Naphthalene is often a recalcitrant petroleum compound that keeps sites from clean closure. This resistance to remediation is due to naphthalene’s relative high adsorption and low solubility rates. Naphthalene has an aqueous solubility of 3.1E1 mg/l compared to benzene at 1.75E3 mg/l . Naphthalene has an affinity of adsorption expressed as the octanol/water partition coefficient (log Kow) of 3.26, while benzene has a log Kow of 2.13. For further comparison, acetone has a high water solubility at 1E6 mg/l and low log Koc of -0.24. In a study of relative degradation rates, the USEPA found a first order kinetic constant of 14.0 L/hg for naphthalene and 0.234 for benzene in activated sludge. Despite these challenges, naphthalene bioremediation with Petrox microbes has been successful at many spill sites.
Microbes initiate metabolism of naphthalene by inserting two oxygen atoms into the naphthalene structure. This initial step is catalyzed by naphthalene dioxygenase. Tests of sites inoculated with Petrox microbes show naphthalene dioxygenase at 1E8 to 1E10.
Petrox microbes thrive on naphthalene to the extent that naphthalene is occasionally used in the QA/QC process to verify Petrox viability and effectiveness. In this test, the Petrox organisms are placed on an agar devoid of a carbon source. The naphthalene is applied to the top plate as the sole carbon source. The Petrox viability is then demonstrated by colony growth on the top plate as shown on the following picture.