Changes of heavy metal concentrations in Shitalakhya river water of Bangladesh with seasons

Heavy metal concentrations in water and fish of the Shitalakhya river was measured to find out the suitability of its water for drinking and irrigation purposes


INTRODUCTION
Pollution of heavy metals in the aquatic environment is now a serious attention for human civilization because currently, it has reached an alarming rate (Mahfuza et al., 2012).These metals mostly raise from human activities like draining of sewerage, industrial waste and effluents, dumping of hospital wastes, municipal waste and recreational operations (Alam et al., 2007;Malik et al., 2010), conversely, metals are also occur in trace amounts naturally and may reached into aquatic ecosystem through leaching of rocks, airborne dust, forest fires and vegetation (Ishaq et al., 2011).As heavy metals are highly persistent and have potential to be toxic to living organisms, incessantly being deposited and incorporated in water, causing heavy metal pollution in the aquatic ecosystem (Fernandes et al., 2008;Ebrahimpour & Mushrifah, 2008;Storelli et al., 2005).The availability of heavy metals in water may have an intense effect on the micro algae which forge the main food source for mollusks in all their growth stages, zooplankton and for larval stages of some crustacean and fish species (Seshan et al., 2010).Moreover, bio-accumulation, as well as bio-magnification, could lead to high toxicity in organisms, even when the exposure level is low and under such position, the toxicity of a moderately toxic metal could be enhanced by synergism and fish population may decline (Haque et al., 2004).Apart from destabilizing the aquatic ecosystem, the bio-accumulation of these toxic metals in the aquatic food web is an impendence to public health and thus their potential large scale effects on ecosystem integrality cannot be disregarded (Rashid et al., 2012).
The river is very important for aquatic species especially for fish and also plays a significant role in assimilating or carrying off industrial and municipal effluents, residential waste water and runoff from agricultural fields which are accountable for river pollution (Alam 2003;Reza & Singh, 2010;Subramanian, 2004).Due to the swift population growth, unplanned urbanization, profound agricultural and industrial production, some rivers and water bodies has reached terrible levels in Bangladesh (Ghafoor et al., 2004).Pollution of the fresh aquatic ecosystem, especially the rivers are no longer within safe limits for human dealings and this can be measured through the heavy metal analysis in water and fishes (Haque et al., 2007).The environments of Bangladesh are particularly influenced by its regional and seasonal emergence and quality of water (MacFarlane & Burchett, 2000).In modern times Bangladesh holds 1176 industries that release almost 0.4 million m 3 of untreated waste water and effluents into the rivers per day (Rabbani & Sharif, 2005).Among the environmental pollutants, metals are of special concern due to their dynamic toxic effect and ability to bio-accumulation in fishes (Censi et al., 2006;Lohani et al., 2008).Discharge of waste water into a water body could reduce the biological oxygen demand (BOD) to such a massive scale that the entire oxygen may be shifted and this would cause the death of all aerobic groups along with fishes (Bhuiyan et al., 2011).
The Narsingdi town is one of the most vital industrial zones of the country and the Shitalakhya river flows through this town, various types of industries have been established on the bank of the river and most of these industries directly or indirectly discharging a huge quantities of wastes and effluents into the river without any treatment, and also municipal and domestic waste water from Narsingdi urban area, find their way untreated into this river (Mottalib et al., 2016;Islam et al., 2014).A significant volume of industrial raw materials for production and processed products are also transported through this river continuously by ships and other water vehicles (Islam et al., 2008).Therefore, the risks of aquatic pollution impact are rising upwards sequentially (Mokaddes et al., 2013).Thus, the present study was an attempt to assessing the present heavy metals pollution condition of the Shitalakhya river.The objectives of the study were as: (i) to investigate the heavy metal concentrations in water of the Shitalakhya river using pollution indices, and (ii) to assess the level of heavy metals contaminations in fish (Notopterus notopterus) of the Shitalakhya river.

Study area
The study area was located in the Shitalakhya river at Narsingdi district of Bangladesh approximately within the latitude between 23°55'36" to 23°91'92" N and longitude between 90°43'54" to 90°71'76" E. The river flows through Gazipur district forming its border with Narsingdi for some distance and then through Narayanganj district and one the most prominent distributary of the Old Brahmaputra river in the flood plain region of Bangladesh (Ahmed et al., 2010).The river is very much alive during the monsoon and carries the major discharge of the Old Brahmaputra river on its way down.The river is about 110.0 km long and widest 0.3 km across and remains navigable year round.The river's maximum depth is 21 m and the average depth is 10 m (Haque, 2008).

Sampling stations
Water samples were collected from five sampling stations namely as Saorait Bazar (St-1), Ghorashal Fertilizer Company (St-2), Jamalpur Bazar (St-3), Ghorashal Ferighat (St-4) and Fuleshawri Bazar (St-5), whereas fish samples were collected from only St-1, St-3 and St-5 stations along the Shitalakhya river of Bangladesh.Stations were selected depending upon the presumed water quality and extent of pollution by prior visiting the study area.St-1 (upstream) located at the 1 km upstream of the Ghorashal Fertilizer Company Limited, where agricultural runoff, animal manure and waste water from municipal drains were the main source of pollution.St-2 (upstream) situated just besides the fertilizer company.Waste water from this industry was the main pollution source at this station.St-3 (upstream) was dominated by cement, textile, pesticide, and fertilizer factory and food beverage industrial park.Heavy metal containing waste water from plant discharge and waste water drains that collect mixed domestic, municipal and industrial waste water were the major pollution source in St-2.St-4 (downstream) situated just near the Ghorashal Bridge and Railway Bridge.Waste water from township, cement, fertilizer and plastic industries were the significant source of pollution at tis station.St-5 (downstream) was severely dominated by large scale industries such as, paper and pulp industry, plastic industrial park, cement factory, pesticide and fertilizer factory and textile industry.Ghorashal Railway Bridge and ferry Ghat were 1 km upstream near the St-5.Waste water drains that collect plant discharge, municipal, industrial and agricultural runoff were the most significance sources of pollution in St-5.considered as pre-monsoon, monsoon and post-monsoon season, respectively.To analyze the water quality, 500 mL water was collected by plastic bottles with double stoppers from each sampling points.Before sampling, the bottle was cleaned and washed with the detergent solution and treated with 5% nitric acid (HNO 3 ) over night.The bottles were finally rinsed with deionized water and dried.At each sampling station, the sampling bottles were rinsed at least three times before sampling was done.Pre-prepared sampling bottles were immersed about 10 cm below the surface water (Tareq et al., 2013).After sampling, the bottles were screwed carefully and marked with the respective identification number.Then the samples were acidified with 10% nitric acid (HNO 3 ), were placed in an ice bath and were brought to the laboratory.The samples were filtered through 0.45 µm micro pore membrane filter and were kept in freeze at 4°C to avoid further contamination until analysis.The 200gm fish samples were collected from each sampling stations for analysis and brought to the laboratory with ice box and kept at freeze for preservation (Ahmad et al., 2010).

Sample analysis
For water sample, at first 50 mL water sample was taken in a beaker by using a pipette.The 2 mL of concentrated HNO 3 was added in the water sample and then for digestion, the beaker was put in the hotplate.After proper digestion, the sample was taken in a 50 mL of volumetric flask and filled with distilled water up to the limit.Then through a filter paper, it was filtered and preserved in a beaker and this process was followed for every water samples.The concentrations of Pb, Cu, Cr, Cd, Zn and Hg in water samples were analyzed by atomic absorption spectrophotometer (AAS-Model: AA-7000, Shimadzu, Japan) following the procedure in the laboratory of the Soil Science, Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh-2201, Bangladesh.The fish samples were at freeze until analysis, and a bit of muscle, the whole liver and two-gill arches from each fish were removed before analysis, and only tissues from each fish were weighed and dried.A microwave digestion against the first-rate method is the concise time, lower consumption of acid and keeping the volatile mixture in the solution (Karadedea et al., 2004).After digestion, the residues diluted to 25 mL with 2.5% of HNO 3 .Instrument calibrated standard solutions were prepared from mercantile ingredients accordingly manufacturers instruction (Hassan et al., 2015).The metal analyses of samples (Cr, Cu, Pb, and Zn) were carried out by using UNICAM-929 atomic absorption spectrophotometer (AAS) in the Food Laboratory of Central Laboratory of Societe de Surveillance (SGS), Bangladesh Limited, Dhaka.The fish species were analyzed by AOAC 19th Edition, 2012 BY ICP-OES, where the lower detection limit was 0.05 ppm.

Heavy metal indexing approach for water
Pollution indices are applied to explore the pollution status of water, in this study, three well-documented methods such as heavy metal pollution index (HPI) stated by Prasad and Bose (2001), heavy metal evaluation index (HEI) stated by Edet and Offiong (2002), and degree of contamination (CD) stated by Brraich and Jangu (2015) were weighted.These indices are often used to investigate the quality of water for drinking as well as irrigation purposes and describe an overall water quality status in relation to heavy metals.For calculating the HPI, Prasad and Bose (2001) considered unit weightage ( ) as a value inversely proportional to the recommended standard ( ) of the corresponding parameter as proposed by Reddy (1995).

Where
is the sub-index of the ith parameter.is is the unit weightage of the ith parameter and n is the number of parameters considered.The sub-index ( ) of the parameter is calculated by: where is is the monitored value of heavy metal of ith parameter and the sign (−) indicates numerical difference of the two values, ignoring the algebraic sign.In computing the HPI for the present study, Pb, Cu, Zn, and Cd were used.The weightage ( ) was taken as the inverse of MAC, the WHO standard for drinking water in ppb and the guide value for the chosen element in ppb, and MAC the maximum admissible concentration/upper permissible.
Heavy metal evaluation index (HEI) method gives an overall quality of the water with respect to heavy metals (Edet & Offiong, 2002) and is computed as: where is is the monitored value of the ith parameter and is the maximum admissible concentration of the ith parameter.
The contamination index (CD) summarizes the combined effects of several quality parameters considered harmful to domestic water (Backman et al., 1998) and the contamination index is calculated from equation below

∑
Where , , and represent the contamination factor, the analytical value, and the upper permissible concentration of the ith component, respectively.

Statistical analysis
The collected data were compiled and tabulated in proper form and were subjected to statistical analysis.The MS office excel 2010 and IBM statistics 20.0 software were used to analyze the collected data.The findings of the study were presented as charts and tabular forms.

Heavy metal contamination in water
The mean concentration of Pb, Cu, Cr, Zn, Cd, and Hg in water were found 0.0065; 0.0240; 0.0069; 0.8170; 0.0044; and 0.0057 mg/L, respectively in pre-monsoon, 0.0029; 0.0151; 0.0019; 0.4270; 0.0015; and 0.0020 mg/L, respectively in monsoon, and 0.0040, 0.0212; 0.0039; 0.6520; 0.0029; and 0.0031 mg/L, respectively in post-monsoon season.The concentration of investigated heavy metals was found higher in pre-monsoon followed by post-monsoon and monsoon, due to the presence of higher level of pollutants into the river water with the lack of heavy rainfall for dilution of pollutants (Ahmad et al., 2010).Moreover, the mean concentrations were observed in decreasing order of Zn > Cu > Pb > Cr > Hg > Cd whereas all the studied heavy metals concentrations were found lower than the standard level  1).The highest Hg (0.0080 mg/L) in water was found at St-5 during the pre-monsoon season, might be presence of electroplating, fertilizer, paper and pulp, plastic and cement industry in the bank of the river which discharged a large amount of waste water into the river water (Mottalib et al., 2016).The Hg concentrations in Turag river water was greatly exceeded the standard level of the surface water quality (Zakir et al., 2006), which is similar to the present study.The study found that concentration of heavy metals was varied from stations to stations and found in order of St-5 > St-3 > St-4 > St-2 > St-1, this might be due to river water flow, locations of industries, municipal and commercial drainage system and agricultural runoff (Hassan et al., 2015).The level of Pb, Cd, and Zn of the Turag river water were found 0.0021, 0.0136 and 0.0191 mg/L, respectively (Mokaddes et al., 2013), almost similar to the present study.The mean concentrations of heavy metal found in the Buriganga river water were observed Pb (0.0654 mg/L), Cu (0.1630 mg/L), Cr (0.5872 mg/L) and Cd (0.0093 mg/L) (Ahmad et al., 2010) reported higher concentrations of heavy metals than the present study.In relation to, the Toxicity Reference Value (TRV) proposed by USEPA (1999) for fresh water, the concentration of Pb, Cu, Zn, Cd, and Hg in water were exceeded the TRV value in great extent whereas Cr found lower than the TRV value (Table 1).
Pearson correlation coefficients (r) was determined to reveal the relationships among the studied heavy metals in the samples during different seasons (Table 2), which may provide notable information on the sources and pathways of these heavy metals into the study area.The coefficient values determined for all the seasons showed significant positive correlation between the studied heavy metals which clearly supported the fact that these heavy metals are from similar pollution sources and pathways into the aquatic environment of the study area (Armah et al., 2010;Hassan et al., 2015).
The concentrations of heavy metal in water of the Shitalakhya river were compared with other major rivers of Bangladesh (Tables 3-5).The study depicted that Buriganga river water was contaminated with lead, chromium, and cadmium in large extent.The Turag, Balu, Meghna, Padma, Dakatia, Passur and Bangshi river showed that the studied heavy metals concentrations were below the permissible level.The Dhaleshwari river water was contaminated by the Pb and Cr pollution; on the other hand, chromium and Hg contents in Shitalakhya river (Islam et al., 2008) water were severely contaminated in large extent.From the overall discussions, the study concluded that the Buriganga river water was contaminated by heavy metals followed by Shitalakhya (Islam et al., 2008) and Dhaleshwari river (Ahmed et al., 2012).The result of the study found that the HPI for all studied metals in three seasons were much lower the critical pollution index value for drinking water of 100.The computed HPI showed that in pre-monsoon, monsoon and post-monsoon season varied between -11.663 to 43.958 (mean = 18.421), -35.619 to -19.858 (mean = -27.661)and -20.635 to 18.765 (mean = -5.989),respectively.According to Prasad and Bose (2001), low heavy metal pollution (HPI<100), heavy metal pollution on the threshold risk (HPI=100) and high heavy metal pollution (i.e.critical pollution index) (HPI > 100), and if the samples have HPI greater than 100, water is not potable.Overall, result stated that the Shitalakhya river water was contaminated with respect to heavy metal but the pollution level was not significant based on HPI analysis.The analyzed HEI of Shitalakhya river water showed that in premonsoon, monsoon and post-monsoon season varied from 4.101 to 8.067 (mean = 5.995); 2.101 to 3.237 (mean = 2.7308); and 2.500 to 5.139 (mean = 3.842), respectively, which revealed that low heavy metal contamination for all sampling stations over the three seasons.Edet et al. (2003) stated the water quality index into three categories which include: low (HEI<400), moderate (400 < HEI < 800) and high (HEI > 800).Thus, the computed HEI of Shitalakhya river water showed that the water quality falls under the lower level of pollution.The CD was used as the reference to estimate the extent of metal pollution and CD may be grouped into three categories as follows: low (CD < 1), medium (CD = 1-3) and high (CD > 3) (Brraich and Jangu 2015).The mean CD in pre-monsoon, monsoon and post-monsoon season were 1.477; -2.429; and -0.6542, respectively, indicated that CD values in premonsoon season were higher, fall in the medium category pollution, followed by post-monsoon (low to medium pollution) and monsoon season (lower level of pollution).The overall CD value suggesting that water was low to medium polluted.Three reported indices CD, HPI and HEI were analyzed for their propriety for contamination exploring of underground water from Medias city and found low, as well as water samples, do not present heavy metal pollution (Hoaghia et al., 2013).Investigation showed that the metal pollution in southern Caspian Sea basin water of two indices namely the HPI and HEI were found below the critical values (Nasrabadi, 2015).Due to the rising pollution of water resources, tow pollution indices HPI and HEI were weighed and found low contamination levels (Sobhanardakani et al., 2014).

Heavy metals contamination in fish
The concentration of Pb, Cu and Cr in fish (Notopterus notopterus) of the Shitalakhya river were found below the lower detection limit (LOD) ˂ 0.05 mg/kg during the pre-monsoon, monsoon and post-monsoon, respectively in the all St-1, St-3, and St-5 sampling stations.On the other hand, concentration of Zn in fish (Notopterus notopterus) were found 25.42, 18.30 and 29.34 mg/kg during the premonsoon, monsoon and post-monsoon, respectively, whereas the highest level of Zn was found 35.59 mg/kg at St-3 during postmonsoon, while the lowest was found 15.82 mg/kg at St-1 during the monsoon season (Table 6).
Moreover, the study also showed that Zn concentration was below the permissible level in fish over the three seasons in all stations except St-5 during the postmonsoon as well as the study stated that fish was safe for human consumption.It might be due to the lower level of metal concentrations in water and low bioaccumulation rate of small fish species.Bio-accumulation also depends on geography, trophic level, size, foraging method and the propensity of metals to undergo bio-magnification in the food chain (Ahmad et al., 2010).A study in the Khiru river revealed that in fish, average bioaccumulation of Cu, Zn, Mn, Pb, and Cd was found 3.65 ± 1.04; 106.39 ± 34.93; 27.52 ± 11.27; 0.0016 ± 0.002; and 0.0043 ± 0.01111 mg/kg, respectively which was within the permissible limit (Rashid et al., 2012).A considerable amount of Pb, Zn and Cr were recorded in fishes sampled from both the Buriganga and Shitalakhya (Narayanganj) rivers.In Buriganga, Pb, Zn, and Cr were found 4. respectively whereas in Shitalakhya, mg/kg were found, respectively, and this finding indicated a major threat to human health in relation to consumption of fishes (Islam et al., 2014).
The comparative study depicted that concentration of Pd in Passur and Shitalakhya river fish were within standard level whereas the Buriganga Dhaleshwari and Sundarbans Reserved Forest (SRF) river fish largely exceeded the permissible level set by FAO (1984), whereas all the river fish observed the lower level of Cu, within the permissible level.The Buriganga and Dhaleshwari river fish were highly contaminated by Cr that exceeded the permissible level than Passur, SRF and Shitalakhya river (Table 7).The highest level of Zn was found 24.35 mg/kg in Notopterus notopterus fish of present studied Shitalakhya river followed by SRF and Passur river (Table 7) and all the values show that the Zn content was within the permissible limit 30.00 mg/L (FAO, 1984).From the overall analysis, it can be stated that the heavy metals contamination in fish species of Dhaleshwari river is much worse than the others.

CONCLUSION
The study found that except Hg rest of the studied heavy metals concentrations were found below than the standard level in water whereas, apart from Cr all the metals were exceeded the TRV in significantly.The HPI and HEI values for all studied metals were satisfactory level but the CD was varied markedly over the three seasons.The Zn was the only dominant metals found in fish whereas concentrations of Pb, Cu, and Cr in fish were found below LOD.The study concluded that the Shitalakhya river water was contaminated by means of heavy metals which undoubtedly revealed that the water of the river is not safe for aquatic environment, especially for aquatic biota.Moreover, the study stated that fish in the Shitalakhya river was safe for human consumption in terms of heavy metal contamination.In this point of view, straightforward management approach along with continuous monitoring and assessment is obvious for protecting the water quality and fish species as well as aquatic biota of the Shitalakhya river.

Table 1 .
Concentration (mg/L) of heavy metals in water of the Shitalakhya

Table 4 .
Heavy metal pollution indices (HPI, HEI and CD) of water

Table 7 .
Comparisons of heavy metals concentrations (mg/kg) in the Shitalakhya river fish in relation to other rivers of Bangladesh