Resumo de eventos cient??ficos
Trace elements determined in sediment cores from Nhecol??ndia Pantanal by INAA
Autor
DAMATTO, S.R.
SANTOS, L.F.
60 YEARS OF IEA-R1: INTERNATIONAL WORKSHOP ON UTILIZATION OF RESEARCH REACTORS
Resumen
Pantanal wetland is the world???s largest wetland, with an estimated area of about
200 000km2. This region is an alluvial plain and the Paraguay River and his tributaries
run through the wetland due to the low declivity of the plain in the north-south and
east-west direction; the water takes almost four months to cross the wetland, forming
different ecosystems, such as floodplains, lakes of fresh or saline water, rivers, and
others. In the last decades, this area has been affected by human activities, without
the suitable planning. The sediment of an aqueous system represents a great source
of study, as it is a deposit of solid material, formed by the wind, ice, or water on the
surface of the earth and the deposition of organic material from animals that live
there. From the sediment chemical analysis in combination with geochemical tools
is possible to estimate a probable source of the elements chemistry, whether natural
or anthropogenic. Trace elements from different sources tend to accumulate in the
sediment fine fraction (silt + clay), and are commonly mobile, what could generate
a transference of some metals to the environment. Therefore, the present work
analyzed the fine (silt + clay) and the coarse (medium sand + fine sand) fraction of
the sediment cores collected in four Salinas from Nhecol??ndia Pantanal performing
the elementary chemical characterization of these sediment fractions and verify a
possible historical impact by anthropogenic sources and also to verify if some element
could accumulate in the sand fraction since the sediments from these ponds have
a high percentage of the coarse (sand) fraction; instrumental neutron activation
analysis technique (INAA) was used in the determination. Four sediment cores were collected in ponds located at Embrapa farm, 19 33023:31"S and 56 4057:56"W in
Nhecol andia Pantanal, Mato Grosso do Sul, using a PVC manual sediment sampler.
The cores were slice every 2cm and dried at 50 C; after drying, the samples were
ground and homogenized. The elements As, Ba, Ca, Ce, Co, Cr, Cs, Eu, Fe (%),
Hf, K (%), La, Lu, Na, Nd, Rb, Sb, Sc, Se, Sm, Ta, Tb, Th, U, Yb, and Zn were
determined (mg kg????1) by Instrumental Neutron Activation Analysis (INAA) and the
analysis were performed in the coarse and in the fine fraction of the sediment. The
samples and reference material were irradiated for 8h at the IPEN Research Reactor
IEA-R1. The element As, Ba and Fe concentrations showed higher values than those
of the Upper Continental Crust, UCC, in the fine fraction of the sediment for the
studied cores. For the coarse fraction only the elements As, Ba and Hf showed
concentrations higher than the UCC values. The majority of the obtained results in
the INAA determination for the coarse and fine fraction suggested that there is no
expressive effect of the human activities in the region and this particular area until
the moment.