EFFECT OF ARSENIC POLLUTION ON SOIL MICROBIAL-POPULATION

In order to estimate the effect of arsenic pollution on soil microorganisms, a field survey was carried out in arsenic polluted (391-459 mg/kg dry soil) and unpolluted (32-43 mg/kg dry soil) fields, and the following results were obtained: The ratio of the number of bacteria to the number of fungi in plot I which was polluted and subjected to submerged conditions in summer was significantly lower than that in the other plots. Fungi appeared to be much more tolerant to As(III) than bacteria and actinomycetes. The ratio of the As(III)-tolerant fungi to the whole fungal population was higher in plot I than in the other plots. The fungal group which predominated in plot I belonged to a unique group and was never observed in the other plots. The diversity index of the fungal flora of plot I was lower than the indices of the other plots. In conclusion, the continuous pollution of soil by As promoted the predominance of As-tolerant fungi, and the effect of As pollution on the microbial population was more drastic in paddy fields than in upland fields.