# Commission Regulation (EC) No 761/2009 of 23 July 2009 amending, for the purpose of its adaptation to technical progress, Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (Text with EEA relevance), Division 2.2.1: Average specific growth rate

Extent: E+W+S+N.I.

The average specific growth rate for a specific period is calculated as the logarithmic increase in the growth variables — rond numbers and one other measurement variable (total frond area, dry weight or fresh weight) — using the formula below for each replicate of control and treatments:
μ i-j = ln( N j ) – ln( N i ) t
where:
— μi-j: average specific growth rate from time i to j
— Ni: measurement variable in the test or control vessel at time i
— Nj: measurement variable in the test or control vessel at time j
— t: time period from i to j
For each treatment group and control group, calculate a mean value for the growth rate along with variance estimates.
The average specific growth rate should be calculated for the entire test period (time ‘i’ in the above formula is the beginning of the test and time ‘j’ is the end of the test). For each test concentration and control, calculate a mean value for average specific growth rate along with the variance estimates. In addition, the section-by-section growth rate should be assessed in order to evaluate effects of the test substance occurring during the exposure period (e.g. by inspecting log-transformed growth curves). Substantial differences between the section-by-section growth rate and the average growth rate indicate deviation from constant exponential growth and that close examination of the growth curves is warranted. In this case, a conservative approach would be to compare specific growth rates from treated cultures during the time period of maximum inhibition to those for controls during the same time period.
Percentage inhibition of growth rate (Ir) may then be calculated for each test concentration (treatment group) according to the following formula:
% I r = (μ C – μ T ) μ C × 100
where:
— % Ir: percentage inhibition in average specific growth rate
— μC: mean value for μ in the control
— μT: mean value for μ in the treatment group

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Source: https://www.legislation.gov.uk/eur/2009/761/annex/VI/division/2/division/2.2/division/2.2.1 (the official version)
Page: https://openlegislation.uk/eu-regulation-2009-761/annex-VI/division-2/division-2.2/division-2.2.1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.