Abstract
In this study, toxic equivalent factors and sediment quality guidelines were employed for the assessment of toxicity potential of PAHs in 2 sediment cores collected from the center (RC) and shoreline (RS) of Reforme lake, SE Nigeria over the last ~1 century. Boundary cross plots of isomeric ratios such as Ant/Ant + Phe (>0.1) vs. Fl/Fl + Pyr (>0.4) and BaA/BaA + Chry (>0.35) vs. Icdp/Icdp + Bper (>0.2) indicated biomass combustion/domestic coal utilization as the main sources of PAHs input. The result revealed toxicity unit indices (TU1, 1.22 - 1.57) for the two cores were above the thresholds of no effect. The highest TU1 value found in the near-bottom layer (RS5, 20 - 25 cm) of the RS corresponding to geological time-frame ~1930-1947 coincided with the period of inhabitation by the European settlers along the lake’s catchments when coal or coal products utilization for domestic and recreational purposes was at its peak. On the other hand, TU2 values were <1 at all depth intervals, revealing unlikely PAH effects to resident organisms. Total toxicity equivalency factors (TEqFs) for the surface sediment of RS and RC were 9.29 ng/g TEqFs and 9.16 ng/g TEqFs, respectively, and indicated that more attention should be paid to BaPyr accumulation in the lake’s sediment.
Highlights
IntroductionTheir ubiquity may be associated with their persistence in the environment and due to their occurrence naturally (crude oil, forest fires or creates) as well as being products from incomplete combustion of organic matter and burning of fossil fuels
Calculation of TU1 was based on the summed ratios between the concentrations of each individual polycyclic aromatic hydrocarbons (PAHs) and their corresponding ISQGs, whereas calculation of TU2 was achieved from the summed ratios between the concentrations of individual PAHs and probable effects level (PEL) values
The highest TU1 value found in the near-bottom layer (RS5, 20 - 25 cm) of the RS corresponding to geological time-frame ~1930-1947 coincided with the period of European occupation of the lake’s catchments when domestic coal or coal products utilization and wood/grass burning for recreational purposes, respectively were at their peak
Summary
Their ubiquity may be associated with their persistence in the environment and due to their occurrence naturally (crude oil, forest fires or creates) as well as being products from incomplete combustion of organic matter and burning of fossil fuels. They have high adsorption capacity towards solid matrices or particulate matter due to their hydrophobic nature (Oyo-ita et al, 2016). They are widely used for environmental monitoring purposes (Liu et al, 2007; Oyo-ita & Oyo-ita, 2012; Oyo-ita et al, 2013)
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