MICROBIALLY MEDIATED GEOCHEMICAL VARIATION AFTER FILTRATION

We have discovered that bacteria pass through 0.1 m m pore size filters. We sought to determine what effects increasing numbers of microbes have on trace element and pH variability over time and the effects of commonly used filtration, acidification and refrigeration-storage techniques on bacteria and geochemical variability. Water samples were collected from acid and neutral pH seeps, within the Contrary Creek Watershed, Virginia, USA and an acidic coal mine in Jiaoluo Township, Anlong gold region, Guizhou Province, China. Over a three week period, acidophilic (pH < 3.9), and neutral pH (> 6.2) bacteria were enumerated using the Acridine Orange Direct Count method. Light and epiflourescent microscopy techniques were employed to measure and photograph bacteria and flocculates. Atomic Absorption Spectroscopy (AAS) was used to measure the concentrations of Al, Pb, Mn, Zn, Ni, Fe and Cu. Our data demonstrate that acidophilic and neutral pH cocci, bacilli and filamentous forms (10³-10⁶/ ml) pass through 0.1m m pore size filters. The average size of bacilli and filamentous forms increase from 2 to 6 microns between weeks 1 and 3. Bacteria multiply and produce trace element (2-95%) and pH (5-250%) variability. Sample splits treated with sodium azide, a biological toxin, do not exhibit such geochemical variability. Trace element concentration decreases 20% from initial measurements as microbial numbers increase 71%, independent of filtration, acidification and refrigeration. Suspended particulates form between days 1-4. Statistical variability increases over time demonstrating that biological processes produce sample heterogeneity, thus yielding inaccurate measurements of trace element concentrations using standard geochemical tools such as AAS. These findings have important implications for the preparation, storage and analysis of aqueous samples in particular acidic mine drainage. We suggest filtration using 0.1 m m pore size filters and chemical analysis within 1 week of sample collection.