Environ. Sci. Technol. 1996, 30, 453-462
A Case History of Contamination by Polychloro-1,3-butadiene Congeners D. BOTTA,* E. DANCELLI, AND E. MANTICA Department of Industrial Chemistry and Chemical Engineering, Polytechnic of Milan, Piazza Leonardo da Vinci no. 32, 20133 Milan, Italy
Recently in Lombardia, Italy, a water contamination by industrial wastes was discovered in an area where an uncontrolled industrial development had taken place. The subject of this paper is a case history of pollution by polychloro-1,3-butadiene congeners, a class of 35 volatile or semivolatile chlorinated compounds still in the presence of other compounds arising from a different source. By comparison of a sample taken from the bottom fraction of a rectification column for the production of tetrachloroethene with the carbon disulfide extract of a water sample collected from a well of the municipal water supply of Milan, the source of pollutants was inferred. The extent of pollution was monitored by liquid-liquid microextraction of the water of 24 wells sited in the north, along the prevailing direction of the movement of the underground water, using hexachloro-1,3butadiene as a marker. The uncertainty of the normative now in force in the assessment of the risk connected with the occurrence of these compounds in drinking water is also discussed.
Introduction The presence of polychloro-1,3-butadiene congeners in the aquatic environment has been observed worldwide in surface- and groundwater, treated and wastewater, sediments of streams, and aquatic organisms. An EEC study with well-documented reports (1) has surveyed a number of areas where this kind of contamination was observed. Very little is known about toxic effects of trichloro-, tetrachloro-, and pentachloro-1,3-butadienes, as very often the individual isomers with well-defined structure and purity were not available. In the literature, we could not find reliable data on the toxicity of pentachloro-1,3butadienes, even though they had been used as pesticides. Some information about toxic effects of trichloro- and tetrachloro-1,3-butadienes has been reported in papers published in the ex-USSR (2-7), but they are not easy to attain. Because of its unusually high toxicity, persistence, and potential for bioaccumulation in several organisms, hexachloro-1,3-butadiene is considered by the U.S. EPA as a priority pollutant to be monitored and controlled (8) and by EEC as a contaminant to be included on the black list.
0013-936X/96/0930-0453$12.00/0
1996 American Chemical Society
Recently, for hexachloro-1,3-butadiene in drinking water, a guideline value of 0.6 µg/L has been set by WHO (9). From the examination of the chemical literature (10, 11) we could realize that polychloro-1,3-butadienes are never intentionally manufactured. They are formed, together with a large variety of chlorinated compounds, through the chlorination of raw C1-C5 hydrocarbons for the production of volatile chlorinated solvents. The reactions occurring during these processes are different, being dependent on the chemical properties of the utilized raw materials (saturated hydrocarbons, ethene, partially chlorinated compounds), on the chosen working conditions, and on the desired products. During the repeated distillation of the solvent, many complex chlorinated derivatives (polychlorobutadienes, polychlorobenzenes, polychlorostyrenes, polychlorocyclopentadienes, polychlorohexadienes, and so on) are accumulating as a bottom fraction. Polychlorobutadienes are always present as unwanted byproducts and formed as relatively small quantities (up to 5% and more of hexachlorobutadiene in the chlorolysis process of 1,2dichloroethane for the production of carbon tetrachloride and tetrachloroethene), but, because of the huge production of volatile chlorinated solvents, the amounts of polychlorobutadienes resulting from the different processes are relevant. Due to a lack of any significant application of this class of products, except for 2-chloro-1,3-butadiene and hexachloro-1,3-butadiene, serious problems of disposal have arisen; in fact, they can only partially be reused, and the remains should be disposed in such a way to prevent any environmental risk. Recently, in Lombardia, Italy, we have been involved in an investigation into some sites contaminated by industrial wastes. At the beginning, we had to identify the organic compounds responsible for the “chemical smell”, which the users of the drinking water distributed by the waterworks named Vialba and Salemi of Milan water supply and, before them, the inhabitants of Bollate and Novate Milanese, two municipalities located upstream, had often complained about. By examining the preliminary analytical data, we found that, among a large variety of pollutants, the polychloro-1,3-butadiene congeners had a relevant role in deteriorating the water quality. This class of compounds comprises 35 members: three monochloro, nine dichloro, 10 trichloro, nine tetrachloro, three pentachloro, and one hexachloro derivatives. This aim of paper is to elucidate the way we could find the source of this contamination.
Experimental Section Sampling. The sample collection from the different wells was only performed after water had run for some minutes in order to eliminate the stagnant water and get a truly representative sample of the aquifer. The bottle was repetitively rinsed with the water to be sampled and afterwards filled until overflow to prevent the presence of residual empty volumes and the loss of volatile compounds at the moment of opening the bottles. The water samples were stored at 4 °C until their use, always within 48-72 h.
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Reagents. The following reagents were used: n-Pentane RS Carlo Erba for ecology; dichloromethane RS Carlo Erba for pesticide analysis; carbon disulfide RS Carlo Erba for spectroscopy; ethanol 95% RS Carlo Erba for spectroscopy; hexachlorocyclopentadiene 98% (GC) Aldrich Chemie; hexachloro-1,3-butadiene 98% Merck for infrared spectroscopy; hydrogen chloride 35% CODEX Carlo Erba in a glass bottle; sodium hydroxide RP Carlo Erba in a glass bottle; anhydrous granular sodium sulfate for residue analysis; and halogenated compound-free mineral water. Glassware. The following glassware was used: tared brown bottles, capacity 1 and 1.15 L with glass stoppers; microseparators according to DIN 38407 (12); graduated glass vials of 1 mL with ground glass stoppers for measuring and storing the pentane extracts; and amber glass screw capped vials of 4.5 mL, with PTFE-coated silicon rubber septa. Closed Loop Stripping and Charcoal Filter Extraction with Carbon Disulfide (CLSA According to Grob (13)). A water sample of 1 L was held at 50 °C, and the headspace gas (about 150 mL) was recirculated by means of a bellow pump for half an hour and forced to pass through a filter containing 1.5 mg of fine pulverized charcoal, which was kept at 70 °C, to prevent water condensation. The filter was then eluted with two aliquots (15 + 10 µL) of carbon disulfide, and the resulting solution was stored in a special vial with a PTFE stopper or in a sealed glass capillary until the analysis. Extraction with Pentane of a Water Sample of 50 mL. For this operation a graduated Erlenmeyer flask of 50 mL filled with water to the mark was typically used; 1 mL of pentane was added and the flask shaken by hand to promote the equilibrium between the two phases. After a few minutes, it was possible to withdraw by a syringe about 90% of the quantity of the added solvent, and then the pentane extract was injected into the gas chromatograph without any further treatment. Microextraction with n-Pentane of Water Samples of 0.5-1 L. Typically, a water sample of 0.5-1 L was extracted with 1-1.5 mL of n-pentane and vigorously shaken by hand or by a mechanical stirrer. After separation as complete as possible of the two layers, purified water was slowly added through the side tube of the microseparator until the extract had risen in the central tube. The pentane extract was then removed by syringe, dried on sodium sulfate, and stored in a glass vial for the subsequent gas chromatographic analysis using an electron capture detector. Due to the lower solvent/water ratio, in this case the pentane mean recovery was in the range of 30-40%. Gas Chromatographic Analysis. The experimental conditions utilized in the GC analyses of the pentane extracts from 50 mL and 1 L water samples were the following: Carlo Erba MEGA Model 5300 gas chromatograph; fused silica HP ULTRA2 capillary column coated with an immobilized methyl phenyl silicone rubber film, length 50 m, internal diameter 0.31 mm, film thickness 0.52 µm; carrier gas hydrogen (GC), flow rate 2.4 mL/min; 1 µL sample of pentane solution on-column injected at 35 °C, initial isothermal period of 2 min and then programmed temperature run from 35 to 200 °C at 4 °C/min, final isothermal period of 10 min; electron capture detector (ECD), detector temperature 300 °C, reference current 1 nA, pulse voltage 20 V, pulse width 0.1 µs; nitrogen auxiliary gas 35 mL/min.
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GC-MS Analysis. The working conditions used in the GC-MS analysis of the water sample collected at well no. 20 of the Salemi waterworks and of the sample from the bottom fraction of a tetrachloroethene rectification column were the following: HP GC-MS-DS Model 5985B; HP Model 5840A gas chromatograph, adapted for capillary columns, fused silica capillary column coated with a SE 54 methyl phenyl silicone rubber film, length 50 m, internal diameter 0.31 mm, film thickness 0.52 µm, helium carrier gas flow rate 2 mL/min. Splitless sample injection, injector temperature 250 °C, sample quantity 1.5 µL. Oven temperature at injection and for 2 min 30 °C and then a programmed temperature run at 4 °C/min to 275 °C, a final isothermal period of 30 min. GC-MS interface: the capillary column was connected by means of a buttconnector to a piece of fused silica capillary column (length 2 m, internal diameter 0.32 mm), persilanized, and permanently inserted into the ion source of the mass spectrometer. The temperature of the transfer line was maintained at 260 °C to avoid any condensation. Scan width 33-350 D, electron impact ion source, source temperature 200 °C, electron beam energy 70 eV. Choice of the Analytical Method. We used two methods for the treatment of water samples: closed loop stripping and elution of the analytes with carbon disulfide after their trapping on a charcoal filter and liquid-liquid extraction with n-pentane, employing an electron capture detector to enhance sensitivity and selectivity to halogenated compounds. The carbon disulfide extract after closed loop stripping was preferred for the GC-MS analysis, because of its larger enrichment factor. As mentioned previously, we utilized hexachloro-1,3-butadiene not only as a marker to trace the plume but also as a quantitative measure of this contamination. Due to lack of standards of the individual congeners, it was a simple and rapid method of evaluating the risk associated with the presence of several components (23 out of 35), although we were aware of the weakness of this choice. A procedure for quantitation of highly volatile halocarbons by liquid-liquid extraction with n-pentane was reported (12), suitable for surface and ground water, and proved to be reliable for halocarbons, mainly nonaromatic, whose boiling points lie between -20 and 180 °C at 1 atm. Having checked its applicability to our problem (the boiling point of hexachloro-1,3-butadiene is 212 °C), we preferred the internal standard instead of the external standard method used in the cited reference to get more reliable data, regardless the matrix variability. Hexachlorocyclopentadiene was chosen as internal standard, being a compound of sufficient purity available on the market and with a gas chromatographic behavior similar to the analyte to be determined. Even though it will be later listed among the byproducts of chlorinated solvent preparation, in the considered samples it was barely detectable and therefore unable to affect the quantitation of hexachloro-1,3-butadiene. Description of the Site. In order to localize the potential source of contamination, we planned a screening survey for polychloro-1,3-butadienes starting from the Salemi waterworks (wells M20, M19, and M17). Figure 1 shows the map of the public and private wells we considered representative to guarantee an adequate areal coverage; the capital letter before the number indicates the city or the town where the wells are sited. Along the way in the
FIGURE 1. Map of the sampled wells. The arrow indicates the prevailing direction of underground water.
northern direction in Novate Milanese samples were collected from wells N17, N4, N27, N28, N25, N30, and N26, distributed on the whole territory, to achieve a detailed picture of the conditions of the aquifer in this town, where all the supplied water needs to be treated by adsorption on active carbon. Obviously, the water samples for analysis had been collected ahead of the carbon towers. Farther in the north, in Bollate, we sampled wells B92, B101, B16, B3, B10, B15, and B13 spread from the west to the east of that territory. The wells B101, B3, and B10 are public, and the first of them is connected to a series of carbon adsorbers, whereas the waters of the remaining two are directly distributed. In the west-west-north of the town of Paderno Dugnano the public well P10, joined to a plant for treatment by active carbon and the only one suitable to be used for water supply, was sampled. In Senago the wells S16, S17, and a piezometer were sampled, all of them being located in the enclosure of the firm suspected to be responsible for
that contamination. Farther in the north of Senago we collected water samples from wells S15, S2, and S13. In Table 1, we have summarized some information useful for identifying the various investigated wells and for characterizing their behavior: well number, depth, and filter position when they were available. The water of the 24 sampled wells (1 L each) was subjected to liquid-liquid microextraction with n-pentane employing the electron capture detector, according to the procedure described in the Experimental Section. Results of the Analyses Performed on the Samples Collected from Well No. 20 of the Salemi Waterworks. Our analytical investigation began in Nov 1984 with the water samples taken from some wells of the Salemi waterworks and was pursued until 1990 with semiannual or annual samplings for monitoring possible variations in time of kind and concentrations of pollutants. At different times the wells 1, 2, 11, 16, 17, 19, and 20 of the same
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TABLE 1
TABLE 2
List of Sampled Wells and Their Characteristics
List of the Compounds Identified by GC-MS Analysis of the Water Sample Collected on June 11, 1987, from the Well M20 of Salemi Waterworks
well no.
well depth (m)
M17
98.48
M19
101.56
M20
102.45
N4 N17 N25 N26 N27 N28 N30
83.6 27 65 100 141.4 91.26
B3 B10 B13 B15 B16 B92 B101 P10 S2 S13 S15 S16 S17 Piez.
60.5 130 120 41.5 46 63.5 100 127 68 57 49.61 49 70 40
filter position (m) 46.1-49.85/52.7 - 56.80/60.1-61.6/ 63.6-65.7/67.5-69/71.1-74.1/ 76.05-80.55/84-86.1/95.6-97.5 47.5 - 50.5/52.5-54.01/56.51-58.02/ 60.02-64.55/69.01-72.73/79.06-80.52/ 82.46-87.02/94.03-98.59/99.09-100.62 45-55.62/61.55-66.05/67.5-72.0/ 73.2-74.72/75.08-78.12/84.41-88.22/ 94.25-100.28 50.5-55/63-75
46-52/65-68/70-77/94.5-95.5 90.8-91.8/95-97/106.5-108 20.31-26.33/30.58-38.08/50.53-52.73/ 67.25-81.36 38.35-59.95 51-65/80-90 /112.5-114/120.5-122 47-65 26-36 55-62/82-84/92.5-94 30-34/41-43/44-57/58-62/62-66
waterworks were sampled, but our particular attention was given to well 20, which was of major concern from the organoleptic point of view and the most contaminated according to our preliminary data. The condensed results of the GC-MS analysis are listed in Table 2, where some 30 peaks are numbered with their chemical names, molecular weights, and structural formulas. Parts of them were identified on the basis of their mass spectra by matching with the computer library after background subtraction. The remaining compounds could not be recognized as their signals were too small with respect to the background or not stored in the computer library. It is worth noticing that, in addition to the predictable contaminants like C2-chlorinated solvents and C7-C9aromatic compounds, there are the peaks corresponding to compounds meaningful for our investigation, being uncommon and typical byproducts of certain production processes. In Table 2, we can observe the presence of two cyclic ethers: 2-ethyl-5,5-dimethyl-1,3-dioxane (Table 2, peak 10) and 2-isopropyl-5,5-dimethyl-1,3-dioxane (Table 2, peak 13). They had proved to be responsible for the “chemical smell” of the water. The source of this pollution was found in a manufacturing plant of alkydic resins sited upstream, about 10 km far from Milan, in the north-northwest direction of underground water movement. A second group of contaminants was found, some chlorinated semivolatile compounds, though not derived from the same source. These substances were present in the water of well no. 20 of the Salemi waterworks and also in that of the other sampled wells, even though less abundantly. They were aromatic chloro derivatives like dichlorobenzenes, peaks 16 and 18 in Table 2, and polychlorinated derivatives belonging to a class of com-
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peak no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 20 21-24 25 26 27 30
name chloroform 1,1,1-trichloroethane benzene carbon tetrachloride trichloroethene toluene tetrachloroethene ethylbenzene m- + p-xylene o-xylene 2-ethyl-5,5-dimethyl-1,3-dioxane 3-ethyl-1-methylbenzene 1,3,5-trimethylbenzene 2-isopropyl-5,5-dimethyl-1,3dioxane 2-ethyl-1-methylbenzene 1,2,4-trimethylbenzene 1,4-dichlorobenzene 1,2-dichlorobenzene tetrachlorobutadiene bis(2-chloroisopropyl) ether tetrachlorobutadiene trans-1H-pentachlorobutadiene cis-1H-pentachlorobutadiene 1,2,4-trichlorobenzene (CS2 impurity) hexachlorobutadiene
mol wt
mol formula
118 132 78 152 130 92 164 106 106 106 144 120 120 158
CHCl3 CH3CCl3 C6H6 CCl4 C2HCl3 C7H8 C2Cl4 C8H10 C8H10 C8H10 C8H16O2 C9H12 C9H12 C9H18O2
120 120 146 146 190 170 190 224 224 180
C9H12 C9H12 C6H4Cl2 C6H4Cl2 C4H2Cl4 C6H12Cl2O C4H2Cl4 C4HCl5 C4HCl5 C6H3Cl3
258
C4Cl6
pounds, which are the subject of this paper, peaks 18, 2126, and 30. If the mass spectra of this group of substances are considered, the presence of compounds having molecular weights 190, 224, and 258 Da, respectively, can be recognized. They are compounds with a number of chloroatoms ranging from 4 to 6, as can be determined from the values of isotopic abundance of mass peaks M+, (M + 2)+, (M + 4)+, and (M + 6)+, to which the following molecular formulas have to be attributed:
C4H2Cl4 (190)
C4HCl5 (224)
C4Cl6 (258)
By calculating the possible number of cycles/or double bonds for these molecules, we arrived at four carbon atoms and two double bonds or cycles. If the presence of two double bonds is assumed, we infer the framework of butadiene with two possible isomers. Alternatively, we could write a cyclic olefinic compound:
By observing the features of mass spectra, we were induced to prefer the first of them. From mass spectra only the detailed structure of congeners is not achievable, but in Table 2 five peaks of different abundance were concluded to be tetrachlorobutadienes, two pentachlorobutadienes, and one hexachlorobutadiene. Being uncommon and surely persistent compounds in the environment, mainly in underground water, polychlorobutadienes were chosen as suitable markers for tracing the
FIGURE 2. Reconstructed plot of the total ion current produced from a sample of a bottom fraction of a rectification column of tetrachloroethene. For working conditions refer to GC-MS analysis in the Experimental Section. The numbers refer to Table 3.
contamination plume. Indeed, in a recently published paper (14), it has been observed that hexachloro-1,3butadiene, in anaerobic conditions, was not completely degraded; dechlorination took place, but it was carried out just to tetrachloro-1,3-butadiene. Study of a Sample of the Bottom Fraction from a Rectification Column of Tetrachloroethene. To verify the relationship between polychloro-1,3-butadiene and chlorinated solvents, we could achieve a sample of the bottom fraction from a rectification column of tetrachloroethene. The reconstructed plot of the total ion current after GC-MS analysis is reported in Figure 2, where two traces are shown with different attenuation factors to get a more detailed picture. The chromatographic peaks, belonging to different chemical classes and containing a variable number of halogen atoms (peaks 2-8), have been assigned on the basis of the data obtained from mass spectrometry. We could take advantage of the characteristic isotopic ratios of chlorine and bromine to attribute the number of halogen atoms to each fragment. Several aliphatic halo derivatives give molecular ion peaks that are hardly detectable, and the less abundant components, passing through the chromatographic column to the ion source, being more influenced by the instrumental background, produce unreliable data. The interpretation process enabled us to list in Table 3 the different chomatographic peaks numbered as in Figure 2. Only the chemical classes or the molecular formulas were assigned to the isomers not distinguishable by mass spectrometry. Among the polychlorobutadienes most interesting for our investigation, nine peaks of different abundance instead of 10 were found for trichlorobutadienes, 10 instead of nine for tetrachlorobutadienes, four instead of three for pentachlorobutadienes, and two peaks instead of one for a molecular weight of 258 and a molecular formula
of C4Cl6 (peaks 55 and 51). Due to the lack of standards, we could not yet decide if the additional congeners were cyclic olefins only on the basis of their mass spectra. The averaged ratios of the chromatographic peak abundance (calculated by their area values) of trichloro-, tetrachloro-, pentachloro-, and hexachloro-1,3-butadienes are 1:4:8:16. In the chromatogram of Figure 2, the peaks corresponding to monochloro- and dichloro-1,3-butadienes are not detectable as they, being more volatile than tetrachloroethene, are both amenable to go to the top of the rectifying column and, being much more reactive than those of higher molecular weight, preferably form more complex polymers and copolymers, usually remaining as pitched residues. We could also recognize the presence of a number of substances like chloroalkanes, chloroalkenes, chlorocyclodienes, chlorobenzenes, chlorostyrenes, and chloronaphthalenes. There are also compounds containing bromine atoms, like trichlorobromoethylene and pentachlorobromo1,3-butadiene, and presumably chlorinated derivatives of fulvene. It deals with a composite mixture of halogenated compounds with different molecular complexity and structure, whose most important components beyond hexachloro-1,3-butadiene are three pentachloro-1,3-butadienes, four tetrachloro-1,3-butadienes, hexachloroethane, and penta- and hexachlorobenzene. Mass Spectra of Polychloro-1,3-butadienes. As stated previously in the reconstructed chromatogram of the total ion current shown in Figure 2, 25 peaks were revealed to be polychlorobutadienes. For the subsequent discussion, it is worth displaying the mass spectra of some of them. Typical examples chosen among the most abundant peaks of tri-, tetra-, penta-, and hexachloro-1,3-butadienes are presented in Figure 3, where the remarkable similarity of the mass spectra in a given class of congeners is outstanding.
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TABLE 3
Identities of Peaks Numbered in Figure 2, Representing the Total Ion Chromatogram of the GC-MS Analysis of a Bottom Fraction from a Rectifiying Column of Tetrachloroethene peak no. 1 2 3 4 5 6 7 8-10 12 13 14 15-17 18 19 20 22 23 24 25 27 28 29 30 31 32 33 34 35 36 37-39 40 42 43 44 45 47 48 50 51 52 53 54 55 56 59-61 62 63 64 65 66 67 72 76, 78 79 80 81 82 88 93 96 97, 98, 100, 102, 103 107 108, 110 111, 115 112, 114 118 121 124 126 a
458
name
mol wt
mol formula
chloroform 1,1,2-trichloroethane tetrachloroethene 1,1,1,2-tetrachloroethane trichloromethylpropene 1,1,2,2-tetrachloroethane trichlorobutadiene trichlorobutadiene trichlorobromoethene trichlorobutenyne 1,2,3,3-tetrachloropropene trichlorobutadiene trichlorobutenyne trichlorobutadiene pentachloroethane trichlorobutadiene trichlorobutadiene tetrachlorobutadiene 1,3-dichlorobenzene trichlorobutadiene 1,4-dichlorobenzene tetrachlorobutadiene 1,2-dichlorobenzene tetrachlorobutadiene tetrachlorobutenyne pentachloropropene tetrachlorobutadiene tetrachlorobutene tetrachlorobutadiene hexachloroethane tetrachlorobutadiene pentachloropropene tetrachlorobutadiene pentachlorocyclobutene (?) tetrachlorobutadiene tetrachlorobutene 1,2,4-trichlorobenzene trans-1H-pentachloro-1,3-butadiene 2H-pentachloro-1,3-butadiene cis-1H-pentachloro-1,3-butadiene pentachlorobutene hexachlorocyclobutene (?) 1,2,3-trichlorobenzene hexachloro-1-propene pentachlorobutene hexachloro-1,3-butadiene pentachlorobutene hexachlorobutene pentachloro-1,3-cyclopentadiene bromopentachloro-1,3-butadiene hexachlorobutene 1,2,3,5-tetrachlorobenzene 1,2,4,5-tetrachlorobenzene hexachloro-1,3-cyclopentadiene 1,2,3,4-tetrachlorobenzene heptachlorobutene hexachlorocyclohexadiene NI pentachlorobenzene NI heptachlorocyclohexadiene octachlorocyclohexadiene hexachlorobenzene octachloro-1,4-cyclohexadiene NI heptachlorostyrene NI NI NI NI NI hexachloronaphtalene heptachloronaphtalene
118 132 164 166 158 166 156 156 208 154 178 156 154 156 200 156 156 190 146 156 146 190 146 190 188 212 190 192 190 234 190 212 190 224 190 192 180 224 224 224 226 258 180 246 226 258 226 260 236 302 260 214 214 270 214 294 284 248 248 282 318 352 282 352 308 342 308 330 342 376 354 332 366
CHCl3 C2H3Cl3 C2Cl4 C2H2Cl4 C4H5Cl3 C2H2Cl4 C4H3Cl3 C4H3Cl3 C2BrCl3 C4HCl3 C3H2Cl4 C4H3Cl3 C4HCl3 C4H3Cl3 C2HCl5 C4H3Cl3 C4H3Cl3 C4H2Cl4 C6H4Cl2 C4H3Cl3 C6H4Cl2 C4H2Cl4 C6H4Cl2 C4H2Cl4 C4Cl4 C3HCl5 C4H2Cl4 C4H4Cl4 C4H2Cl4 C2Cl6 C4H2Cl4 C3HCl5 C4H2Cl4 C4HCl5 C4H2Cl4 C4H4Cl4 C6H3Cl3 C4HCl5 C4HCl5 C4HCl5 C4H3Cl5 C4Cl6 C6H3Cl3 C3Cl6 C4H3Cl5 C4Cl6 C4H3Cl5 C4H2Cl6 C5HCl5 C4BrCl5 C4H2Cl6 C6H2Cl4 C6H2Cl4 C5Cl6 C6H2Cl4 C4HCl7 C6H2Cl6 C6HCl5 C6HCl5 C6Cl6 C6HCl7 C6Cl8 C6Cl6 C6Cl8 C8H2Cl6 C8HCl7 C8H2Cl6 C4H2Cl8 C8HCl7 C8Cl8 C9HCl7 C10H2Cl6 C10HCl7
NI ) not identified.
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FIGURE 3. Examples of mass spectra of tri-, tetra-, penta-, and hexachloro-1,3-butadiene.
FIGURE 4. Mass spectrum of 1,1,4,4-tetrachloro-1,3-butadiene (peak no. 35 in Table 3).
Only in the case of tetrachloro-1,3-butadienes can some differences be noticed. In the mass spectrum relative to the peak 35 in Figure 4 an isotopic cluster at 130, 132, 134, and 136 is suggestive of a fragment ion containing three chlorine atoms, C2HCl3. By comparison with the spectrum of a compound recently synthesized by us, the structure of 1,1,4,4-tetrachloro-1,3-butadiene has to be assigned. By examining the mass spectra shown in the above reported figures, it can be argued that the most significant fragmentation results from the loss of a chlorine radical or of a hydrogen chloride molecule, as it has been schematically represented in Figure 5. Pollution Conditions by Polychloro-1,3-butadienes of the Aquifer between Milan and Senago. By comparing the data resulting from analysis of a sample of the bottom fraction from the rectification column of tetrachloroethene with those obtained from the water samples from the wells of Salemi waterworks and particularly from well no. 20, we could better define the different classes of pollutants. It has been shown that in the bottom fraction from the rectification column of tetrachloroethene, beyond tetrachloro-1,3-butadienes, pentachloro-1,3-butadienes, and hexachloro-1,3-butadiene, whose presence in the water
from wells of Salemi waterworks had been reported, there were also trichloro-1,3-butadienes and that the abundance of the isomers for each class of compounds was quite high. Moreover, there was, albeit in smaller concentrations, a number of other chlorinated compounds of different classes. This information enabled us to put some hypotheses forward about the possible sources of pollution; it might be due to a poor disposal of wastes derived from the recovery either of exhausted trichloroethene, a solvent widely used in degreasing of metallic pieces, or of exhausted tetrachloroethene, commonly used in the dry cleaning of clothes. According to the commercial specifications, these solvents should contain less than 50 ppm (mg/kg) of residue, in which the polychloro-1,3-butadienes are surely present. If such a residue, because of ignorance or fraud, is illegally disposed, a risk for damage of water resources arises. Alternatively, it might be inferred that the presence in that area of an important chemical industry had over the years used huge amounts of halogenated solvents and spread in the subsurface the wastes from the manufacturing processes also containing the chlorinated compounds we were tracing. So far, we could not decide between the two possibilities, even if we were inclined to opt for the second one, since we had found beneath a big chemical firm the maximum concentration of the water pollutants. During this stage of our investigation the assessment of the pollution was performed by measuring the concentrations of hexachloro-1,3-butadiene in the water samples of the 24 above-mentioned wells. The reason for this working choice was the lack of suitable standards to be used for calculating the response factors of various polychloro-1,3butadiene congeners to ECD. We are now planning to prepare at least some of them. Hexachloro-1,3-butadiene is sold at a purity level of 98% (GC), acceptable for our purposes. Assessment of the Contamination by Polychloro-1,3butadienes. The wells located in the western areas of Novate Milanese and Bollate have proved to be the least
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FIGURE 5. Prevailing pathways of fragmentation of polychloro-1,3-butadiene congeners.
FIGURE 6. Graphical representation of the level of contamination of the different wells measured on the basis of hexachloro-1,3 butadiene concentration.
involved in the pollution of aquifers by polychloro-1,3butadienes, since the tracer concentrations of all of them resulted to be less than 10 ppt. Going to the east, the concentrations of pollutants tended to increase and the same occurred moving from the south to the north. The three wells of Salemi waterworks had an odd behavior with respect to what was generally observed farther in the north, the concentrations of hexachloro-1,3-butadiene were 40.6 ppt for the well M20, 31.9 ppt for M19, and 21.4 ppt for M17. The depths of the three wells are very similar, but the fluctuations of the values of pollutant concentrations from well to well inside the same area were due to the position and the number of their filters. If deeper water, usually less contaminated than the shallow one, is withdrawn, a dilution of the pollutants occurs. Moving farther to the
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north, the pollution remained high: 196.9 ppt for the piezometer and 155.5 ppt for the well S17, 70 m deep. The maximum level, 266.2 ppt, was measured for the well S16, 49 m deep. All of these three wells are sited in Senago, inside the enclosure of a chemical manufacturer. Therefore, we believe that just beneath this firm is the core of the contamination, and more work is needed to determine its exact location. Going on ahead a small distance (some hundred meters), the concentrations of hexachloro-1,3butadiene in water decrease quickly: 41.5 ppt for the well S15, 50 m deep, 20.2 ppt for the public well S2, 68 m deep, and 9.8 ppt for the well S13, 57 m deep. A graphical representation of contamination of the different wells is presented in Figure 6.
Conclusions Considering the industrial processes in which the polychloro-1,3-butadiene congeners are formed, we have drawn the conclusion that the manufacturing or the recovery of the widespread volatile chlorinated solvents (mainly trichloro- and tetrachloroethene) are responsible for the environmental diffusion of polychloro-1,3-butadienes. However, since the residual quantities of these congeners in both solvents are restricted to 50 ppm (50 g/ton), assuming that the products are marketed by reliable firms, we think that an accumulation stage had necessarily occurred. Possibly, high-boiling wastes containing polychloro-1,3butadienes together with other manufacturing residues from different sources had been improperly disposed, and after having contaminated the soil, they had reached the aquifer as a sink. In order to locate the source of pollution, we decided to trace the polychloro-1,3-butadienes as they are not ubiquitous contaminants and therefore meaningful to a limited number of manufacturing activities. We chose to monitor 24 public and private wells along the way between Milan and Senago, as sampling points of the aquifer, assuming hexachloro-1,3-butadiene as a tracer for the quantitative analyses. In this case, hexachloro-1,3-butadiene was the most abundant member of this class of compounds. Actually, the profiles of the bottom fractions from the rectification of the volatile chlorinated solvents vary in a wide range; in some cases, hexachloro-1,3butadiene is hardly detectable. Thus, following the variations of its concentration at the level of ppt (ng/L) over a distance of 7 km in a straight line, we could plot the plume of the contamination in the northern direction, along the prevailing path of the underground water, until the attainment of the maximum value of concentration of the tracer, beneath a chemical industry in Senago. During all this back way to the source of contamination, we met some difficulties due to the remarkable fluctuations of concentration of the tracer in waters of the different wells. These variations were only partially attributable to the distribution of the wells on territory; they were also dependent on depths of the wells and on position of the filters. Drawing waters from the cleaner inferior aquifer and mixing them with those from upper aquifer, a dilution takes place of the more seriously contaminated waters. We also met some analytical difficulties because of the presence of a number of interfering substances. As an example, in the case of two piezometers sited upstream and downstream, a pit was used in the past as a illegal landfill for large quantities of wastes from several manufacturing activities, so we could not employ our method of analysis and were forced to reject the obtained data because of their unreliability. Having determined the occurrence and the nature of pollution and located its source in a good approximation (because of the hostile attitude of the management of the firm, we could not ascertain whether the source of pollution was a facility for the production of chlorinated solvents or for their recovery), we must now face the problem of the toxicological meaning of the presence of these contaminants at such a low level with the aim to clarify whether soil remediation and water treatment needs to be put into action to remove their potential for detrimental effects on human health or only to consider the volatile solvents, spread on the whole territory.
In our opinion, halogenated compounds other than the volatile ones are not seriously enough considered to be linked to the public health. The higher-boiling halocarbons are always underestimated, as their analysis is more expensive and usually more time-consuming. Actually, they are often more harmful, owing their high environmental resistance, high toxicity, and greater potential for bioaccumulation. According to EEC regulations (EEC Directive no. 80/778) (15) concerning drinking water quality, the persistent chloroorganics are classified as pesticides and related products (parameter no. 55 for which a maximum admissible concentration, MAC, of 0.1 µg/L for individual compounds and of 0.5 µg/L for total are set). The parameter no. 55 of the above-mentioned directive is comprehensive for persistent organochlorinated insecticides, herbicides, fungicides, polychlorinated biphenyls (PCBs), and polychlorinated terphenyls (PCTs). The already mentioned limits are 300 times less than the MAC of 30 µg/L, the value accepted for the parameter no. 32 (including organohalogenated compounds not contained in the parameter no. 55) of the same normative for the volatile chlorinated solvents. From the concentration levels of hexachloro-1,3-butadiene found during our investigation on waters of the wells in the area between Milan and Senago, it can be observed that a quarter of the sampled wells exceeds the limit of 100 ppt set by regulation for individual component and of 500 ppt for total. On the other part, drawing a conclusion, we must keep in mind that while we are aware at least partially of the toxicological properties of hexachloro-1,3-butadiene, very little is known about the possible effects of the others congeners, whose chromatographic peaks have also relevant area values, despite their penalized response factors to ECD. It cannot in principle be excluded that some of the trichloro-, tetrachloro-, and pentachloro-1,3-butadiene isomers might be more toxic than hexachloro-1,3-butadiene. The chlorinecontaining molecular fragments which have been identified to date as having genotoxic activity (16) are present also in congeners other than hexachloro-1,3-butadiene. We think that the contamination of the aquifer investigated by us is certainly a source of concern for human health and should be checked as soon as possible for a definitive location of its source and for its removal.
Acknowledgments We are very indebted to Mr. Lucio Ogliani for his technical assistance during the whole work.
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Received for review March 7, 1995. Revised manuscript received September 15, 1995. Accepted September 20, 1995.X ES9501575 X
Abstract published in Advance ACS Abstracts, December 1, 1995.
