Enantiomeric fraction and isomeric composition to assess sources of DDT residues in soils.

Chiral pesticides such as o,p'-DDT can undergo enantioselective microbial degradation in soil. Hence, the enantiomeric fraction (EF) of o,p'-DDT was used as an approach to assess potential recent inputs of DDT in the lower part of the Ebro River basin (NE Spain), a region heavily impacted by agricultural and industrial activities, including a dicofol production and a chloro-alkali plants. The EFs of five out of nineteen soils were not different from the racemic value (0.505±0.010), confirming that the Ebro River and some of its tributaries, Segre and Cinca rivers, transported fresh DDT residues despite its ban in Spain during the 90 s. o,p'-DDT/p,p'-DDT ratios in soils suggest that recent use of technical DDT and/or DDT-contaminated dicofol may be responsible for the fresh DDT inputs in the Segre River, while in the Ebro River, they indicate a dominant contribution of technical DDT, likely related to the residues accumulated by the chloro-alkali plant discharges.