Evaluation of Heavy Metal Levels in Fish and Their Potential Health Risks to Humans

Worldwide environmental pollution is interpreted as a multidimensional international threat to human health as it interferes with the regular operations of the environment [1], [2]. There are numerous varieties of pollution, but one of the predominant to be explored here, especially in emerging nations, is water contamination [3]. Industrial sludge [4], agricultural runoff [5], municipal wastewater [6], oil spills [7], and stormwater runoff [8] are the vital sources of water contamination. Water contaminants include chemical waste [9], heavy metals [10], volatile organic compounds (VOCs) [1], food processing wastes [11], fertilizers and pesticides [12], poisons generated by livestock operations [13] etc. Heavy metal contamination brings about an abundance of toxicities with adverse effects on aquatic faunal communities, it is a significant threat to aquatic environments [14]. They are environmental pollutants as well as food contaminants categorized as substances with densities above 5 g/cm3. Heavy metals mercury (Hg), lead (Pb), nickel (Ni), arsenic (As), zinc (Zn), copper (Cu), tin (Sn) and cadmium (Cd) are among the contaminants from the category of industrial pollutants that are particularly hazardous to aquatic creatures along with human health [15]. These substances participate in a variety of biogeochemical cycles following entering the environment, and eventually, they might get bio-magnified and bio-accumulated into the chain of food from lower levels of trophic status to higher levels of trophic status [16]. Heavy metals are complicated to manage because they are chemically stable molecules and therefore non-biodegradable, exhibit a propensity for accumulating in sediments, and possess an extended period of half-life in the environment. Bio-magnification and bioaccumulation in live tissues, as well as the inability to eliminate organic contaminants by precipitation, oxidation, or bioremediation, prove certain elements of particular concern. These metals are ultimately disposed of in aquatic environments, particularly rivers and the sea. Even minor modifications in the condition of the environment, such as its physical and chemical characteristics, may possess an adverse effect on fish, which are particularly susceptible to these modifications, on their typical physiology [17]. Due to the incredible propensity of their tissue to store contaminants such as heavy metals and other organic compounds, in aquatic ecosystems fish are at the highest level of the trophic pyramid, which are regarded as being strong bio-indicators. Water contamination from a variety of places with heavy metal contaminants inevitably leads to the biological accumulation of carcinogenic metals in fish muscle [18].

Fish is a predominant indispensable food in our everyday diets because of their amazing nutritional attributes (vitamins, high-quality proteins, and essential omega-3 fatty acids) and adequate dietary properties. In response to this, fish manufacturing and consumption are expanding continuously on a worldwide scale. By 2029, it is anticipated that worldwide fish output will increase from one hundred seventy-six Mt in the base period to 200 Mt, according to predictions, the amount of fish consumed worldwide will increase by 16.3%, or 25 Mt, to 180 Mt. [19]. Over the past thirty years, the total quantity of fish produced in Bangladesh has jumped by almost six times (7.54 lakh MT in 1983-1984 to 46.21 lakh MT in 2020-2021). Around 3.57% of the nation's GDP and 26.50% of agricultural GDP in 2020–2021 were provided by the fishing and aquaculture sector [20]. The absorption of heavy metals in their body is more intense throughout several fish organs, including the gill, skin, GIT, digestive tract, muscle, and bones or they could consume these elements directly from the water. Eventually, these metals exhibit carcinogenic and non-carcinogenic impacts on human beings [20]-[24]. The vast majority of the heavy metals that gather in the aquatic system originated from anthropogenic activity, including farming, landfill erosion, embarking and docking, domestic discharges, pharmaceutical waste products and industrial wastes, and some specific natural processes [14], [25], [26]. Metal pollution is also significantly influenced by smelting processes, mineral extraction, and other industrial operations incorporating metal [27]. while producing fish, people use numerous types of fish feeds and water sources. They also serve as a major source of pollution, more particularly heavy metal contamination [28]. Since metalloid compounds frequently form covalent bonds, this characteristic is responsible for their extremely toxic properties. Covalent bonds between heavy metals and organic groups can result in the formation of lipophilic compounds or ions [29], and their lipophilic character, which allows them to pass through the membrane. By interacting with cell organelles, these metallic compounds exhibit harmful consequences [30]. Metal poisoning in humans has been linked to a wide range of health issues, especially damage to the kidneys and skeleton, neuropathy, endocrine disturbance, heart problems, and malignancies [31], [32].

This study focuses on assessing the levels of heavy metal contamination in three commonly consumed fish species, viz. Mozambique tilapia (Oreochromis mossambicus), Labeo bata, and Olive barb (Puntius sarana) sourced from the Rajshahi City Corporation area in Bangladesh. By analyzing the concentrations of Cd, Pb, Cr, and Mn in these fish, this research aims to evaluate the potential health risks posed to consumers. Our findings underscore the necessity for continuous monitoring and stringent regulatory measures to safeguard public health against the dangers of heavy metal exposure through fish consumption. This study not only highlights the pressing issue of heavy metal contamination of fish in Bangladesh but also contributes to the broader discourse on environmental health and food safety globally.

Though fish is one of the major sources of protein and is commonly consumed food by the people of Bangladesh, it is quite an appropriate source to analyze health risk assessment of heavy metals. The concentrations of Cd, Pb, Cr and Mn in the fish samples have been measured shown in Table 2 and graphically presented in Fig. 2, Fig. 3, Fig. 4 & Fig. 5. Every evaluated data set has been compared with the allowable limit (Table 3).

Superscript ‘a’ letter in each column means a significant difference at p<0.05. The SPSS analysis is carried out in IBM SPSS software.

The World Health Organization (WHO) has established guidelines for the maximum levels of cadmium, lead, chromium, and manganese in fish. According to the WHO, the maximum level of cadmium in fish muscle tissue should not exceed 0.05 mg/kg WW, while the maximum level of lead is 0.3 mg/kg WW. The WHO has not established specific limits for chromium and manganese in fish. [50]. In the European Union (EU), the maximum levels of cadmium, lead, chromium, and manganese in certain fish species are set by Regulation (EC) No 1881/2006. For example, the maximum level of cadmium in certain fish species is 0.5 mg/kg wet weight (WW), while the maximum level of lead is 0.3 mg/kg WW. The maximum levels for chromium and manganese vary depending on the fish species. The maximum level of chromium for all fish species is 0.5 mg/kg WW and 1.0 mg/kg WW for manganese [51], and in the United States, the Food and Drug Administration (FDA) has established maximum levels for cadmium, lead, and mercury in fish. For example, the maximum level of cadmium in fish is 0.1 mg/kg WW for most species, while the maximum level of lead is 0.15 mg/kg WW. The FDA also has not established specific limits for chromium and manganese in fish. [52]. In addition, according to FAO (Food and Agriculture Organization), in Bangladesh, the maximum permissible level of Cd was 0.25 mg/kg, and that for Pb, Cr, Mn was 0.3, 0.1–1.0, 2.0 mg/kg wet weight (WW) respectively [54].

Cd contents in the fish samples ranged from 0.0181 to 1.1083 mg/kg (Table 2). Here the maximum amount (1.1083 mg/kg) of Cd is found in Labeo bata fish (sample no Ka-B) at the Katakhali region, while the minimum amount (0.0181 mg/kg) of this metal is in Mozambique tilapia fish (sample no Ka-M) at the same location. Present results indicate that the Cd concentration in 91.67% of fish samples lies within the safe level (0.25 mg/kg) [53].

Heba et al. (2023) estimated Cd content in muscles of five freshwater fish species from Manzalah Lake (Egypt) and they recorded 1.4 μ/g (wet weight) Cd in C. gariepinus, 1.36μ/g in S. galilaeus, 1.34μ/g in T. zillii, 1.32μ/g in O. niloticus and 1.19μ/g in O. aureus [49]. According to Mielcarek et al. (2020), the levels of Cd in freshwater fish species from Poland, specifically smoked fish products, ranged from 0.02 to 97.0 μg/kg [54]. According to Jarosz-Krzeminska et al. (2021), the muscle of Mozambique tilapia zillii that lives in the Elemi River in Ado-Ekiti has an estimated 60.0 µg/kg of Cd in smoked rainbow trout from a Polish fish farm [55].

The concentrations of Pb in the fish samples varied from 0.3032 to 4.7812 mg/kg (Table 2). The highest content is found in Mozambique tilapia (sample no Me-B) at the Katakhali area, while for lowest content is found at the Binodpur area in Labeo bata fish (sample no Bn-B). But from the following investigation, it has been indicated that Pb concentration in 100% fish samples exceeded the maximum permissible limit for Pb (0.3mg/kg)[53].

Mahjoub et al. (2021) determined heavy metal content in fish muscles from the Mechraâ-Hammadi Dam in Morocco and found Pb content ranged from 0.034–0.074 mg/kg of wet weight in E. Lucius, 0.045–0.087 mg/kg in S. lucioperca, 0.017–0.043 mg/kg in M. salmoides, 0.051–0.115 mg/kg in L. macrochirus and 0.049–0.106 mg/kg in S. erythrophthalmus [56]. Ahmad Razali Ishak et al. (2020) estimated Pb in Mozambique tilapia fish (Oreochromis niloticus) from selected areas in Kuala Lumpur. The highest concentrations of Pb were detected in the gills (0.151 ± 0.12 mg/g) followed by bones (0.108 ± 0.09 mg/g) and the least in muscle tissues (0.078 ± 0.05 mg/g) [57]. Djedjibegovic et al. (2020) estimated Pb content in Blue musse (0.161 ± 0.072 mg/kg wet weight), Black tiger shrimp (90.014 ± 0.008 mg/kg), Atlantic mackerel (0.007 ± 0.005 mg/kg) [58].

Cr concentration in these fish samples is found from 1.0255 to 3.1414 mg/kg (Table 2), where the maximum concentration is sample no Ka-M in Mozambique tilapia at the Katakhali region and the minimal one is sample no Me-S in Puntius sarana at Meherchondi. From the above investigation, 100% of the sample exceeds the permissible limit (1 mg/kg) [53]. Accumulating at a huge amount of Cr may cause carcinogenic effects to the consumers.

Pradip et al. (2019) found the Cr concentration among the most consumable seven fishes (Cirrhinusmrigala, Cirrhinusreba, Catla catla, Lebio rohita, Crossocheiluslatius, Clupisomagarua, and Mystustengara) tissues ranged from 0.28 ± 0.03 to 1.74 ± 0.31 mg/kg in river Ganga [59]. Aminul et al. 2018 quantified the amount of Cr in the six available fish species (Mastacembelus armatus, Channa punctatus, Puntius puntio, Mystusvittatus, Metapenaeus spinulatus and Amblyceps mangois) ranging from 0.006-0.159 mg/kg at Dhaleshwari River, Tangail, Bangladesh [60]. Nyantakyi et al. 2021 found 16.10 ± 0.2 mg/kg Cr concentration in Clarias gariepinus and 57.9 ± 4.2 mg/kg in Sarotherodongalilaeus [61].

Lastly, the content of manganese (Mn) varied from 0.8897 to 1.6245 mg/kg (Table 2), in this case, the maximum content is 1.6245 mg/kg (sample no Ka-B) in Labeo bata at Katakhali region and for minimum one it is 0.8897 mg/kg (sample no Bn-B) in Labeo bata fish at Binodpur. According to this study, 100% of the sample lie in between the permissible limit (2mg/kg) [53]. So, they may not be able to cause toxicity to our health.

Safiur et al. estimated the content of Mn in five commercially important marine fishes (i.e.Sillaginopsispanijus, Trichiuruslepturus, Harpadonnehereus, Rita rita and Coiliadussumieri) ranged from 14.54 to 18.45 mg/ kg (dry weight basis) [62]. Mohammad Belal et al. 2022 estimated heavy metals in 15 types of commonly consumed fish muscles and found 6.637 mg/kg of Mn from the Lower Meghna River and Adjacent Areas of Bangladesh by using the method called Energy Dispersive X-ray Fluorescence (EDXRF) [63]. A Hossain et al. 2016 found 17.842 mg/kg Mn in fish (O. niloticus) flesh and 50.317 mg/kg in fish (A. testudineus) liver in different fish markets of Dhaka city, Bangladesh [64].

For the health risk assessment, the EDI, THQ, CSF, and CR values are tabulated in Table 4. The average THQ and HI values are given in Table 5. The result found that only the Labeo bata fish from two specific regions (Ka-B and Me-B) have THQ values greater than 1, indicating an imminent health threat. The rest of the fishes have a safe range of THQ values that is less than 1, as per USEPA risk study [35].

For the CR value of Cd metal 91.67% of the sample lies between 10⁻⁴ to 10⁻⁶ except for the sample Ka-B, Which might have significant health impact. Whereas for the metal concentration of Pb 100% of the samples CR value is within the permissible limit of 10⁻⁴ to 10⁻⁶. But in case of Cr we have a complete opposite scenario where 100% of the samples CR value exceeds the permissible limit ranging from 9.49 × 10⁻⁴ to 1.45 × 10⁻³ which shows significant carcinogenic risk for the consumption of these contaminated fish. As there is no CSF value available for Mn so it is not possible to assess the CR value for this metal.

After investigating all the metals concentration in three fish species we have the value of HI greater than 1 for 100% of the fish species. Where HI for Labeo bata being the highest of 1.4024 and lowest 1.0448 for Puntius sarana. Consumption of these fish species impose a significant hazard threat in human health.

The study underscores the alarming levels of heavy metal contamination in fish from the Rajshahi City Corporation area, which poses a considerable health risk to the local population. The detected concentrations of Cd, Pb, Cr, and Mn in the fish samples frequently surpassed the limits recommended by global health organizations, highlighting a pressing need for regulatory action. The accumulation order of metals was Pb > Cd > Mn > Cr. The health risk assessments, including the EDI, THQ, CR, and HI, collectively suggest that prolonged consumption of these fish could lead to serious health issues, both carcinogenic and non-carcinogenic. This research calls for urgent intervention to control pollution sources and protect aquatic ecosystems, as well as public health. Enhanced monitoring and strict enforcement of environmental regulations are crucial to reducing the contamination levels in fish and ensuring the safety of food supplies. Additionally, raising awareness among consumers about the potential risks associated with heavy metal exposure from fish is essential. Moving forward, there is a need for integrated approaches combining pollution prevention, fishery management, and public health strategies to address and mitigate the impact of heavy metal contamination in aquatic environments.