Concentrations and Toxic Implications of Dioxin-Like Polychlorinated Biphenyls in Soil Samples from Electrical Power Stations in Lagos, Nigeria

Dioxin-like polychlorinated biphenyls (dl-PCBs) are ubiquitous chemicals which mediate toxicity in a way similar to polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. In silico modeling was used to predict the absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of eight dioxin-like PCBs in soil samples of 12 power stations in Lagos, Nigeria. Concentrations of Σdl-PCB₈ in soil samples ranged from 490 to 61,000 pg g^-1 , with mean concentrations of 17,000 pg g^-1 . The corresponding toxic equivalent (TEQ) concentrations of Ʃdl-PCB₈ ranged from 0.01 to 450 pg TEQ g^-1 , with a mean value of 42 pg TEQ g^-1 . Mean TEQ concentrations for Ʃdl-PCB₈ in soil samples from all but one of the sites exceeded the Canadian guideline value of 4 pg TEQ g^-1 and the US and German guideline values of 5-10 pg TEQ g^-1 . However, the TEQ concentrations obtained were all below the US action level of 1000 pg TEQ g^-1 . The ADMET predictions revealed that all studied dl-PCBs are inhibitors of three major isoforms (1A2, 2C9, and 2C19) of cytochrome P450 enzyme. Acute oral toxicity (median lethal dose) predictions revealed that all target dl-PCBs were class III compounds. Hepatotoxicity and carcinogenicity were positive, signifying that the studied compounds all have a tendency to elicit these effects. Occupational daily TEQ exposure via soil ingestion was estimated for an average adult worker weighing 70 kg. The maximum exposure obtained was 0.14 pg TEQ kg^-1  body weight day^-1 , which is half of the European Food Safety Authority (EFSA) tolerable daily intake (TDI) for dioxin-like compounds. This raises concern over the possible exceedance of the EFSA TDI for these workers if other dietary and nondietary exposure pathways and dioxin-like compounds are considered. Environ Toxicol Chem 2022;41:800-809. © 2021 SETAC.

Sawmill Activities Near the Lagos Lagoon, Nigeria: Polycyclic Aromatic Hydrocarbons and Embryotoxic Evaluations of Sediment Extracts Using Clarias gariepinus

The physicochemical parameters and 16 priority PAHs in surface water, porewater and sediment at a sawmill wastes-impacted and High-Rise study sites on the Lagos lagoon in Nigeria were assessed. Further, the embryotoxic effects of sediment organic and porewater extracts from the study sites were evaluated in Clarias gariepinus (African sharptooth catfish) embryos for 26 h. High molecular weight PAHs dominated the PAHs profile especially in the sediment. Source apportionment of the PAHs in the three environmental matrices revealed mainly pyrogenic sources. Developmental abnormalities and decreased hatching success were observed in C. gariepinus embryos exposed to extracts from the Okobaba site compared to High-Rise study site. The results demonstrate the potential though non-significant ecological risk of sawmill activities near the lagoon on water quality and fisheries. Further studies are recommended to provide holistic evidence-based information to promote sustainable fisheries in the lagoon in support of the UN SDGs 13 (climate action) and 14 (life below water).

Wet nitrogen and phosphorus deposition in the eutrophication of the Lagos Lagoon, Nigeria

Air pollution is influenced by wind-aided particulate suspension, open-air waste burning, and fossil fuel combustion. The pollutants from these sources eventually deposit on ambient surfaces. Atmospheric wet deposition into Lagos Lagoon may be significant additions to the nutrient levels of the eutrophic lagoon. Precipitation was monitored at three stations in the Lagos Lagoon basin from May to November, 2012, in order to estimate the contribution of wet deposition to the nutrient cycles of the lagoon. Water samples were digested with potassium persulfate, and the species of phosphorus (P) and nitrogen (N) were analyzed by colorimetric methods. The mean [NO₃^-+NO₂^-]-N level was 0.39 ± 0.51 kg ha^-1 month^-1. The average total N was 3.16 ± 6.39 kg ha^-1 month^-1. The mean soluble reactive P was lower than the [NO₃^-+NO₂^-]-N averaging 0.06 ± 0.09 (at control site S2) to 0.24 ± 0.10 kg ha^-1 month^-1 (at site S1). Average total P was 1.25 ± 0.82 kg ha^-1 month^-1. The annual total N (May-September) was 4.55 (at S2) to 32.4 kg ha^-1 year^-1 (at S3). The annual total P (May-November) over Lagos Lagoon basin was 5.06 kg ha^-1 year^-1 (at S2). This study demonstrated that wet deposition of anthropogenically derived nutrients to the Lagos Lagoon is ongoing and may represent a considerable proportion of the total nutrient loading to it. The increased P availability in the wet deposition is likely responsible for the water hyacinths, which usually blossom on Lagos Lagoon during the late rainy season, and the reported harmattan-season bottom water hypoxia.

Assessment of nitrogen and phosphorus loading by atmospheric dry deposition to the Lagos Lagoon, Nigeria

Surface water pollution has been found to be considerably driven by the contributions of airborne particles, open-air waste burning and fossil fuel combustion, ammonia volatilization from excreta, fertilizer and derivatives from explosive factories. Atmospheric deposition into the Lagos Lagoon is suspected to be a major contributor to the nutrient levels of the lagoon. Atmospheric dry nutrient deposition was monitored at six stations around the Lagos Lagoon from January to June 2012 in order to estimate the contribution of atmospheric deposits into the lagoon's nutrient cycles. Species of phosphorus (P) and nitrogen (N) in the lagoon water were analyzed by colorimetric methods. Mean [NO(-) 3 + NO(-) 2]-N was 3.08 ± 2.10 mg m(-2) day(-1) (0.55-8.73 mg m(-2) day(-1)). The (NO(-) 3 + NO(-) 2)-N was only about 2 % of total N but [NH(+) 4 + organic]-N was approximately 38 % of total N. Particulate N was about 60 % of total N. Average total N was 144 ± 94.9 mg m(-2) day(-1) (48.0-285 mg m(-2) day(-1)). Average soluble reactive P was significantly lower than [NO(-) 3 + NO(-) 2]-N averaging about 0.12 ± 0.12 mg m(-2) day(-1). Soluble reactive P (SRP) was less than 2 % of total P but soluble organic P was about 86 % of total P. Particulate P accounted for about 12 % of total P. Average total P was 4.56 ± 10.1 mg m(-2) day(-1) (0.48-31.6 mg m(-2) day(-1)). This study shows that atmospheric deposition of nutrients into the Lagos Lagoon is taking place and this may represent a considerable proportion of the total nutrient loading of the lagoon.

Fractionation and ecotoxicological implication of potentially toxic metals in sediments of three urban rivers and the Lagos Lagoon, Nigeria, West Africa

The potential environmental impact of sediment-bound Cd, Cr, Cu, Pb and Zn in three trans-urban rivers in Lagos state and in the Lagos Lagoon was assessed by use of the modified Community Bureau of Reference (BCR) sequential extraction. The quality of the data was checked using BCR CRM 143R and BCR CRM 701. Good agreement was obtained between found and certified/indicative values. Of the rivers, the Odo-Iyaalaro, was generally the most contaminated and the Ibeshe the least. Higher concentrations of metals were generally found in the dry season compared to the wet season. Cadmium and Zn were released mostly in the acid exchangeable step of the sequential extraction, indicating that they have the greatest potential mobility and bioavailability of the analytes studied. Chromium and Cu were associated mainly with the reducible and oxidisable fractions, and Pb predominantly with the reducible and residual fractions. Sediments with the highest pseudototal analyte concentrations also released higher proportions of analytes earlier in the sequential extraction procedure. The study suggests that, during the dry season, potentially toxic metals (PTM) may accumulate in sediments in relatively labile forms that are released and can potentially be transported or bioaccumulate in the rainy season. Application of risk assessment codes and Hankanson potential risk indices indicated that Cd was the element of greatest concern in the Lagos Lagoon system. The study indicated that there is a need to strengthen environmental management and pollution control measures to reduce risk from PTM, but that even relatively simple strategies, such as seasonal restrictions on dredging and fishing, could be beneficial.

Assessment of occupational exposure to polycyclic aromatic hydrocarbons via involuntary ingestion of soil from contaminated soils in Lagos, Nigeria

Soils from 12 sites in Lagos area, Nigeria impacted by anthropogenic activities were extracted by ultrasonication and analysed for the concentration of 16 priority polycyclic aromatic hydrocarbons (PAHs) by gas chromatograph-mass spectrometer (GC-MS). The concentration of the sum of PAHs ranged from 0.2 to 254 μg/g at these sites. The sum benzo[a]pyrene-equivalent dose (BaPeq) at the sites ranged from 0.0 (K, forest soil) to 16.7 μg/g (C, the lubricating oil depot soil). Mean daily intake (MDI) for the composite soils samples when compared that of food revealed that some of the individual PAH in samples from sites A (Dump site), C (Depot and loading point for used for black oil), F (Dump site), G(petroleum depot), H (Roadside) and L (Car park) exceeded the recommended the recommended MDI threshold for food, indicating some risk associated with activities on these sites based on this ingestion estimate exceeded value. 8.2 × 10(-6), 7.1 × 10(-7), 1.2 × 10(-4), 4.9 × 10(-7), 7.3 × 10(-7), 1.4 × 10(-5), 7.9 × 10(-5), 4.6 × 10(-6), 3.4 × 10(-7), 2.4 × 10(-7), 2.2 × 10(-7) and 1.1 × 10(-4) estimated theoretical cancer risk (ER) for an adult with a body weight of 70 kg working on sites were composite soil samples A, B, C, D, E, F, G, H, I, J, K and L respectively were sampled. The ER from occupational exposure to surface soil based on oral ingestion were all higher than the target risk of 1 × 10(-6) for normal exposure but were all within the 1 × 10(-4) for extreme exposure for most of the sites except for site C and L. The differences in concentration and risk were related to the different activities (e.g., handling of petroleum products, open burning, bush burning) undertaken at these locations. However, it should be noted here that the resultant risk could be overestimated, since these calculations were based on an exhaustive extraction technique which may be different from uptake by the human guts (bioavailability study).

Multivariate analysis of potentially toxic metals in sediments of a tropical coastal lagoon

Surface sediments collected from the Lagos Lagoon, Nigeria, and three adjoining rivers were analysed for their physicochemical properties and pseudo-total concentration of the potentially toxic metals (PTM) Cd, Cr, Cu, Pb and Zn. The concentration of the PTM varied seasonally and spatially. Odo-Iyaalaro was observed to be the most polluted river, with highest concentrations of 42.1 mg kg(-1), 102 mg kg(-1), 185 mg kg(-1), 154 mg kg(-1) and 1040 mg kg(-1) of Cd, Cr, Cu, Pb and Zn, respectively, while Ibeshe River was the least contaminated, apart from a site affected by Cu from the textile industry. Some of the sediments were found to be above the consensus-based probable effect concentrations and Dutch sediment guideline for metals. Overall metal concentrations were similar to those reported for other tropical lagoon and estuarine systems affected by anthropogenic inputs as a result of rapid urbanisation. Due to the large number of samples, principal component analysis was used to examine relationships within the data set. Generally, sediments collected during the dry season were observed to have higher concentration of PTM than those collected during the rainy season. This means that PTM could accumulate over a prolonged period and then be released relatively rapidly, on an annual basis, into tropical lagoon systems.

The contribution of roadside soil to phosphorus loading in the eutrophic Lagos Lagoon, Nigeria

Roadside soils were sampled from the Lagos Lagoon catchment during the wet and dry seasons over the period 2005-2009. Lagoon sediment samples were also collected within the same period. All samples were digested with aqua regia to determine total phosphorus and extracted with 0.5 M sodium bicarbonate to determine the bioavailable fraction (Olsen-P). A segmented flow analyser method was used for analysis and good accuracy was demonstrated for two reference soils (SO-2 from CCMET and SRM 2711 from NIST). The Lagos Lagoon is a hypereutrophic water body (1270 ± 1170 μg P L(-1)), with significant areas of anoxia and water hyacinth growth. The total phosphorus concentrations in roadside soils (16 sites; mean ± 2 S.D.) were 285 ± 279 mg kg(-1) in the wet season and 424 ± 629 mg kg(-1) in the dry season, indicating that rainwater leaching is a major source of phosphorus in the lagoon. The bioavailable fractions were 5.17 ± 3.47 mg kg(-1) (2.1 ± 1.5% of the total) in the wet season and 13.0 ± 8.7 mg kg(-1) (4.3 ± 4.5% of the total) in the dry season.

Comparison of three sequential extraction protocols for the fractionation of potentially toxic metals in coastal sediments

In the determination of the best sequential extraction procedures (SEP) for the speciation of metals in sediment samples from the Lagos lagoon system, three sequential extraction procedures were compared for the fractionation of Cd, Cr, Cu, Pb, and Zn. The SEP compared included a modified Tessier's procedure carried out in five steps, while the two other procedures were the three-step original Community Bureau of Reference (BCR) and the modified BCR techniques (four steps). Quantification of the metal concentration was achieved with a flame atomic absorption spectrophotometer. The results obtained by the three methods were compared, and the modified BCR and Tessier SEP were found to extract more Cu, Cr, Pb, and Zn in the reducible phase and therefore a decrease in the oxidizable phase than the original BCR SEP. The most mobile elements were found to be Cd, Pb, and Zn. These are of environmental concern, as these potentially toxic metals could be easily released into the aquatic environment with consequent ingestion by aquatic organisms, thereby entering the food chain. The mass balance (percent recovery) was found to be between 85% and 115% in most cases. Prior to the comparison, the analytical performance of the laboratory was tested using a secondary reference material, GLAURM, using the three-step modified BCR procedure. The results showed high reliability of the analytical performance of the laboratory for all the metals considered.