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Toxicity of Leachates from the Aba-Eku Landfill Leachate Lagoon, Ibadan, South-Western Nigeria

Adeola A. Oni, Amusat T. Hassan and Peijun Li

Landfill monitoring is necessary to avoid adverse environmental impacts. Toxicity tests are now incorporated into landfill hazard assessment. Toxicity of leachate in a lagoon draining the Aba- Eku landfill, Ibadan, Nigeria was investigated using bioassays. 96hr bioassays were carried out using arthropods (Insecta - larvae of Chironomus sp.; Culex pipiens); amphibians (tadpoles of Bufo regularis); and fish (seven and fourteen weeks old fingerlings of Clarias gariepinus). Physico-chemical parameters were analysed using American Public Health Association standard methods. Toxicity results showed reduced mortality in Chironomus sp.(10%); Culex pipiens however showed a reduced toxicity with increasing leachate concentration. 96 hr LC50 in Culex pipiens was 20% leachate. No mortality of leachate was observed in tadpoles of Bufo regularis and fourteen week old fingerlings of Clarias gariepinus. Percentage mortality in seven week old fingerlings of Clarias gariepinus was 37.5%. Filtering of leachate reduced mortality in C. gariepinus from 37.5% to 12.5%. Due to the low mortality, LC50 for all organisms except Culex pipiens were indeterminate. The observed mortalities were not concentration dependent. Toxicity test results were supported by leachate analysis which showed considerable reduction in contaminant levels except for suspended solids (144.94 ± 117.99 mg/l and chloride (597.98 ± 209.73 mg/l) which exceeded and approached regulatory limits respectively. Leachate strength and toxicity was reduced by natural attenuation. Absence of a dose dependent response may be due to the leachate’s unstable nature. Sediment presence may have reduced toxicity via contaminant sorption. Low-cost attenuation processes are useful in reducing contaminant levels in leachate.