Identification of Alkyl-methoxypyrazines as the Malodorous Compounds in Water Supplies from Northwest Spain Francesc Ventura • Jordi Quintana • Mariano Go ´mez • Mo ´nica Velo-Cid Received: 25 February 2010 / Accepted: 14 June 2010 / Published online: 6 July 2010 Ó Springer Science+Business Media, LLC 2010 Abstract A study of organic compounds which caused several odor problems in water supplies from NW Spain was carried out. Sour dish-cloths, potato bin and musty were the main descriptors associated with these events. Closed loop stripping analysis combined with sensory-GC and GC/MS detection was used. The compound producing the initial odor event was 3,5-dimethyl-2-methoxypyrazine, identified for the first time as the compound responsible for odor incidents in finished water. Concentration levels were up to 300 ng/L in the effluent from an activated sludge wastewater treatment plant (WWTP) and 3 ng/L in finished water. 3-isobutyl-2-methoxypyrazine and other alkyl methoxypyrazines were the compounds responsible for the odor events that occurred several months later. Concen- tration levels in the mg/L range were measured in the activated sludge of a WWTP. Keywords 3,5-Dimethyl-2-methoxypyrazine Á 3-i-Propyl-2-methoxypyrazine Á 3-i-Butyl-2-methoxypyrazine Á Odor events Á Water The presence of bad taste or smell in drinking water is usually perceived by consumers as unsafe and the major cause of complaints. The European Directive includes the taste and odor parameter in water intended for human consumption. Therefore, a rapid response to identify the compound(s) responsible of the event and to remove it in the treatment process is of paramount importance to guarantee safe and aesthetic water. Both natural and anthropogenic compounds are the sources of pollutants producing taste and odors in water. Geosmin, 2-methyl-isoborneol (MIB) and haloanisoles are by the far the most commonly reported compounds of biological origin causing musty and earthy off-flavors in water at ng/L levels (Malleviale et al. 1987; Suffet et al. 1995). Industrial and sewage effluents, leachates from landfills, pipe joint lubricants, etc. have been frequently described as the source of taste and odors coming from anthropogenic compounds. Closed loop stripping analysis (CLSA), a preconcentra- tion technique developed by Grob and Zu ¨rcher (1976) is the analytical tool most frequently reported in the literature used to identify the compound or compounds responsible for taste and odor episodes (Boleda et al. 2007). Other extraction techniques such as solid-phase micro-extraction (SPME) (Diaz et al. 2004) or stir-bar sorptive analysis (SBSE) (Benanou et al. 2003) have also been gaining more relevance in odor and taste analysis. All these techniques can be combined with GC/MS detection to identify compounds at ng/L levels or lower. Additionally, sensory-GC has been also used to discriminate compounds with characteristic and/or intense odors from others in complex chromatograms by sniffing at an olfactory port and thus helping to identify the compound(s) responsible for an event (Ventura et al. 1997). From September 2008 until March 2009, several odor incidents have been noticed in wastewater, river and F. Ventura (&) Á J. Quintana AGBAR. Aigu ¨es de Barcelona, Gral. Batet 5-7, 08028 Barcelona, Spain e-mail: fventura@agbar.es M. Go ´mez Labaqua, Rua Secundino Lopez 1, 15702 Santiago de Compostela, Spain M. Velo-Cid Augas de Galicia, Pza Camilo Diaz Valin ˜o 7-9, 15705 Santiago de Compostela, Spain 123 Bull Environ Contam Toxicol (2010) 85:160–164 DOI 10.1007/s00128-010-0053-6