Lagos lagoon sediment organic extracts and polycyclic aromatic hydrocarbons induce embryotoxic, teratogenic and genotoxic effects in Danio rerio (zebrafish) embryos

Abstract

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.

Keywords: Embryotoxicity; Genotoxicity; Lagos lagoon; Sediment; Teratogenicity; Zebrafish embryos.

Fig. 1

Map of Lagos lagoon showing sampling sites for sediment collection

Fig. 2

Embryotoxicity and teratogenicity of PAHs to zebrafish. Percent mortality (a), hatch rate (b), abnormalities (c) and heart rate (beats per minute (d)) at 72 hpf of exposure to increasing concentration of naphthalene, phenanthrene, pyrene and benzo[a]pyrene and a PAH mixture, as well as DMSO (0.05 % v/v) and untreated control. The exposure concentrations of individual compounds were 2.5, 25 and 50 μM. The concentrations for the PAH mixtures are set at low (L), medium (M) or high (H); see Table 1 for concentrations of individual PAHs within each mixture. Data are presented as average ± SE, and significant differences (p ≤ 0.05) to vehicle control are marked (*). Where error bars are not visible, the number of animals alive or affected between repeats was the same or similar

Fig. 3

Embryotoxicity and teratogenicity of extracts from Lagos lagoon sediments to zebrafish. Percent mortality (a), hatch rate (b), abnormalities (c) and heart rate (beats per minute (d)) at 72 hpf following exposure to increasing concentration of sediment extract (eQsed/mL) from the four sampling sites Ilaje, Iddo, Atlas Cove and Apapa, as well as DMSO (0.25 % v/v) and untreated control. Data are presented as average ± SE, and significant differences (p ≤ 0.05) to vehicle control are marked (*). Where error bars are not visible, the number of animals alive or affected between repeats was the same or similar

Fig. 4

Representative images of teratogenic effects observed at 72 hpf following exposure of zebrafish to individual compounds, PAH mixture and sediment extracts from sampling regions. Exposures were as follows: 0.05 % DMSO control (a), 50 μM naphthalene (b), 50 μM phenanthrene (c), 2.5 μM pyrene (d), 25 μM B[a]P (e), 50 μM PAH mixture (f), water control (g), 0.25 % DMSO control (h), 25 mg Ilaje eQsed/mL (i), 6.25 mg Iddo eQsed/mL (j), 25 mg Atlas Cove eQsed/mL (k) and 2.5 mg Apapa eQsed/mL (l). Examples of defects: S scoliosis, SG stunted growth, PO pericardial oedema, YSO yolk-sac oedema, EH elongated heart, TTC tail tip curvature

Fig. 5

Oxidative damage to DNA in zebrafish measured at 24, 48 and 72 hpf, upon exposure to selected PAHs and PAH mixture (a) and sediment extracts (b). The exposure concentrations of individual compounds were 2.5, 25 and 50 μM. The concentrations for the PAH mixture are set at low (L) or high (H); see Table 1 for concentrations of individual PAHs within each mixture. Data are presented as average ± SD, and significant differences (p ≤ 0.05) in elevated levels are marked (*) in comparison to vehicle control within the same time point, as well as between time points for a given concentration ()