How to Estimate Environmental Releases of Chemical Substances

Little Pro on 2017-11-09

The final concentration of a chemical substance in various environmental compartments (air, water, soil, etc) depends on its environmental emission rates and environmental distribution and fate behavior. Thus the first step in environmental risk assessment is always  to quantify the emissions of a chemical into water, air, soil and/or solid waste. The estimated emission rates will then be used in exposure models such as EUSES to calculate predicted enviromental concentrations (PEC). In this article, we will show you how to define an emission scenario, how to calculate emission rates for both local environment and regional environment,  and how to use them for environmental risk assessment. 

Elements of Typical Emission Scenario

A typical emission scenario includes the following elements as a minimum requirement.

Elements Example Explanation
Scenario Name Consumer use of cosmetics 

 There will be environmental releases when a substance itself is manufactured, when the substance is used to formulate cosmetics or when consumers directly use cosmetic products.

Each emission scenario must be established for each life-cycle stage separately. This includes manufacture, formulation, industrial use, professional use, consumer use, service-life and disposal.

Tonnage 2,000t/y  This is the estimated total tonnage used for above specific scenario/use. For example, the total tonnage of a substance manufactured in EU may be 10,000/y. 3,000t/y may be used to formulate cosmetics in EU.  In this case, 2,000t/y shall be used since market research data shows that only 2,000t/y is available for release in EU. Many cosmetic products produced in EU will be exported to other countries. 
F-prodregion 0.1

This is the fraction of amount available for release in a hypothetical region in EU 27 countries  (area: 200km x 200km, population: 20 million). It is used to calculate tonnage at regional level.  

EU is treated as a continent, not a region under EUSES and EU's chemical risk assessment scheme.  

By default, for uses at industrial sites, it is set equal to 100% of the tonnage for the use, while for widespread uses it is set equal to 10%.

In this case, we have used default value 10% since consumer use is widespread. 

F-mainsource 0.002

Fraction used at main source (F-mainsource) is the  fraction of amount of the regional tonnage amount that is available for release to a local environment.  A local environment is a standard small town with 10,000 people and 1 STP.  This is very important for estimating local environmental emissions and PEC-local.

F-mainsource=Population connected to 1 average-sized STP (10,000)/Total population in hypothetical region (2,000,000)*Safety factor (SF=4)

Default value for industrial use (i.e, production, formulation) is always 1.

In this case, we have used default value 0.002 for wide dispersive use.

Emission days 365 days For consumer use, the default number of emission days is 365/y. For industrial uses, this number is the actual number of emisson days per year. 
Release factors
  • air: 100%
  • water:100%
  • soil: 0

 Release factor is the fraction of the amount available for release to air, water and soil. The sum of 3 release factors do not have to be 100%!

Default emission days and release factors are given in REACH's environmental release categories (ERC). They are very conservative. In this case, we have used default release factors for ERC (8a)- wide dispersive use anyway. It is very important to consider on-site risk management measures and use realist release factors for calculating environmental emissions. 

Release factors can also be found in OECD's Emission Scenario Documents (ESD).

With above info, we can now start calculating both local environmental emission rates and regional environmental emission rates. The picture below shows you what needs to be calculated for both industrial use and wide dispersive use.

How to Calculate Environmental Emissions

How to Estimate Environmental Emission Rates

The table below shows you how to calculate local and regional emission rates. We will use above emission scenario as an example.

Item Equation Emission Rates
Local daily release rate (kg/d) 

Tonnage*1000*F-prodregion*F-mainsource*Release factor (air, water, soil)/Emission days

Example (release to waste water):


  •  To air: 1.09kg/d
  • To waste water: 1.09kg/d
  • To soil: 0
Regional daily release rate (kg/d)

Tonnage*1000*F-prodregion*Release factor (air, water, soil)/Emission days

Example (release to waste water):


  •  To air: 547.9kg/d
  • To waste 547.9kg/d
  • To soil: 0

Note: Above process needs to be repeated for each relevant emission scenario/use. The estimated regional environmental emission rates for each scenario/use need to be accumulated to estimate the total regional release to surface water, wastewater and air. 

How to Use Estimated Emission Rates for Environmental Exposure Assessment

Estimated environmental releases are used as key input parameters in environmental exposure models to calculate predicted environmental concentrations (PECs). They are two types of PECs: PEC-local and PEC-region. How they are calculated as listed as follows:

  • PEC-local: It is calculated by SimpleTreat model. Local emission rate is a key input parameter for the model.  The model simulates the fate of organic substances in sewage treatment plant (STP). It is used to calculate the concentration of a substance in waste water and the concentration in sludge after STP treatment. 
  • PEC-region: It is calculated using SimpleBox model (level III Mackay-type fugacity multimedia model). The model simulates environmental fate of chemicals as fluxes (mass flows) between a series of well-mixed boxes of air, water, sediment and soil on regional, continental and global spatial scales. Calculated PEC-region are  steady state concentrations in various environmental compartments. 

Both SimpleTreat and SimpleBox models have been incorporated to EUSES. Emission rates are also key input parameters for EUSES to calculate PECs.

References and More Readings

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 Tags: Topics - CRAEnvironmental Risk Assessment