TOXICITY OF INDUSTRIAL EFFLUENTS FROM OLOGE LAGOON, LAGOS, NIGERIA ON EARLY LIFE STAGES OF Oreochromis niloticus AND Clarias gariepinus

Abstract

An investigation on the toxicity of industrial effluents from Agbara environs of Ologe lagoon on the fingerlings and juveniles of Oreochromis niloticus and Clarias gariepinus was undertaken. This study was pertinent to ascertain the environmental impact of industrial waste on the Ologe lagoon and the fish fauna using the fingerlings and juveniles of Oreochromis niloticus and Clarias gariepinus as biomarkers. A preliminary study was carried out bi-monthly for 12months on the lagoon as a reference point. Five (5) sample stations were selected. The samples collected from each of the five stations were mixed together at 1:1 ratio. The composite mixture was analysed for physicochemical and heavy metal analyses. During this period, fish samples, Oreochromis niloticus and Clarias gariepinus were collected and used for histopathological analyses. All analyses were carried out bi-monthly immediately after sample collection. At the completion of the preliminary study, effluents were collected from three point sources. Effluents collected from the three sources were: Guinness Nigeria Ltd, Nigerian bottling companies and a confluence from Hotels (as a domestic source). These were identified point of effluent entry into the lagoon. The effluents samples were collected once every month. The samples were used for physicochemical and heavy metal analyses. Eighty (80) specimens each of O. niloticus and C. gariepinus were collected from the effluent point sources. Fish organs (liver, gill, kidney and heart) were used for histopathological analyses. Physicochemical parameters were analysed using standard methods, heavy metal analysis were carried out using Atomic Absorption Spectrophotometer (AAS). Fish organs were sectioned in 5-7 micron thickness for histopathology. Bulk samples of effluents were collected and used for acute and sub-lethal toxicity test in the Laboratory. A 96hrs lethal bioassay was carried out under room temperature. Five serial dilutions: 0%, 20%, 40%, 60%, 80% and 100% of industrial effluents 20 fish were stocked per tank and each treatment was carried out in triplicate. Physico-chemical parameters: temperature, pH, dissolved oxygen and conductivity in the treatment tanks were monitored for the 96hours. At the end of the acute study, gills and liver of the fish were sectioned for histological examination. Based on the results of the acute text, sub-lethal limits were set: 0% (control), 5%, 15%, 25%, and 35%. Trials were carried out in triplicates for twelve (12) weeks. Physico-chemical parameters: temperature (0C), pH, Conductivity (ppm) and dissolved oxygen (mg/l) were measured in each treatment tank on a weekly basis. Weekly length (cm) and weight (g) data obtained were used to calculate growth parameters: mean weight gain (MWG), percentage weight gain (PWG), daily weight gain (DWG), specific growth rate (SGR) and survival rate. At the end of the experiment the gills and livers of the cultured fish were sectioned for histological examinations. Blood samples were collected from fish on the toxicity trials and analysed for haematological parameters: Packed Cell Volume (PCV), Red blood cells (RBC), White Blood Cell (WBC), Neutrophil and Lymphocytes. The results for preliminary study showed that mean values for physico-chemical parameter and heavy-metals in Ologe lagoon ranged from: 8.62±0.39 - 11.82±0.09 for pH, 4.68±0.68 - 7.35±2.7mg/l for DO, 166.75±26.8 - 430.5±62.5mg/l for TDS, 226.8±51.08 - 1216.9±14.23mg/l for COD, 42.54±5.0 – 166.75±0.26mg/l for BOD, 21.62±2.49 – 775.1±15.51mg/l for Cl-1, 1.18±0.9 – 390.25±2.18mg/l for Cr, 0.22±0.03 – 1.15±0.03mg/l for Cu and 0.21±0.23 – 0.6±0.03mg/l for Pb. The physico-chemical parameters in acute toxicity treatments for O. niloticus (fingerlings and juveniles) ranged from: 27.73±0.31 – 29.4±0.30C for Temp., 3.02±0.15 – 16.4±0.36mg/l for DO, 7.43±0.06 – 7.6±0.2 pH and 80.1±0.1 – 80.2±0.1μS/cm for conductivity. While in C. gariepinus, they ranged from: 27.67±0.29 – 28.3±0.10C for Temp., 4.17±0.29 – 8.63±0.15mg/l for DO, 7.13±0.15 – 8.17±0.29 for pH and 103.3±11.5 – 118.3±2.8ppm for conductivity. Physico-chemical parameters in the sub-lethal toxicity treatments for C. gariepinus (fingerlings and juveniles), ranged from: 25.03±0.62 – 26.3±2.30C for Temp., 1.97±0.15 – 4.72±1.75mg/l for DO, 7.25±1.69–8.06±0.2 for pH and 339.7±10.5–486.0±45.81ppm for conductivity. While in O. niloticus, the values ranged from: 23.94±2.19–28.12±0.160C for Temp., 2.89±2.17 – 7.68±0.08mg/l for DO, 7.57±0.1–7.89±0.6 for pH and 175.79±9.54– 265.95±18.99ppm for conductivity. The LC50 96hrs for O. niloticus fingerlings was 39.2% and 36.1% for juveniles. Lower values of LC50 96hrs were obtained for C. gariepinus fingerlings (34.0%) and juveniles (19.63%). There were increase in length and weight of fish during the sub-lethal toxicity study, but growth decreased with increase in effluent concentration. The haematological parameters decreased with increase in concentration of effluents at acute toxicity level. However at sub-lethal level, white blood cells (WBC) increase with increase in effluent concentration, showing resistance to toxicity and increase in body defence. Histology of gills and liver showed increase in lesions with increasing effluent concentrations. Fishes in the control (0%) showed no visible lesions. Observed lesions at the acute test in the liver were: hepatic mono-nuclear cell infiltration and multi-focal coagulative necrosis. In the gill there were severe gill lamella necrosis and degeneration. The sub-lethal test showed increase in tissue damage, but showed adaptive responses. The result of physicochemical and heavy metals from Ologe lagoon and the effluents exceeded the WHO and National Environmental Standards and Regulations Enforcement Agency (NESREA) standards. Therefore, Ologe lagoon was fairly polluted.