Heavy metals (Cadmium, Mercury and Arsenic) accumulation in different organs of Sperata sarwari collected from Indus River, Head Taunsa, Dera Ghazi Khan, Punjab, Pakistan

This study was conducted to analyze the accumulation of cadmium, mercury and arsenic in different organs of Sperata sarwari. The fish were collected from Indus River, Head Taunsa, Dera Gazi Khan, Punjab, Pakistan. The organs of collected fish were separated and frozen at -20 oC. The organ samples were digested by using perchloric acid and nitric acid. The concentration of accumulated metals in organs was measured by using an atomic absorption spectrophotometer. The kidney was found most targeted organ for the accumulation of above mentioned heavy metals. All other organs also accumulate a significant amount of heavy metals. This study concludes that heavy metals of cadmium, mercury, and arsenic are found in the natural water and accumulate in different organs of Sperata sarwari.

Heavy metals are accumulated in river bed due to discharged wastewater from agriculture and industry. The suspended sediments in water absorbed heavy metals and absorbed heavy metals in turn release into different water channels. The outward flow of heavy metals from the mainstream poses a potential threat to the ecosystem [6-8]. The distribution of heavy metals also poses a risk to human health. [9, 10]. Fish are particularly limited to the aquatic environment and vulnerable to the effect of pollutants [11]. Fish is a test organism that indicates the ecosystem's health because fish is more sensitive to toxicants in comparison with invertebrate [12] Heavy metals are produced through anthropogenic and natural resources. The heavy metals pollution occurs through the process of weathering, deposition, waste discharge and also via wastewater treatment plants [13]. Considering the anthropogenic sources coal combustion is the source of emission of different heavy metals [14]. Heavy metals contamination is a serious threat due to long persistence nature, biomagnification and bioaccumulation in the food chain [15]. River pollution in Pakistan is increasing day by day due to rapid industrialization. The liquid influx of effluents from industries and domestic wastes adversely affects aquatic organisms [16]. Metallic pollution in rivers has been increased in recent years. Rivers are a hub for the growth of different animals and plant species. The accumulated metals in rivers move up to higher trophic levels through the food chain [17] Pollution in rivers is a cause of economic and health losses.

Materials and methods Sampling
Fish was collected from Head Taunsa, It is barrage situated on the Indus River, Taunsa, Dera Gazi Khan, Punjab, Pakistan. Fish was dissected and organs were separated. Organs were frozen in an icebox and shifted to the Department of Zoology, Islamia University of Bahawalpur. The organs were kept in the laboratory at -20 ºC for further analysis.

Sample digestion
The organs were accurately measured (1g tissue) in a 100 ml flask. 1 ml perchloric acid and nitric acid were added and heated on a heating mantle to about 120 O C. The process ended when a clear and transparent solution was obtained. The digested samples were diluted using distilled water. The final volume of about 10 ml was used after adding distilled water was used for analysis. The accumulation of metals was detected by the flame photometer method [18]. Data analysis Data were analyzed using SPSS version 20. Means were compared by using Tukey's Test. One way ANOVA was applied (P < 0.05) Results Cadmium Cadmium accumulation (ppm) was reported maximum in the kidney and liver, the value of Cd was 83.05±1.25 and 82.45±0.85 respectively in both organs. In gills, the accumulation (77.15±1.07) was less as compared to kidney and liver but in muscles, the accumulation (71.85±1.36) was lower as compared to the above-mentioned organs. In the skin, the accumulation of Cd was minimum (42.97±1.36). The accumulation of Cd was found in this order Kidney > Liver > Muscles > Gills > Skin (Table 1, Fig. 1).

Arsenic
The accumulation of arsenic (ppm) was reported maximum in kidney and gills 0.63±0.02 and 0.61±0.02. The liver showed less accumulation of arsenic (0.43±0.01) as compared to kidney and gill. In muscles, the accumulation (0.32±0.01) of arsenic was more than the above-mentioned organs. In skin minimum, arsenic accumulation (0.26±0.01) was reported. The accumulation of arsenic was found in this order Kidney > Gills > Liver > Muscles > Skin (Table 1, Fig.  2).

Discussion
Increasing development and the human population destroys the ecosystem especially the aquatic ecosystem. Heavy metals such as Cu, Cr, Cd, and Pb accumulate in fish and other aquatic animals. Essential and nonessential metals both accumulated in different trophic levels of the food chain. Non-essential metals are known to be toxic for fish even at low concentration although they have no role in proper metabolic functioning. The management of heavy metal concentration is necessary because fish is consumed by a human in the world widely. The runoff water from different streams carries heavy metals and tends to accumulate in aquatic species and more commonly in fish [19]. Gills are the important site for the entry of heavy metals and act as indicator organs for the pollution of water. The accumulation of metals in gills may be due to metal interaction with mucus. The accumulated metals are difficult to remove from tissues. Arsenic accumulates in aquatic habitats and subsequently shifted to higher trophic levels.
The arsenic may also target humans. Arsenic occurs in different organic forms and taken up by aquatic organisms. In inorganic form, arsenic is very toxic but its accumulation percentage is low. Arsenic accumulation depends upon the species and tissues [33] In the present study, the maximum amount of arsenic was found in the kidney and minimum in the skin. The accumulation order of arsenic in the studied fish was as Kidney > Gills > Liver > Muscles > Skin. Kousar