# PEARL

### General Information

PEARL is an acronym of Pesticide Emission Assessment at Regional and Local scales. It is a one-dimensional numerical model of pesticide behaviour in the soil-plant system which has been developed by two Dutch institutes (Alterra and RIVM) in close co-operation.

The PEARL development team consists of (in alphabetical order):

Aaldrik Tiktak (RIVM)
Daniel van Kraalingen (Alterra)
Erik van den Berg (Alterra)
Jos Boesten (Alterra)
Minze Leistra (Alterra)
Ton van der Linden (RIVM).

PEARL web site: http://www.pearl.pesticidemodels.eu/

### Short Model Description

Summary of process descriptions

Water flow in soil is described by Richard’s equation including a range of possible lower boundary conditions (for instance groundwater levels that fluctuate in response to the rainfall input). Soil evaporation and plant transpiration is calculated via multiplying a reference evapotranspiration rate with soil and crop factors. For the FOCUS scenarios, crop growth is simulated with a simple growth model that assumes a fixed length of the growing season. In this growth model, both the leaf area index and the rooting depth are a function of the development stage of the crop. Heat flow in soil is described with Fourier’s law. The thermal properties are a function of porosity and water content and are therefore a function of time and soil depth. PEARL is based on: (i) the convection/dispersion equation including diffusion in the gas phase with a temperature dependent Henry coefficient, (ii) a two-site Freundlich sorption model (one equilibrium site and one kinetic site), (iii) a transformation rate that depends on water content, temperature and depth in soil, (iv) a passive plant uptake rate. The model includes formation and behaviour of transformation products and describes also lateral pesticide discharge to drains (but drainage is switched off for the FOCUS scenarios). PEARL does not simulate preferential flow. Volatilisation from the soil surface is calculated assuming a laminar air layer at the soil surface. PEARL uses an explicit finite difference scheme that excludes numerical dispersion (the dispersion length was set to 5 cm).

Short description of the PEARL software package

PEARL does not simulate water flow and soil temperatures, but uses output from the Soil Water Atmosphere (SWAP) model, so the software package for simulation consists of two models: SWAP and PEARL. The simulation of leaching to groundwater with PEARL requires that first the hydrology of the soil system during the simulation period is computed with SWAP. Daily SWAP output is written to a file which is one of the input files needed for PEARL. However, the user only has to specify input to PEARL: the PEARL model itself organises the input for the SWAP model.

The PEARL User Interface was developed as a user-friendly environment for running FOCUS scenarios. The interface is an integrated environment for data storage and data retrieval, model control and viewing of output data as shown in the next figure.

The user interface is linked to a relational database for easy data access. It generates the input files for the PEARL model and calls the model. Summary outputs are transferred back to the PEARL database where they can be accessed. More comprehensive model outputs can be viewed with a separate graphical program, XYWin. The FOCUS input is stored in the database in such a way that all data that should not be changed by the user are locked. The user can generate a FOCUS scenario for a desired crop-location combination with a wizard.

History of PEARL development

PEARL is based on PESTLA (PESTicide Leaching and Accumulation; Boesten & Van der Linden, 1991; Van den Berg and Boesten, 1999) and PESTRAS (PEsticide TRansport Assessment; Tiktak et al., 1994; Freijer et al., 1996), the latter being a modification of PESTLA version 1. PESTLA was based on the numerical model developed by Leistra & Dekkers (1976). The Leistra & Dekkers model was based on (i) Richard’s equation, (ii) the convection/dispersion equation, (iii) linear sorption that was a function of soil depth and (iv) a transformation rate that was a function of temperature and soil moisture. The Leistra & Dekkers model was used in Dutch pesticide registration from 1976 until 1989 after which it was superseded by the PESTLA model that was used from 1989 until 2000. The PESTRAS model was used in Dutch pesticide registration from 1996 until 2000 for volatile compounds. Since 2000 the PEARL model is used in Dutch pesticide registration.

### Role and Place in FOCUS scenarios calculation

PEARL is used for assessment of pesticide leaching in the EU evaluation process and input for all nine groundwater scenarios, including all possible crops, has been developed. PEARL calculates the leaching at the FOCUS target depth (default is 1 m), but also allows for evaluation of leaching at greater depths. For the nine scenarios the total depth of the soil system in PEARL is at least 3 m. As PEARL is able to describe fluctuating groundwater tables and can use information on transformation rates in subsoils, effects of these processes can be studied as well.

### Current use outside FOCUS

PEARL is used in Dutch pesticide registration for first and higher tier assessments. Higher tier assessments include the interpretation of lysimeter studies for pesticide registration. PEARL is also used for national Dutch assessments of trends in reductions of emissions to groundwater.
For uses outside FOCUS it is recommended to register at the PEARL website.

### Excerpt of existing model documentation

• Boesten, J.J.T.I. and A.M.A. van der Linden, 1991. Modeling the influence of sorp-tion and transformation on pesticide leaching and persistence. Journal of Environmental Quality 20: 425-435.
• Boesten, J.J.T.I. & B. Gottesbüren, 2000 Testing PESTLA using two modellers to simulate bentazone and ethoprophos behaviour in a sandy soil. Agric. Water Management 44: 283-305.
• Freijer, J.I., A. Tiktak, S.M. Hassanizadeh and A.M.A. van der Linden, 1996. PESTRAS v3.1.: A one dimensional model for assessing leaching, accumulation and volatilisation of pesticides in soil. RIVM report 715501007, Bilthoven, the Netherlands.
• Leistra, M. and W.A. Dekkers, 1976. Computed leaching of pesticides from soil under field conditions. Water, Air and Soil Pollution 5: 491-500.
• Leistra, M., A.M.A. van der Linden, J.J.T.I.Boesten, A. Tiktak and F. van den Berg, 2000. PEARL model for pesticide behaviour and emissions in soil-plant systems. Description of processes. Alterra report 13, RIVM report 711401009, Alterra, Wageningen, 107 pp.
• Tiktak, A., A.M.A. van der Linden and F.A. Swartjes. 1994. PESTRAS: A one dimensional model for assessing leaching and accumulation of pesticides in soil. RIVM report 715501003, Bilthoven, the Netherlands.
• Tiktak, A., F. van den Berg, J.J.T.I. Boesten, M. Leistra, A.M.A. van der Linden & D. van Kraalingen (2000). Pesticide Emission Assessment at Regional and Local Scales: User Manual of Pearl version 1.1. RIVM Report 711401008, Alterra Report 28, RIVM, Bilthoven, 142 pp.
• Van den Berg, F. and J.J.T.I. Boesten, 1999. Pesticide leaching and Accumulation model (PESTLA) version 3.4. Description and User’s Guide. Technical Document 43, DLO Winand Staring Centre, Wageningen, The Netherlands, 150 pp.
• Van den Berg, F. , J.H. Smelt, J.J.T.I. Boesten & W. Teunissen (1999) Volatilization of methyl isothiocyanate from soil after application of metam-sodium with two techniques. Journal of Environmental Quality 28: 918-928.
• Van Dam, J.C., J. Huygen, J.G. Wesseling, R.A. Feddes, P. Kabat, P.E.V. van Walsum, P. Groenendijk and C.A. Van Diepen, 1997. Theory of SWAP version 2.0. Simulation of water flow, solute transport and plant growth in the Soil-Water-Atmosphere-Plant environment. Technical Document 45, DLO Winand Staring Centre, Wageningen, The Netherlands.

 Package FOCUS_PEARL_4.4.4.exe (11/Apr/2011, 1 file, 23 MB) Test Results Word Getting Started Comments The scenarios defined in this download package and shell generate tier 1 outputs that are in accordance with Sanco/13144/2010 version 1, 604pp and Generic Guidance for Tier 1 FOCUS Ground Water Assessments (version 2.0) The installation of Interbase (ensures transfer of data between database and user interface). This is only required on PCs where FOCUS PEARL has not been installed before. InterBase6_5.zip

### FOCUS_PEARL_3.3.3

 Package FOCUS_PEARL_3.3.3.exe.zip (22/May/2006, 1 file, 30 MB) Test Results HTML, Word Getting Started Comments Release Notes for FOCUS_PEARL_3.3.3 (Word)

### FOCUS_PEARL_2.2.2

 Package FOCUS_PEARL_2.2.2.exe.zip (7/Aug/2003, 1 file, 38 MB) Test Results HTML, Word Getting Started Comments Differences between PEARL_2.2.2 and PEARL_1.1.1 (including Known Bugs for PEARL_2.2.2) : HTML or Word Warning (1/September/2004):The calculation of the temperature-dependency of the sorption coefficient contains an error which implies that the model does not consider this dependency. Thus all calculations are performed with a sorption coefficient that is no function of temperature. This bug influences only results of runs in which the molar enthalpy of sorption was set to a non-zero value. Such runs are exceptional because zero is the default value and because measurements of this molar enthalpy are usually not available. Warning (3/November/2004):FOCUSPEARL_2.2.2 sometimes crashes for substances (parents or metabolites) with Freundlich exponents exceeding 1.0. In such case, the run stops saying that a negative concentration occurred. If no such error message occurs, there is no problem. There are no work arounds to avoid this error. The user could consider to modify the value for the Freundlich exponent to a value of 1.0; the run would then be completed without error.It is anticipated that this bug will be solved in the next release.

### FOCUS_PEARL_1.1.1

 Package FOCUS_PEARL_1.1.1.exe.zip (5/Jan/2001, 1 file, 20 MB) Test Results HTML, Word Getting Started Comments Warning :An error has been discovered in the parameters describing water withdrawal by cotton (in the Sevilla and Thiva scenarios). This error results in a simulated transpiration of water by cotton that is far too low. As a consequence, the water percolation and leaching concentrations are overestimated. Problem will be addressed in next release. Warning :Inconsistencies have been discovered in the PEARL water balance for irrigated deep rooting crops (citrus, apples and vines) in the Sevilla scenario. The current bottom boundary condition for Sevilla results in a simulated transpiration of water for deep rooting crops that is too low (34 to 54% of potential transpiration). This leads to an overestimation of the water percolation and of leaching concentrations. Problem will be addressed in next release. Warning :PEARL v1.1.1 cannot be used with Office 2000 because the database is not compatible with Office 2000. However, PEARL will run if you have installed Microsoft Access 2000 over an existing Microsoft Access 97 installation. If you have a computer with pre-installed Office 2000, consider to proceed as follows: 1) remove the existing Office 2000 installation, 2) install Office 1997, 3) re-install Office 2000, 4) install PEARL. Problem will be addressed in next release. Warning (21/October/2003) :PEARL 1.1.1 contains a bug for the option ‘Kf user defined’ in the ‘Freundlich sorption’ screen; the model will not run for this option. The bug has been solved in FOCUS_PEARL_2.2.2.