Heavy Metal content in Drinking Water of Madurai City

P.S. Navaraj

A study has been made to measure Zn, Cu & Pb concentrations at consumer points of 4 zones [ North, South, East & West ] in Madurai City during winter, summer and raining seasons of 1996 ñ 1998. The study indicates that the concentration of heavy metals in certain areas of the city are higher than the concentration at the supply source indicating that there is contamination on-line either by way of seepage of contaminated water or due to corrosion of pipes supplying thought the results are well within the maximum permissible limits (ie) view of bioaccumulation of heavy metals, continues surveillance is necessary.

Keywords : Heavy Metals, Zinc, Copper, Lead.

INTRODUCTION

Heavy metals are harmful and insidious pollutants because of their non-biodegradable nature and their potential to cause adverse effects in human beings beyond certain level of exposure and absorption. Heavy metals can alter biochemical activities such as inhibition of enzymes, genetic damage and hypertension. Some of heavy metals like Cd, Cr, Zn are Carcinogenic.

There is an increase in epidemiological and other evidences, indicating an association between water quality and mortality from cardiovascular and other chronic diseases. It has also been observed that diseases other than cardiovascular have been associated with heavy metals in water. Statistically significant positive correlation between mortality from various types of cancer and concentration of several trace elements in water supplies have also been shown.

The concentration of heavy metals and their variation in raw water, the efficiency of the treatment plant in removing these heavy metals and the ways and means of the distribution system are of prime importance in relation to the ultimate quality of drinking water reaching the consumer. The concentration of these metals in the water reaching the consumer may vary greatly with locality and time. Monitoring quality of water at consumer end is therefore essential.

A study was undertaken to asses the heavy metal contents in drinking water at consumer end points at Madurai city. The effect of seasons on the heavy metal contents was also analysed.

MATERIALS AND METHODS

The main source of water supply for Madurai city is by Vaigaidam, boring and well water. Lake and river sources are minimum. In Madurai city coporation water from the source is taken to the water treatment plants and from where the safe water is taken to the consumer. The entire water is subjected to conventional water treatment process essentially consisting of alum assisted coagulation, sand filtration and chlorine disinfection. The entire water supply is distributed through the service reservoirs only. This enables steady conditions from the inlet trunk mains and caters to the peak demand of the consumer most of the pipe line supplying water to the city from the service reservoirs are laid underground certain parts of the main water trunk conveying water from Master Balancing reservoirs (MBR) to the service reservoirs and also either underground or submerged.

SAMPLING

Sampling is done Madurai city in such the entire area is divided into 4 Zones (East, West, South, North) 20 sites in each Zone is tested. Samples were drawn in the month of Dec.(Winter), Apr (Summer), Sep (Monsoon) during 1996-1998.

Analytical Procedure: Since the samples collected were essentially of unpolluted nature, care was taken to see that the interval between collection of sample and its analysis did not exceed 72 hours.

For metal analysis, the water samples were concentrated by evaporation. One litre of water sample along with 10 mL of conc. HNO3 was evaporated in a 500 mL beaker on low flame at about 800C mL beaker. Sufficient washings were given to ensure complete transfer. The evaporation was continued with 10 mL of aquaregia to near dryness. The residue was then extracted with 1 percent HNO3 and the solution then made to 10 mL in a standard flask and stored in polythene bottles previously cleaned with 1:1 HNO3 for further analysis.

Inductively coupled plasma-atomic emission sepectrophotometer (ICP-AES) of Thermo Jerrel Ash-ICP 300 was used for analysis. The metals were estimated in the sample by aspirating the sample solution directly into the plasma of the instrument. The instrumental parameters for the individual elements were set according to the requirements. Calibration was done using standard solutions concentrations around 5 ppm of respective metal. Stock solutions were prepared by dissolving appropriate amount of the pure metals or their salts. Dilution of the stock solution was made as and when required. The minimum concentrations of metal which could be detected by the instrument was about 0.02 ppm.

HEAVY METAL

TABLE 1 - Concentration for Zn (ppb) at Various Locations

		1996			1997			1998
Zone	Winter	Summer	Monsson	Winter	Summer	Monsson	Winter	Summer	Monsson
North	105	110	204	114	90	130	210	100	325
South	90	132	216	120	208	180	185	140	380
West	110	106	210	80	140	176	180	150	300
East	70	156	254	140	168	125	110	160	320
MBR	106	108	206	86	94	126	114	106	302
	W	S	M	W	S	M	W	S	M
MORE	1	3	3	3	3	3	3	3	3
LESS	3	1	1	1	1	1	1	1	1

TABLE 2 - Concentration for Cu (ppb) at Various Locations

		1996			1997			1998
Zone
	Winter	SummerMonsson	Winter	Summer	Monsson	Winter	Summer	Monsson
North	4	3	19	10	8	16	12	7	21
South	8	10	17	10	9	20	14	12	29
West	10	9	7	3	6	12	9	6	24
East	8	5	14	10	8	7	12	9	25
MBR	6	6	10	5	7	10	10	8	22
	W	S	M	W	S	M	W	S	M
MORE	3	2	3	3	3	3	3	3	3
LESS	1	2	1	1	1	1	1	1	1

TABLE 3 - Concentration for Pb (ppb) at Various Locations

		1996			1997			1998
Zone	Winter	Summer	Monsson	Winter	Summer	Monsson	Winter	Summer	Monsson
North	3	7	6	5	7	6	7	8	4
South	4	8	7	6	5	10	3	5	5
West	4	3	4	5	9	9	2	3	8
East	2	5	8	3	4	8	5	6	10
MBR	3	6	5	4	6	7	6	7	6
	W	S	M	W	S	M	W	S	M
MORE	3	2	3	3	2	3	1	1	2
LESS	1	2	1	1	2	1	3	3	2

RESULTS & DISCUSSIONS

The results of the analysis are shown in Table 1-3. The values indicated are the average of duplicate analysis performed at each shown in Madurai city.

1. Most of the time the concentration of Zn is less at the consumer end point than at supply source (MBR) (Fig. 1). This may be due to precipitation of Zn salts in the distribution system. This behaviour is not so prominent in case of Cu and Pb indicating these metals are added on in the distribution system.

2. It is observed from Fig. 2-4 that the probability of online contamination by Zn, Cu & Pb is much more during summer season as compared to winter and monsoon.

3. Probability of contamination by Zn is less than that of Cu & Pb.

4. The concentration of heavy metal is slowly increasing over a period of time.

5. All the values are within the maximum permissible limits.

Most of the trace inorganic metal contaminant are adequately removed from raw water by the physical and chemical treatment process of coagulation settling and filteration. However the deterioration of water quality by the corrosion of metal piping and joints formed by using solder or flux containing Pb and other heavy metals has been widely acknowledged. Several studies have noted that dissolution or corrosino of soldered joints and brass fittings and faucets are significant sources of Pb,Cu,Zn,Crand Ni in tap water.

Cu and Pb are strongly complexed by humic substances and therefore these metals will affect the solubility of these metals from corrosion products. Corrosion of lead pipes ,solders result in the formation of precipitates like lead hydroxide and Lead carbonate in the distribution system, These precipitates form on the surface of the corroding metal and dissolve slowly. It is observed that organic waters are very alaline and plumbosolvic.Lead most often distributed system in the dissolved form. The solubility decreasing with the increasing pH. AbovepH8 the solubility of Pb is below .001mg/L regardless of alkalinity and in ph6.5 the solubility could approach .1mg/L.

Some metal solubilities like Pb increase with temperature. The solubility doubled between winter and summer when water temperature varied between 7.5 to 15 degree celicious. Site factor and plumbing age are most important in the metal content of water. It is found that the most recent plumbing system will have the highest Pb level. Grounding of household electrical system to the plumbing also contribute positively to higher Pb level in the water system.

CONCLUSION

From the above observations one may infer that though the heavy metal content is within the maximum permissible limits, the trend indicates that if the things are not kept under control and immediate preventive measures like control of pH, alkalinity and use of corrosion inhibitors are not undertaken, the drinking water itself may lead to a health hazard to Madurai citizens. At this point, one should also take a look at the clinical data available, which indicates that the death rate from all causes in Madurai is 20% higher that the rates for Madurai District as a whole and about 40% higher than the rate for adjoining Kamarajar and Dindigul Districts.

In view of the above findings it needs to be stressed that there has to be a routine monitoring system for heavy metal content at the consumer end points. Further, the treatment procedure has to be suitably modified whenever large fluctuations in heavy metals are noticed.

REFERENCE

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