Martin Kočárek Czech University of Life Sciencieas Prague Faculty of Agrobiology Food and Natural Resources Department of Soil Science and Soil Protection

Introduction Pesticides are significant tools to achieve high and quality harvest The application can bring some risk like soil, water, plants and animals contamination An ideal pesticide has to stay in the soil just for the time which is necessary to reduce weeds, but not longer for his residues to affect consequent growth To decrease a risk accompanied by pesticides application we try to model their movement and degradation by prediction models

The main processes involved in pesticides behaviour before their entrance to the soil Photodecomposition Transport in the air Adsorption by plant leafs

The main factors affecting pesticides behaviour after their entrance to the soil Pesticides undergo many transformation and transportation processes Ratio among liquid, solid and gaseous phases Availability of applicable reactants Physical-chemical properties of soil Physical-chemical properties of pesticides

The main factors involved in pesticides behaviour after their entrance to the soil Climatic conditions Simple degradation processes like hydrolysis and oxidation Composition and activities of microorganisms

The main factors involved in pesticides behaviour

Soil temperature and soil moisture

Pesticide Sorption absorption - sorption (penetration into) a 3D matrix adsorption – sorption to a 2D surface Sorbate: the molecule ad- or absorbed Sorbent: the matrix into/onto which the sorbate ad- or absorbs Ability of soil to bind various substances from the dispersion medium

Pesticide Sorption sorption affects transport: generally, molecules which are sorbed are less mobile in the environment sorbed molecules are not available for phase transfer processes (air-water exchange, etc) and degradation: sorbed molecules are not bioavailable sorbed molecules usually shielded from UV light (less direct photolysis) sorbed molecules cannot come into contact with indirect photoxidants

Pesticide Sorption Mineral Colloids –C–Clay minerals –P–Primary silicates –I–Insoluble phosphates of Al, Fe –P–Polymeric silicic acids (H 2 SiO 3 ) –H–Hydrated oxides (Al, Fe, Mn), sesquioxides Organic Colloids –H–Humic substances –P–Protein, lignin Combined Colloids – Organo-mineral complexes

Electronegative – ACIDOIDS –N–Negatively chargedX-H………H + –A–Adsorption of cations –(–(Clay minerals, humic substances, H 2 SiO 3 ) → most of the soil colloids Electropositive – BASOIDS –P–Positively charged X-OH………OH - –A–Adsorption of anions –(–(hydrates of sesquioxides) Ampholyte – AMPHOLYTOIDES –(–(hydrated polymers of sesquioxides) Soil Coloides

Pesticide Sorption Permanent –i–isomorphic substitutions in the crystal lattice of clay minerals –O–Octahedron : Al 3+ → Fe 2+, Tetrahedron: Si 4+ → Al 3+ Variable –p–pH-dependent charge –I–Is formed by the dissociation of carboxyl groups –n–negative charge increases with increasing of soil pH Origin of Soil Colloid Charge

Evaluation of Sorption Freundlicha equation: S = amount of organicall chemicals adsorbed into weight unit of the soil K f and n = empirical constant C = equilibrium concentration of organic chemicals in soil solution Langmuir equation: S= amount of organicall chemicals adsorbed into weight unit of the soil C = equilibrium concentration of organic chemicals in soil solution K 1 = adsorption constant related to bond strength S max = maximum of adsorbed chemicals

Pesticide Sorption Pesticide The structural formula Molecular weight Solubility in water [µg.L -1 ] KOCDT50GUS = log(DT 50 ) × (4 - log(K oc )) Chlorotoluron 212, ,76 Metribuzin 214, ,88 Prometryn 241,3736, ,83,18 Terbuthylazin 229,78,522586,53,19 Tested Pesticides

Pesticide Sorption Tested Soils

Pesticide Sorption Tested Soils SoilLocationpH KCl Cox (%) CEC (mmol+/100g) Clay (%) Greyic Phaeozem - Loess Čáslav6,531,3529,7513,4 Haplic Chernozem - LoessPraha -Suchdol7,212,0126,3819,3 Arenosol Epieutric -SandSemice5,740,669,133,5 Haplic Cambisol - GneissHumpolec4,371,6326,009,9 Haplic Chernozem - LoessIvanovice na Hanné6,281,7727,1311,4 Haplic Cambisol - QuartziteJince4,991,6123,6320,3 Arenic Chernozem - Grevel sandVleké Chvalovice6,940,9214,136,4 Stagnic Chernozem Siltic - MarliteMilčice7,432,9240,3815,8 SandPolabí8,110,025,633,3 Haplic Cambisol - SyenitePředbořice5,031,7122,884,8 Haplic Luvizem - LoessHněvčeves5,631,0324,0013,9 LoessPraha - Suchdol7,400,4424,1324,5 Dystric Cambisol - GneissVysoké nad Jizerou4,792,3128,4216,9

Pesticide Sorption-Detected values of Freundlich equation parameter (K f ) Soil / SubstrateChlorotoluron K f for n=1.2 Metribuzin K f for n=1.31 Prometryn K f for n=1.17 Terbuthylazin K f for n=1.21 Greyic Phaeozem - Loess 3,340,78433,66632,9496 Haplic Chernozem - Loess 4,641,02844,26913,5284 Arenosol Epieutric - Sand 2,190,3643,86662,6979 Haplic Cambisol - Gneiss 3,73110,81165,7823,4749 Haplic Chernozem - Loess 4,07380,90454,14313,1247 Haplic Cambisol - Quartzite 3,91292,76396,91623,9737 Arenic Chernozem - Grevel sand 2,16730,42382,54022,5067 Stagnic Chernozem Siltic - Marlite 11,8941,30766,51394,7802 Sand 0,46140,08671,20291,214 Haplic Cambisol - Syenite 4,40864,528,02894,7937 Haplic Luvizem - Loess 2,70820,63943,87912,9095 Loess 0,84670,17171,08270,9133 Dystric Cambisol - Gneiss 7,4971,552811,3786,3507

Pesticide Sorption -Adsorption Isotherm Haplic Cambisol Dystric Cambisol Haplic Luvisol Chlorotoluron sorption in laboratory and fild conditiones

Pesticide Sorption -Adsorption Isotherm

Pesticide Sorption Pedotransfer rules Using the regression analysis were evaluated pedotransfer rules for individual pesticides for prediction of Freundlich equation parameter (K f ) at a constant value of parameter n PesticideRegression equationeR2R2 p Chlorotoluron Kf = -0,91 + 2,01*humus [%] 85,60,0000 Metribuzin Kf = 1,74 + 0,28*humus [%] - 0,24*pH_KCl 58,80,0118 Prometryn Kf = 9,51+ 1,24*humus [%] - 1,24*pH_KCl 80,40,0003 Terbuthylazin Kf = 4,36+ 1,16*humus [%] - 0,38*pH_KCl - 0,006*KVK [mmol.kg -1 ] 89,3 0,0001

Maps of Kf coefficient of different pesticides

Pesticide degradation The change of pesticide concentration is described by following equation: Where: c = concentration t = time k r = constant of reaction n = order of reaction

Pesticide degradation Zero order: n=0 First order: n=1 Second order: n=2

Pesticide degradation - Afect of soil horizon, soil moisture and soil temperature Tab. 3: Chlorotoluron half life (DT 50) under the laboratory conditions. Tab. 4: Analysis of Variance for half life (DT 50) - Type III Sums of Squares

Tab. 2: Chlorotoluron half life (DT 50) under the field conditions. Pesticide degradation - Affect of repeated application

Pesticide degradation - Affect of growth

Pesticide degradation - Affect of shading geotextile 0-5 cm

Pesticide Presistence Definition: The ability of a chemical to retain its molecular integrity and hence its physical, chemical, and functional characteristics in the environment through which such a chemical may be transported and distributed for a considerable period of time. (Source: GILP96) Persistence is evaluated using DT-50 or DT-90. Time for disappearance of 50% or 90% the chemical (days).

Pesticide Presistence

Pesticide Transport Capacitive equation: The movement of water between the horizons is derived from the retention capacity of soil Richards equation :  = volumetric soil water content [L 3 L -3 ] t = time [T] H = the total potential [L] K(h) = unsaturated hydraulic conductivity[LT -1 ] x, y, z = coordinate axes [L] vx, vy, vz = flow rate of water [LT -1 ] The movement of water in the soil

Pesticide Transport Substances dissolved in water are transported by convection and hydrodynamic dispersion Convection equation : Dispersion equation : Convective-dispersive equation : q a = advection flow [ML -2 T -1 ] c = concentration of the solution [ML -3 ] v = fluid velocity in the soil[L -1 T -1 ]. q d = flow caused by hydrodynamic dispersions[ML -2 T -1 ] c = concentration of the solution [ML -3 ], D = hydrodynamic dispersion [L 2 T -1 ]

Chlortoluron concentration in each sampled position 35 day after herbicide application Haplic CambisolHaplic Phaeozem

Average chlortoluron concentration detected 35 days after herbicide application

Average chlortoluron concentrations in Days148 Days 35 Days

Comparision of measured and predicted values of chlortoluron concentration in soil

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