S-Metolachlor sorption in soils amended with olive oil residues: effect of organic waste transformation

Herbicides are the main type of pesticides causing water contamination. The chloroacetanilide herbicide Smetolachlor is frequently detected in ground and surface waters, and represents a potential source of water pollution. The addition of organic residues to soils to reduce losses of organic pollutants constitutes sometimes an efficient method to control contamination. One of the recent technologies used in olive-oil extraction is a continuous centrifuge two-phase process that in Spain alone generates huge amount of organic residues. The use of this residue, which contains major proportion of organic matter, can be a low-cost alternative for their disposal and at the same time can help reducing pesticide contamination by increasing its retention. The aim of the present study was to evaluate the effect of two organic residues from olive oil production, fresh and transformed in the soil, on the sorptiondesorption of the herbicide S-metolachlor. Measurements on unamended and fresh-amended soils were made and compared with those made after 20 months of the organic wastes maturation in a field which had received addition of these wastes for nine years. These wastes modified the physicochemical properties of the unamended soil, increasing content of TOC, DOC, EC and reducing pH. Amendment increased S-metolachlor sorption and decreased desorption. The aging of the organic matter in the field-amended soils revealed important differences in Smetolachlor behavior in these soils, as referred to the sorption-desorption dynamic, mainly due to the lower DOC content of field amended soils.