Heavy metals lead in water, sediments and fish in floating cages in Tigris River, Middle of Baghdad, Iraq

Author:   Abd J. Kadhim

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The present study aimed to gather detailed information on the distribution of some heavy metals (Cu, Pb, Zn, Fe and Cd) among the major components of the aquatic ecosystem (water, sediments and fish “Common carp”) of Jadiriya districts in the city of Baghdad. Such information is needed to identify the effect of fish cages on the aquatic ecosystem. Water and sediment samples were collected from three sites, as follows: before the cages area (Be), in the cages area (CA) and after the cage area (Af). Fish samples were collected from the studied cages. Water sediments and fish samples were collected monthly for one year period from April 2012 to March 2013.

 Heavy metal analyses were carried out by using furnace atomic absorbance spectrophotometer. Pearson correlation coefficients were calculated between heavy metals in both fish and water in the cages site. The lowest concentrations of the water heavy metals were recorded in spring and summer times, while winter and autumn showed the highest water heavy metal concentrations.  Average concentrations of Cu, Zn and Fe in water were below the maximum acceptable levels recommended by FAO.  On the other hand, average Pb and Cd concentrations in water from the three test sites were 0.314 and 0.025 ppm for (Be), 0.323 and 0.030 ppm for (Ca) and 0.365 and 0.026 ppm for (Af) respectively which were higher than FAO levels which could prove that fish cages are not the source of these metals. Concentrations of all studied heavy metals of the sediments at the (CA) site were significantly higher than that in the (Be) and (Af) sites due to the adsorption capacity of organic matter. On the other hand annual average of most sediment, heavy metals, especially Pb, in the (Be) site were higher than that in the (Af) site, which means that the release of heavy metals from the power station sited inferior to the cages site could be the main source of heavy metals accumulated around and under cages. The mean concentrations of Cu, Fe and Cd in the fish samples of the present study were lower than the maximum permitted concentrations proposed by FAO.  However, mean levels of Pb and Zn were higher than the limits given for fish.

Thus, fish in the cage area accumulate Pb to levels exceeded the maximum permitted level (about 4 times), this could represent a significant health risk to humans consuming diets rich in fish. The flow of industrial effluents discharged to the Tigris river accumulates in the fish flesh reared in this area and causes heavy pollution by the most dangerous heavy metals (Pb and Cd) than those caused directly or indirectly by cages.