Biochemical and ecological control of geosmin and 2-methylisoborneol in source waters.

The majority of all biologically caused taste-and-odor outbreaks in drinking water characterized worldwide are caused by microbial production of ( )-geosmin [( )-(4S,4aS,8aR)-4,8adimethyloctahydronaphthalen-4a-ol] and ( )-2-methylisoborneol (2-MIB) {(1R-exo)-1,2,7,7-tetramethylbicyclo[2.2.1]heptan-2-ol}. Since they were first identified in the early 1960s, these two earthy-muddy-smelling metabolites have been the focus of considerable research, which has collectively produced over 400 scientific articles, reports, websites, and conference proceedings. Yet despite this substantial body of knowledge, geosmin and 2-MIB remain poorly understood throughout much of the water industry, and misconceptions which impede the prediction, treatment, and control of these volatile organic compounds (VOCs) persist. This paper reviews salient aspects of our current knowledge on the sources and properties of geosmin and 2-MIB which are essential to understanding and managing drinking water malodors. In particular, we highlight some key factors regulating the storage and release of these compounds by cells. These important factors are often overlooked and may contribute to some of the apparent ambiguity of many taste-and-odor outbreaks.