Definition: microbiologically influenced corrosion (MIC) refers to corrosion brought about by the presence and/or activities of microorganisms in biofilms on the surface of the corroding material. Most materials, including metals, polymers, glass and ceramics can be degraded in this manner.

A number of microbiological organisms, notably bacteria, fungi and algae have been associated with corrosion damage in water systems. These microorganisms can influence corrosion by effects such as differential aeration cells, the production of corrosive species such as mineral and organic acids, ammonia, and reduction of sulfate to sulfide. The various types of microbes tend to act synergistically in the corrosion of materials with their interactions typically being of a complex nature.

Even though the harmful corrosive influence of microbes has been known for more than 60 years, many practicising engineers are still surprised to learn that the activity of microorganisms can lead to severe degradation of various construction materials.

Historical note:
Microorganisms, including bacteria, were first observed (actually seen) in 1676 by Antoni van Leeuwenhoek, a Dutch (Delft) cloth merchant by trade but with an interest in optical microscopy.

There is a connection between van Leeuwenhoek and the famous Delft painter Vermeer (perhaps you have seen a Scarlett Johansson movie recently - hint: pearl earring) in that he was the curator of Vermeer's estate (coincidentally also appointed as such in 1676).

References:

MTI Publication No.13, "Microbiologically Influenced Corrosion: A State-of-the-Art Review", Second Edition, 1989.

P.M. Tierno: "The Secret Life of Germs", Atria, 2001.

N. Schneider: "Vermeer - the complete paintings", Taschen, 2000.

Links:

Visit http://www.sprinklernet.org/ for several articles on MIC. Type the term MIC into the search box.

Visit www.pmengineer.com and type microbial corrosion into the search box.