The ETX software program calculates a (log) normal distribution through toxicity data entered by the user. This gives a species sensitivity distribution (SSD).

This distribution is subsequently tested for statistical criteria on normality. The estimated 5th percentile and median of the calculated distribution are presented, each with their respective two-sided 90% confidence interval. With the calculated SSD species sensitivity distribution (species sensitivity distribution) the potentially affected fraction (PAF) of species at a given environmental concentration can be estimated, or an expected ecological risk (EER) at a series of environmental concentrations. The program also offers the opportunity to estimate the 5th percentile of very small data sets using the so called small sample method.

The techniques offered with ETX are used in environmental risk assessment and in derivation of environmental quality standards (EQS) in the Netherlands and Europe. The techniques are frequently used in the field of ecotoxicology. The purpose of ETX is to offer the user the calculation methods as described in the scientific literature. You can find an overview of the underlying literature in the Manual.


Since some users kept reporting error messages on 'Microsoft's Data Acess Components (MDAC)' and 'Microsoft.ACE.OLEDB registration', we decided to omit the use of MDAC altogether. The current version (ETX 2.3.1, November 2023) should therefore no longer prompt for MDAC related errors.

Download ETX

Download the program ETX 2.3.1

Download the file named ETX onto your computer. Unzip the file, which will show a single installer file called ETX 2.3.msi. Double clicking it will invoke the program installer, which takes you through the installation process in just a few steps.

Software requirements

The Microsoft .NET framework is a prerequisite for installing ETX 2.3.1 This software package is already preinstalled when using Windows as operating system. In case it is not, the .NET framework version can be downloaded for free from the Microsoft website.


Download the Manual.

The manual was written for ETX version 2.0. The technical and scientific description in the manual still apply to ETX 2.3.1 as the content of the software has not changed.  In the manual, only the section on the installation procedure described in the manual of ETX 2.0 is outdated.

Citing ETX

The current version of ETX can be cited as ETX 2.3.1 The preferred citation can be found in the manual.


The previous current version (ETX 2.3) of this program was released in August 2020 and entailed a fix to prevent errors with MSTM MDAC (Microsoft Data Access Components). Version 2.2 was released in September 2017;  ETX 2.1 was released in February 2015 and the first version (ETX 2.0) was released in 2004. The current update does not concern any technical, scientific changes.


There is no helpdesk to answer questions of users. However, we welcome your comments on the program and its functioning at