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The toxic effects of herbicides (Machete, Saturn) and pesticides (Diazinon and Malathion) on green algae, Scenedesmus obtusiusculus, and cyanobacteria, Anabaena flos aquae, were studied.
The results indicated that Machete and Saturn, in comparison to Diazinon and Malathion, were more toxic. On the other hand it was revealed that green algae was more sensitive to the pesticides than the cyanobacteria. When we added 3.199 mg/l machete (EC50 of this toxicant for Anabaena flos aquae) to a mix algal culture, the growth rate of green algae after 6 days of treatment was reduced 0.95 times, while it was 4.5 for the cyanobacteria. Treating the culture with 10.53 mg/l of Saturn for the same period of time revealed that the growth rate for green algae and the cyanobacteria increased 1.19 and 7 times, respectively. Hence, we can conclude that pesticides are capable of decreasing the diversity of the phytoplankton species in an aquatic ecosystem that from the fisheries point of view could cause serious problems.

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Fingerlings of Silver Carp (Hypophthalmichthys molitrix) were used in an ecotoxicological investigation. The fish were exposed to (0.3-10 mg/l) Machete, (3-5 mg/l) Saturn, (1.5-13 mg/l) Diazinon and (1-10 mg/l) Malathion to measure the toxicity effect of these chemicals on mortality, feeding and ingestion rate. Methods for investigation on mortality were according to TRC (1984) and feeding behavior, according to Gould Equation (1951). Porbit analysis was used for evaluation of obtained data. LC₁₀ of these toxic compounds were 0.17-0.23, 2.85-3.73, 0.6-0.95, 0.87-1.34 mg/l for Machete, Saurn, Diazinon and Malathion respectively. Experiments showed that Machete and Diazinon in comparison with Saturn and Malathion were highly toxic for fingerlings of silver carp. At first fish showed to be disturbed, then moved rapidly and exhausted. A secretion of excess mucus was also noticed and eye-ball became expanded. There was also blanching of the skin. The fish surfaced sometimes on their side and became unbalanced which resulted in death. Abnormal behavior of fish became greater with the increase of pesticides concentration. In these exposures pH was decreased, in contrast with the amount of water hardness. LC₁₀, LC₅₀ and LC₉₀ form 24 to 96 hours were mostly decreased. Feeding experiments showed that 8 hours exposure below the LC₅₀ values reduced 50 percent of feeding and ingestion rates.