Thiacloprid adsorption and leaching in soil: Effect of the composition of irrigation solutions

- Thiacloprid sorption was not greatly affected by irrigation solution and amendment.
- Thiacloprid batch adsorption was not modified in the DOC range tested (3-300 mg L− 1).
- In leaching studies DOC solutions and fertiormont enhanced thiacloprid retention.
- Pesticide co-transport is facilitated at high DOC concentrations.

Pressure on groundwater resources has increased during the last decades due to the growing demand, especially in arid and semiarid regions, such as the Mediterranean basin, with frequent drought periods. In order to partially remediate this environmental problem of world concern, irrigation of agricultural lands with adequately treated wastewaters (TWW) is becoming a common management practice. The complex composition of these low-quality waters may influence the behavior of organic contaminants in soils. A calcareous soil with low organic carbon content was selected for the assessment of the adsorption and leaching of the neonicotinoid insecticide thiacloprid (THC). Different solutions were evaluated: TWW after a secondary treatment, a saline solution and solutions with a range of dissolved organic carbon concentration (DOC, 3-300 mg L− 1). The addition of an organic fertilizer (fertiormont) to the soil was also assessed, in an attempt to reduce THC mobility. Sorption of thiacloprid, a relatively polar pesticide, was similar under all the conditions considered, though an adsorption decrease was observed when DOC concentration increased. The transport of THC through soil columns was retarded with all the treatments, with the lower effects corresponding to TWW and the saline solution. Addition of fertiormont and irrigation with DOC at 3 mg L− 1 resulted in a reduction of pesticide leached (34% and 38%, respectively) in comparison with the control (66%), but surprisingly not for DOC at high concentration (55%), possibly due to co-elution of the pesticide with DOC. Therefore the transport of polar compounds, like THC, could be affected by the composition of the irrigation solutions, altering their impact to environmental water resources.

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