Welcome in Aix enProvence Scientific Committee

Volatility potential of crop protection products:

proposal for a classification

On behalf of the UIPP Working Group Water - Soil - Air

Presented by Nicolas Marquet
Union des Industries de la Protection des plantes (UIPP)

2, rue Denfert-Rochereau, 92100 Boulogne-Billancourt, France

In the last decade, some publications have shown that pesticides may be detected at trace amount levels in the atmosphere after their application on leaves or soil; this presence is linked to several parameters which may influence volatilisation potential e.g. physico-chemical properties, climatic factors, targets (leaves, soil), spray equipment.

Conditions leading to such a transfer have been examined and one parameter identified which could contribute to the prediction of the volatilisation.

Data of about 80 pesticides originating from on going studies performed during the development of these products have been compiled and analysed in order to propose a potential classification.

Com. 12
Pesticide transfer trough grassed or forested strips
Lacas Jean-Guillaume, Dagès Cécile, Souiller Claude, Gouy véronique, Gril Jean-Joël, Carluer Nadia.
Cemagref

UR Qualité des eaux et prévention des pollutions

3 bis quai Chauveau, 69336 Lyon, France.

[e-mail]

Despite the legislation and continuous improvement of agricultural practices, pesticide may hazardously move from the plots to the water resources and generate concentrations higher than the maximum levels fixed by the 80/788/EEC directive for drinking water. Then, grassed or forested buffer strips may represent possible management tools to avoid or reduce the transfer from the application site to the main water bodies.

Initially developed in the United-States to limit erosion and diffuse pollution by nutrients, the use of these systems has been extended from the 1990s to the reduction of diffuse contamination by pesticide. The monitoring of natural grassed strips has shown their potential to reduce pesticide transfer in runoff. Experiments led in controlled conditions (rainfall or runoff simulations, laboratory soil columns or physical models) have permitted to better understand the involved mechanisms. Pesticide fluxes and concentrations abatements in runoff seem directly linked to the soil infiltration capacity of a grassed or forested strip, which is often much higher than the one of the agricultural field because of a more developed root system and a higher organic matter content. Pesticide in the remaining runoff can also be trapped by the strip organic surface material, but this process mainly concerns the compounds with a high adsorption coefficient.

The broad existing results on these systems however still need to be supplemented by specific studies on pesticide fate into the soil and sub-soil layers in order to determine to what extent these compounds can be retained into the soil matrix or move further to the ground or surface water resources, via a macroporous or sub-surface transfer.

Com. 13

Adsorption of Triasulfuron on Soils and Soil Colloid Components

Alba Pusino,¹ Ilaria Braschi² and Carlo Gessa²

_{1Dipartimento di Scienze Ambientali Agrarie e Biotecnologie Agro-Alimentari, Università di Sassari, Viale Italia 39, 07100 Sassari, Italy. 2Dipartimento di Scienze e Tecnologie Agro-Ambientali, Università di Bologna, Viale Fanin 40, 40127 Bologna, Italy}

The adsorption of the herbicide triasulfuron [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide] on three soils, homoionic montmorillonite (Fe³⁺, Al³⁺, Ca²⁺, or Na⁺-exchanged), soil organic matter (H⁺ and Ca²⁺-saturated), and an amorphous iron oxide were studied using the batch equilibration technique. The adsorption on Fe- and Al-exchanged montmorillonite was rapid, and equilibrium was attained after 5 min. In contrast, Ca- and Na-exchanged montmorillonite were ineffective in the adsorption of triasulfuron. A Fourier transform infrared (FT-IR) study of Fe- and Al-montmorillonite samples after the interaction with triasulfuron suggests that the adsorption mechanism involves the protonation of triasulfuron at the triazine moiety from acidic water molecules co-ordinated to the exchangeable cations. The lack of adsorption on montmorillonite saturated with Ca and Na ions reflects the lower acidity of these ions, compared with Fe and Al. The extent of triasulfuron adsorption on humic acid is rather high at low pH and decreases with increasing pH of the suspension. Humic matter is an important adsorbent only at pH values lower than 5, when both triasulfuron and humic acids are partly in the un-dissociated form. Experiments on amorphous iron oxide substantiated the same pH dependence as described above, although this adsorbent is the only colloid surface which exhibits a significant affinity to the triasulfuron molecule at pH values near to neutrality. Adsorption isotherms on soil conformed to the Freundlich equation. The highest level of adsorption was measured on soils with low pH and high organic carbon content. The adsorption on soils was negatively correlated with pH.

Com 14
Time effect upon bentazone behaviour
BOIVIN Arnaud., PERRIN-GANIER C. & SCHIAVON M.
Laboratoire Sols et Environnement, UMR n°1120 INPL/ENSAIA-INRA

2, avenue de la Forêt de Haye, BP 172 , 54505 VANDOEUVRE-lès-NANCY cedex FRANCE

[e-mail]
Bentazone is a post emergence herbicide used in many crops. Previous sorption / desorption batch experiments indicated that only 20 % of the product is sorbed on soils. In addition, field experiments have showed that 4 % of the sprayed quantity on cultivated areas can leach to surface water. Thus, surface water may be threatened by bentazone contamination. To complete bentazone characterisation, our purpose was to assess time effect upon its behaviour in soils.

In laboratory studies, bentazone was added on three different soils (sandy, silty and clay soil). Bentazone degradation, sorption / desorption kinetics and isotherms measurements were achieved at different times.

60 days after treatment, mineralization products amounts vary from 2 % (sandy soil) to 9 % (clay soil). Maximum mineralization occurs after 30 days for each soil. Sorbed quantities increase from 27 % after 7 days to 72 % after 60 days while desorbed amounts decrease from 65 % to 11 %, in average for the three soils. Bentazone behaviour is similar in the clay and silty soils while in the sandy soil the adsorption is lower and the desorption more important (46 % and 20 % after 60 days respectively). In aged soils, a large part of residues (bentazone and its degradation products) becomes non-available to water and the proportion of non-extractable products increases. In addition, bentazone releasing kinetics indicates a coupled effect of time and soil type upon herbicide availability.

By coupling a quantitative and a qualitative approach, this study allows us to understand how physicochemical interactions between soils and bentazone evolve with time. These data are crucial to determine bentazone surface water potential contamination.

Keywords : bentazone, soil, time-effect


Com. 15
Adsorption of the herbicide prosulfocarb on model soil colloids.
M. Nègre¹, I. Passarella¹, A. Baglieri², M. Gennari<sup>2



1</sup>Università di Torino, DI.VA.P.R.A. Settore Chimica Agraria, Via Leonardo da Vinci, 44, 10095 Grugliasco, (TO), Italy

² Università di Catania, D.A.C.P.A. Settore Scienze Agrochimiche, Via S. Sofia 98, 95100, Catania, Italy.
The purpose of this work was to assess the role of some soil colloids in the interaction of the thiocarbamate herbicide prosulfocarb with the soil surfaces. The extent of adsorption of prosulfocarb has been determined on a humic acid extracted from an histosol, a synthetic aluminium hydroxide and a natural montmorillonite. The amount adsorbed was negligible on alluminium hydroxide, very high (> 95 %) on humic acid, and intermediate on montmorillonite (42 %). The affinity of prosulfocarb for the humic acid was predictable according to its low solubility (13.2 mg l^-1), and its high Kow (44500), while the interaction with the montmorillonite was not expected because of the low polarity of the molecule. The interaction with the montmorillonite followed a S-isotherm typical of a collaborative adsorption indicating that the adsorbed molecules promoved further adsorption. The desorption isotherm indicated that the process was completely reversible. Adsorption isotherms on humic acid and alluminium hydroxide were not measurable because of the respective too high and too low affinity of prosulfocarb for such adsorbents.

In order to obtain some information on the interaction of prosulfocarb with some soil surfaces closer to the real one than pure soil colloids, adsorption has also been studied on the complexes montmorillonite-aluminium hydroxide, and montmorillonite-aluminium hydroxide-humic acid. The extent of adsorption on the binary system montmorillonite-aluminium hydroxide was lower than that on pure montmorillonite confirming that the aluminium hydroxide did not play any role. The ternary system montmorillonite-aluminium hydroxide-humic acid exhibited a higher affinity for the herbicide than pure montmorillonite and the isotherm was C-type confirming the predominant role of the humic acid in both the extent and the mecchanism of interaction.

The adsorption isotherms obtained on the model soil colloids have been compared to those obtained on different soils.

The results have pointed out that the use of artificial soil colloids, although not completely representative of real soil surfaces, but much less complex, allows to improve the understanding of the soil surficial interactions with pesticides.

Com. 16
SOIL STRUCTURE ROLE ON THE BENTAZONE AVAILABILITY TO WATER TRANSFER
Guimont S., Perrin-Ganier C., Schiavon M.
Laboratoire Sols et Environnement (ENSAIA/INRA/INPL)

2, avenue de la forêt de Haye 54500 Vandoeuvre-lès-Nancy FRANCE

[e-mail]
Once organic compounds penetrate the soil, their transport behaviour may be affected by soil structure. The aim of this study was to determine the role of fine porosity on the retention of pesticides during their water transfer through the soil.

We performed micro-columns experiments using six types of agricultural soil, distinct by their texture and organic matter content. As a model of pesticide for this work, the herbicide bentazone characterised by a high water solubility (570 mg.L^-1) was selected. ¹⁴C-labelled bentazone solution droplets were applied on the columns of soils brought to different initial water content. After six days under controlled conditions (air protected, darkness, 20°C), micro-columns were first leached with distilled water and centrifuged at two successive increasing speeds. Three water fractions were collected representative respectively of “mobile water”, “mesoporosity” and “microporosity” filled water. Volumes and radioactivity level were measured for each fraction.

The radioactivity analysis of the different soil-water fractions shows significant influence of the initial water level. When applied in dry conditions, according to the soils, the bentazone is distributed mainly in the mobile water (from 40 to 80 %) revealing the high transfer potential of bentazone, and from 7 to 22 % in the meso and microporosity water fractions. The resting part stays in the soil. On the other hand, in wet conditions, the residues found in the mobile water decrease on behalf of the part staying in the soil, 3 to 13 % are measured in the meso and microporosity water fractions. Two of the studied soils - one silt sand texture and 5,8 % of humified organic matter, and the other silty and low organic matter – reveal rather different behaviours. The residue proportion found in the microporosity is ten times higher for the first soil. We can conclude that studying impact of soil structure and water content on the soil transfer of organic molecule is of great interest to reveal pesticide transport dynamics from surface to groundwater.
Keywords : transfer, bentazone, soil structure, water content