LEC 481 - Behaviour of Pollutants in the Environment

November 2025

Practical session: Using the GREAT-ER 3.0 model to predict the fate and behaviour of organic chemicals in rivers

GREAT-ER 3.0

http://www.cefic-lri.org/lri-toolbox/great-er

· A support tool for environmental risk assessment and river basin management.

· PC based software which predicts concentrations of chemicals in rivers across Europe.

· A GIS based system that produces a simple and clear visualisation of predicted chemical concentrations and water quality along a river by colour coding results.

· Designed for use at a post screening level in EU risk assessment process.

· Accessible to anyone involved in risk assessment and environmental management (version 3.0 is open source).

· GREAT-ER has been implemented for a variety of river basins: 4 in the UK, 1 in Italy, 3 in Germany and 1 in Belgium.

Geography-referenced Regional Exposure Assessment Tool for European Rivers

1. Setting up and running the model for the artificial sweetener Sucralose

Open the program and begin a new session

· File > New Session

· Name > Choose a name for your session

· Substance > None

· Catchment > Aire

Comments > Add any helpful comments

· Click OK

Firstly we shall setup the simulation

· Click on simulation > Edit Model Parameters

· Click on the River tab

· Change the mode to ‘Mode 2 – basic 3 processes removal’ on the drop down menu

Turn all submodel switches to No except sedimentation

Input chemical data

· Substance > New

· Name your chemical

***Using sucralose as a test chemical, complete as many of the boxes as possible. Any box with an “X” next to it HAS to be completed for the model to run and these parameters represent the minimal requirement. Create a new sheet to record parameter values and sources of information.

· NEXT > Click the Phy. Chem. Properties Tab

· We must now input: Molar Mass, Kow, Koc Vapour Pressure and Water solubility (WARNING – CHECK UNITS!)

This information can be found from various sources. Data from journal papers are more reliable, so first you should try searching using Google Scholar or Web of Science. However, various chemical databases are also available on the web e.g. PubChem.

· NEXT > Click WWTP Removal tab.

Input 0 into: Fraction Removed (Primary), (AS), (TF)

· NEXT > Click River Removal tab.

Input 0.029 into: k (sed) – this is a sediment removal rate. Enter zero for k(deg) and k(vol).

· NEXT > Click Emission Data tab.

Domestic Consumption is a per capita emission rate in kg/year/person. Per capita emission rates are available on the “Domestic Consumption data” sheet of the spreadsheet. This sets the default emission rate from every STP to the river, although individual emissions can be defined if necessary.

· Click OK

We can check to make sure we haven’t missed anything.

· Click on Simulation > Missing Parameters?

This will display any parameters not completed required to run the model. If any are missing, please complete them. Otherwise, proceed.

· Click Simulation > Start… the model will run, taking several seconds depending on computer speed.

2. Output Instructions

When the simulation is complete it will display a new layer on the map showing a coloured line for the chemical concentration in the river (green to red, low to high) and a colour key in the layer panel.

We want to produce a graph of the concentration profile from the most upstream sewage treatment works to the outlet of the catchment.

· Zoom to the most upstream sewage treatment works of the Aire, which is marked as a red dot. If you click on the zoom button seen here:

· With the zoom+ button selected, drag a box on the area you want to zoom into. If you zoom into the wrong place or zoom in too far click on:

· Now click on the ‘Downstream Concentration Profile’ button from the main toolbar and then click on the stretch just downstream of the sewage treatment works (126812). Be careful, the river line is made up of many small lines, so make sure you zoom in as far you can and then click as close to the sewage treatment works as possible. A graph of the concentration profile will pop up. Check your result with the expected graph seen in the excel spreadsheet found in the “Example Model Data” sheet.

· Click Table > Show and choose the concentration profile option > OK

Stretch 126812 is the first stretch of the River Aire. “Stretch_ID” numbers are not in numerical order.

· Click Export in the left hand corner of the table (you may find that the table needs to be moved in order to reveal the button) > Name the table as something memorable and save it to a new folder, save as type CSV. You will have several of these output tables by the end of the session and will need to distinguish between them all.

· Open the file you have just created and delete the last 5 columns and the extra “Stretch_ID” column (it doesn’t matter which one).

· Plot “km_end” against “C_SIMSTART” (XY scatter).

· Plot measurement data on the same chart. The measurement data is available from the “Measured” sheet. Remember to copy the km column. Compare your modelled result with the measured data.

3. Risk Assessment

Substance > Edit > Risk Assessment, PNEC – check units!

A PNEC is required to perform. the risk analysis. These can be found from various sources.

Analysis > Risk Analysis, creates and adds a new layer to the map “Risk: PEC/PNEC”, you may need to refresh the view by hiding the layer and then making it visible again.

The new layer will be colour coded like the concentration layer, but this only has 2 categories: <1 = green and >1 = red. These categories can be customised.

Aquatic risk is suspected when RQ≥1.

4. Assignment

The assignment for this module involves writing-up the Great-er practical session for the fluorochemical PFOS. This involves re-running the model using PFOS specific physicochemical data and emission data for the river Aire. Once the model has been run you can compare the model predictions of in-stream concentrations with the measurement dataset provided. A short introductory section providing some background information on PFOS as well as Great-er should be included. The main objective is to demonstrate an understanding of the sources and fate of persistent chemicals using an established industry risk model. You don’t need to provide a detailed description of all of the model input parameters, but an appreciation of the main processes that affect PFOS and the pros and cons of the use of such model compared to a generic approach should be included in your report. (max 2500 to 3000 words)

If you would like to discuss this further after the practical session please contact me by email ([email protected]) and we can arrange a meeting. Submission date Friday 28^th November 2025.