Аннотация (русский):
Fish contamination by heavy metals, even at low levels, has an adverse effect on human health. Mercury (Hg), cadmium (Cd), and lead (Pb) are the most common heavy metals that contaminate sea foods. Rainbow trout is a fish species which is widely cultured in fresh water regions, e.g. in Yasuj, southwest of Iran. Heavy metal contamination was measured in three different culture areas (A, B, and C), with three different feed pellets used in Yasuj farms (I, II, and III). The sampling was conducted during February-April 2018 and the metals were measured using cold vapour atomic absorption with a Perkin Elmer 4100. The mean values of Hg, Cd, and Pb levels in the muscular tissue of the samples were 0.022, 0.105, and 1.07 mg/kg, respectively. Concentrations of Hg and Cd in edible tissues of rainbow trout were lower than the permitted values set by the WHO, the FDA, and the EC. The samples fed on mixture pellets III showed a significantly higher Hg content and a lower concentration of Cd in the muscle tissue compared to those given feed mixtures I and II (P < 0.05). Pearson correlation tests revealed significant correlations between the Cd and Pb concentrations and the weight of the fish samples (r = –0.519, r = –0.580). The lowest Cd concentration (0.076 mg/kg–1) was found in site A located close to the spring and not polluted by sewage from urban or rural areas. The study showed a correlation between the concentration of heavy metals in the fish samples and their weight, the degree of pollution, and the feeding mixture used in the farms.

Ключевые слова:
Rainbow trout, heavy metals, mercury, cadmium, lead

INTRODUCTION
Heavy metals in contaminated food crops, even
at low concentrations, produce deleterious effects on
human health [1]. Metals pollution naturally occurs in
the environment; however, human activities including
mining and other industries have particular effects on
the ecosystem, as well as the aquatic environment [2–4].
Despite the progress in sewage effluent technologies,
water contamination is still a threat in many developing
countries due to sewage discharge [5]. Heavy metals have
an impact on aquatic ecosystems and eventually enter the
human’s food chain [6]. Rainbow trout (Oncorhynchus
mykiss L.), a native fish of North America, is known as
one of the most valuable members of the Pacific trout that
became the main freshwater fish species farmed in Iran
[7, 8]. The first farm of this fish in Iran was established
in 1959. Its production increased from 599 tons in 1978 to
140 000 tons in 2016, making Iran one of the worldleading
producers of this salmon [9].
Mercury, cadmium, and lead are known as toxicants
associated with fish consumption [10]. They are listed as
sixth most dangerous contaminants by the International
Program of Chemical Safety (IPSC) [11]. Lead poisoning
can affect various systems of the body including renal,
haematological, cardiovascular, gastrointestinal, and
reproductive systems [12]. Renal exposure to cadmium
results in its deposition in proximal tubular cells and
causes renal failure due to decreased glomerular
filtration rates. Also, skeletal system anomalies occur
due to the secondary effects of renal dysfunction and
accumulation of lead in bones [13]. Methyl mercury
exposure through the consumption of contaminated fish
in prenatal period leads to serious abnormalities such
Research Article DOI: http://doi.org/10.21603/2308-4057-2019-2-329-338
Open Access Available online at http:jfrm.ru
Heavy metal content in farmed rainbow trout
in relation to aquaculture area and feed pellets
Majid Majlesi1 , Janmohammad Malekzadeh1,* , Enayat Berizi2 ,
Mehdi Akbartabar Toori1
1 Department of Nutrition Sciences, School of Health and Nutrition Sciences,
Yasuj University of Medical Sciences, Yasuj, Iran
2 Department of Food Hygiene and Quality Control, School of Nutrition and Food Sciences,
Shiraz University of Medical Sciences, Shiraz, Iran
* e-mail: malekjmd@yums.ac.ir
Received May 13, 2019; Accepted in revised form August 27, 2019; Published October 21, 2019
Abstract: Fish contamination by heavy metals, even at low levels, has an adverse effect on human health. Mercury (Hg), cadmium
(Cd), and lead (Pb) are the most common heavy metals that contaminate sea foods. Rainbow trout is a fish species which is widely
cultured in fresh water regions, e.g. in Yasuj, southwest of Iran. Heavy metal contamination was measured in three different culture
areas (A, B, and C), with three different feed pellets used in Yasuj farms (I, II, and III). The sampling was conducted during February-
April 2018 and the metals were measured using cold vapour atomic absorption with a Perkin Elmer 4100. The mean values of Hg,
Cd, and Pb levels in the muscular tissue of the samples were 0.022, 0.105, and 1.07 mg/kg, respectively. Concentrations of Hg and
Cd in edible tissues of rainbow trout were lower than the permitted values set by the WHO, the FDA, and the EC. The samples
fed on mixture pellets III showed a significantly higher Hg content and a lower concentration of Cd in the muscle tissue compared
to those given feed mixtures I and II (P < 0.05). Pearson correlation tests revealed significant correlations between the Cd and Pb
concentrations and the weight of the fish samples (r = –0.519, r = –0.580). The lowest Cd concentration (0.076 mg/kg–1) was found in
site A located close to the spring and not polluted by sewage from urban or rural areas. The study showed a correlation between the
concentration of heavy metals in the fish samples and their weight, the degree of pollution, and the feeding mixture used in the farms.
Keywords: Rainbow trout, heavy metals, mercury, cadmium, lead
Please cite this article in press as: Majlesi M, Malekzadeh J, Berizi E, Toori MA. Heavy metal content in farmed rainbow trout in
relation to aquaculture area and feed pellets. Foods and Raw Materials. 2019;7(2):329–338. DOI: http://doi.org/10.21603/2308-4057-
2019-2-329-338.
Copyright © 2019, Majlesi et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International
License (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix,
transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.
Foods and Raw Materials, 2019, vol. 7, no. 2
E-ISSN 2310-9599
ISSN 2308-4057
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Majlesi M. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 329–338
as cerebral palsy, mental backwardness, neurological
disorders, and infant mortality [14]. Fish, which is
an important aquatic component of the human food
chain, has been a subject of investigation with regard to
metal pollution [15]. Therefore, numerous reports have
described metal residues in types of fish species [16–20].
The accumulation of heavy metals in fish tissues is
influenced by a number of factors such as feeding habits,
nourishment sources, habitat, age, and size [21–23]. In
this study, concentrations of heavy metals (Hg, Cd, and
Pb) were assessed in fish feed mixtures and edible tissues
of rainbow trout farmed in three different culture areas.
STUDY OBJECTS AND METHODS
Study area and sample collection. Between
February and April 2018, rainbow trout (Oncorhynchus
mykiss L.) samples were collected from six farms (five
fishes from each farm) in three different culture areas
in Yasuj, southwest of Iran (Fig. 1), the third leading
producer of this trout in the world [9]. The culture areas
were located very close to the spring (site А: 30.502935,
51.743184), downstream of cities and villages (site
B: 30.710630, 51.514926), and downstream of a rural
area (site C: 30.789658, 51.329715). Their choice was
determined by the level of contamination probability.
The farms used a raceway farming system, with water
supplied by the spring. All the farms practiced manual
feeding with commercial pellets two times a day. The
fish were collected randomly from two farms in each
area (10 fishes in each site). The experiments were
approved by the Animal Care and Use Committee
of Yasuj University of Medical Sciences (YUMS) in
compliance with the ‘Guidelines for the Care and Use
of Animals’. At first, the samples’ biological parameters
were recorded including wet body weight and total
length. Then, they were washed, preserved in ice-boxes,
and transported to the Food Chemical Laboratory at
YUMS for heavy metal (Hg, Cd, and Pb) determination.
The fish were filleted, placed in polyethylene bags, and
kept at −20°C prior to analysis.
Four pellets of three types (I, II, and III) of
commercially manufactured feed mixtures were
frequently applied in the aquaculture trout farms during
the fish sampling (12 pellets) and studied to determine
the content of heavy metals.
Analytical procedures. Both feeds and fillets were
oven-dried at 105°C for 1 h and then cooled. To measure
the level of heavy metals, the samples (dry weight) were
digested in a mixture of 6 mL concentrated HNO3 (super
pure quality; Romil Ltd., Cambridge, UK) and 2 mL
H2O2 (supra pure quality; Merck, Darmstadt, Germany)
in a microwave digestion system (MARSXpress, CEM).
When cooled to room temperature, the digested sample
solutions were filtered and adjusted to 50 mL with
ultrapure water. The levels of Hg, Cd, and Pb content
were determined using cold vapour atomic absorption
with a Perkin Elmer 4100 (FIMS 400 Perkin Elmer Inc.,
USA). The blank samples were also processed to avoid
possible contamination during the analysis [22].
Human health risk assessment. The estimated
daily intake (mg/kg bw/day) (EDI) of heavy metals was
measured to evaluate the daily/weekly intake of heavy
metals by the human body through the consumption
of fish [24]. The daily intake of metals in adults was
calculated as:
EDI (mg/kg bw/day) = (EF·ED·FIR·CF·CM)/(WAB·TA)×10–3 (1)
Where EF and ED are the exposure frequency
(365 days/year) and the exposure duration (60 years),
respectively; FIR is the fish ingestion rate (25.2 g/day for
Iran); CF is the conversion factor to convert fresh weight
to dry weight (0.208); CM is the metal concentration in
Figure 1 Location of Yasuj, southwest of Iran and the study area (site A: 30.502935, 51.743184, site B: 30.710630, 51.514926,
site C: 30.789658, 51.329715)
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the fish tissue (μg/g dry weight); WAB is the average body
weight for adults (65 kg for Iran); and TA is the average
exposure time for non-carcinogens (EF·ED) [4].
The percentage of provisional tolerable weekly
intake (PTWI) and target hazard quotient (THQ)
were calculated for each heavy metal by the following
equations:
PTWI = EWI/PTWI × 100 (2)
THQ = EDI/RfD (3)
where PTWI, EWI, and RfD are provisional tolerable
weekly intake (mg/kg bw/week), estimated weekly
intake (mg/kg bw/week), and oral reference doses
(mg/kg/day), respectively.
When the THQ is less than one, the risk of
noncarcinogenic toxic effects for exposed consumer
populations is presumed to be low. When it is greater than
or equal to one, it is considered as a concern for consumer
populations, indicating potential health risks [25].
Biomagnification factor. The biomagnification
factor (BMF) is the ratio between the concentration of
an element in fish and the concentration of this element
in its diet. The BMF was calculated by the following
equation: [26]:
BMF = Cfish/Cfeed (4)
where Cfish is a heavy metal concentration in fish edible
tissues and Cfeed is a metal concentration in trout
commercial pellets.
Statistical analysis. Statistical analysis was
performed using the SPSS Statistics 19.0 software
package. The mean and standard deviation (mean ± SD)
levels of metal concentrations were reported for different
areas and foods. The differences between heavy metal
levels in edible tissues of fish from different farms
and in different commercial foods were tested by the
one-way analysis of variance (ANOVA), followed by
Duncan’s post hoc test. The Pearson correlation test
was used to check for significant relationships between
metal concentrations, length, and net weight of fish.
P < 0.05 was considered as the level of significance.
RESULTS AND DISCUSSION
Heavy metal concentration in rainbow trout.
Concentrations of heavy metals in edible tissues of
rainbow trout farmed in three different areas are shown
in Fig. 2.
The mean ± SD levels of Hg in the muscle tissues
of rainbow trout farmed in sites A, B, and C were 0.021
± 0.0027, 0.023 ± 0.0026, and 0.024 ± 0.0027 mg/kg–1,
respectively. The lower mercury level in site A,
compared to the other two sites, had no significant
difference (P > 0.05). In addition, the mean
concentration of Cd in sites A, B, and C were 0.076,
0.119, and 0.120 mg/kg–1, respectively. The lowest Cd
concentration was found in edible tissues of the fishes
farmed in locations close to the spring, not polluted
by sewage from urban or rural areas. The highest Pb
concentration was detected in site B (1.171 mg/kg–1),
followed by sites C and A (0.893 mg/kg–1) (P < 0.05).
The fishes cultured in sites B and C had significantly
higher contents of cadmium and lead, compared to those
farmed in site A (P < 0.05). The results indicated that
concentrations of Hg and Cd were below the permitted
values determined by [27–29]. However, the level of Pb
in the muscle tissue of farmed trout exceeded the value
set by the WHO [30] (Table 1).
Below the levels established by the WHO, the
FDA, and the EC were heavy metal concentrations in
different fish species studied in Turkey, in the Barents
Sea commercial fish, the fish from Lake Chini in
Malaysia, wild fresh water fish from the Khersan river
in Iran, rainbow trout and freshwater fish species from
Lake Pamvotis in Greece [11, 31–35]. In addition, Bat
et al. reported that the Cd, Hg, and Pb concentrations
in Cyprinus carpio from the Karasu Stream, Sinop and
in four fish species from Sarikum Lake were within
certified values allowed to consumers [36, 37].
The Pb content was higher than the WHO allowed
level in the fish cultured along the river’s upstream in
Figure 2 Heavy metal levels in muscle tissue of farmed
rainbow trout from three aquaculture sites (G: site A; Be: site
B; Ch: site C). All results are expressed as means ± SD for five
fish in each group. a and b: groups with different letters differ
significantly (P < 0.05)
Table 1 Maximum permissible limit of heavy metals established by international organisations
Heavy metal, μg/g–1 In this study WHO (2007) FDA (2001) FAO (2007) EC Regulation No. 1881/2006
Hg 0.022 0.5 0.05–1.0 0.5 0.5–1.0
Cd 0.105 0.5 4.0 0.5 0.5
Pb 1.070 0.5 1.7 2.0 1.0
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Ghadirabad, Pakistan, wild fresh water fish from the
Khersan river in Iran, farmed and wild rainbow trout in
the Zayandeh Rood river in Iran, and fresh water fish in
North Mexico (4298 mg/kg) [16, 19, 20, 33]. These data
support the findings in our study. Table 2 demonstrates the
comparison of heavy metal levels in the muscle tissue of
rainbow trout from different locations reported in literature.
However, lower Hg, Cd, and Pb levels in site A,
compared to the other sites, indicated an important
role of water supply in trout aquaculture with regard to
heavy metals accumulation in fish tissues. The release of
industrial wastewater and pollutants caused by human
activities increased the lead content in Liza fish from
the Karun River in Iran and from the coast of Cochin
in India [44, 45]. It was also reported that wild carps in
the downstream areas of the Ravi and the Indus rivers
in Pakistan showed a high contamination by heavy
metals [46, 47].
Emara et al. observed significant differences in the
Cd and Pb accumulation in the muscle tissue of fish in
two distinct farms using different water sources [48].
Based on health standards, the concentration of heavy
metals such as lead was higher in Mugil cephalus and
Trachurus mesiteraneus in the Gulf of Iskenderun [49].
Wagner and Boman reported a greater amount of
calcium and iron in the contaminated areas, compared
to non-industrial zones [41]. High levels of cadmium
and nickel were recorded in fish from Kuetsjarvi Lake
(Russia) due to the contamination of surrounding
regions and the proximity of smelting plants. A lower
concentration of heavy metals in fish was detected
in the areas away from factories and contaminating
sources [52]. Power plants can reduce water acidity
which causes an increase in the water solubility of lead
and cadmium, resulting in high accumulation of the
metals in aquatic organisms [11].
Table 2 Heavy metal levels in edible tissue of rainbow trout from different locations according to literature data: mercury (Hg),
cadmium (Cd), lead (Pb)
Fish species Region Unit Heavy metals Ref.
Hg Cd Pb
Rainbow trout Hamadan, Iran mg/kg dw – 3.74 ± 4.24 14.07 ± 14.56 [38]
Large sea trout Sinop fish market, Turkey mg/kg–1 wet wt 0.15–0.42 0.012–0.044 0.08–0.23 [39]
Wild rainbow trout Khersan river, Iran mg/kg dw 0.023 ± 0.004 0.110 ± 0.028 1.120 ± 0.130 [33]
Rainbow trout Gilan, Mazandaran and
Chabahar, Iran.
μg/kg (ppb) 22.1 ± 0.8 36 ± 32.2 249.4 ± 88.6 [40]
Farmed rainbow
trout
Chaharmahal-va-Baghtiari,
Iran
μg/g dw
0.314 ± 0.195 0.097 ± 0.058 1.108 ± 0.400 [16]
Wild rainbow trout Zayandeh-Rood river, Iran μg/g dw 0.292 ± 0.181 0.130 ± 0.068 1.201 ± 0.373 [16]
Rainbow trout Khorramabad, Iran mg/kg dw 0.297 ± 0.04 0.123 ± 0.03 0.741 ± 0.02 [34]
Rainbow trout Karakaya Dam Reservoir,
Turkey
μg/kg ww – 0.00052 0.053 [41]
Brown trout Munzur Stream, Tunceli,
Turkey
μg/kg–1 0.01 ± 0.00 4.08–2.83 0.10 ± 0.00 [42]
Rainbow trout Chaharmahal and Bakhtiari,
Iran
mg/kg–1 – – 12.40 [43]
Rainbow trout Yasuj, Iran mg/kg–1 0.022 0.105 1.07 this study
Table 3 Health risk parameters for the Iranian population consuming farmed rainbow trout cultured in Yasuj compared to other
studies
Health risk
parameter
This study [42] [50] [38] [51]
Hg Cd Pb Pb Hg Cd Pb Hg Cd Pb Cd Pb
EDI, mg/kg
bw/day
0.17×10–5 0.84×10–5 0.86×10–4 0.77×10–3 0.008 0.039 4 0.007 0.007 0.004 0.12×10–4 0.18×10–4
EWI, mg/kg
bw/week
0.12×10–4 0.59×10–4 0.6×10–3 0.54×10–2 – – – 0.049 0.048 0.027 0.87×10–4 1.30×10–4
PTWI, mg/kg
bw/week
0.004 0.007 0.025 – – – – – – – – –
PTWI, % 0.30 0.84 2.41 – – – – – – – 1.25 0.52
RfD, mg/kg
bw/day
0.0003 0.001 0.004 – – – – – – – – –
THQ 0.0059 0.008 0.021 0.22 0.037 0.014 0.097 – – – 12.46×10–3 9.28×10–3
TTHQ 0.0349 – 0.146 – – – –
EDI: Estimated Daily Intake; EWI: Estimated Weekly Intake; PTWI: Provisional Tolerable Weekly Intake; RfD: Oral Reference Dose;
THQ: Target Hazard Quotient; TTHQ: total THQ
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Health risk assessment. Several parameters widely
used to assess human health risks include the estimated
daily intake (EDI), the estimated weekly intake (EWI),
the target hazard quotient (THQ), and the provisional
tolerable weekly intake (PTWI). Health risk assessment
values including the EDI, the EWI, the THQ, and the
PTWI with regard to farmed rainbow trout are presented
in Table 3. These parameters showed the following
pattern in all the samples under study: Pb > Cd > Hg.
We found that the EDI, the EWI, the PTWI, and the
THQ obtained here were far below the recommended
amounts, compared to the set values (RfD and PTWI) or
other studies (Table 3). The THQ values were lower than
one for all three studied metals. The findings indicated
that the consumption of farmed rainbow trout in the
study area does not pose a potential non-carcinogenic
risk to human health.
Feeds and heavy metal concentrations. The mean
± SD contents of heavy metals in the commercial
feed mixtures (I, II, and III) used in the rainbow trout
farms of this region are shown in Table 4. The results
indicated some differences in commercial feeds based
on the content of heavy metals. Food I contained higher
levels of Pb (5.8 mg/kg–1) compared to the European
Commission Regulations (EC) [53]. Using different raw
materials in fish pellets resulted in some alteration of
heavy metal contents in fish feed mixtures.
The mean concentrations of Hg, Cd, and Pb
in muscle tissues of rainbow trout with regard to the type
of food consumed in each of the farms are presented
in Fig. 3.
We observed that various commercial mixtures could
influence the accumulation of heavy metals in farmed
rainbow trout. The concentrations of Hg, Cd, and Pb in
the fishes that consumed pellet II were 0.05, 0.076, and
0.893 mg/kg–1, respectively. Using pellet III resulted in
a higher content of mercury and a lower concentration
of cadmium, compared to the fishes fed on mixtures
I and II (P < 0.05). On the whole, we concluded that
the accumulation of heavy metals in fish was mainly
influenced by water, food, and sediment. However, the
accumulation of these elements in water and food is
due to various factors including ecology, metabolism,
pollution of slope water, food, and sediment, as well
as other factors such as solubility, temperature, and
interaction of various parameters [54, 55].
In our study, however, food intake had a significant
effect on the concentration of heavy metals in
rainbow trout muscle tissue: the consumption of
pellet III resulted in a marked increase in mercury
and a considerable reduction in cadmium and
lead. Researchers have reported that there is a
large association between the concentration of
heavy metals in fish and its nutritional habits [22].
Mixture I had higher levels of Pb (5.8 mg/kg–1)
compared to the values established by the European
Commission Regulations (EC) [53]. Using different
raw materials to prepare feed pellets resulted in some
alteration of heavy metal contents in the commercial
food mixtures. The accumulation of heavy metals in
fish depends on food habits, reproductive status, size,
and sex [21, 56]. Deep sediments contain large amounts
of heavy metals. Compared to the epipelagic organisms,
benthos occupying the deepest layers of water is the
largest source of heavy metals [22].
Biomagnification factor. The BMF values for
all the metals were under 1 (Table 5). Actually,
the concentrations of the examined metals in the
commercial pellets used in this region were higher
than those in the rainbow trout tissues. As Table 5
demonstrates, the BMF values for the three metals had
the following pattern: Hg > Pb > Cd (Table 5). The BMF
was applied to show the capability of a contaminant to
bioaccumulate. When a metal BMF is less than one, it
indicates that no biomagnification occurred in the bio
system [26]. The current study showed that the BMF
values were lower than one for all the metals (Table 5),
suggesting that these metal contaminants were not
biomagnified by rainbow trout from the diet. This
finding was similar to the result obtained by Varol et al.
[57]. Nevertheless, biomagnification implies inadequate
Table 4 Heavy metal levels in commercial feed mixtures
consumed by farmed rainbow trout in three different
aquaculture sites
Feed
mixtures
Lead (Pb) Cadmium (Cd) Mercury (Hg)
I 5.8 ± 0.365* 0.61 ± 0.093 0.075 ± 0.013
II 4.52 ± 0.259 0.54 ± 0.106 0.063 ± 0.018
III 4.15 ± 0.384 0.66 ± 0.076 0.071 ± 0.026
All results are expressed as means ± SD (mg/kg–1) for three feed
mixtures
* indicates a higher level of lead in pellet I compared to the European
Commission standards
Figure 3 Heavy metal concentrations in muscle tissue of
farmed rainbow trout in relation to the type of commercial
feed mixture (C: pellet I; F: pellet II; B: pellet III). All results
are expressed as means ± SD for six fish in each group. a and
b: groups with different letters differ significantly (P < 0.05)
Feed mixture
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information on the real threat from heavy metals in an
aquatic food chain [58].
Physical characteristics and heavy metal levels.
Table 6 shows the biometric characteristics of the
sampled rainbow trouts. The relationship between metal
concentrations and fish size (length and weight) is shown
in Table 7. Increasing the weight and length of farmed
trouts generally reduced the concentration of the three
heavy metals. The Pearson correlation test revealed
significant negative associations between the cadmium
and lead concentrations and the weight of the fish
samples (r = –0.519 and r = –0.580, respectively).
Few studies have focused on the relationship between
physical characteristics and heavy metal accumulation.
To the best of our knowledge, this is the first study on
the relationship between the length and weight of farmed
rainbow trout and the concentration of mercury, lead,
and cadmium. Most of the authors have found a negative
relationship between heavy metal accumulation and the
size of fish (length and weight). They suggested that
metabolic activity is one of the most important factors
affecting the accumulation of heavy metals in marine
fish [59]. Higher metabolic activity in juvenile fish leads
to a higher accumulation of heavy metals [60, 61].
The correlation between the spectroscopic
parameters and the concentration of heavy metals has
been reported to be negative in various species of fish
[61]. Heavy metal content in fish after a certain age
remains almost constant [62]. In contrast to our results,
Widianarko et al. found that in sturgeon species in the
Caspian Sea, a higher accumulation of heavy metals
with an increase in age, length, and weight of fish [63].
In general, there is a consensus that metals in living
organisms are detoxified and depleted by a special
mechanism, which is significantly dependent on the
Table 5 Biomagnification factors of three metals
Aquaculture
farms
Lead (Pb) Cadmium (Cd) Mercury (Hg)
Site A 0.15 0.11 0.28
Site B 0.25 0.22 0.36
Site C 0.37 0.22 0.38
Table 6 Biometric characteristics of farmed rainbow trout
sampled from different farming sites
Feed mixtures Length, cm Weight, g
Site A 33.66 ± 2.33 504.66 ± 122.65
Site B 28.16 ± 2.78 262.00 ± 77.80
Site C 34.83 ± 5.07 446.33 ± 226.37
All results are expressed as means ± SD for eight fish in each group
Table 7 Relationships between heavy metal concentrations
and farmed rainbow trout length and weight
Physical
characteristics
Lead
(Pb)
Cadmium
(Cd)
Mercury
(Hg)
Length
Pearson correlation
–0.383 –0.296 –0.217
sig. (two-tailed) 0.116 0.232 0.386
Weight
Pearson correlation
–0.580* –0.519* –0.266
sig. (two-tailed) 0.012 0.027 0.286
* indicates a significant correlation (P < 0.05)
metabolism in the particular weight [64, 65]. Therefore,
the negative relationship between heavy metal
concentrations and the size of fish does not necessarily
mean that a certain amount of metals will accumulate
in the body at the beginning of the growth, and no more
metals will be subsequently absorbed [66]. It has also
been suggested that the absorption of metals in lowcontaminated
water sources is more affected by nutrition
[67]. In other words, a significant reduction in the
amount of heavy metals in organs at the maturity stage
is due to a decrease in the daily fish diet with age [68].
The fish at the highest nutritional level are expected to
have the highest accumulation of heavy metals [69, 70].
CONCLUSION
According to the results of the study, the levels of
mercury, cadmium, and lead in the muscle tissue of
rainbow trout farmed in Yasuj were found to be below
the permitted values. The findings showed that the
health risk assessment parameters (EDI, EWI, THQ)
were far below the recommended values. This indicated
that the consumption of farmed rainbow trout in the
study area did not have any adverse effect on human
health caused by heavy metal contamination.
However, the release of urban and rural wastewater
and pollutants from human activities into the rivers
leads to increased levels of lead and cadmium in the fish
farmed in the downstream fields of the countryside and
cities. Moreover, the application of various commercial
pellets containing different levels of heavy metals can
affect the accumulation of these metals in farmed trout.
CONFLICT OF INTEREST
The authors declare that there is no conflict of
interest.
ACKNOWLEDGEMENTS
We would like to thank Mr. E. Sharifpoor for his
technical assistance.

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