PESTICIDE PARTITIONING WITHIN A SURFACTANT-AIDED SOIL WASHING - - PowerPoint PPT Presentation

PESTICIDE PARTITIONING WITHIN A SURFACTANT-AIDED SOIL WASHING SYSTEM

Paloma Martina D. Cuartero Chemical Engineering Contra Costa Community College Lab Mentor: Peng Wang Faculty Advisor: Prof. Arturo Keller Funded by: US Department of Interior

BACKGROUND

Pesticide Contamination Surfactants

Surfactants in water/soil system is present as:

Monomers; Micelles, which are aggregates of the monomers and form

when the monomer concentration reaches the Critical Micelle Concentration (CMC) value;

Sorbed surfactants in the soil particles

Monomer Conc. = CMC

Monomer Micelle

OBJECTIVE

To investigate pesticide partitioning behavior

within a surfactant-aided soil washing system. WHAT WE DID…

Study the sorption behaviors of pesticides and surfactants

• nto soil particles;

Study the pesticide sorption in the presence of surfactants; Investigate the effect of surfactants on desorption of

pesticides.

MATERIALS

Soil Samples

Agriculture (Ag)#1, Ag#2,

Ag#3

Clayey Sediment

Pesticides

Atrazine Diuron

• Surfactants

Triton (Nonionic) Linear Alkyl Sulfate (LAS) Sodium Dodecyl Sulfate

(SDS) (Anionic)

Benzalkonium Chloride

(BC) (Cationic)

• Batch Equilibrium Technique was used to conduct all

sorption and desorption experiment. Procedure:

• 1. Weigh 2grams of soil
• 2. Add various amounts of pesticide and surfactant
• 3. Mix for about 20 hours
• 4. Centrifuge the samples
• 5. Analyze the aqueous phase using High Performance

Liquid Chromatography

METHOD

High Performance Liquid Chromatography (HPLC)

RESULTS

Diuron sorption in the absence of surfactant

20 40 60 5 10 15 20 25

Aqueous conc. (mg/l) Sorbed conc (mg/kg) Ag#1 Ag#2 Ag#3 Clayey Sediment

Triton sorption

0.E+00 2.E+04 3.E+04 5.E+04 5 10 15 20 25

Triton aqueous conc (g/l) Triton sorbed conc. (mg/kg) Ag#1 Ag#2 Ag#3 Clayey Sediment

• Soil organic matter (SOM)

and the soil clay content are the dominant parameters in terms of pesticide sorption.

• The triton sorption shows

an increase then starts to level off.

• BC, LAS, and SDS shows

the same sorption pattern but to a different extent.

Diuron sorption in the presence of Triton (Diuron: 15.95ppm)

2 4 6 8 10 12 14 16 5 10 15 20 25 Triton aqueous conc. (g/l) Diuron aqueous conc. (mg/l)

Ag#1 Ag#2 Ag#3 Clayey Sediment

• In presence of low concentration surfactants, the concentration of

pesticide in the sorbed phase increases.

sorbed phase aqueous phase

Diuron sorption in the presence of BC (Diuron conc.: 15.95ppm)

2 4 6 8 10 12 14 5 10 15 20 25

BC aqueous equilbrium conc. (g/l) Diuron aqueous conc. (mg/l) Ag#1 Ag#2 Ag#3 Clayey Sediment

BC, being a cationic surfactant, sorbs more into the soil particles which explains the much lower Diuron aqueous concentration at the first stage.

Diuron desorption in the presence of Triton (2.0267 g/l)

20 40 60 2 4 6 8 10 12 14 Diuron aqueous conc. (mg/l) Diuron sorbed conc. (mg/kg) Ag#1 Ag#2 Ag#3 Clayey Sediment Ag#1 (water)

Comparing Ag#1 and Ag#1(water), the enhanced desorption happened after cycle #2.

CONCLUSION

• The presence of surfactant has a significant effect in the

pesticide partitioning within the soil washing system

• Different surfactants have different potential to enhance

pesticide desorption. This enhancement is surfactant and soil dependent.

• The enhanced desorption happens only if the surfactant

concentration is higher than a certain value which is also surfactant and soil dependent.

FUTURE PLANS

• Statistical Analysis on the experimental data to determine

which parameters are dominant in terms of surfactant sorption.

• Conduct Batch Experiments to investigate the effect of

surfactant on dispersion of soil particles especially of soil colloidal particles (<2µm).

ACKNOWLEDGEMENTS

Peng Wang

• Prof. Arturo Keller

Samantha Freeman, Liu-Yen Kramer

• Dr. Nick Arnold, Andrew Morill, & Evelyn Hu

Internships in NanoScience, Engineering and Technology (INSET) California NanoSystems Institute (CNSI) Center for Science Excellence (CSE) University of Santa Barbara (UCSB) Contra Costa College

QUESTIONS?

sorbed phase aqueous phase

soil particle Sorbed surfactant pesticide

chemicals silica particulate hydrophobic less hydrophobic

SOIL PROPERTIES

56.8% 28.2% 15.0% Clayey 83.9% 58.4% 57.8% 75.5% Sand 13.0% 3.1% Sediment 16.4% 25.5% Ag#3 23.4% 18.8% Ag#2 13.5% 11.0% Ag#1 Silt Clay