Occurrence and fate of organochlorinated pesticides and PAH in agricultural soils from the Ebro River basin.

This study was aimed to assess the presence and fate of 22 organochlorinated pesticides (OCHs) and their degradation products and 16 Environmental Protection Agency-priority polycyclic aromatic hydrocarbons (PAHs) in soils of the Ebro River basin (NE Spain) during a 3-year period. The study site is characterized by a long and active agricultural history where pesticides have largely been used. Soils were extracted using pressurized liquid extraction followed by gas chromatography-mass spectrometry. This procedure was optimized in terms of multiresidue analysis and effective cleanup and proved to have excellent analytical performance (recoveries ranging between 71% and 133%, standard deviation <14%, and a method detection limit from 0.19 to 7.38 microg/kg). Soils form the Ebro basin showed a prevalence of 4,4'-DDT and 4,4'-DDE, found in 53% and 88% of the soil samples between 0.13 and 58.17 microg/kg-dw (dry weight), respectively, indicating a slight decreasing trend of DDT within time. PAHs were detected in all soil samples at concentrations up to 465 microg/kg-dw, and the phenanthrene/anthracene (<10) and fluoranthene/pyrene (>1) ratios indicated combustion processes as the main source attributing to the burning of weeds and vegetable wastes after harvesting. No traces of any of the OCHs and PAHs were detected in groundwater, indicating that leaching for agricultural fields is not an important process of transport for these compounds. Overall, we propose the need to perform a monitoring program to evaluate the temporal tendencies and potential impact of pesticides and PAH in soils.