iInvestigation of polybrominated flame retardants and potentially toxic metals in soil,sediment and water,of the Obafemi Awolowo Unversity dumpsite and receiving stream
This study investigated the occurrence and levels of polybrominated flame retardants and potentially toxic metals in soils, sediment and water of the Obafemi Awolowo University Dumpsite and its receiving stream. It also monitored the temporal, spatial and seasonal distribution of the analytes in the matrices and evaluated the health risk of the potentially toxic metals in soils and sediments of the study area. These were done with a view to evaluating the pollution status of the studied area with respect to polybrominated fire retardants and potentially toxic metals. Sampling was done on seasonal basis comprising of May- August and November-February, respectively, for wet and dry seasons. Soil samples of the dumpsite and land space towards the stream were collected using an auger at 0-15 cm and 15-30 cm depths and 50 m away from each other. Water and sediment samples were collected from the receiving stream at six different points that included the upstream and downstream points. Extraction of polybrominated diphenyl ethers (PBDEs) from water, sediment and soil samples were done using liquid-liquid extraction and soxhlet extraction methods with dichloromethane as the extraction solvent. Clean-up of the extracted samples was done using multi-layer silica gel chromatography. The potentially toxic metals were analysed using Inductive Couple Plasma Optical Emission Spectrometry while Gas Chromatography Mass Spectrometry was employed for the quantification of the PBDEs. The total mean values of PBDEs in the dumpsite soil ranged from 0.36 ± 0.34 ng/g BDE - 47 to 13.84 ± 28.18 ng/g BDE- 153. Total PBDEs indicated that concentrations in 0-15 cm layer were higher than those in the 15-30 cm layer. The concentration of Ʃ6PBDEs in the stream water ranged from 0.03 – 0.31 ng/ml while the values in the sediments ranged from 0.83 – 10.43 ng/g with BDE-153 occurring as the dominant congener in all the matrices analyzed. Seasonal variability of PBDEs in the matrices indicated that higher levels were found during the wet season in the dumpsite and the receiving stream. The mean values of potentially toxic metals in the dumpsite soil ranged between 3.12 mg/kg Ni and 15500 mg/kg Al. Geo-accumulation study indicated that the soil of the dumpsite and stream sediment were practically unpolluted with, Fe, Cr, Al and Si; strongly polluted with Zr; while the soil and sediment samples were polluted with respect to Se, As, Th, U and Y. Mean levels of the potentially toxic metals in the dumpsite were higher in wet season than dry season. The mean values (mg/kg) of potentially toxic metals in the sediment of Asunle stream ranged from 0.10 Sr to 7260 Fe. The health risk assessment of most of the potentially toxic metals in the dumpsite soil and sediments of Asunle stream revealed that their chronic daily intake for both carcinogenic and non-carcinogenic effects gave hazard quotient for exposure that exceeded the acceptable USEPA value of 1.0. This study revealed that the environmental matrices of the area under investigation contained higher levels of PBDEs and potentially toxic metals than recommended by WHO and USEPA.