汚泥脱水に用いる有機高分子凝集剤の毒性試験とその評価

抄録

The toxicity of organic polymer flocculants (e. g., polyacrylamide) used for the dewatering ofmunicipal sludge was evaluated by using two different toxicity assays: Closterium ehrenbergii algal toxicitytest and Bacillus subtilis rec-assay.
First, the algal toxicity of the effluent from a pilot-scale sewage treatment plant was investigated with and without addition of a flocculant (0, 0.05, 0.10, and 0.20 mg/L). No clear evidence on the algal toxicity causedby the flocculant was observed on both asexual and sexual reproduction tests of Closterium ehrenbergii. Alsoit was found that the algae growth inhibition of various types of flocculants (i. e., cationic, anionic, ampholyticand non-ionic) was in the order of 1 to 20 mg/L, which was mainly due to the molecular weight (MW) fractionof greater than 100, 000.
Then, DNA damaging toxicity of these flocculants was investigated by the rec-assay, which indicated thateight among ten flocculants caused the direct DNA damages with LC50=0.1 to 10 mg/L. The DNA damaging flocculants were also fractionated into their components and by MW. The experimental results showed thatthe lethal effects were mainly contributed by the polymer fraction of MW greater than 100, 000, although the DNA damaging toxicity was not detected in that fraction. The refore, the detected DNA damaging toxicity ofthe flocculants could be manifested as the combined effects of various components, such as polymers, origomers, monomers, and additives.