RESULTS AND DISCUSSION
1. PAH Concentrations in Bottom Ash
Table 2 lists the analytical results for PAHs in
each bottom ash (A-J), given as averages of triplicate
analyses. The values in parentheses indicate results
with average surrogate recoveries less than 50%.
Concentrations of PAHs were calculated using
an IS method so that the results would not be affected
by the recovery efficiency. The results were corrected
for losses using a previously developed procedure
[12-16]. Perraudin et al. [17] proposed that surrogate
recovery should be in the range of 60-120% and
results should be considered invalid for recovery
rates less than 50% even if the deuterated standards
were used to determine the corresponding compounds.
Thus, in the present study, when surrogate
recovery was greater than 50%, the concentrations
of the corresponding PAHs were considered reliable.
When surrogate recovery was less than 50%, the
results were regarded as a reference.
The sum of the US-EPA 16 PAH concentrations
in bottom ash obtained from ten incinerators ranged
from 63 to 1578 ìg kg-1 dry weight. Among the 16
PAHs, concentrations varied by one to two orders
of magnitude. Similar levels have been found in
several previous studies. Morselli and Zappoli [5]
reported total PAH concentrations in bottom ash of
389-760 ìg kg-1, and Johansson and van Bavel [14]
measured concentrations in weathered bottom ash
of 479-3589 ìg kg-1. In addition, Horii et al. [18]
recently reported a range of 9-1531 ìg kg-1 for ash
samples obtained from incinerators in Korea. Although
incinerator characteristics such as the operating
condition, furnace type, and waste type affect
the concentrations of PAHs, no clear correlation
between PAH concentrations and incinerator characteristics
was confirmed in the present study.
Previous studies have investigated the concentrations
of the US-EPA 16 PAHs in other environmental
media such as sediments and soil [3]. For
comparison, Table 3 presents the concentrations
ranges of these PAHs found in the present study and
in previous studies of soils. In previous studies,various soils with different emission sources were
investigated. In Table 3, we classified these soils into
three sampling locations: I: no industrial or traffic
source existed near the site; II: the site was in an
industrial or traffic area; III: the site was near a specific
industrial plant.
In the present study, the total PAH concentrations
in bottom ash were in the range of sampling
location class-I and class-II. However, the total PAHs
for most ash, except for Ash-J, were lower than 576
ìg kg-1. Thus, the content of ash analyzed in the
present study was similar to those in sampling location
class-I. Additionally, comparison with PAH
background soil concentrations reported by the
Agency for Toxic Substances and Disease Registry
[27] showed that the concentrations of each PAH
identified in the present study were within the range
of the background soil concentrations. Total PAH
concentrations of bottom ash were nearly in the
range of rural soil or background levels, even though
the bottom ash was a combustion product. This result
probably reflects the combustion conditions created
by state-of-the-art incinerators. As Vehlow et al. [8]
reported, a number of countries including Japan and
some EU countries have highly sophisticated MSW
incinerators. Strict combustion control has been required
in Japan since enactment of a law concerning