Study of Chemical and Physical Properties and the Soil Sorption

of Metolachlor and Carbofuran in Three Tropical Soils

José A. Dumas, Peter Nkedi-Kizza and

Rafael Montalvo-Zapata

Organic Matter

ClayThe environmental fate of pesticides The environmental fate of pesticides

applied to soils is determined by sorption applied to soils is determined by sorption and degradation processes.and degradation processes.

The nature of organic matter will The nature of organic matter will determine soil aggregates as well as determine soil aggregates as well as pesticide sorption and degradation. pesticide sorption and degradation.

IntroductionTwo main soil components associated to Two main soil components associated to pesticide sorption are clay and organic matterpesticide sorption are clay and organic matter

Organic matter participates in translocation of micronutrients from the soil to the plant, enhances water retention, increases seed germination rates and percentages, and stimulates development of micro flora populations in soils. At the same time organic matter provides sorption surfaces for pesticides and other types of xenobiotics compounds.

Organic matter

Organic Matter – Humic and fulvic acids

Humic acid-pesticide interaction

Van der Waals and electrostatic interactions.

How pesticide’s sorption occurs?

Hypothesis

Chemical and physical properties of humic Chemical and physical properties of humic and fulvic acid are strongly different from and fulvic acid are strongly different from one soil type to another and hence affect one soil type to another and hence affect some pesticide interactions.some pesticide interactions.

Objectives

Characterize and compare chemical and Characterize and compare chemical and physical properties of three Puerto Rican physical properties of three Puerto Rican soils (two carbonatic soils and one organic soils (two carbonatic soils and one organic soil) soil)

Characterize the relationship of sorption of Characterize the relationship of sorption of metolachlor and carbofuran to organic metolachlor and carbofuran to organic matter properties in three tropical soilsmatter properties in three tropical soils

North Coastal Limestone Aquifer

South Coastal Alluvial Aquifer

Chemico-pharmaceutical industries

High urban development

Hydrogeographic (HP) map of Puerto Rico

Sampling areas and Soil Series Selected

TiburonesCatano

Aguilita

Methods Soils were collected from three or four point ons in each sampling Soils were collected from three or four point ons in each sampling

area from top to 60 cm depth.area from top to 60 cm depth. Samples were air dried, ground and sieved. Samples were air dried, ground and sieved. Characterization of soil physical and chemical propertiesCharacterization of soil physical and chemical properties

• pH, CEC, CaCOpH, CEC, CaCO3 3 content, organic carbon content content, organic carbon content (Walkley-Black method), particle size. (Walkley-Black method), particle size.

• Extraction of fat fraction, humic and fulvic acid content.Extraction of fat fraction, humic and fulvic acid content.• Characterization of humic and fulvic acid fraction by Characterization of humic and fulvic acid fraction by

derivative UV-Vis, and determination of E4/E6 ratio.derivative UV-Vis, and determination of E4/E6 ratio.• Determination of ATR-IR spectrum of humic and fulvic Determination of ATR-IR spectrum of humic and fulvic

acid fractions.acid fractions.• Determination of total acid content of humic and fulvic Determination of total acid content of humic and fulvic

acid fractionsacid fractions To develop sorption isotherms curves of metolachlor and carbofuran To develop sorption isotherms curves of metolachlor and carbofuran

(Batch slurry method).(Batch slurry method).

Soil properties

Soil Series

pH CCE

%

Clay

%

Silt

%

Sand

%

WHC

AguilitaAguilita 8.188.18 63.1363.13 47.6847.68 22.8822.88 29.4429.44 4545

CataCataññoo 8.608.60 14.0114.01 4.564.56 3.363.36 92.0892.08 2222

TiburonesTiburones 4.074.07 0.840.84 17.4417.44 2.842.84 79.7279.72 3838

CCE-Calcium carbonate equivalen; WHC-Water holding capacityt

Organic matter properties

Soil Series HA

mg1

FA

mg1

HA/FA OC

%

Fat

mg/kg OC

AguilitaAguilita 600600 590590 1.01.0 4.084.08 950950

CataCataññoo 2525 8484 0.30.3 0.530.53 161161

TiburonesTiburones 990990 490490 2.02.0 7.937.93 27302730

HA-humic acid; FA-fulvic acid; 1mg/50g soil; OC-organic carbon

Fulvic and Humic acid properties

Soil Series E4/E6 Total Acidity

(meq/g humic)

HA FA HA FA

AguilitaAguilita 5.55.5 10.010.0 1.41.4 2.82.8

CataCataññoo 4.94.9 6.56.5 NDND 0.440.44

TiburonesTiburones 3.23.2 10.410.4 1.61.6 3.23.2

E4/E6-absorbance ratio at 400 and 600 nm

Potentiometric tiltration of Fulvic acid

8

8.5

9

9.5

10

10.5

11

11.5

12

12.5

0 2 4 6 8 10 12 14 16 18

ml HCl 0.102 N

pH

Aguilita AF Tiburones AF Catano AF

-COOH

Phenolic OH

Potentiometric tiltration of Humic acid

6

7

8

9

10

11

12

13

0 2 4 6 8 10 12 14 16 18

ml 0.1022 N HCl

pH

pH Aguilita pH Catano pH Tiburones

Non clearly defined acidic group protons

Derivative spectrum of Humic acid (100ug/mL)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

200 250 300 350 400 450 500 550 600 650

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

200 250 300 350 400 450 500 550 600 650

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

200 250 300 350 400 450 500 550 600 650

Aguilita

Catano

Tiburones

Derivative spectrum of Fulvic acid (100ug/mL)

Aguilita

Catano

Tiburones

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

200 250 300 350 400 450 500 550 600 650

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

200 250 300 350 400 450 500 550 600 650

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

200 250 300 350 400 450 500 550 600 650

Main functional groups of Fulvic acids (β-humus) identified by ATR-IR

Aguiliita

Catano

Tiburones

Benzene rings

Hydroxy groupsAromatic C-H

Si-H

C=O

C-O

Main functional groups of Humic acids identified by ATR-IR

Aguiliita

Catano

Tiburones

Structure of pesticides

Metolachlor Carbofuran

Chloroacetanilide Carbamate

Chemical and physical properties of Metolachlor and

Carbofuran

Name Family Sol.(mg/

L)

Koc(mL/g)

Kow pKb

MET cloroacetanilide 530 200 2820 NA

CAR carbamate 700 14-160 17-26 NA

MET-metolachlor; CAR-carbofuran

Sorption isotherms for Metolachlor

R2

= 0.9478

R2

= 0.9747

R2

= 0.963

0.00

20.00

40.00

60.00

80.00

100.00

120.00

0 5 10 15 20 25

Ce (mg/L)

Cs

(mg/

Kg)

Catano Aguilita Tiburones

Soil sorption coefficient

Soil Series Metolachlor

Kd

AguilitaAguilita 3.63.6

CataCataññoo 1.21.2

TiburonesTiburones 9.39.3

ConclusionCarbofuran sorption coefficient for CataCarbofuran sorption coefficient for Catañño o

soil series was higher than that found for soil series was higher than that found for Tiburones or Aguilita soils and also higher Tiburones or Aguilita soils and also higher than the sorption value reported in than the sorption value reported in literature.literature.

Fulvic and Humic acid properties of Fulvic and Humic acid properties of CataCatañño series are different from those of o series are different from those of Tiburones and Aguilita series.Tiburones and Aguilita series.

Data suggest that nature of organic matter Data suggest that nature of organic matter is a primary factor to be considered for an is a primary factor to be considered for an adequate interpretation of sorption and adequate interpretation of sorption and desorption pesticide data.desorption pesticide data.

Conclusion

This project was funded by the TSTAR program. We appreciate the excellent technical support of Norma Corchado and Esteban Rivera from the Central Analytical Laboratory, without whose assistance this work could not have been conducted.

Acknowledgement