Strategies for the extraction of free and bound polycyclic aromatic hydrocarbons in run-off waters rich in organic matter

The objective of this study was to optimize and characterise extraction methods to examine the effects of wood ash application on polycyclic aromatic hydrocarbons (PAHs) concentrations in run-off waters for the evaluation of their distribution by storage in the different compartments (free and bound to dissolved organic matter, DOM), what influence their stability and persistence. The feasibility of solid phase extraction (SPE) and stir bar sorptive extraction (SBSE) for the determination of eight PAHs in run-off water samples has been evaluated. Both are appropriate to determine PAHs in run-off waters, but SPE is suitable for the determination of overall PAHs, while SBSE is used for the determination of free PAHs. The combination of both extraction techniques can then be used to estimate PAHs bound to DOM. Another approach based in the only use of SBSE is proposed for the estimation of all PAHs fractions (free, bound to DOM, and overall), once we are able to estimate the fraction percentage the free concentration represents. The percentage of free fraction was variable in the run-off waters with medium levels of DOM depending on the number of aromatic rings, molecular weight and water solubility of PAHs.