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ARTICLE IN PRESS

S. Orecchio et al. / Environmental Research 107 (2008) 371–379 377

bark PAH concentrations between green areas, road and areas usually are restricted to PAHs within a given molecular mass.
characterized by intensive human activities are in agreement with PAHs of molecular mass 178 and 202 are commonly used to
differences of PAHs contents (in lichens) measured in others cities distinguish between combustion and petroleum sources.
(Nielsen, 1996). Phenanthrene and anthracene are two structural isomers. In
In most of the urban sampling sites, the same distribution of 19 particular, phenanthrene is more thermodynamically stable than
PAHs (expressed as weight percentage) is observed. Phenan- anthracene; therefore, in PAH petrogenic pollution the ph/an ratio
threne, fluoranthene and pyrene are the three most abundant is very high, while during the combustion processes the high
components in nearly all the samples. Chrysene was found at low temperatures favour anthracene formation with a lowering of the
concentration in 15 of the 16 sites investigates (from 0 up to 38 mg/ ph/an ratio.
kg). A very high concentration (142 mg/kg) of chrysene has been With the aim to add a further contribution to the knowledge of
measured in the bark of station (no. 3) located neighbouring the the source of polycyclic aromatic compounds, we take into
harbour. This anomalous result can be explained by considering consideration as well the fluoranthene/pyrene-ratio (fl/py). Gen-
that environmental man-made sources of chrysene include diesel erally, a fl/py ratio o1 indicates vehicular emission, a ratio of E1.0
and aircraft turbine exhausts. In this study, perylene was found at indicates that the contamination by PAHs was due to combustion
high concentration (87 mg/kg) in the bark of station no. 13 processes (wood smoke) as the source and a ratio 41is
(Industrial area) (located near a petroleum depot). This compound characteristic of emission of coal combustion.
does occur in petroleum products including fuel oil, diesel fuel, The analytical data indicate that polycyclic aromatic com-
etc. pounds found in 15 stations seem to be of pyrolytic origin as the
Usually three processes can generate polycyclic aromatic major source of PAHs in the bark samples, whereas the high values
compounds: of ph/an ratio indicate contamination from petroleum products.
The data shown in Fig. 6 indicate that the station no. 2
(Indipendenza 2) is influenced by this type of emission but the
(i) incomplete combustion,
(ii) release of petroliferous products, station no. 13 (Industrial area) by both types of emissions. Station
(iii) diagenetic processes (degradation of organic matter). no. 2 is near three petrol pumps and station no. 13 is near a cast
iron foundry, which uses fossil coal and a fuel depot. These results
are in good agreement with the real type of emissions of the areas
The molecular patterns of single PAHs generated by each taken into consideration and with the results of other researches
sources are like fingerprints and it is possible to hypothesize on biomonitoring (Macaluso et al., 2000; Culotta et al., 2002,
which processes generate PAHs by studying their distribution in 2005).
barks. In this study, in addition to diagnostic ratios, principal
If we group the polycyclic aromatic compounds in different component analysis (PCA) was also employed to identify simila-
classes, depending on the number of aromatic rings present in rities/dissimilarities between ambient and source PAH profiles.
their structure, it can be observed that PAHs having 3 and 4 rings, PCA is the oldest and most widely used multivariate statistical
found in barks of all sites under investigation, contribute from 75% technique in environmental sciences. The principle of PCA is to
to 97% of the total except for the station no. 13 (Industrial Area), transform the original set of variables into a smaller set of linear
where 5-ring PAHs contribute about 40%. combinations that account for most of the variance of the original
Sources of the PAHs pollution in the systems under investiga- set. The primary function of this analysis is the reduction of the
tion have been estimated, in a similar way to those reported for number of variables while retaining the original information as
other matrices (Giacalone et al., 2004), by using distribution much as possible, and thus variables with similar characteristics
indices related to concentration ratios of some polycyclic aromatic can be grouped into factors.
compounds. To minimize confounding factors such as differences The analysis was carried out using XLSTAT software. Two
in volatility, adsorption, water solubility, etc., ratio calculations principal components (PC1 and PC2) were identified based on PAH

Fig. 6. Plot of ratio of phenanthrene.anthracene versus ration of fluoranthene/pyrene.