The test species is the duckweed (Lemna gibba or Lemna minor). The test is performed according to OECD guideline 221. Progress in growth (number of fronds, growth rate and frond area) are the observation parameters. Then evaluation of frond area is performed by measuring the frond area via the computer program IPS Visiometrics, version 1.105 at time 0, 3, 5, and 7 days. 
The principle of evaluation can be summarised as follows:

• taking digital pictures of each test assay at days 0, 3, 5 and 7

• saving the pictures for further evaluation

• segmentation of pictures by selecting threshold levels (colour, brightness)

• differentiation of areas to be evaluated

• measuring of frond areas by IPS Visiometrics

• export of data to spreadsheet analysis and calculation of frond areas as pixels

The test duration is 7 days. The design is semi-static with renewal periods of the test medium every 2 to 3 days. Analytical control samples are taken from representative concentration levels over the entire test period, prior to and after each renewal of the test solution.