Los metales trazas en fracciones geoquímicas de núcleos de sedimentos de la laguna Unare

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 fractions geochemistry in six sediment core of the lagoon Unare, Venezu- ela. A procedure of sequential extraction of met- als 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 supe- rior 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 con- centrations to the surface, which suggests an alteration of the natural geochemical cycles that tends to a diminution of the manganese contri- butions 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 this 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.