ACTA CARSOLOGICA	29/1	7	107-116	LJUBLJANA 2000
COBISS: 1.08
RECENT MEASUREMENTS OF WATER QUALITY IN MRZLEK SPRING
NOVEJŠE MERITVE KVALITETE VODE V IZVIRU MRZLEK TJAŠA JUG1 & MARKO VUDRAG2 & MLADEN FRANKO1
1	Nova Gorica Polytechnic, P.O. Box 301, 5001 NOVA GORICA, SLOVENIA
2	Institute of Public Health of Ljubljana, Zaloška 29, 1000 LJUBLJANA, SLOVENIJA
Prejeto / received: 31. 12. 1999
Izvleček	UDK: 556.34.06
Tjaša Jug & Marko Vudrag & Mladen Franko: Novejše meritve kvalitete vode v izviru Mrzlek
Da bi ugotovili morebitno onesnaženje pitne vode izvira Mrzlek (pri Solkanu, Slovenija), so bile opravljene analize 66 elementov in anionov, kot so nitrati, nitriti, sulfati, kloridi, fosfati, bromidi in fluoridi ter določeni trihalometani v klorirani vodi. Onesnaževanje reke Soče s težkimi kovinami upada in tudi koncentracija trihalometanov v pitni vodi je relativno nizka in v zadnjih petih letih ne narašča. Večje koncentracije nitratov v Mrzleku kažejo možno onesnaževanje zaradi kmetijstva na Banjšicah. V grobem so bile podobne koncentracije večine elementov in anionov zabeležene tako v Mrzleku kot v Soči. V Mrzleku so bile višje koncentracije Ca, Fe, Zn, nitratov in kloridov, medtem ko so bile koncentracije Mn, Mg, Ba, As in sulfatov bistveno večje v Soči. Kvaliteta pitne vode iz Mrzleka za zdaj ustreza vsem standardom. Ključne besede: pitna voda, težke kovine, THM, anioni, Mrzlek, Soča, Slovenija.
Abstract	UDC: 556.34.06
Tjaša Jug & Marko Vudrag & Mladen Franko: Recent measurements of water quality in Mrzlek spring
Recent investigations of drinking water quality related to the spring Mrzlek near Solkan, Slovenia are de-scribed. Multielemental analyses of 66 elements and anions such as nitrate, nitrite, sulphate, chloride, phosphate, bromide and fluoride in water from the spring Mrzlek and the river Soča, as well as determination of trihalomethanes in chlorinated water, were carried out to reveal eventual impacts of environmental pollution on the quality of drinking water from spring Mrzlek. It was observed that the pollution of the river Soča with heavy metals is recently decreasing, while the concentrations of trihalomethanes in drinking water are rela-tively low and have not increased during the last five years. At present the quality of drinking water from the spring Mrzlek meets all the standards. Higher concentrations of nitrate in the spring, however, indicate potential pollution from farming on the Banjšice plateau. In general, quite similar concentrations of most elements and anions were observed in the spring Mrzlek and the river Soča. Higher concentrations of Ca, Fe, Zn, nitrate and chloride were observed in the spring, while concentrations of Mn, Mg, Ba, As, and sulphate were significantly higher in the river.
Key words: drinking water, heavy metals, THM's, anions, Mrzlek spring, Soča river, Slovenia.
INTRODUCTION
The spring Mrzlek near Solkan (Slovenia) (Fig. 1), which lies at the bottom of the river Soča bed, is a typical karst spring with its catchment area on the Banjsice plateau lying about 800 m above the spring. For many years the spring Mrzlek has served as the major and the most important source of drinking water for the Nova Gorica area. Therefore, its pollution represents a serious hazard to water quality and consequently to human health. This was the main reason for careful water quality control and intensive investigations (Kranjc, 1997; Janež, 1997; Vudrag, 1997; Vudrag, 1998) of the spring Mrzlek, which primarily focused on the possibilities of mixing between the spring water and the water from the river Soča.
The construction of the Solkan Hydroelectric power plant in 1984 significantly aggravated the situation since the level of the river Soča in the HE plant's basin was raised by over 20 metres above the spring Mrzlek and enhanced the possibility of water mixing. Hydrogeological studies based upon isotopic analyses have confirmed partial mixing of waters, which is strongly affected by the hydrological conditions and the quantity of water in the spring (Kranjc 1997). The spring is therefore exposed to pollution from the river Soča, which carries heavy metals such as chromium, lead, zinc, cadmium, mercury and others. These are released with effluents from a cement plant, as well as from the former lead and zinc, and mercury mines located upstream of the river Soča and its affluents. The exposure to organic pollutants is also possible through the release of untreated municipal wastewater, runoff from the motorways, local industry and farming. This is of particular concern since the presence of organic pollutants and other compounds, such as humic and fulvic acids, leads to the formation of chlorinated organic compounds (trihalomethanes -THM's) during the chlorination of water (Rook 1973). Therefore, some heavy metals in river sediments and THM's in drinking water were monitored to reveal eventual long term changes in their concentrations.
Since the Banjsice area is not industrialised, but is mostly a rural area, pollution of the spring Mrzlek through the water from the river Soča remains a main concern. However, due to the un-known and hardly predictable mixing ratio, it is impossible to clearly distinguish between the sources of eventual direct pollution, and that pollution caused by the river Soča. Multielemental analyses of waters from the river Soča and spring Mrzlek, covering 66 elements, have therefore been carried out to identify elements which could serve as indicators of pollution of the spring by the river. In addition, determination of representative anions such as sulphate, chloride, nitrate, bromide, phosphate, and fluoride was also carried out.
EXPERIMENTAL
Sediments were taken from the river bottom, dried for 24 hours at 60°C and then sieved through a 2 mm mesh. After grinding, the sediments were dissolved in HNO3 + HCl (1:3) and analysed by ETAAS on a Hitachi atomic absorption spectrometer.
Water samples were collected simultaneously from the spring Mrzlek and from the river Soča close to the spring (Sampling point No 1 on Fig. 1). Samples were taken about every four months, in order to coincide with the most characteristic hydrometeorological conditions of spring Mrzlek and river Soča.
Fig. 1: Location of the spring Mrzlek and the sampling points near the spring (sampling point 1) and near the Solkan HE power plant dam (sampling point 2).
Source: National topographic map 1:25000, © Geodetska uprava RS, 1996. Reprinted with the
permission of Geodetska uprava RS no. 90411-55/2000-2 from 9th March 2000.
Sl. 1: Lokacija izvira Mrzlek in zajemnih mest v bližini izvira (1) in pri jezu HE Solkan (2).
For multielemental analysis the samples were collected into 100 ml polyethylene flasks, which were previously rinsed with diluted HNO3, deionized water, and with a portion of filtered sample. Water was filtered through a 0.45 mm membrane filter and acidified with suprapure grade HNO3 on site. Samples for ion chromatographic analysis were stored untreated. They were collected into 500 ml polyethylene flasks, which were previously rinsed with deionized water and with a portion of sampled water. Shortly after the sampling (max. 1 hour) all samples were placed into a refrigera-tor where they were stored at 4°C until the analysis or shipment to the laboratory for analysis.
For determination of THM's the samples were collected into 1 l glass bottles which were pre-viously heated to eliminate traces of organic compounds. 10 ml aliquots of samples were heated in vials at 60°C for 45 minutes and analysed by the headspace GC method on a HP-6890 gas chromatograph with EC detector using an SPB-608 column and N2 as the carrier gas at 10.5 ml/min flow rate. Concentration of THM's was calculated as the sum of the concentrations of chloroform, chlorodibromomethane, dichlorobromomethane, and bromoform.
Ion chromatographic analysis was performed on a Metrohm IC 690 ion chromatograph with suppressor and conductometric detector. For the determination of nitrate and bromine the Anion/R anion exchange column (Altech) was used as a separation column. An aqueous solution containing 2.0 mmol/l NaHCO3 and 1.3 mmol/l Na2CO3 served as the eluent at a flow rate of 2.9 ml/min. For the determination of chloride, sulphate, nitrite, phosphate, and fluoride the Anion dual 2 anion exchange column (Metrohm) was used. A solution containing 2.0 mmol/l NaHCO3, 1.3 mmol/l Na2CO3, and 15% acetone was used as the eluent at a flow rate of 0.8 ml/min.
Multielemental analysis of water samples by ICP-MS was carried out by Actlab Ltd. (Ontario, Canada) using SLRL-4 and NIST 1643D water samples as control materials for low and high concentration ranges, respectively.
RESULTS AND DISCUSSION
Long term monitoring of heavy metals in the sediments indicates that the pollution of the river Soča with heavy metals has been declining since the year 1988, as is evident from Fig. 2 for the case of Cd.
At the same time, the presence of trihalomethanes in the water after chlorination (Fig. 3) indi-cates pollution by organic substances and/or the presence of natural precursors of trihalomethanes, such as humic substances, in untreated water from the spring Mrzlek. It can be observed that fol-lowing an apparent trend of increasing concentrations during the years 1995 and 1996 the concentrations of THM's are recently relatively low and constant.
Multielemental analyses of waters have revealed that several elements are mostly present in concentrations below the limit of detection (LOD) of the analytical technique or just above the LOD value in both waters. Therefore, they are not useful for identification of pollution sources or eventual mixing of waters. These elements include Li, Cr, Co, Ni, Ga, Se, Zr, Nb, Mo, In, Cs, La and all lanthanides, Re, Au, and Tl.
Other elements (Na, Al, Si, K, Ca, Ti, V, Fe, Cu, Zn, Br, Rb, Sr, Y, Cd, Sb, I, Pb, Bi, and U) can be classified into a group of elements exhibiting quite similar concentration ranges in both waters during the measurement campaign. Their actual concentration ranges are shown in Table 1.
Fig. 2: Cadmium in sediments collected from the Solkan HE plant basin near the spring Mrzlek (sampling point 1), and near the plant's dam at Solkan (sampling point 2). Results are expressed in mg Cd per kg of dry sediment.
Sl. 2: Kadmij v sedimentih, nabranih v akumulacijskem bazenu HE Solkan blizu izvira Mrzlek (1) in v bližini jezu pri Solkanu (2). Rezultati so v mg Cd na kilogram suhega sedimenta.
Fig. 3: Concentrations of trihalomethanes in drinking water. Sl. 3: Koncentracije trihalometanov v pitni vodi.
Table 1: Actual concentration ranges of elements in the water from the spring Mrzlek and the river Soča. Elements with concentrations below LOD are not shown.
Tabela 1: Razpon koncentracij elementov v vodah izvira Mrzlek in Soče. Elementi s koncentracijami pod mejo določljivosti niso prikazani.
	Concentration range (ppb)			Concentration range (ppb)	
	Mrzlek	Soča		Mrzlek	Soča
Ca	41400 - 52000	35200 - 50000	Cu	0.9 - 7	0.3 - 3
Mg	2640 - 7070	6130 - 10600	Ti	0.3 - 0.5	0.2 - 0.6
Na	740 - 1710	660 - 1570	Mn	0.2 - 1.5	1.2 - 3.3
Si	660 - 1200	530 - 1120	Rb	0.2 - 0.6	0.3 - 0.7
K	220 - 1120	270 - 760	U	0.14 - 0.17	0.15 -0.25
Fe	140 - 180	110 - 170	Pb	0.1 - 1.3	0.1 - 1.5
Sr	38 - 60	47 - 78	V	0.1 - 1	0.07 - 0.9
Br	11 - 92	8 - 83	As	0.04 - 0.3	0.2 - 0.5
Zn	5 - 18	2 - 6	Sb	0.03 - 0.06	0.06 - 0.09
Ba	5 - 8	9 - 15	Y	0.014 - 0.017	0.007 - 0.02
Al	3 - 21	6 - 22	Cd	0.01 - 0.02	0.01 - 0.02
I	2 - 19	0.9 - 8	Bi	0.006 - 0.01	0.007 -0.027
Table 2: Concentrations (mg/l) of selected metals in the water from the spring Mrzlek and the river Soča. Reported values represent the average of two determinations.
Tabela 2: Koncentracije (mg/l) izbranih kovin v vodah izvira Mrzlek in Soče. Prikazane vrednosti so povpreček dveh določanj.
		Mg	Mn	Ba	As	Ca	Fe	Zn
14. 5.	Soča	6130 ±120	1.7 ± 0.3	9.2 ± 0.5	0.32 ± 0.03	35200± 1100	137 ± 7	1.7 ± 0.3
1998	Mrzlek	3460 ± 70	0.2 ± 0.04	4.5 ± 0.2	0.09 ± 0.007	41400 ± 1200	168 ± 8	7.8 ± 1.6
1. 9.	Soča	8300 ± 170	2.7 ± 0.5	15 ± 0.8	0.31 ± 0.02	42800 ± 1300	152 ± 8	6.2 ± 1.2
1998	Mrzlek	4180± 80	0.5 ± 0.1	6.5 ± 0.3	0.1 ± 0.008	52000 ± 1600	171 ± 8	22 ± 4.4
13. 1.	Soča	6210 ± 120	1.7 ± 0.3	10 ± 0.5	0.19 ± 0.02	50000 ± 1500	167 ± 8	4.4 ± 0.9
1999	Mrzlek	2800 ± 50	0.3 ± 0.06	6.1 ± 0.3	0.04 ± 0.003	51600 ± 1600	181 ± 9	10 ± 2
15. 9.	Soča	7140± 130	3.1 ± 0.1	13.6 ± 0.3	0.36 ± 0.02	43600 ± 400	130 ± 2	4.3 ± 0.2
1999	Mrzlek	4560 ± 40	0.39 ± 0.07	5.0 ± 0.2	0.21 ± 0.02	49500 ± 1500	134 ± 6	18 ± 2
29. 9.	Soča	10450 ± 150	1.6 ± 0.3	12.37 ± 0.05	0.46 ± 0.05	42100 ± 500	113 ± 3	5.3 ± 0.8
1999	Mrzlek	7140 ± 70	1.4 ± 0.1	7.73 ± 0.07	0.26 ± 0.02	48300 ± 100	140 ± 2	11.6 ± 2.1
It was also observed that during the measurement campaign some elements such as Mg, Mn, Ba, and As exhibited a clearly higher range of concentrations in the water from the river Soča, compared to the water from the spring Mrzlek. Detailed analysis of the results further confirm that the concentrations of Mg, Mn, Ba, and As were at all times significantly higher in the river compared to the spring, as shown in Table 2. Inspection of temporal variations of concentrations how-ever indicates, that some elements (for example Ca, Fe, Zn) in the water from the spring show constantly higher concentrations compared to those detected in the river (Table 2).
In the case of anions, the concentration of sulphate is generally higher in the river Soča, while concentrations of chloride and nitrate are significantly higher in the spring Mrzlek as shown in Table 3. Concentrations of other measured anions were in all cases below the LOD of the ion chromatographic technique (0,05 mg/l) for these ions.
Table 3: Concentrations of sulphate, chloride and nitrate in the water from the spring Mrzlek and the river Soca.
Tabela 3: Koncentracije sulfatov, kloridov in nitratov v vodah izvira Mrzlek in Soce.
		Concentration of anions (mg/l)		
		sulphate	chloride	nitrate
15. 9. 1999	Soča	6,99 ± 0,05	1,17 ± 0,02	2,37 ± 0,03
	Mrzlek	5,40 ± 0,05	1,26 ± 0,02	4,15 ± 0,03
29. 9. 1999	Soča	5,10 ± 0,05	0,92 ± 0,02	3,28 ± 0,03
	Mrzlek	4,58 ± 0,05	1,57 ± 0,02	4,84 ± 0,03
CONCLUSIONS
Pollution of the river Soča with heavy metals, as evidenced by their presence in sediments, is declining. This is most probably due to the decreased exploitation of mercury, lead and zinc at the mines upstream, which were releasing their waste waters into the rivers Idrijca and Koritnica, respectively, and consequently into the river Soča. With the decline of pollution in the river Soča, there is less threat of pollution by heavy metals to the spring Mrzlek. However, the presence of organic pollutants and compounds such as humic and fulvic acids still remains a problem. This is due to the formation of carcinogenic trihalomethanes during the chlorination process. It is however important to note that the concentrations of trihalomethanes in drinking water are not increasing and remained at the level of 4 - 12 mg/l during the last five years, which means always below the threshold limit values for drinking water (Uradni List RS 1997).
Some elements, like Ca, Fe, and Zn, are already present in the spring water at concentrations higher than those measured in the river. At the same time a similar trend was observed for chloride and nitrate ions. This shows that, at present, the pollution of the river Soča cannot be the source of
these elements and anions in the spring Mrzlek, regardless of the extent of water mixing. Most probably, their higher concentrations originate from differences in natural background and possi-bly from environmental pollution on the Banj{ice plateau. This is predominantly originating from farming, which might account for higher concentrations of nitrate compared to the river So~a.
While concentrations of most elements are very similar between the river So~a and the spring Mrzlek, the concentrations of some elements such as Mg, Mn, Ba, and As are significantly higher in the river. Increases in concentrations of these elements in the water from the spring, could there-fore be an indication of pollution from the river due to the mixing of waters. This opens up the possibility of using the results of the regular drinking water monitoring program to reveal any eventual effects of mixing on the water quality.
REFERENCES
Janež, J. 1997: Vodno bogastvo Visokega krasa: Ranljivost kra{ke podzemne vode Banj{ic,
Trnovskega gozda, Nanosa in Hru{ice, Geologija Idrija. Kranjc, A. (Ed) 1997: Karst Hydrogeological Investigations in South - Western Slovenia, (A., ed.),
ZRC-SAZU, Ljubjana. Rook, J. J. 1974: Water Treat. Examin., 23, 234 Uradni list RS 1997, 46, 4125 - 4666.
Vudrag, M., Hojak, M., Maver, L., Franko, M. 1997: Solkan hydroelectric power plant and the drinking water quality in Nova Gorica-Slovenia, International Symposium on Environmental Epidemiology in Central and Eastern Europe: Critical Issues for Improving Health, Smolenice, Slovak Republic, p 102. Vudrag, M., Hojak, M., Maver, L., Franko, M. 1998: Hidroelektrarna Solkan in kakovost pitne vode v Novi Gorici, 2. Slovenski kongres preventivne medicine.
ACKNOWLEDGEMENT
This research was financaly supported through grants from Soške elektrarne Nova Gorica, Ministry of Health of Republic of Slovenia, and Ministry of Science and Technology of Republic of Slovenia.
Technical assistance from the staff of the Institute of Public Health of Nova Gorica and the Institute of Public Health of Novo Mesto is greatly appreciated.
NOVEJŠE MERITVE KVALITETE VODE V IZVIRU MRZLEK
Povzetek
Izvir Mrzlek je tipičen kra{ki izvir, ki služi kot glavni vir pitne vode za območje Nove Gorice, zato je kakovost izvira bistvenega pomena za {ir{o populacijo. Ob izgradnji HE Solkan pa je postal izvir dodatno izpostavljen onesnaženju, saj se je gladina reke Soče dvignila za več kot 20 metrov nad izvir. S tem se je povečala verjetnost vdora reke Soče v izvir ter možnost njegovega onesnaženja.
Da bi razjasnili možne vplive onesnaževanja reke Soče na kakovost pitne vode smo opravili določitve koncentracij 66 elementov ter anionov: nitrata, nitrita, sulfata, klorida, fosfata, bromida in fluorida v vodi iz izvira Mrzlek in reki Soči, ter določitve koncentracij trihalometanov v klorirani pitni vodi iz vodovoda Mrzlek. Rezultati analiz sedimentov kažejo, da se onesnaževanje reke Soče s težkimi kovinami po letu 1988 zmanjšuje. To se odraža predvsem na koncentracijah svinca in kadmija, upadanje koncentracij težkih kovin pa sovpada z zaprtjem rudnika svinca in cinka v Rablju ter opuščanjem idrijskega rudnika živega srebra, ki so bili pomembni onesnaževalci reke Soče in njenega povodja.
Koncentracije trihalometanov v klorirani pitni vodi so bile v letih 1995 do 1998 relativno nizke (4 - 12 mg/l) in ne kažejo trendov naraščanja, kar nakazuje, da onesnaženje izvira Mrzlek z naravnimi (huminske substance) in antropogenimi (komunalne odplake, mineralna olja ipd.) organskimi polutanti ni veliko.
V splošnem so območja koncentracij večine merjenih elementov in ionov v izviru Mrzlek in reki Soči pod mejo zaznavnosti (Li, Cr, Co, Ni, Ga, Se, Zr, Nb, Mo, In, Cs, Re, Au, Tl in lantanidi ter bromid, fluorid in fosfat) ali podobna (Na, Al, Si, K, Ca, Ti, V, Fe, Cu, Zn, Br, Rb, Sr, Y, Cd, Sb, J, Pb, Bi in U). Izjema so elementi Mg, Mn, Ba, in As ter sulfat, ki so v v reki Soči prisotni v bistveno višjih koncentracijah kot v izviru Mrzlek in nam torej lahko služijo kot potencialni pokazatelji stopnje mešanja vode iz reke Soče in izvira Mrzlek. Predstavljeni rezultati pa tudi nakazujejo možnost uporabe podatkov rednega programa monitoringa kakovosti pitne vode za napovedovanje stopnje mešanja z vodo reke Soče ter vpliva mešanja na kakovost pitne vode iz vodovoda Mrzlek.
Kakovost pitne vode iz izvira Mrzlek trenutno ustreza vsem standardom, vendar smo v izviru Mrzlek ugotovili višje koncentracije Ca, Fe, Zn, nitrata in klorida kot v reki Soči. Najverjetneje je vzrok višjih koncentracij različno naravno ozadje ter možnost onesnaževanja na vodozbirnem področju izvira Mrzlek (Banjška planota) predvsem zaradi kmetijstva (nitrat), saj reka Soča ne more biti vzrok povišanih koncentracij omenjenih elementov in anionov v vodi iz izvira, ne glede na intenzivnost mešanja.