ELECTRON-MICROSCOPIC CHARACTERIZATION OF IRON AND MANGANESE OXIDE HYDROXIDE PRECIPITATES FROM AGRICULTURAL FIELD DRAINS .1.

Scanning and transmission electron microscopic examination of drain pr ecipitates revealed the presence of a slime/organic layer and fungi, b acteria (including filamentous and Fe bacteria), and possibly actinomy cetes. Most of the filamentous structures were encrusted with Fe and M n compounds. Treating the samples with acidified NH2OH.HCl and leucobe rbelin blue revealed some structures similar to Hyphomicrobium and Ped omicrobium spp., yeast cells, cocci, fungal spores, and relics of diat oms and amoebae. Both, scanning and transmission electron microscope-e nergy-dispersive analysis of X-rays showed a clear association of micr obial structures with Fe and Mn oxides. It was suggested that Fe and M n were being precipitated in the drains. However, the precipitates wer e not stable under natural conditions, and therefore we concluded that these precipitated oxides were also undergoing reductive dissolution. It thus appeared that precipitation of Fe and Mn, particularly Mn, ha d been mediated microbiologically in the drains.