Comparison of two standard odor intensity evaluation methods for odor problems in air or water

Government agencies responsible for ensuring healthful water and/or air quality are often faced with resolving public complaints of nuisance odors. Understanding variations in odor intensity may ultimately lead to the establishment and application by such agencies of quantitative limits for effective odorant control. An odor panel was trained in suprathreshold odor intensity evaluation using both the ASTM Method E544 (Butanol Method) and the APHA Method 2170 (Flavor Profile Analysis (FPA) Method). A linear mixed model was fitted to the panel data, taking into account the fixed effects of concentration levels and the random effects of panelists and sessions. The FPA method proved easier to administer and revealed less inter-session variance than the ASTM Method, suggesting its greater utility in applications involving odor panels. For both methods, there was a high standard deviation, relative to the mean. This finding indicates that the intensity scales may be useful for understanding relative odor intensities, but should not be used as a precise measure, or as a basis for establishing regulatory limits.

Sensory evaluation of the odors produced during bromophenol formation using a multi-level statistical model

In response to reports of medicinal taste and odor problems in suburban Paris, a lab scale study was conducted to investigate the contribution of different water quality parameters - pH, phenol, bromide, chlorine, temperature and dissolved oxygen levels - on bromophenol medicinal odor formation using the Flavor Profile Analysis (FPA) method. A study of six parameters at 2 levels (64 experiments) analyzed by the FPA method suggests that chlorine at high concentration is more important as a controlling agent than phenol under similar conditions and the ratio of HOBr:Phenol and the time for reaction will control subsequent brominated products of reaction. Results from a three-level statistical model indicate that high pH was associated with lower odor intensities, whereas high levels of chlorine, phenol and temperature were associated with high odor intensities. Potential worst case scenarios of water quality conditions were determined for evaluation by chemical identification and kinetics.

Effects of chlorine and chloramines on earthy and musty odors in drinking water

Water treatment plants in the US may operate under the assumption that chlorine masks earthy and musty odors from geosmin and 2-methylisoborneol (MIB) in drinking water. To test this hypothesis, we evaluated the effects of chlorine and chloramines on geosmin and MIB by two sensory analysis approaches - a statistical Pairwise Comparison Test, and Flavor Profile Analysis (FPA). All Pairwise Ranking test statistics were significant (p<0.05); we conclude that panelists can differentiate minor differences in geosmin and MIB concentrations in a Pairwise Comparison Test even in the presence of chlorine. FPA appeared to be more challenging in discerning subtle differences in concentrations of geosmin or MIB than did the Pairwise Comparison Test, and the presence of chlorine (0.5-20 mg/L) and chloramines (3-24 mg/L) confused the panelists (i.e showed a larger error in the intensity of response reported by the panel), but did not necessarily mask geosmin or MIB.

Taste and odor profiles (off-flavors) in the drinking waters of the Barcelona area (1996-2000)

The Aigües de Barcelona laboratory systematically monitors the organoleptic quality of the water it supplies. The water comes mainly from the Llobregat and Ter rivers, with the two sources having cleary differentiated chemical characteristics. Water is monitored by the tasting panel, which works according to FPA (Flavor Profile Analysis) principles. This paper reports the results from the period 1996-2000: characteristic organoleptic profiles, evolution of descriptors and the overall organoleptic evaluation of the water. The results show that in Llobregat water the descriptors chlorinous, medicinal, rubbery and salty are the most relevant, whereas in Ter water fresh nature/grassy and metallic are. The Aesthetic Quality Index drawn up by our laboratory confirms that Ter water has better organoleptic quality than Llobregat water. Monitoring also found that neither water lost quality significantly within the distribution network.

Flavor Profile Analysis and GC/MS Detection of Phenolic Iodinated Disenfection Byproducts in Drinking Water for the USA Space Program

Reactions of iodine and phenol were investigated to determine which iodophenols were produced and their odor properties. The research was performed in support of the USA space program that applies iodine to disinfect potable water for spacecraft use. Higher concentrations (50 mg/l) and higher iodine:phenol (e.g. 10:1) ratios resulted in the formation of greater iodophenol concentrations and higher substituted iodophenols. The reactions were fast and nearly complete within 1 hour. For pH 5.5 and 8 and all iodine:phenol ratios, formation of monosubstituted compounds indicated that 2-iodophenol was favored over 4-iodophenol. At the intermediate iodine:phenol ratios of 1:1 and 2:1, substantial amounts of the diiophenols formed and persisted for up to 32 days. The diiodophenols were not detected at iodine:phenol ratios of 0.2:1 and 10:1. The compound 2,4,6-triiodophenol was the major product formed at a 10:1 iodine:phenol ratio and the formation of this trisubstituted phenol appeared nearly complete. Odor evaluation indicated that the iodophenols have much lower odor threshold concentrations (OTC) than phenol. The 2- and 4- iodophenol had OTC values of ≅ 1 and 500 μg/l, respectively, with odors described as “medicinal, phenol, chemical”.

The Environmental Fate and Mechanism of Formation of 2-Ethyl-5,5′-Dimethyl-1,3-Dioxane (2EDD) – a Malodorous Contaminant in Drinking Water

A malodorous chemical, 2-ethyl-5,5′-dimethyl-1,3-dioxane (2EDD) created a drinking water taste and odor episode in Pennsylvania (USA) during 1992. The odor episode occurred as the result of a reaction between propionaldehyde and neopentyl glycol in the waste tank of a resin manufacturer. Samples of this waste water were extracted and analyzed. An in situ aqueous preparation of 2EDD was completed to demonstrate that 2EDD could have formed under the conditions found in the waste water. The stability (fate) of 2EDD was studied at different aqueous pHs (pH3, 5, 7, and 9). Some hydrolysis of 2EDD was found at pHs<7 after one week, but 2EDD appeared to be stable at pH 9. The odor characteristics and odor threshold of 2EDD were determined by the method of flavor profile analysis. The odor threshold concentration of 2EDD was found to be between 5 and 10 ng/l and was described as having a sweet, tutti fruitti odor (near the odor threshold concentration) and a burnt, sickening sweet odor at higher concentrations. This study also discovered that slight antagonism in chloraminated drinking water may occur at or near the threshold odor level of 2EDD.

Distribution-Generated Taste-and-Odor Phenomena

The objectives of this study were to investigate various distribution conditions that directly affect the production of tastes and odors, identify the chemical causes, and develop guidelines to help water utilities solve or prevent these types of problems. This paper presents four case studies of taste-and-odor problems generated in distribution systems. Two types of problems will be presented, (1) problems that occur in association with pipe or reservoir lining material leaching into the water and (2) problems that are caused by a continuation of chemical reactions in the water within the distribution system. The sensory method used was flavor profile analysis (FPA) and the chemical methods were closed loop stripping analysis (CLSA) or liquid-liquid extraction (LLE) coupled with gas chromatography/mass spectrometry (GC/MS). Bromophenols and bromodichloroiodomethanes were found to be the cause of the medicinal odors, while alkyl benzenes and naphthalene were found to be associated with the oil-base paint type of odors.

The Drinking Water Taste and Odor Wheel for the Millennium: Beyond Geosmin and 2-Methylisoborneol

The “Taste and Odor Wheel” developed over the last 15 years has been updated to include new compounds identified in the eight classes of odorants, four tastes, and one mouth feel/nose feel category. Over the last 10 years, other types of odors have been identified, in addition to chlorinous and ozonous odors of disinfectants, the earthy compound geosmin, and the musty compound 2-methylisoborneol (2-MIB). Sophisticated instrumental analysis, e.g., gas chromatography/mass spectrometry (GC/MS), and sensory analysis, e.g., flavor-profile analysis (FPA), have been successfully combined with sensory GC to identify various odorants.