Interactions between polycyclic aromatic hydrocarbons and natural aquatic humic substances. Effect of chlorination

The effect of chlorination on the interactions between polycyclic aromatic hydrocarbons (PAH) and aquatic humic substances (AHS) was studied. Low levels of PAH were dissolved in prechlorinated AHS and formation of strong irreversible bonding was determined by solvent extraction of the samples after various PAH-AHS contact times, followed by GC/MS analysis. Partition-like interactions were studied by sealing AHS and prechlorinated AHS in dialysis tubes in a lake water system containing low levels of dissolved radioactively labeled PAH. Concentrations of PAH outside and inside the dialysis tubes after establishment of equilibrium in the system were determined by liquid scintillation counting of the water samples. No significant formation of strong PAH-AHS bonding was evident from the contact-time experiment. Interpretation of the results was complicated by the presence of ascorbinic acid in the samples, used for removal of residual chlorine prior to addition of PAH. The dialysis experiment showed that chlorination of AHS affected the formation of partition-like bonding to PAH. When a low level of chlorination was applied to the system no significant change in bonding capacity was observed. The PAH-AHS partition coefficient decreased when the level of chlorination increased. When excess chlorine was added to the AHS leaving a residual chlorine concentration in the samples, a negative partition coefficient was obtained for the system, i.e. the PAH remained in the lake water system outside the dialysis tubes.