Page 4 - TraceMetals_seagrass_algae

120 L. Campanella et al. / Environmental Pollution 111 (2001) 117±126
All the chemicals used in sample treatments were
ultrapure grade. The water used for solution prepara-
tion and cleaning was obtained from a Millipore Milli-
Q system. All the glassware was cleaned prior to use by
soaking in 10% HNO3 for 24 h and rinsed with Milli-Q
water. Analytical quality control was performed with
BCR certi®ed reference materials CRM 279 (sea let-
tuce), 278 (mussel tissue) and 403 (seawater) (Table 2).
2.3. Statistical methods
Mean metal concentrations were calculated together
with standard deviations. As far as pooled samples
are concerned, the standard deviations illustrate the
variability within di€erent replicates, while in the case of
the mollusc analysis they represent the metal content
variation among individuals.
The existence of signi®cant di€erences between metal
concentrations in di€erent sites and species was tested
by a two-way analysis of variance. The comparison
between metal contents in organisms collected in the
harbour versus those collected at the other stations
was performed by contrast analysis. In both cases data
were log-transformed prior to analysis to achieve
homogeneity of variances and absence of relation
between variances and means. Correlations between
metals and between species were studied on untrans-
formed and log-transformed data (Pearson product-
moment correlation).
3. Results
The metal concentrations in the biota are shown in
Tables 3±5. Table 3 reports the data concerning the
metal contents in the di€erent compartments of Posido-
nia oceanica. The mean levels of Cd and Zn in the leaves
are 2.38 and 121 mg gÀ1 dry wt., respectively, while in
the rhizomes these metals average 0.75 and 80 mg gÀ1
dry wt. On the contrary, Pb and Cr are more con-
Table 2
Analysis of certi®ed reference materials: certi®ed values and found values (mean‹S.D.)a
Metal CRM 279 (sea lettuce) CRM 278 (mussel tissue)
Certi®ed Found Certi®ed
(mg gÀ1 dry wt.)
Cd 0.274‹0.022 0.29‹0.01 0.34‹0.02
Cr (10.7)c 9.3‹0.4 0.80‹0.08
Cu 13.14‹0.37 12.9‹0.5 9.60‹0.16
Pb 13.48‹0.36 14.7‹0.4 1.91‹0.04
Zn 51.3‹1.2 50‹3 76‹2
a Number of replicates: CRM 279=24, CRM 278=30, CRM 403=5.
b Original values given on a w/w basis were recalculated on a w/v basis.
c Not certi®ed values.
d Values close to the detection limits.
centrated in the rhizomes than in the leaves (5.81 and
1.16 mg gÀ1 dry wt. vs. 2.72 and 0.59 mg gÀ1 dry wt.,
respectively) whereas Cu reaches similar levels in both
compartments (leaves 13.2 mg gÀ1 dry wt., rhizomes 11.6
mg gÀ1 dry wt). In leaf material Cd, Cr, Pb and Zn
concentrations decrease in the following order: leaf
tip>whole leaf>leaf basal tissue. In contrast, Cu levels
are quite similar in all leaf sections.
In both P. oceanica and P. pavonica the highest Cd,
Pb and Zn contents were recorded in the ®fth site, the
Favignana harbour (Tables 3 and 4). The organisms
collected in this station also contained high levels of Cr
and Cu.
A similar trend was noticed in Monodonta turbinata
and Patella caerulea (Table 5). The di€erences in metal
levels among molluscs collected in di€erent sampling
stations were tested by two-way analysis of variance and
turned out to be statistically signi®cant at P level
<0.001 (Table 6). In particular, Cd, Cu, Pb and Zn
contents in M. turbinata from station 5 were higher than
those observed in individuals from the other stations
(Cd: P<0.01; Cu, Pb, Zn: P<0.001). Similarly, Cd, Pb
and Zn contents in P. caerulea from station 5 were
higher than those observed in individuals from the other
stations (P<0.001). The two-way analysis of variance
also revealed signi®cant di€erences in Cd, Cu and Zn
accumulation between the two gastropod molluscs
(Table 6).
Since data on metal concentrations in macrophytes
and molluscs suggested that some relations may exist
between metals and species, both untransformed and
log-transformed data were tested for Pearson correla-
tion. Signi®cant positive correlations (untransformed
data, P<0.05) were found in the leaves of P. oceanica
between Pb and Zn (r=0.96) and in P. pavonica
between Cd and Cu (r=0.93). As regards gastropods a
signi®cant positive correlation between Pb and Zn
(untransformed data, P<0.05, r=0.95) and a negative
one between Cr and Cu (log-transformed data, P<0.05,
r=À0.89) were found in P. caerulea.
CRM 403 (seawater)
Found Certi®ed Found
(ng lÀ1)b
(mg gÀ1 dry wt.)
0.36‹0.02 20.35‹ 2.10 21.1‹0.7d
(108.6)c 101‹3
0.73‹0.02 242‹9
256.4‹24.3 26.0‹0.7d
9.1‹0.3 25.08‹5.36 1767‹104
1738‹197
2.00‹0.05
78‹5