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MATERIAL AND METHODS RESULTS AND DISCUSSIONS
CONCLUSION
INTRODUCTION
SORPTION OF PESTICIDES ON VARIOUS MATRICES FROM TWO
CONSTRUCTED WETLANDS
VALLÉE1 R., DOUSSET1 S., BILLET1 D., BENOIT2 M.
1 LIEC, UMR 7360 CNRS-Université de Lorraine, BP 70239, 54506 Vandoeuvre-Lès-Nancy, France, [email protected]
2 Aster, UR 055, INRA, 662 Avenue Buffet, 88500 Mirecourt, France
- The region Lorraine shows a high proportion of clay soils, consequently around 20% of agricultural land are drained. This percentage can reach 70% in some
watersheds. Water from these drained fields may create a pesticide contamination in rivers.
- Within the context of the ‘Zone Atelier Moselle (ZAM)’, in collaboration with the Rhin-Meuse Water Agency, the ANSES Nancy, the ‘Chambre Régionale d’Agriculture
de Lorraine and the INRA Mirecourt, remediation zones were implemented in drainage outlet in order to reduce pesticide export towards surface waters.
- The objective of this study is to asses the effectiveness of constructed wetlands (CW) on the sorption capacities of the different matrices found in these constructed
wetlands.
Selected pesticides
Clay Silt Sand OC N CaCO3
pH
(H2O) CEC
Specific
surface
- - - - - - - - - - - - g.kg-1 - - - - - - - - - - - - - cmol+.kg-1 m².g-1
Jallaucourt
Soil (Jso) 624 350 25 12.3 1.4 <1 7.87 37.8 72.5 ± 0.2
Straw (Jst) / / / 359.0 12.2 / / / 0.5 ± 0.3
Ollainville
Soil (Oso) 594 360 45 15.0 1.5 <1 7.51 33.0 58.3 ± 0.2
Sediment (Ose) 563 391 45 17.0 1.7 1.3 7.16 30.5 50.1 ± 0.1
Main characteristics of substrates
2,4-MCPA Isoproturon Napropamide Boscalid Prochloraz Tebuconazole
Water solubility
at 20°C (mg.L-1) 29.4.104 70.2 74.0 4.6 26.5 36.0
Vapour pressure
at 25°C (mPa) 4.0 10-1 5.5 10-3 2.2.10-2 7.2 10-4 1.5 10-4 1.30 10-3
Sorption
coefficient
Koc (L.kg-1)
n.d. 122
(36-241)
839 (435-1 609)
809 (750-1 200)
500 (-)
769 (102-1 249)
Half-live
at 20°C (days) 24
(7-41)
12 (7/2-18.2)
308 (120-400)
246 (27-372)
223.6 (22.1-936.1)
365 (-)
Sorption studies
- The results clearly demonstrate the importance of sorption in the effectiveness of a CW, related to physico-chemical properties of pesticides and substrates.
- The retention was greater for pesticides with hydrophobic properties (low solubility and high Koc). In addition, the organic carbon content and nature of the substrate was
found to have a strong effect on sorption.
- On the field, sorption alone does not determine the effectiveness of a CW to reduce pollution. Nevertheless, the adsorption reduces pesticide concentrations during the
first rainfall events after treatment and the formation of non-desorbable residues increases the residence time of pesticides in the CW.
- Then vegetation and organic matrices (straw, dead leaves,…) should be maintained inside of the CW in order to increase their effectiveness.
0
50
100
150
200
250
300
0 1 2 3 4
x/m
(m
g.k
g-1
)
Ceq (mg.L-1)
Jallaucourt-Straw Isoproturon
Napropamide
Prochloraz
0
2
4
6
8
10
12
14
16
0 1 2 3 4
x/m
(m
g.k
g-1
)
Ceq (mg.L-1)
Jallaucourt-Soil Isoproturon
Napropamide
Prochloraz
Adsorption isotherms
• Kf values ranged from 0.74 to 442.6 mg1-nLnkg-1 and the n observed ranged from 0.14 to 1.12.
Desorption isotherms
- The desorbed amounts varied from a few percentages to more than 70%.
- Desorption capacity : Boscalid > Tebuconazole > Napropamid > Isoproturon > Prochloraz > 2,4-MCPA.
- No significant desorption was observed for 2,4-MCPA.
- No hysteresis can be defined when 0.7 < H < 1 ; then the adsorption of Boscalid is highly reversible (0.53
< H < 0.89).
- The others H values ranged from 0.59 and 0.50 for Tebuconazole to 0.44 and 0.16 for Prochloraz.
- The straw had the largest amounts of non-desorbable residues, 12.1 mg.kg-1 for 0.125 mg.L-1 initial
concentration.
The authors wish to thank R. Cherrier and F-X. Schott (Chambre Régionale d’Agriculture de Lorraine), the farmers who granted us access to the experimental fields, A. Ortar (ANSES,
Nancy) for field data ,We thank also the Zone Atelier Moselle, M. Pitrel (Rhin-Meuse Water Agency ) for financial support.
Drain discharge and flowmeter
Bundle of straw
Device exit
Jallaucourt
Drain discharge and flowmeter
Device exit
Ollainville
Nearly 80 pesticides were analysed in waters flowing into and out of these
constructed wetlands.
Six pesticides were selected for laboratory on the basis of their :
- Frequency of use and detection in waters.
- Physico-chemical properties.
The mixtures were shaken for 24 h at 20 ± 1 °C
Four successive desorption steps were performed for initial concentrations
of 0.125 and 2 mg.L-1.
V : 10 mL H2O
C0 : at 0.05 to 4 mg.L-1
M : 2 g of soil and
sediment or
0.2 g of straw
30 min at 10 000 g Sorbed pesticides
x/m = 𝑽
𝑴 × (C0 – Ceq)
Ceq : pesticides
analysis in UHPLC
Adsorption
Freundlich Equation
x/m = Kf × Ceqn
(Kf in mg1-nLnkg-1)
Hysteresis coefficient
H = 𝒏𝒅𝒆𝒔
𝒏𝒂𝒃𝒔
Freundlich adsorption and desorption isotherms
Kf : 442,6 ; n : 1,1 Kf : 16,3 ; n : 0,7
Kf : 20,5 ; n : 0,8 Kf : 0,7; n : 0,7
150
200
250
300
1,04
11,73
0,96
15,8
1,04
8,16 12,1
0
10
20
0,125
mg/L
2
mg/L
0,125
mg/L
2
mg/L
0,125
mg/L
2
mg/L
0,125
mg/L
2
mg/L
mg
/kg
221,2
Oso Ose Jso Jst
Non-desorbable amounts of pesticides on different substrates
Pesticides :
• adsorption capacities: Prochloraz (442.6 to 16.,3
mg1-nLnkg-1) >> Tebuconazole - Boscalid >
Napropamid > 2,4-MCPA-Isoproturon (20.5 to
0.7 mg1-nLnkg-1), in relation with pesticide
solubility and Koc.
Substrates :
• retention capacity : Straw (442.6 to 20.5 mg1-nLnkg-1)
>> Sediments > soil (16.3 to 0.7 mg1-nLnkg-1),
• the straw presented an adsorption 20 to 30
times higher than other substrates.
Experimental sites and sampling
Physico-chemical properties of pesticides (FootPrint, 2011)