Environmental Engineering Reference
In-Depth Information
and assists in finding whether the ratio is compromised by degradation. Ranges and
reliable (degradation-independent) threshold values of PAH ratios can be estimated,
either for individual sources or for a group of sources of interest. Because of the
higher degradability of petrogenic PAHs, petrogenic assessments should take into
account at least dissolution and evaporation.
6.3
Can the Borneff-6, 16 EPA, and 10 VROM PAHs Be Used
to Calculate the Proposed Indicator—and, if so, Which
Uncertainties are Introduced by This Approach?
All the proposed indicators contain parent PAHs only, which make it difficult to
trace petrogenic sources. We believe that after a local case study has taken into
account a wider range of alkylated and parent PAHs, it is possible to establish the
EPA16 as an indicator of pyrogenic and petrogenic sources.
All three indicators are suitable mainly for pyrogenic sources. Specifically,
Borneff-6 has only one LMW parent PAH (easily degradable), making it inadequate
to detect petrogenic contamination. Even though some LMW PAHs are included in
the VROM10 PAH compilation, important ones such as pyrene (useful for discrimi-
nating petrogenic/pyrogenic or different combustion sources) are omitted.
Alkylated homologues are petroleum-specific, but they cannot be measured by
using the standard EPA methods. Of the three proposed PAH compilations, the most
adequate for identifying pyrogenic or petrogenic sources seems to be the ʣPAH16,
although it does not take into account certain important parent PAHs (e.g., N0, BeP,
PER, D0) nor, most importantly, does it take account of alkylated PAHs. Under
degradation conditions, the parent compounds are those that are lost first-some-
times preferentially over the alkylated ones.
Certain ratios within the ʣPAH16 (e.g., LPAH/HPAH) are able either to describe
patterns, in which degradation has occurred, or in which the targets are recalcitrant.
Even for very complex systems, it should be possible to establish a diagnostic set of
PAH indicators (e.g., the EPA16 indicators) after implementing a full scan analysis
and a tiered approach (historic records, source inventories, background concentra-
tions, weathering check, and parent and alkylated PAHs and data analysis). If the
compounds that we expect to be present or absent in the sources are empirically
known, the number of analytes to be investigated can be reduced. Establishing the
levels and correlations of a small subset of indicators can reduce the effort of exten-
sive analysis of PAHs while providing adequate data analysis and resolution, which
are necessary for monitoring programs. We suggest that the next step in using a small
subset of all the PAHs for the source characterization in sediments would be to imple-
ment an inference protocol (e.g., a multi-valued logic, or a PMF), in which conclu-
sions drawn from multiple PAH ratio combinations are applied to weight the ʣPAH16
ratios in a standardized manner on the basis of source composition and degradation.
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