Future work

Future experiments to address the effect of salicylate addition on PAH

degradation should focus on the following goals. First, other PAH-contaminated soils should be tested in addition to the single MGP soil tested in this research. If additional [13_C]

salicylate were available, SIP could be used to identify the organisms selected for by spike versus continuous addition. Mineralization assays with various PAH will be straightforward to carry out and will reveal any increase in PAH degradation rates caused by salicylate addition. If salicylate is found to increase PAH degradation rates, its efficacy should be further tested in a pilot scale remediation project. In addition, isolates from salicylate enrichment cultures should be characterized. Improved understanding of the diversity and physiology of PAH-degrading organisms will help with management decisions for PAH- contaminated sites.

Supplements such as specific carbon sources or surfactants have been hypothesized to stimulate populations of degrading organisms or increase the available concentration of a contaminant (Ogunseitan and Olson 1993; Tiehm et al. 1997; Wang et al. 1998; Chen and Aitken 1999). The results of adding supplements to a contaminated environment will probably be contaminant- and site-specific. Environmental regulations may also dictate whether a supplement can be added to a particular site. Adding nonspecific carbon sources

such as acetate or molasses would presumably pass regulatory scrutiny, but adding a carbon source such as salicylate, which can be toxic to humans in high enough doses, may not easily acquire regulatory approval. Addition of salicylate in an ex situ treatment, such as a

bioreactor, may be seen as a safer option than addition of salicylate in situ.

While salicylate addition was not found to stimulate PAH degradation rates in the MGP soil studied in this work, some previous work examining PAH degradation rates in complex matrices following salicylate addition has shown increased degradation rates of naphthalene in activated sludge (Cardinal and Stenstrom 1991), naphthalene in soil

(Ogunseitan and Olson 1993), and pyrene in soil (Vanderford 2001). Previous work in which salicylate was not found to increase PAH degradation rates have hypothesized that salicylate was used as a carbon source instead of an inducer or that salicylate addition stimulated non- PAH degrading organisms (Carmichael and Pfaender 1997). The body of evidence to date suggests that salicylate can stimulate naphthalene removal in contaminated systems by increasing the abundance of naphthalene-degrading organisms.

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