Abstract:
For
the
first
time
in
Africa,
studies
investigating
the
polycyclic
aromatic
hydrocarbons
(PAHs)
levels
in
lichens
(species
Parmotrema
austrosinense
(Zalhbr.)
Hale)
was
performed
successfully
using
various
sample
preparation
techniques.
Sampling
campaigns
were
conducted
at
5
different
sites
across
South
Africa.
Different
sample
preparation
techniques
were
explored,
and
it
was
found
that
a
quick,
easy,
cheap,
effective,
rugged
and
safe
(QuEChERS)
technique
using
n-‐
hexane:acetone
(1:1,
v/v),
never
before
applied
to
lichens,
provided
the
best
recoveries
of
internal
standards
(deuterated
phenanthrene
and
pyrene),
the
highest
total
peak
area
for
all
PAHs
of
interest
and
relative
standard
deviations
(%RSDs)
comparable
with
the
other
preparation
techniques
explored
(ultrasound
assisted
extraction,
Soxhlet
and
microwave
assisted
extraction).
Statistical
analysis
confirmed
that
QuEChERS
performed
significantly
better
than
the
other
sample
preparation
techniques.
The
optimized
sample
preparation
technique
met
the
study’s
requirements,
since
it
was
a
fast
method,
with
good
recoveries,
using
less
solvents
and
minimal
energy.
It
was
determined
that
the
internal
standard
needs
a
prolonged
equilibration
time
(12
hr)
on
the
lichen
matrix
for
optimal
recoveries,
a
new
finding.
Matrix
matched
standards
were
prepared
and
strong
matrix
effects
were
found;
both
strong
enhancement
(for
the
lighter
PAHs)
and
strong
suppression
(for
the
heavier
PAHs)
were
observed.
The
use
of
matrix
matched
standards
were
found
to
be
imperative
for
the
accurate
determination
of
PAH
concentrations
in
the
samples,
described
for
the
first
time
in
this
study,
since
the
matrix
effects
were
found
to
be
PAH
and
lichen
specific
and
are
crucial
for
accurate
quantitation.
Varying
chlorophyll
contents
of
the
extracts
was
observed
using
fluorescence
spectroscopy,
despite
being
prepared
in
an
identical
manner
and
being
of
the
same
lichen
species.
Therefore,
the
chlorophyll
content
needs
to
be
given
along
with
determined
PAH
concentrations
in
lichens,
based
on
a
dried
weight
basis
to
allow
for
comparison
between
studies. All
the
lichen
samples
contained
naphthalene,
acenaphthylene,
acenaphthene,
fluorene,
phenanthrene
and
benzo[a]pyrene.
It
was
seen
that
a
full
range
of
PAHs
in
terms
of
mass
was
extracted
and
identified,
thus
Parmotrema
austrosinense
(Zalhbr.)
Hale
was
an
appropriate
choice
of
lichen
species.
The
order
of
most
impacted
sites
to
least
impacted
was
found
to
be
Pretoria
Industrial
Area
(total
PAH
concentration
1001
ng.g-‐1)
>
Daspoort
2
(737
ng.g-‐1)
>
Daspoort
3
(693
ng.g-‐1)
>
Bulk
urban
site
(633
ng.g-‐1)
>
Cathedral
Peak
(547
ng.g-‐1)
>
Cape
Point
Nature
Reserve
1
(525
ng.g-‐1)
>
Cape
Point
Nature
Reserve
2
(514
ng.g-‐1)
>
Cape
Point
Nature
Reserve
3
(425
ng.g-‐1).
The
PAH
profiles
and
PAH
ring-‐size
profile
were
used
for
source
diagnostics
and
was
seen
to
vary
according
to
the
types
of
pollution
sources.