metals, ions, carbonates, soluble organic matter, etc., that may modify
metals bioavailability and therefore their toxicity.
Regarding to metal concentration in different sediment fractions
(Table 7), the IPS index has presented negatively correlation with the
presence of Zn in all sediment fractions, except for the residual fraction,
Pb presented negative correlation with the exchangeable fraction and
associated to the iron and manganese oxyhydroxides and the same for
As with the exchangeable fraction. On the other hand, Pb bound to the
organic matter and sulfides and Zn associated to the iron and manganese
oxyhydroxides presented negatively correlation with the macroinvertebrates
index IBMWP. Finally, only the most bioavailable fraction
of Pb presented negatively correlation with the macrophytes index
IVAM. According to this, the metals (considering both compartments,
water and sediment), which seem to contribute in higher extend to
the reduction of biological quality were Pb and Zn. Those elements
presented a negatively influence on macroinvertebrates, diatoms and
macrophytes communities. Arsenic and Cr that seemed to have a significant
negative influence on macroinvertebrates and diatoms, and Ni
only negatively influenced diatom communities (Table 7).