Kehinde O. Olayinka

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.

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.

Statistical analyses and risk assessment of potentially toxic metals (PTMS) in children’s toys

Abstract Chemical exposure of children, especially from toys, is an engineering concern. The concentration and availability of potentially toxic metals (PTM) in children’s toys were determined to assess the risk that these metals pose to children. Samples of 25 toys imported from China to Nigeria were purchased. Ternary acid digestion, followed by Atomic Absorption Spectrophotometry, was used to determine the concentration of PTM in the sample. Simulations of the saline and stomach acid extraction conditions were performed to determine the concentrations of PTM that could leach out from the toys during children’s mouthing behaviours (available PTM), including chewing, sucking and swallowing. The total concentrations of PTM in the toys ranged from 3.55–40.7, 3.21–38.2, 9.78–159, 3.55–11.2, and 36.1–106 mg/kg for Cd, Cr, Cu, and Pb, respectively. Availability studies showed concentrations ranging from 2.60–5.60 mg/kg for Pb, 0.53–2.03 mg/kg for Cd and 0.15–2.88 mg/kg for Ni after saline extraction, and the concentrations after stomach acid extractions ranged from 3.33–7.10 mg/kg, 1.15–3.15 mg/kg and 1.33–1.81 mg/kg for Pb, Cd and Ni, respectively. Statistical analysis showed a positive correlation between the total concentration of PTM and toys made from PVC materials. The risk assessment study showed that Cd posed the highest risk, with a hazard index (HI) as high as 4.50 for saline extraction. The study revealed that more precaution is needed during the manufacture of children’s toys.

Studies and Transactions on Pollution Assessment of the Lagos Lagoon System, Nigeria

The Lagos Lagoon system is a brackish coastal lagoon—the largest in the West African coast with a large series of estuaries—located between longitude 3o23′ and 3o40′E and between latitude 6o27′ and 6o48′N. It is a shallow expanse of water (0.3–3 m deep), 50 km long and 3–13 km wide and separated from the Atlantic Ocean by a narrow strip of barrier bar complex. This report is on the levels of pollution and nutrients status of the Lagos Lagoon system including physicochemical properties, pesticides organochlorines (OC), polyaromatic hydrocarbons (PAHs), heavy metal species and nutrients observed between 2002 and 2008. Watersheds of the highways on the lagoon had higher concentrations of nutrients (phosphorus and nitrates) relative to other locations on the Lagoon. The western part of the Lagoon was found to have higher concentrations of Cd, Cu, Pb and Zn than the other points. Lagos Lagoon and the adjoining creeks show high anthropogenic input of PAHs and other persistent organic pollutants (POPs). The major hydrocarbon index in most samples was at C29, C31 and C27, indicating vascular plants sources. Mean PBT levels in water and in sediment increased with time between 2004 and 2007. PBT distribution in the lagoon followed the pattern, sediment > biota > water, though some exceptions occurred where the biota bioaccumulated more PBTs than are found in both sediment and water. The Lagoon biota bioaccumulated organochlorine pesticides above allowable limits and thus pose a high risk to human health. The levels of some pollutants in the Lagoon have negatively impacted on the environmental quality which has indirectly affected the social and economic activities of the dependants and this requires improved management strategies to ameliorate. Indeed with the high population that the estuary/lagoon system supports, consideration for its designation as an international waterbody and its concomitant attention is now paramount.

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).

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.

Bioaccessibility-Based Risk Assessment of PAHs in Soils from Sites of Different Anthropogenic Activities in Lagos, Nigeria Using the Fed Organic Estimation Human Simulation Test Method

ABSTRACT The aim of this study was to carry out a bioaccessibility-based risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soils from sites of different anthropogenic activities in Lagos, Nigeria. Using an in vitro gastrointestinal model—Fed Organic Estimation Human Simulation Test method (FOREShT), the concentration of bioaccessible 16 priority US Environmental Protection Agency (USEPA) PAHs in soils were determined. Total concentration of 16 priority USEPA PAHs was also determined. The concentration range was 702–253,922 ng g−1 and 92–760 ng g−1 for total and bioaccessible PAHs, respectively. For persons involved with activities at these sites no health risks were observed, based on bioaccessibility values of PAHs. Mean daily intake of PAHs from these soils were below the oral mean daily intake threshold for PAHs in food. Also, overall estimated theoretical cancer risk (2.5 × 10−09, 6.5 × 10−07, 5.5 × 10−10, 2.7 × 10−09, 6.5 × 10−10, 9.5 × 10−10, 2.0 × 10−09, and 4.1 × 10−07 for the eight sites based on their bioaccessible concentration) for exposure to PAHs in surface soils were below the health guidelines for extreme (1 × 10−04) and normal (1 × 10−06) exposures.

Concentrations of polychlorinated biphenyls in soil and indoor dust associated with electricity generation facilities in Lagos, Nigeria

Concentrations of 7 indicator polychlorinated biphenyls (PCBs) were measured in dust and soil samples from 12 power stations collected over the two major seasons of the Nigerian climate. Median ƩPCB7 concentrations in soil ranged from 2 ng/g for power station A to 220 ng/g for power station I; while those in dust ranged from 21 ng/g for power station L to 2200 ng/g for power station I. For individual congeners, median PCB concentrations ranged from 3.8 ng/g for PCB 101 to 52 ng/g for PCB 180 in dust, and <0.07 ng/g for PCB 28 to 5.9 ng/g for PCB 153 in soil. The type of power station activity exerted a significant influence on concentrations of ΣPCB7 in dust and soil (generation > transmission > distribution). Congener patterns in dust and soil samples were compared using principal component analysis (PCA) with those in transformer oil samples from 3 of the power stations studied and with common PCB mixtures (Aroclors). This revealed congener patterns in soil were more closely related to that in the transformer oil than dust. Congener patterns in most samples were similar to Aroclor 1260. Concentrations of PCBs in soil samples close to the transformers significantly exceeded those in soil sampled further away.

Use of the Physiologically Based Extraction Test for the Assessment of Bioaccessibility of Toxic Metals in Vegetables Grown on Contaminated Soils

Background An important concern for human health is the uptake of toxic metals by vegetables from soils and their consumption by humans. Objectives To assess the oral bioaccessibility of metals in vegetables (spinach, pumpkin, celosia, okro leaves and waterleaf) grown on contaminated soils collected from five different sites in Lagos, Nigeria. Methods The soil and vegetables were acid digested and the total metal concentrations (copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb) and zinc (Zn)) were determined using a flame atomic absorption spectrophotometer. A bioaccessibility study of the edible parts of the vegetables was estimated using the modified in vitro physiologically based extraction test (PBET). Results The results for total concentration showed that individual vegetable types differed in their levels of metal uptake. The values were in the range of 0.5-13.5 mg/kg for Cd, 2.0-221 mg/kg for Cu, 2.5-37.7 mg/kg for Cr, 10-250 mg/kg for Zn. Pb was below the detection limit. The transfer factor from soil to vegetable followed the order of Cd >Zn > Cu > Cr >Pb. Discussion For the PBET study, metals were solubilized mostly in the gastric phase, and the results varied in the range of 0.4-114.4 mg/kg for Cu, 0.1-2.4 mg/kg for Cd, and 0.8-137 mg/kg for Zn, but there was little or no bioaccessibility in the intestinal phase. Cr and Pb were non-detectable in either the gastric or intestinal phase. Conclusions Although the level of metals (Cd, Cu and Zn) available for absorption in the gastric phase were found to be low in most of the vegetables studied, the experiment revealed that metals are likely released in the human gut after intake of vegetables grown on contaminated soil.