SORPTION OF PRETILACHLOR ON PADDY SEDIMENTS

The sorption of the acetanilide pretilachlor by 44 sediments (solid fraction suspended in paddy water) from Italian paddy fields was studied in batch experiments, using the apparent distribution coefficient K-d. The specimens of paddy sediments were either air-dried or submerged for 20 days to simulate the redox conditions resulting from paddy draining and flooding. The sorption in distilled water (H2O) or in presence of background electrolytes (0.01M) either indifferent (non-reactive with soil surfaces, NaCl) or potentially reactive (KH2PO4) was compared. Two groups were recognised by their different K-d variance and organic matter (OM) When OM content was above 9%, a direct relationship between OM and K-d was found, and the effects of electrolytes and dry/submersion treatments on sorption were significant. For OM < 5%, no significant relationship was found between K-d and OM itself, albeit the effect of treatments were still significant. Submersion depressed sorption in both cases, while the electrolytes had mixed effects only for OM > 9%. The H2O-treatment showed the highest difference between dry and submerged conditions, followed by NaCl-treatment, while KH2PO4 had no difference. Water-dry samples, and KH2PO4-treated ones (dry and submerged) showed the highest K-d. A model for estimating Kd as a function the environmental conditions is proposed (OM > 9%). The OM1/2 was the best describing parameter.