The effects of LMWOAs on biodegradation of multi-component PAHs in aqueous solution using dual-wavelength fluorimetry Xing-Yuan Wei a , Ling-Zi Sang b , Jia-Ning Chen a , Ya-Xian Zhu b , Yong Zhang a, * a State Key Laboratory of Marine Environmental Science, Environmental Science Research Center, Xiamen University, Xiamen 361005, PR China b Department of Chemistry, Xiamen University, Xiamen 361005, PR China Biodegradation processes of dissolved multi-component PAHs in a mixture and effects of LMWOAs were investigated using a dual-wavelength fluorimetry. article info Article history: Received 26 December 2008 Received in revised form 3 May 2009 Accepted 8 May 2009 Keywords: Biodegradation PAHs Low molecular weight organic acids Bacteria abstract Biodegradation of dissolved fluorene (Flu), phenanthrene (Ph) and pyrene (Py), three polycyclic aromatic hydrocarbons (PAHs), singly or as a mixture of the three, by two bacterial strains, MEBIC 5140 (Myco- bacterium flavescens) and MEBIC 5141 (Mycobacterium scrofulaceum), as well as the effects of low molecular weight organic acids (LMWOAs), e.g. malic acid, citric acid and butyric acid on biodegradation of the three PAHs in mineral salts medium aqueous solution were investigated using a newly established dual-wavelength fluorimetric method. The results showed that biodegradation processes can be moni- tored simultaneously, quickly and simply by dual-wavelength fluorimetry. Both co-metabolism and inhibitory effects were found during the biodegradation of the three PAHs by MEBIC 5140 and MEBIC 5141. Positive effects of butyric acid and negative effects of citric acid on biodegradation of the three PAHs in a mixture were observed. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are pollutants that are ubiquitous in the air, water, soil and sediments. They are potential health hazards because of their toxic properties including carci- nogenicity and mutagenicity (Mastral and Callen, 2000). Accord- ingly the removal of PAHs from contaminated environments is of great interest. Microbial biodegradation is believed to be one of the principal means of successfully removing PAHs from natural environments and has been studied extensively (Yuan et al., 2000; Zhang et al., 2004). However, PAHs are refractory to biodegradation because of their hydrophobic nature, resulting in a tendency for them to be adsorbed to the soil and sediment matrix, and also their low solubility in water. Recently, there has been a particular interest in the availability and accessibility of PAHs. Some reviews (Ehlers and Luthy, 2003; Semple et al., 2003, 2004) have sought to clarify definitions and highlight the requirement for methods to assess the bioavailable/bioaccessible fraction of hydrophobic contaminants, including PAHs in the environment. Generally, there are two phases of PAHs, dissolved fraction and adsorbed on solid particles, in the aquatic environment (Zhang et al., 2004). More and more evidence shows that the dissolved fractions of PAHs are the major component that is bioavailable to microorganisms in aquatic environment (Sikkema et al., 1995). In other words, the biodegradation of PAHs mainly depends on their solubility in aqueous solution (Sridhar et al., 2007). In order to better understand the bioavailability of PAHs and their biodegra- dation processes, it is necessary to investigate the biodegradation processes of dissolved PAHs in aqueous solution, especially the relationship between their solubility, bioavailability and their biodegradation. PAHs exist as mixtures in the environment, and many interac- tions exist within a mixture of PAHs whereby the potency of known genotoxic and carcinogenic PAHs is enhanced (Kaiser, 1997). Interactions among PAHs play a key role in their bioavailability and thus affect their biodegradation (Luthy et al., 1997; Guha et al., 1999; Amellal et al., 2001; Meyer and Steinhart, 2000). However, many previous studies only focused on the biodegradation of individual PAHs or other organic contaminants by microorganisms, and studies of the biodegradation of PAH mixtures were rarely carried out, especially the effect of one PAH component on the biodegradability of other co-existing components. It is well known that PAHs usually co-exist with many other substances in the natural environment, such as low molecular weight organic acids (LMWOAs), one type of dissolved organic matter. Some surfactants or phytochemicals might be released * Corresponding author. Tel.: þ86 592 2188685; fax: þ86 592 2184977. E-mail address: yzhang@xmu.edu.cn (Y. Zhang). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2009.05.012 Environmental Pollution 157 (2009) 3150–3157