EFFECT OF PHENOL AS A CONTAMINANT ON THE WILD PEARL OYSTER PINCTADA IMBRICATA RADIATA IN QATAR: ECOTOXICOLOGICAL APPROACH AND USE OF OYSTER SHELL STRUCTURE AS A POTENTIAL MITIGATION TOOL FOR PHENOLS REMOVAL FROM WATER

Abstract

Phenol removal is a vital environmental concern due to its toxicity and hazard effects. The current study investigates the removal of phenol by Pearl oyster Pinctada imbricata radiata for the first time in this region. The first objective of this study was to investigate the ecotoxicity of Pearl oyster Pinctada imbricata radiata for different concentrations of phenol by measuring the activity of some biomarkers of oxidative stress such as Catalase (CAT) and Superoxide Dismutase (SOD) activities. The biometric analysis of the maitained Pinctada imbricata radiata showed that the dominated size class was (4.5 cm -5.5 cm) in length representing 70% of the population. Furthermore, the biometric relations (length, width, and height versus weight) between size classes of Pinctada imbricata radiata showed negative allometric growth. The total proteins values decreased over time during the 96h acute toxicity experiment with no significant differences (p ? 0.001). CAT and SOD enzymatic activities for both gills and digestive glands showed an increase in values compared to the control organisms with significant differences (p < 0.001). These results indicated that Pearl oyster Pinctada imbricata radiata is an excellent bioindicator of phenol pollution and should be used for other pollutants indicator and in marine environmental pollution monitoring programs. The second objective was to use silver-impregnated oyster shell nanoparticles (OSNP-S) as a novel technique for the detoxification of phenol from water. Pearl oyster shell nanoparticles (OSNP) were prepared by a simple ball-milling process and impregnated with silver. A batch adsorption study was conducted at different pH values, temperatures, and initial phenol concentrations. The physical and chemical characterization of both OSNP and OSNP-S were determined with Scanning Electron Microscopy (SEM) and Fourier transform infrared spectrophotometer (FTIR). The surface area, pore radius, and pore volume were measured with Brunauer, Emmett, & Teller (BET) and Transmission electron microscope (TEM). Batch adsorption isotherms (Langmuir isotherm, Freundlich isotherm, Temkin isotherm, and Dubinin-Radushkevich isotherm models) were used. The results indicated that BET surface area, Langmuir surface area and pore volume of the OSNP were the highest comparing to OSNP-S. However, OSNP-S had the highest average pore volume (145.4 A?). The results of the batch analysis that was conducted at pH 6 were in favor of OSNP in terms of adsorbing the highest amount of phenol removal (36.98%). Whereas, at pH 10, the removal result was in favor of OSNP-S (25.89%). The highest phenol removal occurred at room temperature (25? C) at both pH conditions. The highest phenol removal of real olive wastewater was at pH 10 and room temperature by OSNP-S (56.78%). Based on the adsorption isotherm model, the adsorption capacity decreased by temperature and the coefficient of determination R2 of the Freundlich adsorption isotherm model showed the best equilibrium data for phenol adsorption with the physical interaction adsorption process. R2 at both pH 6 and pH 10 ranged from (0.9318- 0.9954). The Gibbs free energy ?G? was in negative sign, indicating that the adsorption process was thermodynamically feasible, spontaneous, and chemically controlled at all temperatures and both pH 6 and pH 10. The thermodynamic parameters of OSNP-S, positive ?H?, and negative ?S? at pH 6 showed that the adsorption process was endothermic with the decrease in the process randomness and the reduced confusion at solid-solution interface. Nevertheless, this was in reverse at pH 10. The phenol desorption was 97.44% and 98.64% by reacting 0.1 M NaOH and 0.1 M HCl respectively.