An expansion of anthropogenic activity around Lagos lagoon, Nigeria, has raised concerns over increasing contaminants entering the lagoon’s ecosystem. The embryotoxicity, teratogenicity and genotoxicity of sediment organic extracts from four sampling zones around Lagos lagoon, Ilaje, Iddo, Atlas Cove and Apapa, as well as the dominant polycyclic aromatic hydrocarbons (PAHs) identified in water measured during the wet season (naphthalene, phenanthrene, pyrene, benzo[a]pyrene and a mixture of these), were assessed with Danio rerio embryos. Embryos were exposed to varying concentrations of toxicants from 0–72 h post-fertilization (hpf). Embryotoxicity at 72 hpf showed a dose-dependent increase in mortality upon exposure to extracts from all zones, except Atlas Cove. Similarly, higher levels of teratogenic effects, such as increased oedema, and haemorrhage and developmental abnormalities resulted from exposure to extracts from Ilaje, Iddo and Apapa zones. Treatment with single PAHs revealed that significant levels of detrimental effects were obtained only for phenanthrene. The modified comet assay revealed that the oxidative damage to DNA was generally low (<12 %) overall for all sediment extracts, but was significantly elevated with Ilaje and Iddo sediment extracts when compared with solvent controls. Oxidative damage was observed with the single PAHs, phenanthrene and benzo[a]pyrene, as well as with the PAH mixture. This study highlights that Lagos lagoon sediment extracts have teratogenic, embryotoxic and genotoxic properties, which are likely due to the high molecular weight PAHs present in the extracts, some of which are known or are suspected human carcinogens.

Abattoirs are positioned close to freshwaters in most developing countries where untreated wastewaters are discharged into with potential risk to aquatic life such as fish and ultimately human health. We assessed physicochemical parameters, antibiotics (oxytetracycline and diclofenac) and algal load of effluent collected from a major abattoir in Nigeria. Furthermore, liver function enzymes, genotoxic and haemotoxic effects of subacute concentration (10% of 96 hLC50 value) of the wastewater were evaluated over a period of 28 d in Clarias gariepinus (The African Sharptooth Catfish). The 96 hLC50 value of the abattoir wastewater against C. gariepinus was 154.14 mL/L (15.4%). Nitrates, phosphates, sulphates, chloride, ammonia, TDS, TSS, BOD5 and heavy metals (Fe and Pb) in the wastewater were above permissible limits while diclofenac and oxytetracycline were below detection limit (BDL). Microalgae in the wastewater were mostly Bacilliariophyta (Navicula spp.) (45.64%) and euglenoids (Euglena and Phacus spp.) (49.48%). Liver function enzymes (LDH, AST, ALT) level were higher in exposed fishes except for ALP which was lower at day 28 compared to control levels. Erythrocytic genotoxic indices (nuclear abnormalities) were significantly higher (p < 0.05) in the exposed fishes particularly at day 28 compared to control. Haematologic indices level such as WBC, MCV MCH, MCHC increased significantly (p < 0.05) while lymphocytes, HGB, RBC, HCT levels decreased significantly (p < 0.05) in the exposed C. gariepinus by day 28 compared to control. These results demonstrate potential adverse effects posed to aquatic fish species in the Ogun River by the discharge of the abattoir effluent. The microalgae species identified in the effluent may be explored for pre-treatment of the effluent before discharge in order to prevent eutrophication and increased pollutant load in the River. The study results will contribute to evidence-based environmental risk management of the River which is relevant to the UN SDGs 6 (clean water and sanitation), 11 (sustainable cities and communities) and 14 (sustaining life below water).

This study evaluated the drinking water quality and associated human health risks in three (3) rural and urban areas each in Ibeju-Lekki and Epe local government areas of Lagos, Nigeria. Two hundred structured questionnaires were administered to stakeholders, and samples were obtained from prevailing drinking water sources in the study areas using standard methods for microbiological, physicochemical, heavy metals and human health risk evaluations. Wells and boreholes were the major sources of drinking water in the rural and urban areas, respectively. Drinking water samples from the study areas contained more than one pathogenic bacterium. The physicochemical parameters except total organic carbon (TOC) were within permissible limits of the Nigerian Standard for Drinking Water Quality (NSDWQ). The mean values of Cd and As exceeded the maximum permissible limit of NSDWQ. The hazard quotient of cadmium and arsenic was greater than 1 indicating potential health risks if the water is not treated. In order to achieve the UN Sustainable Development Goal 6 on clean water and sanitation by the next decade (2030), we recommend that frequent monitoring, treatment and stakeholders education on drinking water treatment techniques should be actively conducted particularly in rural areas in the state, country, region and continent.