African Journal of Biotechnology Vol. 9(31), pp. 4938-4941, 2 August, 2010
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2010 Academic Journals
Full Length Research Paper
Analysis and determination of mercury, cadmium and
lead in canned tuna fish marketed in Iran
Ebrahim Rahimi1*, Mazyar Hajisalehi2, Hamid Reza Kazemeini3, Ali Chakeri2, Amin
Khodabakhsh2, Mohammad Derakhshesh3, Mahdi Mirdamadi2, Abdol Ghaffar Ebadi4, Seyed
Ali Rezvani5 and Maryam Fallah Kashkahi5
1Department of Food Hygiene, Faculty of Veterinary Medicine, Islamic Azad University, Shahr-e Kord Branch, Iran.
2Veterinary Medicine, Faculty of Veterinary Medicine, Islamic Azad University, Shahr-e Kord Branch, Iran.
3Researchers Club, Islamic Azad University, Shahr-e Kord Branch, Iran.
4Department of Biological Sciences, Islamic Azad University, Jouybar Branch, Jouybar, Iran.
5Department of Agricultural Extension and Education, Islamic Azad University, Garmsar Branch, Garmsar, Iran.
Accepted 21 June, 2010
The objective of this study is to determine mercury, cadmium and lead concentrations in 60 canned
tuna fish samples produced and distributed in Iran after digestion by the standard methods of the
Association of Official Analytical Chemists. Mercury contents in canned tuna fish were determined by
cold vapor atomic absorption spectrophotometry while cadmium and lead were determined by graphite
furnace atomic absorption spectrophotometry. The metal contents, expressed in ?g g-1 wet weight for
mercury, cadmium and lead varied from 0.010 to 0.401 (average of 0.125), 0.008 to 0.150 (average of
0.050) and 0.021 to 0.301 (average of 0.096), respectively. The values were comparable and in the range
of the literature values. The results of this study indicate that tuna fish produced and marketed in Iran
have concentrations well below the standards of FAO/WHO levels of these toxic metals.
Key words: Canned tuna fish, heavy metals, mercury, cadmium, lead.
Fish is widely consumed in many parts of the world by
humans because it has high protein content, low saturated
fat and also contains omega-3, calcium, phosphorus, iron,
trace elements like copper and a fair proportion of the B-
vitamins known to support good health (Tucker, 1997).
Beside good health benefits of fish, there have been
many reports on contamination of fish by chemicals in the
environment (Tuzen and Soylak, 2007). Heavy metals are
considered the most important constituents of pollution
from the aquatic environment and the sea because of
their toxicity and accumulation by marine organisms,
such as fish (Inskip and Piotrowsiki, 1985; Emami et al.,
2005). While mercury, cadmium and lead can be tolerated
*Corresponding author. E-mail: Rahimi@iaushk.ac.ir. Tel: +98
381 3361060. Fax: +98 311 6259809.
at extremely low concentrations, they are extremely toxic,
persistent and not easily biodegradable (Ikem and
Egiebor, 2005), and high contaminated fish may cause
health risk to human. The toxic effects of heavy metals,
particularly mercury, arsenic, cadmium and lead, have
been broadly studied (Porto et al., 2005; Houserova et
al., 2007; Catsiki and Strogyloudi, 1999). The major source
of exposure of humans to heavy metals is through food
ingestion (Ikem and Egiebor, 2005).
Tuna which was recognized as a predator is able to
concentrate large amounts of heavy metals (Inskip and
Piotrowsiki, 1985). Canned tuna fish are frequently and
largely eaten in Iran, so the toxic metal content should be
of some concern to human health. Publication on the
concentrations of heavy metals in pressed or canned fish
in Iran is limited. Canned tuna fish from the Persian Gulf
area were used because of the heavy trafficking of oil in
this region that is expected to contaminate the water way
(Emami et al., 2005). The objectives of this study was to
analysis and determine the content of mercury, cadmium
Rahimi et al. 4939
Table 1. Recovery of mercury, cadmium and lead (?g g-1) in canned tuna samples.
Metal Concentration added (?g g-1)
Concentration recovered (?g g-1)
Table 2. Mean contents of mercury, cadmium and lead (?g g-1) in canned
and lead by precise methods in canned tuna fish
produced and distributed in Iran.
MATERIALS AND METHODS
All glassware used were soaked in detergent solution overnight
before being rinsed and soaked in 10% (v/v) HNO3 overnight,
followed by rinsing with distilled water. All reagents used were of
analytical reagent grade Merck, Germany. Standard stock solutions
of mercury, cadmium and lead were prepared by diluting concen-
trated solutions to obtain solutions of 1000 mgl-1. Canned tuna
samples were purchased from popular supermarkets in Sahr-e Kord
and Isfahan, Iran, during September 2008 - June 2009. Sixty tuna
cans were used in this study.
After opening, each cans oil was drained off and the meat was
homogenized thoroughly in a food blender with stainless steel
cutters. Each sample was then taken and digested promptly as
follows: for mercury determination, 1 ± 0.001 g of homogenized
sample was weighed into a 100 ml Erlenmeyer flask and 1 ml of
concentrated HCl was added, and then, 10 ml of conc HNO3 and 5
ml of conc. H2SO4 were slowly added. The flask was then placed on
top of a steam bath unit to complete dissolution. It was then
removed from the steam bath, cooled and the solution transferred
carefully in to a 20 ml volumetric flask; for the reduction of mercury,
5 ml SnCl2 was used. For the determination of lead and cadmium,
about 10 ± 0.001 g of homogenized sample were weighed into a
200 ml beaker and 10 ml of concentrated HNO3 were added. The
beaker was covered with a watch glass, and after most of the
sample was dissolved by standing overnight, it was then heated on
a hot plate with boiling until any vigorous reaction had subsided.
The solution was allowed to cool, transferred into a 50 ml volumetric
flask and diluted to the mark with distilled water (Voegborlo et al.,
1999). For each run, a duplicate sample, spiked samples for
recovery and two blanks were carried through the whole procedure.
Validity of analytical methodology was checked by spiking the
samples with various concentrations of heavy metals for the recovery.
The recoveries of the metals were determined by adding increasing
amounts of metals to the samples which were then subjected to the
digestion procedure. The resulting solutions were analyzed for the
metal concentrations. The results are reported in Table 1.
Mercury was determined in all the digests using cold vapor atomic
absorption spectrophotometry flow infection mercury/hydride analyzer
(FIAS 4100, Perkin Elmer, USA), equipped weigh hollow cathode
mercury lamp operated at a wave length of 253.7 nm. Quartz
absorption cell was used for the mercury determination.
Cadmium and lead concentrations were determined by graphite
furnace atomic absorption spectrophotometry (Perkin Elmer 4100,
USA), employing paralytic platform graphite tubes (Perkin Elmer,
AS-40), ascorbic acid and palladium for matrix modification.
RESULTS AND DISCUSSION
Sixty samples of canned tuna fish were analyzed for
mercury, cadmium and lead. Good recoveries of spiked
samples show accuracy of the analytical methods (Table
1). The results of this study indicated that the concen-
tration varied form 0.010 to 0.401 with mean ± SD value
of 0.125 ± 0.085?g g-1 for mercury, from 0.008 to 0.150
with a mean value of 0.050 ± 0.039?g g-1 for cadmium
and from 0.021 to 0.301 with a mean value of 0.096 ±
0.058?g g-1 for lead (Table 2).
Many previous literatures have shown that the occur-
rence of toxic elements contamination is related to length,
weight, age and sex of fish (Agusa et al., 2005; Emami
Khansari et al., 2005; De Marco et al., 2006; Storelli et
al., 2002). Season and place are also important in the
4940 Afr. J. Biotechnol.
Table 3. Mercury, cadmium and lead level (?g g-1) in canned tuna fish reported internationally.
Australia 0.01 - 0.89
Libya 0.20 - 0.66
0.004 - 0.500
- 0.025 - 0.494
0.18 - 0.86
USA 0.02 - 0.76
0.045 - 0.253 0.005 - 0.072
0.010 - 0.401 0.008 - 0.150
levels of toxic elements accumulation in fishes (Kagi and
Schaffer, 1998). However, good agreements were observed
when our results were compared with those reported by
other authors (Committee for Inland Fisheries of Africa,
Mercury has been recognized as severe environmental
pollutant, with high toxicity even at low concentrations
and it has the ability to enter into biological systems
(Porto et al., 2005). It has strong tendency to accumulate
in aquatic food chain, and about 95% of the methyl
mercury in humans originated from ingested fish
(Houserova et al., 2007; Voegborlo and Akagi, 2007).
Mercury and methyl mercury are neurological toxicants to
humans. In addition, methyl mercury is also classified as
a Group C possible human carcinogen (Commission of
the European Communities, 2001). Base on the wet
weight, all of the canned tuna fish samples commonly
consumed by Iranians analyzed in this study had mercury
concentrations below 0.5?g g-1 wet weights; the guideline
level established by European Communities and Joint
FAO/WHO Expert Committee on Food Additives (Food
Agriculture Organization, 1976; Commission of the
European Communities, 2001). Mercury concentrations
in canned tuna fish found in this study were in good
agreement with those reported by other studies (Table 3).
Lead is known to induce reduced cognitive development
and intellectual performance in children and increased
blood pressure and cardiovascular disease in adults
(Commission of the European Communities, 2001). The
maximum lead level permitted for canned fishes is 0.2 ?g
g-1 according to the European communities (Commission
of the European Communities, 2001). In this study, the
mean, lowest and highest lead levels in samples were
0.096 ?g g-1, 0.021 ?g g-1 and 0.301 ?g g-1, respectively,
and only 6.7% of samples showed slightly elevated levels
of lead (>0.2 ?g g-1). The results were compared with the
literature values (Table 3). The fact that toxic metals are
present in high concentrations in fishes is of particular
importance in relation to the FAO/WHO (1976) standards
for lead and cadmium as toxic metals. The maximum
0.01 - 0.12
0.09 - 0.32
0.06 - 0.14
0.02 - 1.0
0.18 - 0.40
0.40 - 0.76
0.076 - 0.314
0.09 - 0.40
0.14 - 0.82
0.03 - 0.51
0.0 - 0.03
0.016 - 0.073
0.021 - 0.301
Suppin et al. (2005)
Voegborlo et al. (1999)
Hgjeb et al. (2009)
Zahari et al. (1987)
Celik and Oehlenschlager (2006)
Tuzen and Soylak (2007)
Ashraf et al. (2006)
Ikem and Egiebor (2005)
Emami Khansari et al. (2005)
0.06 - 0.25
0.08 - 0.66
0.07 - 0.64
0.0 - 0.05
permissible doses for an adult are 3 mg lead and 0.5 mg
cadmium per week, but the recommended sources are
only one-fifth of those quantities.
Cadmium may accumulate in the human body and may
induce kidney dysfunction, skeletal damage and repro-
ductive deficiencies (Tuzen and Soylak, 2007). The mean
of cadmium concentration in analyzed canned fish
samples were lower than the European communities
(maximum 0.05 mg Cd/kg) (Commission of the European
Communities, 2001), but, out of total 60 samples
analyzed, 27 (45%) showed slightly elevated levels of
cadmium (>0.05 ?g g-1). However, these are approximately
8 times below the codex committee on Food Additives
and Contaminants (CCFAC, 2001) draft guideline of 0.5
?g g-1. The lowest and highest cadmium levels were
0.008?g g-1 and 0.150?g g-1, respectively. Cadmium
contents in literature have been reported in the range of
0.0 -0.0.66 ?g g-1 in canned tuna fish samples in previous
studies (Table 3).
The levels of some toxic elements in analyzed canned
fish samples were found to be above legal limits. The
level may be reduced by more careful handling practices
and processing of raw materials. Canned fish samples
should be analyzed more often in Iranian supermarkets
with respect to toxic elements. This study improves the
baseline data and information on mercury, cadmium and
lead concentration in canned tuna fish commonly marketed
in Iran. Such data provide valuable information on safety
of fishes commonly consumed by the public.
We would like to gratefully acknowledge Manoochehr
Ahmadi, Elham Ebadati, Mahdi Reisi and Amir Shakerian
for the sincere help in performing technical parts of the
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