Modellng Snowmelt-Induced Processes (Proceedngs of the Budapest Symposum, July 986). IAHS Publ. no. 55,986. Chemcal behavour of hydrophobc mcro - pollutants durng the meltng of snow NORBERT SIMMLEIT* Insttut Fresenus, Im Masel 4, D-6204 Taunussten 4, Federal Republc of Germany REIMER HERRMANN S WOLFGANG THOMAS Lehrstuhl fur Hydrologe, Unverstat Bayreuth, Postfach lo 2 5, D-8580 Bayreuth, Federal Republc of Germany ABSTRACT Durng two perods of snow meltng daly bulk samples of snow were taken on a Dolomte plateau n the rural karst regon of northeast Bavara (Federal Republc of Germany). The snow samples were analysed for PAHs by HPTLC and for BHCs by GC. Conductvty and ph were also measured. Molecular substance ratos, pollutant loadngs and enrchment factors n the meltwater were calculated from the concentraton data. Wth the frst 40% of meltwater 90% of H -ons, 70-80% of BHCs and 60-70% of PAHs were released from the snow cover. In the frst 20% of meltwater the H -ons were enrched by 4-6 tmes and some PAHs were enrched by 2.5 tmes. BHCs showed a more contnuous release n the frst 40% of meltwater causng.5-fold ncreased concentratons. Durng the meltng of snow the ratos of more hydrophobc to less hydrophobc mcropollutants ncreased n the snow cover. After a long perod of meltng hydrophobc contamnants were accumulated n the snow cover towards the end of one meltng event nvestgated. The dynamcs of the release of pollutants from the snow cover s dscussed n terms of the mcro-dstrbuton of atmospherc pollutants n the snow crystal. It s possble to use a nearby karst sprng as a natural lysmeter for tracng the release of snow consttuents durng the meltng. However, only -3% of the nput of mcropollutants were detected n the karst water. Le comportement chmque des mcropolluants hydrophobes pendant la fonte des neges RESUME Pendant deux pérodes de la fonte des neges des échantllons journalers de nege ont été prs sur un plateau des Dolomtes dans une régon rurale karstque en Bavère du nord-est (Republque Fédérale d'allemagne). Les échantllons de nege ont été analysés pour les PAHs par HPTLC et pour les HCHs par GC. En plus,la conductvté et le ph ont été détermnés. Les résultats des mesures de concentraton ont été utlsés pour *The experments were carred out at the Lehrstuhl f. Hydrologe (Unversty of Bayreuth, FRG). 335
336 N.Smmlet et al. calculer les rapports et les charges des polluants et les facteurs d'accumulaton dans l'eau de fonte. Dans les premers 40% de l'eau de fonte, 90% des ons H, 70-80% des HCHs et 60-70% des PAHs ont été lbérés par la couche de nege. Dans les premers 20% de l'eau, les ons d'hydrogène ont été enrchs 4-6 fos et quelques PAHs ont été enrchs 2.5 fos. Les HCHs ont été lbérés d'une manère plus contnue dans les premers 40% de l'eau fonte, provoquant une accumulaton de.5 fos. Pendant les fontes des neges le rapport entre les polluants plus hydrophobes et les polluants mons hydrophobes augmentat dans la couche de nege. Après une fonte des neges de longue durée, les polluants hydrophobes se sont accumulés dans la couche de nege vers la fn de la fonte. En partant de la dstrbuton mcroscopque des polluants atmosphérques dans les flocons de nege, la dynamque de la lberaton des polluants par la couche de nege a été dscuté. Il est possble d'utlser une source karstque avosnante comme lyslmètre naturel pour observer la lbératon des consttuants de la nege au cours de la fonte. Pourtant seulement -3% des mcro-polluants ntaux ont été détectés dans l'eau karstque. INTRODUCTION Durng the last decades several nvestgatons have dealt wth the norganc chemcal composton of snow (Sendtner, 887; Henrksen, 972; LaBarre, 973; Gjessng 8s Gjessng, 973; Olver et al., 974; Herrmann, 977). A very wde range of concentratons were found especally between polluted and unpolluted snow. However, only a few publcatons n whch the organc consttuents of snow were analysed (Herrmann, 978; Schrmpff et al., 979; Meyers & Htes, 982) are known to the authors. Herrmann (978) and Schrmpff et al. (979) frst determned the concentraton of organc mcropollutants n the snow cover. The occurrence of contamnants n snow s due to the deposton of arborne pollutants ether by wet deposton (scavengng effect of snow flakes) or by dry deposton of aerosol partcles. The authors of these publcatons showed that there s a regonal pattern of contamnants n the snow cover of northeast Bavara (Federal Republc of Germany), whch can be explaned by anthropogenc nfluences and orographc effects. Untl the meltng of snow the pollutant load of the snow cover s ncreased by atmospherc deposton processes (F0rland & Gjessng, 975). Snce the work of Johanesson & Henrkssen (978) t s known that wth the frst 30% of meltwater, 90% of the ons accumulated are released from the snow cover. Ths can result n a sudden ncrease of the acdty of natural waters n geologcally poorly buffered basns, causng n extreme cases an extncton of fsh populatons. In the meantme the observaton of the sudden release of onc speces from the snow cover n the frst fracton of meltwater has been confrmed n other studes and
Chemcal behavour of mcropollutants 337 dfferent regons (Benare & Munn, 980; Jeffres & Senkn, 983; Johannes et al., 980; Zottl et al., 985). Wthn the scope of a research project whch was amed at the evaluaton of the mpact of atmospherc deposton of organc mcropollutants on the groundwaters n a karst regon (Smmlet & Herrmann, 986), we also consdered the pollutant load of the snow cover durng wnter. Assumng that due to the very hgh permeablty of the geologcal structure the accumulated pollutants n the snow cover could reach the groundwater qute rapdly, we were nterested n the chemcal behavour of non-onc, hydrophobc mcropollutants n meltwater, sol water and groundwater durng the meltng of snow. For that purpose we analysed some selected organc contamnants durng and after the meltng of snow n the snow cover and n the groundwater sampled n a nearby karst sprng, n order to detect any possble changes n the groundwater qualty due to a potental release of pollutants from the snow cover. As model substances we chose some carcnogenc speces of the polycyclc aromatc hydrocarbons (PAHs)(Schoental, 964), whch are products of combuston processes, and the a- and Y~ somers hexachlorocyclohexane (BHC) (Table ). The latter chemcal s s commonly used as a pestcde (lndane) and s found, lke the TABLE Organc mcropollutants nvestgated Compound Structure Molecular Water solublty weght (25 C, \mol ~ L ) BHC a-bhc 24* y-bhc 0t Fa.3* 5 C 0.35% BaP 0.05- BghP 276 0.00094 Industreverband Pflanzenschutz t Oehme & Man0 (984). S May & Wask (978) McKay & Shu (977). (982).
338 N.Smmlet et al. PAHs, n the bulk precptaton of the samplng area throughout the year (Thomas, 98). MATERIAL AND METHODS Samplng stes and samplng perod Durng the wnter of 984 snow, bulk precptaton and karst water samples were taken from two samplng stes, stuated on a Dolomte plateau (450 m a.m.s.l.) n Upper Francona, Federal Republc of Germany (Smmlet & Herrmann, 986). In ths rural area the composton of snow s very unform and the concentratons of contamnants are low, as the regonal survey of Herrmann (978) and Schrmpff et al. (979) showed. The samplng staton NF was stuated n the basn of the karst sprng n the Lepoldstal. The hydrologcal stuaton of ths area s descrbed n detal by Kanz et al. (978). The snow cover (24 cm thck) was manly a result of snowfalls durng January. At the begnnng of February the meltng started very rapdly and the water content of the snowpack was reduced by 60% n the frst four days. On the ffth day the perod of meltng was fnshed by a ranstorm (30 mm). Durng the meltng bulk samples of snow were taken from an area of 0 x 0 m n daly ntervals. Water samples from the nearby karst sprng were collected daly throughout February. The second samplng staton VF was stuated drectly above the cave n Stenamwasser. The snow cover (8 cm thck) was due to snowfalls at the end of February. At the begnnng of March the meltng of snow started. Because of the large daly temperature varatons (day: -0 C, nght: 0 to -9 C) the meltng lasted three weeks. Durng ths tme 8 mm precptaton were deposted on the snowpack. Agan bulk samples of snow were taken daly from a small, unform area above the cave. Throughout March and Aprl addtonal samples of trcklng water were collected from two trcklng stes n the cave 2 m and 7 m below the snow cover. Analyss The bulk samples of snow were taken wth a glass plate and transported n 5 glass beakers to the laboratory for meltng. All glassware was cleaned wth acetone and heated to 75 C. After thawng, the ph and the specfc conductvty (20 C) of the snow were determned by usng a ph-glass electrode (Ingold 405-88) and a conductvty electrode (Metrohm EA 070). The melted snow and the bulk precptaton samples were lqud-lqud extracted wth dstlled dchloromethane. The concentrated extract was purfed on an Al 2 0 3 -column (Berl et al., 984) and analysed for PAHs (benzo(a)pyrene (BaP), fluoranthene (Fa), benzo(gh)perylene (BghP)) by hgh performance thn layer chromatography (HPTLC) accordng to the method of Herrmann (978). The BHCs were determned by gas chromatography (GC) usng a glass capllary column (OV 0)(Thomas, 98). The average recovery rates were 95% for PAHs (detecton lmt 0.45 ng l" ) and 90% for BHCs (detecton lmt
Chemcal behavour of mcropollutants 339 0.04 ng ). Another, more selectve extracton method was chosen for the karst water samples n order to acheve lower detecton lmts. These water samples from the sprng and the cave were taken n 2 glass bottles and were lqud-lqud extracted wth dstlled hexane. The concentrated extract could be used wthout further purfcaton for the analyss of PAHs by HPTLC and BHCs by GC. The mean recovery rates were 90% for BHCs (detecton lmt 0.03 ng ) and 85% for PAHs (detecton lmt 0.5 ng ). RESULTS The frst meltng event The meltng of snow The behavour of selected parameters of the snow cover durng the meltng of snow at staton NF s shown n Fg.l. The rapd meltng durng the frst days untl the ranfall s ndcated by the water loss of 60% of the orgnal water content. On account of the snow cover snkng n the course of the meltng, Im - - lmb os cm 50-25- 20- Ib- 0-5- PH "9 I 2 (mm) wate rcontent spec conducta nee (20 C) t t PH Fluoranthene ( 5 "8 l a -BHC J I - b.u- 4.5-200- 00-50- 00-50- ] molecular rato: Fa/ a -BHC ] I t Fa >, 3.2 4.2 5.2 6.2 t \ t t j FIG.l Varaton 984 ranfall of the chemcal composton of the snow cover durng meltng from 3 to 7 February.984 at staton NF. t 7.2 ]
340 N.Smmlet et al. the snow densty vared between 0.25 and 0.30 g cm 3. Wth the frst 40% of meltwater the conductvty of the snow cover decreased by 60% showng that the ons were released mmedately from the snowpack wth the frst meltwater fractons. As an example the ph-curve s shown n Fg.l. Due to the loss of 90% of the orgnal hydrogen content wth the frst 40% of meltwater, the ph of the snow cover ncreased from 4.6 to 5.6. Ths result s n accordance wth the results of other nvestgatons cted above. In prncple, all organc mcropollutants nvestgated show the same behavour as the ons. They are also released manly wth the frst 40% of meltwater. But the molecular ratos between the less soluble and the more water soluble contamnants (water solublty data: Table ) ncrease durng the meltng. As an example the molecular raton Fa/a-BHC s shown n Fg.l; t ncreases from 77 to 33 n the course of the meltng. Ths ndcates that the more water soluble pollutants are released more easly from the snow cover than the less water soluble; more hydrophobc mcropollutants. Therefore wth the frst 40% of meltwater 60% of BghP and BaP, 70% of Fa, 65% of Y-BHC and 80% of a-bhc molecules were released from the snowpack. Knowng the water loss of the snow cover and the changes of the pollutant concentratons, t s possble to calculate the concentratons of pollutants n the meltwater. In Table 2 we relate these concentraton values to the orgnal concentraton data TABLE 2 Relatve meltwater concentratons of snow consttuents related to ther concentratons n the snow cover at the begnnng of the meltng at staton NF Fracton of meltwater (%) Calculated enrchment H + BghP BaP factors Fa (underlned a-bhc f>,l): y-bhc 0-20 20-40 40-60 3.8 0.9 0.3 2.6 0.2 0.9 2.5 0.3 0.7.3 2.0 0.3.5.7 0..0.5 0.9 of the snowpack at the begnnng of the melt n order to obtan enrchment factors of the concentratons n the frst fractons of meltwater. In the frst 20% of the meltwater the hydrogen on actvty was 3.8 tmes hgher than n the orgnal snowpack. Ths s n accordance wth the nvestgatons of Johannesson & Henrksen (978) who measured a 3 to 6 tmes enrchment of ons n the frst meltwater fracton. However, the more hydrophobc PAHs (BghP, BaP) were enrched only 2.5 tmes n the frst 20% of meltwater. In contrast, the less hydrophobc organc contamnants are concentrated about.5 tmes n the frst 40% of meltwater, showng a more contnuous release.
Chemcal behavour of mcropollutants 34 The response of the karst sprng The response of the karst sprng due to the meltng of snow and the ranstorm s shown n Fg.2. The meltwater caused a tenfold ncrease of the dscharge of the karst sprng. The sudden release of ons from the snowpack can be observed n the sprng water by the ncrease of conductvty. At the same tme the ph of the calcareous water decreased by 0.4 ph unts, ndcatng the arrval of the meltwater enrched n hydrogen ons. (Is ) dscharge 0 500 7.2 23.2 I I 2.3 50 I 0.3 984 M 4.5 n.d. n.d. 28.4 BaP/Fa n.d. n.d. 0.24 M: calculated mean values of melt water -, perod of snow meltng n.d. not detectable FIG.2 Mean parameter values for dfferent dscharge phases of the karst sprng at staton NF. The dscharge maxmum s manly due to the ranstorm whch dluted the sprng water from 500 to 470 ymhos cm. In general the concentratons of organc mcropollutants n ths karst water are 25 tmes lower for PAHs and 25 tmes lower for BHCs than n the orgnal meltwater. The decreasng molecular ratos of less water soluble to more water soluble substances between meltwater and sprng water suggest that adsorpton n the karst system happens preferentally to the less water soluble contamnants. Wth the occurrence of suspended solds n the sprng water these ratos ncrease agan, because n ths case a large amount of less water soluble pollutants reach the karst sprng adsorbed on suspended
342 N.Smmlet et al. partcles. Mcropollutant balances Snce there was no other precptaton nput to ths basn durng the followng weeks, we were able to observe the hydrograph recesson to the ntal low water level. Knowng the meltwater and precptaton nput, t s possble to calculate nput and output (sprng water) loadngs of mcropollutants for ths karst system by ntegratng the hydrograph (Smmlet & Herrmann, 986). As shown n Fg.3 the adsorpton of the hydrophobc mcropollutants n the karst system seems to be very hgh, because Contamnant balance for the perod At: 02.02. - 27.02.984 nput output \q m At pg IB 2 - At 3.30 0.04 retenton 99 0.30 0.0 97 snow meltng (hatched column: nput by precptaton) FIG.3 Daly loadngs of selected mcropollutants n a small karst basn durng February 984: nput: meltwater + precptaton (hatched) at staton NF, output: karst sprng n the Lepoldstal. only -3% of the total nput reaches the karst sprng. Despte the hgh retenton, t s possble to observe the arrval of the PAHs together wth the ncrease of suspended solds n the sprng water. The more water soluble BHCs reach the sprng ndependently from the suspended partcles at hghwater flow and can be detected a long tme after the nput has ceased, ndcatng a leachng effect. The second meltng event The meltng of snow The snow cover was due to snowfall at the end of February and the meltng started at the begnnng of March. The frst perod of meltng lasted untl further snowfall ncreased
Chemcal behavour of mcropollutants 343 the water content of the snow cover agan. In ths perod 25% of the orgnal water content was lost as meltwater (Fg.4), Agan wth ths frst meltwater 90% of the H -ons (5.6 tmes enrchment n the meltwater), and 80% of the BHCs- as well as 50% of the PAHs-molecules were released from the snow cover, confrmng the results of the frst meltng event. The molecular ratos of more hydrophobc to less hydrophobc organc compounds ncreased durng ths perod (Fg.4). J" "B Fluoranthene (Fa) 500 0M' :r: Lndane (y-bhc) 5 200;9 3.4- Benzopyrene (BaP) 50-00 50-000- 400-200- 00- molecular rato Fa/0 -BHC l l molecular rato BaP/Fa ' _J I ' ' J ^ FIG.4 Varaton of the chemcal composton of the snow cover durng meltng from 29 February to 9 March 984 at staton VF. New snowfalls ncreased the water content of the snowpack agan and deposted addtonal arborne pollutants on the snow cover. Afterwards a rapd, fnal meltng of snow began, whch caused a compacton of the snowpack (snow densty ncreased from 0.2 to 0.4 g cm 3 ). Durng ths perod of meltng the ratos between less water soluble and more water soluble organc pollutants ncreased slghtly. However, n contrast to the frst perod the absolute concentratons of the organc consttuents augmented, ndcatng that they were no longer contnuously released wth the meltwater. Ths resulted n a 3-4 fold accumulaton of organc mcropollutants n the last patch of snow exstng whch could not be explaned only
344 N.Smmlet et al. by dry deposton onto the remnant snowpack. The onc speces were once more suddenly released from the snow cover wth the frst meltwater. Response of the percolaton water After each of the two meltng perods the drppng rate of the two percolaton stes n the cave below the snow cover ncreased, wth a delay of one to two days. However no organc mcropollutants could be detected n ths karst water. Ths can only be explaned by the hgh adsorpton of the contamnants n the sol layer. For ths reason drppng stones cannot be used as natural lysmeters for the nvestgaton of the behavour of organc mcropollutants n the karst system. DISCUSSION Johannesson & Henrksen (978) supposed that snow crystals are formed n a relatvely clean atmosphere. As they fall the crystals can scavenge aerosol partcles and gases can be adsorbed on ther surface. At the begnnng of the snow meltng process, water flms are formed between the snow crystals n whch the ons from the crystal surface can dssolve. For ths reason a sudden release of onc speces can be observed n the frst fracton of meltwater. Atmospherc, hydrophobc contamnants are manly adsorbed on aerosol partcles smaller than 0 ym (Mller, 984). Frst of all these partcles can act as condensaton nucle durng the formaton of snow crystals. Secondly these partcles are scavenged by fallng snow flakes and thrdly they can be deposted drectly on the snow cover by dry deposton processes (Ibrahm et al., 983). Nothng s known about the mcro-dstrbuton of pollutants n snow crystals. But we can presume that the hydrophobc, arborne pollutants are concentrated n the centre of a snow flake due to adsorpton on the condensaton nucle and on the surface of a snow flake due to the scavengng effect. Therefore at the same tme as the sudden release of ons, hydrophobc compounds whch are adsorbed on suspended aerosol partcles n the water flm between the snow crystals can be released. These partcles can penetrate the snowpack because at the begnnng of snowmelt macropores are formed (Marsh & Woo, 984). However, as snowmelt contnues the snow cover wll consoldate and ts densty ncrease. Wth ncreasng snow densty the permeablty of the snowpack decreases (Colbeck & Anderson, 982). Therefore t mght be possble that no further transport of partcles through the snowpack can occur, despte the loss of bulk snow durng meltng. Ths would result n an accumulaton of mcropollutants at the end of a lengthy meltng perod. It s probable that we could not observe ths effect n our frst meltng event because ths event was termnated prematurely by a ranstorm. As far as the water solublty of the nvestgated mcropollutants s concerned, slght dfferences n ther behavour can be detected between dfferent compounds. PAHs show a sudden release wth the frst flush of meltwater contanng the scavenged
Chemcal behavour of mcropollutants 345 aerosol partcles and most of the H -ons. In contrast, the less hydrophobc BHCs whch are dssolved n meltwater to a larger extent show a more contnuous leachng wth the frst 40% of meltwater. In any case less than 3% of the organc mcropollutant nput reaches the groundwaters n carbonate terrans despte the hgh permeablty of the karst systems. The organc contamnants are adsorbed on the top layer of the sols, as the analyss of sol materal from the samplng stes showed (Smmlet & Herrmann, 986). However, further research s needed to trace organc contamnants durng the snowmelt and to detect ther snks n dfferent envronmental systems. REFERENCES Benare, M. & Munn, R.E. (980) Wet and dry deposton, ncludng meltng phenomena and snowpack chemstry. In: Effects of Acd Precptaton on Terrestral Ecosystems (ed. by T.C.Hutchnson 8s M.Havas), 579-582. Plenum Press, New York. Berl, R., Kaa, W. & Thomas, W. (984) Spatal and temporal concentraton gradents of PAH (fluoranthene, benzo(a)pyrene, gamma-bhc and 2,4 D n samples of sol, sol water and groundwater n an agrcultural research area. Fresenus Z. Anal. Chem. 39, 72-79. Colbeck, S.C. & Andersson, E.A. (982) The permeablty of a meltng snow cover. Wat. Resour. Res. 8, 904-908. F0rland, E.J. & Gjessng, Y.T. (975) Snow contamnaton from washout/ranout and dry deposton. Atmos. Envron. 9, 339-352. Gjessng Y.T. & Gjessng E. (973) Chemcal composton of an antarctc snow profle. Vatten 6, 233-237. Henrksen, A. (972) Quantatve chemcal analyss of snow. Vatten 5, 409-42. Herrmann, A. (977) Chemcal composton of a polluted snow cover, In: Isotopes and Impurtes n Snow and Ice (Proc. Grenoble Symp., August-September 975), 2-26. IAHS Publ. no.8. Herrmann, R. (978) Regonal pattern of polycyclc aromatc hydrocarbons n NE-Bavaran snow and ther relatonshp to anthropogenc nfluence and ar flow. Catena 5, 65-75. Ibrahm, M., Barre, L.A. & Fanank, F. (983) An expermental and theoretcal nvestgaton of the dry deposton of partcles to snow, pne trees and artfcal collectors. Atmos. Envron. 7, 78-788. Industreverband Pflanzenschutz e.v. (982) Wrkstoffe n Pflanzenschutz- und Schadlngsbekampfungsmtteln - physkalsche-chemsche-toxkologsche Daten (Plant protecton and pestcdes - physcal-chemcal-toxcologcal data). Jeffres, D.S. & Senkn, R.G. (983) Changes n snowpack, stream and lake chemstry durng snowmelt n Turkey Lake watershed. VDI-Berchte Nr.500, 377-386. Johanesson, M. & Henrksen, A. (978) Chemstry of snow meltwater: changes n concentraton durng meltng. Wat. Resour. Res. 4, 65-69. Johannes, A.H., Galloway, J.N. & Troutman, D.E. (980) Snow pack storage and on release. In: Proc. Int. Conf. Ecologcal Impact
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