Abstract
In order to investigate appropriate microbiological indicators for organic pollution of river water, water samples were collected from 10 rivers distributed in northeast Kyushu, and the following points were examined : (i) cell number of colony-forming bacteria on nutrient-poor and nutrient-rich agar medium, (ii) cell number of directly-counted bacteria, (iii) a flora of heterotrophic bacteria, (iv) cell number of LAS-assimilable bacteria, (v) biodegradability of LAS, (vi) a range of environmental variables. The results indicated that the ratio of the cell number of bacteria grown on nutrient-poor medium (1/20 PYG medium) to that grown on nutrient-rich medium (PYG medium : polypeptone 5.0g, yeast extract 2.5g, glucose 1.0g and agar 15g in 1,000ml of distilled water) is important as an indicator of organic pollution, as well as both the cell number of colony-forming bacteria and that of directly-counted bacteria. The ratio of bacterial number decreased with increase of BOD in the river water (ratio 3 or more, BOD 0.8-0.9mg·l-1 ; ratio 2-3, BOD 0.9-2.0mg·l-1 ; ratio 1-2, BOD 2.0-2.9mg·l-1).
Biodegradability of LAS were more useful as an indicator of bacterial activity in river water contaminated by some domestic waste water than the cell number of LAS-assimilable bacteria.
