File Entry: Comportamiento de los metales trazas Cu, Pb, Mn y Zn en fracciones geoquímicas de núcleos de sedimentos de la laguna Unare, Venezuela

The concentrations of the metals
Cu, Pb, Mn and Zn in fra ctions geochemistry in
six sediment core of the lagoon Unare, Venezuela.
A procedure of sequential extraction of metals
was determined, for each fraction was used
reagents different and conditions of digestion
and the concentrations of metals determined
with spectrophotometer of Atomic Absorption.
The fractionating of metals indicated an order of
decreasing concentration as it follows: residual
fraction > organic/sulfur matter > carbonates>
interchangeable. The metals displayed values
in the reactive phase between : n.d-7,90; 0,00-
4,90; 133,95-961 ,79 and 0,05-9,61 IJg /g for Cu,
Pb, Mn and Zn, respectively; being observed
in most of the core an increase in the superior
layers caused by diagenetics processes,
changes in the textural composition (contained
of clay or organic matter) due to the anthropics
contributions that the lagoon receives. The Mn
presented in core 1, 2 and 3 the smaller concentrations
to the surface, which suggests an
alteration of the natural geochemical cycles that
tends to a diminution of the manganese contributions
through tlíe time. In the Zn, its vertical
distribution reflects a strong relation between the
metal, the organic matter and texture in relation
to the depth, which is of sandy and poor texture
in organic matter, with a contained minor of th is
metal. The concentrations average of metals
total are were: 36,31; 7,57; 445,60 and 64.07
IJg/g for Cu, Pb, Mn and Zn respectively. These
results are analogous to the reported ones for
sediments no contaminated; nevertheless, some
metals in the reactive phase, showed to slight
increases towards the surface, indicating recent
contamination, product of the intervention that
has undergone this lagoon in the last decades
and to the contributions of the Unare river.