The Toxic Effect of 4-(Phenylazo) phenol Derivatives on Various Oligochaetes

Abstract

Twenty-three derivatives of 4-(phenylazo) phenol showed a toxic effect on several aquatic oligochaetes in vitro. The present study was undertaken to determine whether these compounds could be effective as annelicides. Five of the compounds with the formula: where R₁ is a halogen or nitro group; R₂ and R₃ are halogen, or halogen and nitro substituents, showed strong toxic effects on Branchiura sowerbyi, Limnodrirus socialis, L. willeyi, and Criodrilus bathybates, occurring in muddy holes. These five compounds, elicited a weaker repellent response in the worms as compared to other compounds, which might contribute to their strong toxic effect. In addition, the rapidity of action of these five compounds may be related to their strong toxic effect. Correlation between the capacity for soil adsorption and toxicity of the five compounds was not observed. P-99 (Yurimin®), 2, 6-dibromo-4-(4-vitrophenylazo) phenol, which was selected among the five compounds for its toxic effect and ease of synthesis, was studied in order to identify the factors which influence its toxicity to the worms. Toxic effect of P-99 decreased in soil with low pH, presumably due to the low solubility of P-99 at low pH. The value of the soil pH suitable for the induction of the toxic effect on the worms was above 5.3. The change of temperature in the soil did not significantly influence the toxic effect in the worms. Minimum concentration of P-99 which had an effect on the movement of B. sowerbyi in vitro was 0.4ppm, and when the recovery method, was applied a significant effect was observed following 5 min-treatment of P-99 at a concentration of 4ppm. The worms exposed to P-99 showed tetanic contractile and convulsive spiral movements, followed by paralysis. Finally the posterior part of the body fell off and the worms died. P-99 elicited contractile activities in isolated muscles of Eisenia foetida, followed by paralysis. Histopathological examination of the worms exposed to P-99, showed that the epidermal tissues were destroyed, and the internal tissues (muscle layers, nervous tissue, alimentary canal etc.) were also affected. Respiration activity of muscle homogenates of the worms was markedly inhibited by P-99, as observed in the case of PCP-Na.