SimpleBox does so by simultaneously solving mass balance equations for each environmental compartment box in the model. SimpleBox is a first-principles model in the sense that it internally derives mass flow rates from physical and chemical substance properties, and characteristics of the environment modeled. It takes user-specified release rates as input, producing exposure concentrations in the environment as output.
SimpleBox is operated as Microsoft Excel spreadsheet, supported by numerical computations in R, which are linked to the spreadsheet via RExcel. Documentation has been published for model versions 1-4 in various technical RIVM documents [1, 2, 3, 4].
SimpleBox has served as 'regional distribution module' in the European Union System for the Evaluation of Substances (EUSES). It is currently used as part of the CHESAR tool, hosted by the European Chemicals Agency  to demonstrate possibilities for 'safe use' of chemicals, which is required for registration of chemical substances under REACH. SimpleBox also serves as fate module in Life Cycle Impact Assessment models .
Designed originally as a research tool, SimpleBox has proven most useful in dedicated environmental fate studies, focused at understanding and predicting environmental fate from fundamental physical and chemical substance properties.
The SimpleBox spreadsheet model, the supporting R-tools and its documentation files are freely available for non-commercial use . It is available for download from https://github.com/rivm-syso/SimpleBox. For more information, please contact firstname.lastname@example.org.
A SimpleBox version capable of handling nanomaterials (SimpleBox4.0-nano) is also available.
This website is also available via http://www.rivm.nl/SimpleBox.