Heavy metal fractionation in Fluvic Entisols under saline conditions in Northeastern Brazil

Resumo

The long-term use of agrichemicals might add some heavy metals to soils and, there is little information about the
dynamics of these elements in soils under saline conditions in semiarid regions. This study aimed to investigate the dynamics of heavy
metals in the diff erent fractions of Fluvic Entisols with saline conditions under long term of coconut cultivation in a semiarid region.
Composite soil samples were collected in fi ve agricultural areas and three areas under native vegetation. Physical, chemical, and heavy
metal analyses were carried out in soil (semi total and fractionated contents). Quality of irrigation water and drainage water was also
evaluated. Analytical results were normalized and subjected to analysis of variance, and means were compared by Scott-Knott test (P < 0.05).
Pearson correlation analysis was also used to assure a minimum correlation of variables justifying its use in the matrix of a factorial
analysis. Semi-total contents of Cr, Ni, Pb and Zn (except Cu in some areas) were lower than previous local assessment and national
guiding values, indicating that they do not cause harmful alterations in soil quality. Analyses of waters showed high levels of HCO3
,
indicating moderate restriction to use (due to the high levels of EC, SAR, Na and Cl). Fractionation of heavy metals revealed low risk of
environmental pollution since most metal contents were bound to the oxidic, organic and residual fractions. The water used in irrigation
contributes to the contents of heavy metals and to the salinity condition of the evaluated soils.