Kchour, Hiba (2019) Agriculture pollution in Lebanese rivers: influence of soil and sediment properties on pesticide persistence. Doctoral Thesis.
The Beqaa region, crossed by Litani river, represents 47% of Lebanon's agricultural economy. The Litani, the largest river of Lebanon, suffers from different kinds of pollution including that caused by widely used pesticides in Beqaa valley. The herbicides fluazifop (FLP), terbuthylazine (TBZ) and triclopyr (TCP) are the most frequently used in Litani basin, therefore their sorption on sediment and soil samples taken from four sites along Litani river Berdaouni, Joub Jannine, Ammiq and Qaraoun, respectively, was investigated.The sorption data obtained for the three herbicides fitted well to Freundlich logarithmic equation both on sediment and soil samples, showing very low sorption coefficient (Kads) values. At pH values of sediments and soils, their colloidal component is negatively charged similarly to the FLP and TCP herbicides, therefore the very low sorption measured is attributable to negative sorption due to the repulsion between species with the same charge. TBZ instead at measured pH values of sediments and soils is in neutral form, therefore, the greatest adsorption observed for TBZ is probably due to a lipophilic effect that is more active for TBZ than for the other two herbicides. This agrees with the higher Kads values observed on samples more rich in organic matter. The low sorption and FLP, TBZ and TCP low degradability make them herbicides at high risk of leaching. The addition of biochar (BC) from coppiced woodlands, to soils and sediments increased considerably Kads values for all three herbicides. The BC effect was more evident on poorer samples in organic matter. These findings suggest that BC addition to Litani basin soil may be considered as an useful tool to prevent FLP, TBZ and TCP leaching in water.
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