Pyrene fate affected by humic acid amendment in soil slurry systems

BACKGROUND: Humic acid (HA) has been found to affect the solubility, mineralization, and bound residue formation of polycyclic aromatic hydrocarbons (PAHs). However, most of the studies on the interaction between HA and PAH concentrated on one or two of the three phases. Few studies have provided a simple protocol to demonstrate the overall effects of HA on PAH distribution in soil systems for all three phases. METHODS: In this study, three doses of standard Elliott soil HA (ESHA), 15, 187.5, and 1,875 μg ESHA/g soil slurry, were amended to soil slurry systems. (14)C-pyrene was added to the systems along with non-radiolabeled pyrene; (14)C and (14)CO(2 )were monitored for each system for a period of 120 days. RESULTS: The highest amendment dose significantly increased the (14)C fraction in the aqueous phase within 24 h, but not after that time. Pyrene mineralization was significantly inhibited by the highest dose over the 120-day study. While organic solvent extractable (14)C decreased with time in all systems, non-extractable or bound (14)C was significantly enhanced with the highest dose of ESHA addition. CONCLUSION: Amendment of the highest dose of ESHA to pyrene contaminated soil was observed to have two major functions. The first was to mitigate CO(2 )production significantly by reducing (14)CO(2 )from (14)C pyrene mineralization. The second was to significantly increase stable bound (14)C formation, which may serve as a remediation end point. Overall, this study demonstrated a practical approach for decontamination of PAH contaminated soil. This approach may be applicable to other organic contaminated environments where active bioremediation is taking place.