Human activities, including agriculture, soil erosion from landfills, and the discharge of industrial and domestic wastewater, are major contributors to elevated trace metal concentration in aquatic ecosystems. While some trace metals are essential, excessive concentrations can pose health risks. This study investigates the levels of Zinc (Zn), Copper (Cu), Iron (Fe) and Chromium (Cr) in the muscle tissues of four commonly consumed fish species (Oreochromis leucostictus, Oreochromis niloticus, Haplochromis pharyngalis, and Haplochromis nyererei), as well as in sediment samples. Both fish and sediment samples were collected from five sites in the Malagarasi River in Tanzania: Ilagala, Igamba, Malagarasi bridge, Mliya Bibi, and Mtego wa noti. Trace metal concentrations were measured using using a Thermo Scientific iCE 3000 Series Atomic Absorption Spectrophotometer. The concentration pattern in both fish species and sediments was: Fe > Zn > Cr > Cu. Oreochromis leucostictus exhibited higher levels of Zn (114.7 ± 49 mg/kg) contamination in its muscle tissues, while H. nyererei shows higher levels of contamination with Cu (6.880 ± 5 mg/kg), Fe (124.8 ± 35 mg/kg), and Cr (7.300 ± 2.7 mg/kg) than the other species. In general, metal concentrations in the muscle tissues of O. leucostictus, O. niloticus, and H. pharyngalis were higher at Illagala and Mliya Bibi while lowest were observed at Mtego wa noti and Malagarasi bridge. Sediments contained higher mean concentrations of trace metals (mg/kg) than fish muscle tissues, with sediment values of 448.2 ± 190 for Zn, 6.860 ± 3 for Cu, 7796 ± 3100 for Fe, and 10.15 ± 6 for Cr. The concentrations of Cu, Fe, and Cr in the sediment were consistently lower at Mtego wa noti than at the other sampling sites. A two-way ANOVA revealed statistically significant differences (P < 0.05) in trace metal concentrations between fish and sediment samples across the various sampling sites. For the majority of cichlids, the essential trace metals were within the permissible limits set by the World Health Organization (WHO), the International Atomic Energy Agency (IAEA), the Food and Agriculture Organization (FAO) and WHO/FAO (30.00–100.0 mg/kg for Zn, 30.00 mg/kg for Cu, 100.0–146.0 mg/kg for Fe, and 0.7300–2.000 mg/kg for Cr). However, Zn in O. leucostictus, exceeded the WHO limit. Additionally, Fe in H. nyererei exceeded WHO/FAO, and Cr levels were above the permissible limits for all four-cichlid species. This highlights the importance of regular monitoring of aquatic ecosystems to prevent trace metal contamination, as neglecting this issue could lead to health risks to community who rely on fish as a primary source of protein.

Variations of Trace Metals in Cichlid Fish Species and Sediment Along Malagarasi River, Tanzania

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发表日期：

2025年8月8日

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Alex Nehemia

摘要

Human activities, including agriculture, soil erosion from landfills, and the discharge of industrial and domestic wastewater, are major contributors to elevated trace metal concentration in aquatic ecosystems. While some trace metals are essential, excessive concentrations can pose health risks. This study investigates the levels of Zinc (Zn), Copper (Cu), Iron (Fe) and Chromium (Cr) in the muscle tissues of four commonly consumed fish species (Oreochromis leucostictus, Oreochromis niloticus, Haplochromis pharyngalis, and Haplochromis nyererei), as well as in sediment samples. Both fish and sediment samples were collected from five sites in the Malagarasi River in Tanzania: Ilagala, Igamba, Malagarasi bridge, Mliya Bibi, and Mtego wa noti. Trace metal concentrations were measured using using a Thermo Scientific iCE 3000 Series Atomic Absorption Spectrophotometer. The concentration pattern in both fish species and sediments was: Fe > Zn > Cr > Cu. Oreochromis leucostictus exhibited higher levels of Zn (114.7 ± 49 mg/kg) contamination in its muscle tissues, while H. nyererei shows higher levels of contamination with Cu (6.880 ± 5 mg/kg), Fe (124.8 ± 35 mg/kg), and Cr (7.300 ± 2.7 mg/kg) than the other species. In general, metal concentrations in the muscle tissues of O. leucostictus, O. niloticus, and H. pharyngalis were higher at Illagala and Mliya Bibi while lowest were observed at Mtego wa noti and Malagarasi bridge. Sediments contained higher mean concentrations of trace metals (mg/kg) than fish muscle tissues, with sediment values of 448.2 ± 190 for Zn, 6.860 ± 3 for Cu, 7796 ± 3100 for Fe, and 10.15 ± 6 for Cr. The concentrations of Cu, Fe, and Cr in the sediment were consistently lower at Mtego wa noti than at the other sampling sites. A two-way ANOVA revealed statistically significant differences (P < 0.05) in trace metal concentrations between fish and sediment samples across the various sampling sites. For the majority of cichlids, the essential trace metals were within the permissible limits set by the World Health Organization (WHO), the International Atomic Energy Agency (IAEA), the Food and Agriculture Organization (FAO) and WHO/FAO (30.00–100.0 mg/kg for Zn, 30.00 mg/kg for Cu, 100.0–146.0 mg/kg for Fe, and 0.7300–2.000 mg/kg for Cr). However, Zn in O. leucostictus, exceeded the WHO limit. Additionally, Fe in H. nyererei exceeded WHO/FAO, and Cr levels were above the permissible limits for all four-cichlid species. This highlights the importance of regular monitoring of aquatic ecosystems to prevent trace metal contamination, as neglecting this issue could lead to health risks to community who rely on fish as a primary source of protein.