ANALYTICAL APPROACH
Letting the Nose Lead the Way Malodorous Components in Drinking Water
1
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 m a n y i n stances, t h e components i m p a r t i n g the characteristic odor to a mixture may be only minor ingredients. To identify the components of a complex m i x t u r e t h e a n a l y t i c a l or o r g a n i c chemist has a n impressive a r r a y of i n s t r u m e n t a t i o n from w h i c h t o choose. However, in problems involving malodor identification, it is often useful to allow the nose to guide t h e 'Also affiliated with Department of Dermatology, School of Medicine, The University of Pennsylvania, Philadelphia, PA 19104 0003-2700/93/0365-699A/$04.00/0 © 1993 American Chemical Society
analytical effort (1—4) and let investigators use their sophisticated i n strumentation to focus on the area(s) of the separated mixture where t h e offending odor(s) elute. The technique often used to determine the identity of an odor involves t h e o r g a n o l e p t i c e v a l u a t i o n 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. N a t u r a l l y occurring metabolites, i n c l u d i n g geosmin ( i r a « s - l , 1 0 - d i methyl-frans-9-decalol) and methylisoborneol (exo- 1,2,7,7-tetramethylb i c y c l o - [ 2 . 2 . 1 ] h e p t a n - 2 - o l ; MIB), generated by certain algae and actinomycetes (6), or certain synthetic compounds such as chlorinated phenols and amines often produce objectionable odors a n d t a s t e s 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 · 699 A
ANALYTICAL APPROACH
Figure 1. Gas chromatogram and GC/MS spectrum of the malodorous component. 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 (o.d.) Stabilwax column (1.0-μΓη 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 during electron impact. Occasionally, utility workers en c o u n t e r m o r e s e r i o u s or u n u s u a l odors, as was the case recently at the Neshaminy water t r e a t m e n t plant, owned by the Philadelphia Suburban Water Company (PSW), in Middletown Township, Bucks County, PA. In J a n u a r y 1992 a commercial haz ardous waste m a n a g e m e n t facility, located 28 miles upstream of the Ne shaminy plant, accepted six t a n k e r loads (- 30,000 gal) of w a s t e w a t e r from a resin coatings manufacturer in Newark, NJ. The water was char acterized as a nonhazardous, resid ual waste but contained substantial concentrations of various byproducts of the resin-manufacturing process. One of these byproducts proved to be a very p o t e n t o d o r - c a u s i n g a g e n t that had a bitter taste. Because this
material was not removed by treat ment at the waste m a n a g e m e n t fa cility or at the sewer plant to which the treated wastewater was dis charged, the sewer plant and the Ne shaminy Creek were subsequently contaminated with the odor-causing agent. Despite extraordinary efforts to re move the odor and to bring in water s u p p l i e s from a l t e r n a t e s o u r c e s , thousands of PSW customers experi enced objectionable tastes and odors in their water for about two weeks. Identifying and quantifying the odor-causing agent became critical priorities. Analytical approach N u m e r o u s samples of creek w a t e r were evaluated using a flavor profile
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a n a l y s i s (9), by which a g r o u p of p a n e l i s t s a t t h e PSW facility a t t e m p t e d to characterize t h e t a s t e s and odors of the samples, which were distinctive but difficult to describe. Most panelists thought that the odor h a d a "sweet" chemical smell, and t h e y also described it as smelling like latex p a i n t and v a r n i s h or as having a nutty or woody odor. Within 72 h after t h e first r e p o r t s of t h e odor problem, flavor profile analysis a n d a b a t t e r y of o t h e r t e s t s (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 offend ing odor. None of the r e s u l t s from these tests could be used to correlate an odor with a contaminant. Closed-loop s t r i p p i n g (CLS) fol lowed 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 t r e a t e d w a t e r s u p plies for low levels of volatile organic compounds, was performed on t h e odoriferous water samples. CLS in volves recirculating helium through a heated, 1-L water sample and col lecting volatile and semivolatile or ganic constituents on an absorbent trap (see Reference 9, Method 6040). PSW workers have used CLS to ana lyze odor-causing compounds such as geosmin and MIB as well as other contaminants at trace levels. T h e C L S - G C / M S a n a l y s e s of stream and wastewater samples pro duced a number of chromatographic c o m p o n e n t s , not seen in previous routine sampling, with mass spectra t h a t could not be m a t c h e d to any known compounds. The critical chal lenge w a s to identify which chro matographic peaks were responsible for the odor. For this task, scientists from t h e PSW facility collaborated w i t h r e s e a r c h e r s a t t h e Monell Chemical Senses C e n t e r who have used smell chromatography and GC/MS analyses to identify charac teristic human odors (3). This collab oration began about 10 days after the onset of the odor incident. Before t h e collaboration began, the sewer p l a n t o p e r a t o r s stopped accepting discharges from the waste manage ment facility and dosed their plant with activated carbon. Odoriferous wastewater remaining at the waste management facility was shipped by truck for off-site disposal. D e t a i l s of t h e Monell C e n t e r ' s smell chromatography procedure— for which no special a d a p t a t i o n of
Figure 3. Mass spectra of the five synthetic 2-alkyl-5,5-dimethyl-1,3-dioxanes. The spectra were generated on a Hewlett Packard 5970 mass-selective detector interfaced to a 5890 gas chromatograph equipped with a 30 m χ 0.25 mm (o.d.) DB-1301 column (1.0-μιτι thickness; J&W Scientific). Detector conditions: 70 eV; ionization chamber, 220 °C. Mass spectrum of 2EDD in Figure 1 displays no Mt - 1 because of its low concentration in the water samples.
Figure 4. Simultaneous injection of synthesized 2EDD and a sample extract 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-1,3-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 h e x a n e e x t r a c t of t h e N e s h a m i n y Creek water was used for the smell c h r o m a t o g r a p h y e x p e r i m e n t s to identify the area of the chromato gram where the likely odorous candi
date emerged (Figure 1). After the retention time of the putative offend ing odor (relative to a series of «-acid ethyl esters) (13) was determined, mass spectra of the components eluting at the same relative r e t e n t i o n t i m e in t h e G C / M S s y s t e m w e r e
carefully examined. One compound had a mass spectrum (Figure 1) that closely matched the spectra of two of t h e u n k n o w n compounds t h a t the PSW laboratory had found in sam ples 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 in formation about t h e p r i n c i p a l r e a g e n t s p r e s e n t in t h e o r i g i n a l r e s i n - m a n u f a c t u r i n g process, r e searchers attempted to interpret the mass spectrum of the unknown com pound. Their work led them to be lieve t h a t two of the unknown com pounds were 5,5-dimethyl-1-3dioxanes and t h a t they could have been made during resin formation by ring-closure reactions of neopentyl glycol with different aldehyde con t a m i n a n t s in t h e presence of trace acid. The class of 1,3-dioxanes is com posed of six-member rings with an oxygen atom at the one and three po sitions. Under electron impact condi tions 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 h i g h e s t molecular weight ion, usually present in low abundance, is M * - l . In addition, a characteristic fragment ion is seen at mlζ = 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. O t h e r 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, M-butanal, isobutanal, and «-pentanal with neopentyl glycol (i, 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 t h a t 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 2EDD and 2-isopropyl-5,5dimethyl-l,3-dioxane. This led to an enhancement of the suspect peak in the reconstructed ion chromatogram (Figure 4). PSW scientists detected 2EDD in samples of raw w a s t e a n d s t r e a m water (trace amounts) as well as in effluents from the waste m a n a g e ment 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 a c t i o n by PSW a n d s e w e r p l a n t p e r s o n n e l . In a d d i t i o n , t h e identification of 2EDD resulted in an analysis of standards for q u a n t i t a tion 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 2EDD concentrations during the height of t h e 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 d o w n s t r e a m from the sewer plant), 5 ppb; water from t h e N e s h a m i n y plant i n t a k e , 0.04 ppb; and drinking water treated by the Neshaminy plant, 0.02 ppb. The t h r e s h o l d odor level for 2EDD in w a t e r a p p e a r s to be - 0.010 ppb (w/vol). In the aftermath of the incident,
the PSW facility, sewer plant operators, and regulatory agencies have required corrective measures at the waste m a n a g e m e n t facility, which a c c e p t s only a r e s t r i c t e d l i s t of wastes for t r e a t m e n t 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 o p e r a t i o n a l c h a n g e s in t h e w a s t e management facility to ensure t h a t this type of incident will not be repeated. I d e n t i f y i n g 2EDD a s t h e odorcausing agent in this incident demonstrates the value of applying specialized a n a l y t i c a l r e s o u r c e s a n d organoleptic evaluations to problems in the field of water treatment. Specifically, using the nose to direct the investigators can be crucial in picking t h e odorous "needle" from the proverbial " h a y s t a c k " of complex mixtures of organic compounds. References (1) McGorrin, R. J.; Pofabl, T. R.; Croasmun, W. R. Anal. Chem. 1987, 59, 1109 A. (2) Sevenants, M. R.; Sanders, R. A. Anal.
Chem. 1984, 56, 293 A. (3) Zeng, X-N.; Leyden, J. J.; Lawley, H. J.; Sawano, K.; Nohara, I.; Preti, G. /. Chem. Ecol. 1991, 17, 1469. (4) Ramstad, T.; Walker, J. S. Analyst 1992, 117, 1361. (5) Marin, A. B.; Acree, T. E.; Barnard, J. Chem. Senses 1988, 13, 435. (6) Cross, T./. Appl. Bacteriol. 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. /. Am. 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. /. Am. Water Works Assoc. 1981, 73, 530. (11) 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. /. Chromatogr. 1963, 11, 463. (14) Noller, C. R. Chemistry of Organic Compounds, 3rd éd.; W. B. Saunders: Philadelphia, 1965; pp. 820-21.
George Preti (far left) received a B.S. degree in chemistry from the Polytechnic Institute of Brooklyn in 1966 and a Ph.D. in organic chemistry from 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 (second from 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 (third from 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 1970 graduate of Drexel University with a B.S. degree in chemistry. Preston Luitweiler (far right) is manager of Research and Environmental Affairs at the Philadelphia Suburban Water Company. He received B.S. and M.S. degrees from Drexel University and is a registered professional engineer.
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