Remediation of PAH-Contaminated Soils and Sediments: A ...

Bioavailability Analytical Methods
Sites contaminated with PAHs can be evaluated using several different
measurements: total extraction, mild organic extraction to assess desorbable
fractions, and bioassays (assessments of bioavailability by uptake and/or toxicity
to microorganisms). Although there are a range of bioassays available to assess
PAH availability, they are time-consuming and can be expensive. An alternative
is to use rapid, reproducible chemical tests to assess bioavailability.
Although total extractable PAH levels are routinely used to assess of
contaminated sites, they will grossly overestimate bioavailable PAHs, and thus
cannot be used to assess or predict the fraction of PAHs that is accessible to
biota (Alexander, 2000; Semple et al., 2003). Different researchers have
proposed several mild organic/aqueous extraction procedures to assess the
readily available PAH fraction in soil and sediments. Some of these extraction
procedures include:
� Extraction with n-butanol: Kelsey et al. (1997) reported that availability of
phenanthrene to bacteria and earthworms could be accurately predicted
with n-butanol extraction. Liste and Alexander (2002) also found good
correlation between butanol extraction and PAH availability to earthworms.
Bogan and Sullivan (2003) found that the n-butanol extractability of 13
PAH compounds was dependent on soil organic matter content.
� Triton X-100 shake: Cuypers (2001) found extraction with Triton X-100
overpredicted PAH availability.
� Solid phase extraction with Tenax beads: In this method, Tenax A (a
porous polymer of 2,6-diphenyl-p-phenylene-oxide) removes the rapidly
desorbing fraction that is equivalent to bioavailable PAH (Uyttebroek et al.,
2007). Cuypers (2001) found extraction with Tenax A to correlate well with
bioavailable PAH.
� Aqueous β cyclodextrin shake: Reid et al. (2000b) proposed β
cyclodextrin aqueous solution extraction to predict availability, and found
that this solution predicted the amount of phenanthrene available to
bacteria. Both Cuypers (2001) and Allan et al. (2006) found extraction with
β Cyclodextrin to correlate well with bioavailable PAHs. Papadopolous et
al. (2007) compared aqueous cyclodextrin extraction to mineralization of
phenanthrene in 4 different soils with different organic matter content
ranging from 4.8 to 27 %. High correlation was found between cyclodextrin
extractability and microbial mineralization of phenanthrene by indigenous
bacteria.
However, no one chemical test predicts the availability of all PAH contaminants
to different organisms in all soils. Thus, these tests are better used along with
bioassays to assess PAH bioavailability in soils (Stokes et al., 2006).
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