| The river Buriganga is an adjacent river of Dhaka city,the capital of Bangladesh having about 18 million people,which is considered as one of the most polluted rivers of Bangladesh.Ground water is the main source for the huge city people and its level going down day by day,so surface water can be an alternative.Attempts have been taken to assess some metals in water,sediments and fish of the Buriganga River by using inductively coupled plasma-mass spectrometry(ICP-MS)for a guideline in future study.Some heavy metals,i.e.,Cr,Mn,Ni,Cu,As,Cd,Hg and Pb were measured by using ICP-MS of water,sediments and fish samples collected from seven sampling sites of the river Buriganga in monsoon(Aug 5,2015)and winter(Feb 7,2016).These were taken into account for detail seasonal and spatial discussion because of their detrimental effects on human health as well as aquatic lives.Levels of Cr and As in water were at below detection limit(BDL)in winter and Ni was found only at site-1(upstreaming)(1.868 mg/L).Most of the heavy metals concentrations were higher in winter than those in monsoon except Cr and As.Levels of the analyzed metals were not in a similar trend in monsoon and winter.Concentrations of the analyzed metals in water were 0.757,0.059,0.005,0.011,0.003,0.004,BDL,0.038 mg/L in Cr,Mn,Ni,Cu,As,Cd,Hg,Pb,in monsoon and BDL,1.528,BDL,0.162,BDL,1.062,0.102,1.213 mg/L in winter respectively.Spatial variation of the analyzed elements was not significant in monsoon while major variation was found in winter.This is reasonable because of continuous water flow during monsoon whereas the water body becomes stagnant in winter.Effluents from various industries mix well with flood water from upstream and those become confined to their discharging places.Cr is one of the most pollutants of the river Buriganga due to presence of a number of tanning factories on the bank of the river(mostly between site-1 and site 2).But the level of Cr in winter at BDL is surprising although it was the highest level among the analyzed elements in monsoon.Pb was found as the seven highest elements with an average level 1.213 mg/L,and the highest level(2.052mg/L)was found at site-1.The level of Hg was 0.102 mg/L in winter and the highest level(0.128 mg/L)was at site-2 followed by 0.120 mg/L at site-3.Similar trend of the studied metals was also observed for sediments and fishes where the metal concentrations for winter were higher than those in monsoon;however,the difference was minimum and unlikely in water.It is reasonable to observe significant seasonal difference of the analyzed heavy metals in water because of dilution and/or washout by the flood and rain water resulting in much lower levels of the metals.In case sediments,the dilution and/or washout factors are insignificant so the different were observed with low variation.Concentrations of the analyzed metals were 42.229,37.579,6.394,14.072,0.181,0.206,0.016,10.407mg/kg in Cr,Mn,Ni,Cu,As,Cd,Hg,Pb,in monsoon and 44.083,39.063,7.138,15.926,0.198,0.227,0.018,11.405 mg/kg in winter respectively.Cr was found as the highest level with an average value 44.083 mg/kg,among the analyzed elements and its highest level(76.441 mg/kg in monsoon and 70.808 mg/kg in winter)was at site-1 that is reasonable because of the tanning factories are there.However,values of degree of contamination,contamination factor,potential ecological risk,and ecological risk factor in the sediment pollution assessment in both the seasons indicate low degree of contamination.The levels of the selected heavy metals were much higher in various fish species collected in winter compared to those in monsoon except As which were at BDL in all the fish species.Interestingly,Cr was also at BDL in water in winter but it was found in three different fish species A.testudineus(2.284 mg/kg)(site-1),H.fossilis(0.352 mg/kg)(site-1)and N.notopterus(0.196 mg/kg)(site-2)out of seven species while a common fish species,H.fossilis was also found at site-2 where the level of Cr was at BDL.The presence of Cr in the,H.fossilis and N.notopterus,A.testudineus species which are carnivore nature and especially H.Fossilis and A.testudineus species are known as bottom feeder.The highest element was Mn and it was 0.915 mg/kg in P.ticto and 47.410 mg/kg in A.testudineus.The health risk indices(HRI)for As were 92 and 170 times higher than the corresponding RfD values indicate the contaminated fish species can be considered as potential health hazard to the exposed population.However,in winter,the HRI values for Cd were from 148 to 2940 times higher than its RfD value for all the fish species.The HRI values for Cd are hundred to thousand periods higher than RfD value representing potential health hazard to the population through consumption of the contaminated fishes.However,according to target hazard quotient(THQ)values for every element for monsoon,there was no potential non carcinogenic health risk from intake of a particular toxic element because of THQ and HI(hazard index)values less than 1.In winter,THQ values were also less than 1 for all the elements and the HI value was 2.720 only for M.vitattus.According to target cancer risk(TR)values Cr and Ni show low cancer risk to the population by consumption of some specific fish species in monsoon while As,Cd and Pb have shown no cancer risk at all by consumption of the contaminated fishes.In winter,Cd and Ni have shown moderate cancer risk through consumption of all the contaminated fishes except N.notopterus for Ni while Pb and Cr have shown low cancer risk to the exposed population except for Cr which has shown moderate cancer risk for A.testudineus. |
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