human exposure to mercury, lead and cadmium through consumption of canned mackerel, tuna, pilchard...
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Human exposure to mercury, lead and cadmium through consumption of cannedmackerel, tuna, pilchard and sardine
H. Okyere, R.B. Voegborlo, S.E. Agorku
PII: S0308-8146(15)00040-0DOI: http://dx.doi.org/10.1016/j.foodchem.2015.01.038Reference: FOCH 16989
To appear in: Food Chemistry
Received Date: 24 June 2013Revised Date: 27 March 2014Accepted Date: 3 January 2015
Please cite this article as: Okyere, H., Voegborlo, R.B., Agorku, S.E., Human exposure to mercury, lead and cadmiumthrough consumption of canned mackerel, tuna, pilchard and sardine, Food Chemistry (2015), doi: http://dx.doi.org/10.1016/j.foodchem.2015.01.038
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Human exposure to mercury, lead and cadmium through consumption of canned
mackerel, tuna, pilchard and sardine
H. Okyere, R. B. Voegborlo∗, S. E. Agorku
Chemistry Department, College of Science, Kwame Nkrumah University of Science &
Technology, Kumasi, Ghana
ABSTRACT
Total mercury (Hg), cadmium (Cd) and lead (Pb) concentrations were determined in canned
fish on the Ghanaian market. Total mercury was determined using an automatic mercury
analyzer while cadmium and lead levels were determined by flame atomic absorption
spectrophotometry. The metal contents in the samples, expressed in µgg-1
(wet weight),
varied from <0.01 to 0.20 with an average value of 0.03 for mercury, from <0.01 to 0.45 with
an average value of 0.34 for cadmium, and from <0.01 to 1.44 with an average value of 0.72
for lead. The results indicate that canned fish from the Ghanaian market have concentrations
well below the permissible FAO/WHO for these toxic metals. Thus considering the
Provisional Tolerable Weekly Intake (PTWI) of Hg, Pb and Cd the levels obtained in this
study are unlikely to constitute a significant exposure to the public through consumption of
moderate amounts.
Keywords: mercury, cadmium, lead, mackerel, tuna, pilchard, sardines, Ghana.
INTRODUCTION
Fish is an extremely important component of the human diet in many parts of the world and
provide nutrients such as protein, omega-3 (n-3) fatty acids (that reduce cholesterol levels and
∗ Correspondence to: R. B. Voegborlo; email: [email protected];
2
the incidence of heart disease, stroke, and preterm delivery) and others that are not easily
replaced (Burger et al., 2005; Daviglus et al., 2002). Fish can be preserved in so many ways
including freezing, salting, pickling, smoking and drying. But the most useful way of
preserving seafood is through canning. Canned products especially canned fish have been
found to contain increasingly high amounts of Hg, Pb and Cd as well as some other heavy
metals. These metals are considered the most important form of pollution of the aquatic
environment because of their toxicity and accumulation by marine organisms; and also
because of their persistent and being not easily biodegradable in nature. Metal pollution of
the sea is less visible and direct than other types of marine pollution but its effects on marine
ecosystems and humans are intense and very extensive (Emami et al., 2005). Effluent
discharges by industry, atmospheric depositions and occasional accidental spills of toxic
chemicals are some of the major sources of pollution of the aquatic environment. Apart from
threat from polluted environment, canned fish is subjected to lead contamination during
canning process. Solder used in manufacture of cans has been recognized as a source of lead
contamination during canning (MAFF, 1983).
The toxic effects of heavy metals particularly mercury, cadmium and lead have been broadly
documented (Narvaes, 2002) as well as levels of heavy metals in fish (Catsiki & Strogyloudi,
1999). Mercury vapour is easily transported in the atmosphere, deposited on land and water,
and then, in part released again to the atmosphere. Trace amounts of mercury are soluble in
bodies of water, where bacteria can cause chemical changes that transform mercury to
methylmercury, a more toxic form. Fish absorb methylmercury from water as it passes over
their gills and as they feed on aquatic organisms. Larger predator fish are exposed to higher
levels of methylmercury from their prey. Methylmercury binds tightly to the proteins in fish
tissue, including muscle and cooking does not appreciably reduce the methyl mercury content
of the fish (FDA, 1994). Over the last few decades, there has been growing interest in
3
determining heavy metal levels in the marine environment and this has also drawn attention
to the measurement of contamination levels in public food supplies particularly fish (Kalay et
al., 1999). Several agencies and organizations such as the US Food and Drug Administration
(US FDA), Food and Agriculture Organization (FAO), and the World Health Organization
(WHO) provide guidelines on the intake of trace elements by humans. The joint FAO/WHO
Expert Committee recommended Provisional Tolerable Weekly Intakes (PTWIs) and
acceptable daily intakes as guidelines for food additives and certain contaminants in foods
(FAO/WHO Expert Committee on Food Additives, 2004). The United States uses reference
dose while the UK/European Union has adopted tolerable daily intake (TDI) to estimate the
amount of a substance that can be ingested daily over a lifetime without appreciable health
risk. These safety guidelines represent an intake where there is essentially no risk, as far as it
can be judged from the available scientific evidence (COT, 2004). Canned fish has become
very popular in Ghana because it is affordable and convenient as fast food. Several brands
have consequently become available on the Ghanaian market manufactured either locally or
imported. Owing to the great consumption of this product, the safety issues related to the
possibility of heavy metals contamination are of concern to human health. Despite the global
concern about the dangers of heavy metal contamination, coupled with numerous
publications on heavy metal levels in processed or canned fishes, publications are scanty in
Ghana. This study seeks to estimate the levels of mercury, lead and cadmium in canned fish
samples purchased in Kumasi. Information on the metal content in canned fish is important to
evaluate the exposure of the population to these toxic metals through consumption.
Consequently, evaluation of the estimated weekly intakes of these metals by adults
consuming the different species for the purpose of possible human health risks was further
undertaken.
4
Materials and methods
Cleaning of glassware and sample containers
All glassware and sample containers used were soaked in detergent solution overnight; rinsed
and soaked in 10% (v/v) HNO3 overnight. They were rinsed with tap water followed by 0.5%
(w/v) KMnO4, tap water again and finally rinsed with distilled water. They were then oven
dried before use.
Reagents and solutions
All reagents used were of analytical reagent grade (BDH Chemicals Ltd, Poole, England)
unless otherwise stated. Double distilled water was used for the preparation of all solutions.
Mercury stock standard solution (1000 mg L-1) was prepared by dissolving 0.0677 g of HgCl2
in the acid mixture HNO3-H2SO4-HClO3 (1:5:1) in a 50 ml digestion flask with heating on a
hot plate at a temperature 200 ± 5oC until the solution became clear. The solution was then
diluted to 50 ml with water. Mercury standard working solutions were freshly prepared by
diluting an appropriate aliquot of the stock solution. Stannous chloride solution (10% v/v)
was prepared by dissolving the salt in 1 M HCl. The solution was aerated with nitrogen gas at
50 ml min-1
for 30 min to expel any elemental mercury from it. Five molar (5 M) NaOH was
prepared by dissolving 20 g NaOH in 100 ml double distilled water. KMnO4 (0.5%) in 0.5 M
H2SO4 was prepared by dissolving KMnO4 in 0.5 M H2SO4. Cadmium and Lead stock
standard solutions of 1000 mg L-1 each were prepared from commercial concentrated
standard solutions for atomic absorption spectrometry (E. Merck). Cadmium and Lead
standard solutions were prepared by diluting the stock solutions for the calibration of the
Atomic Absorption Spectrophotometer.
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Sampling and sample preparation
A total of one hundred and eighty (180) samples of canned fish comprising twenty-eight
brands of mackerel, twenty-five brands of sardines, two brands of pilchards and five brands
of tuna were purchased from retail outlets in Kumasi in Ghana. Samples were transported to
the laboratory, coded for easy identification and then stored in clean dry place until time for
preparation. For each canned fish sample, the fish sauce was carefully drained, the content
homogenized and a portion was taken for chemical analysis. Most of the fish sauce consisted
of tomato, water and salt; and in some cases vegetable oil and spices.
Digestion procedure
The fish samples were digested for total mercury determination by an open flask procedure
which was developed by Akagi and Nishimura (1991). In this digestion method, 0.5 g of
homogenized fish sample was weighed into 50 mL volumetric digestion flask, and 1 mL
distilled H2O, 2 mL HNO3:HCIO4 (1:1 v/v) and 5 mL H2SO4 were added in turns. The
mixture was then heated at a temperature of 200 + 50C for 30 min. The sample solution was
then cooled and diluted to 50 mL with double distilled water.
Determination of mercury
Determination of mercury in all the digests were carried out by cold vapor atomic absorption
spectrophotometry (CVAAS) using an automatic mercury analyzer model HG-5000 (Sanso
Seisakusho Co., Ltd, Japan) developed at the National Institute of Minamata Disease
(NIMD).
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Determination of cadmium and lead
The digested sample was used for Cd (228.8nm) and Pb (217.0nm) determination using the
SOLAAR (S Series 711239 v1.23) Flame Atomic Absorption Spectrometer using the
appropriate instrumental conditions.
Quality Assurance
For quality assurance, the instruments were calibrated based on a linear four-point calibration
curve for each element. Standard calibration curves with an r2 between 0.999 and 0.998 were
run during measurements. Continuing calibration verification was performed by analyzing a
standard solution and a blank solution for each of the element at intervals. To verify the
quality of the results, matrix spike/matrix spike duplicates were analysed with each batch of
about 10 samples for each element. For each run, a triplicate sample and three blanks were
analysed. An analytical spike recovery was done by adding increasing amounts of a standard
solution of each element to an aliquot of the digested sample. A matrix spike recovery of the
elements from fish was determined by adding increasing amounts of the solution of each
element to known amounts of two different samples. They were all taken through the
digestion procedure. The resulting solutions were analysed for the concentration of the three
elements using the appropriate instrumental method. The accuracy of the analytical method
used was evaluated by analysis of certified reference material (CRM), Fish Homogenate
IAEA 407 for Hg, Pb and Cd. Four replicates were performed. All the samples were taken
through the digestion procedure. The resultant solutions were analysed for the elemental
concentrations. Precision was determined by conducting five replicate analyses of some of
the samples. All samples were analysed in duplicate and sometimes in triplicate by the
instrument for consistency.
7
RESULTS AND DISCUSSIONS
Total mercury, lead and cadmium concentrations were determined in different canned fish
samples using a rapid open flask procedure. In this study validation of the methodology used
was performed by carrying out recovery studies and analyzing a certified reference material.
Precision was carried out by repeated analysis of samples and yielded results which agreed to
within 8 %. The accuracy of the analytical technique used in this study was determined by
carrying out recoveries and analysis of certified reference material Fish Homogenate IAEA-
407 Certified Reference Material (CRM) from the International Atomic Energy Agency
(IAEA). Results for recoveries for mercury (Hg), lead (Pb), and cadmium (Cd) are presented
in Tables 1, 2 and 3 respectively. Recoveries for Hg in fish ranged from 96 to 105%, from 95
to 107% for Pb and from 100 to 103% for Cd. For assessing the method performance using
CRMs, the measured values of the CRMs were compared with the certified values following
a procedure described by Linsinger (2010). Using Linsinger’s formula, the expanded
uncertainty values obtained were larger than the difference between the certified and the
measured values for Hg, Cd and Pb. The measured mean values for Hg, Cd and Pb were
therefore not significantly different from the certified values. The validity of the method has
been proven by the agreement between the measured and the certified values. The results for
Hg, Cd and Pb in the Certified Reference Material (CRM) are presented in Table 4.
Concentrations of metals in canned fishes and comparison with international dietary
standards and guidelines
The concentration ranges and averages of metals in the various canned fishes analysed are
presented in Table 6 together with some dietary standard and guidelines. Irrespective of the
fish brand or source, the range (µgg-1
wet weight) obtained for the metals in the samples
analyzed are as follows: mercury (<0.01-0.20), cadmium (<0.01 - 0.45) and lead (<0.01 -
8
1.44).
Total mercury (Hg) concentrations in various brands of canned fishes
The summary of results for mercury levels in the various brands of canned fish are presented
in Table 5. A total of 180 samples were analysed for mercury. Mercury levels (µgg-1 wet
weight) ranged from <0.01 to 0.08 with an average of 0.02 ± 0.02 (n = 84) for mackerel, from
<0.01 to 0.04 with an average of 0.02 ± 0.01 (n = 75) for sardines, from 0.01 to 0.03 with an
average of 0.02 ± 0.01 (n = 6) for pilchards and from 0.12 to 0.20 with an average of 0.16 ±
0.03 (n = 15) for tuna. The maximum mercury level was obtained for the tuna brands in this
study and this is attributed to the fact that tuna is recognized as a predator able to concentrate
large amounts of heavy metals. Fish accumulate substantial concentrations of mercury in
their tissues and this can represent a major dietary source of this metal to humans. Mercury is
well known to induce alterations in the normal development of the brain of infants and at
higher level may induce neurological changes in adults (Commission of the European
Communities, 2001). However, the results obtained for mercury in the canned fish analysed
are below the World Health Organisation (WHO) threshold limit of 0.5 µgg-1.
For the mackerel species, Super A1 brand recorded the lowest mercury concentration (<0.01
µgg-1 wet weight, n = 84) whereas Lavy recorded the highest (0.08 µgg-1 wet weight, n = 84).
Analysis of variance showed significant difference in concentrations within the mackerel
species (P<0.05). For Pilchard canned brands, Pomo recorded the least mercury concentration
(0.01 µgg-1
wet weight, n = 6) whereas Vega recorded the highest (0.03 µgg-1
wet weight, n =
6).Analysis of variance showed significant difference in concentrations within the species
(P<0.05). Obaapa recorded the lowest mercury concentration (<0.01 µgg-1
wet weight, n =
75) for sardine brands of fish whereas Talisha recorded the highest (0.04 µgg-1
wet weight, n
= 75). Analysis of variance showed significant difference in concentrations within the species
(P<0.05). For tuna fish, Pomo tuna flakes recorded the least mercury concentration (0.12 µgg-
9
1 wet weight, n = 6) whereas Nampa recorded the highest. Analysis of variance showed
significant differences in concentrations within the species (P<0.05).
All the samples recorded mercury concentrations below the 0.5 µgg-1 limit recommended by
the FAO/WHO (1972) and adopted by many countries (CIFA, 1992). The levels of mercury
in the tuna samples are not alarming when compared to some other areas of the world
(Emami Khansari et al., 2005; CIFA, 1992). The mercury content of tuna fish has variously
been reported as ranging from 0.043 to 0.253 µgg-1
(Emami Khansari et al., 2005), below
which the values of this study fall. Mean mercury levels reported here are lower compared to
values reported for mullets in the Tyrrhenian Sea, an area close to naturally occurring
mercury deposits (CIFA, 1992). However, they were similar to levels in other tropical, less
industrialized areas like Indonesia, Thailand and Papua New Guinea (CIFA, 1992). Agorku
and Voegborlo (2005) reported mercury concentrations in canned tuna fish in Ghana below
the WHO/FAO threshold of 0.5 µgg-1 wet weight. Mercury concentration in the canned tuna
fish analysed in this study showed that the levels were below what was reported by Agorku
and Voegborlo (2005) and Emami Khansari et al. (2005). The concentrations of mercury in
muscle samples of fish from the Persian Gulf were 0.049–0.402 µg g−1
(Raissy and Ansari,
2014). The concentration of mercury reported by FDA (2000) ranged from 0.082 to 0.160
µgg-1
wet weight. These results are comparable with what was reported in this study. The
variation of mercury concentration in the different brands of canned fish analysed could be
attributed to the fact that some fish are older than others. The low levels could be that the
waters in which the fish are obtained have not yet been polluted significantly with mercury.
Only few data are available for comparison in Ghana (Agorku and Voegborlo, 2005). Among
the brands of canned mackerel analysed for mercury, all are in tomato sauce except Golden
country which is in oil sauce. All the tuna canned fish are in oil sauce. For sardine brands,
Lasco, Ohene, B.B, Swallow brand A1, Talisha and Geisha are in tomato sauce while the rest
10
are in oil sauce. The age, source of fish and size of fish could contribute to the levels of
mercury in the fish. With the exception of Bobo, Sankofa, Rising star, Star kist and Ohema
all the canned fish are imported. The highest mercury concentration was obtained in one of
the local brands, Nampa tuna. This means that the canned fish consumed in Ghana both
imported and local do not contribute significantly to the body burden.
Total cadmium concentrations in various brands of canned Fish
One hundred and fifty-one samples out of the total one hundred and eighty samples were
analyzed for cadmium. One hundred and forty-seven out of the samples analyzed were below
detection (<0.01). The summary of results for cadmium levels in the various brands of canned
fishes analyzed are presented in Table 4. Cadmium levels (µgg-1 wet weight) ranged from
<0.01 to 0.44 for mackerel and from <0.01 to 0.45 for tuna. The results for Cd levels were
below detection (<0.01) for both canned sardine and pilchards. The average cadmium
concentration (µgg-1
wet weight) is 0.44 ± 0.01 (n = 68) for mackerel and 0.30 ± 0.29 (n = 13)
for tuna. For tuna canned fishes, Rising star brand recorded the highest Cd concentration 0.45
µgg-1
wet weight and Sankofa recorded the lowest 0.04 µgg-1
wet weight. The rest of the
canned tuna fish recorded <0.01 value for cadmium. For mackerel brand fishes, Golden
Country brand recorded the highest concentration (0.44 µgg-1
wet weight, n = 68) and Vega
recorded the lowest (0.43 µgg-1
wet weight, n = 68) while the rest were <0.01 µgg-1
. The
concentrations of cadmium in the canned tuna fish from the Mediterrean Coast of Libya
reported by Voegborlo et al., (1999) ranged from 0.09 - 0.32 µgg-1. Good agreement was
observed when the results of this study were compared with those reported by other authors
(CIFA, 1992).The cadmium concentrations were low compared to fish from the coast of
Phillipines and in the Northern Indian Ocean (CIFA, 1992). Waqar et al., (2005), recorded
cadmium levels (wet weight) in the range of 0.02 to 0.38 µgg-1
for salmon, 0.07 to 0.64 µgg
-1
11
for tuna and 0.01 to 0.69 µgg-1 for sardines. The highest cadmium concentration was recorded
in sardine. This is in contradiction with what was recorded in this study in which canned tuna
recorded the highest concentration. However the results in this study in general are below
what was reported by Waqar et al., (2005). In all the canned fish analyzed canned tuna fish
recorded the highest cadmium concentration of 0.45µgg-1
followed by mackerel (0.44 µgg-1
wet weight). The concentration of cadmium in canned tuna fish reported by Emami Khansari
et al., (2005) ranged from 0.005 to 0.072 µgg-1
. These results are by far lower than what was
obtained in this study. The Food and Drugs Administration (FDA) of USA also reported
cadmium concentration ranging from 0.006 to 0.088 µgg-1
. These levels are also lower than
what was obtained in this study. The concentration of cadmium varied from one brand of fish
to the other. The variation of the cadmium concentration in the different canned fish analysed
could be attributed to the variation in the age of the fish and the source of the fish. Levels of
Cadmium in canned Sardine and canned Mackerel in Turkey ranged from 0.004 to 0.011 and
0.005 to 0.01 µgg-1
respectively (Manthey-Karl et al., 2014).
For all the samples analyzed and irrespective of the brands, the concentration of cadmium in
the canned fish samples were below the 0.5 mg Cd/kg stipulated by the Codex Committee on
Food Additives and Contaminants (CCFAC, 2001). Cadmium is known to accumulate in the
human body and it induces kidney dysfunction, skeletal damage and reproductive deficiencies
(Commission of the European Committees, 2001). The low concentrations of cadmium in the
canned fishes analyzed suggest that the exposure of the general public to cadmium through
the consumption of canned fish is not significant.
Total lead (Pb) concentrations in various brands of canned fish
One hundred and thirty-nine samples out of the total one hundred and eighty samples were
analyzed for lead. One hundred and twenty-nine out of the samples analyzed were below
12
detection (<0.01). The summary of results for levels of lead in the various brands of canned
fishes are presented in Table 4. Lead (Pb) levels (µgg-1 wet weight) ranged from <0.01 to 0.69
for mackerel, from <0.01 to 1.44 for sardine and from <0.01 to 0.3 for tuna. All the lead
concentration levels in pilchard brands of canned fish recorded were below detection (<0.01).
The average lead concentration (µgg-1
wet weight) is 0.77 ± 0.47 (n = 55) for sardine. For
mackerel Bella brand recorded the highest (0.69 µgg-1
wet weight, n = 71) whereas the rest
recorded below detection (<0.01). For tuna brand canned fishes Pomo tuna flakes recorded the
highest (0.3 µgg-1
wet weight, n = 10) whereas the rest recorded below detection (<0.01). For
canned sardine B.B. brand recorded the highest (1.44 µgg-1
wet weight, n = 55) whereas Flash
brand canned sardine recorded the lowest (0.05µgg-1 wet weight, n = 55). All the pilchard
brands recorded lead concentration below detection (<0.01). These results are lower than what
was recorded by Khanesari et al., (2005) and Ikem and Egiebor, (2005). Several researches
have been carried out to determine lead levels in canned fish (César et al., 2002, Mustafa &
Mustafa, 2006). The concentration of lead determined in canned sardines (sardinella
brasiliensis) from Brazil (César et al., 2002) ranged from 0.77 to 2.15 µgg-1
wet weight. The
results are by far greater than what was obtained in this study (<0.01 – 1.44). Mustafa et al
(2006) recorded lead concentration in the range of 0.09 to 0.4 µgg-1
for canned fish marketed
in Turkey. Some concentrations of lead obtained in this study are higher than what was
reported by Mustafa et al., (2006). Levels of Lead in canned Sardine and canned Mackerel in
Turkey ranged from 0.005 to 0.08 and 0.015 to 0.02 µgg-1 respectively (Manthey-Karl et al.,
2014).
Metal pollution of the sea is less visible and direct than other types of marine pollution but its
effects on marine ecosystems and humans are intense and very extensive. The toxic effects of
lead have been broadly studied (Narvaes, 2002). The concentrations of lead obtained in this
study are less than 2.0 µgg-1
wet weight threshold limit set by the World Health Organisation
13
(WHO, 1996). The low concentrations of lead in the canned fishes analyzed suggest that the
exposure of the general public to lead through the consumption of canned fish is not
significant.
Provisional Tolerable Weekly Intakes (PTWI)
A Joint FAO/WHO expert committee on food additives has recommended a provisional
permissible tolerable weekly intakes (PTWIs) of mercury, cadmium and lead at
concentrations of 5, 7 and 25 µg kg-1
body weight respectively (FAO/WHO, 2004).
For mercury the highest concentration obtained for this study was recorded in nampa tuna
fish (0.2 µgg-1 wet weight). An adult who weighs 60kg must consume about 1500 g of the
nampa tuna (150 g per can) which is about ten (10) cans per week in order to accumulate
300µg of mercury in a week which is the limit set by FAO/WHO expert committee on food
additives. This means that for the other species of fishes which have lower concentrations
more than 10 cans per week will have to be consumed in order to accumulate that much of
mercury in an adult which is highly unlikely for an individual. Moreover the eating habits of
Ghanaians are such that the consumption rate of canned fish is quite low even though data on
the rate of consumption of canned fish in Ghana is unavailable. For cadmium the highest
concentration obtained for this study was recorded in Rising star tuna fish (0.45 µgg-1
). An
adult who weighs 60 kg must consume about 933 grams of the Rising star tuna fish (155g per
can) which is about six (6) cans per week in order to consume 420 µg of cadmium the limit
set by the joint FAO/WHO committee (2004). Even though it is possible for one to consume
six (6) cans of the tuna each week, most Ghanaians prefer taking their fish in other forms
such as fried, salted etc. So the rate of consumption of canned fish is low even though data on
the rate of consumption of canned fish in Ghana is unavailable. The highest lead
concentration was recorded in B.B. sardine (1.44 µgg-1
wet weight). A 60 kg adult must
14
consume about 1042 g of the B.B. sardine (215 g per can) which is about five (5) cans per
week in order to accumulate 1500 µg of lead concentration which is the limit set by the joint
FAO/WHO committee (2004) for 60 kg weight of an adult. Again, it is possible for one to
consume that much of can fish per week but the eating habits of Ghanaians as discussed
before is such that the consumption rate of canned fish is quite low even though data on the
rate of consumption of canned fish in Ghana is unavailable.
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Table 1 Recovery of mercury from canned fish
Sample Hg added (µg) Hg Found (µg) Hg Recovered (µg) % Recovery
0 0.090 - -
Manny
(MA1)
0
0.089
-
-
(0.5g)
0.025 0.114 0.024 96
0.025 0.113 0.024 96
0.05 0.141 0.051 102
0.05 0.141 0.052 105
Table 2. Recovery of lead from canned fish
Sample Pb added (µg) Pb Found(µg) Pb Recovered (µg) % Recovery
18
Pomo tuna flakes
(PF3)
0
0.3
-
-
(0.5g) 0 0.3 - -
2.0 2.2 1.9 95
2.0 2.4 2.1 105
3.0 3.5 3.2 106
3.0 3.4 3.1 103
Table 3 Recovery of cadmium from canned fish
Sample Cd added (µg) Cd Found (µg) Cd Recovered (µg) % Recovery
Sankofa (SAN3)
(0.5g)
0
0.04
-
-
0 0.03 - -
2.0 2.10 2.06 103
2.0 2.04 2.01 101
3.0 3.05 3.02 101
3.0 3.04 3.01 100
Table 4 Results for Hg, Cd and Pb in certified reference material (CRM-IAEA 407 fish
19
tissue)
Metal Range(µgg-1
) Average(µgg-1
) IAEA Range(µgg-1
) IAEA
Average(µgg-1
)
Hg 0.213-0.216 0.215(n = 4) 0.216-0.228 0.222
Cd 0.184-0.187 0.186(n = 4) 0.185-0.193 0.189
Pb 0.115-0.118 0.117(n = 4) 0.10-0.14 0.120
Table 5 Range of values of metals in canned fishes from local markets in Ghana (µgg-1
wet weight)
n: Number of samples analyzed
FAO/WHO,1972
Metal Mackerel Sardine Pilchards Tuna
WHO/FAO(1972)
Standards (µgg-1)
Hg <0.01-0.08(n = 84) 0.01-0.04 (n = 75) 0.01-0.03 (n = 6) 0.12-0.20 (n = 15) 0.5
Cd <0.01-0.44(n=68) <0.01 (n = 64) <0.01(n = 6) <0.01-0.45(n=13) 0.5
Pb <0.01-0.69(n=71) <0.01-1.44 (n = 55) <0.01(n = 3) <0.01-0.3(n=10) 2.0
20
Highlights
• The fish species were imported mackerel, tuna, pilchard and sardine available in local
markets
• Analysis is performed using CVAAS for mercury
• Cadmium and lead were determined by Flame AAS
• Concentrations obtained in this study were well below the permissible FAO/WHO
levels
• Concentrations are unlikely to constitute a significant exposure to the population
through consumption considering the Provisional Tolerable Weekly Intake (PTWI)