22 October 2018

Geosmin and 2-Methylisoborneol – nontoxic but stinky terpenoids that make your drinking water unpalatable

Natural compounds

Geosmin and 2-Methylisoborneol are frequently occurring representatives of a vast range of taste and odor compounds negatively affecting water quality.

Cyanobacteria produce and release a vast range of noxious metabolites including cyanotoxins as well as taste and odor compounds. The occurrence of both, toxins and taste and odor compounds adversely impact water quality leading to concerns for public health, drinking water supplies, aquaculture and tourism.

Fig. 1: Cyanobacterial taste and odor compounds such as geosmin and 2-methylisoborneol adversely impact water quality.

The usually nontoxic taste and odor compounds consist of a vast range of substances of algal origin, including terpenoids, ionones, pyrazines, sulphurous compounds, aldehydes, amines and others. Terpenoidic geosmin and 2-methylisoborneol are related to most frequent and intense episodes of taste and odor issues in source and water supplies.

Fig. 2: Structures of geosmin (left) and 2-methyl-isoborneol (right).

Geosmin, a bicyclic sesquiterpene, can be recognized by its muddy/earthy smell with a very low odor threshold of 4 ng L-1 in water. The bicyclic terpenoid 2-methylisoborneol has a strong musty smell with an odor threshold of around 6 ng L-1. Besides the chlorine smell from the often applied disinfection as final water treatment step, earthy and musty off-odors are the second most frequent cause of consumer complaints. Although both terpenoids are produced by many organisms including also actinomycetes, cyanobacteria seem to be the main source, which is why they might be useful as indicators for a drinking water treatment process’ adequacy for the removal of cyanobacterial metabolites.

SMILES:

  • GSM: O[C@]12[C@H](CCC[C@]2(CCCC1)C)C
  • MIB: CC1(C2CCC1(C(C2)(C)O)C)C

References:

  • Ho L, Sawade E, Newcombe G. 2012. Biological treatment options for cyanobacterial metabolite removal – A review. Water Res 46:1536-1548. doi: 10.1016/j.watres.2011.11.018.
  • Kaloudis T, Triantis TM, Hiskia A. 2016. Taste and Odour Compounds Produced by Cyanobacteria. In: Handbook of Cyanobacterial Monitoring and Cyanotoxin Analysis. John Wiley & Sons, Ltd, pp 196-201. doi: 10.1002/9781119068761.ch20.

Picture:
Cyanobacterial bloom at Lake Erie shoreline: https://www.sciencedaily.com/images/2014/10/141015101503_1_900x600.jpg (last accessed: 23/09/2018)