Abstract
BackgroundThe present study was planned to estimate the heavy metal concentrations in water samples and fish tissue residue (liver and muscle) of cultured Oreochromis niloticus as well as metallothionein (MT) gene expression in fish liver. Fish samples were collected from different private fish cultures in Kafr El-Sheikh governorate during April 2018–April 2019 in order to assess the public health risks associated with consuming cultured fish. Therefore, we investigated the concentrations of four metal elements (cadmium [Cd], copper [Cu], lead [Pb], and zinc [Zn]) in both fish tissues (muscle and liver) and water samples during the four seasons. Other water parameters (pH value, chemical oxygen demand, dissolved oxygen, alkalinity, total hardness, ammonia, and nitrite) were also determined.ResultsNH3 values were above recommended limits mostly along the year. The trend of metal mean contents found in the fish were in decreasing order of Zn > Cu > Pb > Cd, and the liver showed greater accumulation than muscle. The highest amounts of metals accumulated in fish liver and muscle were recorded in winter and autumn, respectively, while the lowest amount was recorded in summer. Regarding fish muscle which is the edible part consumed by human, the concentration of studied metals was within the safe limits for seafood except for Pb. MT showed a significant high level in response to metals accumulated in fish liver. A positive correlation occurred between MT levels and Cu and Pb concentrations across different seasons.ConclusionIn conclusion, MT expression levels seem to be sensitive to the heavy metals in natural habitats making it a powerful biomarker of heavy metals pollution in fish cultures. In addition, cultured fish in this study could be unfit for human consumption due to a high level of Pb in the edible part of fish. Therefore, greater attention should be set to Pb sources accumulated in cultured fish in Kafr El-Sheikh governorate.
Highlights
Metal pollution is an important worldwide problem, which is growing at an alarming rate
Water parameters and heavy metal concentration Seasonal variations in water parameter and heavy metal concentrations are presented in Table 2 in reference to the permissible limits of water parameter and heavy metal concentrations: pH 7–8.5, chemical oxygen demand (COD) ≤ 10, D.O ≥ 5, alkalinity 20–150, NH3 ≤ 0.5, Cd ≤ 0.003, Cu ≤ 1, Pb ≤ 0.5, and Zn ≤ 2 (Egyptian Environmental Law 48decision 92, 2013). pH did not vary noticeably between summer, spring, and autumn, but is higher in winter (8.03)
All heavy metal concentrations in water were under permissible limits
Summary
Metal pollution is an important worldwide problem, which is growing at an alarming rate. An accelerated release of heavy metals into the aquatic environment poses serious water pollution problems because of their toxicity (Tulasi et al 1989), Girgis et al Bulletin of the National Research Centre (2019) 43:131. Metallothioneins (MTs) are a family of low molecular weight cytosolic proteins that contain highly conserved cysteinyl residues. These residues allow MT to bind, transport, and store various essential (Zn and Cu) and non-essential (Cd and Hg, mercury) heavy metals via thiolate bonding (Isani and Carpenè 2014). The present study was planned to estimate the heavy metal concentrations in water samples and fish tissue residue (liver and muscle) of cultured Oreochromis niloticus as well as metallothionein (MT) gene expression in fish liver. Other water parameters (pH value, chemical oxygen demand, dissolved oxygen, alkalinity, total hardness, ammonia, and nitrite) were determined
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