace levels of bioaccumulated Pb could lead
to headaches, abdominal pain, and various symptoms
related to the nervous system [25]. For Zn, the EDI as a
result of sh consumption was lower than the PDTI60.7
value for a grown person (Table 2). Nevertheless, the
bioaccumulation of Zn in sh muscle still poses some
measure of health risk, especially to regular consumers
of sh. A major difference between this study and the
ndings of Gorur et al. [29] and Gu et al. [30] is that metal
concentrations were highest in the esh (muscle) of the sh
and lowest in the gills; however, in this study as opposed
to their ndings metal concentrations were highest in the
gills and liver, and lowest in the muscles of all sh species
tested. Our results were against expectation since usually
sh are prone to metals adsorbing onto their gill surfaces
while a large amount of metallothionein induction is also
known to occur in sh liver [29].
Conclusion
In conclusion, trace metal pollution of both marine
and freshwater resources represents an important
environmental and public health concern due to their
toxicity and accumulation (bioconcentration) in the food
chain. Additionally, these ndings point to a need for
further and detailed research to determine the extent of
metal bioconcentration by different dietary sh species
and the extent to which this bioconcentration could be
a danger to public health. We suggest that more specic
recommendations regarding human consumption are
done according to periodic evaluations of levels of
environmental pollutants vis a vis bioaccumulation levels
in dietary sh species.
Acknowledgements
The authors would like to thank Mrs. Yolanda Niharoo
for her technical assistance toward metal analysis and
Golden Pond Trading 67(Pty) Ltd. for providing huge
support toward this study.
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