In this study, two organochlorine pesticides (Aldrin and Chlordane) were assessed in different fish samples imported to Bangladesh from overseas. Concentrations of the two pesticides were below the limit of detection and therefore, subsequent result and discussion will concentrate on the concentration of trace metals in fishes and associated health risk.
3.1 Concentration of trace metals in fish muscles
In the present study, concentration of As, Pb, Cr, Cd, Ni, Co, Mn, Fe, Cu, and Zn (mg/kg-ww) were assessed in the samples of imported fishes from four countries (India, Myanmar, Oman and United Arab Emirates). Table 1 provides a summary of the mean concentrations of the trace metals in the analyzed fish samples. All metal concentrations were determined on a wet-weight basis.
Table 1
Mean concentrations (mg/kg ww) of trace metals in muscle tissues of some fishes imported to Bangladesh from different countries.
Sources
|
Sample name
|
As
|
Pb
|
Cr
|
Cd
|
Ni
|
Co
|
Mn
|
Fe
|
Cu
|
Zn
|
India
|
L. rohita
|
0.008
|
0.004
|
0.053
|
0.001
|
0.043
|
0.037
|
0.149
|
2.275
|
0.084
|
1.927
|
O. ruber
|
0.05
|
0.070
|
0.083
|
0.005
|
0.016
|
BDLa
|
BDL
|
1.895
|
0.055
|
0.898
|
UAE
|
S. australasicus
|
0.124
|
0.065
|
0.069
|
0.074
|
0.034
|
BDL
|
BDL
|
10.77
|
0.112
|
9.245
|
E. acuminatus
|
0.148
|
0.008
|
0.053
|
0.083
|
0.03
|
BDL
|
0.291
|
7.141
|
0.632
|
4.594
|
A. maculatus
|
0.137
|
0.004
|
0.013
|
0.003
|
0.011
|
BDL
|
BDL
|
2.669
|
0.182
|
3.641
|
T. toli
|
0.558
|
0.006
|
0.109
|
0.056
|
0.059
|
BDL
|
0.718
|
9.286
|
0.495
|
6.188
|
L. johnii
|
0.022
|
0.004
|
0.01
|
0.001
|
0.023
|
BDL
|
BDL
|
2.38
|
0.199
|
3.154
|
Oman
|
T. toli
|
0.113
|
0.010
|
0.071
|
0.015
|
0.024
|
BDL
|
0.504
|
7.384
|
0.536
|
7.004
|
Myanmar
|
L. rohita
|
0.013
|
0.009
|
0.049
|
0.001
|
0.011
|
BDL
|
0.126
|
2.795
|
0.218
|
2.552
|
E. splendens
|
0.034
|
0.013
|
0.017
|
0.007
|
0.044
|
BDL
|
0.456
|
1.78
|
0.106
|
2.007
|
C. cynoglossus
|
0.027
|
0.070
|
0.038
|
0.008
|
0.036
|
BDL
|
0.78
|
4.576
|
0.09
|
2.975
|
a Below Detection Limit |
Trace metal concentration varied in different fish species from 0.001–0.650 mg kg− 1 for As, 0.002–0.073 mg kg− 1 for Pb, 0.01–0.168 mg kg− 1 for Cr, 0.001–0.108 mg kg− 1 for Cd, 0.007–0.08 mg kg− 1 for Ni, ND- 0.080 mg kg− 1 for Co, ND- 0.0780 mg kg− 1 for Mn, 0.954–13.60 mg kg− 1 for Fe, 0.034–0.646 mg kg− 1 for Cu, and 0.812–17.248 mg kg− 1 for Zn, average of which leads to the following ranking: Fe (4.81) > Zn (4.02) > Mn (0.43) > Cu (0.25) > As (0.11) > Cr (0.05) > Co (0.04) > Ni (0.03) > Pb (0.024) > Cd (0.023).
3.1.1 Arsenic (As)
Arsenic concentration in the muscles of fish samples were 0.01 ± 0.007 mg kg− 1 in L. rohita (India); 0.05 ± 0.01 mg kg− 1 in O. ruber (India); 0.12 ± 0.02 mg kg− 1 in S. australasicus (UAE); 0.15 ± 0.001 mg kg− 1 in E. acuminatus (UAE); 0.14 ± 0.002 mg kg− 1 in A. maculatus (UAE); 0.56 ± 0.09 mg kg− 1 in T. toli (UAE); 0.02 ± 0.001 mg kg− 1 in L. johnii (UAE); 0.11 ± 0.001 mg kg− 1 in T. toli (Oman); 0.01 ± 0.001 mg kg− 1 in L. rohita (Myanmar); 0.03 ± 0.002 mg kg− 1 in E. splendens (Myanmar); 0.03 ± 0.001 mg kg− 1 in C. cynoglossus (Myanmar). This results shows that among all the fishes investigated, T. toli from UAE contained the highest amount of arsenic and L. rohita from India have been found to carry the minimum amount followed by L. rohita from Myanmar (Table 1). Considering the average As concentration, fish from UAE were more contaminated than fish imported from Oman, India and Myanmar (Fig. 2).
In literature, similar As accumulation level has been reported in fish from Bangladesh such as: 0.04–0.8 mg kg− 1 (Islam et al., 2015), 0.077–1.486 mg kg− 1 in highly consumed cultured fish (Ahmed et al., 2015), 0.139 ± 0.00 in L. rohita and 0.141 ± 0.01 in T. ilisha (Saha & Zaman, 2013). Previous studies also reported higher arsenic content comparing to present study in fish from Bangladesh (Raknuzzaman et al., 2016; Ahmed et al., 2019; Rahman et al., 2012). Fish from India has been found to contain arsenic as 0.35 ± 0.08 mg kg− 1 in L. rohita from tropical wetlands (Kumar & Mukherjee, 2011); 2.9 ± 0.6 mg kg− 1 in hilsa shad from Ganga river of India (Mohanty et al., 2017). Arsenic concentration has been recorded in higher magnitude comparing to present study in previous studies for fish from Oman (Sadeghi et al., 2019), Arabian Gulf (Kamal et al., 2015), Persian Gulf (Cunningham et al., 2019), Pakistan (Shah et al., 2009).
Arsenic is a toxic component for all living beings including human; chronic contact with which has long been found to cause lung cancer, skin carcinoma, kidney and bladder cancer, neuropathy in both the peripheral and central nervous systems (Liu et al., 2011; Medeiros et al., 2012; Kapp, 2018). The International Agency for Research on Cancer (IARC) has also classified inorganic arsenic as class 1 human carcinogen. (IARC, 2012). The maximum arsenic level permitted for fish samples is 0.10 mg kg− 1 (FAO, 2006). The present observation showed that level of As in all fish samples from UAE (except L. johnii) and from Oman was higher than this proposed acceptable limit.
3.1.2 Lead (Pb)
Present study found the amount of Pb in different imported fish samples as 0.004 ± 0.002 mg kg− 1 in L. rohita (India), 0.07 ± 0.003 mg kg− 1 in O. ruber (India), 0.07 ± 0.01 mg kg− 1 in S. australasicus (UAE), 0.01 ± 0.001 mg kg− 1 in E. acuminatus (UAE), 0.004 ± 0.001 mg kg− 1 in A. maculatus (UAE), 0.01 ± 0.001 mg kg− 1 in L. rohita (Myanmar), 0.01 ± 0.003 mg kg− 1 in T. toli (UAE), 0.004 ± 0.002 mg kg− 1 in L. johnii (UAE), 0.01 ± 0.001 mg kg− 1 in T. toli (Oman), 0.01 ± 0.001 mg kg− 1 in E. splendens (Myanmar), 0.07 ± 0.003 mg kg− 1 in C. cynoglossus (Myanmar). Maximum lead content has been observed in O. ruber from India and C. cynoglossus from Myanmar and minimum was observed in L. rohita from India, A. maculatus from UAE, and L. johnii from UAE (Table 1). Fish from India were more contaminated with Pb than other samples and fish imported from Oman were with minimum concentration (Fig. 2).
Present results were almost similar to those reported earlier in fish from different regions of Bangladesh, for example, 0.07 − 0.63 mg kg− 1 (Raknuzzaman et al., 2016), 0.017–0.09 mg kg− 1 (Ahmed et al., 2015), 0.04–1.6 mg kg− 1 (Islam et al., 2015) and also fish (Arius bilineatus) from Oman studied by Al-Busaidi et al. (2011) ranging 0.02–0.154 mg kg− 1 and fish (Scomber scombrus) from Spain reported by Olmedo et al. (2013) as 0.004 mg kg− 1. Moreover, higher level of Pb in comparison to present results has been observed as well in fish from Bangladesh (Saha & Zaman, 2013; Ahmed et al., 2019; Rahman et al., 2012), India (Krishna et al., 2014; Malik et al., 2010), Oman (Sadeghi et al., 2019; Ali et al., 2013), Arabian Gulf (Kamal et al., 2015; Alizada, et al., 2020), Malaysia (Alam et al.,2012), Persian Gulf (Agah et al., 2009; Cunningham et al., 2019).
Lead is a non-essential environmental contaminant which can induce serious human health risk such as neurotoxicity, nephrotoxicity, increased risk of heart disease, decreased lung function and many other adverse health effects summarized in several reviews (Liu, et al., 2010, Medeiros et al. 2012, Cunningham, et al.2019). The maximum legislative limit for Pb specified by EU standard and Bangladesh Gazette S. R. O. No. 233-Act 2014 is 0.30 mg kg− 1. In this study, Pb concentration in imported fish were all within this safe limit.
3.1.3 Chromium (Cr)
Concentrations of Cr were observed in the extent of: 0.05 ± 0.02 mg kg− 1 in L. rohita (India), 0.08 ± 0.01 mg kg− 1 in O. ruber (India), 0.07 ± 0.001 mg kg− 1 in S. australasicus (UAE), 0.05 ± 0.001 mg kg− 1 in E. acuminatus (UAE), 0.01 ± 0.001 mg kg− 1 in A. maculatus (UAE), 0.11 ± 0.06 mg kg− 1 in T. toli (UAE), 0.01 ± 0.001 mg kg− 1 in L. johnii (UAE), 0.07 ± 0.001 mg kg− 1 in T. toli (Oman), 0.05 ± 0.001 mg kg− 1 in L. rohita (Myanmar), 0.02 ± 0.001 mg kg− 1 in E. splendens (Myanmar), and 0.04 ± 0.001 mg kg− 1 in C. cynoglossus (Myanmar). The highest level of Cr was detected in T. toli imported from UAE followed by O. ruber from India. The lowest amount of chromium was recorded in L. johnii (UAE). Fish from India and Oman had more Cr in the muscle samples than fish samples imported from other countries (Fig. 2).
Chromium concentration in literature has been documented in ranges: 1.054–1.349 mg kg− 1 in fish from Bangladesh (Ahmed et al., 2015), 7.52–10.2 mg kg− 1 in O. ruber from Oman Sea, Iran (Sadeghi et al., 2019), 12–27 mg kg− 1 in O. rubber from Persian Gulf (Agah et al., 2009), 10.4 ± 5.3 and 11.8 ± 5.1 mg kg− 1 in imported sardine and mackerel from Egypt (Abou-Arab et al., 1996), 0.96 mg kg− 1 in L. rivulatus from India (Sankar et al., 2006).
Lower level of Cr corresponding to present study has also been reported in previous studies: 0.04–1.75 mg/kg ww in seafood from Marmara, Aegean, and Mediterranean seas in Turkey (Turkmen et al. 2008), 0.04–1.5 mg kg− 1 in fish form Bangladesh (Islam et al., 2015), 0.79 ± 0.27 (µg/g dry wt) in A. maculatus from Malaysia (Alam et al.,2012), 0.422 ± 0.02 and 0.437 ± 0.01 mg kg− 1 in L. rohita and hilsa shad respectively from central market of Rajshahi in Bangladesh (Saha & Zaman, 2013), 0.219 ± 0.008 mg kg− 1 in muscles of L. rohita from India (Malik et al., 2010), 0.22 mg/kg in Stolephorus indicus from UAE (Alizada, et al., 2020), 0.3 ± 0.05 mg kg − 1 in Scomberomorus commerson (Narrow-barred Spanish mackerel) from Oman (Ali et al., 2013).
Chromium is considered as one of the 14 most toxic heavy metals (Irwin et al., 1997). Acute exposure of exceedingly high doses of chromium (VI) compounds to humans has been found to be associated with severe respiratory, neurological, cardiovascular, hematological, gastrointestinal, and renal effects (Chen et al., 2009, Carson et al., 1987). Also, numerous studies have revealed that hexavalent form of chromium can surge the odds of lung cancer (Ishikawa et al., 1994). Maximum permissible limit for Cr has been set as 1 mg kg− 1 (EU, 2008); present results for Cr content in imported fish samples were below this limit.
3.1.4 Cadmium (Cd)
The level of Cd in studied imported fish samples was as such: 0.001 ± 0.01 mg kg− 1 in L. rohita (India), 0.005 ± 0.002 mg kg− 1 in O. ruber (India), 0.07 ± 0.04 mg kg− 1 in S. australasicus (UAE), 0.08 ± 0.01 mg kg− 1 in E. acuminatus (UAE), 0.003 ± 0.03 mg kg− 1 in A. maculatus (UAE), 0.06 ± 0.02 mg kg− 1 in T. toli (UAE), 0.001 ± 0.002 mg kg− 1 in L. johnii (UAE), 0.02 ± 0.001 mg kg− 1 in T. toli (Oman), 0.001 ± 0.001 mg kg− 1 in L. rohita (Myanmar), 0.01 mg kg− 1 in E. splendens (Myanmar), 0.01 ± 0.001 mg kg− 1 in C. cynoglossus (Myanmar). E. acuminatus from UAE was found to have the maximum Cd content followed by S. australasicus also from UAE and the minimum Cd content found in L. rohita from India and Myanmar and also L. johnii imported from UAE. In regard to the average Cd concentration in fish from different regions, fish from UAE contained the highest amount and fish from India had the minimal (Fig. 2).
Previous studies exhibited lower or equivalent Cd range to present study in fish from Bangladesh are: 0.001–0.003 mg kg− 1 (Ahmed et al., 2015), 0.033 − 0.075 mg kg− 1 in coastal areas (Raknuzzaman et al., 2016), 0.001–0.6 mg kg− 1 (Islam et al., 2015), 0.09– 0.87 mg kg− 1 (Rahman et al., 2012). Saha & Zaman (2013) found higher Cd (1.365mg kg− 1) in fish from central market of Rajshahi City in Bangladesh. Present study observed lower cadmium level comparing to fish form India (Krishna et al., 2014; Malik et al., 2010; Sankar et al., 2006). In case of fish from Oman, Al-Busaidi et al. (2011) found corresponding range of Cd (0.01–0.034 mg kg− 1) in Arius bilineatus to present study while Ali et al. (2013) found higher level of Cd (1.1 ± 0.5 mg kg− 1) in Indian Mackerel (Rastrelliger kanagurta). Olmedo et al. (2013) reported 0.003–0.046 mg kg− 1 Cd in Scomber scombrus from Spain which coincides to present observations. Present study also observed similar Cd level to those reported in fish from Arabian Gulf (Kamal et al., 2015; Alizada, et al., 2020) and Turkey (Turkmen et al., 2008).
In human system Cd has no biological role and is a highly toxic component potential to cause chronic toxicity even with a presence of a very low concentration (Turkmen et al., 2009). Its bioaccumulation in the human body may lead to pulmonary, hepatic, skeletal, reproductive and renal effects, and even cancer (Misra et al., 1997; Baselt, 2000; Rahmani et al., 2018). Regulatory agencies such as the U.S. Department of Health and Human Services (DHHS), the International Agency for Research on Cancer (IARC) have declared Cd and its compounds as carcinogenic to human (ATSDR, 2012). According to EU standards and FAO/WHO, Cd concentration in fish should not exceed 0.05 mg/kg (WHO, 2011; EC, 2006). In the present study, E. acuminatus, S. australasicus and, T. toli from UAE exceeded this legislative limit.
3.1.5 Nickel (Ni)
The observed level of nickel in the muscle of imported fish was as 0.04 ± 0.02 mg kg− 1 in L. rohita (India), 0.02 ± 0.002 mg kg− 1 in O. ruber (India), 0.03 ± 0.006 mg kg− 1 in S. australasicus (UAE), 0.03 ± 0.001 mg kg− 1 in E. acuminatus (UAE), 0.01 ± 0.003 mg kg− 1 in A. maculatus (UAE), 0.06 ± 0.02 mg kg− 1 in T. toli (UAE), 0.02 ± 0.002 mg kg− 1 in L. johnii (UAE), 0.02 ± 0.001 mg kg− 1 in T. toli (Oman), 0.01 ± 0.001 mg kg− 1 in L. rohita (Myanmar), 0.04 ± 0.003 mg kg− 1 in E. splendens (Myanmar), 0.04 ± 0.002 mg kg− 1 in C. cynoglossus (Myanmar). Highest amount of Ni was observed in T. toli (UAE) among all the fishes and the lowest nickel concentration was found in A. maculatus (UAE) and L. rohita (Myanmar). Figure 2 shows that in average Ni content were almost in similar level in imported fish muscle samples from all the regions; only fish samples from Oman amidst were in the lowest margin in terms of nickel accumulation.
As compared to present observations, earlier studies reported higher nickel accretion in fish from Bangladesh ranging: 0.04–1.4 mg kg− 1 (Islam et al., 2015); 0.69– 4.36 mg kg− 1 in edible fish from Bangshi River (Rahman et al., 2012); 0.1 − 0.56 mg kg− 1 in commercial fish from coastal areas (Raknuzzaman et al., 2016). Higher level of Ni accumulation (3.49 ± 0.97 mg kg− 1) has also been documented in fish from India (Kumar & Mukherjee, 2011). Sadeghi et al. (2019) found considerably elevated amount of nickel (64.45–94.71 mg kg− 1) in muscles of O. ruber collected from Oman Sea. Earlier studies also articulated higher Ni concentration in relation to present study in fish from Arabian Gulf (Kamal et al., 2015; Alizada et al., 2020), Persian Gulf (Agah et al., 2009; Cunningham et al., 2019). With regard to imported fish, El-Nemr (2003) found 4.73 ± 2.85 mg kg− 1 as average Ni concentration in imported frozen fish in Egypt which is quite higher to present study.
Nickel exists in very low levels in the environment usually but its compounds are an eminent environmental threat to human causing a variety of pulmonary adverse health effects, such as lung inflammation, fibrosis, asthma, bronchitis, emphysema and higher risk of lung and nasal cancers (ATSDR, 2005; Forti et al., 2011). Nickel and nickel compounds have been concluded as human carcinogen according to IARC working group (IARC, 1990). Values of Ni concentration in imported fish samples of present study did not exceed the maximum permissible limit for Ni set as 0.5–0.6 mg kg− 1 in fish food (WHO, 1985).
3.1.6 Cobalt (Co)
In the present study, the extent of Co was only found in L. rohita from India as 0.04 ± 0.03 mg kg− 1 and was below the detection limit for the rest of the imported fish samples. In literature, Co concentration was reported in imported frozen fish in Egypt as ranging from below the detection limit to 17.27 mg kg− 1 by El-Nemr (2003). Andreji et al. (2006) also recorded a minor level of Co ranging from 0.06 to 0.28 mg/kg wet weight in fish muscle collected from Lower Nitra River, Slovakia. Moreover, Co extent of current study also coincides with the observations conducted by Alizada et al. (2020) in tissues of Indian anchovy (Stolephorus indicus) from the UAE coast, Arabian Gulf where the concentration of Co was specified as below the detection limit.
Sivaperumal et al. (2007) investigated fish, shellfish and fish products from internal markets of India and documented the average Co ranged as 0.02 to 0.85 mg kg− 1. Turkmen et al. (2008) reported the cobalt level as 0.04–0.41 mg kg− 1 in sea food captivated from Marmara, Aegean and Mediterranean Sea. Earlier studies exhibited higher level of cobalt accumulation in fish from Persian Gulf (Agah et al., 2009; Cunningham et al., 2019), Turkey (Mendil et al., 2010), Iran (Hosseini et al., 2015) with respect to the present study.
Cobalt in trace amount is essential nutritionally for humans and other mammals as it is a key constituent of the vitamin B12 complex, however it has harmful health effects when taken in higher concentrations (ATSDR, 2004; Medeiros et al., 2012). Chronic exposure to Co can initiate vomiting, diarrhea, increased blood pressure, dermatitis, thyroid damage, nerve damage, severe effects on the lungs, including asthma, pneumonia (ATSDR, 2004). As information about maximum permissible limits of Co has not been designated yet in case of fish and fishery products (Rahman et al., 2012), present samples can’t be stated as completely safe or not for human consumption.
3.1.7 Manganese (Mn)
Manganese quantity was detected as 0.15 ± 0.12 mg kg− 1 in L. rohita (India), 0.29 ± 0.004 mg kg− 1 in E. acuminatus (UAE), 0.72 ± 0.28 mg kg− 1 in T. toli (UAE), 0.5 ± 0.02 mg kg− 1 in T. toli (Oman), 0.13 ± 0 mg kg− 1 in L. rohita (Myanmar), 0.46 ± 0.005 mg kg− 1 in E. splendens (Myanmar), 0.78 ± 0.041 mg kg− 1 in C. cynoglossus (Myanmar). In parallel, Mn concentration was below the detection limit for O. ruber (India), S. australasicus (UAE), A. maculatus (UAE), L. johnii (UAE).
Highest level of Mn was recorded in C. cynoglossus (Myanmar) followed by T. toli (UAE) and the lowest was found in L. rohita (Myanmar). Fish samples from India contained the lowest amount of manganese followed by fish samples imported from Myanmar (Fig. 2).
Earlier analysis on Mn concentration in fish samples of Bangladesh has indicated a relatively higher extent in respect to present study (Saha & Zaman, 2013; Rahman et al., 2012; Ahmed et al., 2015). Kumar et al. (2012) recorded 2.0 ± 0.7 mg kg− 1 Mn in hilsa shad collected from Ganga River of India. Sankar et al. (2006) studied heavy metal residues in fish and shellfish collected from Calicut region of Kerala in India and found 0.49 mg kg− 1 manganese in muscles of Lutjanus rivulatus which coincides to the Mn level of present study. Present study also coincides with the former investigations by Ali et al. (2013) as reported 0.2 ± 0.1 mg kg− 1 Mn in samples of Scomberomorus commerson (Narrow-barred Spanish mackerel) and Rastrelliger kanagurta (Indian Mackerel) collected from Oman and Turkmen et al. (2008) in fish from Marmara, Aegean and Mediterranean Sea. Studies on fish samples of Persian Gulf have denoted lower level of Mn as regards to the present findings (Agah et al., 2009; Cunningham et al., 2019). Higher level of Mn has also been exhibited in former investigations (El-Nemr, 2003; Islam et al., 2010; Mendil et al., 2010).
The essential trace metal, Mn is a cofactor for a number of enzymatic reactions and plays a pivotal role in cerebral function, in the maintenance of well-balanced nervous and immune system, blood sugar regulation, blood clotting and the formation of cartilage, bone formation, metabolism of amino acids, cholesterol and carbohydrates (Goyer and Clarkson, 2001). While insufficient intake of Mn may result in manganese deficiency leading to bone malformation and skeletal defects, heart disease, abnormal glucose tolerance, and so forth; chronic exposure to excessive levels can cause severe clinical neurological disease, and also affects the respiratory system, an inflammatory response in the lung able to induce impaired lung function over time (ATSDR, 2012). As the maximum allowable limit of Mn in fish and fishery products has not been set, comparison of the present findings was not conceivable in case of Mn toxicity.
3.1.8 Iron (Fe)
The amount of Fe was discerned in the present observation was as 2.28 ± 1.63 mg kg− 1 L. rohita (India), 1.9 ± 0.14 mg kg− 1 O. ruber (India), 10.77 ± 3.36 mg kg− 1 S. australasicus (UAE), 7.14 ± 0.05 mg kg− 1 E. acuminatus (UAE), 2.67 ± 0.02 mg kg− 1 A. maculatus (UAE), 9.29 ± 3.95 mg kg− 1 T. toli (UAE), 2.38 ± 0.11 mg kg− 1 L. johnii (UAE), 7.38 ± 0.03 mg kg− 1 T. toli (Oman), 2.8 ± 0.04 mg kg− 1 L. rohita (Myanmar), 1.78 ± 0.002 mg kg− 1 E. splendens (Myanmar), and 4.58 ± 0.05 mg kg− 1 C. cynoglossus (Myanmar).
Maximum amount of Iron was found in S. australasicus (UAE) and the minimal was in E. splendens (Myanmar). Considering the average amount in fish samples from different countries, fish samples imported from Oman were with the highest magnitude and fish from India were with the least amount (Fig. 2).
In comparison to present findings, relatively higher level of iron content has been reported in previous studies on fish muscles from Bangladesh as in ranging from 0.55 to 14.43 mg Fe/100 g fish samples by Wheal et al. (2016), 31.80- 296.02 mg kg− 1 in freshwater fish of Bangladesh recorded by Sharif et al. (1993). Higher iron accumulation has also been exhibited in earlier reports in fish samples from India (Dhanakumar et al., 2015), Marmara, Aegean and Mediterranean Sea (Turkmen et al. 2008), Black sea of Turkey (Mendil et al., 2010), commonly consumed fish in Iran (Hosseini et al., 2015), frozen and canned marine fish of Korea (Islam et al., 2010). The current results of iron concentration coincide with those found in commonly consumed fish in Oman (Ali et al., 2013), fish from Red Sea and Arabian Gulf (Kamal et al. 2015), imported sardine in egypt (Abou-Arab et al., 1996), fish from Persian Gulf. (Agah et al., 2009; Cunningham et al., 2019).
Iron is an essential nutrient for all living organisms and it plays a crucial role in human health supporting oxygen binding and transport, electron transport, oxidative metabolism, DNA synthesis and cellular proliferation. (Valko et al., 2005). However, toxicological aspects are significant concerning iron deficiency, chronic iron overload and unintentional severe exposures to iron which possibly can initiate liver damage, inducing fibrosis, cirrhosis, and increased risk of hepatic cancer; iron overload also may bring about endocrinopathies and cardiac dysfunction and iron deficiency is related to anemia resulting in depleted working capacity and inhibit intellectual development (Goyer and Clarkson, 2001; Medeiros et al., 2012). The maximum permissible limit for iron concentration in fish has been set as 100 mg/kg by WHO (1989) and present findings were far beyond this safe limit.
3.1.9 Copper (Cu)
The mean magnitude of Cu in the imported fish samples were as 0.08 ± 0.05 mg kg− 1 L. rohita (India), 0.06 ± 0.01 mg kg− 1 O. ruber (India), 0.11 ± 0.01 mg kg− 1 S. australasicus (UAE), 0.63 ± 0.01 mg kg− 1 E. acuminatus (UAE), 0.18 ± 0.01 mg kg− 1 A. maculatus (UAE), 0.5 ± 0.09 mg kg− 1 T. toli (UAE), 0.2 ± 0.02 mg kg− 1 L. johnii (UAE), 0.54 ± 0.01 mg kg− 1 T. toli (Oman), 0.22 ± 0.01 mg kg− 1 L. rohita (Myanmar), 0.11 ± 0.02 mg kg− 1 E. splendens (Myanmar), and 0.09 ± 0.01 mg kg− 1 C. cynoglossus (Myanmar).
E. acuminatus (UAE) contained highest amount of Cu content among all the imported fish samples and O. ruber (India) had the lowest level of Cu followed by L. rohita (India). Figure 2 showed that fish samples of Oman had the most copper concentration and fish samples imported from India had the minimal copper amount.
Comparatively elevated level of Cu in earlier studies has been recorded as ranging from 1.3 − 1.4 mg kg− 1 in commercial fish and crustaceans collected from coastal area of Bangladesh (Raknuzzaman et al., 2016); 8.33– 43.18 mg kg− 1 in edible fishes collected from Bangshi River, Dhaka (Rahman et al., 2012); 0.658–3.459 mg kg− 1 in cultured fish in Bangladesh (Ahmed et al., 2015); 10.27–16.41 mg kg− 1 in fish from Karnaphuli River estuary (Ahmed et al., 2019). Kumar & Mukherjee (2011) investigated fish collected from Tropical Wetlands in India and found 5.30 ± 0.31 mg kg− 1 Cu in L. rohita which is higher than present findings. Malik et al. (2010) found 0.398 ± 0.002 mg kg− 1 Cu in muscles of L. rohita from freshwater lake of Bhopal which is similar to present results. Present results also coincide with earlier investigations of Cu in fish from Persian Gulf (Agah et al., 2009), fish from Marmara, Aegean and Mediterranean Sea (Turkmen et al., 2008). The current study found lower copper level in fish muscles with respect to those earlier reports (Krishna et al., 2014; Sadeghi et al., 2019; Ali et al., 2013; Kamal et al., 2015; Alizada et al., 2020; El-Nemr, 2003; Mendil et al., 2010).
Copper is an essential nutrient which plays a crucial role in biological transfer of electrons and as an indispensable part of numerous metalloenzymes associated with hemoglobin formation, metabolism of carbohydrate and drug/xenobiotic, maintenance of nervous system structure and function, antioxidant defense mechanism (ATSDR, 2004; Medeiros et al., 2012). Copper deficiency can lead to blood and nervous system disorders, leukopenia, normocytic and hypochromic anemia, and osteoporosis in adults (ATSDR, 2004). Nevertheless, exposure to higher doses of copper has been disclosed to have noxious health effects. Copper accumulation has been found to be associated with hepatic cirrhosis, renal tubular damage, gastrointestinal distress, death of neurons with neurological symptoms, impaired immune system, abnormalities of the nervous system and cornea (ATSDR, 2004; Goyer and Clarkson, 2001). Copper concentration in present study was found as below the maximum allowable limit which is 30 mg kg− 1 (FAO, 1983).
3.1.10 Zinc (Zn)
Zinc level was perceived in the present study as 1.93 ± 1.09 mg kg− 1 in L. rohita (India), 0.9 ± 0.07 mg kg− 1 mg kg− 1 in O. ruber (India), 9.25 ± 7.1 mg kg− 1 in S. australasicus (UAE), 4.59 ± 0.004 mg kg− 1 in E. acuminatus (UAE), 3.64 ± 0.85 mg kg− 1 in A. maculatus (UAE), 6.19 ± 2.36 mg kg− 1 in T. toli (UAE), 3.15 ± 0.002 mg kg− 1 in L. johnii (UAE), 7 ± 0.1 mg kg− 1 in T. toli (Oman), 2.55 ± 0.14 mg kg− 1 in L. rohita (Myanmar), 2.01 ± 0.04 mg kg− 1 in E. splendens (Myanmar), 2.98 ± 0.19 mg kg− 1 in C. cynoglossus (Myanmar).
The maximal Zn concentration was recorded in S. australasicus (UAE) followed by T. toli (Oman) and the minimal was found in O. ruber (India). Considering the original source, fish samples imported from Oman were with the highest amount of Zn and fish from India were with the lowest amount.
Considerably higher level of Zn has been noted in previous studies on fish samples from Bangladesh (Raknuzzaman et al., 2016; Rahman et al., 2012), fish collected from India (Kumar & Mukherjee, 2011, Krishna et al., 2014), fish from Red Sea and Arabian Gulf (Kamal et al., 2015), frozen and canned marine fish of Korea (Islam et al., 2010). Several studies found similar Zn content in fish (Sankar et al., 2006, Ali et al., 2013, Alizada, et al., 2020, Agah et al., 2009, Cunningham et al., 2019, Turkmen et al. 2008). Ahmed et al. (2015) reported trace elements from highly consumed cultured fish (Labeo rohita, Pangasius pangasius and Oreochromis mossambicus) and observed lower amount of Zn (1.850–3.735 mg kg− 1) in comparison to the present study. Malik et al. (2010) also mentioned insubstantial amount of Zn, 0.48 ± 0.02 mg kg− 1 in muscles of L. rohita sampled from freshwater lake of Bhopal, India which is comparatively lower concerning present observations.
Zinc, ubiquitous in the environment, is an essential micronutrient for rudimentary cell activities and a constitutional component of numerous proteins, including enzymes concerning cellular signaling pathways and transcription factors (Goyer and Clarkson 2001; ATSDR, 2005). Zinc deficiency results in severe health consequences such as growth retardation, poor appetite, skin changes, mental lethargy and immunological abnormalities (Ahmed et al., 2015). Even though Zn toxicity is rare, ingesting excessive levels considerably higher than the Recommended Dietary Allowances (RDAs) for zinc can likewise have adverse health effects. Taking too much zinc into the body through food, water, or dietary supplements for several months may lead to anemia, suppressed immunity, damage of pancreas, and decrease levels of high-density lipoprotein (HDL) cholesterol, copper deficiency, and possible genitourinary complications (ATSDR, 2005). Maximum allowable limit of zinc as set by FAO (1983) is 30 mg/kg for fish and current findings were much lower than this safe limit.