Exposure Modelling

Exposure modelling

Environmental risk assessment for chemicals like plant protection products is based on the estimation of possible ecotoxicological effects in relation to the expected exposure in terms of predicted environmental concentrations (PEC). PEC values are usually estimated with computerised models that simulate the environmental fate of chemicals according to their physico-chemical properties and intended application patterns.


ecotox consult • Dr. Michael Meller • ecotoxicological consulting service...

...supports you with modelling the distribution and fate as well as expected exposure concentrations of chemicals

  • in the environmental compartments surface water, sediment, groundwater, soil and air,
  • applying internationally standardised and accepted exposure models (e.g. FOCUS) and/or specific national models (e.g. EVA, EXPOSIT).


Exposure modelling using the example of exposure to plant protection products in surface water with FOCUS

Exposure modelling in context of the EU evaluation procedure for plant protection products is conducted with a standardised package of models provided by the FOCUS working group (FOrum for Co-ordination of pesticide fate models and their USe).

The FOCUSsw package estimates surface water PEC values, maxima and time-weighted average concentrations in a tiered approach, applying simple kinetics in step 1 and 2 and more detailed modelling in step 3 and 4. Substance entries via spray drift, run-off and drainage are considered. Step 1 assumes one single loading corresponding to the maximum annual application while step 2 considers sequential applications and differentiates between two standard scenarios (Northern and Southern Europe). Step 3 takes into account a range of realistic worst case scenarios in terms of specific combinations of crop, soil type, weather conditions, topography and adjacent water body. These scenarios were defined to cover the major part of agricultural area in the EU. In addition to the spray drift calculator which is implemented in the SWASH user shell, models used in FOCUS step 3 are MACRO (drainage), PRZM (run-off) und TOXSWA (environmental fate in the water body). The effect of risk mitigation measures (e.g. drift-reducing application techniques or buffer zones) on predicted exposure concentrations can be estimated in step 4 with the SWAN software.


Evaluation of exposure profiles

At least since the revision of the EU guidance on tiered risk assessment for plant protection products for aquatic organisms in edge-of-field surface waters (EFSA Journal, 2013;11(7):3290), there is an increasing demand to assess not only single exposure concentrations but their time-dependent course, the so-called exposure profile. For the further development of environmental risk assessment schemes and specifically in higher tier aquatic risk assessment, the analysis of exposure profiles and adequate linking to ecotoxicological results is needed.

Figure 1: The predicted environmental concentration of a chemical as a function of time (exposure profile)

Figure 1: The predicted environmental concentration of a chemical as a function of time (exposure profile)


ecotox consult supports you with exposure modelling for plant protection products in surface water with these tools:

  • Steps 1-2 in FOCUS
  • SWASH (Surface WAter Scenario Help), PRZM (Pesticide Root Zone Model), MACRO and TOXSWA (TOXic substances in Surface Waters)
  • SWAN (Surface Water Assessment eNabler)
  • We use R for detailed analysis and graphical evaluation of FOCUS results.

ecotox consult is specialised in scientific consulting and contract research in ecotoxicology and environmental risk assessment. Risk assessment for plant protection products is one of our core areas of expertise. Therefore, we are also ready to support you with our experience in linking exposure to effects and integrating exposure modelling results into the risk assessment.

For further questions and information, please feel free to contact us.

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