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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)