Abstract
Polycyclic aromatic hydrocarbons (PAHs) are the ubiquitous contaminants in the environments. Owing to their low water solubilities and high partition coefficients, these compounds are easily deposited onto the particles of soils and sediments. Biodegradation is the only one mechanism for the natural attenuation of PAHs in soil environments. However, the bioavailability of PAHs will be diminished by sorption and by other environmental factors.Petroleum often contains PAHs and some trace elements. Therefore, PAHs and trace elements will coexist in a petroleum-contaminated soil. However, the interaction between the bioavailability of PAHs and trace element receives less attention. Therefore, the purpose of this study is to elucidate the effect of trace elements on the biodegradation of PAHs. Results obtained in this study showed that the biodegradation rate of PAHs decreased as the molecular weight and concentration of PAHs increased. The degradation rate was in the order of naphthalene, phenanthrene and pyrene. The addition of trace elements will change the activity of P. putida, subsequently decreasing the biodegradation rate of PAHs in aqueous solution. The biodegradation of PAHs could be significantly inhibited when the concentration of cadmium was higher than 10 mg/l. Whereas 50 mg/L of arsenic was needed to obtaine the obvious inhibition. This means that the cadmium has a higher inhibition effect than arsenic on the degradation of PAHs. Moreover, chromium has little effect on the inhibition of the biodegradation of PAHs due to the low solubility product of chromium hydroxide.In the soil-amended system, PAHs exhibited a biphasic desorption behavior. The rate constants of fast desorption and slow desorption were 0.0027 and 0.0001 hr-1, respectively. Biological reaction was the rate-limiting factor for controlling the residue of PAHs in fast desorption region. On the contrary, desorption of PAHs was dominant in the slow desorption stage. Also, the amendment of trace elements could inhibit the biodegradation of PAH in soil system. However, the extent of inhibition was less than that in aqueous system. Unlike the effect on trace element in aqueous solution, the addition of cadmium had less inhibition effect than arsenic on the degradation of PAH in soil environment. This may be attribute to that cadmium can be significantly uptake by microorganism.