Removal of α- and β- Endosulfan from Soils by Using Natural and Synthetic Surfactants

Aims: The aim of this work was studying a process of surfactant-assisted soil washing for the remediation of a soil spiked with α- and β-endosulfan (6,7,8,9,10,10-Hexachloro-1,5,5a,6,9,9a-hexahydro- 6,9-methano-2,4,3-benzodioxathiepine-3-oxide).

Place and Duration of Study: The work was carried out at UPIBI-IPN during 2016.

Methodology: An agricultural soil was collected and spiked with a commercial pesticide. Ten surfactants (nonionic, ionic, cationic, zwitterionic and natural) were selected for washing the soil using concentrations ranging between 0.001 to 0.2% w/w for each surfactant. Residual endosulfan concentrations were evaluated before and after washing soil process. Moreover, the extraction efficiency was related to surface tension and critical micellar concentration (CMC) of every surfactant.

Results: Better extraction efficiency was observed for α-endosulfan, its average extraction efficiency was around 73% and 55% for β-endosulfan. These values were significantly higher (up to 40%) than those observed in control experiments (water without surfactant). The maximum extraction of α-endosulfan was 90% and it was obtained using canarcel 20 at 10 times CMC. On the other hand, the maximum extraction of β-endosulfan was around 80% when surfactant polafix LO was used at a concentration of 700 times CMC, indicating that the surfactant-assisted soil washing process was suitable for extraction of pesticides from polluted soil. However, the wastewater produced should be treated in a subsequent process.

Conclusion: Natural surfactants did not show CMC in the range of concentration tested. Guar gum did not show a reduction of surface tension, even when concentration increases up to 1200 mg/L. In the case of mesquite seed gum, the surface tension slightly decreases from 73 to around 65 dyn/cm. Tween 80, canarcel 20 and emulgin W-400 showed a CMC of 65, 60 and 10 mg/L. CMC of dehyquart A, surfacpol A and texapon KD was of 160, 250 and 900 mg/L, respectively. Considering all surfactants, the extraction obtained of α-endosulfan is in the range of 65 to 94% with a mean of 79%, while extraction of β-endosulfan was in the range of 41 to 80%, with a mean of 61%. Accordingly to the nature of surfactants, best extraction efficiencies were obtained as follows nonionic > nonionic natural > ionic. Best extraction efficiency of α-endosulfan was 94% obtained with canarcel 20 (C* of 11.6) while for β-endosulfanthebest extraction efficiency was 80% obtained using canarcel 20 (C* of 11.6) and guar gum (383 mg/L). This information is highly valuable for designing a soil washing process for treatment of pesticide-polluted soil using natural compoundsas surfactants.