General Information

STEPS1-2 in FOCUS is a stand-alone Surface water Tool for Exposure Predictions -Steps 1 & 2 for the derivation of PEC values in water and sediment based upon the chosen scenario. The tool requires a minimum of input values (molecular weight, water solubility, DT50soil, Koc, DT50sediment/water, number of applications, application interval and application rate) and is designed to evaluate both active substances and metabolites.

STEPS1-2 in FOCUS is a true windows development that was programmed using Microsoft© Visual Basic and runs under Microsoft©Windows 95/98/NT/2000.

STEPS1-2 in FOCUS developer: Michael Klein (

Affiliation: Fraunhofer-Institut for Molecular Biology and Applied Ecology

STEPS1-2 in FOCUS web site: ---


Short Model Description

At Step 1 inputs of spray drift, run-off, erosion and/or drainage are evaluated as a single loading to the water body and "worst-case" surface water and sediment concentrations are calculated. The loading to surface water is based upon the number of applications multiplied by the maximum single use rate unless 3 x DT50 in sediment/water systems (combined water + sediment) is less than the time between individual applications. In such a case the maximum individual application rate is used to derive the maximum PEC as there is no potential for accumulation in the sediment/water system. For first order kinetics the value of 3 * DT50 is comparable to the DT90 value.

At Step 2 inputs of spray drift, run-off, erosion and/or drainage are evaluated as a series of individual loadings comprising drift events (number, interval between applications and rates of application as defined in Step 1) followed by a loading representing a run-off, erosion and/or drainage event four days after the final application. This assumption is similar to that developed by the United States EPA in their GENEEC model (Parker, 1995). Degradation is assumed to follow first-order kinetics in soil, surface water and sediment and the registrant also has the option of using different degradation rates in surface water and sediment.


Role and Place in FOCUS scenarios calculation

The major objective of FOCUS is to implement a harmonised approach for European Tier 1 and Tier 2 risk assessments according to Council Directive 91/414/EEC. The process implementation and the scenario definitions for STEPS 1-2 in FOCUS were defined by the FOCUS Working Group on Surface Water Scenarios.


Current use outside FOCUS



Excerpt of existing model documentation

  • 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.1. 221 pp.  



Latest version: Focus_STEPS_ONE_TWO_3.2

Package STEPS1-2_version (22/May2015, 1 file)
Getting Started


1)     Package calculates PEC at STEP 2 using some updated crop interception values as described in  Generic guidance for Surface Water Scenarios, version 1.4
2)     Package calculates metabolite formation from active substance mass running off / draining from soil, in addition to formation from active substance mass arriving by spray drift, as described in  Generic guidance for Surface Water Scenarios, version 1.4

previous version : FOCUS_STEPS_ONE_TWO_2.1

Package STEPS1-2_version (22/Mar/2011, 1 file, 3 MB)
Documents on getting started: Format_for_changing_scenario_data_for_STEPS_1_2_in_FOCUS.doc
Comments 22/Mar/2011

The software package for WinXP, Vista, Windows7 (both 32-bit and 64-bit): STEPS1-2_version

Package (10/Jun/2003, 1 file, 3 MB)
Test Results HTML, Word
Getting Started
Comments 22/Jul/03 : WARNING

There is a problem on step 2 in the report, section, "Results of the calculation for the respective single application pattern" if multiple applications has been selected:
The results on day 0 often come out as 0.0 for surface water and for sediment.
If that happens the user should take the respective numbers from the main form of steps1-2 where they are reported correctly.
The bug will be fixed soon.


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