Introduction

Water is essential to any country's areas of politics and economy, including farming, fisheries, management of forestry, agriculture, livestock production, and other creative industries that greatly impact the region's development (1) . A lake constitutes a substantial expanse of water bordered by terrestrial formations that host numerous aquatic species, including fish. The lake's water quality has significantly deteriorated due to numerous factors, such as wastewater discharge, salting, and municipal sewage (2) . In Kurdistan, surface water like rivers, artificial lakes (dams), ponds, springs, along with springs, and wells' groundwater are vital for life activities. The availability and quality of these water sources depend on environmental conditions, including the chemical composition of parent rocks, precipitation levels, soil formation processes, and the duration water remains underground (3) .

Darbandikhan Lake, located approximately 60 kilometers to the southeast of the urban center of Sulaymaniyah, is fed by the Tanjaro and Sirwan Rivers. This dam is crucial for the local population, providing drinking and irrigation water. The Darbandikhan dam is rich in aquatic species and supports fishing activities (4) . Heavy metal contamination impacts freshwater environments, primarily due to wastewater discharge from commercial, industrial, and agricultural activities. This polluted water contains hazardous levels of heavy metals, which harm aquatic life and human health (5) .

Hydrilla verticillata plant effectively removes cadmium and lead from contaminated water. Studies indicate that as metal concentration increases, the plant's uptake of both metals also rises, with a higher lead absorption rate than cadmium. This suggests that H. verticillata is more efficient at accumulating lead than cadmium under these conditions. In addition, other studies have explored chemical treatments for heavy metal removal by creating biological surfaces that adsorb natural and synthetic substances (6 and 7) .

The river under examination flows through several minor and major industrial zones, polluting Darbandikhan Lake. Furthermore, solid garbage generated in Sulaymaniyah is deposited indiscriminately beside the river, while the city's sewage effluent empties into the Tanjaro River, located south of the metropolitan area. As a result, the primary goal of this study is to quantify the concentrations of heavy metals (Cd, Co, Cr, Cu, Pb, and Hg) within the dorsal and caudal peduncle regions of the common carp sampled from Darbandikhan Lake, Sirwan, and the Tanjaro River.

Methods and Materials

The study examined common carp (Cyprinus carpio) from Sirwan station, Darbandikhan dam, and Tanjaro River (Figure 1). Heavy metal concentrations in the dorsal and caudal region of the fish were analyzed over six months, from August 2021 to January 2022. Darbandikhan Lake, located 60 kilometers southeast of Sulaymaniyah City in the Kurdistan Region, is a significant public health concern due to water contamination. Its hydrological contribution comes from the Tanjaro and Sirwan Rivers, atmospheric precipitation, and groundwater from nearby springs. The issue of water contamination represents a considerable public health concern (8).

Figure 1.Sampling locations for heavy metal analysis in Cyprinus carpio across the Kurdistan Region.

Fish specimens measuring an average length 25 cm were selectively chosen to mitigate variations in heavy metal accumulation. To isolate heavy metals from the fish, local fishermen procured specimens on-site utilizing a fishing net and transported to the laboratory in an ice box.

The Food and Agriculture Organization of the United Nations (1983) dissected fish specimens to extract meat from the dorsal region and caudal peduncle, then frozen, dried, and incinerated. Ash samples were weighed, digested, and filtered. The solution was filtered and stored. Heavy metal content was quantified using an ICP-OES system with Argon gas and a nebulizer gas flow rate. Analysis was performed at 14-16°C using three independent sample replicates.

Statistical analysis

The dataset derived from this research was subjected to statistical analysis employing fundamental statistical techniques and was organized into tables via the XLSTAT software application version (2016). The means were evaluated through ANOVA (Duncan LSD) at a significance threshold of 95% (p < 0.05).

Results

A recent study involved collecting flesh samples from the dorsal and caudal sections of fish to evaluate the levels of heavy metals Cd, Hg, Pb, Co, Cu, and Cr. Table 1 shows the concentrations of these heavy metals in the dorsal flesh from August 2021 to January 2022. The peak concentration of Hg in the dorsal flesh was observed in January 2022, measuring 4.29 ppb, whereas it was below the detection limit from August 2021 to October 2021. The highest concentration of Cd in dorsal flesh was observed in August 2021 at 78.13 ppb, and its concentration varied significantly (p < 0.05) over the study period. Pb reached its highest concentration in dorsal flesh in August 2021 at 227.35 ppb, while it was below the detection limit from November 2021 to January 2022. The peak concentration of Cu in dorsal flesh occurred in November 2021 at 32737.11 ppb, with a significant difference (p < 0.05) noted throughout the study period. Co showed its highest concentration in dorsal meat in October 2021 at 1213.93 ppb, varying significantly over the study period, whereas Cr remained below the detection limit from August 2021 to January 2022.

Table 2 displays the concentrations of the heavy metals analyzed in caudal flesh from August 2021 to January 2022. The highest concentration of Hg was observed in January 2022. Cd showed its highest concentration in August 2021 at 151.86 ppb, with significantly different concentrations observed throughout the study period (p < 0.05). Pb peaked in September 2021 and was below the detection limit from November 2021 to January 2022. Cu reached its highest concentration in November 2021 at 37126.65 ppb, with significantly different concentrations noted during the study period (p < 0.05). Co recorded its highest concentration in October 2021 at 1604.13 ppb, showing significant variability across the study period. Cr remained below the detection limit throughout the study period.

The heavy metal levels in carp flesh, in general, are shown in Table (3) with (p < 0.05) significance level, where the maximum levels of Hg in fish were recorded in January 2022. The Hg concentration from August 2021 till October 2021 was below the detection limit; the highest concentration of Cd was recorded in August with (115 ppb) with a significant difference in concentration throughout the study, while the highest levels of Pb were recorded in September 2021 with (193,98 ppb). Between November 2021 and January 2022, the concentration of Pb was below the detection limit. The concentration of Cu was recorded every month of the study period, but the highest levels were found in November 2021 (34931.88 ppb), when the concentration changed significantly. The highest concentration of Co was found in October 2021 (1409.03 ppb), when the concentration changed significantly. During the study period, the concentration of Cr was below the detection limit.

Chart 1.Concentration of Hg in ppb in fish flesh

Chart 2.Concentration of Cd in ppb in fish flesh

Chart 3.Concentration of Pb in ppb in fish flesh

Chart 4.Concentration of Cu in ppb in fish flesh

Chart 5.Concentration of Co in ppb in fish flesh

The concentration of studied heavy metal in dorsal flesh in the study locations is shown in Table (4) with (p < 0.05). Significantly, Cr was not detected in any area, and no statistically significant differences were found for Cd and Pb. Hg and Cu were significantly higher in Sirwan, and Co in Tanjaro.

In Table 5, Cr was undetected across all locations, and no significant differences were observed for Cd, Pb, and Co. Cu levels were notably higher in the Sirwan location. In Table 6, Cr was not detected in any locations. No significant differences were observed for Cd and Pb. Co levels were higher in both Darbandikhan and Tanjaro. Cu was significantly elevated in the Sirwan River. Chart 10 displays the concentration of Co in parts per billion (ppb) in fish meat.

Chart 6.Concentration of Hg in ppb in fish flesh

Chart 7.Concentration of Cd in ppb in fish flesh

Chart 8.Concentration of Pb in ppb in fish flesh

Chart 9.Concentration of Cu in ppb in fish meat

Chart 10.Concentration of Co in ppb in fish flesh

Charts 6 to 10 collectively illustrate the various heavy metal concentrations studied in fish flesh across the research station.Regarding the correlation between the stations and the study period, Table 7 shows the concentration of these heavy metals in the dorsal flesh. Similar correlations are evident in Table 8 for specific heavy metal concentrations and Table 9 for overall concentrations in fish meat (p < 0.05).

Cr was not detected in any position during the study period. Hg was found only in Sirwan and Darbandikhan in November 2021, Darbandikhan in December 2021, and in Sirwan in January 2022. Cd levels were notably higher in August 2021 in Tanjaro. Pb was not detected at any study locations from November 2021 to January 2022. Cu levels were significantly elevated in Sirwan in November 2021. Co levels were notably higher in Tanjaro in October 2021, as detailed in Table 7.

Cr was undetectable. Hg was detected in Sirwan and Darbandikhan only in November 2021 and again in Sirwan in January 2022. Cd was found in Tanjaro in August 2021. Pb was present in Sirwan in September 2021 but was not detected in any location from November 2021 to January 2022. Cu levels were elevated in Sirwan in November 2021. Co was notably higher in Tanjaro in October 2021, as indicated in Table 8.

Table 9 displays the levels of Mercury across all months and locations studied, with exceptions for certain months and locations. Cd was notably higher in Tanjaro in August 2021, Pb in Sirwan in September 2021, Cu in Sirwan in November 2021, and Co in Tanjaro in October 2021. Cr was below detectable levels in all months and locations.

Discussion

Fish species like C. carpio and Tinca tinca from Lake Beysehir, Turkey, and Oreochromis mossambicus and Clarias gariepinus from South Africa show high metal accumulation in their gills and intestines (9 and 10).

A study in Al-Masab Alamm River, Al-Nassiriya, Iraq, found that heavy metal levels in water, sediment, algae, and fish samples surpassed acceptable limits established by the World Health Organization and the Food and Agriculture Organization (11) . n the same way, research into the ecosystem of the Euphrates River near Al-Nassiriya City Center in South Iraq found high levels of heavy metals in many parts of the ecosystem. Lead and copper mostly gathered in the liver (12). C. carpio showed different concentrations of heavy metals, indicating a gill > liver > kidney > muscle pattern. This highlights the distinct accumulation patterns present in various fish organs (12) .

Research on carp fingerlings revealed distinct metal concentration patterns in fish muscles, which can accumulate in tissues like the liver, muscles, and intestines, potentially posing health risks and affecting fish consumption safety (13 , 14 , 15 , 16).

Heavy metals accumulated in fish impact fish health andimpact fish health and pose risks to human beings' health through the food chain, particularly in heavy metal-contaminated environments (17) . Monitoring heavy metal concentrations in fish is essential for evaluating freshwater pollution and possible risks linked to human consumption (17) . Also, the testing of metal levels in muscle tissues follows safety rules set by different countries and the WHO. This ensures that fish don't have too many metals like Zn, Cu, Pb, and Cd (18 and 19) , lowering the risk to public health.

The cadmium (Cd) levels in the muscles of Carassius carassius exceeded the permissible limits established by Turkish regulations. In contrast, Oreochromis niloticus exhibited acceptable concentrations of Zn and Cu in its muscle tissues compared to other studies. Overall, the non-essential metals, such as Cd and Pb, were found in O. niloticus at lower levels than reported in the existing literature (20) . Fish are important indicators of heavy metal pollution in water bodies, with pollution levels varying regionally due to local sources and environmental awareness (21).

Heavy metals tend to accumulate in various tissues, such as the liver, muscles, and bones, posing health risks to fish and humans (22) . They are among the most concerning pollutants globally, defined by their high density (>5 mg/ml) (23).

Conclusions

The levels of heavy metals in both dorsal and caudal muscles showed distinct patterns: Cr was undetected throughout all months studied; Cd levels peaked in August 2021; Cu levels were highest in November 2021; and Co concentrations were highest in October 2021. Across all locations, Cr remained below detectable levels. No significant differences were noted in Pb and Cd concentrations. Cu levels were notably higher in Sirwan for both muscle types. Co levels were higher in Tanjaro in the dorsal muscle but did not show significant differences in the caudal muscle.

Notably, muscle tissue beneath the dorsal fin had lower concentrations of heavy metals than the caudal peduncle portion, suggesting it may be safer for human consumption.

Conflicts of interest

The authors declare that there is no conflict of interest.

Ethical Clearance

This work is approved by The Research Ethical Committee.

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