Sorption of PFOS to different solid components as a function of aqueous chemistry

Abstract: Knowledge of fate and transport of chemical contaminants in the environment is essential for reducing their adverse effects to humans and wildlife. Surface and ground waters serve as drinking water which helps to sustain life. It is undeniably true that the understanding of chemical contaminants behavior in the environment is important to better prevent their negative effects. This study was conducted for understanding the distribution of a persistent organic pollutant (POP), the perfluorooctane sulfonate (PFOS) including its isomers between aqueous and solid phases and to understand the mechanisms affecting its distribution in surface and groundwater. Different sorbents with geo-environmental significance were selected. Variation of aqueous chemistry was done in order to understand the effect of different environmental conditions on PFOS sorption behavior. To perform this study, suspension of goethite (38.54g/L), fine soils and peat with particle size less than 0.5 mm and mm respectively, two fractions of steel slag (i.e., size of >0.9 mm and between 0.9 and 2 mm) and white powder of Al(OH)3 were used. The levels of total and PFOS isomers were quantified using an Ultra-Performance Liquid chromatograph coupled to a triple quadrupole mass spectrometer XEVO-TQS. Results showed that sorption of PFOS was mostly depending on pH; sorption decreased as pH increased. The electrostatics interaction was suggested to be the main mechanism that controls the sorption. Results of this study showed that goethite, peat, Al(OH)3 and soil can sorb PFOS with respective maximum log Kd up to 2.31, 2.12, 1.98 and 1.89 at pH around 4.50. The addition of humic acid (HA) and fulvic acid (FA) affected the sorption capacity depending on pH range and sorbent. The HA which has a high molecular weight showed an enhanced sorption, implying the existence of hydrophobic interactions. The addition of Na2SO4 to the system increased the sorption at high pH, when the sorbent surface bears less average positive charge. However, the sulfate competed with sorption at low pH. The influence of Na2SO4 to enhance the sorption, was understood in term of changing the solution ionic strength and salt-out effect which affected the sorption of PFOS. In this study, it is revealed that PFOS isomers had different sorption affinity to different sorbents depending on solution chemistry and nature of sorbent. Regarding the sorption capability of slag, the silica reduced slag sorbed more than the aluminum reduced slag. The small slag size-fraction demonstrated a lower sorption capacity for PFOS sorption. The present of HA and SO42- demonstrated the capability to enhance the PFOS sorption to slags. iii The PFOS sorption to slag needs to be further explored for understanding well the sorption kinetics and mechanism controlling the sorption. Furthermore, more studies of influence of sulfate could be important, since their influence on PFOS sorption was not well documented.