How to Use EUSES to Estimate Predicted Environmental Concentrations (PEC)

Little Pro on 2016-10-14

We hope you have enjoyed learning how to calculate predicted no-effect concentration (PNECs) for a specific environment compartment (water, soil, sediment, etc) from our previous tutorial. To determine the risk of a substance to a given environmental compartment, we still need to compare PNEC values with predicted environmental concentrations (PECs). Quite often measured exposure data is not available, in which case we need to reply on exposure assessment models to estimate environmental exposure levels. In this tutorial, we will teach you how to use EUSES to calculate predicted environmental concentrations (PECs). 

What is EUSES?

The European Union System for the Evaluation of Substances (EUSES) is a free tool developed by the European Commission to assist authorities, research institutes and companies to estimate environmental exposure levels of industrial chemicals and biocides. EUSES is easy to use. Only a few data on substance properties are needed to calculate PECs for tier 1 assessment. If the use of default exposure estimates and tier 1 assessment do not lead to PEC/PNEC<1, a refined assessment is possible in EUSES by including more specific information on releases.

EUSES tutorial

Click here to download EUSES.

How to start with EUSES?

Once you have downloaded EUSES, unzip it and run it, you will see the following screen. The first thing you should do is to create a "new study". The next thing you should do is to select "assessment types" and then click "start".

EUSES Screenshot

How to select assessment type

When you run EUSES for a new study for the first time, you will need to choose EUSES assessment models and run mode (See screenshot below).

EUSES assessment type

Different models are available. In this tutorial, we will choose type I environmental assessment for both local scale and regional scale. Usually both local scale and regional scale are chosen to calculate both the regional concentration (PECregional) and the local concentration (PEClocal). In addition, continental PEC values are derived in EUSES, but they are not used in the risk assessment. For new substances, only local scale is selected

The local concentration is calculated for each local point source. The regional concentration mainly serves as estimates for background levels, and the estimates of these are so-called steady-state concentration, i.e. the concentration obtained at releases and fate processes taking place over infinite time within 10% of the size of the EU.

Three types of run mode is available: direct, interactive and outline. In this tutorial, we recommend interactive mode because you can see  intermediate results such as predicted environmental concentrations (PECs). 

  • Direct mode: minimum user input, no intermediate result, good for beginners.
  • Interactive mode: intermediate results are shown. Good for refined assessment; default parameters and intermediate results can be over-written. 
  • Outline mode: only suitable for expert users. 

EUSES Input Data

The following information needs to be input to EUSES to estimate predicted environmental concentrations (PECs).  It is also the minimum information you need to gather before you run EUSES.  In addition, if you would like to use EUSES to calculate PNECs and risk characterization result, you should also collect various eco-tox endpoints such as LC50/EC50/NOEC. 

Parameter Description Unit
Substance Identification Chemical name, description, CAS no. -
MOLW Molecular Weight g/mol
MP Melting Point Celsius Degrees
BP Boiling Point Celsius Degrees
VP Vapor Pressure Pa
SOL Water solubility mg/L
LogKow octanol-water partition coefficient -
Biodegradability Screening results of biodegradability study -
Tonnage  Production tonnage, import and export tonnage -
Use pattern Use title,  use category, industry category and life cycle stage (production, formulation, industrial use, professional use, consumer use, service life, waste treatment). See REACH use descriptors
Emission data

Release fractions based on environmental release categories (ERC) or SPERC and emission days.

Please note that default release percentage and emmission days in EUSES shall not be used.

Read: How to calculate environmental emissions of chemical substances.

The picture below is the user input interface of EUSES. 


You may have noticed that each field is followed by a letter u, s, d, o. Those letters mean undefined, user input, default value and output value respectively. If you have changed some output values or default values, you can simply type "??" to get the original values back. 

After you have input physio-chemical properties, you will be required to provide tonnage  information and use patterns. Then click "next" and "next" until you see PECs calculated by EUSES (please refer to later example). 

Tip 1: If you enter the number first and then the unit, EUSES assumes that you want to enter the value in the given unit and does not convert the number. However, if you change the unit and not the number, EUSES assumes that you want to convert the number to this unit and recalculates it according to its new unit. 

Tip 2: For your first assessment, please do not change any EUSES output values in the following pop-up screens. They are calculated by EUSES by using the information you have provided. 

  • Partition coefficients and bio-concentration factors
  • Degradation and transformation rate
  • Remove constants soil

However, if you have actual data on partition coefficients (for example, organic matter-water partition co-efficient Koc), bio-concentration factors, or degradation data (DT50), you are recommended to input them to EUSES to do a refined assessment. Please refer to refined EUSES assessment at the end of this article. 

EUSES Output Data

EUSES output data includes all of the following:

  • Partition coefficients and bio-concentration factors (intermediate result)
  • Degradation and transformation rate (intermediate result)
  • Remove constants soil (intermediate result)
  • PEC-local, PEC-region and PEC-continental for various compartments such as fresh water, marine water, STP micro-organism, air, sediment, and soil (calculated by EUSES)
  • Predicted no-effect concentration (PNEC) (calculated if various eco-tox endpoints are provided).
  • RCR values (RCR=PEC/PNEC, if RCR<1, risk is acceptable.)

Note: As a Tier 1 exposure estimation model, EUSES is simple to use and is specifically developed to quickly evaluate substances. However, EUSES is inherently conservative. Refined assessment or higher level models may be needed if a substance does not pass tier 1 risk assessment. 

Example: Calculation of PECs by EUSES 

Let's assume that you need to calculate predicted environmental concentrations for substance A. The substance is to be imported to EU to formulate cosmetics. Its physio-chemical properties, tonnage information and use pattern is listed as follows. The selected assessment type is type I enviromental exposure (local scale and regional scale). The run mode is "interactive". 

Parameter Result
Molecular Weight 240 g/mol
Melting point 105 Celsius Degrees
Boiling Point 210 Celsius Degrees
Vapor Pressure 0.0008 Pa
Water solubility 38mg/L (Qsar class: hydrophobics)
LogKow 3
Biodegradability Not biodegradable
Tonnage info Import 99t/y to EU, no production in EU
  • Use title: formulation of cosmetics, 100%  
  • Industry: 5 personal/domestic use
  • Use category: 15 cosmetics
  • Life-cycle stage: formulation only
  • Enviromental release category: ERC 2 formulation
Emission fraction and emission days
  • Default release fractions of ERC 2: 2.5% to air,  2% to water,  and 0 to soil;
  • Emission days: 240 days/year;
  • Fraction of local main source: 1 (assuming there is only 1 formulator that will consume all 99t/y).

Here are the screenshots of inputting above values in EUSES step by step. User input values  are marked in orange.

Step 1: Enter physio-chemical info and tonnage info

EUSES input value

Step 2: Enter use pattern

EUSES Use Patterns

Step 3: Enter release fractions and emission days

In absence of more specific emission fractions, default values based on ERCs can be used in EUSES to derive environmental exposure estimates(PECs).

EUSES Release Fraction

Step 4: STP configuration

EUSES STP Configuration

Step 5: View regional PEC values and local PEC values

EUSES PEC values

Please note that the final PEC values are equal to the sum of regional PEC values and local PEC values. After you have obtained above PEC values, you can compare them with PNEC values to do risk characterization. 

Refined EUSES Assessment

Instead of relying on the minimum info required by EUSES to calculate PECs, you can input more actual values (see table below) or replace some EUSES output values to do a refined assessment.

Parameter Default assessment Refined assessment
Partition co-efficient and bio-concentration factors They are calculated by QSAR models based on substance structure, melting point, vapor pressure and logKow. Reliable measured data (e.g. organic carbon -water partition co-efficient Koc values, BCF value) should be used in preference to QSAR outputs.
Degradation in various compartments They are estimated from bio-degradability screening study.

Reliable measured degradation data (e.g. DT50 values ) should be used.

Lower DT50 values lead to lower PECs.

Release factors or rates (before STP) Default release factors based on the enviromental release categories of a use.

The default release factor can be refined by taking into account i) release preventing techniques or ii) onsite RMM with set effectiveness. Release factors from industry-specific SPERCs can also be used.

Lower release factors lead to lower PECs

Discharge rate of the biological sewage treatment plant (STP) 2 000 m3 /day

For site-specific assessment, the flow rate can be changed according to the site-specific data. 

Higher rate leads to lower PECs.

Receiving surface water flow rate 18 000 m3 /day (corresponding to a dilution factor of 10)

For site-specific assessments, the flow rate or the dilution factor can be changed according to the site-specific data.

Higher flow rate leads to lower PECs.

Biological sewage treatment plant (STP) By default, the releases to fresh and marine water are expected to be treated in a standard biological STP for all uses

Choose use STP or by-pass STP based on actual situation.

Using STP lowers PECs.

Application to agricultural soil of the sludge of the biological sewage treatment plant (STP) The sludge is by default assumed to be applied to agricultural soil

For site-specific assessments, if incineration or other waste treatment of the sludge is foreseen, then agricultural application of sludge does not take place.

Incineration lowers soil PECs significantly.

Daily use amount at a site Annual use amount at the site They are calculated from the “tonnage per use”

The daily and annual use amount at a site for a use can be overwritten by the registrant based on actual situation.

Lower use amount leads to lower PECs.

Daily widespread use amount in standard town It is calculated from the “tonnage per use”, corresponding to the consumption in a standard town of 10 000 inhabitants, multiplied by a safety factor of 4 Registrants can overwrite this value, for example, if they have sufficient information to demonstrate that the use of the substance is evenly distributed in space and time. In this case, it is possible to divide the default tonnage by a factor of maximum 4.
Time pattern of release to water Continuous The pattern of release to water can be changed to intermittent (i.e. if the releases take place less than once per month and for no more than 24 hours).

Main Reference


Good job. You have learned what EUSES and PECs are and how to use EUSES to calculate predicted environmental concentrations (PECs). Please subscribe our newsletter to keep updated of our new articles.

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 Tags: Topics - CRAEnvironmental Risk Assessment