T90 Minerals, Microbes, and Health

Monday, 1 November 2010
8:00 AM - 12:00 PM
Room 302

ANTIMICROBIAL CLAY MINERAL DEPOSITS AND FE(II) EXCHANGED SMECTITE

Paper number: T90-8
Program: Technical Sessions
Time: 9:45 AM – 10:00 AM

Authors

Abstract

The use of clay minerals for medicinal purposes is an ancient practice which has been utilized with varying results. Recent evidence reveals that clay mineral deposits rich in Fe(II) have the ability to limit or completely prevent bacterial growth. These clay deposits have the unique ability to kill bacteria while promoting skin cell growth. Ferrous iron either in the form of pyrite or adsorbed on the interlayer spaces of 2:1 expandable clay minerals has the potential to form hydroxyl radicals and hydrogen peroxide via the Fenton reaction which can be highly toxic to bacteria. The exact antimicrobial mechanism found in these clay deposits remains enigmatic. Here we provide evidence showing that both natural clay mineral deposits and Fe(II) exchanged smectites (using 1M FeCl­2) have a bactericidal effect on E. coli K12.

Antimicrobial clay minerals were collected from the Oregon Minerals Technology (OMT) mine in Oregon approximately 20 miles east of Crater Lake. The primary rock types in the OMT deposit are dacite and andesite, which have been hydrothermally altered into mixed-layered clay minerals rich in nano-scale pyrite. Samples from OMT along with Fe(II) exchanged smectites produced in the lab were reacted with 400µL of 5x107 CFU/mL E. coli in nutrient broth with 200mg of clay and incubated for 24 hours at 37°C. After incubating 100uL of dilutions ranging from 10-5 to 10-7 were plated on nutrient agar to measure bacterial colony forming units.

Clay samples from some horizons in the deposit are antimicrobial while other horizons promote bacterial growth. Quantitative mineralogy of the OMT samples reveals that the clays consist primarily of rectorite and smectite. Natural clay samples that are antimicrobial contain pyrite while the clay deposits that promoted growth contain hematite and maghemite with no pyrite. Iron exchanged smectites completely prevented the growth of E. coli and provide evidence that soluble Fe(II) adsorbed on clay minerals in addition to pyrite is bactericidal.