Role of Irrigation with Raw and Artificial Wastewaters on Pesticide Desorption from Two Mediterranean Calcareous Soils

Abstract

Irrigation of agricultural soils with low-quality waters, a common practice in arid and semiarid regions, may affect the fate of organic pollutants increasing the risk of groundwater contamination. Desorption of thiacloprid (THC) and fenarimol (FEN) preadsorbed on two calcareous soils (SV, RM3) has been investigated using different solutions: MilliQ water (control), urban treated wastewater (WW), anionic (A22, BP) and non-ionic (TW-80, TX-100) surfactants, dissolved organic matter from sewage sludge (SS-Ph, SS-MQ), and inorganic salt solutions (CaCl2, (NH4)2SO4). WW did not affect in general pesticide desorption. Desorption of THC was significantly enhanced with BP (up to 35.4 % in SV) at concentrations higher that those normally found in WW, while that of FEN was reduced at high concentrations of A22, a fact attributed to precipitation of the surfactant salt with Ca2+ from soils. The non-ionic surfactant TW-80 at levels with environmental relevance (ca. 4–80 mg l−1) drastically enhanced FEN solubilization from soils (an increase between 52 % and 90 %). Inorganic salts in solution in the concentration range studied (5–10 mM) only influenced FEN desorption, but the effect was variable depending on the salt and on the soil. Finally, FEN desorption from RM3 increased linearly with increasing concentrations of SS-MQ (R2 = 0.994), whereas it decreased as the SS-Ph concentration increased in solution (R2 = 0.846). It can be concluded that pesticide desorption is mainly controlled by the composition of the irrigation solution, with a higher effect especially on the more hydrophobic compound.