Seasonal physico-chemical attributes of the river Buriganga , Turag and Balu , Bangladesh

Seasonal physico-chemical attributes (p , EC, TSS, TDS, DO, BOD, COD, Cl, HCO 3, NO3-N, NH4-N, Na, K, Ca, Mg, Fe, Zn, Cu, Ni, Al, Pb, Cd, Cr, and Hg) of the river Buriganga, Turag and Balu have been studied to determine the polluti n level of these rivers. It was revealed that most of the attributes exceeded the standard values set by GOB. Specially the parameters measured for the river Buriganga and Turag were in d a ger level. The level of pollution was much higher in winter and summer seasons compared t o monsoon.


INTRODUCTION
Dhaka is one of the most densely populated cities in the world (WHO, 1992).There are number of rivers around the city such as the Buriganga, Turag, Balu, Bongshi, Karnatali etc. (GOB, 1997), but most of them are biologically dead or about to die (Karn & Harada, 2001;Bangladesh River System, 2004).All of Dhaka's sewage and industrial wastes are flushed directly or indirectly into these rivers (Ahmed & Reazuddin, 2000;Subramanian, 2004).The major polluting industries are tanneries, textiles, dying, pulp and paper and steel re-rolling mills which are located beside the Buriganga, Turag and Balu river.(Ahmed, 1985).These industries are discharging heavy metals like Fe, Zn, Pb, Co, Mo, Cd, Ni, Cr, Hg, As, (Ahmed & Reazuddin, 2000) and some acids and solvents like H 2 SO 4 , HCl, carboxylic acids, phenol, organic acids, triphenyle methane etc. (Rahman,1997;Ahmed, 2007) and some dying materials like Paranitraniline red, Mauveine, Heptamethine, Fuchsine, Rhodamine, Quinoline, Solvent red 164, Pararosaniline etc. (Jones, 1952;OSA, 1943).In Dhaka, the tannery industries of Hazaribag are discharging their wastewater into the Buriganga river through three outfalls (Kawser et al., 2011).Some other industries located in the Fatullah (Narayanganj) industrial area (mainly textiles and steel re-rolling mills) discharged their effluents partly via the floodplain of the Buriganga river.Tongi industrial area (mainly textiles and steel re-rolling mills) drains out its wastewater through a canal to the Turag river and the southern part of the Turag is connected with the Buriganga.Effluents of the Tejgaon industrial area (textile, chemical, paper & steel re-rolling mill) are being discharged as diluted forms via drains and lowland into the rivers Buriganga , Turag and Balu (Rahman et al., 2001).
According to GECA (1995) the above mentioned rivers have lost their ecological health.The ecological disaster has imposed an economical vulnerability to Bangladesh.But still a comparative status of these three rivers have not been studied.It is necessary to obtain sufficient scientific data on these rivers to manage the river ecosystems.To address this national need, the present research has been designed to investigate the physico-chemical attributes of the river Buriganga, Turag and Balu around the capital Dhaka.

MATERIALS AND METHODS
Sampling site selection : Samples were collected from 4 locations of each river based on the industrial density at their banks, such as for the Buriganga the locations were Sadarghat, Jhauchor, Bosilla and Sluicegate; for the Turag the points were Ashiulia, Tongi, Pagar and Ujhampur; and for the Balu the locations were Ulukhola, Kanchon, Isapura and Demra as shown in Figure 1.
Sampling seasons: Water samples were collected in three distinct seasons: Summer (March-May), Monsoon (June-August) and winter (Dec-Feb) in the year of 2011 to 2012.

Sample collection and preservation:
All the water samples were collected by water sampler (Model: UWITEC, A-3510).Samples were preserved in two methods, one for normal for non metallic analysis and other for metallic analysis which was preserved by adding very few drops of HNO 3 as reported by (Chapman, 1996).

Sampling points
Sample analysis: Proper sampling procedure was followed carefully to inhibit the intrusion of any foreign particles that may affect the results.Some parameters like Temperature, pH and DO were measured instantly at the spot by Hanna instrument -H19033 (Gupta, 2000).Rest of the samples were analyzed in laboratory.TSS and TDS were determined by Filtration process (Lenore et al., 1998).BOD, COD and HCO 3 were determined by titrimetric method (Lenore et al., 1998); Cl by Mohr volumetric method (Chapman, 1996); HNO 3 -N and NH4-N by Micro-Kjeldahl distillation method (Gupta, 2000); Na and K by Flame-photometric method (Lenore et al., 1998); Ca and Mg by EDTA titrimetric method (Lenore et al., 1998); Fe, Zn, Cu, Ni, Al, Pb, Cd, Cr and Hg by Atomic Absorption Spectrophotometric (AAS) method (Glanje, 1996).

RESULTS AND DISCUSSION
Buriganga : Physico-chemical parameters have been presented in Table 1.Water of this river was highly acidic (average pH-4.05) in winter.It may be due to low water volume, high amount of dying and tannery disposal etc.But in summer the pH was 6.05 and in monsoon it was 7.16 which did not deviate much from the standard value.This finding is different from the findings of Kamrul et al. (2008) and Kamal et al. (1999).The EC value was 753 ms/cm in winter whereas in summer it was 678.50 ms/cm and 552 ms/cm in monsoon.In winter the DO was very low (2.3 mg/l).But in winter TSS, TDS, BOD and COD values were 158.25, 1015.17,68.36 and 139.21 mg/l respectively which were much higher than the standard values, but in summer the values were 3.45, 49.35, 126.39 mg/l respectively and in monsoon which were 4.69, 35.95 and 90.88 mg/l respectively (Table 1).Values of these three parameters were more or less similar with the findings reported by Kamrul et al. (2008); Begum et al. (2010), Masuduzzaman & Rafiq (2006) who worked on water quality status of the surrounding rivers of Dhaka.The concentration of Cl (82.49),NO 3 -N (21.28), and NH 4 -N (9.78) mg/l were also highest in winter.Although in summer these values were 5-10% and 10-30% less than those in winter and in monsoon respectively, however all were beyond the standard values.Kawser et al., (2011) worked on the effect of textile and tannery effluents on the water quality of the river Buriganga, where they found the value of BOD, TDS, TSS, Na, K, Ca, Fe and Cl were 74.0, 2188, 899.6, 707.7, 53.5, 46.7, 0.135, and 78.81mg/l respectively during summer season.The results of the present study were more or less similar to the BTMA report of 2007.The HCO 3 value was 113.13mg/l in summer and 80.24 mg/l in monsoon but in winter the value was zero because HCO 3 does not exist if the pH is below 4.23 (Trivedi & Gurdeep, 1997).In winter the concentrations of Na, K, Ca, and Mg were 58.10, 7.14, 16.01 and 19.06 mg/l, respectively (Table 1).It was found that all recorded heavy metal concentrations in water crossed the safety limit in summer, monsoon and winter.Among these the Fe, Zn, Cu, Ni, Al, Pb, Cd, Cr and Hg concentrations were highest in winter, which were 1.79, 0.85, 0.21, 0.04, 1.42, 0.11, 0.05, 0.04 and 0.05 mg/l, respectively.These results indicate that the river Buriganga is highly polluted.Rahman et al. (2007) reported 20-70 ppm Pb and 0.03-0.43ppm of Cd in textile effluent discharging zone of Turag river during summer.In summer the values were slightly lower but in monsoon it was about half of the winter value although all the values were much higher than the standard values (Table 1).Turag: This river is also highly polluted like Buriganga and most of the pollutant concentrations were higher in winter than those of summer and monsoon.In winter the average pH was 5.39 near by the industrial area, whereas in summer it was 7.20 and 7.28 in monsoon (Table 1).The DO was only 3.49mg/l and the other values were very high such as EC, TSS, TDS, BOD, COD, Cl, HCO 3 , NO 3 -N, NH 4 -N were 477 ms/cm, 103.75 mg/l, 197.12 mg/l, 55.91 mg/l, 185.78 mg/l, 70.93 mg/l, 80.94 mg/l, 31.74 mg/l, 16.57mg/l in winter, respectively (Table 1).In summer the values were 5-10% less than winter and 10-30% less in monsoon but all exceeded the standard limits.The ionic concentration like Na-15.96, mg/l, K-4.44 mg/l, Ca-14.38 mg/l, and Mg-15.85 mg/l were in winter (Table 1).The heavy metals were present highest in winter such as Fe-2.54 mg/l, Zn-0.55 mg/l, Cu-1.34 mg/l, Ni-0.02 mg/l, Al-3.68 mg/l, Pb-0.08 mg/l, Cd-0.01 mg/l, Cr-0.15 mg/l and Hg 0.10 mg/l (  1).The ionic concentrations were Na-9.97 mg/l, K-3.22 mg/l, Na-9.97 mg/l, and Mg-11.95mg/l in winter but 7.35mg/l, 1.90mg/l, 15.44mg/l and 8.93mg/l in monsoon (Table 1).This river also exceeded the standard limit of heavy metal concentrations but not as severe as for the Buriganaga and Turag river in any respect.In winter the concentration of Fe, Zn, Cu, Ni, Al, Pb, Cd and Cr was 1.36mg/l, 1.21mg/, 0.018mg/l, 0.014mg/l, 1.38mg/l, 0.034mg/l, 0.013mg/l and 0.035mg/l, respectively (Table .1).Delwar & Hadiuzzaman (2005) conducted a research on water quality of the Shitalakhya and the Balu river.They found that the value of Al, Cd, Cr, Pb, Hg and Zn was 2.95, 0.006, 0.028, 0.074, 0.0032, and 0.246 mg/l respectively in the Shitalakhya whereas in the Balu river the values were 2.16, 0.006, 0.022, 0.0, 0.0010 and 1.12 mg/l respectively.It is assumed that the pollution level has been rapidly increased after 2005 and reached to this severe level in 2012.It was found that the Hg concentration was very high in winter than other two seasons and than other two rivers, which was 0.285mg/l and very higher than the standard value 0.005mg/l (Table 1).The most probable reason might be that huge area near the river side was under Boro cultivation and the pesticide used for Boro cultivation might contain large amount of Hg which would come down to the river in that season.

Fig. 1 .
Fig. 1.Map showing the study sites.(All round-red marks are the sampling points)

Table 1 . Seasonal physico-chemical properties (average value) of the river Buriganga, Turag and Balu in different seasons
Roy et al. (2010)oon the values were comparatively low due to high tide and dilution effect.Roy et al. (2010)reported 0.59 mg/l Zn, 0.127 mg/l Cu, 0.0 Pb and 0.0006 mg/l Cd in Karanapara canal of Savar.Better water quality was recorded in this river compared Buriganga and Turag, such as the pH was 6.70, 7.16 and 6.71 in summer, monsoon and winter respectively (Table1).However, the contaminant loading in winter were slightly higher such as EC-330.25 ms/sec, TSS-41.08 mg/l, TDS-50.35mg/l,DO-4.49mg/l,BOD-28.99mg/l,COD-26.90mg/land Cl-27.54mg/lcomparativelythanothertwo seasons as reported in Table1.The HCO 3 was present in summer, monsoon and winter as 106.18 mg/l, 89.24mg/l and 132.24 mg/l, respectively (Table.1).The value of NO 3 -N and NH 4 -N was 19.19mg/l and 9.96 mg/l in winter but 8.37 mg/l and 7.48 mg/l in monsoon (Table Balu: