The urbanization, industrialization and commercialization, has had its effects to the significant upswing of waste streams 123. In addition, most developing country are challenged by poor funding, legislation and sensitization of the populace on waste reduction, reuse and recycling 4. Due to poor or inadequate waste management policies in most developing countries, the application of landfills system have become a threat to biodiversity 4.

Huge streams of untreated and unsegregated waste are seen littered across most metropolis with potential infringement of the ecosystem. These wastes undergoes environmental transformation infringing on vital components of the ecosystem, including soil, are and water are most obliged media of environmental pollution. For instance leachates from dumpsites infiltrate to pollute groundwater or swept by runoff thereby causing surface water contamination. Toxicants from leachate have been found to have attendant adverse effect on biodiversity especially groundwater resource and aquatic biota 356.

Yenagoa Metropolis is the capital city of Bayelsa State, which is a deltaic wetland that forms part of the Niger Delta Region. Its climate is humid tropical, with high precipitation that favour the transformation and mobility of leachate contaminants 4. Heavy metals are major toxic component in waste leachate, in contaminated soil can enrich the ecosystem, and accumulated in food chain complexes with potential adverse effects 7.

Heavy metals like Cadmium can cause acute systemic impairment of the heart, brain, and kidney 7. Heavy metal like iron from the Niger Delta Region have been reported for fish kill 8, inhibit plant growth and metabolic processes like; ascorbic acid and chlorophyll levels of 9. Consequently, the Ecotoxicological assessment of leachate from municipal solid waste dumpsites have become necessary.

Table 1 presents the results of general physicochemical properties of the leachates. The leachate from Akenpai station had pH of 5.87 and turbidity of 94.33NTU, also the leachate indicated BOD5 and COD level of 75.33 and 95.67 mg/l respectively. The physicochemical properties of leachate from Etegwe station had pH of 5.57 and turbidity of 211.00NTU, also the BOD5 and COD level of the leachate were 81.67 and 111.00 mg/l respectively. The physicochemical assessment of leachate from Opolo market station recorded pH of 6.33, turbidity of 182.33NTU, as well as BOD₅ and COD level of 61.33 and 84.33 mg/l respectively (Table 1). The physicochemical properties of leachate from Kpansia market station had pH value of 6.13 and turbidity of 198.00NTU, BOD5 of 53.00 mg/l and a COD level of 74.33 mg/l respectively (Table 1).

The physicochemical properties of leachate from the first station of the central dumpsite was more acidic with pH of 4.87 and turbidity of 285.67NTU, also BOD5 and COD level of 109.67 and 130.67 mg/l respectively (Table 1). The physicochemical properties of leachate from the second station of the central dumpsite indicated pH level of 5.20, turbidity of 232.67NTU, as well as BOD5 and COD levels of 93.00 and 124.00 mg/l respectively (Table 1).

Table 2 presents results of the rapid toxicity screening of fingerlings and adult catfish assayed against leachates from 6 dumpsite stations. Result of the all leachates bioassay against the fingerling indicated total mortalities (Table 1). Furthermore at concentrations of 500 and 1000ppm in less than 8 hours. On the other hand, the toxicity bioassay of leachates from all dumpsites against the adult catfish significantly (p<0.05) induced no mortalities at the already established concentrations (500 and 1000ppm), within 96 hours. Notwithstanding, sublethal effects against the adult fish were observed during the bioassay.

Meanwhile the negative control induced no mortality to both adult and fingerlings throughout the exposure of the bioassay at 500 and 1000ppm. On the other hand, the positive control significantly (p<0.05) induced total mortalities to both fingerling and adult fish at 500 and 1000ppm respectively. As such, the fingerling bioassay that induced mortalities at concentration ≤ 500ppm is further subjected to final screening, as opposed to the adult species that had no adverse effects at concentrations ≥1000ppm.

Table 3 presents the results of the final screening of leachates from the dumpsite stations, assayed against the fingerlings. Leachates from the Akenpai station had No Observable Adverse Effect Level (NOAEL) at concentration of 50ppm, while Lowest Observable Adverse Effect Level (LOAEL) was induced at concentration of 75ppm with mortality rate of 13.33% (p<0.05). Meanwhile, the minimal lethal concentration (LC100) was indicated at concentration of 200ppm within exposure of 5 hours (p<0.05), with mortality time of 10 hours.

Table 3 presents the results of the final screening of leachates from the dumpsite stations, assayed against the fingerlings. Leachates from the Akenpai station had No Observable Adverse Effect Level (NOAEL) at concentration of 50ppm, while Lowest Observable Adverse Effect Level (LOAEL) was induced at concentration of 75ppm with mortality rate of 13.33% (Figure 1). Meanwhile, the minimal lethal concentration (LC₁₀₀) was indicated at concentration of 200ppm within exposure of 5 hours (p<0.05), with mortality time of 10 hours.

Furthermore, based on the dose-response curve statistical assessment of the leachate from the Akenpai station induced mortality with LC₅₀ value of 124.57ppm (Figure 1). The physicochemical properties of leachate from Akenpai station had pH of 5.87 and turbidity of 94.33NTU, also the leachate indicated BOD5 and COD level of 75.33 and 95.67 mg/l respectively (Table 25). Table 3 presents the results of the final screening of leachates from the dumpsite stations, assayed against the fingerlings. Leachates from the Akenpai station had No Observable Adverse Effect Level (NOAEL) at concentration of 50ppm, while Lowest Observable Adverse Effect Level (LOAEL) was induced at concentration of 75ppm with mortality rate of 13.33% (Figure 1). Meanwhile, the minimal lethal concentration (LC₁₀₀) was indicated at concentration of 200ppm within exposure of 5 hours (p<0.05), with mortality time of 10 hours. Furthermore, based on the dose-response curve statistical assessment of the leachate from the Akenpai station induced mortality with LC₅₀ value of 124.57ppm.

Results of the final screening of leachates from the dumpsite at Etegwe station, assayed against the fingerlings had NOAEL value at concentration of 25ppm (Table 3). However, LOAEL was induced at concentration of 50ppm with mortality rate of 16.67%. Meanwhile, the minimal lethal concentration (LC₁₀₀) was significantly (p<0.05) induced at concentration of 175ppm within exposure of 4 hours. Furthermore, based on the dose-response curve statistical assessment of the leachate from the Etegwe station induced mortality with LC₅₀ value of 95.38ppm (Figure 2).

Leachates from the Opolo Market station, indicated NOAEL at concentration of 75ppm (Table 3). However, LOAEL was induced at concentration of 50ppm with mortality rate of 3.33%. Meanwhile, the minimal lethal concentration was reported at concentration of 225ppm, within exposure of 10 hours. Furthermore, leachate from the Opolo market had LC₅₀ value of 157.95ppm as presented in Figure 3.

Furthermore, results of the toxicity bioassay from leachate in the Kpansia Market station against the fingerlings induced NOAEL at concentration of 100ppm (Table 3). Notwithstanding, the LOAEL was induced at concentration of 125ppm with mortality rate of 13.33%. Meanwhile, the minimal lethal concentration (LC₁₀₀) was significantly (p<0.05) induced at concentration of 225ppm within exposure of 7 hours. Furthermore, based on statistical assessment of the dose-response curve of the leachate from the Kpansia market station induced mortality with LC₅₀ value of 123.82ppm (Figure 4).

In terms of mortality rate result of the toxicity bioassay from the first station of the central dumpsite (CDS 1) showed NOAEL at concentration of 25ppm (Table 3). However, the LOAEL was induced at concentration of 50ppm with mortality rate of 26.67%. In addition, the minimal lethal concentration (LC₁₀₀) was induced with significant difference (p<0.05) at concentration of 150ppm within exposure of 3 hours. Notwithstanding, based on the statistical dose-response assay, leachate from the first station of the central dumpsite demonstrated mortality with LC₅₀ value of 67.97ppm (Figure 5).

Furthermore, compared to the first station of the central dumpsite, results showed that the second station of the central dumpsite (CDS 2), similarly had NOAEL and LOAEL at concentrations of 25 and 50ppm respectively (Table 25). However, a dissimilar mortality rate of the LOAEL was induced at 23.33%. Notwithstanding, the minimal lethal concentration (LC₁₀₀) value of CDS 2 was demonstrated a concentration of 175ppm within similar exposure of 3 hours compared to CDS 1. Based on the statistical dose-response analysis the CDS 2 demonstrated toxicity with LC₅₀ value of 76.65ppm (Figure 6).

On a general basis the order of toxicological activities of the leachates are reported as; CDS 1<CDS2<Etegwe< Akenpai<Kpansia market<Opolo Market. An earlier study of the characterization of leachates from the Niger Delta reported the levels of heavy metals in leachate as; Cadmium (0.00 – 0.17 mg/l), Chromium (0.00 – 0.46mg/l), Copper (0.00 – 0.70mg/l), Manganese (0.20 – 0.60mg/l), mercury (0.00 – 0.27 mg/l), Fe (0.20 – 8.41mg/l), lead (0.27 – 2.77 mg/l) and Zinc which ranged from 0.00 – 4.10 mg/l 12. In their study, the order of toxicological activities of the heavy metals were; Iron>Lead>Zinc>Manganese>Copper>Chromium>Mercury>Cadmium 12. The toxicity of the leachates from MSW dumpsite is largely attributed to the presence of heavy metal. Notwithstanding, high level of iron is not farfetched as it is a typical characteristic of the Niger Delta region 81314. Another study by Ohimain et al., 8, reported high mortality of in a bioassay of ground water containing high level of iron (5.119 - 11.131mg/l), with acidic pH (3.97 - 6.40) against fingerlings of Clariasgariepinus.

The result on pH of leachate from Jeram Sanitary Landfill in Malaysia was less acidic (7.35), the BOD and COD levels were 27,000 and 51,200 mg/l respectively, with acute toxicity test against Orechromismossambicus indicating LC₅₀ value of 3.2% v/v 15. Comparatively, leachate of our study was more acidic. However, the acidity of leachate from dumpsite may vary depending on its characteristics in terms of maturity and stability 1516, type of waste stream and even climatic condition of the location. Other factors may include waste composition, technology adopted, and the dumpsite mode operation, physicochemical properties, meteorological and hydrogeological 1718.

Another author reported mortality of dumpsite leachate against tilapia specie (Sarotherodonmossambicus) with LC₅₀ values of 1.4 and 12% v/v in two respective sampling months 19. Toxicity test of leachate using fish Tawes was carried out and result demonstrated toxicity with LC50 value of 0.358%, with clinical signs of protruded eyes and brown skinned stomach 20. Carp (Cyprinus carpio) from Malasia were tested against dumpsite leachates from three different locations, results had COD and ammonia levels of 1640 - 7600 mg/l and 321.22 - 956.86 mg/l respectively, and also toxicities were demonstrated with LC₅₀ values of 1.132, 2.0 and 3.822% respectively 21.

As reported by Sisinno et al. 22 the 48hours acute toxicity of pure and treated dumpsite leachate were investigated against zebrafish (Brachydanio rerio) with LC₅₀ values of pure leachate samples inclusive in the range of 2.2 - 5.7% (v/v). Another author reported LC50 values as 19.2% and 53.0% after 48 hours for adults and fingerlings of Japanese killifish medaka (Oryziaslatipes), respectively 23.

The research investigated the toxicological activities of leachate from Municipal Solid Waste dumpsite. The results obtained revealed varying degree of toxicity from the leachates. The highest degree of toxicity was demonstrated from the most acidic leachate, with more adverse effect on the fingerlings. This study confirmed that leachates from dumpsite are toxic to biodiversity. Hence policies to characterize, treat, reduce, reuse and recycle waste stream should be encouraged. In addition regulators and all stakeholders should enact laws to check anthropogenic activities.