Page 3 - Tranchina_alli_2004

CHEMISTRY, MINERALOGY AND RADIOACTIVITY IN POSIDONIA OCEANICA 205

2 MATERIALS AND METHODS

2.1 Sampling

Thirty-four samples of sediment were collected in four geographical sites (see Fig. 1),
namely Carini, Egadi Islands, Marsala and Trapani, from sedimentary basins inside the Posi-
donia meadows. For each site, three locations near the coast inside the P. oceanica meadows
(transects) and three bathymetric depths (stations) were considered. Samples from different
transects at the same depths were analyzed as a whole. The bathymetric range was between 3
and 10 m.

P. oceanica samples were collected at the same sites and depths (3, 6 and 10 m) as the
sediments. Twenty plants were sampled at each station. Sampling of sediments and
P. oceanica, and plant fractioning (rhizomes, scales, and leaves) were carried out by other
colleagues within the same MIR Project, and details can be found elsewhere (Calvo et al.,
2002). No root samples were collected.

Epibiota and sediments were removed from P. oceanica samples by gentle scraping with a
glass slide and rapid rinsing with distilled water, to minimize the loss of elements (Ledent
et al., 1995; Campanella et al., 2001).

2.2 Mineralogical Measurements

All sediments were treated after being dried and sieved through a 2-mm meshed sieve. The
samples were milled to obtain particles of a size smaller than 4 mm. The powder was directly
measured for mineralogical features by X-ray diffraction (XRD).

The samples were mixed with H3BO4, and a thin chip was obtained to determine the
elemental composition by X-ray fluorescence (XRF). The samples were characterized by
X-ray diffractometry using the X’ Pert Pro, Philips Analytical. Major and minor chemical
elements, were measured by XRF (PW 1400, Philips Analytical).

2.3 Metal Measurements

The sediment samples, after sieving on 2-mm meshes, were dried at 105 8C for 48 h and then
milled to obtain a size of approximately 100 mm using a Fritsch Pulverisette 2. Milled
samples were then digested using the Open-Cavity Microwave Star 2 (CEM Corporation)
(see Cook et al., 1997, for a review of different techniques). Five milliliters of HCl 37%
were added to a 500 mg aliquot of the sample, and kept at 75 8C for 5 min. Afterwards,
7.5 ml of 65% HNO3 were added and heated up to 95 8C; after 15 min, the temperature
was raised to 110 8C for 10 min. Fifteen milliliters of H2O2 were then added, and the tem-
perature was kept at 110 8C for a further 10 min. After cooling, the solution was filtered,
and distilled water was added to make the volume up to 25 ml.

The same drying and milling procedures were used for P. oceanica samples. The milled
sample was then divided into two parts: the first for flame atomic absorption spectropho-
tometry (FAAS) analysis and the second for the gamma spectrometry analysis. Both aliquots
were stored in hermetically sealed polyethylene containers until analysis time.

For FAAS analysis, a quantity of 500 mg was digested in the above-mentioned open-
cavity microwave using the following procedure. Five milliliters of 65% HNO3 and 5 ml
of distilled and deionized water were first added to the 500 mg sample aliquot and heated
for 3 min at 50 8C; the temperature was then raised to 70 8C and maintained for 10 min.
Five milliliters of 70% HClO4 were then added and temperature was raised to 98 8C for