ANALYTICAL APPROACH
Malodorous Components in DrinKing k t e i
George Preti' Monell Chemical Senses Center 3500 Market St.
Philadelphia, PA 19104
Thomas S. Gittelman, Paul B. Staudte, and Preston Luitweiler Philadelphia Suburban Water Company 762 Lancaster Ave.
Bryn Mawr, PA 19010
Odors originating from biological or industrial sources are likely to come from a complex mixture of volatiles and other compounds. In many instances, the components imparting the characteristic odor to a mixture may be only minor ingredients. To identifjr the components of a complex mixture the analytical or organic chemist has a n impressive array of i n s t r u m e n t a t i o n from which t o choose. However, in problems involving malodor identification, it is often useful to allow the nose to guide the 'Also affiliated with Department of Dermatology, School of Medicine, The University of Pennsylvania, Philadelphia, PA 19104
0003-2700/93/0365-699A/$04.00/0 0 1993 American Chemical Society
analytical effort (1-4) and let investigators use their sophisticated instrumentation to focus on the area(s) of the separated mixture where the offending odor(s) elute. The technique often used to determine the identity of a n odor involves t h e organoleptic evaluation of a chromatographic eluant (called smell chromatography) (4, 5). In this technique continuous olfactory sampling of the gas chromatographic eluant is carried out to determine where components containing the odor of interest emerge. Naturally occurring metabolites, including geosmin (trans- 1,10- di methyl-trans-9 - decalol) and methylisoborneol (exo- 1,2,7,7-tetramethylbicyclo 42.2.1 I h e p t a n - 2 - 01; MIB) , generated by certain algae and actinomycetes (6),or certain synthetic compounds such as chlorinated phenols and amines often produce objectionable odors and tastes in public drinking water supplies (6-8). This can cause consumers to question the overall safety and quality of the water supply. Water utility companies routinely face a range of natural and synthetic odor-causing substances. ANALYTICAL CHEMISTRY, VOL. 65, NO. 15, AUGUST 1,1993
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ANALYTICAL APPROACH
Figure 1. Gas chromatogram and GUMS spectrum of the malodorous component.
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Peak A (relative retention index 5.04) is where the musty, nutty, sweet odor of interest elutes. Smell chromatography and ethyl pentanoate co-injection results (area B) are superimposed. The insert shows the mass spectrum of the unknown compound possessing the malodor of interest. Smell chromatography experiments were performed with a Perkin Elmer 990 gas chromatograph equipped with a 30 m x 0.53 mm (0.d.) Stabilwax column (1.O-pm thickness; Restek, Inc.). Sample analysis was performed under the following chromatographic conditions: injection at 30 "C, held for 10 min, and followed by a temperature program of 3 "C/min to 220 "C.MS conditions: 70 eV; ionization chamber, 150 "C.
Figure 2. Reaction of 1, 3-dioxanes auring electron impact. Occasionally, utility workers encounter more serious or unusual odors, as was the case recently at the Neshaminy water treatment plant, owned by the Philadelphia Suburban Water Company (PSW), in Middletown Township, Bucks County, PA. In January 1992 a commercial hazardous waste management facility, located 28 miles upstream of the Neshaminy plant, accepted six tanker loads (- 30,000 gal) of wastewater from a resin coatings manufacturer in Newark, NJ. The water was characterized as a nonhazardous, residual waste but contained substantial concentrations of various byproducts of the resin-manufacturing process. One of these byproducts proved to be a very potent odor-causing agent that had a bitter taste. Because this 700 A
material was not removed by treatment at the waste management facility or at the sewer plant to which t h e treated wastewater was discharged, the sewer plant and the Neshaminy Creek were subsequently contaminated with the odor-causing agent. Despite extraordinary efforts to remove the odor and to bring in water supplies from a l t e r n a t e sources, thousands of PSW customers experienced objectionable tastes and odors in their water for about two weeks. Identifying a n d quantifying t h e odor -causing agent became critical priorities.
Analytical approach Numerous samples of creek water were evaluated using a flavor profile
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analysis ( 9 ) ,by which a group of panelists at t h e PSW facility a t tempted to characterize the tastes and odors of the samples, which were distinctive but difficult to describe. Most panelists thought that the odor had a "sweet" chemical smell, and they also described it as smelling like latex paint and varnish or as having a nutty or woody odor. Within 72 h after t h e f i r s t reports of t h e odor problem, flavor profile analysis a n d a battery of other tests (e.g., EPA method 502.2 volatile organic screen and liquid-liquid extraction followed by GC analysis for phenols and aldehydes) were performed on creek samples containing the offending odor. None of the results from these tests could be used to correlate an odor with a contaminant. Closed - loop stripping (CLS) followed by thermal desorption onto a gas chromatograph/mass spectrome ter (10-12),a procedure routinely used by the PSW research laboratory to test raw and treated water supplies for low levels of volatile organic compounds, was performed on the odoriferous water samples. CLS involves recirculating helium through a heated, 1-L water sample and collecting volatile and semivolatile organic constituents on a n absorbent trap (see Reference 9, Method 6040). PSW workers have used CLS to analyze odor - causing compounds such as geosmin and MIB as well as other contaminants at trace levels. The CLS-GC/MS analyses of stream and wastewater samples produced a number of chromatographic components, not seen i n previous routine sampling, with mass spectra that could not be matched to any known compounds. The critical challenge was to identify which chromatographic peaks were responsible for the odor. For this task, scientists from the PSW facility collaborated with researchers a t t h e Monell Chemical Senses Center who have used smell chromatography a n d GC/MS analyses to identify characteristic human odors (3).This collaboration began about 10 days after the onset of the odor incident. Before the collaboration began, the sewer plant operators stopped accepting discharges from the waste management facility and dosed their plant with activated carbon. Odoriferous wastewater remaining at the waste management facility was shipped by truck for off-site disposal. Details of t h e Monell Center's smell chromatography procedurefor which no special adaptation of
Figure 3. Mass spectra of the five synthetic 2-alkyl-5,5-dimethyl-1,3-dioxancW. The spectra were generated on a Hewlett Packard 5970 mass-selective detector interfaced to a 5890 gas chromatograph equipped with a 30 m x 0.25 mm (0.d.) DB-1301 column (1.0-pm thickness; J&W Scientific). Detector conditions: 70 eV; ionization chamber, 220 "C. Mass spectrum of 2EDD in Figure 1 displays no M? -1 because of its low concentration in the water samples.
Figure 4. Simultaneous injection of synthesized 2EDD ar containing the target odor. Top: Portion of reconstructed ion chromatogram from a sample of Neshaminy Creek extract (Finnigan 4510) where putative 2EDD elutes. Bottom: Same area of the chromatogram when synthetic 2EDD and 2-isopropyl-5,5-dimethyl-l,3-dioxane are co-injected with the Neshaminy Creek extract. Note enhancement of putative 2EDD peak with synthetic 2EDD.
gas chromatographic equipment was needed-have been published (3). A hexane extract of t h e Neshaminy Creek water was used for the smell chromatography e x p e r i m e n t s to identify the area of the chromatogram where the likely odorous candi-
date emerged (Figure 1).After the retention time of the putative offending odor (relative to a series of n-acid ethyl esters) (13)was determined, mass spectra of the components eluting at the same relative retention time in t h e GC/MS system were
carefully examined. One compound had a mass spectrum (Figure 1)that closely matched the spectra of two of t h e unknown compounds t h a t the PSW laboratory had found in Samples exhibiting the odor. By this time (- 20 days since the odor was noticed), the PSW facility had obtained facts about the waste t h a t caused the incident. Using information about t h e principal reagents present in t h e original resin-manufacturing process, re searchers attempted to interpret the mass spectrum of the unknown compound. Their work led them to believe that two of the unknown compounds were 5 , 5 - d i m e t h y l - 1 - 3 dioxanes and t h a t they could have been made during resin formation by ring-closure reactions of neopentyl glycol with different aldehyde contaminants in the presence of trace acid. The class of 1,3-dioxanes is composed of six-member rings with an oxygen atom at the one and three positions. Under electron impact conditions these compounds readily lose a hydrogen from the two position (see Figure 2); consequently, the parent ion is generally not present. Instead, t h e highest molecular weight ion, usually present in low abundance, is M$-l. In addition, a characteristic fragment ion is seen a t m/z = 115 in each compound as a result of the loss
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ANALYTICAL APPROACH of the alkyl group a t the two position. Other salient features of the mass spectra appear to derive from dissociation of the ring structure. PSW personnel synthesized five different 5,5-dimethyl- 1,3-dioxanes by reacting acetaldehyde, propanal, n-butanal, isobutanal, and n-pentanal with neopentyl glycol (1, 14). The compounds formed and their corresponding mass spectra are shown in Figure 3. Odor comparisons, smell chromatography, and GC/MS analyses performed independently in the Monell and PSW laboratories showed that 2-ethyl-5,5-dimethyl- 1,3-dioxane (2EDD) was the predominant odorcausing agent in the waste associated with the incident. This finding was further confirmed by simultaneous injection of a Neshaminy creek extract containing the target odorcausing component and a mixture of synthetic BEDD and 2-isopropyl-5,5dimethyl- 1,3-dioxane. This led to an enhancement of the suspect peak in the reconstructed ion chromatogram (Figure 4). PSW scientists detected BEDD in samples of raw waste and stream water (trace amounts) as well as in effluents from the waste management facility, the sewer plant, and the treated drinking water from the Neshaminy plant. Identification and synthesis of 2EDD linked the problem irrefutably to the waste management facility and supported emergency action by P S W a n d sewer plant personnel. In addition, t h e identification of 2EDD resulted in an analysis of standards for quantitation of the observed peaks and the development of a very sensitive, selective ion-monitoring mode of analysis that could be used to detect the compound and provide reasonable quantitation at low part-per-trillion levels. Estimates of BEDD concentrations during the height of the incident, based on comparisons of water samples with measured concentrations of the synthetic 2EDD, were as follows: wastewater from the resin coatings manufacturer, 950 ppb; effluent from the sewer plant, 10 ppb; water from the west branch of the Neshaminy Creek (- 300 ft downstream from the sewer plant), 5 ppb; water from the Neshaminy plant intake, 0.04 ppb; and drinking water treated by the Neshaminy plant, 0.02 ppb. The threshold odor level for 2EDD in water appears to be - 0.010 ppb (w/vol). In the aftermath of the incident, 702 A
the PSW facility, sewer plant operators, and regulatory agencies have required corrective measures a t the waste management facility, which accepts only a restricted l i s t of wastes for treatment and operates under the close scrutiny of the PSW facility and the sewer plant operators. A program of routine odor evaluations has been implemented, and chemical testing has been expanded. These steps represent fundamental operational changes in t h e waste management facility to ensure that this type of incident will not be repeated. Identifying BEDD as t h e odorcausing agent in this incident demonstrates the value of applying specialized analytical resources and organoleptic evaluations to problems in the field of water treatment. Specifically, using the nose to direct the investigators can be crucial in picking the odorous “needle” from the proverbial “haystack” of complex mixtures of organic compounds. References (1) McGorrin, R. J.; Pofabl, T. R.; Croasmun, W. R. A n a l . Chem. 1987, 59, 1109 A. (2) Sevenants, M. R.; Sanders, R. A. Anal.
Ckem. 1984,56,293 A. (3) Zeng, X-N.; Leyden, J. J.; Lawley, H. J.; Sawano, K.; Nohara, I.; Preti, G. J. Chem. Ecol. 1991, 17, 1469. (4) Ramstad, T.; Walker, J. S. Analyst 1992, 117, 1361. (5) Marin, A. B.; Acree, T. E.; Bamard, J. Ckem. Senses 1988, 13,435. (6) Cross, T. J. Appl. Bacterial. 1981, 50, 397. ( 7 ) Identification and Treatment of Tastes and Odors in Drinking Water, Mallevialle, J.; Suffet, I. H., Eds.; American Water Works Association Research Foundation: Denver, CO, 1987. (8) Lalezary, S.; Pirbazari, M.; McGuire, M. J. I. A m . Water Works Assoc. 1986. 78(a),*62. ( 9 ) Standard Methods for the Examination of
Water and Wastewater. Fronson, M.A.H., Ed.; American Public Health Association, American Water Works Association, and Water Environment Federation: Baltimore, MD, 1992; Sect. 2170B. (10) McGuire, M. J.; Hwang, C . J.; Krasner, S. W.; Izaguirre, G. J. A m . Water Works Assoc. 1981, 73, 530. ( 1 1 ) Hwang, C . J.; Krasner, S. W.; McGuire, M. J.; Moylan, M. S.; Dale, M. S. Environ. Sci. Technol. 1984, 18, 535. (12) Staudte, P. B.; Yohe, T. L. In Proceedings of the American Water Works Association Water Quality Technology Conference; American Water Works Association: Denver, CO, 1989. (13) van den Dool, H.; Kratz, P. D. J. Chromatogr. 1963, 11, 463. (14) Noller, C. R. Chemistry of Organic Compounds, 3rd ed.; W. B. Saunders: Philadelphia, 1965; pp. 820-21.
George Preti f a r left) received a R.S. degree in chemistyfiom the Polytechnic Institute of Brooklyn in 1966 and a Ph.D. in organic chemistryfrom the Massachusetts Institute of Technology in 1971. That same year, he joined the Monell Chemical Senses Center in Philadelphia. He is also an adjunct associate professor in the Department of Dermatology, School of Medicine at The University of Pennsylvania. His research centers on the structure of human odors, the use of odors as chemical signals that influence reproductive endocrinology, and the use of diagnostic tools to determine normal and abnormal conditions. Thomas S. Gittelman (secondfiom left) is a research chemist with the Philadelphia Suburban Water Company, where his research has focused on the identification and treatment of organoleptic chemicals in drinking water. He graduated from The Pennsylvania State University in 1972 with a B.S. degree and from Drexel University in 1978 with an M.S. degree. Paul B. Staudte (thirdfiom left) is a research chemist with the Philadelphia Suburban Water Company, where he is involved in the development and application of analytical methods. He is a 1970graduate of Drexel University with a B.S. degree in chemistry. Preston Luitweiler (far right) is manager of Research and Environmental Afairs at the Philadelphia Suburban Water Company. He received B.S. and M.S. degrees fiom Drexel University and is a registered professional engineer.
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