TRICYCLAZOLE-CLAY COMPLEXES AS POTENTIAL SMART DELIVERY SYSTEMS: RELEASE IN WATER AND ENVIRONMENTAL FATE IN ALLUVIAL AND SANDY SOILS

A. Cabrera, R. Celis, L. Cox, M.C. Hermosín Instituto de Recursos Naturales y Agrobiología, Avda. Reina Mercedes 10, 41012 Sevilla, Spain

INTRODUCTION

Tricyclazole is a systemic fungicide used for the control of rice blast caused by Pyricularia oryzae

After its application on paddy fields by aerial fumigation is frequently detected in surrounding waters

The aim of this work was the modification of natural mineral clays with Fe3+ cation or a biopolymer to increase

the adsorption capacity for tricyclazole and the preparation of tricyclazole-clay complexes to be used as

controlled release formulations (CRFs).

MATERIALS AND METHODS

Fungicide

S

NN

N

CH3

Tricyclazole

Mineral clays

SWy (standard smectite,

CEC 76 meq/100g)

CTI (smectite low content mineral, 30-33% smectite)

SH (CEC 44 meq/100g)

Cation and biopolymer

O

O

NH3

+

OHO

OH

O

OO

NH3

+

OH

O

OH

OH NH

O

O

OHNH3

+

OH

OO

NH3

+

OH

OH

O

CH3

Fe3+

Chitosan (ch)

MW 189,24 g mol-1

Water solubility 596 mg L-1

log Kow 1,4 (pH 7, 20 ºC)

Soils

Soil Sand (%) Silt (%) Clay (%) CO (%) pH CaCO3 (%)

Alluvial 19,8 43,7 36,4 1,38 8,23 25,9

Sandy 95,7 1,2 3,0 0,27 8,43 3,8

Fungicide-clay complexes

Ground mixing (GM)

Weak complex (WC)

Strong complex (SC)

Tricyclazole Triciclazol Arcilla Clay Clay

5 ml MeOH 1 ml MeOH

1 min 24 h

Tricyclazole

5μM Triciclazol

(8 ml)

Clay (20 mg)

Centrifugation

Shaking 24 h

HPLC Analysis

Adsorption at one concentration

Adsorption-desorption isotherms

Adsorption Ci = 1,2,5,7, 10 µM

Freundlich equation Cs = Kf CeNf

Desorption from initial adsorption at 10 mM

Hysteresis index H = Nfdes/Nfa

Release kinetics in water

Dissipation studies Leaching studies

250 ml H2O

Shaking

Aliquot 2 ml (0-168 h)

HPLC Analysis

Commercial tricyclazole or formulation (a.i. 2 mg)

Tricyclazole 2.2 kg ha-1

Soil (300 g)

100% moisture

Extraction

Centrifugation HPLC

Analysis

First order kinetics

C = C0 e-kt

Tricyclazole 2.2 kg ha-1

Soil

Sea sand {

Sea sand {

MeOH

extraction

HPLC Analysis

RESULTS AND DISCUSSION Adsorption at one concentration

Adsorption-desorption isotherms

Release kinetics in water

Dissipation studies Leaching studies

SWy

SWch

4

SWch

6

SWFe

% T

ricycla

zole

adsorb

ed

0

20

40

60

80

100

120

7±1

87± 2

71± 2

99 ± 1

CTI

CTI

ch4

CTI

ch6

CTI

Fe0

20

40

60

80

100

120

13 ± 0

38 ± 140± 8

94 ± 1

SH

SHch

4

SHFe

0

20

40

60

80

100

120

22 ± 0

38 ± 0

100 ± 0

Fe3+ ions favor the protonation of tricyclazole, being adsorbed at the interlayer; render greatest adsorption

Clay Kf a (mmol LNf kg-1)

Nf a

r2 Kd0,5

(Lkg-1) Kf des

(mmol LNf kg-1)

Nf des r2 H

SWch4 1517 (1419-1622)a 1.3 ± 0.1b 0.99 1270 2618 (2571-2666)a 0.4 ± 0.1b 0.96 0.28

SWch6 448 (430-466) 1.0 ± 0.0 0.99 435 993 (978-1008) 0.5 ± 0.0 0.99 0.48

SWFe 5321 (3500-8089) 0.4 ± 0.2 0.74 7993 4688 (4040-5440) 0.2 ± 0.1 0.53 0.41

CTIFe 3083 (2727-3486) 0.3 ± 0.0 0.95 5185 3715 (3648-3784) 0.1 ± 0.0 0.80 0.38 aNumbers in brackets are standard errors of the mean. bMean ± standard error

Ce ( M)

0 1 2 3 4 5

Cs (

mo

l kg

-1)

0

1000

2000

3000

4000

5000

SWch4

SWch6

SWFe

CTIFe

Tricyclazole adsorption on the modified clays followed the order: SWFe > CTIFe > SWch4 > SWch6

Three different kinds of isotherms were observed: SWch6 (Nf = 1, lineal) due to hydrophobic interactions SWch4 (Nf > 1)polar and hydrophobic interactions SWFe and CTI Fe (Nf < 1) polar and ionic interactions

Time (h)

0 20 40 60 80 100 120 140 160 180

Tri

cycla

zo

le in

so

lutio

n (

M)

0

10

20

30

40

50

Commercial tricyclazole

SWch4

SWch6

Time (h)

0 20 40 60 80 100 120 140 160 180

SWFe

CTIFe

Time (h)

0 20 40 60 80 100 120 140 160 180

Tric

ycla

zo

le re

lea

se

d (%

)

0

20

40

60

80

100

GM WC SC

Chitosan modification increased tricyclazole adsortption only on SWch4 because the polymer enters in the interlayer making it available for tricyclazole

The tricyclazole-smectite complexes assayed showed a slow release profile of the fungicide, but SWFe-tricyclazole released less than 50% of active ingredient CTIFe GM and WC showed good properties as slow release formulations, tricyclazole release was greater than 80%.

Time (d)

0 20 40 60 80 100 120

% T

ricycla

zo

le

0

20

40

60

80

100

Commercial tricyclazole

SWch4 WC

CTIFe WC

Formulation t1/2 (d) r2

Commercial 150 (136-168)a 0.936

SWch4 WC 131 (111-160) 0.835

CTIFe WC 141 (127-160) 0.925

No significant differences were observed on tricyclazole half life with the formulation in the alluvial soil

aNumbers in brackets are standard errors of the mean

Volume added (ml)

0 200 400 600 800 1000

% T

ricycla

zole

leach

ed

0

1

2

3

4

5

6

Commercial

SWch6 WC

CTIFe WC

Sandy soil Tricyclazole leaching decreased in the sandy soil when applied as clay complexes as compared to the commercial product

Tricyclazole was not detectd in the leachates of the alluvial soil and soil depth distribution did not change from commercial to complexes

Formulation Alluvial

soil

% Leached

% Extracted

0-5 cm

% Extracted 5-10 cm

% Extracted 10-15 cm

% Extracted 15-20 cm

% Total

recovered

Commercial 0 63 ± 2 11 ± 4 0 0 74 ± 2

SWch4 WC 0 59 ± 1 4 ± 3 2 ± 0 0 65 ± 1

CTIFe WC 0 58 ± 3 7 ± 2 0 0 65 ± 2

Formulation Sandy

soil

% Leached

% Extracted

0-5 cm

% Extracted 5-10 cm

% Extracted 10-15 cm

% Extracted 15-20 cm

% Total

recovered

Commercial 75 ± 1 0 1 ± 0 3 ± 0 5 ± 1 84 ± 1

SWch6 WC 65 ± 2 3 ± 0 4 ± 0 5 ± 1 8 ± 1 85 ± 2

CTIFe WC 69 ± 3 2 ± 0 2 ± 0 3 ± 0 6 ± 0 82 ± 2

Leaching studies

The formulations favor the retention of the fungicide to the alluvial soil as compared to the commercial formulation

Commercial tricyclazol leaches faster in the sandy soil than from the formulations

CONCLUSIONS

The adsorption of tricyclazole increased in the clays modified with cations. The greatest increase was observed on SWFe, which could be tested as filter to treat contaminated waters, due to its high capacity of adsorption

For sandy soils, SWch-tricyclazole complexes decreased the tricyclazole leached concentration

Alluvial soil

The tricyclazole-smectite complexes with Fe3+ or chitosan allow to mantain lower fungicide concentration in the water table on flooded systems for rice cultivations, meanwhile mantaining the soil depth distribution and persistence in the soils.

ACKNOWLEDGMENTS: CSIC (JAE-Doc), JUNTA DE ANDALUCÍA (AGR-264 and P11-AGR-7400) co-financed by EU FEDER-FSE (PO 2009-2013)