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, romain.vallee@univ-lorraine.fr

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)