Differential response of Tilapia guineensis fingerlings to inorganic fertilizer under various salinity regimes.

The influence of salinity on the response of the estuarine teleost, Tilapia guineensis fingerlings to acute toxic effects of inorganic nitrogen-phosphorus-potassium (NPK) (15: 15: 15) fertilizer was investigated using semi-static bioassay. The toxicity of NPK fertilizer was found to increase significantly with increase in the salinity level from 0.05 %. to 32.4 %o. The 96 hr LC50 value at salinity of 32.4 %o was 0.11 mg/l and was found to be significantly (p < 0.05) higher than the toxicity values at any other salinity level of media evaluated. The implication of the findings is that pollution control standards and/or safe limits for brackish water ecosystem should consider variations in salinity regimes for greater relevance and reliability.

Relative toxicity of spent lubricant oil and detergent against benthic macro-invertebrates of a west African estuarine lagoon.

The relative acute toxicity of spent lubricant oil and detergent was evaluated against hermit crab, Clibanarius africanus (Aurivillus) and periwinkle, Tympanotonus fuscatus (L) from the Lagos lagoon in laboratory bioassays. Based on the derived toxicity indices, the detergent (96 hr LC50 = 5.77ml/l) was found to be 1.73 times more toxic than spent engine oil (96 hr LC50 = 10.01 ml/l) when acting singly against C africanus and 18.73 times (96 hr LC50-48.67 ml/l) more toxic (96 hr LC50 = 911.57 ml/l) when acting singly against T. fuscatus. On the basis of the computed susceptibility factors, C. africanus was found to be about eight times and ninety-one times more susceptible to the toxic effect of detergent and spent lubricant oil respectively. The randomized analysis of variance (ANOVA) showed that there was significant difference (Fcal 58.83 Ftab 3.87; DF 13; p > 0.05) between all treatments of spent lubricant oil and detergent during the 96 hr exposure period of test animals. At 5% level of significance the Student Neuman-Keuls (SNK) test further revealed significant differences in the mean mortality response of test animals exposed to toxicants at all concentrations and untreated control. The results obtained in this study suggest that the estuarine benthic macroinvertebrates, which play key roles in the environment, may serve as useful in-situ sentinels for biomonitoring studies of petroleum pollutants in fragile aquatic ecosystems such as the Lagos lagoon.

Impact of refined petroleum spills on water quality, macro-invertebrate and microbial communities of a tropical aquatic environment.

Water quality characteristics, benthic macro-invertebrates and microbial communities of three first order streams in South West Nigeria were investigated to assess the effects of refined petroleum five months after spillage. All physical and chemical conditions except temperature and pH were significantly different (P<0.01) at the upstream control stations and impacted stations reflecting the perturbational stress. The benthic macro-invertebrate fauna were dominated by arthropods, but the faunal spectrum was dissimilar at all the stations studied. Sampling stations at the epicentre of the spill showed considerable reduction in faunal compositions and relative abundance. Generally, the microbial density and diversity were highest in both soil and water samples from impacted sites than in control sites. There was a significantly higher proportion (P < 0.05) of hydrocarbon utilizers in soil than in water samples in all stations except in samples from stations (P<0.05).

Toxicological response and sensitivity of estuarine macro-invertebrates exposed to industrial effluents.

The evaluation of toxicological response and sensitivity of some tropical estuarine benthic macro-intertebrates, Clibanarius africanus (Aurivillus) and Tympanotonus fuscatus var radula L. under acute exposure to effluents from brewery, paint and textile industrial establishments in Lagos state, Nigeria was carried out in static laboratory bioassays. On the basis of computed toxicity factors (96h LC50 ratios), the brewery effluent was found to be 6.90 times more toxic than the other test media against the exposed animal. The toxicity sensitivity ranking order for the test animals revealed that C. africanus was more susceptible to the toxicants than T. fuscatus. The relevance of the results in toxicity evaluation and setting realistic environmental standards for aquatic ecosystems in Nigeria is discussed.