Pesticide sorption on two contrasting mining soils by addition of organic wastes: Effect of organic matter composition and soil solution properties

Recovery of mining areas has been encouraged for social and environmental purposes, mainly through revegetation policies, which usually need addition of exogenous organic residues to increase organic matter in soils. At the same time these remediation strategies must establish soil capability of coping with organic pollutants. Therefore two contrasting mining soils from south of Spain, a very acid soil from Nerva (Riotinto area, SW), and a basic soil from Alquife (SE), were evaluated for their retention ability of two pesticides, thiacloprid and fenarimol, in native soils and soils amended with organic residues. Three residues from urban sewage sludges at three concentrations (2–10%) were considered: a stabilized (SSL) and two composted (CLV and CSL) sludges. Results show that pesticide sorption was increased in both soils after amendment, being higher after addition of SSL and CLV and with a strong association between pesticide sorption and soil organic carbon (OC), as revealed by multivariate analysis. Important soil solution properties, not directly related with pesticide sorption, were electrical conductivity and specific UV absorbance which were able to discriminate between both mining soils. Additionally dissolved OC and the humification index separated SSL, a fresh sludge, from the other two composted amendments. Sorption parameters normalized to the organic carbon content (KOC) for both mining soils were generally lower than others reported, a fact maybe related with high soil metal loading.