Khwam pen phit khong paraquat to sarai thale lae sarai namchut cell dieo.
1985
Wanna Ruttanagosrigit
Optimum conditions for growth of Nitzschia closterium and Chlorella sp. were determined using the rate of oxygen produced. The maximum growth of N. closterium was attained at 25 deg. C., 20,000 lux and pH 7. On the other hand, that of Chlorella sp. was 30 deg. C., 18,000 lux and pH 5. The EC50 value of paraquat on N.closterium at pH 5,7 or 9 was 0.58, 2.52 or 16.2 mg/l. These values showed that paraquat worked more effectively on N.closterium at lower pHs. The statistical analysis also showed significant differences among the EC50 values and the slopes of toxicity curves. At a median effective concentration the relative toxicity of paraquat increased 6.4 times with pH decrease from 9 to 7, but increased 4.3 times with the pH decrease from 7 to 5. The EC50 value of paraquat on Chlorella sp. at pH 5,7 or 9 was 0.079, 0.095 or 0.072 mg/l. Paraquat was most toxic to Chlorella sp. at pH 9 and least toxic at pH 7. The toxicity of paraquat to Chlorella sp. enhanced 1.2 times by lowering the pH from 7 to 5 or 1.3 times by elevating the pH from 7 to 9. The statistical analysis indicated significant differences among the toxicity of paraquat at these three pH levels. Treatment of paraquat at the concentration from 0.18 to 18 mg/l on 14 x 10(exp.5) cells/ml of N.closterium for a period of 1 hour resulted in a decrease of photosynthetic rate of 4.1 to 40.8 % at pH 5, 2.2 to 32.8 % at pH 7 and 9.5 to 61.5 % at pH 9. Respiratory rate was inhibited at the same level of paraquat from 24.2 to 100 % at pH 5, 27.3 to 65.9 % at pH 7 and 22.0 to 80.8 % at pH 9. The effect of paraquat on photosynthetic rates of Chlorella sp. varied from 19.5 to 76.7 % at pH 5, 15.2 to 72.1 % at pH 7 and 18.8 to 89.0 % at pH 9. The respiratory rates varied from 8.8 to 100 % at pH 5, 0 to 96 % at pH 7 and 0 to 100 % at pH 9.
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