Page 13 - Tranchina_alli_2004

CHEMISTRY, MINERALOGY AND RADIOACTIVITY IN POSIDONIA OCEANICA 213

been estimated to vary in the ranges 0.3 –0.5, 1.3 –6.0, 0.5 –1, 0.5 –1.2 and 7 – 10 Bq kg21 for
137Cs, 40K, 214Bi, 228Ac and 210Pb, respectively. Ranges of variation for LDL in tissues (for a
5 –15 g dry weight sample and a measurement time of 3.5 Â 105 s) have been estimated as

1.8 –3.1 (1 –1.5), 30 – 50 (13 – 23), 7– 11 (2.7 – 4.2), 5.5 –10 (2.5 – 5) and 14– 25 (7 –
13) Bq kg21 for 137Cs, 40K, 214Bi, 228Ac and 210Pb in scales (rhizomes), respectively. The

small amount of available sample has not allowed us to lower these detection limits.

The availability of large quantities of P. oceanica (about 10 kg wet weight per sample) and

longer measurement times enabled Molero et al. (1999) and Sanchez-Cabeza and Molero

(2000) to detect specific activities of different isotopes well below our lowest detection
limits. As far as 40K is concerned, they obtained a range of 186 –532 Bq kg21 dry weight,

although no details were reported on the tissues analysed. It should be noted that an activity
of 100 Bq of 40K is present in about 3.2 g of total potassium. The 228Ac specific activity

values have been found to be below the LDL in most cases for P. oceanica samples.

4 CONCLUSIONS

The chemical and mineralogical composition of sediments, trace-metal concentrations and
radionuclide specific activities in sediments and P. oceanica samples from meadows in
north-western coast of Sicily (Italy) have been determined. X-ray fluorescence and diffrac-
tometry, atomic absorption spectrophotometry and high-resolution gamma spectrometry
have been used. Standard statistical techniques have allowed detailed comparisons among
values from different sites and/or different types of samples.

This work has confirmed that P. oceanica is a good biomonitor of heavy-metal pollution.
No correlation of trace-metal concentrations in sediments and plant has been detected.
Nevertheless, a correlation between Cd concentration in plant and seawater has been
reported, and a similar behavior assumed for Pb, in the literature (Sanchiz et al., 2000).
Therefore, metal concentrations in P. oceanica might indirectly be a measure of bioavailable
metal concentrations in the environment rather than total concentrations.

The plant/sediment ratio of concentrations is particularly large for Zn. This also applies
to Cd, since it was always under the detection limits in sediments. This indicates that bio-
enhancement takes place in Posidonia.

The potassium concentrations (proportional to 40K activity determined by gamma spec-
trometry), with values in rhizomes higher than in scales, is in general agreement with the
known important role of this element in plant growth.

Acknowledgements

The authors gratefully acknowledge the collaboration of G. Rizzo and F. D’Agostino, from
the Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Universita` di Palermo,
for assistance with FAAS. The collaboration of S. Calvo and coworkers, from the Diparti-
mento di Scienze Botaniche, Universita` di Palermo, is also gratefully acknowledged. The
MIR project has been supported by CIPE-MIUR grant, Cluster 10, Ambiente Marino,
Italy, leader G. La Loggia.

References

Baroli, M., Cristini, A., Cossu, A., De Falco, G., Gazale, V., Pergent-Martini, C. and Pergent, G. (2001). Concen-
trations of trace metals (Cd, Cu, Fe, Pb) in Posidonia oceanica seagrass of Liscia Bay, Sardinia (Italy), in
Faranda, F. M., Guglielmo, L., Spezie, G. (eds.), Mediterranean ecosystems: structures and processes.
Springer, Berlin, pp. 95– 99.