Odorous Products of the Chlorination of Phenylalanine in Water:  Formation, Evolution, and Quantification

• Published in: Environmental science & technology Vol. 38; no. 15; pp. 4134 - 4139
• Main Authors: Freuze, Ingrid, Brosillon, Stéphan, Herman, Dorine, Laplanche, Alain, Démocrate, Christian, Cavard, Jacques
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.08.2004
• Subjects: Acetonitriles - analysis; Applied sciences; Chemical and Process Engineering; Chlorine - chemistry; Disinfectants - chemistry; Drinking water and swimming-pool water. Desalination; Engineering Sciences; Exact sciences and technology; Imines - analysis; Odorants - analysis; Paris; Phenylalanine - chemistry; Pollution; Taste; Ultraviolet Rays; Water - chemistry; Water Purification; Water Supply; Water treatment and pollution; France; Europe; Paris; Ile-de-France; France, Paris; Drinking water treatment; Organic matter; Chlorination; Phenylalanine; Chlorine; Reaction product; Pollutant formation; Disinfection; Chemical reaction kinetics; Aminoacid; Model compound; Water quality; Qualitative analysis; Odor
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es035021i

To explain some of the possible origins of an odor episode which took place in a drinking water supply in the region of Paris (France), the chlorination reaction in water of phenylalanine was studied. This amino acid was chosen for first experiments because of its physical and chemical particular properties. Changes in the different byproducts formed were followed by high-performance liquid chromatography (HPLC) over a period of time. N-chlorophenylalanine (mono-N-chlorinated amino acid) and then phenylacetaldehyde were the major products formed for the lower chlorine to nitrogen molar ratios. For Cl/N molar ratios of 1 and beyond, phenylacetonitrile and N-chlorophenylacetaldimine appeared and increased with the chlorination level. N-chlorophenylacetaldimine was quantified by using its difference of stability in various organic solvents. Our attention was first directed to the monochlorinated derivative but further examination indicated that it could not be responsible for odor troubles:  it dissociated before reaching the consumer's tap and it was produced at consistently low yields under conditions relevant to drinking water treatment. On the contrary, chloroaldimine appeared to be a very odorous and water-stable product:  it strongly smells of swimming pool with a floral background. The odor detection threshold is about 3 μg·L-1 and it can persist for more than one week at 18 °C. It is now suspected of being a source of off-flavor concerns among consumers.