With the purpose of studying the transient variation of heavy metals and their impact on the area of study,
surface sediments were collected in Mid Orinoco, Venezuela, in February 2001 and April 2002. Using air-acetylene flame
atomic absorption spectrophotometry, the mean concentrations for these elements were determined as follows: Fe (56.82 μg
g-1) > Mn (271.35 μg g-1) > Zn (86.02 μg g-1) > Ni (9.35 μg g1) > Cu (5.77 μg g-1) > Co (5.37 μg g-1) > Cr (4.48 μg g-1) >
Pb (2.56 μg g-1) > Cd (0.15 μg g1). Mercury was undetected. Concentrations were larger than they had been in February 2001
for all elements except iron. All metals were bound to fine sediment particles; all but Pb and Zn were bound to organic matter;
and all save Zn, Pb, Fe, and Cd were associated to carbonates. Cu, Ni, Zn, and Pb values were higher for some stations than
those reported in the literature, suggestive of anthropogenic intervention. Mean concentrations are, however, below those
reported for other important rivers in the world.