Division 1.2 DEFINITIONS

The following definitions and abbreviations are used for the purposes of this Testing Method:

Biomass: is the dry weight of living matter present in a population expressed in terms of a given volume; e.g. mg algae/litre test solution. Usually ‘biomass’ is defined as a mass, but in this test this word is used to refer to mass per volume. Also in this test, surrogates for biomass, such as cell counts, fluorescence, etc. are typically measured and the use of the term ‘biomass’ thus refers to these surrogate measures as well.

Coefficient of variation: is a dimensionless measure of the variability of a parameter, defined as the ratio of the standard deviation to the mean. This can also be expressed as a percentage value. The mean coefficient of variation of average specific growth rate in replicate control cultures should be calculated as follows:

1. 1..

   Calculate % CV of average specific growth rate out of the daily/section-by-section growth rates for the respective replicate.

2. 2..

   Calculate the mean value of all the values calculated in point 1 to get the mean coefficient of variation of the daily/section-by-section specific growth rate in replicate control cultures.

EC_x : is the concentration of the test substance dissolved in the test medium that results in an x % (e.g. 50 %) reduction in growth of the test organism within a stated exposure period (to be mentioned explicitly if deviating from full or normal test duration). To unambiguously denote an EC value deriving from the growth rate or from the yield, the symbols ‘E_rC’ and ‘E_yC’ are used respectively.

Growth medium: is the complete synthetic culture medium in which test algae grow when exposed to the test substance. The test substance will normally be dissolved in the test medium.

Growth rate (average specific growth rate): is the logarithmic increase in biomass during the exposure period.

Lowest Observed Effect Concentration (LOEC): is the lowest tested concentration at which the substance is observed to have a statistically significant reducing effect on growth (at p < 0,05) when compared with the control, within a given exposure time. However, all test concentrations above the LOEC must have a harmful effect equal to or greater than those observed at the LOEC. When these two conditions cannot be satisfied, a full explanation must be given for how the LOEC (and hence the NOEC) has been selected.

No Observed Effect Concentration (NOEC): is the test concentration immediately below the LOEC.

Response variable: is a variable for the estimation of toxicity derived from any measured parameters describing biomass by different methods of calculation. For this method, growth rates and yield are response variables derived from measuring biomass directly or any of the surrogates mentioned.

Specific growth rate: is a response variable defined as the quotient of the difference of the natural logarithms of a parameter of observation (in this Testing Method, biomass) and the respective time period.

Yield: is the value of a measurement variable at the end of the exposure period minus the measurement variable’s value at the start of the exposure period to express biomass increase during the test.