FOCUSPEARL serves as a shell for the numerical model PEARL, which is an acronym for Pesticide Emission Assessment at Regional and Local scales. PEARL is a one-dimensional, dynamic, multi-layer model, which describes the fate of a pesticide and relevant transformation products in the soil-plant system. It has been developed by the WEnR, PBL, and RIVM institutes. The most important processes included in PEARL are: pesticide application and deposition, convective and dispersive transport in the liquid phase, diffusion through the gas and liquid phase, equilibrium sorption, non-equilibrium sorption, first-order transformation, uptake of pesticides by plant roots, lateral discharge of pesticide with drainage water, and volatilization of pesticide from soil and plant surfaces. PEARL uses the SWAP soil hydrological model to provide soil moisture fractions and water fluxes.
PEARL is also part of the GeoPEARL and GEM applications. Another related tool is PEARLNEQ, which is used to estimate long-term sorption parameters based on data from experimental aged-sorption studies with soil.
Leaching assessment
The main purpose of FOCUSPEARL is to assess leaching potential of substances according to the EU tiered scheme. This scheme aims to protect groundwater against contamination with pesticides above the level of 0.1 µg/L, with special regard to the groundwater as a source for drinking water. Central to the EU scheme are 9 leaching scenarios which were developed by the FOCUS working group. These scenarios are based on climate and soil data for different locations in the EU and correspond to 9 FOCUS zones, representing realistic worst-case conditions for leaching for each. Additionally, parametrizations for a range of standard crops were derived. The scenarios and crop parametrization are used to assess leaching in the EU scheme at tier 1 and 2. The FOCUS scenario Kremsmünster is also used in the Dutch national scheme at tier 1. This scenario is considered most appropriate for conditions in the Netherlands. FOCUSPEARL includes all required input data to perform leaching assessment for the 9 FOCUS scenarios. More information on the FOCUS scenarios can be found on the web page of FOCUS DG SANTE.
Soil exposure assessment
The second use of FOCUSPEARL is for exposure assessment of soil organisms to plant protection products at tier 3A of the scheme developed by EFSA. This scheme prescribes that at tiers 1 and 2, exposure assessment should be carried out using the analytical model PERSAM. Should the assessment at Tier 2 still indicate an unacceptable risk to soil organisms, the applicant has the option to move to tier 3A, which uses the same scenarios as for tier 2 but with a dynamic fate model—i.e. FOCUSPEARL or FOCUS PELMO. For this purpose PERSAM can generate a transfer file, which is read by FOCUSPEARL in order to generate a run to assess soil exposure concentration (PECsoil).
