Assessment of Physico-Chemical Properties, Some Heavy Metals and Arsenic of River Teesta in Jalpaiguri District, West Bengal, India

Manika Saha^1*, Suman Sengupta², Biswajit Sinha³, Dipu Kumar Mishra⁴

¹Department of Chemistry, Ananda Chandra College, Jalpaiguri, West Bengal, India, Pin-735101

² Department of Chemistry, Ananda Chandra College, Jalpaiguri, West Bengal, India, Pin-735101

³Department of Chemistry, University of North Bengal, Darjeeling, West Bengal, India, Pin-734013

⁴Department of Chemistry, University of North Bengal, Darjeeling, West Bengal, India, Pin-734013

*Corresponding Author E-mail: msahagd@gmail.com, sengupta.sum@gmail.com, biswachem@gmail.com, dipukumarmishra@gmail.com.

ABSTRACT:

River Teesta, being the most significant river in Jalpaiguri district of West Bengal, India, has been providing natural water to satisfy the requirements of this area. Other than irrigation related agriculture, fishing is one of the prime sources of income for a large number of rural people of this region. Bathing, washing clothes and utensils in river water is common practice in rural areas. Thus, the quality of water of the river Teesta is of prime importance as it can affect the livelihood of the residents of this area. Though this natural resource of water is continuously exploited due to ever increasing demand of people, no assessment regarding status of water quality has been made so far. So this study is attempted to observe physico-chemical properties, As and heavy metal contamination of the river Teesta. Various physico-chemical parameters such as temperature (air and water), pH, Conductivity, salinity, Total dissolved solid, DO, BOD, free CO₂, Alkalinity, Total hardness, Ca-hardness, Mg-hardness, Phosphate are recorded season wise. The results furnished for these parameters are seasonally varied and are found to depend on environmental and other factors. Most of the parameters are within acceptable range compared to given by WHO. The study of heavy metals (As, Pb, Cu, Ni, Zn) reveal that concentration level of all these metal are either below detection limit or well within the prescribed limit of reported optimum standard of water quality.

KEYWORDS: River Teesta, Water quality, Seasonal variation, WHO, Heavy metal pollution.

INTRODUCTION:

Water is one of the most important natural resources to fulfil basic needs of mankind. Rapid growth in population demands the developmental up gradation like urbanisation, construction of barrages on the rivers, setting up of industries, and increase in production of crops.

The consequences of all these factors lead to exploitation of natural resources like water bodies extensively. The surface water bodies are being polluted increasingly by the domestic sewage (while passing through the villages), by leaching of pesticides from agricultural land and by industrial wastes. Among various types of water pollutants metal ions are most concerned because of their toxicity and non-biodegradable nature¹ and persistent and bio-accumulative character². Metal pollutants are introduced or enter into aquatic system through rocks and soil in contact with surface water, decomposition of dead organic matter, precipitation of air, and discharge of surface water runoff after rain and industrial emissions³. The water quality of a river system is defined by various physico-chemical characteristics and these parameters tend to change due to different kinds of pollution, seasonal fluctuation and water extraction. This type of study of any water body provides a good impression about water quality and sustainability of the aquatic and surrounding ecosystem.

Many researchers in India studied various aspects of water quality for different surface water bodies^4,5,6,7,8.Teesta, one of the major rivers of northern region of West Bengal originates in Sikkim and after flowing through almost the entire state meets its main rivulet Rangeet near Rongpo enters into West Bengal. One study of water quality of the course of the Teesta within Sikkim had been done⁹. But no studies regarding physico-chemical parameters and heavy metal analysis have been found on this river during its course post Sikkim. This study is very significant as river water has been used for agriculture, fisheries and other purposes of daily livelihood by village people. It is of prime importance to assess the water quality. More over this study shall work as a future reference. This river enters into Jalpaiguri district near Sevoke of Darjeeling district of West Bengal and after traversing a long stretch through the district it reaches Bangladesh and finally meets Brahmaputra. In the present study attempts have been made to assess seasonal variation of physicochemical parameters of the river Teesta and investigate the levels of heavy metals and Arsenic within Jalpaiguri district, India and compared with WHO standard¹⁰. Among the two study sites chosen, one (S-I) was at Gajoldoba, Jalpaiguri (26°45ʹ18ʺ N, 88°35ʹ41ʺ E) the lower end of the Teesta barrage, and the other (S-II) was at Kandobari, Jalpaiguri (26°24ʹ05ʺ N, 88°48ʹ05ʺ E). Water samples were collected from the two stations in three phases, e.g. in the month of May (pre-monsoon or summer), July-August (Monsoon) and in January (Postmonsoon orWinter) during 2015-2016.

Material and methods:

Water samples were collected in clean polythene bottles of 1 litre capacity keeping no space to prevent the escape of any dissolved gas. In addition to that, water samples were collected in duplicate form by two glass DO bottles with the capacity of 135 ml – 150 ml.

Temperature (both air and water), pH, free CO₂, total dissolved solid (TDS), conductivity and salinity were recorded at sampling site. For pH, TDS, conductivity and salinity water analyzer kit had been used. DO was also determined at the collection site using Wrinkle method. Water samples were immediately brought to the departmental laboratory where other parameters like total alkalinity, total hardness, calcium hardness, phosphate were measured within few hours following standard methods¹¹.

For heavy metal analysis, water samples were collected in clean polythene bottles with the capacity of 250 ml and acidified immediately with 2 ml of conc. HNO₃ per litre of water and preserved in refrigerator at 4⁰C¹¹.

Results and discussions:

Temperature:

Temperature is one of the most important physical parameters of water which is location dependant, varies seasonally. During pre-monsoon at S-2 the water temperature was greater than air temperature which may be due to less water depth. But at S-I, the water temperature was lower than air in all times.

pH:

Natural pH range of a river is largely determined by the ecology and soils of the area (www.marlborough.govt). This is also influenced by the dissolved inorganic compounds as well as by biochemical processes. The average pH recorded in two study sites through the seasons were in the range 7.55 to 8.35. Lowest pH was observed in the summer and highest in the winter. Relatively high pH value in the monsoon compared to summer may be attributed to inflow of alkaline water from the surrounding area. During winter water flow in the river reduced and became almost stagnant leading to the high growth rate of phytoplankton and algal population. The high pH value in winter is due to photosynthetic activity and low CO₂ concentration, (Fig-1) which was in agreement with the study of Ganga River¹².

Electrical conductivity:

Electrical conductivity measures the ability of water to conduct electric current, this occurs by the presence of dissolved ions liberated by decomposition of plant and other organic and inorganic wastes. EC values of water samples ranged from 80.1-254.4 µS/cm. The high EC value at S-II may be due to increased ion concentration and low water flow compared to S-I. Highest EC values were recorded during post-monsoon. (Fig-2)

Total Dissolved Solid (TDS):

Total Dissolved Solid of a water body is controlled by many factors like geographical location of water body, drainage, rainfall, and deposition of organic matter at bottom level, flow of water and water content of the river. In the present study, TDS values were recorded in the range between 35 – 131 mg/lit. The high value recorded in during winter may be due to stagnancy and low depth of water and high rate of deposition of organic matter. (Fig-3)

Dissolved Oxygen (DO):

Dissolved Oxygen is one of the most important parameters to detect water pollution. Dissolved oxygen is essential for sustenance and metabolic activity of all aquatic living organisms. The small portion of oxygen is diffused into water from air which may increase due to strong turbulence. But the most important source of oxygen is through the process of photosynthesis of aquatic plants¹³. The DO concentration was varied from 6.4 to 9.3 mg/lit at S-I and 6.35 to 9.13 mg/lit at S-II. The small increase in DO concentration during monsoon may be due to aeration of increased water. But remarkable high concentration of DO observed in winter may be due to the enhanced photosynthetic activity of plankton and plant undergrowth. Present trend (Fig-1) in the observation was also reported⁹ in the study of River Teesta of Sikkim. This result also allowed positive co-relation with pH, temperature.

Biological Oxygen Demand or BOD:

Biological Oxygen Demand indicates level of pollution in water due to biodergradable organic matter. Microbial decomposition of these organic matters causes oxygen depletion and hence BOD level increases. The BOD concentration ranged from 0.78 to 2.03 mg/lit. At both the stations, high BOD level observed in the pre-monsoon period (Fig-4).This must be due to high rate of biological oxidation at elevated temperature.

Free Carbon-di-oxide:

Free CO₂ originates in water due to respiration of aquatic species, decomposition of organic matter or through diffusion from air. Some of the dissolved CO₂ forms carbonic acid (H₂CO₃), a weak acid with water and generate H⁺ and bicarbonate and carbonate ions in equilibrium. The water with high pH gets neutralised so that pH decreases. In the present study free CO₂ varied between 0.44 to 2.64 mg/lit at all sites. Relatively higher level of free CO₂ was recorded in summer. Low concentration in winter may be due to enhanced rate of photosynthesis by algae and macrophytes, thereby increasing the level of dissolved oxygen. Comparatively high concentration of free CO₂ in pre-monsoon period observed might be due to decomposition of organic matter and low precipitation as carbonate and bicarbonate. Concentration level of free CO₂ indicates the low pollution level of the water of Teesta River.

Alkalinity:

Alkalinity is a measure of ability of substances present in water to neutralise its acidity. It indicates the solutions power to buffer its pH. It is rendered by the salts of carbonates, bicarbonates, phosphate etc. along with hydroxyl ion in free- state, so it protects environment for fish or other aquatic life. In this study total alkalinity was measured at pH 4.25 (methyl orange alkalinity). At both the stations alkalinity was recorded as minimum in monsoon and maximum in winter. The high alkalinity value at S-II in post-monsoon compared to pre-monsoon (month of May) may be attributed to high rate of precipitation of CO₂ as water depth was very low and almost stagnant.

Total hardness:

Total hardness is mainly caused by calcium and magnesium which largely combined with bicarbonates and carbonates (temporary hardness) and with sulphates, chlorides and other ions (permanent hardness). In the present study, the maximum value of hardness was recorded during winter and minimum during summer (pre-monsoon). Wide fluctuation of hardness observed at S-II. This seasonal variation was in agreement with values reported⁹ in the study for this river in its Sikkim course. From the hardness values, it may be concluded that river water can be classified as moderately hard. Total hardness values were in positive correlation with alkalinity. (Fig-5)

Ca-Hardness :

Calcium is an important micronutrient in aquatic environment present in the water due to passage through deposition of limestone, dolomite, gypsum and other calcium containing rocks. Calcium concentration was determined maximum in winter and minimum in the monsoon period. (Fig-6)

Mg-Hardness:

Magnesium is also an important element contributing to hardness but present in lower concentration than calcium. It is an essential constituent of chlorophyll. In the present study, Mg concentrations were varying from 5.45 - 20.24 mg/lit. At S-I, maximum value was recorded in summer but at S-II, Mg-hardness was recorded maximum in winter. (Fig-6)

Phosphate:

Phosphate ions in natural water exist in ionic state as salts, in organic form or sometimes in a particular species. Phosphorus is an essential nutrient in living organisms. It’s concentration in water is low as it is rapidly taken up by plants and bacteria and it is less soluble. Phosphates form salts with calcium and magnesium and goes out of solution and precipitated. Inorganic phosphate ranged from 0.06 -0.41 mg/lit at S-I and nil to 0.29 mg/lit at S-II. At both the stations, its concentration was high during pre-monsoon. Its concentration was nil in winter at S-II due to its utilisation by algae and macrophytes in their growth¹⁴.

Samp le preparation for heavy metal:

Collected water was thoroughly mixed by shaking and 100 ml of the sample was transferred into a beaker and digested with concentrated nitric acid. Finally, digested sample was transferred into a 100 ml. volumetric flask by making up the volume to 100 ml using distilled water. Analytical reagents were used for analysis. Heavy metal analysis was done using atomic absorption spectrophotometer (Varian 80A) with acetylene gas as a fuel and air as an oxidizer. The concentrations of the metals were determined from calibration curves. Calibration curves were prepared separately for all metals by running suitable concentrations of the standard solutions. The estimation of Arsenic concentration was done by using “Merckoquant” Arsenic analysis kit.

Table for water quality parameters studied in river Teesta in Jalpaiguri, West Bengal, India.

Table : 1

Parameters	Unit		May	July-Aug	January	Average
Env. Temp	˚C	S1	29.1	26.1	20.00	25.07
Env. Temp	˚C	S2	29.4	31.8	23.90	28.37
Water Temp	˚C	S1	25.10	23.40	15.00	21.17
Water Temp	˚C	S2	30.50	29.40	20.20	26.70
pH		S1	7.80	8.20	8.35	8.12
pH		S2	7.55	7.90	8.27	7.91
Cond.	µs/cm	S1	80.10	90.40	111.9	94.13
Cond.	µs/cm	S2	132.5	130.3	254.4	172.27
Salinity	ppt	S1	0.00	0.00	0.00	0.00
Salinity	ppt	S2	0.00	0.00	0.00	0.00
TDS	mg/lit	S1	40.20	47.00	55.50	47.57
TDS	mg/lit	S2	91.00	65.80	131.00	95.93
DO	mg/lit	S1	6.40	6.70	9.30	7.46
DO	mg/lit	S2	6.35	6.60	9.13	7.36
BOD	mg/lit	S1	1.30	0.92	0.78	1.00
BOD	mg/lit	S2	2.03	1.62	1.20	1.62
Free CO2	mg/lit	S1	2.22	1.76	0.44	1.47
Free CO2	mg/lit	S2	2.64	1.76	1.32	1.91
Alkalinity	mg/lit	S1	32.00	32.00	42.00	35.33
Alkalinity	mg/lit	S2	34.00	30.00	128.00	64.00
Total Hardness	mg/lit	S1	37.00	30.00	40.00	35.67
Total Hardness	mg/lit	S2	42.00	35.00	122.00	66.33
Calcium	mg/lit	S1	8.41	7.57	14.72	10.23
Calcium	mg/lit	S2	9.67	8.41	38.69	18.92
Magnesium	mg/lit	S1	6.95	5.45	6.14	6.18
Magnesium	mg/lit	S2	7.85	6.46	20.24	11.52
Phosphate	mg/lit	S1	0.41	0.06	0.11	0.19
Phosphate	mg/lit	S2	0.29	0.20	0.00	0.16
As	mg/lit	S1	0.00	0.00	0.00	0.00
As	mg/lit	S2	0.00	0.00	0.00	0.00
Pb	mg/lit	S1	BDL	0.00	BDL	0.00
Pb	mg/lit	S2	BDL	0.00	BDL	0.00
Ni	gm/lit	S1	BDL	0.00	BDL	0.00
Ni	gm/lit	S2	BDL	0.00	BDL	0.00
Cu	gm/lit	S1	BDL	0.00	BDL	0.00
Cu	gm/lit	S2	BDL	BDL	BDL	0.00
Zn	gm/lit	S1	0.10	0.00	BDL	0.03
Zn	gm/lit	S2	BDL	0.10	BDL	0.03

Heavy metal pollution has become a serious environmental problem due to the toxic, persistent, non-biodegradable and bio-accumulative nature of these pollutants¹⁵. One of the main sources of these heavy metals into surface water is due atmospheric deposition by urban –industrial runoff¹⁶. Many metals like Fe, Cu are essential for living organisms when present in small concentrations.

Copper is an essential trace element in the nutrition of plants and animals including human being. It is required for function of some enzymes. But high levels are toxic to organisms and it inhibits algal growth, thereby affects the food chain¹⁷. Metals like Pb, Ni are not needed in metabolic activity. Lead is toxic to aquatic organisms at low concentrations¹⁸. Zinc is an essential element for animals and plants but may be toxic to aquatic organisms at high concentration. The mean concentration of the heavy metals was observed in the order of Pb>Cr>Fe>Ni>Zn>Cd>Cu for the study of water in dying wetland Pallikaranai, Tamilnadu¹⁹ .The heavy metal analysed in the water samples of Adyar river, Chennai showed the order of Fe>Cu>Zn>Cd>Pb²⁰.

The water sample’s analysis for the present study showed the concentrations of metals in the following ranges : Pb : BDL (Below Detection Limit); Cu : BDL; Zn : BDL – 0.1 mg/lit; Ni : BDL. In any of the water samples collected from both sites arsenic was not detected.

Pb, Cu, Zn and Ni concentrations were within the limit as prescribed by Irrigation Standards²¹.

All the metal ion concentrations were found to be within the limit given by Drinking Water Standard²² and effluent discharge standards²³.

Figure-1(Seasonal variation for pH and DO)

Figure-2(Seasonal variation for Conductivity)

Figure-3(Seasonal variation for TDS))

Figure-4(Seasonal variation for BOD and freeCO₂)

Figure-5 (Seasonal variation for alkalinity and Total Hardness)

Figure-6 (Seasonal variation of Ca-Hardness and Mg- Hardness)

Conclusion:

From the present study of water samples collected from river Teesta flowing through the Jalpaiguri district reveals that seasonal variation of different physicochemical parameters are significant and are found to depend on various environmental and local factors as cited by many researchers in their studies. Many parameters are within the permissible limit as prescribed by WHO or other bodies and few parameters are in the border line. Various physicochemical characteristics like free CO₂, DO, BOD and conductivity indicated low pollution level and good for fisheries and irrigation. Attempts have also been made to get an impression regarding contamination of some of the heavy metals of this aquatic system. Arsenic has not been detected in any analysis and other metals (Cu, Pb, Zn, Ni) are either in below detection limit or in very low concentration.. Present study is highly significant as no such studies covering physicochemical characteristics and detection of trace metal have been made in this part of the river, so it may serve as the basis for comparison in future studies. Since present study is conducted after Gajoldoba barrage and the flow of water is controlled by the dam which, in most of the time is a minor portion of the water discharged in the actual course of river Teesta, the result of these is highly dependent on the aforesaid factors.

Acknowledgement:

We extend our gratitude to University Grants Commission for sanctioning the research grant, we are grateful to the former and present Principals, Ananda Chandra College, Jalpaiguri for giving permission to use laboratory of the college and for other administrative help. We are really indebted to Dr. Tanmay Datta, Associate Professor, Department of Zoology, A. C. College, Jalpaiguri and Dr. Amal Kumar Patra, Assistant Professor, Department of Zoology, Vivekananda College, Kolkata and all the faculty members of the Department of Chemistry of A. C. College, Jalpaiguri, for their valuable suggestions during the study.

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Received on 14.05.2017 Modified on 19.06.2017

Asian J. Research Chem. 2017; 10(3):399-404.

DOI: 10.5958/0974-4150.2017.00068.2