Ecotoxicity of Bromacil, Malathion and Thiabendazol on Fish, Daphnia magna and Cyanobacteria in Gaza City, Gaza Governorate, Palestine

Abstract

This study investigated the toxicity of bromacil, thiabendazole, and malathion to cyanobacterial mats, fish and Daphnia magna. Toxicity to cyanobacteria were measured by the reduction of population growth of cyanobacterial mats and metabolic reaction changes ( reduction of eclectic conductivity of growth media, pH changes, dissolved oxygen reduction and biomass), in the range of 0-29.67 (mg/l). Whereas toxicity to D. magna was measured in the range mentioned a bove by recording mortality percentage ,while toxicity to fish by measuring losing sensation. The same toxicity parameters were measured for binary mixtures of the above mentioned compounds. Growing the cyanobacterial mats under laboratory conditions showed four phases of growth, and that cyanobacterial mats adapted and grew fast under laboratory conditions. Toxicity tests showed significant % growth reduction as the concentrations of bromacil and thiabendazole increased in the growth, whereas malathion showed no toxic effect to cyanobacteria. Percentage of electric conductivity reduction was pronounced in bromacil and thiabendazole exposure and consequently the effect on the pH of growth media. Malathion showed inverse effect. Mixtures (bromacil+malathion) and (thiabendazol+malathion) showed antagonistic effect.Long term effects of the tested compound on % EC reduction was not significantly different. Moreover, bromacil and thiabendazole mixture showed synergistic effects on %EC reduction and pH changes. Dissolved oxygen (DO) in all experiments was not significantly affected.Toxicity on D. magna showed that malathion was the most toxic compound and has EC50 equals to 0.43(mg/l) compaired to that of bromacil 0.59 (mg/l). Mixture toxicity of bromacil and malathion showed larger EC50 value (0.64 TU) indicating potential antagonistic effect. Toxicity to fish showed that thiabendazole is several time more toxic than malathion. Relative toxicity (RT) calculation indicates that thiabendazole has a value equal to 0.276 whereas malathion has a value equal one. This indicates that thiabendazole is nearly 4 times more toxic than malathion.An interesting outcome of the study is that bromacil and thiabendazole have strong effect on the population growth of cyanobacterial mats and on the metabolic activities as measured by %EC reduction , pH changes and or %DO reduction. Contamination of bromacil, thiabendazole and malathion may severely damage the ecosystem. Furthermore, fish and D. magnawere sensitive to low concentrations of these pesticides. These data suggest potent threats to aquatic organisms from organic contamination. Our results maybe the first of its kind in the region and may be considered as a guideline for future studies.