1. Introduction

Land and water are precious natural resources on which rely the sustainability of agriculture and the civilization of mankind. Unfortunately, they have been subjected to maximum exploitation and severely degraded or polluted due to anthropogenic activities. The pollution includes point sources such as emission, effluents and solid discharge from industries, vehicle exhaustion and metals from smelting and mining, and nonpoint sources such as soluble salts (natural and artificial), use of insecticides/pesticides, disposal of industrial and municipal wastes in agriculture, and excessive use of fertilizers[1,2]. Each source of heavy metals contamination has its own damaging effects to plants, animals and ultimately to human health, but those sources that contaminates soils and waters are of serious concern due to the persistence of these heavy metals in the environment and carcinogenicity to human beings. These heavy metals cannot be destroyed biologically but are only transformed from one oxidation state or organic complex to another[3, 4]. The environmental parameters of waters effect toxicity of the metal either by influencing physiology of organisms or by altering chemical form of the metal in water. In general, metals are less toxic at lower temperatures and high salinity than at high temperatures and lower salinity. Toxicity of a metal is also dependent upon residence time of metals concerned. Generally, most metals have a long residence time and hence exert their toxic effect over a long time.

The toxicity of heavy metals has long been concerned since it is very important to the health of people and ecology. With the growing interest in pollution of marine environment, many countries are conducting monitoring studies on metals in aquatic marine environment. Therefore, this heavy metal pollution possessing a potential threat to the environment and human health has become a national and international problem. Extensive work has been carried out recently all over the world on heavy metals in different rivers[5-7]. In Western Europe, 1,400,000 sites were affected by heavy metals[1], of which, over 300,000 were contaminated, and the estimated total number in Europe could be much larger, as pollution problems increasingly occurred in Central and Eastern European countries[8]. In India, use of heavy metal fungicides in agriculture is increasing as seed-dressing agents. Antifouling properties of mercury compounds are yet used in pulp mills, industrial and domestic sewage wastes from various sources are now a threat to the survival of fishes and other organisms. The common feature of these metals is that they are all relatively toxic even at fairly low concentrations and are readily concentrated by aquatic organisms , and plants. The seriousness of heavy metal contamination is further compounded by the fact that they are generally water soluble, non-degradable, vigorously oxidizing and are strongly bonded to many biochemicals inhibiting their functions. Today, additional quantities of heavy metals are being added to estuarine and coastal regions from agricultural and industrial waters, hospitals, domestic sewage and from the polluted atmosphere. At sufficiently high concentrations, heavy metals are toxic to marine and estuarine organisms and to their consumers at higher trophic levels including man.

The preservation of aquatic resources for ecosystem and human health and well-being is a paramount concern worldwide and it has become evident that approaches to managing aquatic resources must be undertaken within the context of ecosystem dynamics in order that their exploitation for human uses remains sustainable[9]. If aquatic resources are not properly managed and aquatic ecosystems deteriorate, then human health and well-being may be compromised. Water quality monitoring for the detection of trends, impacts, and improvements is further complicated because the issues of concern and available resources are constantly changing[10]. Although it is not always possible to predict new and emerging threats to aquatic ecosystems, baseline water quality monitoring must be maintained to facilitate the early detection of such threats. The success of local, regional, and global efforts to curb rates of water quality degradation is only possible if sufficient monitoring data are available that enable the tracking of trends over time and space.

The problem of environmental pollution due to heavy metals has begun to cause concern now in most of the major metropolitan cities in Maharashtra state and Mumbai is not an exception to it. The day by day increasing tremendous industrial pollution[11-20] has prompted us to carry the systematic and detail study of water pollution due to toxic heavy metals in Vasai Creek of Mumbai which is becoming highly polluted due to rapid urbanisation and industrialisation.

2. Materials and Methods

2.1. Area of Study

Vasai Creek is an estuarine creek, one of the two main distributaries of the Ulhas Creek in Maharashtra state of western India. The Ulhas Creek splits at the northeast corner of Salsette Island into its two main distributaries, Vasai Creek and Thane Creek. Vasai Creek which lies between latitude 19.315°N longitude 72.875°E, forms the northern boundary of Salsette Island, and empties west into the Arabian Sea. The Creek receives domestic raw sewage as well as industrial waste water effluent from surrounding habitation and nearby industrial belt. The activities like cattle washing, cloth washing, and religious activities like immersion of idols of Lord Ganesha and Deity Durga during Ganesh festival and Navratri festival is also a major source of pollution of creek water.

2.2. Climatic Conditions

Climate is subtropical, with mild winters and warm summers. The weather is typical coastal sultry and humid. The average rainfall of records from 1500 mm to 2000 mm. The place experiences the onset of the monsoon in the month of June and experiences monsoon till the end of September. The average temperature recorded in varies from 25 to 37 degrees.

2.3. Requirements

The chemicals and reagent used for analysis were of analytical reagent grade. The procedure for calculating the different parameters were conducted in the laboratory. The laboratory apparatus were soaked in nitric acid before analysis and then rinsed thoroughly with tap water and de-ionised distilled water to ensure any traces of cleaning reagents were removed. Finally, it is dried and stored in a clean place. The pipettes and burette were rinsed with the same solution before final use.

2.4. Water Sampling and Sample Preparation

The water samples were collected randomly four times in a month in morning, afternoon and evening session at four different sampling stations namely near Vasai Bunder (S-1) , Bhayandar west side of Railway Bridge (S-2), Bhayandar east side near RetiBundar (S-3), and Ghodbundar site (S-4) along the Vasai Creek (Figure 1). The samples were collected and subsequently analysed for a span of two years starting from October 2009 to September 2011. The sampling was done in three shifts i.e. morning shift between 07:00 a.m. to 09:00 a.m., afternoon shift between 02:00 p.m. to 04:00 p.m. and evening shift between 07:00 p.m. to 09:00 p.m. Polythene bottles of 2.5 L and 2.0 L were used to collect the grab water samples (number of samples collected, n = 19). The bottles were thoroughly cleaned with hydrochloric acid, washed with tape water to render free of acid, washed with distilled water twice, again rinsed with the water sample to be collected and then filled up the bottle with the sample leaving only a small air gap at the top. The sample bottles were stoppard and sealed with paraffin wax. Water samples (500 mL) were filtered using Whatman No. 41 (0.45 μm pore size) filter paper for estimation of dissolved metal content. Filtrate (500 mL) was preserved with 2 mL nitric acid to prevent the precipitation of metals. The samples were concentrated to tenfold on a water bath and subjected to nitric acid digestion using the microwave-assisted technique, setting pressure at 30 bars and power at 700 Watts[21,22]. About 400 mL of the sample was transformed into clean glass separating funnel in which 10 mL of 2% ammonium pyrrolidine dithiocarbamate, 4 mL of 0.5 M HCl and 10 mL of methyl isobutyl ketone (MIBK) are added[23]. The solution in separating funnel was shaken vigorously for 2 min and was left undisturbed for the phases to separate. The MIBK extract containing the desired metals was then diluted to give final volumes depending on the suspected level of the metals[24]. The sample solution was then aspirated into air acetylene flame in an atomic absorption spectrophotometer.

Figure 1. Map Showing Sampling Stations along Vasai Creek of Mumbai

2.5. Heavy Metal Analysis by AAS Technique

The analysis for the majority of the trace metals like aluminum (Al), cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), strontium (Sr) and manganese (Mn) was done by Perkin Elmer ASS-280 Flame Atomic Absorption Spectrophotometer. Arsenic (As) was determined by hydride generation coupled with an atomic fluorescence detector, while mercury (Hg) was analysed with a cold-vapour atomic adsorption spectrophotometer. The calibration curves were prepared separately for all the metals by running different concentrations of standard solutions. A reagent blank sample was taken throughout the method, analyzed and subtracted from the samples to correct for reagent impurities and other sources of errors from the environment. Average values of three replicates were taken for each determination.

2.6. Quality Control/Assurance

Water samples were collected in polythene bottles that were free from heavy metals and organics and well covered while transporting from field to the laboratory to avoid contamination from the environment. All reagents were standardised against primary standards to determine their actual concentrations. All instruments used were calibrated before use. Tools and work surfaces were carefully cleaned for each sample during grinding to avoid cross contamination. Replicate samples were analysed to check precision of the analytical method and instrument. To validate the analytical procedures used, the spike recovery test was conducted on some samples for Al, As, Cd, Cr, Ni, Pb, Sr, Mn and Hg.

3. Results and Discussion

Although there is no clear definition of what a heavy metal is, density is in most cases taken to be the defining factor. Heavy metals are thus generally defined as those having a specific density of more than 5 g/cm³. Heavy metals are among the most common environmental pollutants, and their occurrence in waters and biota indicate the presence of natural or anthropogenic sources. Although adverse health effects of heavy metals have been known for a long time, discharge of heavy metals continues and is even increasing in some areas, in particular in less developed countries. The main threats to human health from heavy metals are associated with exposure to lead, cadmium, mercury and arsenic (arsenic is a metalloid, but is usually classified as a heavy metal). Their accumulation and distribution in soil and aquatic environment are increasing at an alarming rate thereby affecting marine life[25-27].The experimental data on concentration (µg/L) of toxic heavy metals like Al, As, Cd, Cr, Hg, Ni, Pb, Sr and Mn in the water samples collected along sampling stations S1, S2, S3 and S4 of Vasai Creek is presented in Table 1. The trend in average concentration of these metals at different sampling stations for the assessment years 2009-10 and 2010-11 is graphically represented in Figures 2-5.

Figure 2. Variation in average concentration values of different toxic heavy metals in water samples collected at S-1 sampling station of Vasai Creek during the assessment year 2009-10 and 2010-11

Figure 3. Variation in average concentration values of different toxic heavy metals in water samples collected at S-2 sampling station of Vasai Creek during the assessment year 2009-10 and 2010-11

Figure 4. Variation in average concentration values of different toxic heavy metals in water samples collected at S-3 sampling station of Vasai Creek during the assessment year 2009-10 and 2010-11

Figure 5. Variation in average concentration values of different toxic heavy metals in water samples collected at S-4 sampling station of Vasai Creek during the assessment year 2009-10 and 2010-11

The effects of aluminum (Al) have drawn our attention, mainly due to the acidifying problems. Aluminum may accumulate in plants and cause health problems for animals that consume these plants. The concentrations of aluminum appear to be highest in acidified aquatic environment[28]. In such aquatic environment the number of fish and amphibians is declining due to reactions of aluminum ions with proteins in the gills of fish and the embryo's of frogs[29, 30]. From the results of present investigation it was observed that Al concentration at different sampling stations lies in the range of 10-25, 28-80, 17-65 and 43-70 µg/L at S1, S2, S3 and S4 sampling stations respectively. The biyearly average Al concentration was found to be 16, 45, 36 and 58 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Al concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.09 at S2 and S3 sampling stations to 1.29 at S1 sampling station (Figures 2-5).

Levels of arsenic (As) are higher in the aquatic environment than in most areas as it is fairly water-soluble and may be washed out of arsenic bearing rocks[31]. Recently, the anthropogenic activities such as treatment of agricultural land with arsenical pesticides, treating of wood using chromated copper arsenate, burning of coal in thermal plants power stations and the operations of gold-mining have increased the environmental pervasiveness of As and its rate of discharge into freshwater habitat [32]. As can also interfere with the fish immune system by suppressing antibody production[33] as well as by lowering macrophage activity and maturation[34]. Several studies are reporting As induced liver fibrosis, hepatocellular damage, inflammation, focal necrosis in addition to hepatocellular carcinoma[35, 36]. In the present investigation it was observed that As concentration at S1, S2, S3 and S4 sampling stations lies in the range of 15-59, 11-51, 15-68 and 10-62 µg/L respectively. The biyearly average As concentration was found to be 35, 26, 47 and 38 µg/L respectively at different sampling stations (Table 1). It was also observed that the average As concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.08 at S4 to 1.26 at S2 (Figures 2-5).

Cadmium (Cd) is typically a metal of the 20 ^th century, and is mainly used in rechargeable batteries and for the production of special alloys. It was the outbreak of the Itai-Itai bone disease in Japan in the 1960s that really drew the attention of the public and regulatory bodies to this heavy metal that had been discharged in the environment at an uncontrolled rate for more than one century. Although emissions in the environment have markedly declined in most industrialized countries, Cd remains a source of concern for populations living in polluted areas, especially in less developed countries[37]. Cd dispersed in the environment can persist in soils and sediments for decades. When taken up by plants, Cd concentrates along the food chain and ultimately accumulates in the body of people eating contaminated foods. By far, the most salient toxicological property of Cd is its exceptionally long half-life in the human body. Once absorbed, Cd irreversibly accumulates in the human body, in particularly in kidneys, the bone, the respiratory tract and other vital organs such the lungs or the liver[38]. In addition to its extraordinary cumulative properties, Cd is also a highly toxic metal that can disrupt a number of biological systems, usually at doses that are much lower than most toxic metals[39-41]. In the present investigation it was observed that Cd concentration at S1, S2, S3 and S4 sampling stations lies in the range of 12-38, 19-114, 14-55 and 15-75 µg/L respectively. The biyearly average Cd concentration was found to be 24, 86, 42 and 43 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Cd concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.07 at S2 to 1.23 at S1 (Figures 2-5).

Chromium (Cr) is one of the most common skin sensitizers and often causes skin sensitizing effect in the general public. A possible source of chromium exposure is waste dumps for chromate-producing plants causing local air or water pollution. Penetration of the skin will cause painless erosive ulceration (“chrome holes”) with delayed healing. These commonly occur on the fingers, knuckles, and forearms. The characteristic chrome sore begins as a papule, forming an ulcer with raised hard edges. Ulcers can penetrate deep into soft tissue or become the sites of secondary infection, but are not known to lead to malignancy[42, 43]. Besides the lungs and intestinal tract, the liver and kidney are often target organs for chromate toxicity[44]. In the present investigation it was observed that Cr concentration at S1, S2, S3 and S4 sampling stations lies in the range of 22-64, 34-103, 80-782 and 54-111 µg/L respectively. The biyearly average Cr concentration was found to be 45, 54, 418 and 88 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Cr concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.06 at S4 to 1.53 at S3 (Figures 2-5).

Mercury (Hg) poisoning has become a problem of current interest as a result of environmental pollution on a global scale. High concentration of mercury, which could pose an ecological hazard, leading to contamination of plants, aquatic resources and bioaccumulation in the food chain[45]. Although elemental mercury is relatively innocuous and non-toxic, it can be converted to organomercurials, which are particularly toxic and are retained in the cells of plants and living organisms. Bodaly et al.[46] have reported that treated sewage water discharged into rivers and similar water bodies could result in an appreciable increase in the build up of alkyl mercury. Further reports by Tanaka[47] and Goldstone et al.[48] have dwelt on the natural alkylation of total mercury in waste water and water bodies. In the present investigation it was observed that Hg concentration at S1, S2, S3 and S4 sampling stations lies in the range of 10-131, 10-101, 10-67 and 12-48 µg/L respectively. The biyearly average Hg concentration was found to be 67, 52, 34 and 28 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Hg concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.08 at S1 to 1.24 at S4 (Figures 2-5).

Nickel (Ni) and nickel compounds have many industrial and commercial uses, and the progress of industrialization has led to increased emission of pollutants into ecosystems. Nickel is a nutritionally essential trace metal for at least several animal species, micro-organisms and plants, and therefore either deficiency or toxicity symptoms can occur when, respectively, too little or too much Ni is taken up. Although a number of cellular effects of nickel have been documented, a deficiency state in humans has not been described[49-52]. Although Ni is omnipresent and is vital for the function of many organisms, concentrations in some areas from both anthropogenic release and naturally varying levels may be toxic to living organisms[53, 54]. Nickel compounds have been well established as carcinogenic in many animal species and by many modes of human exposure but their underlying mechanisms are still not fully understood[55]. Nickel can cause cancer of the lungs and nasal passages. The most common effect of nickel exposure is an allergic reaction. Approximately 10-15% of the population is sensitive to nickel. The most common reaction is a rash at the site of contact. Less frequently, some people that are sensitive to nickel suffer asthma attacks after exposure. Some workers exposed to high levels of nickel have developed chronic bronchitis and changes to their lungs. In the present investigation it was observed that Ni concentration at S1, S2, S3 and S4 sampling stations lies in the range of 15-105, 18-125, 15-146 and 10-145 µg/L respectively. The biyearly average Ni concentration was found to be 49, 77, 93 and 89 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Ni concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.08 at S3 to 1.20 at S1 and S2 (Figures 2-5).

Table 1. Heavy Metal Content in Water Samples Collected at different Sampling Stations along Vasai Creek of Mumbai (values in µg/L) Heavy Metals Al As Cd Sampling Stations S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4 Month-Year October-09 17 51 44 67 44 23 60 34 24 103 49 51 November 15 37 34 59 36 21 51 27 21 93 41 47 December 14 33 24 56 30 22 44 23 18 89 45 40 January-10 13 31 17 55 26 17 43 27 15 88 41 27 February 12 35 65 46 17 11 15 17 12 19 14 21 March 13 32 37 45 26 13 24 23 17 38 25 17 April 12 30 31 43 23 16 28 30 13 74 36 23 May 10 40 38 44 29 21 26 37 24 89 41 35 June 18 43 23 48 30 25 54 50 28 94 43 45 July 16 49 32 61 35 28 61 58 30 97 49 51 August 15 66 42 67 41 35 68 62 31 102 44 61 September 17 73 32 66 45 48 65 61 25 108 53 66 October 15 55 40 70 59 29 64 49 31 111 54 74 November 20 43 38 63 52 38 55 43 38 114 50 61 December 18 30 29 60 46 30 59 49 35 100 47 55 January-11 16 28 24 66 41 25 56 41 31 105 42 41 February 18 35 54 64 25 15 23 24 20 86 31 15 March 20 33 31 60 33 21 31 29 24 78 40 23 April 19 30 36 54 30 24 43 35 29 73 29 28 May 25 43 65 54 15 15 15 10 15 25 25 15 June 16 50 29 58 35 30 55 42 23 88 50 45 July 18 64 27 60 39 33 61 49 25 91 55 58 August 17 69 38 65 44 42 67 52 26 95 51 63 September 19 80 43 64 48 51 65 51 29 100 50 75 AVERAGE 16 45 36 58 35 26 47 38 24 86 42 43 Range 10-25 28-80 17-65 43-70 15-59 11-51 15-68 10-62 12-38 19-114 14-55 15-75 Median 17.5 54 41 56.5 37 31 41.5 36 25 66.5 34.5 45

Table 1. Heavy Metal Content in Water Samples Collected at different Sampling Stations along Vasai Creek of Mumbai (values in µg/L)(continue) Heavy Metals Cr Hg Ni Sampling Stations S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4 Month-Year October-09 60 35 378 101 120 85 53 34 65 107 109 121 November 52 39 243 95 97 73 44 36 52 84 119 108 December 43 34 147 86 74 50 35 32 36 43 123 113 January-10 42 35 80 78 61 43 44 29 18 18 136 145 February 41 74 146 80 42 33 24 22 15 22 120 99 March 29 82 255 71 25 23 14 17 20 40 81 65 April 34 59 344 63 12 14 13 12 23 55 41 48 May 22 62 478 54 16 20 19 16 27 72 39 41 June 47 39 398 81 19 30 23 14 35 86 33 36 July 51 49 357 96 70 61 23 25 54 98 76 64 August 46 43 513 105 116 72 30 24 91 103 91 75 September 55 53 631 111 126 86 51 35 99 106 104 94 October 64 51 525 110 128 101 67 40 95 125 146 138 November 56 56 221 106 107 76 59 42 56 107 135 125 December 58 41 334 96 86 55 50 48 33 89 139 130 January-11 50 37 267 90 77 43 44 33 25 45 134 134 February 34 84 156 82 45 35 29 39 22 56 129 115 March 40 73 299 75 31 28 20 24 26 49 94 90 April 38 65 457 68 15 31 15 18 39 61 71 88 May 27 103 738 71 10 10 10 12 42 75 15 10 June 44 50 750 82 26 33 24 18 45 86 25 39 July 47 58 765 95 68 57 30 31 68 94 68 71 August 51 43 771 102 110 81 40 29 90 100 87 88 September 58 41 782 107 131 99 58 38 105 119 105 103 AVERAGE 45 54 418 88 67 52 34 28 49 77 93 89 Range 22-64 34-103 80-782 54-111 10-131 10-101 10-67 12-48 15-105 18-125 15-146 10-145 Median 43 68.5 431 82.5 70.5 55.5 38.5 30 60 71.5 80.5 77.5

Ecological and toxicological aspects of lead (Pb) and its compounds in the environment have been extensively reviewed[56-61]. There is agreement by all authorities on five points. First, Pb is ubiquitous and is a characteristic trace constituent in rocks, soils, water, plants, animals, and air. Second, more than 4 million metric tons of Pb is produced worldwide each year, mostly for the manufacture of storage batteries, gasoline additives, pigments, alloys, and ammunition. The widespread broadcasting of Pb through anthropogenic activities, especially during the past 40 years, has resulted in an increase in Pb residues throughout the environment-an increase that has dislocated the equilibrium of the biogeochemical cycle of Pb. Third, Pb is neither essential nor beneficial to living organisms; all existing data show that its metabolic effects are adverse. Fourth, Pb is toxic in most of its chemical forms and can be incorporated into the body by inhalation, ingestion, dermal absorption, and placental transfer to the foetus. Fifth, Pb is an accumulative metabolic poison that affects behaviour, as well as the hematopoietic, vascular, nervous, renal, and reproductive systems. In the present investigation it was observed that Pb concentration at S1, S2, S3 and S4 sampling stations lies in the range of 25-163, 17-146, 152-276 and 119-195 µg/L respectively. The biyearly average Pb concentration was found to be 79, 94, 191 and 158 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Pb concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.04 at S4 to 1.11 at S1 (Figures 2-5).

Table 1. Heavy Metal Content in Water Samples Collected at different Sampling Stations along Vasai Creek of Mumbai (values in µg/L)(continue) Heavy Metals Pb Sr Mn Sampling Stations S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4 Month-Year October-09 106 102 177 153 84 95 253 122 63 108 57 72 November 78 86 162 131 63 85 121 85 42 87 43 59 December 42 51 152 123 48 54 76 50 36 56 29 54 January-10 25 17 157 119 34 32 15 38 20 39 14 50 February 36 37 170 141 45 25 74 71 27 79 164 139 March 48 45 181 135 62 30 114 102 52 117 292 183 April 43 85 189 167 77 43 160 123 79 167 421 150 May 63 132 190 159 87 38 255 146 103 202 522 233 June 59 123 205 168 103 47 299 158 96 142 426 167 July 88 125 214 185 114 62 311 147 76 175 331 182 August 149 146 213 174 103 81 328 174 63 161 105 135 September 163 134 201 195 118 92 400 179 54 105 91 113 October 124 121 228 168 95 105 321 129 66 136 52 85 November 118 106 276 175 87 87 210 177 47 99 39 74 December 78 86 178 183 73 79 169 145 43 81 26 89 January-11 57 35 159 150 46 56 87 126 54 48 43 72 February 45 49 166 169 52 40 58 149 66 76 156 137 March 44 57 175 125 66 54 167 100 78 120 278 189 April 41 99 188 147 84 45 203 108 87 183 495 250 May 56 121 197 155 102 51 277 119 94 219 688 301 June 53 129 205 159 105 56 312 148 75 198 501 243 July 107 118 210 168 98 77 321 135 61 167 315 186 August 137 123 194 174 90 92 334 146 66 153 199 115 September 140 131 198 162 89 101 341 150 52 118 157 107 AVERAGE 79 94 191 158 80 64 217 126 63 127 227 141 Range 25-163 17-146 152-276 119-195 34-118 25-105 15-400 38-179 20-103 39-219 14-688 50-301 Median 94 81.5 214 157 76 65 207.5 108.5 61.5 129 351 175.5

Strontium (Sr) compounds that are water-insoluble can become water-soluble, as a result of chemical reactions. The water-soluble compounds are a greater threat to human health than the water-insoluble ones. Therefore, water-soluble forms of strontium have the opportunity to pollute aquatic environment. For children exceeded strontium uptake may be a health risk, because it can cause problems with bone growth. In the present investigation it was observed that Sr concentration at S1, S2, S3 and S4 sampling stations lies in the range of 34-118, 25-105, 15-400 and 38-179 µg/L respectively. The biyearly average Sr concentration was found to be 80, 64, 217 and 126 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Sr concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.05 at S1 to 1.23 at S2 (Figures 2-5).

Manganese (Mn) is one out of three toxic essential trace elements, which means that it is not only necessary for humans to survive, but it is also toxic when too high concentrations are present in a human body. Excess manganese interferes with the absorption of dietary iron. Long-term exposure to excess levels may result in iron-deficiency anaemia. Increased manganese intake impairs the activity of copper metallo-enzymes. The presence of manganese in drinking water supplies may be objectionable for a number of reasons unrelated to health. At concentrations exceeding 0.15 mg/L, manganese stains plumbing fixtures and laundry and causes undesirable tastes in beverages[62]. Oxidation of manganese ions in solution results in precipitation of manganese oxides and incrustation problems. Even at concentrations of approximately 0.02 mg/L, manganese may form coatings on water distribution pipes that may slough off as black precipitates[63]. The growth of certain nuisance organisms is also supported by manganese[62, 64]. The presence of "manganese" bacteria, which concentrate manganese, may give rise to taste, odour and turbidity problems in the distributed water. Highly toxic concentrations of manganese in soils can cause swelling of cell walls, withering of leafs and brown spots on leaves. In the present investigation it was observed that Mn concentration at S1, S2, S3 and S4 sampling stations lies in the range of 20-103, 39-219, 14-688 and 50-301 µg/L respectively. The biyearly average Mn concentration was found to be 63, 127, 227 and 141 µg/L respectively at different sampling stations (Table 1). It was also observed that the average Mn concentration for assessment year 2010-11 was higher than that obtained for the assessment year 2009-10 by a factor of 1.11 at S2 to 1.20 at S4 (Figures 2-5).

4. Conclusions

The real problem today is not whether heavy metals are toxic or not , since we know that they are : but what concentrations are permissible/safe levels in our waters which do not produce harmful effects on users of water and biological life from the waters. Although much work has been done on heavy metal pollutants , there is still a great need for information on influences of metals and their toxicities fully. It is impossible to prevent pollution of environment totally, but metal pollution and toxicity could be minimized by certain precautionary measures like development of adequate environmental control and management programmes and continuous scientific monitoring of our aquatic environment must be built up. It is expected that the experimental data obtained on pollution level from such continuous monitoring will help to reduce pollution threat to aquatic environment.

ACKNOWLEDGEMENTS

The authors are thankful to SAP Productions for developing and maintaining the paper template.