The rapid growth of industry and agriculture has resulted in increased emissions of heavy metals in recent decades, which poses a major environmental risk to invertebrates, fish and humans(] Uluturhan And kucuksezginf , 2007). Heavy metals should be highlighted among the pollutants, because of the effects of their bioaccumulation in marine environments.( Nadmitov ,et.al.,2015 and Slomanka, 2007). Significant amounts of these metals are released into waterways where they can be highly deposited and biomagnified in the water , soil and aquatic food chain, resulting in both sub-lethal effects and deaths in local fish populations.( Megeerj, et.al.,2000 ; Xu Yj, et.al.,2004 and Jasim, et.al.,2014).
Table (1) shows the ranges of lengths and weights of the golden carp fish Carassius auratus (Linnaeus) grouped from three study sites located on the Euphrates for the period 2015-2016, while Table (2) shows the difference in the seasonal values of some characteristics The physical and chemical properties of the Euphrates River in the study sites. Table (3) shows the seasonal concentrations of the studied heavy elements (Cd, Pb, Zn, Fe, Mn, Se and Ni) in the soluble and particulate form of the Euphrates water in the studied sites and the Table (4) shows the seasonal concentrations of the seven heavy elements studied In the muscles of the three classes of Carassius auratus (Linnaeus).
The results of the current study found the annual rates of heavy metals concentrations in the waters of the river as dissolved form were The order of has been taken as follows:
Iron> Zinc> Nickel> Manganese> Cadmium> Lead> Selenium.
While The concentrations of these elements in water as particular form have taken the following order:
Iron> Zinc> Manganese> Cadmium> Lead> Nickel> Selenium.
Heavy elements in the water as a particular form in the present study had higher concentrations compared with the dissolved form and this is attributed to the process of adsorption, as these elements tend to linkage on the surfaces of some materials, especially particulate matter and organic mud that spreading in the water column (Demina , et.al.,2009 and Dhurgham, 2018).
The results of the current study stated that there is a quarterly variation in the concentrations of the studied elements, the highest concentrations was recorded in summer, while lowest concentrations were in winter and for both forms dissolved and particular due to the large number of pollutant sources and to the difference in capacity of the river to receive different amounts of discharged substances, As that Discharges from domestic, manufacturing and other man-made activities have contributed to high levels of concentrations of heavy metals in freshwater.( Vinodhini and Narayanan ,2008).
in addition to the difference in temperature between seasons, which affects directly and indirectly on the concentration of trace elements in water , or may be due to differences in the values of both pH and the values of salinity and water hardness in addition to the difference in the amount of total dissolved substances, as well as total suspended materials that directly affects the readiness of the elements for living organisms(Kumar and Achyuthan ,2007 And Dhurgham, 2014).
Mitigating factor may play the primary role in influencing the concentration of elements in addition to the change in the water level of river, and may be the life activities for some organisms also play a role in influencing the concentration of these elements, which in turn is affected by many factors including the amount of food, reproduction and the length of the lighting (Salman , 2011). Also, as a result of the study, the low concentrations of some elements in some seasons, is because of the ability of these elements to accumulate in the bodies of living organisms, or to be removed continuously by removal process or by the linkage with through the process of adsorption on some suspended Substances materials and therefore deposition (Dhurgham, et.al., 2014).
The relationship between some physical and chemical properties of water with a concentration of heavy metals dissolved and particulate matter shown by the results of statistical analysis, it was found that there is a direct significant correlation relationship between the concentration of heavy studied elements in the water of the river and the temperature, as it increases the concentration in hot seasons because of the high temperature (Abd and Musa ,2009) . the cause of the low concentration of elements in the spring is due to that this season is the growing season and thus the plants absorb the bulk of these elements in this season because they are necessary to complete the biological processes, while in the summer, the concentration of these elements increase due to several reasons, mainly because of the high temperature and thereby increase the evaporation rates as well as increased degradation of the dead organisms which leads to lack of absorption of these elements by the living organisms. Bacteria, especially, anaerobic sulfur bacteria a key role in the reduction of most of these elements as the heavy elements mixed with organic materials through analysis by bacteria (Park, et.al., 2008).
The results of the present study showed that the concentration of heavy elements in the waters of the river both in dissolved and particular form affected by the values of pH, as the results of statistical analysis shown there is a reverse correlation between them, as the pH of water affect the solubility of heavy metals by increasing the amount of adsorbed elements on organic matter by the increase of the pH values and thus lead to the deposition (Odum, 2000). while the decrease in the pH values will lead to increase competition between the elements ions and hydrogen ion to link to active sites, also it's working to dissolve the complex (carbonate/ elements), leading to release the items to the water column (Forstner & Wittmann, 1981).
The electrical conductivity and salinity have been found by the results of statistical analysis that there is a significant reverse between them and the concentration of studied heavy elements as they affect the process of absorption and adsorption of these elements in organic matter (Kathikeyani , et.al., 2002).
Found by the results of statistical analysis of the current study that the amount of total suspended Substances associated closely to the concentration of river water as particular form due to the abundance of phytoplankton in the Euphrates River , as the plankton concentrate large amounts of heavy elements in the water through absorption (Dhurgham , et.al., 2014).
The results of the present study showed that the annual mean concentration of the studied heavy metals (Cd, Pb, Zn, Fe, Mn, Se, Ni) in the muscles of the first category, second and third of the Gold carp fish Carassius auratus (Linnaeus) The arrangement in the muscles of the three groups in the studied sites is as follows
Zinc> Iron> Nickel> Manganese> Selenium> Lead> Cadmium.
The current study showed that the third category of fish Carassius auratus (Linnaeus) contained the highest concentrations of heavy elements than for first and second category, and this may be because the increase of concentration of the element by the increase of the size and length of fish (Dhurgham , 2014 and ] Blasco , et.al.,1998).
That the concentration of Zinc element, as is evident from the results was high compared to other elements and the reason This component is important for preserving the gonads and protecting the marine ecosystem from the effects of cadmium toxicity, and this purposely fishes to consume large quantities of this component. (Dhurgham , 2014 and Hammoud, et.al.,2005).
Add to that the study showed that In the muscles of the three types of fish studied, the concentration of the selenium element was high and there was proof of the absorption of that element from water into the bodies of living organisms , including fish, and this is strong evidence on the basis of fish as a critical indicator for suggesting the existence of pollution of these dangerous heavy elements (Benson , et.al., 2007).
The relationship between the concentrations of heavy metals studied in the muscles of Carassius auratus (Linnaeus) with some studied physical and chemical properties, they found a direct significant correlation relationship between temperature and the amount of heavy elements, with the highest concentration of these elements in fish muscle was in summer, spring and attributed the reason to increase the accumulation of heavy elements in the warm seasons compared to the cold seasons, as the high temperature causes an increase of metabolic events and the high level of metabolism and thereby increase the concentration of heavy elements within the body of fish (Zayed , et.al.,1994).
In fresh water, heavy metals accumulate and grow through the food chain. The bioaccumulation patterns of heavy metals are calculated by fish absorbance and excretion rates. Different variables such as water's physical and chemical properties as well as seasonal changes are the explanation for substantial metal augmentation in various fish tissues. (Romeo , et.al., 1999). Stern metal residual problems in the fish epithelium are due to the presence of higher concentrations of metal in water and (Wong , et.al., 2001).