ODSTRAŇOVANIE ŽELEZA A MANGÁNU Z VODY FILTRÁCIOU PRÍRODNÝMI MATERIÁLMI Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 29 ANALYSIS TRICHLORO- AND TETRACHLORO-ETHYLENE IN WATER 1Ján ILAVSKÝ, 1Danka BARLOKOVÁ 1Department of Sanitary and Environmental Engineering, Faculty of Civil Engineering of the Slovak University of Technology, Radlinského 11, 813 68 Bratislava, Slovakia jan.ilavsky@stuba.sk, danka.barlokova@stuba.sk *Corresponding author Received 10 December 2011, accepted 25 February 2012 Abstract: The method for determination of trichloroethylene (TCE) and tetrachloroethylene (TTCE), also known as perchloroethylene (PCE), in water at 1 – 30 mg.l-1 concentrations was elaborated. Water (1000 ml) is extracted by manual shaking (5 minutes) at 5-7 oC with n-pentane (0,5 ml) in the presence of internal standard (1-Cl-n-hexane, 1-Cl-n-octane) and the extract chromatographed using split-splitless injection technique. The recoveries of 28 chlorinated hydrocarbons in water at 5 mg.l-1 concentrations for each compound relative to internal standard (R=100%) are also introduced. The FID and ECD detectors (in the case of ECD detector without of internal standard) were used in final stage of determination. Keywords: capillary gas chromatography, microextraction, water analysis, chlorinated hydrocarbons 1. Introduction Organic Compounds of chlorine and other halogens present in water predominantly come from human activities or are influenced by them. It is mainly chemical industry (production of synthetic polymers, fibers, organic solvents, etc.) engineering (degreasing and surface treatment of metals), metallurgical and electrical industry (microelectronics), agriculture (pesticides), communal undertaking (chemical cleaning of clothes) and others that are responsible for abrupt increase in contamination of all kinds of water including rain water. Moreover, the organohalogen compounds are formed in the course of water disinfection itself as undersirable products of chlorination of different hydrocarbons of biogenic or synthetic origine. On the basic of present knowledge, these substances are considered to by very dangerous for environment as well as for human being itself. Many organohalogen compounds are very resistent to oxidative, photolytic and other physicochemical degradation processes and therefore they stay in aqueous medium for a long time. The half-times of decay of some chlorinated hydrocarbons in aqueous medium are given in Table 1 [1,2]. Table 1 Half-times of decay of some chlorinated hydrocarbons in aqueous medium [1,2] Compound Half-time of decay tetrachloroethylene 6 years trichloroethylene 9 months chloroethylenes 6 – 12 weeks chloromethanes 10 – 33 weeks chloroethanes 10 – 33 weeks As organohalogens belong among substances detrimental to aqueous medium and biological life, they should not be present in water. However, the requirement of absolute zero concentration of these substances even in drinking water is hardly realizable for the present. The concentration ranges of some chlori- nated hydrocarbons in different kinds of mailto:jan.ilavsky:@stuba.sk mailto:danka.barlokova:@stuba.sk Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 30 water statistically processed according to literary resources [3] are given in Table 2. Table 2 Concentration ranges of trichloro-ethylene (TCE) and tetrachloroethylene (TTCE) in different kinds of water [3] Water TCE [µg/l] TTCE [µg/l] Surface water 0.01 - 11 0.1 - 1300 Drinking water 0.1 - 15 0.1 - 200 Ground water 0.1 - 150 0.1 - 1000 Rain water 0.1 - 13 0.1 - 50 Waste water up to 2000 0.1 - 6000 The International Agency for Research on Cancer has classified trichloroethylene and tetrachloroethylene as a Group 2A carcinogen, which means that it is probably carcinogenic to humans [4]. Maximum contaminant level (USEPA) for TCE and TTCE in drinking water is 0,005 mg/l (according to the requirements of the Regulation of the Government of the Slovak Republic No. 496/2010 on drinking water, the contaminant level is 0,01 mg/l). The granular activated carbon in combination with packed tower aeration are required for effective removing TCE and TTCE from water [5]. The analysis of volatile organohalogene compounds (VOC) in water samples requires a several steps: a) isolation and preconcentration of the pollutants from water, b) trace organic analysis by capillary gas chromatography (GC), c) identification and quantitative determi- nation individual compounds. Sample preparation methods include static headspace, dynamic headspace (purge and trap), solvent extraction and solid-phase microextraction techniques, or direct injection of water into gas gromatograph. The advantages and disadvantages of these methods are presented and discussed [6]. The chlorinated hydrocarbons in water can by analyzed by injection water directly into a gas chromatograph [7-14]. This method is profitable because of simplicity. The rests of salts deposited in the injector after evaporation of water bringcauses the problems. However, such problems can be solved by simple exchange of glass tube of the injector after 50 – 100 analyses (according to quantity of the dosed volume of sample). The sensitivity of this method reaches 0,1 mg/l H2O. The chlorinated hydrocarbons in water can be determined by using the “headspace” method. This method is either static, i.e. carried out in closed system [15-17] or dynamic, the so-called stripping or purge and trap, with adsorption, i.e. on Tenax [18-20]. The dynamic method is more sensitive and if we use a detector ECD, we can analyze these componds even when they are present in concentrations under 0,01 mg/l H2O. The static headspace method is an attractive method regarding its rapid times and simplicity, i.e., no sample workup is required outside the vial [21]. In static headspace method a sample of water is placed into a vial, sealed, and heated to a specific temperature. All of the compo- nents volatile at or below the pre-set temperature escape from the sample to form a gaseous "headspace" above the sample. After a certain period of time, the headspace gas is extracted from the vial and injected into a gas chromatograph with selective detector. The sensitivity for static headspace is typically in the sub micro- gram range. However, it depends on the volatility of the compounds. In dynamic headspace method the sample is purged with ultra pure nitrogen while being heated in a Teflon vessel. As the nitrogen stream exits the vessel it passes through the thermal desorption tube filled with an adsorbent material. The outgassed products are collected onto the adsorbent material. Following the predetermined collection time, the tubes are transferred to a thermal desorption unit which is inline http://en.wikipedia.org/wiki/International_Agency_for_Research_on_Cancer http://en.wikipedia.org/wiki/International_Agency_for_Research_on_Cancer http://en.wikipedia.org/wiki/Carcinogen http://en.wikipedia.org/wiki/Tetrachloroethylene%23cite_note-2 Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 31 with the gas chromatograph and selective detector (GC/MS or GC/ECD). The thermal desorption unit heats the individual tubes while a flow of gas is applied through the tube. The collected analytes are flushed from the sorbent and collected onto a cold trap within the thermal desorption unit. The cold trap is heated rapidly after purging the entire sample from the sample tube and collected in the cold trap. The collected analytes are then swept from the cold trap into the GC/MS for analysis as a volatile sample. The static headspace method is less expensive than the purge-and-trap since no expensive purging equipment is used here. With the headspace method, multiple runs can be performed on a single sample vial, whereas the purge-and trap method is essentially destructive; the sample may only be purged and analysed once [21]. The disadvantage of the purge-and-trap method is associated with the problems related to the use of adsorbents, such as overloading, carryover, and breakdown with repeated heating and purging cycles. Solid-phase microextraction (SPME) is a relatively new technique, first published in 1989 [22]. A thin fused silica fiber coated with a layer of polymeric adsorbent material is introduced directly into the aqueous sample, whereupon the analytes diffuse into the fibre coating until equilibrium is established, thus being extracted in amounts determined by their distribution coefficients and concentra- tions. Subsequently, the analytes are desorbed thermally in GC injector. The method is effective, sensitive to wide range of compounds (detection limits are typically from 20 ng/l to 200 ng/l, except for the very light VOCs), less expensive and easier to use then well-established methods such as purge and trap and traditional head-space analysis techniques. Solid-phase microextraction has been applied to quantitative analysis of organohalogens in drinking water [23-29]. The temperature has a very direct influence on extraction. A higher temperature reduces the time to reach equilibrium because of faster diffusion in the water. However, it lowers the total amount absorbed on the fibre as the distribution coefficients decrease. For this reason the SPME method requires examination of the extraction time, fibre coating-water distribution coefficient, equilibration curves for VOCs compound, adsorption heat and analytes volatility. The extraction methods are frequently used for determining the chlorinated hydro- carbons present in water. In literature issued in our country as well as abroad many methods of extraction of the halogenated organic compounds from water have been described. They differ from each other by kind and amount of the used extractant (ratio water : solvent) as well as by the recovery of extraction. n-Pentane [30-38], n-hexane [31,33,39,40], methylcyklohexane [31,33,42], isooctane [31-33], petroleum ether [43], mixture of n-hexane + diisopropylether [39,41], etc are used for extraction. By comparing the efficiencies of extraction methods with each other, it has been found that no significant differences appear if different extractants are used [44]. The effectiveness of extraction mainly depends on affinity of dissolved substance to extractant (the measure of which is distribution coefficient, i.e. the ratio of concentration of organohalogen in extractant to its concentration in water) and phase ratio (the ratio of extractant volume to sample volume) as well as on number of extraction steps. The extraction can be carried out either in one step or in several steps in series (the extraction is performed either with successive addition extractant or in countercurrent of water and solvent). The efficiency of extraction is affected by extent of the interface contact, solubility of the investigated substances in both phases, ionic strenght and pH of the medium. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 32 A comparison of extraction methods with the headspace or stripping methods is presented in papers [45,46]. For instance, the stripping method is about ten times more sensitive method then micro- extraction for compounds with boiling points up to 200 oC. On the other hand, the stripping method necessitates special apparatus and is slow and therefore it is less convenient for routine analysis of organohalogens in water when compared with microextraction. In most cases the cappilary gas chromatography with an ECD detector or the GC/MS combination is used in final stage of determination. If a FID detector appropriate for the chlorinated hydro- carbons containing 1 or 2 chlorine atoms in a molecule is used, we must choose a volitale solvent (or a column with more polar phase) so that the solvent should not interfere with waves of the analyzed substances. In view of the above – mentioned facts, we have paid attention to the possibility of using microextraction for the analysis of the chlorinated hydrocarbons in water. The experimental part of this paper comprises the results of investigation represented by the recovery of 28 chlorinated hydro- carbons obtained by microextraction with n-pentane. 2. Experimental 2.1 Instrumentation Gas chromatograph Carlo Erba (VEGA 6000) equipped with an ECD or FID detectors and split-splitless injector system was used. For the chromatographic separation (in the case of FID detector) a glass capillary columns with stationary phase PEG 400, TRITON TX-305 and UCON LB550+ IGEPAL CO 880 (4:1) were used. For the chromatographic separation (in the case of ECD detector) a silica capillary column DB-5 wet with silicone stationary phase SE-54 was used. Chromatograms were integrated with DP 700 (Carlo Erba) integrators. 2.2 Microextraction One litre of water containing defined content of chlorinated hydrocarbons was subjected to microextraction (at + 5-7 oC) with 0,5 ml of n-pentane containing internarnal standard (in the case when a FID detector was used) by intense manual shaking 5 minutes. The glass extraction flask, equipped with a male joint (1) and conical stopper (5) was used to extraction (A). After extraction (B) the solvent thin layer separator (2) containing side arm for water (3), capillary for extract (4) was connected to the extraction flask (Figure 1) [47]. In this case the n-pentane extracts are easily accessible and can be injected immediately by means of a syringe into a gas chromatograph. Fig.1 Solvent thin layer separator for microextraction of water 2.3 Chemicals For the analysis of the chlorinated hydrocarbons certified standards from Slovak Metrology Institute and standards from Supelco (purity at least 98 %) were used. As the internal standards 1-Cl-n- hexane, 1-Cl-n-octane or 1-Cl-n-dodecane Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 33 were used (purity at least 98% - Supelco, Bellefonte, USA). Solvent (n-pentane) was highly purified and checked chromatogra- phically (E. Merck, Darmstadt, Germany). 3. Results and discussion It results from literature review that n- pentane is most frequently used as extractant in extraction methods. Because of volatility of lower chlorinated hydrocarbons and boiling point of n- pentane we may expect lower losses of the analyzed components for this solvent than for extractants with higher boiling point. For this reason, it is serviceable to add into extractant an internal standard exhibiting similar volatility as analyzed compounds. The recoveries (average of five analysis) of some chlorinated hydrocarbons with respect to 1-Cl-n-hexane as internal standard (R=100%) for equal concentration of each component (5 mg/l of water) are given in Table 3. Table 3 The recoveries of volatile chlorinated hydrocarbons from water by microextraction with n-pentane Compound Recovery [%] FID detector 5 mg/l % RSD dichloromethane 1.74 5.63 trichloromethane 3.79 5.42 dichlorobromomethane 4.27 5.86 chlorodibromomethane 3.051 6.31 tribromomethane 6.921 6.58 tetrachloromethane 57.20 5.12 1,1-dichloroethane 4.32 4.39 1,2-dichloroethane 1.05 6.92 1,1,1-trichloroethane - - 1,1,2-trichloroethane 2.71 5.38 1,1,2,2-tetrachloroethane 7.141 4.92 1,2-dichloropropane 6.12 5.14 1,1-dichloroethylene - - 1,2-dichloroethylene (trans) 4.71 4.95 trichloroethylene 34.75 3.82 tetrachloroethylene 85.98 3.73 1 the recovery with respect 1-Cl-n-octane (IS) Table 3 continued 1,3-dichloropropene (trans) 1.16 6.38 1,3-dichloropropene (cis) 3.44 4.78 2-chloroethylvinylether 4.62 5.41 chlorobenzene 1.68 5.17 1,3-dichlorobenzene 58.171 3.32 1,4-dichlorobenzene 54.861 3.60 1,2-dichlorobenzene 53.231 3.98 1,3,5-trichlorobenzene 77.622 4.09 1,2,4-trichlorobenzene 77.102 4.18 1,2,3-trichlorobenzene 76.972 4.37 1,2,3,5-tetrachlorobenzene 85.772 3.89 1,2,4,5-tetrachlorobenzene 85.862 3.54 pentachlorobenzene 94.852 3.84 hexachlorobenzene 97.712 3.32 Compound Recovery [%] ECD detector 5 mg/l % RSD dichloromethane 8.12 7.58 trichloromethane 9.75 7.21 dichlorobromomethane 11.62 6.89 chlorodibromomethane 12.20 6.45 tribromomethane 14.68 6.14 tetrachloromethane 76.20 6.06 1,1-dichloroethane 8.65 6.37 1,2-dichloroethane 9.84 6.18 1,1,1-trichloroethane 27.92 6.52 1,1,2-trichloroethane 14.58 6.20 1,1,2,2-tetrachloroethane 15.32 6.36 1,2-dichloropropane 11.26 6.78 1,1-dichloroethylene 9.41 7.15 trichloroethylene 41.92 5.89 tetrachloroethylene 86.56 5.22 1,3-dichloropropene (trans) 7.68 7.34 1,3-dichloropropene (cis) 7.82 7.21 chlorobenzene - - 1,3-dichlorobenzene 39.72 5.76 1,4-dichlorobenzene 38.98 5.92 1,2-dichlorobenzene 38.58 4.89 1,3,5-trichlorobenzene - - 1,2,4-trichlorobenzene - - 1,2,3,5-tetrachlorobenzene - - 1,2,4,5-tetrachlorobenzene - - pentachlorobenzene - - hexachlorobenzene - - 2 the recovery with respect 1-Cl-n-dodecane Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 34 The values obtained for the investigated compounds show that microextraction into n-pentane is convenient for tetrachloro- methane, trichloroethylene, tetrachloro- ethylene, dichlorobenzene and other higher chlorinated benzenes. The recovery of other chlorinated hydrocarbons are relatively low which is due to stronger hydrogen bonds between the OH groups of water and the chlorine atoms in a molecule of hydrocarbon. The efficiency of isolation is significantly affected by polarity of the extracted compounds (its solubility in water). Therefore the solubilities of some chlorinated hydrocarbons in water taken from literature are given in Table 4. The values of recovery given in Table 3 were obtained by reverse extraction of 0,5 ml of n-pentane containing 5 mg of eachcomponent (including 1-Cl-n-hexane as internal standard) with water (1 litre). The extraction was performed by intense manual shaking for 5 minutes. Table 4 The solubilities of some chlorinated hydrocarbons in water [48,49,50] Compound Solubility [g/l at 20 oC] chloromethane 7.25 dichloromethane 19.80 trichloromethane 8.20 tetrachloromethane 0.78 chloroethane 4.1 1,1-dichloroethane 5.5 1,2-dichloroethane 8.7 1,1,1-trichloroethane 0.48-4.4 1,1,2-trichloroethane 1.1-4.6 1,1,2,2-tetrachloroethane 2.87 pentachloroethane 0.5 hexachloroethane 0.05 1,2-dichloropropane 2.8 1,3-dichloropropane 2.7 1,2,3-trichloropropane 1.9 tribromomethane 3.1 chloroethylene 0.40-2.66 1,1-dichloroethylene 0.4 Table 4 continued chloroethylene 0.40-2.66 1,1-dichloroethylene 0.4 1,2-dichloroethylene (trans) 8.8 1,2-dichloroethylene (cis) 3.5 trichloroethylene 1.1 tetrachloroethylene 0.149 chlorobenzene 0.502 1,3-dichlorobenzene 0.143 1,4-dichlorobenzene 0.065 1,2-dichlorobenzene 0.137 1,3,5-trichlorobenzene 0.006 1,2,4-trichlorobenzene 0.031 1,2,3-trichlorobenzene 0.018 1,2,3,5-tetrachlorobenzene 0.0051 1,2,4,5-tetrachlorobenzene 0.00046 1,2,3,4-tetrachlorobenzene 0.00592 If we compare data in Table 3 with Table 4, we can see that the recovery of chlorinated hydrocarbons are consistent with their solubility in water. The highest recovery appear if the solubility falls under 1 g/l of water. The data in Table 4 may serve as orientation for determination of other chlorinated hydrocarbons in water by using microextraction as well. Furthermore, it results from Table 3 that the recovery increases with number of the chlorine atoms in a molecule of hydro- carbon which manifests itself e.g. in the series di-, tri- and tetrachloromethane or mono-, and as far as hexachlorobenzene. The recovery of extraction are usually affected by concentration of the analyzed substance in water which is most conspicuous if the concentration is very low. It is very important to taken this fact into consideration, especially if the recovery are low which is usual in the case of microextraction. The errors due to the change in recovery produced by varying concentration may be reduced by drawing the analytical curve for a given concen- tration range. The values for analytical curve of trichloroethylene and tetrachloroethylene Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 35 in the concentration range 1 – 30 mg/l of water were obtained by the use of micro- extraction of model sample of water (1 litre) containing know quantity of the analyzed substances with 0,5 ml of n- pentane containing 5 mg of 1-Cl-n-hexane. The analytical curves are represented in Figure 2 which shows that it is practically possible to execute linearization of the curve in the investigation concentration region and thus to neglect the variation of recovery with concentration. Fig. 2 The analytical curves of trichloroethylene (TCE) and tetrachloroethylene (TTCE) in the concentration range 1 – 30 mg/l of water PTCE – area of TCE elution peak, PTTCE – area of TTCE elution peak, PIS – area of IS elution peaks We have also had the reason for paying attention to TCE and TTCE because these two substances belong among the most frequent contaminants of ground waters. We analyzed real samples of water in the same way as described for determining the analytical curve. This method was used to determine the areal and vertical distribution of groundwater contaminated by chlorinated hydrocarbons water source, the Red Willows in Piestany. Water source yielding 80 l / s was located 350 m from the plant site, there was used organic solvents based on chlorinated hydrocarbons in manufac- turing process. Inadequate provision of storage facilities and handling facilities to the leakage of chlorinated hydrocarbons caused degradation of groundwater and soil in the area of this plant site. The pollution spread to an area 4.2 square kilometers with an average depth range of 15 m. Within the monitoring we analyzed 164 samples, 88 samples in TCE content and content TTCE 47 was equal to or higher than 0.01 ug/l. From the total number of samples the limit value of 0.01 mg/l for drinking water (GR 496/2010) exceeded for TCE 27 samples and for TTCE 3 samples. Repeated analyzes of ground- water samples in the following years confirmed the existing pollution of groundwater and water resource Red Willow was declared unsuitable for public drinking water supply. The chromatogram of a model sample of water containing chlorinated hydrocarbons represented in Figure 3 may serve as an example of the determination of trichloroethylene and tertachloroethylene in water frequent contaminants of ground waters. The developed method was used for analytical determination TCE and TTCE in ground waters of accident regions. Fig. 3 The gas chromatogram of a model sample of water containing trichloroethylene and tetra- chloroethylene together with aromatic and saturated hydrocarbons Elution peaks (Fig. 3): 1 - benzene, 2 - octane, 3 – trichloroethylene, 4 - methylbenzene, 5 - tetrachloroethylene, 6 - nonane, 7 - 1-Cl-n-hexane (IS), 8-ethylbenzene, 9 - 1,3-dimethylbenzene, 10 - 1,4-dimethylbenzene, 11-1,2-dimethylbenzene, 12-decane, 13-iso-propyl- benzene, 14-n-propylbenzene, 15-sek-buthylben- zene, 16- iso-buthylbenzene, 17- undecane, 18- n-buthylbenzene Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 36 Figure 4 shows the gas chromatogram of chlorinated hydrocarbons mixture with identification of individual elution peaks. Identification of components is based on certified standard allowance into n-pentane solvent. For the analysis of chlorinated hydrocarbons in water a microextraction with the following gas capillary chromato- graphy equipped with ECD can be used. ECD detector is more sensitive to amount of chlorine atoms in compound. Therefore, the recoveries of trichloroethylene and tetrachloroethylene (in table 3) are higher when using of ECD detector rather than FID detector. Fig. 4 Gas chromatogram of the model mixture of chlorinated hydrocarbons (concentration of each component of 1 mg) in 0,5 ml of n-pentane before the microextraction Elution peaks (Fig. 4): 1– 1,1-dichloroethylene, 2– dichloromethane, 3– trichloromethane, 4– 1,1,1-trichlorothane, 5– 1,2-dichloroethane, 6– tetrachloromethane, 7– 1,2-dichloropropane, 8– trichloroethylene, 9–dichlorobromomethane,10–1,1,2-trichloro- ethane, 11–dibromochloromethane,12– tetrachloro- ethylene, 13–tribromomethane, 14–1,1,2,2-tetra- chloroethane. 4. Conclusions The above-mentioned considerations indicate that the microextraction methods of trichloroethylene and tetrachloro- ethylene isolation is very rapid, simple, economically profitable and with low detection limit (0,1 mg/l of water). The recovery of trichloroethylene into n- pentane is above 40% and for tetra- chloroethylene it is higher than 85%. These values are influenced by number of chlorine atoms in molecule and their solubility in water. The results of this study give provide data important for quantitative analysis of these compounds in water and they can be used for routine quantitative analysis involving microextraction and capillary gas chromatography. 5. References [1] MC CONNEL G., FERGUSON D.M., PEARSON C.R.J. Chlorinated hydrocarbons and the environment. Endeavour 34, 13-18, (1975). [2] DILLING W.L., TEFERTILLER N.B., KALLOS G.J. Evaporation rates and reactivities of methylene chloride, chloroform,1,1,1-trichloroethane, trichloro- ethylene, tetrachloroethylene, and other chlorinated compounds in dilute aqueous solutions Environ. Sci. Technol. 9, 833, (1975). [3] ATRI, F.R. Chlorierte Kohlenwasserstoffe in der Umwelt.III. Landschaftsentwicklung und Umweltforschung 34, 134, (1985). [4] IARC monograph. Tetrachloroethylene, Vol. 63, p. 159. Last Updated May 20, 1997. Last retrieved June 22, (2007). [5] EUR 21680 EN European Union Risk Assessment Report. Volume 57. Tetra- chloroethylene. Part1 – Environment. Institute for Health and Consumer Protection, Final report, pp. 154, (2005). [6] MARCZAK M., WOLSKA L., CHRZANOWSKI W., NAMIEŚNIK J. Microanalysis of Volatile Organic Compounds in Water Samples – Methods and Instruments. Microchimica Acta 155, 331-348, (2006). [7] HARRIS L.E., BUDDE W.L., EICHELBERGER J.M. Direct analysis of water samples for organic pollutants with gas http://pubs.acs.org/doi/abs/10.1021/es60107a008 http://pubs.acs.org/doi/abs/10.1021/es60107a008 http://pubs.acs.org/doi/abs/10.1021/es60107a008 http://pubs.acs.org/doi/abs/10.1021/es60107a008 http://pubs.acs.org/doi/abs/10.1021/es60107a008 http://pubs.acs.org/doi/abs/10.1021/es60107a008 http://www.inchem.org/documents/iarc/vol63/tetrachloroethylene.html https://springerlink3.metapress.com/content/?Author=Marcin+Marczak https://springerlink3.metapress.com/content/?Author=Lidia+Wolska https://springerlink3.metapress.com/content/?Author=Wojciech+Chrzanowski https://springerlink3.metapress.com/content/?Author=Jacek+Namie%C5%9Bnik https://springerlink3.metapress.com/content/0026-3672/ https://springerlink3.metapress.com/content/0026-3672/155/3-4/ http://pubs.acs.org/doi/abs/10.1021/ac60349a001 Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 37 chromatography-mass spectrometry. Anal. Chem. 46(13), 1912, (1974). [8] FUJI T. J. Direct aqueous injection gas chromatography-mass spectrometry for analysis of organohalides in water at concentrations below the parts per billion level. J. Chromatogr. 139(2), 297, (1977). [9] NICHOLSON A.A., MERESZ O., LEMYK B. Determination of free and total potential haloforms in drinking water. Anal. Chem. 49(6), 814, (1977). [10] GROB K., HABICH A. Trace analysis of halocarbons in water; Direct aqueous injection with electron capture detection, J. High. Resol. Chromatogr. 6(1), 11, (1983). [11] PFAENDER F.K., JONAS R.B., STEVENS A.A., MOORE L., HASS J.R. Evaluation of direct aqueous injection method for analysis of chloroform in drinking water, Environ. Sci. Technol. 12(4), 438, (1978). [12] ZLATKIS A., WANG F. S., SHANFIELD H. Direct GC analysis of aqueous samples at the part-per-billion and part-per-trillion levels. Anal. Chem. 55(12), 1848, (1983). [13] JOLLEY R. L., SUFFET I. H. Concentration Techniques for Isolating Organic Constituents in Environmental Water Samples. Advances in Chemistry 214, 3, (1987). [14] MEHRAN M.M., COOPER W.J., MEHRAN M. Comparison of direct headspace and aqueous injection techniques for halogenated hydrocarbons in water. J. Chromatogr. Sci. 24, 142, (1988). [15] DIETS E.A., SINGIE K.F. Determination of chlorinated hydrocarbons in water by headspace gas chromatography. Anal. Chem. 51(11), 1809, (1979). [16] KOLB B. Application of an automated head- space procedure for trace analysis by gas chromatography. J. Chromatogr. 122, 553, (1976). [17] KURÁŇ P., SOJÁK L. Environmental analysis of volatile organic compounds in water and sediment by gas chromatography. J. Chromatogr. 733(1-2), 119-141, (1996). [18] MCNALLY M.E., GROB R.L. Determination of the solubility limits of organic priority pollutants by gas chromatographic headspace analysis. J. Chromatogr. 260, 23-32, (1983). [19] Castello G., Gerbino T.C., Kanitz S. Gas chromatographic analysis of halocarbons in drinking water by headspace extraction and mixed column separation. J. Chromatogr. 247(2), 263, (1982). [20] MINDRUP R. Trace analysis of organics in water by gas chromatography. Pergamon Ser. Environ. Sci. 3, 325, (1980). [21] ROE V.D., LACY M.J., STUART J.D., ROBBINS G.A. Manual headspace method to analyze for the volatile aromatics of gasoline in groundwater and soil samples. Anal. Chem., 61(22), 2584, (1989). [22] BELARDI RG, PAWLISZYN J. The application of chemically modified fused silica fibers in the extraction of organics from water matrix samples and their rapid transfer to capillary columns. Water Qual. Res. J. Can. 24, 179, (1989). [23] ARTHUR C.L., PRATT K., MOTLAGH S., PAWLISZYN J. Environmental analysis of organic compounds in water using solid phase micro extraction. J. of High Resolution Chromatogr. 15(11), 741, (1992). [24] CHAI M., ARTHUR C.L., PAWLISZYN J., BELARDI R.P., PRATT K.F. Determination of volatile chlorinated hydrocarbons in air and water with solid-phase microextraction Analyst, 118, 150, (1993). [25] ARTHUR C.L., CHAI M., PAWLISZYN J. Solventless injection technique for microcolumn separations. J. Microcol. Sep. 5(11), 51, (1993). [26] PAGE B.D., LACROIX G. Application of solid-phase microextraction to the headspace gas chromatographic analysis of halogenated volatiles in selected foods. J. Chromatogr., 648(1), 199, (1993). [27] NIRI V.H., BRAGG L., PAWLISZYN J. Fast analysis of volatile organic compounds and disinfection by-products in drinking water using solid-phase microextraction–GC/time- of-flight mass spectrometry. J. Chromatogr. 1201, 222, (2008). [28] EICHELBERGER J.W., BUDDE W.L. Method 524.2 Measurement of purgeable compounds in water by capillary column gas chromatography/mass spektrometry.US EPA, Cincinnati, Ohio, (1989). [29] NILSSON T., PELUSIO F., LARSEN B., MONTANRELLA L., FACCHETTI S., MADSEN J.Ø. An evaluation of solid-phase Microextraction for analysis of volatile organic compounds in drinking water. J. High. Resol. Chromatogr. 18(10), 617, (1995). [30] HAGENMAIER H., WERNER G., JÄGER W., Quantitative Determination of Volatile Halogen Hydrocarbons in Water Samples by Capillary Gas Chromatography and electron capture detector. Z. Wasser Abwasser Forsch. 15, 195, (1982). [31] MEHRAN M.F., SLIFKER R.A., COOPER W.J. A simplified liquid-liquid extraction method for analysis of trihalomethanes in drinking water. J. Chromatogr. Sci. 22, 241, (1984). http://pubs.acs.org/doi/abs/10.1021/ac60349a001 http://pubs.acs.org/doi/abs/10.1021/ac60349a001 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44B861M-P7&_user=10&_coverDate=09/21/1977&_rdoc=8&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235248%231977%23998609997%23269982%23FLP%23display%23Volume)&_cdi=5248&_sort=d&_docanchor=&_ct=24&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4337dcdad23cb9cddc039decafefe920&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44B861M-P7&_user=10&_coverDate=09/21/1977&_rdoc=8&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235248%231977%23998609997%23269982%23FLP%23display%23Volume)&_cdi=5248&_sort=d&_docanchor=&_ct=24&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4337dcdad23cb9cddc039decafefe920&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44B861M-P7&_user=10&_coverDate=09/21/1977&_rdoc=8&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235248%231977%23998609997%23269982%23FLP%23display%23Volume)&_cdi=5248&_sort=d&_docanchor=&_ct=24&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4337dcdad23cb9cddc039decafefe920&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44B861M-P7&_user=10&_coverDate=09/21/1977&_rdoc=8&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235248%231977%23998609997%23269982%23FLP%23display%23Volume)&_cdi=5248&_sort=d&_docanchor=&_ct=24&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4337dcdad23cb9cddc039decafefe920&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44B861M-P7&_user=10&_coverDate=09/21/1977&_rdoc=8&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235248%231977%23998609997%23269982%23FLP%23display%23Volume)&_cdi=5248&_sort=d&_docanchor=&_ct=24&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4337dcdad23cb9cddc039decafefe920&searchtype=a http://pubs.acs.org/doi/abs/10.1021/ac50014a036 http://pubs.acs.org/doi/abs/10.1021/ac50014a036 http://pubs.acs.org/doi/abs/10.1021/es60140a016 http://pubs.acs.org/doi/abs/10.1021/es60140a016 http://pubs.acs.org/doi/abs/10.1021/es60140a016 http://pubs.acs.org/doi/abs/10.1021/ac50047a047 http://pubs.acs.org/doi/abs/10.1021/ac50047a047 http://pubs.acs.org/doi/abs/10.1021/ac50047a047 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44Y41RT-RB&_user=10&_coverDate=07/07/1976&_alid=1601279525&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_st=13&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=da4d00011324fd219b53bfc131c91de9&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44Y41RT-RB&_user=10&_coverDate=07/07/1976&_alid=1601279525&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_st=13&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=da4d00011324fd219b53bfc131c91de9&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44Y41RT-RB&_user=10&_coverDate=07/07/1976&_alid=1601279525&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_st=13&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=da4d00011324fd219b53bfc131c91de9&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-B&_user=10&_coverDate=05/10/1996&_alid=1601273876&_rdoc=5&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=975c8fad097a1072e34ca03c154e6cf6&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-B&_user=10&_coverDate=05/10/1996&_alid=1601273876&_rdoc=5&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=975c8fad097a1072e34ca03c154e6cf6&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-B&_user=10&_coverDate=05/10/1996&_alid=1601273876&_rdoc=5&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=975c8fad097a1072e34ca03c154e6cf6&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44WCY84-3&_user=10&_coverDate=12/31/1983&_alid=1601273876&_rdoc=16&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3c60028002e825677d5c635e405bfdaf&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44WCY84-3&_user=10&_coverDate=12/31/1983&_alid=1601273876&_rdoc=16&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3c60028002e825677d5c635e405bfdaf&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44WCY84-3&_user=10&_coverDate=12/31/1983&_alid=1601273876&_rdoc=16&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3c60028002e825677d5c635e405bfdaf&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44WCY84-3&_user=10&_coverDate=12/31/1983&_alid=1601273876&_rdoc=16&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3c60028002e825677d5c635e405bfdaf&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-453BVY0-7&_user=10&_coverDate=10/01/1982&_alid=1601273876&_rdoc=14&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=39e825e832a4b6d6779274471446a036&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-453BVY0-7&_user=10&_coverDate=10/01/1982&_alid=1601273876&_rdoc=14&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=39e825e832a4b6d6779274471446a036&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-453BVY0-7&_user=10&_coverDate=10/01/1982&_alid=1601273876&_rdoc=14&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=39e825e832a4b6d6779274471446a036&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-453BVY0-7&_user=10&_coverDate=10/01/1982&_alid=1601273876&_rdoc=14&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=41&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=39e825e832a4b6d6779274471446a036&searchtype=a http://onlinelibrary.wiley.com/doi/10.1002/jhrc.v15:11/issuetoc http://xlink.rsc.org/?DOI=AN9931801501 http://xlink.rsc.org/?DOI=AN9931801501 http://xlink.rsc.org/?DOI=AN9931801501 http://onlinelibrary.wiley.com/doi/10.1002/mcs.1220050108/abstract http://onlinelibrary.wiley.com/doi/10.1002/mcs.1220050108/abstract http://onlinelibrary.wiley.com/doi/10.1002/mcs.1220050108/abstract http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44CPWJH-PH&_user=10&_coverDate=10/01/1993&_alid=1605190996&_rdoc=1&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=1&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fc9a902c2cf675fae17776802039cdb8&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44CPWJH-PH&_user=10&_coverDate=10/01/1993&_alid=1605190996&_rdoc=1&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=1&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fc9a902c2cf675fae17776802039cdb8&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44CPWJH-PH&_user=10&_coverDate=10/01/1993&_alid=1605190996&_rdoc=1&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=1&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fc9a902c2cf675fae17776802039cdb8&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-44CPWJH-PH&_user=10&_coverDate=10/01/1993&_alid=1605190996&_rdoc=1&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_sort=r&_st=13&_docanchor=&view=c&_ct=1&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fc9a902c2cf675fae17776802039cdb8&searchtype=a http://www.sciencedirect.com/science/journal/00219673 http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235248%232008%23987989997%23694831%23FLA%23&_cdi=5248&_pubType=J&view=c&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=42496118a982b8c8c87407c2e1571bbc Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel MareUniversity - Suceava Volume XI, Issue 1 – 2012 38 [32] RICHARD J.J., JUNK G.A. Liquid extraction for rapid determination of halomethanes in water. J. AWWA 69, 22, (1977). [33] VARMA M.M., SIDDIQUE M.R., DOTY K.T., MACHIS A. Analysis of trihalomethanes in aqueous solutions: A comparative study. J. AWWA 71, 389, (1979). [34] BIZIUK M., PRZYJAZNY A. Methods of isolation and determination of volatile organohalogen compounds in natural and treated waters. J. of Chromatogr. 733(1-2), 417, (1996). [35] WEIL L., JANDIK J., EICHELSDÖRFER D. Organic halogenated compounds in swimmingpool water, I. Determination of volatile halogenated hydrocarbons. Z. Wasser Abwasser Forsch. 13, 141, (1980). [36] TRUSSELL A.R., UMPHRES M.D., LEONG L.Y., TRUSSELL R.R. Precise analysis of trihalomethanes. J. AWWA 71, 385, (1979). [37] PERUZII P, CURSI V, GRIFFINI V. Application of capillary gas chromatography with electron capture detection and split- splitless injection to the evaluation of volatile halogenated hydrocarbon removal using hydrogen peroxide after break-point chlorination in drinking water treatment. J. High. Resol. Chromatogr. 8, 450, (1985). [38] EKLUND G., JOSEFSSON B., ROOS C. Determination of volatile halogenated hydrocarbons in tap water, seawater and industrial effluents by glass capillary gas chromatography and electron capture detection. J. High. Resol. Chromatogr. 1, 34, (1978). [39] NORIN H., RENBERG L. Determination of trihalomethanes (THM) in water using high efficiency solvent extraction. Water Research 14(10), 1397, (1980). [40] RENSBURG J.F.J., HUYSSTEEN J.J., HASSETT A.J. A semi-automated technique for the routine analysis of volatile organohalogens in water purification processes. Water Research 12(2), 127, (1978). [41] RENSBURG J.F.J., HASSETT A.J. A low- volume liquid-liquid extraction technique. J. High. Resol. Chromatogr. 5(10), 574, 1982. [42] MIEURE J.P. A Rapid and Sensitive Method for Determining Volatile Organohalides in Water. J. AWWA 69, 60, (1977). [43] REUNANEN M., KRONELD R. Determination of volatile halocarbons in raw and drinking water, human serum, and urine by electron capture GC. J. Chromatogr. Sci. 20(10), 449, (1980). [44] DRESSMAN R.C., STEVENS A.A., FAIR J., SMITH B. Comparison of methods for determination of trihalomethanes in drinking water. J. AWWA 71, 392, (1979). [45] SHOTTMEISTER R.C., ENGERVALD W. Einige Aspekte der Isolierung und Anreicherung flüchtiger organischer Mikroverunreinigungen aus Wasser. Acta Hydrochim. Hydrobiol. 9(5), 479, (1981). [46] OTSON R., WILLIAMS D.T., BOTHWELL P.D. A comparison of dynamic and static head space and solvent extraction techniques for the determination of trihalomethanes in water. Environ. Sci. Technol. 13(8), 936, (1979). [47] HRIVŇÁK J. Solvent thin layer separator for microextraction of water. Anal. Chem. 57(11), 2159, (1985). [48] HUTCHINSON T.C., HELLEBUST J.A., MACKAY D., MASCARENKAS R.A., SHIN W.Y. The Correlation of the Toxicity to Algae of Hydrocarbons and Halogenated Hydrocarbons in the Aquatic Environment, edited by B.H. Afghan and D. Mackay, Plenum Press, p. 581, (1978). [49] BANERJEE S. Solubility of organic mixtures in water. Environ. Sci. Technol. 18(8), 587, (1984). [50] CONNOR M.S. Comparison of the carcinogenic risks from fish versus groundwater contamination by organic compounds. Environ. Sci. Technol. 18(8), 628, (1984). http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-14&_user=10&_coverDate=05/10/1996&_alid=1606348776&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bdcca2b0a2c928ea3d636edad351a2e0&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-14&_user=10&_coverDate=05/10/1996&_alid=1606348776&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bdcca2b0a2c928ea3d636edad351a2e0&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-14&_user=10&_coverDate=05/10/1996&_alid=1606348776&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bdcca2b0a2c928ea3d636edad351a2e0&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TG8-3VJRR06-14&_user=10&_coverDate=05/10/1996&_alid=1606348776&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5248&_docanchor=&view=c&_ct=2&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bdcca2b0a2c928ea3d636edad351a2e0&searchtype=a http://onlinelibrary.wiley.com/doi/10.1002/jhrc.1240080819/abstract http://onlinelibrary.wiley.com/doi/10.1002/jhrc.1240080819/abstract http://onlinelibrary.wiley.com/doi/10.1002/jhrc.1240080819/abstract http://onlinelibrary.wiley.com/doi/10.1002/jhrc.1240080819/abstract http://onlinelibrary.wiley.com/doi/10.1002/jhrc.1240080819/abstract http://onlinelibrary.wiley.com/doi/10.1002/jhrc.1240080819/abstract http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48CFTKS-1B3&_user=8157715&_coverDate=12/31/1980&_rdoc=3&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231980%23999859989%23419148%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=34&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=36813db5284183a543b4019e16f92640&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48CFTKS-1B3&_user=8157715&_coverDate=12/31/1980&_rdoc=3&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231980%23999859989%23419148%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=34&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=36813db5284183a543b4019e16f92640&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48CFTKS-1B3&_user=8157715&_coverDate=12/31/1980&_rdoc=3&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231980%23999859989%23419148%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=34&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=36813db5284183a543b4019e16f92640&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48C77J9-JS&_user=8157715&_coverDate=12/31/1978&_rdoc=6&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231978%23999879997%23418197%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=11&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=71d6f4f3980eb561d32c0f14d1b5722e&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48C77J9-JS&_user=8157715&_coverDate=12/31/1978&_rdoc=6&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231978%23999879997%23418197%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=11&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=71d6f4f3980eb561d32c0f14d1b5722e&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48C77J9-JS&_user=8157715&_coverDate=12/31/1978&_rdoc=6&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231978%23999879997%23418197%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=11&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=71d6f4f3980eb561d32c0f14d1b5722e&searchtype=a http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V73-48C77J9-JS&_user=8157715&_coverDate=12/31/1978&_rdoc=6&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%235831%231978%23999879997%23418197%23FLP%23display%23Volume)&_cdi=5831&_sort=d&_docanchor=&_ct=11&_acct=C000058966&_version=1&_urlVersion=0&_userid=8157715&md5=71d6f4f3980eb561d32c0f14d1b5722e&searchtype=a http://pubs.acs.org/doi/abs/10.1021/es60156a007 http://pubs.acs.org/doi/abs/10.1021/es60156a007 http://pubs.acs.org/doi/abs/10.1021/es60156a007 http://pubs.acs.org/doi/abs/10.1021/es00126a012 http://pubs.acs.org/doi/abs/10.1021/es00126a012 http://pubs.acs.org/doi/abs/10.1021/es00126a012 http://pubs.acs.org/doi/abs/10.1021/es00126a012