Niveles de Cd, Cr, Ni y Pb extraídos mediante Mehilich-3 y DTPA en un suelo agrícola sobre sedimentos cuaternarios

Abstract

The aim of this study was to determine the concentrations of extractable Cd, Cr, Ni and Pb in soils samples from a 10 ha grassland field at Castro Ribeira de Lea, Lugo (Spain). Eighty soil samples were collected at two layers of the A horizon, from 0 to 20 cm depth and from 20 cm to a variable depth defined by the boundary of the studied surface horizon, which ranged from 25 to 48 cm. Extractions of the studied elements were performed using two different solutions: Mehlich-3 and DTPA. The Mehlich-3 solution extracted higher concentrations for all the four heavy metals of interest at the two soil depths analyzed. The highest concentration recorded was for Pb_Mehlich-3 (3.54 mg·kg^-1 at 0 - 20cm and 2.67 mg·kg^-1 at >20cm depths). However, mean Ni, Cr, and Cd concentrations extracted with Mehlich 3 were not higher than 0,30 mg·kg^-1, while concentrations extracted with DTPA still were smaller, below 0.16 mg·kg^-1- The strongest correlations between extractable concentrations of heavy metals and soil general properties were Ni_DTPA - pH; Ni_Mehlich-3 - pH at >20 cm and 0-20 respectively; Ni_DTPA - Clay at 0-20cm, Cr_Mehlich-3 and Cd_Mehlich-3 - OM at 0-20 cm. Correlations with soil pH were negative, showing increasing extractability with increasing soil acidity. This notwithstanding, in our study case, the concentrations of heavy metals in the studied soil under grassland were far from levels, which are considered could be hazardous for agricultural soils. Thus, the results obtained suggest that the agricultural management (fertilizers, pesticides, etc) was appropriate in this area.