Surface Water

Surface water is the second environmental compartment covered by the activities of FOCUS.

The possibilities of contamination of surface waters by the application of plant protection products (PPP) are already recognised for a long time. Main processes involved in the loading of surface waters with plant protection products are e.g. drift, drainage and run-off. The estimation of the concentration of the active substance of PPP is therefore required in the registration process in the European Union according to Directive 91/414/EEC.

The activities to determine the Predicted Environmental Concentration (PEC) in surface waters were distinguished into two parts. Firstly, the inventory of possible mathematical models suitable for this task and secondly, the development of a tiered approach to estimate these PECs for the benefit of the registration. The first part has been carried out from 1995 through 1996 and the second part from 1997 through 2002 (see Documentation of FOCUS Surface water).

 Overview From the possible existing models as inventoried by the FOCUS Working Group on Surface Water Models (FOCUS, 1997, see Documentation in FOCUS Surface water) a selection of useful models was made to start from in the development of the surface water scenarios (FOCUS 2001, see Documentation in FOCUS Surface water).

The FOCUS surface water scenarios are used to assess the potential contamination of active substances and metabolites of plant protection products to surface water. They form a part of the review process for active substances in the EU.

The FOCUS concentration estimation methodology was developed as a tiered approach with four levels of assessment. The Step 1 has been defined as a relatively simple calculation based on a maximal loading and a fixed scenario, while the Step 2 allowed multiple applications and regional variation across Europe. Step 3 of the approach consists of the scenarios developed, while Step 4 allows a detailed site-specific approach in case all Steps fail. The FOCUS surface water scenarios are a set of ten standard combinations of weather, soil and cropping data and water bodies, which collectively represent agriculture in the EU for the purposes of a Step 3 EU-level assessment of concentration estimation. The scenarios and their derivation are described in detail in a published report (FOCUS 2001, see Documentation in FOCUS Surface water).

The scenarios have been implemented as sets of input files for three simulation models estimating the influence of drainage, run-off and fate on the final concentration estimations. The model MACRO is used to estimate the drainage as a sub-surface loading to surface waters, the model PRZM accounts for run-off as a superficial loading to surface water and finally the model TOXSWA, which takes into account the dissipation processes in surface waters itself. The results of the MACRO-model or the PRZM-model are used as input into the model TOXSWA in addition to the drift input. The resulting concentrations from TOXSWA are used in the risk assessment process to calculate the Toxicity Exposure Ratios (TER) for aquatic organisms.

To minimise the influence of the user on the outcome of the PEC estimation as many as possible of the input variables have been fixed, leaving only the dossier data as main input data. To take care of this input process and to guide the user through the correct scenarios to run depending on the use of the PPP a computerised shell is developed as well. This shell, called SWASH, helps the user through the exposure assessment.

Within FOCUS, processes for maintenance of and support to models and FOCUS model software have been set up which are accessible via this website, including:

  • Distribution. The input files and simulation models can all be downloaded from this site.
  • Version control. This website is the definitive source of the currently approved version of the scenarios and associated models and input files. It also includes information on differences between successive versions.
  • Documentation.
  • User support. This includes an email helpdesk for registered users, and email notification of any bugs, and new versions.


  • FOCUS (1997). Surface Water Models and EU Registration of Plant Protection Products. European Commission Document 6476/VI/96.


  • FOCUS (2001). "FOCUS Surface Water Scenarios in the EU Evaluation Process under 91/414/EEC". Report of the FOCUS Working Group on Surface Water Scenarios, EC Document Reference SANCO/4802/2001-rev.2. 245 pp.


    • Main text SWS Scenarios (doc)
    • Appendices
      1. Existing National Scenarios (doc)
      2. Parameterisation of spray drift input (doc)
      3. Parameterisation of drainage input (doc)
      4. Parameterisation of runoff input (doc)
      5. Parameterisation of fate in surface water (doc)
      6. Hydrological responses of the FOCUS surface water bodies simulated by TOXSWA (doc)
      7. Test Protocol and results for Steps 1, 2 & 3 comparisons (doc)
      8. SWASH User Manual (doc)
      9. STEPS 1-2 in FOCUS User Manual (doc)
      10. MACRO in FOCUS User Manual (doc)
      11. PRZM in FOCUS User Manual (doc)
      12. TOXSWA in FOCUS User Manual (doc)
      13. Parameterisation of irrigation requirements (doc)
  • • Generic Guidance for Surface Water Scenarios (version 1.4): document based on official guidance document of FOCUS Surface Water Scenarios in the context of 91/414/EEC and Regulation (EC) No 1107/2009 [full citation is FOCUS (2001). "FOCUS Surface Water Scenarios in the EU Evaluation Process under 91/414/EEC". Report of the FOCUS Working Group on Surface Water Scenarios, EC Document Reference SANCO/4802/2001-rev.2. 245 pp.]. This document does not replace the official FOCUS report. However, a need was identified to maintain the definition of the FOCUS surface water scenarios and the guidance for their use in an up-to-date version controlled document, as changes become necessary. That is the purpose of this document Generic_FOCUS_SWS_versioncontrol_1_4.pdf (May/2015).  The latest version 1.4 differs from the  previous version 1.3 (Dec/2014). in that the report has been updated regarding some STEP 2 crop interception values and describes the way that STEPS_ONE_TWO 3.2, SWASH 5.3 and TOXSWA 4.4.3, facilitate the simulation of metabolites within the FOCUS surface water bodies. The earlier version 1.2  and  even earlier version 1.1 remain available.