Nitrate-Nitrogen Content of Well Water and Soil from Selected Areas in the Jaffna Peninsula

This paper describes the results of a study concerning the amount of nitrate present in drinking water and soil in selected locations in the Jaffna Peninsula. In several places the ameunt of nitrate-nitrogen is above the safe. level ~pa:*ed in the WHO International Standard for ddnking water.


Introduction
In the Jaffna Peninsula there is a small acreage of Paddy lands but the majority of the cultivated lands is used for agricultural activity concerned with short term crops.Water for these is obtained from wells situated close by.Drinking water is also obtained from wells.In villages,each house or a group of houses has its own well.But in the Jaffna town and coastal areas like Kayts water is supplie'd by the Municipality and for this purpose the water is drawn from'we~ls in the adjoining villages -Thirunelvely and Kondavil.These villages have a -reasonable agricultural activity.Over the years it has been noted that Jaffna farmers have been using increasing quantities of fertilizers and attempts have been made to study the effect of large scale use of fertilizers on the ground water and soil.One of the serious problems is the increasing levels of nitrates and nitrites in drinking water which can be hazardous.Other sources of nitrates and nitrites are animal and human urine and excreta.It is also possible that some of the other nitrogen containing compounds are oxidised to nitrites and nitrates over the years.
It is well known that nitrates and nitrites above a certain level in drinking water and soil may came serious health problems due to their toxicity.It has been reported10 that if the drinking water contain more than 10 ppm nitratenitrogen (45 ppmnitrate), it could affect the health of infants and children.
Apparently a microorganism in the gastrointestinal tract ean convert nitrate into nitrite which under the biochemical conditions oxidises the 'Few in haemoglobin to ~e + + + , producing methaemoglobin.Methaemoglobin cannot transport oxygen in the blood and the resulting oxygen deficiency produces the characteristic bluish skin colour 8,9,10.Therefore nitrates in the water consumed by infants may give rise to methaemoglobinaemia (blue babies).
That methaemoglobinaemia 'is associzfted with high nitrate content in drinking water, was first discovered in 1945.Since that time about 2000 cases of blue babies have been reported from North America and Europe.8Excess of nitrate in the drinking water could also affect older children and adults.The nitrates can be converted to the nitrites which in turn can produce nitrosamines by reaction with suitable amino compounds in the body.10 Nitrosamines are carcinogenic and hence a hazard to human health.
Increased nitrogen in the soil also may cause serious health problems because some p,lants such as carrots could store this excess nitrate and then reduce it partly to nitrite within itself.The nitrites could convert haemoglobin to methaemoglobin or produce nitrosamines and thus the carrots containing excess nitrate is a health hazard?2. Experimental Methods and Materials several methods3 are available for the estimation of nitrates.One method is to determine the total oxidised nitrogen and then subtracting the colorirnetrically estimated value for the nitrite!The alpha naphthylamine-pink colour method1 may be employed to determine the amount of nitrite colorirnetrically.Reduction of nitrate and nitrite with hydrogen generated by either iron filings in sulphuric acid or Devardas alloy in alkaline solution has been employed to estimate total oxidised nitrogen.The reduction of nitrate to nitrite could be carried out by cadmium-copper reagent2 and a-naphthylamine-pink colour method could be used to determine the total oxidised nitrogen.(It should be noted that oc- naphthylamine is carcinogenic).Another method uses 2:6 xylenol as indicator in a colorimetric determination of nitrates.
In our investigation, the nitrate-nitrogen was estimated by nitrophenoldisulphonic acid yellow colour method6 This method depends upon the nitration of position 6 of phenol-2, 4-disulphonic acid.
OH OH S03H HNO, r H,

Nitrate-Nitn1gc~t7 Content of Well Water and Soil
Phenol-2, 4-disulphonic acid was prepared6 by heating a mixture of phenol and conc H , S 0 4 i n boiling water bath.

SO,H
(PDSA) The amount of sodium, potassium and calcium In uater samples were determined immediately after collection using a Corning Model 400 flame photometer.The flame intensities for sodium were corrected for interference by calcium by the standard -addition method?The samples were collected in clean dry dark glass bottles with bakelite screw caps and when necessary they were stored at OOC.The nitrate-nitrogen was determined within three days of collection.
Two litres of water samples were concentrated and made up to 25ml with distilled water in a volumetric flask.These samples were used for colorimetric determinations.
The samples for colorimetric measurements were prepared as follows: Concentrated Water sample (25ml) The aqueous extract of the soil or water sample was evaporated to dryness previous to determination since the reaction must be effected in the virtual absence of water.The product behaves as a nitrophenolic type indicatorit is colourless in acid and yellow when neutralised or in alkaline solution.
Ammonium hydroxide was therefore used to shift the pH to the.yellow range for colorimetric determination.
The optical densities of test soIutions were measured in a colorimeter (Corning 252) using a 420nm filter and from the results obtained nitrate-N content was calculated using a reference graph.
Standard nitrate solution containing 1OPg nitrate-nltrogen per ml was prepared according to .knownprocedurei6 5.00, 10.00, 12.00, 14.00, 16.00, 18.00, 20.00, 23.00, 25.00 and 30.00 ml aliquots of this solution were taken and subjected to identical procedures as in the case of test samples and optical densities were measured.

1 Nitrate in Soil
The results (Table I) shows that in several areas in the Jaffna Peninsula the soil samples have nitrates above the safe level.In plots where there is no cultivation, the amount of nitrate in soil adjoining the well is below 20 ppm in tnajority of cases.But in those plots where there is cultivation the soil adjoining the well seems to have fairly large quantity of nitrate, usually above 30 ppm.The results however are not conclusive.

Nitrate in well water
The .water samp'les from wells in plots where there is no cultivation have relatively low nitrate-nitrogen levels.Thus the wells in the following localities where there is no cultivation have less than 18 ppm of nitrate-nitrogen.
The water samples from the wells in plots where there is agricultural activity have nitrate-nitrogen levels between 20 and 50 ppm.The villages of Kondavil and Urumpirai where there is intense agricultural activity have very high nitrate-nitrogen level (30-50 pprn).Even water samples from wells in plots in these villages where there is no cultivation have more than 20 pprn of nitratenitrogen.
The water samples from the wells in Thirunelvely and Kondavil from which water is drawn for town supply have a high nitrate-nitrogen levels (26-33 ppm) which are about three times the safe level.Our investigations also indicate that the nitrate-nitrogen levels in the water of the wells used for town supply gradually increases year by year.Thus the nitrate-nitrogen level of Thirunelvely water supply well water increased from 15 pprn in December 1976 to about 22 pprn in December 1980 and to about 27 pprn in May 1982 (Table 11).Similarly the nitrate-nitrogen level in the water sample from the town water supply well from Kondavil increased from 22 pprn in December 1976 to about 30 pprn in December 1980 and to about 34 pprn in May 1982.
It is apparent that the indiscriminate use of fertilizer is the chief reason for the rapidly increasing nitrate-nitrogen level in well water.We feel that the Jaffna farmers are using fertilizers far in excess of what is required.This conclusion is supported by the fact that the quantity of fertilizer sold in Jaffna is very large.
In certain parts of the Jaffna town area where there is no cultivation the nitrate-nitrogen level in well water approaches 20 ppm.This is probably due to inadequate sewerage disposal facilities.Also in thickly populated areas the wells are situated close to the soakage pits of the toilets and this may result in increased nitrate-nitrogen levels in well water.With increasing demand for houses, the local authorities are willing to reduce the minimum distance between the wells and septic tanks from 35 ft to about 25 ft.This could cause serious health problems in a district like Jaffna where the limestone rock is faiily close to the earth surface and hence minimum soakage and absorption is possible.* Report from water resources board -Jaffna.

Conclusion
The Nitrate-Nitrogen level in well water in the Jaffna Peninsula is well above the safe level of .loppm and is increasing year by year.The possible reason for this is the increase in the use of fertilizer.

1 3 a
S h ; o r 15 min.)Filtrate Shake with Ca(OH), and Filtrate (i) Pipette 5.0 ml (ii) Evaporate on a I steam bath J. Residue I (i) Phenol-2,.Cdisulphonic acid.(ii) Add 20 ml water after 15 min Solution I NH,OH Alkaline solution (Yellow) (made to 100 ml with distilled wate).Alkaline solution (Yellow) (made to 100 ml) ~a j e s w a r ~ Mageswaran and S. Mahalingam

Table 1 .
Amount of Nitrate-Nitrogen in well water and soil and the amounts of Na.K and Ca in well water ,

Table 1 (
contd.) Amount of Nitrate -Nitrogen in soil is expressed as p g of Nitrate -Nitrogen per g of soil where as that in well water as f i g of Nitrate -Nitrogen per ml of water.The sodium values given are values corrected for interference by calcium. *

Table 2
. Jaffna Mun~cipality Water Supply December 1976 ' ~e c e m b e r 1980 February 1982